phys

effects of medium upon sound wave

acoustic propagation properties

The effects of the sound wave upon the biologic tissue through which it passes.

bio effects

pressure

concentration of force in an area (Pa)

density

concentration of mass in a volume

distance

measure of particle motion

3 acoustic variables used to differ between sound waves and other types of waves

pressure, density, distance

period

time it takes a wave to vibrate a single cycle or one time from the start of one cycle to the start of the next

period determined by

source only

period adjustable?

no

Frequency

the number of complete wavelengths that pass a point in a given time

frequency determined by

source

frequency adjustable?

no

infrasound

less than 20 Hz

audible sound

between 20 Hz and 20 kHz

ultrasoun

greater than 20 kHz

3 bigness parameters

amplitude, power, intensity

amplitude

bigness of a wave
-difference between max and ave

amplitude determined by

source

amplitude adjustable?

yes

peak to peak amp is the difference between

maximum and minimum values
-twice the value of the amplitude

power

the rate at which work is done or energy is transformed

power determined by

source

power adjustable?

yes

intensity

concentration of energy in a sound beam

intensity determined by

source

intensity adjustable?

yes

intensity and power __________ related

directly

wavelength determined by

source and medium

wavelength adjustable?

no

wavelength and F relationship

inverse

wavelength equation

speed/F

prop speed

The rate that sound travels through a medium

prop speed determined by

medium

prop speed adjustable

no

2 characteristics of a medium that affect the speed of sound

-stiffness
-density

stiffness

ability of an object to resists compression

density describes

the relative weight of a material

stiffness and speed relationship

direct

density and speed relationship

inverse

bulk modulus is the same as

stiffness

elasticity and compressibility are the opposite of

stiffness

is stiffness or density more important?

stiffness

pulse duration

the actual time from the start of a pulse to the end of that pulse

pulse duration determined by

source

pulse duration adjustable?

no

pulse duration equation

# cycles X period
or
# cycles / F

2 characteristics create pulses of long duration

-many cycles in the pulse
-individual pulses with long periods

2 characteristics create pulses of short duration

-few cycles in a pulse
-individual cycles with short periods

SPL

the distance of the pulse start to end

SPL determined by

source and medium

SPL adjustable?

no

SPL and # of cycles in a pulse relationship

direct

SPL and wavelength relationship

direct

SPL and F relationship

inverse

PRP

the time from the start of one pulse to the start of the next pulse

PRP determined by

source and depth

PRP adjustable?

yes

PRP and depth relationship

direct

transmit time is called the

pulse duration

PRF

number of pulses per second

PRF determined by

source

PRF adjustable?

yes

PRF and depth relationship

inverse

duty factor

the percentage or fraction of time that the system transmits a pulse

duty factor determined by

source

duty factor adjustable?

yes

duty factor equation

pulse duration/ PRP X 100

how to change duty factor

alter the depth

duty factor units

none

spatial intensity

refers to distance or space

peak intensity

maximum value

average intensity

the mathematical middle value

temporal intensity

refers to all time, transmit, and receive

pulsed intensity

Refers only to the transmit time

temporal intensities from largest to smallest

I tp, I max, I pa, I ta

rank of intensities from largest to smallest

SPTP, Im, SPPA, SPTA, SATA

sound waves weaken or __________ as they travel in the body

attenuate

decibels based on mathematical construct called

logs

decibel notation is

logarithmic
a ratio

decibel notation does not measure

absolute numbers

decibels report

relative changes

decibels require

Two intensities

3 dB means

double

10 dB means

ten times larger

-3dB means

half

-10 dB means

one tenth

attenuation determined by 2 factors

path length and frequency of sound

distance and attenuation relationship

direct

F and attenuation relationship

direct

3 processes contribute to attenuation

reflection, scattering, absorption

2 form of reflection

specular, diffuse

specular reflection

Reflection of light off a smooth surface

diffuse/backscatter reflection

reflection from a rough surface

scattering reflection

redirection of sound in many directions

Rayleigh scattering

Special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength
-RBC's

absorption

energy converted to heat

attenuation coefficient equation

frequency/2
(dB)

total attenuation equation

attenuation coefficient x distance
(dB)

lowest attenuator

water

highest attenuator

air