physics exam 1

what kind of energy is sound

mechanical

what does sound need (can’t travel through a vacuum)

medium

source of sound waves in ultrasound

piezoelectric transducer

repetitious wave is considered

cyclical

ultrasound waves are what kind of wave

longitudinal

units of frequency

Hz (per second)

human audible frequency range

20-20,000 Hz

infrasonic frequency range

0-20 Hz

ultrasonic frequency range

>20 kHz

diagnostic frequency range

2-12 MHz

mechanical vs electromagnetic waves

mechanical needs a medium, electromagnetic doesn’t

two types of mechanical waves

longitudinal and transverse

transverse waves def

particles move across/perpendicular to wave propagation direction

compression def

when molecules are drawn close together giving a high density, high pressure

rarefraction def

when molecules are drawn apart giving a lower density, lower pressure

peaks on a drawn wave are compressions are rarefractions

compression

low areas on a drawn wave are compression or rarefraction

rarefraction

acoustic variables created by sound

pressure, density, temperature

pressure def

concentration of force, or force per area

pressure units

pascals (Pa)

maximum pressure elevation is called

pressure amplitude

density def

weight of a material

density and speed relationship

inversely related

density units

kg/cm³

what symbol is density represented by

greek roe (ρ)

7 acoustic parameters

-wavelength

-period

-frequency

-amplitude

-power

-propagation speed

-intensity

what symbol is used to represent wavelength

lambda (λ)

wavelength def

distance from one peak to another (or one peak compression to another peak compression, or one rarefraction to another rarefraction)

wavelength units

unit of length

wavelength is determined by

both source and medium

wavelength in soft tissue

1mm or less (0.77mm for a 2MHz beam and smaller for higher frequencies)

is wavelength adjustable

no

wavelength and frequency relationship

inversely related

what symbol is propagation velocity represented by

c

wavelength equation

lambda (λ) = c/f

period def

the time that transpires between occurrence of one compression and next compression (or rarefraction to rarefraction)

period units

units of time

what symbol is period represented by (2)

P, T

period and frequency relationship

inversely related

frequency def

number of times per second the disturbance is repeated at any point

what is frequency determined by

source

in phase waves def

a pair of waves peaks occur at the same time and location

out of phase waves def

two waves peaks occur at different times

interference def

two waves combine and form a single wave, losing their individual characteristics

two types of interference

constructive, deconstructive

constructive interference def

a pair of in phase waves form a single wave of greater amplitude than either of its components

constructive interference involves in or out of phase waves

in phase

deconstructive interference involves in or out of phase waves

out of phase

deconstructive interference def

a pair of out of phase waves results in the formation of a single wave of lesser amplitude than either of its components

3 parameters that describe the size or magnitude of a sound wave

amplitude, intensity, power

units for amplitude in us

dB

what is amplitude determined by

source (but decreases as sound propagates through body)

does a change in amplitude change the frequency of a wave

no

power def

rate of energy transfer or rate at which work is performed

power units

watts (or mW)

power, intensity, amplitude proportion

power = intensity = amplitude²

power can be indirectly assessed by

dB settings, mi, ti

intensity def

concentration of energy (power) in a sound beam

how to calculate intensity

divide the beams power but the beams cross sectional area

units of intensity

W/cm²

intensity is determined by

source

is intensity adjustable

yes

intensity equation

intensity = power/area

decibel def

a unit used to measure intensity of a sound or power level of an electrical signal comparing it with a given level on a log scale

decibels is a comparison/ratio between

final value and initial value

3dB rule

each 3dB gain doubles the power

a 10dB increase results in

10 fold increase of power/intensity

propagation speed def

the rate at which the wave propagates through the medium

propagation velocity/speed units

units of distance per time (m/s)

speed and stiffness relationship

directly related

density and speed relationship

inversely related

what has the greatest influence on speed

stiffness

compressibility def

measure of how much the volume of the material changes for a given distorting force (pressure)

bulk modulus def

inverse of compressibility

speed of sound in soft tissue

1540 m/s

imaging 1 cm requires how much time

13 microseconds

propagation velocities in the body from slowest to fastest (11)

air, lung, fat, water, brain, soft tissue, liver, kidney, blood, muscle, bone

period is determined by

source

power is determined by

source

speed is determined by

medium

is speed adjustable

no

is power adjustable

yes

is amplitude adjustable

yes

is frequency adjustable

no

is period adjustable

no

attenuation def

decrease in wave amplitude (or intensity) due to mechanical interaction with the medium

distance and attenuation relationship

directly related

frequency and attenuation relationship

directly related

soft tissue attenuation rate

0.5 dB/cm

attenuation coefficient formula

attenuation coefficient = frequency/2

how to calculate attenuation

find attenuation coefficient, multiply by depth (cm)

why does acoustic shadowing occur with bone

absorbs at a higher rate than soft tissue

what two mediums attenuate the most

air and bone

order of attenuation in different media (from lowest to highest attenuation) (7/8)

water, blood (urine, other biologic fluids), fat, soft tissue, muscle, bone and lung, air

half layer thickness def

thickness that will reduce the intensity to half of its original value

half layer thickness depends on what two factors

medium, frequency of sound

what will cause a thin half value

high frequency sound, media with high attenuation rate

what will cause thick half value

low frequency sound, media with low attenuation rate

3 types of attenuation

absorption, reflection/scattering, refraction

how much wave energy that is lost to heat bc of absorption is dependent on what

interactions within medium and frequency