physics principles Flashcards
what is sound
a mechanical, longitudinal wave.
what does longitudinal mean?
parallel from the sound source.
what does 1 complete cycle mean?
it means 1 compression & 1 rarefaction
λ
wavelength
c
propagation speed
f
frequency
what does wavelength depend on?
frequency & propagation speed
what is propagation speed determined by?
a medium
what is frequency determined by?
a sound source
mediums with fast propagation speed = ______
longer wavelength
mediums with slower propagation speed = ______
shorter wavelength
infrasound
<less than 20Hz
audible sound
20 - 20,000Hz
ultrasound
> greater than 20,000Hz
diagnostic ultrasound
2 - 20MHz
power
rate of flow of energy
intensity
power/area
amplitude
height of pressure wave
why do we use decibels?
to describe how much our intensity has changed
a reduction of 6dB means the intensity is reduced by how much?
1/4. 25%
adjusting overall gain from 25dB to 28dB will cause what affect to the intensity of the echoes?
there was an increase of 3dB which means the intensity was doubled.
in soft tissue..
1.54 mm/ms or 1540 m/s
bulk modulus
stiffness
is propagation speed affected by frequency or wavelength?
NO
impedance
obstruct or hinder
each medium has it’s own _______.
impedance
what is impedance dependent on?
the medium
Z
impedance
p
density
Z = pc means…
impedance = density & propagation speed
interface
tissue change
when sound encounters interface what can happen?
some sound can be reflected (bounce back) & the rest continues traveling or is transmitted.
attenuation
weakening of sound
what does attenuation depend on?
a medium
what is the average rate of attenuation in soft tissue?
1/2 dB/cm/MHz
decibels change in ..
intensity
frequency & attenuation are ______ related.
directly
increase in frequency = _____________
increase attenuation
how much is the frequency going to attenuate per cm?
half the frequency
4 MHz will attenuate ___
2 dB/cm
8 MHz will attenuate _______
4 dB/cm
What are Pulsed Ultrasound Parameters?
PRF, PRP, SPL, PD, DF
PRF
Pulsed Repetition Frequency
PRP
Pulsed Repetition Period
SPL
Spatial Pulse Length
PD
Pulse Duration