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A level Physics assignment-'Waves'.
I need to resubmit a ten page assignement on waves-their properties and their use in the medical proffession. Including detail downt to a cellular level explaining how the individual processes work and also including diagrams.
This piece needs to be at A level standard.
The reason that I am now seeking help-is our lecturer has been particularly difficult-(not just with me)-to the point that their has now been a complaint against him. I am not here to discuss that or earn any sympathy-but in short it has cost me time-and with 5 weeks left of my course and still 4 Alevel science pieces to complete-...you can prob see my point.
I would be grateful for any help at all.
Cheers and good luck to all!
This piece needs to be at A level standard.
The reason that I am now seeking help-is our lecturer has been particularly difficult-(not just with me)-to the point that their has now been a complaint against him. I am not here to discuss that or earn any sympathy-but in short it has cost me time-and with 5 weeks left of my course and still 4 Alevel science pieces to complete-...you can prob see my point.
I would be grateful for any help at all.
Cheers and good luck to all!
Scroll to see replies
sazzarooo
I need to resubmit a ten page assignement on waves-their properties and their use in the medical proffession. Including detail downt to a cellular level explaining how the individual processes work and also including diagrams.
This piece needs to be at A level standard.
The reason that I am now seeking help-is our lecturer has been particularly difficult-(not just with me)-to the point that their has now been a complaint against him. I am not here to discuss that or earn any sympathy-but in short it has cost me time-and with 5 weeks left of my course and still 4 Alevel science pieces to complete-...you can prob see my point.
I would be grateful for any help at all.
Cheers and good luck to all!
This piece needs to be at A level standard.
The reason that I am now seeking help-is our lecturer has been particularly difficult-(not just with me)-to the point that their has now been a complaint against him. I am not here to discuss that or earn any sympathy-but in short it has cost me time-and with 5 weeks left of my course and still 4 Alevel science pieces to complete-...you can prob see my point.
I would be grateful for any help at all.
Cheers and good luck to all!
Waves are two types either transverse or longitudinal,transverse like light,Xray gamma longitudinal like sound
soundwaves are mechanical ,while lightwaves are electromagnetic,transverse waves like light can travel in vacuum and they propegate perpindicular to the direction of their motion while longitudinal travel (propegate)parrallel to the direction of motion
transverse waves can be ploarised but polarisation decreases the intensity as it allows waves of only one direction of propegation to pass while long itudinal can be polarised,
when a wave long itudinal or trasverse are reflected from a boundary,it superpose with the original wave ,this will cause resonance to occure where an envelops are formed ,the stationary wave will consist of nodes and antinodes,nodes are places where you can find particles so the two waves at the point are out of phase and cancel out,maximum particles can be found in the antinodes region or the envlope where the two waves reinforce and the resultant amplitude equals the amplitude of both reflected and original wave,waves can damp due to air resistance or as a matter of fact drag force,so the amplitude starts decreasing.
waves can diffract this will lead them to superpose where they are inphase and cancel out where they are out of phase,thus will lead fringes to be formed where the wavelength of the wave can be measure using lambda=xs/D where x is the fring spacing,s is the slit spacing and D is the distance from the source to the screen if it was light
waves diffract you can drow different sizes of apperatures and the diffraction pattern formed,also they can be reflected where in the total reflection the incident angelequals the reflected angle the illusional line in the middle perpendicular to the surface is the normal,more over when waves move from deep boundary to shallow boundary they diffract so they become slower and bend twards the normal but the wavelengths decreases so that the frequency is the same
,moreover waves have particle and wave properties
where by enistine theory
enistine suggested that waves come as packets of equal energy called quantums and by planks equation the energy of a wave can be found where E=hf
thus showed that waves energy depends on frequency and not on intensity as it was thought that whatever the frequency if the intensity was enough electrons would be emitted from the electroscope ,this is the photoelectric effect where they used an electroscope with a shiney zinc on the top they shone ultraviolet light on it,and found out that the leaf fell now that was as ultraviolet light had enough frequency and thus energy to emit the electrons from the zinc and caused it to be less negative(the electroscope is negatively charged)
hmm the minimum energy that is needed to emit electrons from a certain metal is the workfunction of that metal.
when they shone other forms of light or radiations of lower frequencies no electrons were emitted even if they shone it for a long time
the minimum frequency where the radiation can have to emit electrons is the threshold frequency
the intensity increases the number of electron emitted per second but not the kinetic energy of the electrons
you can drow graphs of frquency against v the stopping voltage and photon energy against the stopping voltage
habosh
Waves are two types either transverse or longitudinal,transverse like light,Xray gamma longitudinal like sound
soundwaves are mechanical ,while lightwaves are electromagnetic,transverse waves like light can travel in vacuum and they propegate perpindicular to the direction of their motion while longitudinal travel (propegate)parrallel to the direction of motion
transverse waves can be ploarised but polarisation decreases the intensity as it allows waves of only one direction of propegation to pass while long itudinal can be polarised,
when a wave long itudinal or trasverse are reflected from a boundary,it superpose with the original wave ,this will cause resonance to occure where an envelops are formed ,the stationary wave will consist of nodes and antinodes,nodes are places where you can find particles so the two waves at the point are out of phase and cancel out,maximum particles can be found in the antinodes region or the envlope where the two waves reinforce and the resultant amplitude equals the amplitude of both reflected and original wave,waves can damp due to air resistance or as a matter of fact drag force,so the amplitude starts decreasing.
waves can diffract this will lead them to superpose where they are inphase and cancel out where they are out of phase,thus will lead fringes to be formed where the wavelength of the wave can be measure using lambda=xs/D where x is the fring spacing,s is the slit spacing and D is the distance from the source to the screen if it was light
waves diffract you can drow different sizes of apperatures and the diffraction pattern formed,also they can be reflected where in the total reflection the incident angelequals the reflected angle the illusional line in the middle perpendicular to the surface is the normal,more over when waves move from deep boundary to shallow boundary they diffract so they become slower and bend twards the normal but the wavelengths decreases so that the frequency is the same
,moreover waves have particle and wave properties
where by enistine theory
enistine suggested that waves come as packets of equal energy called quantums and by planks equation the energy of a wave can be found where E=hf
thus showed that waves energy depends on frequency and not on intensity as it was thought that whatever the frequency if the intensity was enough electrons would be emitted from the electroscope ,this is the photoelectric effect where they used an electroscope with a shiney zinc on the top they shone ultraviolet light on it,and found out that the leaf fell now that was as ultraviolet light had enough frequency and thus energy to emit the electrons from the zinc and caused it to be less negative(the electroscope is negatively charged)
hmm the minimum energy that is needed to emit electrons from a certain metal is the workfunction of that metal.
when they shone other forms of light or radiations of lower frequencies no electrons were emitted even if they shone it for a long time
the minimum frequency where the radiation can have to emit electrons is the threshold frequency
the intensity increases the number of electron emitted per second but not the kinetic energy of the electrons
you can drow graphs of frquency against v the stopping voltage and photon energy against the stopping voltage
soundwaves are mechanical ,while lightwaves are electromagnetic,transverse waves like light can travel in vacuum and they propegate perpindicular to the direction of their motion while longitudinal travel (propegate)parrallel to the direction of motion
transverse waves can be ploarised but polarisation decreases the intensity as it allows waves of only one direction of propegation to pass while long itudinal can be polarised,
when a wave long itudinal or trasverse are reflected from a boundary,it superpose with the original wave ,this will cause resonance to occure where an envelops are formed ,the stationary wave will consist of nodes and antinodes,nodes are places where you can find particles so the two waves at the point are out of phase and cancel out,maximum particles can be found in the antinodes region or the envlope where the two waves reinforce and the resultant amplitude equals the amplitude of both reflected and original wave,waves can damp due to air resistance or as a matter of fact drag force,so the amplitude starts decreasing.
waves can diffract this will lead them to superpose where they are inphase and cancel out where they are out of phase,thus will lead fringes to be formed where the wavelength of the wave can be measure using lambda=xs/D where x is the fring spacing,s is the slit spacing and D is the distance from the source to the screen if it was light
waves diffract you can drow different sizes of apperatures and the diffraction pattern formed,also they can be reflected where in the total reflection the incident angelequals the reflected angle the illusional line in the middle perpendicular to the surface is the normal,more over when waves move from deep boundary to shallow boundary they diffract so they become slower and bend twards the normal but the wavelengths decreases so that the frequency is the same
,moreover waves have particle and wave properties
where by enistine theory
enistine suggested that waves come as packets of equal energy called quantums and by planks equation the energy of a wave can be found where E=hf
thus showed that waves energy depends on frequency and not on intensity as it was thought that whatever the frequency if the intensity was enough electrons would be emitted from the electroscope ,this is the photoelectric effect where they used an electroscope with a shiney zinc on the top they shone ultraviolet light on it,and found out that the leaf fell now that was as ultraviolet light had enough frequency and thus energy to emit the electrons from the zinc and caused it to be less negative(the electroscope is negatively charged)
hmm the minimum energy that is needed to emit electrons from a certain metal is the workfunction of that metal.
when they shone other forms of light or radiations of lower frequencies no electrons were emitted even if they shone it for a long time
the minimum frequency where the radiation can have to emit electrons is the threshold frequency
the intensity increases the number of electron emitted per second but not the kinetic energy of the electrons
you can drow graphs of frquency against v the stopping voltage and photon energy against the stopping voltage
Wow - that must have taken you ages
Im impressed.Just as a point the workfunction quantum theory stuff isnt actually wave stuff. Its proof that light is a particle... so you cant really put it in technically. Also you are kind of mixed up. E=hf is not the energy of a wave. It is the energy of a photon - ie a particle of light.
Energy of a wave is proportional to its amplitude squared. The diffraction stuff is all correct though.
For a positive input you could mention things like x rays and their relation to medicine. They are produced by accelerating electrons at high speed into a solid piece of tungsten. This rapid deceleration produces photons of high energy - ie X rays. The energy curve is called a Brehmstrahlung. Or "braking curve" I think. Obviously x rays have a high frequency = high energy hence they can penetrate deep inside the body.
Gamma rays produced by radioactive sources do a similar thing. Used for imaging and the like. The gamma rays can pass through all tissue so it reaches the detectors. If you pick your source right you can get it to emit two or three gamma rays at once and therefore work out exactly where it came from. Obviously though they are not the kind of things you want hanging around in the body for a long time.
Similarly gama rays can be used to treat cancerous tissue by inserting a gamma source... although to be fair it is normally an alpha source. The energy then frazzles (degenerates?) the cells to kill the cancer.
Gamma rays produced by radioactive sources do a similar thing. Used for imaging and the like. The gamma rays can pass through all tissue so it reaches the detectors. If you pick your source right you can get it to emit two or three gamma rays at once and therefore work out exactly where it came from. Obviously though they are not the kind of things you want hanging around in the body for a long time.
Similarly gama rays can be used to treat cancerous tissue by inserting a gamma source... although to be fair it is normally an alpha source. The energy then frazzles (degenerates?) the cells to kill the cancer.
F1 fanatic
Wow - that must have taken you ages Im impressed.
Just as a point the workfunction quantum theory stuff isnt actually wave stuff. Its proof that light is a particle... so you cant really put it in technically. Also you are kind of mixed up. E=hf is not the energy of a wave. It is the energy of a photon - ie a particle of light.
Energy of a wave is proportional to its amplitude squared. The diffraction stuff is all correct though.
Im impressed.Just as a point the workfunction quantum theory stuff isnt actually wave stuff. Its proof that light is a particle... so you cant really put it in technically. Also you are kind of mixed up. E=hf is not the energy of a wave. It is the energy of a photon - ie a particle of light.
Energy of a wave is proportional to its amplitude squared. The diffraction stuff is all correct though.
aha I get it now thanx
well it's kinda related so I though it can be just added up aslo it's right what wave has a momentum and so cause cause pressure hence force yet it's too small to be noticed right ?? or am I getting confused again 
ps cant you give me the equation of wave's energy??
habosh
aha I get it now thanx well it's kinda related so I though it can be just added up aslo it's right what wave has a momentum and so cause cause pressure hence force yet it's too small to be noticed right ?? or am I getting confused again
ps cant you give me the equation of wave's energy??
well it's kinda related so I though it can be just added up aslo it's right what wave has a momentum and so cause cause pressure hence force yet it's too small to be noticed right ?? or am I getting confused again ps cant you give me the equation of wave's energy??
ok, particles of light have a definite momentum... that is what you are probably thinking of... but there is a thing caleed radiation pressure. And so although waves do not have a momentum per se they can exert a force.
If we are talking quantum theory the momentum is:
p = h/lambda
As for the energy of a wave it varies depending on the wave. So for a wave on a string it is:
E per unit length =(1/2)rho *A^2 * w^2
where rho is the density of the string & w the angular frequency of the string.
It could also be pointed out that a wave hasthe general equation:
y=Asin(kx-wt) which is a wave travelling to the right (for conventional axis) with amplitude A
Hey thanks-your responses are great. However, I think your brains would be better utilised if I am more accurate. The assignment was set as follows;
Level two assignment.
'The use of sound waves and electromagnetic waves in the diagnosis and treatment of medical conditions'.
The assignment should cover the following:
1. The difference between sound waves and electromagnetic waves.
2. The electromagnetic spectrym and it's members. Common properties of electromagnetic waves.
3. A brief summary of the following techniques. (About half to 1 side of A4 wach including diagrams).
Ultrasound-scanning, breaking kidney stones, physiotherapy
Radio-waves-NMR imaging
I.R. waves-heat lamps
Visible light-laser treatments-endoscopy
U.V. waves-skin treatment
X-ray-CT/CAT scans
Y-ray-y camera, radiotherapy
You should be aiming at about 5/6 sides of A4 including diagrams
Also include bibliography
Then there is a second paper, going into more depth, for all those wishing to complete the assignment at A level. This was not supported by class work; but up to the student to reasearch and complete-as follows;
How ultrasound waves are produced and detected (piezo electric transducers). How reflection of ultraspound from different types of body tissue is used to produce an image.
A reasonably detailed explanation of the effect of radio waves on water molecules in human tissue when subjected to intense magnetic fields. In addition, how NMR reveals structure within soft tissue.
The use of optical fobres in endoscopes and how they use internal reflection to transmit light to the sight of the investigation and send an image back to the user.
The type of U.V light used in skin treatment and how this light is produced.
How an x-ray tube works and how x-rays are detected in scanners using scintilllation detectors.
The radioisotope injected into the body to release y-rays and how a y camera
detects and produces an image.
The radioisotope used to treat cancerous cells and how they are targeted. How y-rays destroy these cells.
This assignment requires a minimum of 10 sides of A4 icluding diagrams.
Cross referenced bibliography must be included.
What do you think? I have done it once and then resubmitted it after my first effort was no good. Teaches comments were undermining and his directions vague. He says the content is good but it isn't written in an 'A level student way. Then after keeping my work for weeks he announced that there will be another 4 pieces for me to complete before the end of the term in 4-5- weeks. I would take it all personaally, except other students are finding him tricky too. We have two lecturers for science and the other is great! But this one often can't answer our questions and people feel caught in a battle of ego's rather than educational stimulus. Anyway-I want to finish this and so I have had to find some appreciation of what an Alevel student would make of this????? Your feedback is great-cheers-so what do you make of this?
Level two assignment.
'The use of sound waves and electromagnetic waves in the diagnosis and treatment of medical conditions'.
The assignment should cover the following:
1. The difference between sound waves and electromagnetic waves.
2. The electromagnetic spectrym and it's members. Common properties of electromagnetic waves.
3. A brief summary of the following techniques. (About half to 1 side of A4 wach including diagrams).
Ultrasound-scanning, breaking kidney stones, physiotherapy
Radio-waves-NMR imaging
I.R. waves-heat lamps
Visible light-laser treatments-endoscopy
U.V. waves-skin treatment
X-ray-CT/CAT scans
Y-ray-y camera, radiotherapy
You should be aiming at about 5/6 sides of A4 including diagrams
Also include bibliography
Then there is a second paper, going into more depth, for all those wishing to complete the assignment at A level. This was not supported by class work; but up to the student to reasearch and complete-as follows;
How ultrasound waves are produced and detected (piezo electric transducers). How reflection of ultraspound from different types of body tissue is used to produce an image.
A reasonably detailed explanation of the effect of radio waves on water molecules in human tissue when subjected to intense magnetic fields. In addition, how NMR reveals structure within soft tissue.
The use of optical fobres in endoscopes and how they use internal reflection to transmit light to the sight of the investigation and send an image back to the user.
The type of U.V light used in skin treatment and how this light is produced.
How an x-ray tube works and how x-rays are detected in scanners using scintilllation detectors.
The radioisotope injected into the body to release y-rays and how a y camera
detects and produces an image.
The radioisotope used to treat cancerous cells and how they are targeted. How y-rays destroy these cells.
This assignment requires a minimum of 10 sides of A4 icluding diagrams.
Cross referenced bibliography must be included.
What do you think? I have done it once and then resubmitted it after my first effort was no good. Teaches comments were undermining and his directions vague. He says the content is good but it isn't written in an 'A level student way. Then after keeping my work for weeks he announced that there will be another 4 pieces for me to complete before the end of the term in 4-5- weeks. I would take it all personaally, except other students are finding him tricky too. We have two lecturers for science and the other is great! But this one often can't answer our questions and people feel caught in a battle of ego's rather than educational stimulus. Anyway-I want to finish this and so I have had to find some appreciation of what an Alevel student would make of this????? Your feedback is great-cheers-so what do you make of this?
sazzarooo
Hey thanks-your responses are great. However, I think your brains would be better utilised if I am more accurate. The assignment was set as follows;
Level two assignment.
'The use of sound waves and electromagnetic waves in the diagnosis and try to serach about ultra sound from google,I think they used it for the stones in the kidney or whatever but not sure,as I took medical physics last yeartreatment of medical conditions'.
The assignment should cover the following:
1. The difference between sound waves and electromagnetic waves.done
2. The electromagnetic spectrym and it's members. Common properties of electromagnetic waves
Level two assignment.
'The use of sound waves and electromagnetic waves in the diagnosis and try to serach about ultra sound from google,I think they used it for the stones in the kidney or whatever but not sure,as I took medical physics last yeartreatment of medical conditions'.
The assignment should cover the following:
1. The difference between sound waves and electromagnetic waves.done
2. The electromagnetic spectrym and it's members. Common properties of electromagnetic waves
.there are radio waves,microwaves ,infra red,visible light,ultraviolet ,x ray and gamma ray more over there is cosmic ray
you can set their frequencies if you want of wavelength or both
ofcourse soundwave's speed is about 330m/s and electromagnetic arre about 3x10^8
visible light consist of redlight-orange-yellow-green-blue-violet
all of electromagnetic waves are transverse,they travel in vacuum,they have the speed of 3x10^8,they convey energy,they can superpose and they can form stationary waves,they can carry energy
all
What do you think? I have done it once and then resubmitted it after my first effort was no good. Teaches comments were undermining and his directions vague. He says the content is good but it isn't written in an 'A level student way. Then after keeping my work for weeks he announced that there will be another 4 pieces for me to complete before the end of the term in 4-5- weeks. I would take it all personaally, except other students are finding him tricky too. We have two lecturers for science and the other is great! But this one often can't answer our questions and people feel caught in a battle of ego's rather than educational stimulus. Anyway-I want to finish this and so I have had to find some appreciation of what an Alevel student would make of this????? Your feedback is great-cheers-so what do you make of this?
mmm I suggest you try some big libraries and google can be really useful try nelson book the one with topics it will give general idea about x rays and gamma rays,I think gamma ionises the cells which damages them but you can go in details,I hope i've helped you,I can't deny this needs alot of work but if you were determained you are going to finish it
good lucka few points about waves:
*oscillatory motion is passed from one point to the next in a medium. this gives rise to wave motion in which information and evergy propagate from one point to another without bulk motion of the medium.
*travelling waves - energy transmitted from one point to another
*standing waves - no net movement of energy
*wave equation: phi(x)=Acos(kt) etc
*take partial derivative wrt to x to obtain the general solution
*delta(KE)=1/2*rho*delta(x)*(partial der of phi wrt to t)^2 etc
*extend to 2D and 3D for travelling waves
*remember to include nodes for standing waves
*standing waves on strings/in pipes/on membranes
*harmonics
*electromagnetic waves - b-fields and e-fields
*interference and diffraction
*huygen's principle
*young's double slits
*reflection/refraction/TIR
*lenses - the lens maker's formula etc
*oscillatory motion is passed from one point to the next in a medium. this gives rise to wave motion in which information and evergy propagate from one point to another without bulk motion of the medium.
*travelling waves - energy transmitted from one point to another
*standing waves - no net movement of energy
*wave equation: phi(x)=Acos(kt) etc
*take partial derivative wrt to x to obtain the general solution
*delta(KE)=1/2*rho*delta(x)*(partial der of phi wrt to t)^2 etc
*extend to 2D and 3D for travelling waves
*remember to include nodes for standing waves
*standing waves on strings/in pipes/on membranes
*harmonics
*electromagnetic waves - b-fields and e-fields
*interference and diffraction
*huygen's principle
*young's double slits
*reflection/refraction/TIR
*lenses - the lens maker's formula etc
habosh
there are radio waves,microwaves ,infra red,visible light,ultraviolet ,x ray and gamma ray more over there is cosmic ray
you can set their frequencies if you want of wavelength or both
ofcourse soundwave's speed is about 330m/s and electromagnetic arre about 3x10^8
visible light consist of redlight-orange-yellow-green-blue-violet
all of electromagnetic waves are transverse,they travel in vacuum,they have the speed of 3x10^8,they convey energy,they can superpose and they can form stationary waves,they can carry energy
you can set their frequencies if you want of wavelength or both
ofcourse soundwave's speed is about 330m/s and electromagnetic arre about 3x10^8
visible light consist of redlight-orange-yellow-green-blue-violet
all of electromagnetic waves are transverse,they travel in vacuum,they have the speed of 3x10^8,they convey energy,they can superpose and they can form stationary waves,they can carry energy
they're all just EM waves, and changing the frequency changed the wavelength!! you can't change one and not the other with EM waves because they all travel at c through a vacuum *hits head against wall*
c=3.01*10^8
Lozza
they're all just EM waves, and changing the frequency changed the wavelength!! you can't change one and not the other with EM waves because they all travel at c through a vacuum *hits head against wall*
c=3.01*10^8
c=3.01*10^8
LO I know that!!!
So whats the problem i didn't say otherwise!!!!??
Ok-well-thanks for your feedback. Are you Alevel students or at UNI>>>? I only ask because it is interesting to me to see what other peeps may be able to manage easily or not, in comparison to me.
I don't have long and I have no physics books here with me at all-so I had better get on with it.
You have been great! Thanx for all your comments and work.
I don't have long and I have no physics books here with me at all-so I had better get on with it.
You have been great! Thanx for all your comments and work.
The thing is, teach has been very sure that he doesn't want anything in there that he HASN'T asked for. I feel I have a fairly good handle on what he has asked for........finally-it's just that the goal posts have been changed so many times that loads of time has been wasted. Having said that-until reading what others have written, I couldn't really get an accurate feel for what he meant by writing it like an A Level student. I have a better idea now. I can send you my efforts if you are not bored of the subject by now?
sazzarooo
The thing is, teach has been very sure that he doesn't want anything in there that he HASN'T asked for. I feel I have a fairly good handle on what he has asked for........finally-it's just that the goal posts have been changed so many times that loads of time has been wasted. Having said that-until reading what others have written, I couldn't really get an accurate feel for what he meant by writing it like an A Level student. I have a better idea now. I can send you my efforts if you are not bored of the subject by now?
go for it - post it up if youd like. Can I just ask if you could change your font though... its REALLY difficult to read
25/11/04 D:\College\Science\Access Science Waves.doc Sarah Perrott
‘The use of sound waves and electromagnetic waves in the diagnosis and treatment of medical conditions’.
What is a wave?
Waves are everywhere. Sound waves, visible light waves, radio waves, microwaves, water waves, stadium waves, earthquake waves and slinky waves are a few examples. In addition to waves, there are phenomena which resemble waves, that we describe as being ‘wavelike’. The motion of a pendulum; of a mass suspended by a spring; of a child on a swing and the wave of the hand can all be seen as wavelike.
Typically, our first thought concerning waves conjures up a picture of a wave moving across the surface of an ocean. The water wave has a crest and a trough and travels from one location to another. One crest is often followed by a second crest which is often followed by a third crest. Every crest is separated by a trough to create an alternating pattern of crests and troughs. A duck or gull at rest on the surface of the water is observed to bob up-and-down at rather regular time intervals as the wave passes by. The waves may appear to be plane waves which travel together as a front in a straight-line direction, perhaps towards a sandy shore. Or the waves may be circular waves which originate from the point where the disturbances occur; such circular waves travel across the surface of the water in all directions.
Another picture of waves involves the movement of a slinky or similar set of coils. If a slinky is stretched out from end to end, a wave can be passed through the slinky by either vibrating the first coil up and down vertically or back and forth horizontally. As the wave moves along the slinky, each individual coil is seen to move out of place and then return to its original position.
Finally, we are familiar with microwaves and visible light waves, radio waves and sound waves. Waves, carry energy from one location to another and if the frequency of those waves can be changed, then we can also carry a complex signal which is capable of transmitting an idea or thought from one location to another.
Most waves require a ‘medium’.
A wave can be described as a disturbance that travels through a medium from one location to another location. Consider a slinky wave as an example of a wave. When the slinky is stretched from end to end and is held at rest, it assumes a natural position known as the equilibrium or rest position. The coils of the slinky naturally assume this position, spaced equally far apart. To introduce a wave into the slinky, the first particle is displaced or moved from its rest position. The particle might be moved upwards or downwards, forwards or backwards; but once moved, it is returned to its original rest position. The act of moving the first coil of the slinky in a given direction and then returning it to its rest position creates a disturbance in the slinky. We can then observe this disturbance moving through the slinky from one end to the other. A single back and forth vibration is a pulse.Whereas the repeating and periodic disturbance which moves through a medium from one location to another is referred to as a wave.
A medium is a substance or material which carries the wave. It is a series of interconnected or merely interacting particles. The interactions of one particle of the medium with the next adjacent particle allows the disturbance to travel through the medium. In the case of the slinky wave, the particles are the individual coils of the slinky. In the case of a sound wave in air, the particles are the individual molecules of air.
Waves transport energy.
Waves are said to be an energy transport phenomenon. As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other. In a slinky wave, a person imparts energy to the first coil by doing work upon it. The first coil receives a large amount of energy which it subsequently transfers to the second coil and so on. In this manner, energy is transported from one end of the slinky to the other, from its source to another location.
Waves are seen to move through an ocean or lake; yet the water always returns to its rest position. Energy is transported through the medium, yet the water molecules are not transported. If we were to observe a gull or duck at rest on the water, it would merely bob up-and-down in a somewhat circular fashion as the disturbance moves through the water; the gull or duck always returning to its original position. Waves involve the transport of energy without the transport of matter.
Types of waves.
Waves come in many shapes and forms. One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction which the waves travel.
A transverse wave.
This is a wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves. If a slinky is stretched out in a horizontal direction across the classroom, and a pulse is introduced into the slinky on the left end by vibrating the first coil up and down, then energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. Transverse waves are always characterized by particle motion being perpendicular to wave motion.
A longitudinal wave.
This is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves. If a slinky is stretched out in a horizontal direction across the classroom, and a pulse is introduced into the slinky on the left end by vibrating the first coil left and right, then energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced leftwards and rightwards. Longitudinal waves are always characterized by particle motion being parallel to wave motion.
Surface waves.
While waves which travel within the depths of the ocean are longitudinal waves, the waves which travel along the surface of the oceans are referred to as surface waves. A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are neither longitudinal nor transverse. In longitudinal and transverse waves, all the particles in the entire bulk of the medium move in a parallel and a perpendicular direction (respectively) relative to the direction of energy transport. In a surface wave, it is only the particles at the surface of the medium which undergo the circular motion.
Any wave moving through a medium has a source. For a slinky wave, it is usually the first coil which becomes displaced by the hand of a person. For a sound wave, it is usually the vibration of the vocal chords or a guitar string which sets the first particle of air in vibrational motion. At the location where the wave is introduced into the medium, the particles which are displaced from their equilibrium position always moves in the same direction as the source of the vibration.
An electromagnetic wave.
This is a wave which is capable of transmitting its energy through a vacuum (i.e., empty space). They are produced by the vibration of electrons within atoms and they have both electric and magnetic components. Electromagnetic radiation is an energy, produced by oscillation or acceleration of an electric charge. All light waves are examples of electromagnetic waves; as are microwaves, x-rays, and TV and radio transmissions. Electromagnetic waves have both electric and magnetic components.
A mechanical wave.
This is a wave which is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another. A sound wave is an example of a mechanical wave. Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and telephone chord waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a telephone chord wave requires a telephone chord.
Finally, before we look into particular types of waves and their uses, let us summarise. We see that the difference between sound waves and electromagnetic waves, is that the latter is able to transmitt energy without a medium , whereas sound requires a medium to be effective.
The electromagnetic spectrum.
The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field. The second part is a magnetic field. So that is why they are called electromagnetic waves. The two fields are at right angles to each other.
Infra Red;
These waves have a very short length, although longer than visible light. Beyond the red end of the visible spectrum, is infra red. A filament lamp emits light and infra red radiation (heat). We can see the red light, and feel the warmth on our skin. Infra-red waves are just below visible red light in the electromagnetic spectrum ("Infra" means "below"). They are used for many tasks, for example, TV remote controls and video recorders, and physiotherapists use heat lamps to help heal sports injuries. Also, infra red pictures may reveal tumours. Because every object gives off IR waves, we can use them to "see in the dark". Night sites for weapons sometimes use a sensitive IR detector.
Ultra violet;
These waves have very high energy and very short wave lengths; shorter than visible light. Some animals like honey bees can see ultra-violet light. Some plants have white flowers, at least you think that they are all white, but they may appear to be different colours to a honey bee because of the amounts of ultra-violet light which they reflect.
Radio waves.
Radio waves have a much longer wavelength that light waves. The longest waves are several kilometers in length. The shortest ones are only millimeters long. Radio waves will make the electrons in a piece of copper wire move; this means that they generate electric currents in the wire. In fact it works both ways: alternating currents in a copper wire generate electromagnetic waves, and electromagnetic waves generate alternating currents. The electric currents at "radio frequencies" (rf) are used by radio and television transmitters and receivers.
Microwaves;
Microwaves have such a short wavelength that some are are very easily absorbed by water. This is why they are used in microwave ovens. Water in your TV dinner absorbs the microwaves, the energy of the microwaves is converted into heat it makes the water molecules vibrate faster.
Gamma Rays;
These rays have very high energy and will even go through metals. So they can be used for finding tiny cracks in metals. Some radioactive materials produce gamma rays. Gamma rays and X-Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is radio-therapy.
The use of sound waves and electromagnetic waves in medecine.
Ultra-sound;
Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen:
The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
Photo courtesy Karim and Nancy Nice
Ultrasound image of a growing fetus (approximately 12 weeks old) inside a mother's uterus. This is a side view of the baby, showing (right to left) the head, neck, torso and legs
In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.
Piezo electric transducers;
The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the probe, there are one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.
Transducer probes come in many shapes and sizes. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image. Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasounc beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, esophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
(cont)
‘The use of sound waves and electromagnetic waves in the diagnosis and treatment of medical conditions’.
What is a wave?
Waves are everywhere. Sound waves, visible light waves, radio waves, microwaves, water waves, stadium waves, earthquake waves and slinky waves are a few examples. In addition to waves, there are phenomena which resemble waves, that we describe as being ‘wavelike’. The motion of a pendulum; of a mass suspended by a spring; of a child on a swing and the wave of the hand can all be seen as wavelike.
Typically, our first thought concerning waves conjures up a picture of a wave moving across the surface of an ocean. The water wave has a crest and a trough and travels from one location to another. One crest is often followed by a second crest which is often followed by a third crest. Every crest is separated by a trough to create an alternating pattern of crests and troughs. A duck or gull at rest on the surface of the water is observed to bob up-and-down at rather regular time intervals as the wave passes by. The waves may appear to be plane waves which travel together as a front in a straight-line direction, perhaps towards a sandy shore. Or the waves may be circular waves which originate from the point where the disturbances occur; such circular waves travel across the surface of the water in all directions.
Another picture of waves involves the movement of a slinky or similar set of coils. If a slinky is stretched out from end to end, a wave can be passed through the slinky by either vibrating the first coil up and down vertically or back and forth horizontally. As the wave moves along the slinky, each individual coil is seen to move out of place and then return to its original position.
Finally, we are familiar with microwaves and visible light waves, radio waves and sound waves. Waves, carry energy from one location to another and if the frequency of those waves can be changed, then we can also carry a complex signal which is capable of transmitting an idea or thought from one location to another.
Most waves require a ‘medium’.
A wave can be described as a disturbance that travels through a medium from one location to another location. Consider a slinky wave as an example of a wave. When the slinky is stretched from end to end and is held at rest, it assumes a natural position known as the equilibrium or rest position. The coils of the slinky naturally assume this position, spaced equally far apart. To introduce a wave into the slinky, the first particle is displaced or moved from its rest position. The particle might be moved upwards or downwards, forwards or backwards; but once moved, it is returned to its original rest position. The act of moving the first coil of the slinky in a given direction and then returning it to its rest position creates a disturbance in the slinky. We can then observe this disturbance moving through the slinky from one end to the other. A single back and forth vibration is a pulse.Whereas the repeating and periodic disturbance which moves through a medium from one location to another is referred to as a wave.
A medium is a substance or material which carries the wave. It is a series of interconnected or merely interacting particles. The interactions of one particle of the medium with the next adjacent particle allows the disturbance to travel through the medium. In the case of the slinky wave, the particles are the individual coils of the slinky. In the case of a sound wave in air, the particles are the individual molecules of air.
Waves transport energy.
Waves are said to be an energy transport phenomenon. As a disturbance moves through a medium from one particle to its adjacent particle, energy is being transported from one end of the medium to the other. In a slinky wave, a person imparts energy to the first coil by doing work upon it. The first coil receives a large amount of energy which it subsequently transfers to the second coil and so on. In this manner, energy is transported from one end of the slinky to the other, from its source to another location.
Waves are seen to move through an ocean or lake; yet the water always returns to its rest position. Energy is transported through the medium, yet the water molecules are not transported. If we were to observe a gull or duck at rest on the water, it would merely bob up-and-down in a somewhat circular fashion as the disturbance moves through the water; the gull or duck always returning to its original position. Waves involve the transport of energy without the transport of matter.
Types of waves.
Waves come in many shapes and forms. One way to categorize waves is on the basis of the direction of movement of the individual particles of the medium relative to the direction which the waves travel.
A transverse wave.
This is a wave in which particles of the medium move in a direction perpendicular to the direction which the wave moves. If a slinky is stretched out in a horizontal direction across the classroom, and a pulse is introduced into the slinky on the left end by vibrating the first coil up and down, then energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced upwards and downwards. Transverse waves are always characterized by particle motion being perpendicular to wave motion.
A longitudinal wave.
This is a wave in which particles of the medium move in a direction parallel to the direction which the wave moves. If a slinky is stretched out in a horizontal direction across the classroom, and a pulse is introduced into the slinky on the left end by vibrating the first coil left and right, then energy will begin to be transported through the slinky from left to right. As the energy is transported from left to right, the individual coils of the medium will be displaced leftwards and rightwards. Longitudinal waves are always characterized by particle motion being parallel to wave motion.
Surface waves.
While waves which travel within the depths of the ocean are longitudinal waves, the waves which travel along the surface of the oceans are referred to as surface waves. A surface wave is a wave in which particles of the medium undergo a circular motion. Surface waves are neither longitudinal nor transverse. In longitudinal and transverse waves, all the particles in the entire bulk of the medium move in a parallel and a perpendicular direction (respectively) relative to the direction of energy transport. In a surface wave, it is only the particles at the surface of the medium which undergo the circular motion.
Any wave moving through a medium has a source. For a slinky wave, it is usually the first coil which becomes displaced by the hand of a person. For a sound wave, it is usually the vibration of the vocal chords or a guitar string which sets the first particle of air in vibrational motion. At the location where the wave is introduced into the medium, the particles which are displaced from their equilibrium position always moves in the same direction as the source of the vibration.
An electromagnetic wave.
This is a wave which is capable of transmitting its energy through a vacuum (i.e., empty space). They are produced by the vibration of electrons within atoms and they have both electric and magnetic components. Electromagnetic radiation is an energy, produced by oscillation or acceleration of an electric charge. All light waves are examples of electromagnetic waves; as are microwaves, x-rays, and TV and radio transmissions. Electromagnetic waves have both electric and magnetic components.
A mechanical wave.
This is a wave which is not capable of transmitting its energy through a vacuum. Mechanical waves require a medium in order to transport their energy from one location to another. A sound wave is an example of a mechanical wave. Sound waves are incapable of traveling through a vacuum. Slinky waves, water waves, stadium waves, and telephone chord waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a telephone chord wave requires a telephone chord.
Finally, before we look into particular types of waves and their uses, let us summarise. We see that the difference between sound waves and electromagnetic waves, is that the latter is able to transmitt energy without a medium , whereas sound requires a medium to be effective.
The electromagnetic spectrum.
The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field. The second part is a magnetic field. So that is why they are called electromagnetic waves. The two fields are at right angles to each other.
Infra Red;
These waves have a very short length, although longer than visible light. Beyond the red end of the visible spectrum, is infra red. A filament lamp emits light and infra red radiation (heat). We can see the red light, and feel the warmth on our skin. Infra-red waves are just below visible red light in the electromagnetic spectrum ("Infra" means "below"). They are used for many tasks, for example, TV remote controls and video recorders, and physiotherapists use heat lamps to help heal sports injuries. Also, infra red pictures may reveal tumours. Because every object gives off IR waves, we can use them to "see in the dark". Night sites for weapons sometimes use a sensitive IR detector.
Ultra violet;
These waves have very high energy and very short wave lengths; shorter than visible light. Some animals like honey bees can see ultra-violet light. Some plants have white flowers, at least you think that they are all white, but they may appear to be different colours to a honey bee because of the amounts of ultra-violet light which they reflect.
Radio waves.
Radio waves have a much longer wavelength that light waves. The longest waves are several kilometers in length. The shortest ones are only millimeters long. Radio waves will make the electrons in a piece of copper wire move; this means that they generate electric currents in the wire. In fact it works both ways: alternating currents in a copper wire generate electromagnetic waves, and electromagnetic waves generate alternating currents. The electric currents at "radio frequencies" (rf) are used by radio and television transmitters and receivers.
Microwaves;
Microwaves have such a short wavelength that some are are very easily absorbed by water. This is why they are used in microwave ovens. Water in your TV dinner absorbs the microwaves, the energy of the microwaves is converted into heat it makes the water molecules vibrate faster.
Gamma Rays;
These rays have very high energy and will even go through metals. So they can be used for finding tiny cracks in metals. Some radioactive materials produce gamma rays. Gamma rays and X-Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is radio-therapy.
The use of sound waves and electromagnetic waves in medecine.
Ultra-sound;
Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen:
The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
Photo courtesy Karim and Nancy Nice
Ultrasound image of a growing fetus (approximately 12 weeks old) inside a mother's uterus. This is a side view of the baby, showing (right to left) the head, neck, torso and legs
In a typical ultrasound, millions of pulses and echoes are sent and received each second. The probe can be moved along the surface of the body and angled to obtain various views.
Piezo electric transducers;
The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the probe, there are one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.
Transducer probes come in many shapes and sizes. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image. Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasounc beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, esophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
(cont)
Radio Waves / MRI Imaging;
MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s. The MRI scan uses magnetic fields and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation. The patient lies inside a large, cylinder-shaped magnet, while radio waves are sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals.
Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above. Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radiowave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be used to find out if it has spread into nearby brain tissue.
The technique also allows us to focus on other details in the brain. For example, it makes it possible to see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of oxygen after a stroke.
The MRI scan is also able to show both the heart and the large blood vessels in the surrounding tissue. This makes it possible to detect heart defects that have been building up since birth, as well as changes in the thickness of the muscles around the heart following a heart attack. The method can also be used to examine the joints, spine and sometimes the soft parts of your body such as the liver, kidneys and spleen.
X ray
These rays are, like light and radio waves, a form of electromagnetic radiation. X-rays have high energy and short wavelength and are able to pass through tissue. On their passage through the body, the denser tissues, such as the bones, will block more of the rays than will the less dense tissues, such as the lung.
A special type of photographic film is used to record X-ray pictures. The X-rays are converted into light and the more energy that has reached the recording system, the darker that region of the film will be. This is why the bones on an X-ray image appear whiter (less energy passes through) than the lungs (more energy passes through). A simple X-ray image can be extremely informative. For example it can show whether or not a bone is broken or whether or not there is a shadow on the lung.
Special X-ray techniques can also be used to investigate other problems with the soft tissues of the body. By injecting special dye into arteries and/or veins the blood vessels can be made visible. By swallowing special dye the gullet and stomach can be examined. Similar dye can be introduced via an enema to examine the back passage and the rest of the large bowel
X-rays are just very high energy photons – they are another form of light energy. However, they are well beyond the range of visible light. When they hit certain materials – particularly mica – they cause the atoms of that material to jump up to a very high energy level – skipping several intermediate levels. As these electrons “fall” back into more stable orbits, they emit photons of lower energy than the X-ray. Some of these can be in the visible range and will be seen as a little flash of light – a “scintillation”. These can be seen under a microscope or detected with a digital camera. X-Rays have so much energy and such a short wavelength that they can go right through you. However, they cannot get through bone as easily as they can get through muscle. This is because your bones contain so much Calcium. X-Ray can also be used to find other problems in your body. If the doctors want to look for ulcers in your guts, they can give you a Barium meal. Like Calcium, the Barium absorbs X-Rays so the doctors can look at parts of your guts and find your ulcers.
CT/CAT Scans;
A CT (computerised tomography) scanner is a special kind of X-ray machine. Instead of sending out a single X-ray through your body as with ordinary X-rays, several beams are sent simultaneously from different angles. The X-rays from the beams are detected after they have passed through the body and their strength is measured. Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have passed through denser tissue such as bone will be weaker. A computer can use this information to work out the relative density of the tissues examined. Each set of measurements made by the scanner is, in effect, a cross-section through the body. The computer processes the results, displaying them as a two-dimensional picture shown on a monitor. CT scans are far more detailed than ordinary X-rays. The information from the two-dimensional computer images can be reconstructed to produce three-dimensional images by some modern CT scanners. They can be used to produce virtual images that show what a surgeon would see during an operation. CT scans have already allowed doctors to inspect the inside of the body without having to operate or perform unpleasant examinations. CT scanning has also proven invaluable in pinpointing tumours and planning treatment with radiotherapy.
MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s. The MRI scan uses magnetic fields and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation. The patient lies inside a large, cylinder-shaped magnet, while radio waves are sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals.
Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above. Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radiowave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
Because the MRI scan gives very detailed pictures it is the best technique when it comes to finding tumours (benign or malignant abnormal growths) in the brain. If a tumour is present the scan can also be used to find out if it has spread into nearby brain tissue.
The technique also allows us to focus on other details in the brain. For example, it makes it possible to see the strands of abnormal tissue that occur if someone has multiple sclerosis and it is possible to see changes occurring when there is bleeding in the brain, or find out if the brain tissue has suffered lack of oxygen after a stroke.
The MRI scan is also able to show both the heart and the large blood vessels in the surrounding tissue. This makes it possible to detect heart defects that have been building up since birth, as well as changes in the thickness of the muscles around the heart following a heart attack. The method can also be used to examine the joints, spine and sometimes the soft parts of your body such as the liver, kidneys and spleen.
X ray
These rays are, like light and radio waves, a form of electromagnetic radiation. X-rays have high energy and short wavelength and are able to pass through tissue. On their passage through the body, the denser tissues, such as the bones, will block more of the rays than will the less dense tissues, such as the lung.
A special type of photographic film is used to record X-ray pictures. The X-rays are converted into light and the more energy that has reached the recording system, the darker that region of the film will be. This is why the bones on an X-ray image appear whiter (less energy passes through) than the lungs (more energy passes through). A simple X-ray image can be extremely informative. For example it can show whether or not a bone is broken or whether or not there is a shadow on the lung.
Special X-ray techniques can also be used to investigate other problems with the soft tissues of the body. By injecting special dye into arteries and/or veins the blood vessels can be made visible. By swallowing special dye the gullet and stomach can be examined. Similar dye can be introduced via an enema to examine the back passage and the rest of the large bowel
X-rays are just very high energy photons – they are another form of light energy. However, they are well beyond the range of visible light. When they hit certain materials – particularly mica – they cause the atoms of that material to jump up to a very high energy level – skipping several intermediate levels. As these electrons “fall” back into more stable orbits, they emit photons of lower energy than the X-ray. Some of these can be in the visible range and will be seen as a little flash of light – a “scintillation”. These can be seen under a microscope or detected with a digital camera. X-Rays have so much energy and such a short wavelength that they can go right through you. However, they cannot get through bone as easily as they can get through muscle. This is because your bones contain so much Calcium. X-Ray can also be used to find other problems in your body. If the doctors want to look for ulcers in your guts, they can give you a Barium meal. Like Calcium, the Barium absorbs X-Rays so the doctors can look at parts of your guts and find your ulcers.
CT/CAT Scans;
A CT (computerised tomography) scanner is a special kind of X-ray machine. Instead of sending out a single X-ray through your body as with ordinary X-rays, several beams are sent simultaneously from different angles. The X-rays from the beams are detected after they have passed through the body and their strength is measured. Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have passed through denser tissue such as bone will be weaker. A computer can use this information to work out the relative density of the tissues examined. Each set of measurements made by the scanner is, in effect, a cross-section through the body. The computer processes the results, displaying them as a two-dimensional picture shown on a monitor. CT scans are far more detailed than ordinary X-rays. The information from the two-dimensional computer images can be reconstructed to produce three-dimensional images by some modern CT scanners. They can be used to produce virtual images that show what a surgeon would see during an operation. CT scans have already allowed doctors to inspect the inside of the body without having to operate or perform unpleasant examinations. CT scanning has also proven invaluable in pinpointing tumours and planning treatment with radiotherapy.
Visible light;
Our eyes can detect only a tiny part of the electromagnetic spectrum, called ‘visible light’. This means that there's a great deal happening around us that we're simply not aware of, unless we have instruments to detect it. Light waves are given off by anything that's hot enough to glow.
This is how light bulbs work - an electric current heats the lamp filament to around 3,000 degrees, and it glows white-hot. White light is actually made up of a whole range of colours, mixed together.
We can see this if we pass white light through a glass prism - the violet light is bent ("refracted") more than the red, because it has a shorter wavelength - and we see a rainbow of colours. Light waves can also be made using a laser. This works differently to a light bulb, and produces "coherent" light. Lasers can be used to treat a wide number of disorders i.e. unwanted hair, eye treatment, skin problems, cosmetic surgery and so on.
Laser Light;
With laser light all the crests and troughs line up with each other. That means that all the light is exactly the same color. Which is called "monochromatic". Also all the waves are going in the same direction. It is much more "orderly" than the other light. It is very organized waves with all the light exactly the same color and going in exactly the same direction. We can also think of light as little particles. With a laser these particles come in a perfectly uniform stream all going in the same direction. Because it is so orderly we can control laser light extremely well, and that is why we can use it to do so many things. Bearing in mind how light interacts with atoms we can look further to see how laser light is produced.
With laser light all the crests and troughs line up with each other. Which means that all the light is exactly the same color. This is called "monochromatic". Also, all the waves are going in the same direction. It is much more "orderly" than the other light. We can also think of light as little particles. With a laser these particles come in a perfectly uniform stream all going in the same direction. Because it is so orderly we can control laser light extremely well.We know that if light of the right color hits an atom, it will bump an electron up to a higher energy level and later the electron falls back down, giving off light of the same color in some random direction. However, if the "brightness" of the light source, which makes the particles of light called photons, come out faster there is a significant change.When a photon hits an atom that is already excited, the atom lets go of the photon and it ends up going in the same direction as the incoming photon. When a photon hits an atom that is already excited, the atom releases a new photon that is completely identical to the incoming photon; same color, going in the same direction.This is called "stimulated emission".
When one photon hits an excited atom there are two photons travelling together. When one of those finds another excited atom, there are three photons, and so on and so on, but they are all exactly the same because they are being cloned by stimulated emission. The number of photons gets amplified. The word laser is short for "light amplification by stimulated emission of radiation". So the incoming light is a wave, and when it hits the excited atom, the atom releases some energy that just makes the wave get bigger.
However, in order to excite the atom, it needs to be hit with a photon to start with. It takes two photons to get two photons; but by exciting a number of atoms simultaneously, without hitting them with protons, a chain reaction can be created. This is called Population Inversion. This is done by pumping electrical energy into the atoms in certain ways or shining different colored light at them. Both these processes stick the atoms into much higher energy levels, and under special conditions then they jump down and accumulate in the one excited energy level instead of going all the way to the ground state.
When an excited atom sends off a photon, it can hit more excited atoms and cause a little landslide of more photons; but the photons can go off in any direction. So mirrors are used to bounce the photons back and forth along one direction through the atoms and a partially reflective mirror is used on one end so that some of the light leaks through. The beam inside the laser is a lot more powerful than the beam that actually comes out.
A laser beam contains a lot of synchronised energy. Instead of being randomised, like ordinary light, all the photons march together. Imagine a lot of people marching together across a wobbly rope bridge. Their synchronised stamping would quickly cause the bridge to resonate and it would probably break. The same sort of thing happens with the laser hitting a material. The photons cause a local heating effect that “burns” the material, breaking molecules apart. If you have ever focussed the light of the sun onto something and seen it burn then you have seen the same effect. Because it is so coherent, laser beams can be focussed with great precision and so the cutting can be very precise.
The use of Optical fibres in Endoscopes;
An optical fibre is like a “tunnel” with extremely reflective walls.They rush down the tunnel with no way out and because only a few can get in at a time, they don’t interfere with each other (very much). By packing a bundle of these fibres together (several hundreds, if not thousands), each can transmit part of an image back to either a microscope or a digital camera to be magnified. Note that some of the fibres can be used to carry illumination down to the far end, too.
The fibres used in an endoscope are generally made either from glass or from a special kind of plastic that can be extruded very, very thin – only a few millionths of a meter in diameter. At that thickness, glass becomes surprisingly flexible.
UV Light ;
Ultra-violet light is produced by exciting atoms that then emit a photon at the right energy level. However, there is no attempt to cause massive secondary emission or to make the light coherent.Though UV light does cause a heating effect – sunlight contains a certain amount of UV, which is what causes sunburn, skin aging, cancer and the like – it is also absorbed by certain pigments in layers just under the skin. The energy thus absorbed is used to power chemical reactions that make certain important vitamins that accelerate skin healing.
Y-rays / Radiotherapy;
A form of electromagnetic radiation, similar to X-rays but of shorter wavelength. Y-rays and X-rays are also used therapeutically to kill tumor cells. Radiotherapy is the use of X-rays to treat disease. It used to be known as radium treatment. Although radiotherapy uses stronger rays than those used for taking pictures it feels no different and is painless. Approximately four out of ten people with cancer will have radiotherapy as part of their treatment. This can either be given from outside the body (external radiotherapy), using X-rays or cobalt irradiation, or from within (internal radiotherapy), by placing radioactive treatment in or close to the tumour being treated. The X-rays work by destroying the cancer cells in the treated area. Although normal cells are also affected, they can repair themselves.
Y-rays are like X-rays but of higher energy. They are also called “gamma rays”. Same principles but they cause more damage. Being of shorter wavelength, they can be used to create very high definition pictures but this definition would rarely be needed in medical applications. Indeed, the damage caused to the patient would normally far outweigh the benefits and I would expect such rays to be used for imaging only under exceptional conditions. I don’t know about “injecting”, though. One could, conceivably, use a radioactive material that emits Y-rays naturally (along with other forms of radiation) and I suppose that this could be made small enough to be swallowed or pushed into a hole in the flesh but I seriously doubt that such a technique would be considered even remotely safe. Technically, it would be like having a light bulb inside you. A scanner placed outside the body would pick up the Y-rays and form an image through either scintillation or (more likely) fluorescence, after focussing the Y-rays onto a suitable detector. However, the source would be in the body for a significant period of time, with no practical way to turn it on or off.
Cancerous cells are destroyed in radio-therapy by burning them. Three separate beams are usually focussed through the body from different angles. Each beam by itself can not cause too much damage but where all three meet (inside the cancer) the combined burning effect kills the cancer cells. Radiotherapy kills all cells in the target area at about a 30% rate of attrition. Cancer cells are simply normal healthy cells that don't go on to differentiate - either partially or fully - they simply duplicate. Therefore, almost as soon as they come into being, they duplicate again. New cells can become anything. Differentiation means to further develop function according to the immediate environment (new cells in a hair become hair-cells, in a kidney, kidney cells, etc.) This takes much more time, before they can again duplicate. At the moment of cell division, they are the most vulnerable. Therefore, radiotherapy administered over time finally kills more undifferentiated (cancer) cells than it does those that are differentiated.
That was the first attempt-rough
Our eyes can detect only a tiny part of the electromagnetic spectrum, called ‘visible light’. This means that there's a great deal happening around us that we're simply not aware of, unless we have instruments to detect it. Light waves are given off by anything that's hot enough to glow.
This is how light bulbs work - an electric current heats the lamp filament to around 3,000 degrees, and it glows white-hot. White light is actually made up of a whole range of colours, mixed together.
We can see this if we pass white light through a glass prism - the violet light is bent ("refracted") more than the red, because it has a shorter wavelength - and we see a rainbow of colours. Light waves can also be made using a laser. This works differently to a light bulb, and produces "coherent" light. Lasers can be used to treat a wide number of disorders i.e. unwanted hair, eye treatment, skin problems, cosmetic surgery and so on.
Laser Light;
With laser light all the crests and troughs line up with each other. That means that all the light is exactly the same color. Which is called "monochromatic". Also all the waves are going in the same direction. It is much more "orderly" than the other light. It is very organized waves with all the light exactly the same color and going in exactly the same direction. We can also think of light as little particles. With a laser these particles come in a perfectly uniform stream all going in the same direction. Because it is so orderly we can control laser light extremely well, and that is why we can use it to do so many things. Bearing in mind how light interacts with atoms we can look further to see how laser light is produced.
With laser light all the crests and troughs line up with each other. Which means that all the light is exactly the same color. This is called "monochromatic". Also, all the waves are going in the same direction. It is much more "orderly" than the other light. We can also think of light as little particles. With a laser these particles come in a perfectly uniform stream all going in the same direction. Because it is so orderly we can control laser light extremely well.We know that if light of the right color hits an atom, it will bump an electron up to a higher energy level and later the electron falls back down, giving off light of the same color in some random direction. However, if the "brightness" of the light source, which makes the particles of light called photons, come out faster there is a significant change.When a photon hits an atom that is already excited, the atom lets go of the photon and it ends up going in the same direction as the incoming photon. When a photon hits an atom that is already excited, the atom releases a new photon that is completely identical to the incoming photon; same color, going in the same direction.This is called "stimulated emission".
When one photon hits an excited atom there are two photons travelling together. When one of those finds another excited atom, there are three photons, and so on and so on, but they are all exactly the same because they are being cloned by stimulated emission. The number of photons gets amplified. The word laser is short for "light amplification by stimulated emission of radiation". So the incoming light is a wave, and when it hits the excited atom, the atom releases some energy that just makes the wave get bigger.
However, in order to excite the atom, it needs to be hit with a photon to start with. It takes two photons to get two photons; but by exciting a number of atoms simultaneously, without hitting them with protons, a chain reaction can be created. This is called Population Inversion. This is done by pumping electrical energy into the atoms in certain ways or shining different colored light at them. Both these processes stick the atoms into much higher energy levels, and under special conditions then they jump down and accumulate in the one excited energy level instead of going all the way to the ground state.
When an excited atom sends off a photon, it can hit more excited atoms and cause a little landslide of more photons; but the photons can go off in any direction. So mirrors are used to bounce the photons back and forth along one direction through the atoms and a partially reflective mirror is used on one end so that some of the light leaks through. The beam inside the laser is a lot more powerful than the beam that actually comes out.
A laser beam contains a lot of synchronised energy. Instead of being randomised, like ordinary light, all the photons march together. Imagine a lot of people marching together across a wobbly rope bridge. Their synchronised stamping would quickly cause the bridge to resonate and it would probably break. The same sort of thing happens with the laser hitting a material. The photons cause a local heating effect that “burns” the material, breaking molecules apart. If you have ever focussed the light of the sun onto something and seen it burn then you have seen the same effect. Because it is so coherent, laser beams can be focussed with great precision and so the cutting can be very precise.
The use of Optical fibres in Endoscopes;
An optical fibre is like a “tunnel” with extremely reflective walls.They rush down the tunnel with no way out and because only a few can get in at a time, they don’t interfere with each other (very much). By packing a bundle of these fibres together (several hundreds, if not thousands), each can transmit part of an image back to either a microscope or a digital camera to be magnified. Note that some of the fibres can be used to carry illumination down to the far end, too.
The fibres used in an endoscope are generally made either from glass or from a special kind of plastic that can be extruded very, very thin – only a few millionths of a meter in diameter. At that thickness, glass becomes surprisingly flexible.
UV Light ;
Ultra-violet light is produced by exciting atoms that then emit a photon at the right energy level. However, there is no attempt to cause massive secondary emission or to make the light coherent.Though UV light does cause a heating effect – sunlight contains a certain amount of UV, which is what causes sunburn, skin aging, cancer and the like – it is also absorbed by certain pigments in layers just under the skin. The energy thus absorbed is used to power chemical reactions that make certain important vitamins that accelerate skin healing.
Y-rays / Radiotherapy;
A form of electromagnetic radiation, similar to X-rays but of shorter wavelength. Y-rays and X-rays are also used therapeutically to kill tumor cells. Radiotherapy is the use of X-rays to treat disease. It used to be known as radium treatment. Although radiotherapy uses stronger rays than those used for taking pictures it feels no different and is painless. Approximately four out of ten people with cancer will have radiotherapy as part of their treatment. This can either be given from outside the body (external radiotherapy), using X-rays or cobalt irradiation, or from within (internal radiotherapy), by placing radioactive treatment in or close to the tumour being treated. The X-rays work by destroying the cancer cells in the treated area. Although normal cells are also affected, they can repair themselves.
Y-rays are like X-rays but of higher energy. They are also called “gamma rays”. Same principles but they cause more damage. Being of shorter wavelength, they can be used to create very high definition pictures but this definition would rarely be needed in medical applications. Indeed, the damage caused to the patient would normally far outweigh the benefits and I would expect such rays to be used for imaging only under exceptional conditions. I don’t know about “injecting”, though. One could, conceivably, use a radioactive material that emits Y-rays naturally (along with other forms of radiation) and I suppose that this could be made small enough to be swallowed or pushed into a hole in the flesh but I seriously doubt that such a technique would be considered even remotely safe. Technically, it would be like having a light bulb inside you. A scanner placed outside the body would pick up the Y-rays and form an image through either scintillation or (more likely) fluorescence, after focussing the Y-rays onto a suitable detector. However, the source would be in the body for a significant period of time, with no practical way to turn it on or off.
Cancerous cells are destroyed in radio-therapy by burning them. Three separate beams are usually focussed through the body from different angles. Each beam by itself can not cause too much damage but where all three meet (inside the cancer) the combined burning effect kills the cancer cells. Radiotherapy kills all cells in the target area at about a 30% rate of attrition. Cancer cells are simply normal healthy cells that don't go on to differentiate - either partially or fully - they simply duplicate. Therefore, almost as soon as they come into being, they duplicate again. New cells can become anything. Differentiation means to further develop function according to the immediate environment (new cells in a hair become hair-cells, in a kidney, kidney cells, etc.) This takes much more time, before they can again duplicate. At the moment of cell division, they are the most vulnerable. Therefore, radiotherapy administered over time finally kills more undifferentiated (cancer) cells than it does those that are differentiated.
That was the first attempt-rough
‘The use of sound waves and electromagnetic waves in the diagnosis and treatment of medical conditions’.
1. The difference between sound waves and electromagnetic waves is sound waves need a medium in order to exist and to be able to transport energy from one place to another. An electromagnetic wave is capable of transmitting its energy through a vacuum. A sound wave is a mechanical wave; slinky waves, water waves, stadium waves, and telephone chord waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a telephone chord wave requires a telephone chord.
2. The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field. The second part is a magnetic field. So that is why they are called electromagnetic waves. The two fields are at right angles to each other.
Electromagnetic radiation is energy, produced by oscillation or acceleration of an electric charge. All light waves are examples of electromagnetic waves; as are microwaves, x-rays, and TV and radio transmissions. Electromagnetic waves have both electric and magnetic components.
3. Ultrasound and Piezo electric transducers: Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the probe, there is one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.
Transducer probes come in many shapes and sizes. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image. Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasound beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, oesophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
Radio waves – MRI Imaging: Radio waves have a much longer wavelength that light waves. The longest waves are several kilometres in length. The shortest ones are only millimetres long. Radio waves will make the electrons in a piece of copper wire move; this means that they generate electric currents in the wire. In fact it works both ways: alternating currents in a copper wire generate electromagnetic waves, and electromagnetic waves generate alternating currents. The electric currents at "radio frequencies" (rf) are used by radio and television transmitters and receivers.
MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s. The MRI scan uses magnetic fields and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation. The patient lies inside a large, cylinder-shaped magnet, while radio waves are sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals. Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above. Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radio wave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
(cont)
1. The difference between sound waves and electromagnetic waves is sound waves need a medium in order to exist and to be able to transport energy from one place to another. An electromagnetic wave is capable of transmitting its energy through a vacuum. A sound wave is a mechanical wave; slinky waves, water waves, stadium waves, and telephone chord waves are other examples of mechanical waves; each requires some medium in order to exist. A slinky wave requires the coils of the slinky; a water wave requires water; a stadium wave requires fans in a stadium; and a telephone chord wave requires a telephone chord.
2. The visible spectrum is just one small part of the electromagnetic spectrum. These electromagnetic waves are made up of two parts. The first part is an electric field. The second part is a magnetic field. So that is why they are called electromagnetic waves. The two fields are at right angles to each other.
Electromagnetic radiation is energy, produced by oscillation or acceleration of an electric charge. All light waves are examples of electromagnetic waves; as are microwaves, x-rays, and TV and radio transmissions. Electromagnetic waves have both electric and magnetic components.
3. Ultrasound and Piezo electric transducers: Ultrasound or ultrasonography is a medical imaging technique that uses high frequency sound waves and their echoes. The technique is similar to the echolocation used by bats, whales and dolphins, as well as SONAR used by submarines. In ultrasound, the following events happen. The ultrasound machine transmits high-frequency (1 to 5 megahertz) sound pulses into your body using a probe. The sound waves travel into your body and hit a boundary between tissues (e.g. between fluid and soft tissue, soft tissue and bone). Some of the sound waves get reflected back to the probe, while some travel on further until they reach another boundary and get reflected. The reflected waves are picked up by the probe and relayed to the machine. The machine calculates the distance from the probe to the tissue or organ (boundaries) using the speed of sound in tissue (5,005 ft/s or1,540 m/s) and the time of the each echo's return (usually on the order of millionths of a second). The machine displays the distances and intensities of the echoes on the screen, forming a two dimensional image like the one shown below.
The transducer probe is the main part of the ultrasound machine. The transducer probe makes the sound waves and receives the echoes. It is, so to speak, the mouth and ears of the ultrasound machine. The transducer probe generates and receives sound waves using a principle called the piezoelectric (pressure electricity) effect, which was discovered by Pierre and Jacques Curie in 1880. In the probe, there is one or more quartz crystals called piezoelectric crystals. When an electric current is applied to these crystals, they change shape rapidly. The rapid shape changes, or vibrations, of the crystals produce sound waves that travel outward. Conversely, when sound or pressure waves hit the crystals, they emit electrical currents. Therefore, the same crystals can be used to send and receive sound waves. The probe also has a sound absorbing substance to eliminate back reflections from the probe itself, and an acoustic lens to help focus the emitted sound waves.
Transducer probes come in many shapes and sizes. The shape of the probe determines its field of view, and the frequency of emitted sound waves determines how deep the sound waves penetrate and the resolution of the image. Transducer probes may contain one or more crystal elements; in multiple-element probes, each crystal has its own circuit. Multiple-element probes have the advantage that the ultrasound beam can be "steered" by changing the timing in which each element gets pulsed; steering the beam is especially important for cardiac ultrasound. In addition to probes that can be moved across the surface of the body, some probes are designed to be inserted through various openings of the body (vagina, rectum, oesophagus) so that they can get closer to the organ being examined (uterus, prostate gland, stomach); getting closer to the organ can allow for more detailed views.
Radio waves – MRI Imaging: Radio waves have a much longer wavelength that light waves. The longest waves are several kilometres in length. The shortest ones are only millimetres long. Radio waves will make the electrons in a piece of copper wire move; this means that they generate electric currents in the wire. In fact it works both ways: alternating currents in a copper wire generate electromagnetic waves, and electromagnetic waves generate alternating currents. The electric currents at "radio frequencies" (rf) are used by radio and television transmitters and receivers.
MRI (magnetic resonance imaging) is a fairly new technique that has been used since the beginning of the 1980s. The MRI scan uses magnetic fields and radio waves, meaning that there is no exposure to X-rays or any other damaging forms of radiation. The patient lies inside a large, cylinder-shaped magnet, while radio waves are sent through the body. This affects the body's atoms, forcing the nuclei into a different position. As they move back into place they send out radio waves of their own. The scanner picks up these signals and a computer turns them into a picture. These pictures are based on the location and strength of the incoming signals. Our body consists mainly of water, and water contains hydrogen atoms. For this reason, the nucleus of the hydrogen atom is often used to create an MRI scan in the manner described above. Using an MRI scanner, it is possible to make pictures of almost all the tissue in the body. The tissue that has the least hydrogen atoms (such as bones) turns out dark, while the tissue that has many hydrogen atoms (such as fatty tissue) looks much brighter. By changing the timing of the radio wave pulses it is possible to gain information about the different types of tissues that are present. An MRI scan is also able to provide clear pictures of parts of the body that are surrounded by bone tissue, so the technique is useful when examining the brain and spinal cord.
(cont)
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