Interaction of Sound and Media Flashcards
as sound waves propagate, what happens to attenuation
it increases
term describing weakening of sound waves as they travel in media
attenuation
decibel notation is described as ___ because it reports relative changes in signal strength
logarithmic
effect of 3dB
doubles
effect of 6dB
4x
effect of 9dB
8x
effect of 10dB
10x
effect of 20dB
100x
effect of -20dB
1/100
effect of -10dB
1/10
effect of 9dB
1/8
effect of 6dB
1/4
effect of -3dB
1/2
Sound waves weaken as they propagate. This decrease in intensity, power, and amplitude as sound travels is called
attenuation
attenuation is determined by 2 factors
path length
frequency
how are distance and attenuation related
directly
how are frequency and attenuation related
directly
3 processes that contribute to attenuation
reflection
scattering
absorption
as sound strikes a boundary, a portion of the wave’s energy may be redirected, or __
reflected
two forms of reflection
specular
diffuse / backscatter
type of reflection that happens when it hits a smooth boundary and the sound is reflected in only one direction, in an organized manner
specular
type of reflection that happens when a wave reflects off an irregular surface and radiates in more than one direction
diffuse reflection or backscatter
random redirection of sound in many directions is called
scattering
how is scattering related to frequency
directly
do high frequency sound beams scatter more or less than low frequency beams?
high frequency beams scatter more
A special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength. (redirects sound wave equally in all directions)
Rayleigh scattering
Rayleigh scattering relationship with frequency
Rayleigh scattering is directly proportional to frequency^4
___ occurs when ultrasonic energy is converted into another energy form such as heat
absorption
attenuation coefficient formula
frequency (MHz) / 2 = atten. coeff. (dB / cm)
total attenuation formula
total atten. (dB) = atten. coeff. (dB/cm) x distance (cm)
Media in which attenuation is the highest
air
media in which attenuation is the lowest
water
the distance sound travels in a tissue that reduces the intensity of sound one-half its original value
half value layer thickness
penetration depth
half boundary layer
half-value layer thickness depends on 2 factors
medium
frequency
acoustic resistance to sound traveling in a medium
impedance
how do we calculate impedance
impedance (rayls, Z) = density (kg/m3) x propagation speed (m/s)
normal incidence is also called
perpendicular
orthogonal
right angle
90 degrees
oblique incidence occurs at the incident sound beam strikes a boundary at what angle
any angle other than 90 degees
units for intensity
w/cm2
intensity of the portion of the incident intensity AFTER striking a boundary
transmitted intensity
sound waves intensity BEFORE striking a boundary is called
incident intensity
conservation of energy equations
incident intensity = reflected intensity + transmitted intensity
100% = IRC% + ITC%
what happens when there is a change in impedances between media
reflection
at an oblique incidence, these two things are always true
conservation of energy
incident angle = reflection angle
change in direction of a wave propagation when traveling from one medium to another
refraction
refraction occurs only under two conditions…
oblique incidence
different propagation speeds between 2 media
