C3: Partical Motion and Wave Propagation Flashcards
define acoustic propagation
-refers to the effects of tissue on sound
define bioeffects
refers to the effects of sound of tissue
what is sound
a propagating variation (eg wave)
do sound waves carry energy or matter
energy
do mechanical waves need a medium to travel
yes
whats the term that refers to the quality of a sound wave
acoustic variables
list the acoustic variables present when sound travels through a medium
- pressure
- density
- particle motion
- temperature
describe pressure as an acoustic variable
how is it expressed?
pressure is expressed as a sine wave…. crests represent high pressure and troughs represent low pressure
what is density
how is it expressed?
- the concentration of particles or mass per unit volume
- with reference to a sine wave… areas of high density (crests) are called compressions and areas of low density (troughs) are called rarefractions
describe the particle motion of longitudinal waves
back and fourth motion, parallel to the direction of travel of the wave
describe the particle motion of transverse waves
up and down motion, perpendicular to the direction of travel of the wave
what type of media can support transverse waves
only solids
what type of media can support longitudinal waves
solids, liquids, gases
what is mode conversion
when on type of wave is converted to another type
what is frequency (f)
the number of cycles per second
in general: a measure of how often something occurs
formula: f = 1/T or f = c/lambda
what is period (T)
the times it takes for one cycle to occur
what is wavelength
the length of space one cycle takes up
whats the avg speed of sound in soft tissue
1.54 mm/us or 1540 m/s
what determines propagation speed
the medium
what are the 3 ways to describe wave strength
amplitude
intensity
power
-total energy over the entire cross sectional area
define amplitude
max. variation of an acoustic variable… strength of the wave is determined by the source of the sound
define intensity
formula?
the [ ] of energy in a sound beam
formula:
I = P/A (power over area)
how is intensity related to amplitude
it is directly to amplitude^2
…. if you double the amp, you quadruple intensity
is there any intensity during the listening phase?
no
describe the changes of intensity throughout a pulse
intensity starts off high and gets weaker w/ time
what is spatial avg and where do we measure it
SA is the avg intensity over the entire beam… measured at the face of the probe
what is spatial peak and where is it found
SP is the peak intensity of the beam, found at the focal point where the beam is the skinniest
how are SA and SP related
formula?
the beam uniformity ratio
BUR: SP/SA
what is temporal peak (TP)
the greatest intensity found in the pulse
what is pulse avg (PA)
avg value for all intensities found in a pulse excluding dead time
what is temporal avg (TA)
avg value for all intensities found in a pulse INCLUDING dead time b/w pulses
do TP and PA have almost identical values
yes
how are TP and TA related
formula?
by duty factor
DF = TA/TP
define duty factor
the % of time the crystal is ringing
SPTA values depend on what factor
depth
what is the speed of sound in fat
1460 m/s
what is the speed of sound in bone
4080 m/s
what is the range equation
what is it used for
D = C x t
D= distance to reflector and back c = speed of sound t = time for round trip
used to calculate the distance of a reflector from the probe
another name for SPTP and SPPA
SPTP = instantaneous peak SPPA = maximum intensity or time averaged half maximum
