USS Flashcards
How would the USS waves are produced?
USS waves are produced by a transducer that converts electrical signal into an uss beam.
It consists of a peizoceramic disc or rectangular plate
what is the plate made of in the transducers?
it is made of compressed microcrystalline lead zirconate titanate -PZT- or PVDF
Hows the two flat faces are made electerically conducting?
with a very thin coating of silver.
what would happen when a DC voltage is applied to the flat face of the disc?
it expands and if the voltage is reversed it contracts
The movement of the face is proportional to the voltage.
T/F?
The voltage produced is inversely proportional to the pressure.
False
The voltage produced is proportional to the pressure.
When the disc is compressed equal and opposite charges and corresponding voltage appear on the two flat faces.
T/F
The transducers can act as both transmitter and a reciever.
True
what is a Curie temperature?
when heated above a certain temp, transducers lose their peizoelectric properties
eg 350C for PZT
what type of voltage is used in pulsed mode?
DC
when the Tx is in contact with a patient and DC is applied, it instantly expands and compresses a layer of the material in contact with it, this also affects the adjacent material therefore a layer or wave of compression travels with a velocity through the material followed by wave of decompression or rarefaction
what type of voltage is used in continuous wave mode?
AC
When AC is applied, the crystal face pulses forward and backwards like a piston producing successive compression and rarefaction
Each compression wave has moved forward by a distance called the wavelength by the time the next one is produced.
the graph of pressure against time is what type of graph?
It is a sine wave.
T/F?
The USS waves can travel in vacuume.
False
The sound waves unlike, x rays and light, require a medium to travel through
T/F?
The USS waves are a transverse wave
false
sound wave is a longitudinal wave
T/F?
X and gamma rays and sound waves can be reflected, refracted and focused
false
unlike X and gamma rays, teh sound waves can be reflected, refracted and focused
T/F?
The greater the density the lower the velocity
True
T/F?
The greater the compressibility the greater the velocity
False
The greater the compressibility, the lower the velocity
T/F?
velocity is independent of temperture
False
Velocity depends on temperature.
How long does it take for sound waves to travel 1cm in average soft tissue?
7 micros
Air has ……..density but is much more…… tahn water or tissue, hence the ….velocity.
Air has ..much lower..density but is much more..compressible.. than water or tissue, hence the ..low..velocity.
T/F?
wavelength is proportional to velocity.
True
what is the unit of measuring intensity of USS?
Intensity of USS measured in watts per square mm- W/mm2-. this is proportional to the square of the wave amplitude and is under the operator’s control.
what is constructive interference?
This is when two waves are in phase/in step, their amplitudes add up.
What is destructive interference?
This is when two waves cancel each other out.
what would happen if two waves are only partially out of phase?
They result in reduced intensity.
T/F?
the transducer vibrates to produce a wavelength in the transducer equal to half the thickness (t) of the PZT disc.
False
the transducer vibrates to produce a wavelength in the transducer equal to TWICE the thickness (t) of the PZT disc.