
what does an ellipse measure?
area





"increase by a factor of" means
multiply

decrease by a factor of means
divide







10^2 = hundreth
centi = c

10^3 = thousandth
milli = m

10^6 = millionth
micro = μ

10^9 = billionth
nano = n

acoustic propagation properties
the effects of the medium upon the sound wave

biologic effect
the effects of the sound wave upon the biologic tissue

sound
 a type of wave that carries enery, not matter from place to place
 must travel through a medium
 is mechanical, longitudinal wave
 travels in a straight line

compressions
are areas of increased pressure or density

rarefactions
are areas of decreased pressure or density

three acoustic variables
 pressure = concentration of force w/i area force / area units= pascal (Pa)
 density = concentration of mass w/i volume units = kg/cm^3
 distance = measure of particle motion units = cm, ft, miles

transverse wave
particles move in a perpendicular direction (right angles or 90) to the direction of the wave

sound is longitudinal wave
particles move in the same direction as the wave

acoustic parameters
 period
 fequency
 amplitude
 power
 intensity
 speed
 wavelength

period
 the time required to complete a single cycle (the start of a cycle to the start of the next)
 units = any unit of time
 determines by = sound source
 can not be changed by sonographer

frequency
 number of certain events that occure in a particular time duration
 units = per second, 1/second = Herts (Hz)
 determined = sound source
 can not be changed by sonographer
 frequency affects penetration and axial resolution

ultrasound
 a wave with a frequency exceeding 20,000Hz (20 kHz)
 frequency is so high that is not audible

audible sound
heard by man, frequencies btwn 20Hz and 20,000Hz

infrasound
 sound with frequencies less than 20Hz
 frequency is so low that is not audible

frequency and period
 are reciprocals
 frequency (Hz) x period (sec) = 1
 period (sec) = 1/ frequency (Hz)
 frequency (Hz) = 1/period (sec)
 when one goes down the other goes up


amplitude
 the difference btwn the average value and the maximum value of an acoustic variable. the variation of an acoustic variable
 units = same as acoustic variables
 pressure=pascals
 density=grams/cubic cm
 particle motion=cm,inches,units of distance
 may be expressed in decibels (dB)
 determined by sound source (initially)
 can be changed by sonographer

power
 the rate that work is performed, or the rate of energy transfer
 units = watts
 determined by sound source (initially)
 can be changed by sonographer

power & amplitude
power is porportional to the wave's amplitude squared
 ex: if amplitude is tripled, the power is increase by a factor of nine:
 3 x 3 = 9

intensity
the concentration of energy in a sound beam. the beam's power devided by the beam's crosssectional area. intensity depends upon bothe the power and the crosssectional area of the beam

