Interaction of sound (Edelmen) Flashcards
The decrease in intensity, power, and amplitude as sound travels
attenuation
Attenuation is determined by
Path length and frequency
More attenuation results in ___ distances and ____ frequencies
longer, higher
Processes that contribute to attenuation
reflection, scattering, absorption
T/F 10 db of attenuation is negative
TRUE
As sound strikes a boundary, a portion of the waves energy may be redirected or
reflected
Two forms of reflection
Specular and diffuse
When the boundary is smooth, the sound of reflected in only one direction in an organized manner
Specular reflection
Wave reflects off an irregular surface, it radiates in more than one direction but back to the transducer
Diffuse reflection (backscatter)
Redirection of sound in many directions
Scattering
Structures dimensions are much smaller than the beams wavelength
Rayleigh scattering
Energy is converted into another energy such as heat
Absorption
Number of decibels of attenuation that occurs when sound travels on cm
Attenuation coefficient : db/cm
Attenuation lowest to hight from water to air
Water, blood, fat, soft tissue, muscle, bone/lung, air.
Distance sound travels in a tissue that reduces the intensity of sound to 1/2 original value
Half-value layer thickness
Synonyms of half value layer thickness
Penetration depth, depth of penetration, half-boundary layer.
You have a thin half value layer with ___ frequency and ____ attenuation
high
Acoustic resistance to sound traveling in a medium
Impedance : rayls
Impedance is calculated by
density and speed
T/F impedance is calculated not measured
TRUE
The incident sound beam strikes the boundary at exactly 90 degrees
Normal incidence
Normal incidence synonyms
Perpendicular, orthogonal, right angle, 90 degrees
Incident sound beam strikes the boundary at any angle other than 90 degrees
Oblique incidence
Sound waves intensity immediately before it strikes a boundary
Incident intensity
Intensity of the portion of the incident sound beam that after striking a boundary, it returns back from where it came
Reflected intensity
Intensity of the portion of the intensity beam that after striking a boundary, continues forward in the same direction it was traveling
Transmitted intensity
Percentage of intensity that passes in a forward direction when a beam strikes an interface between two media
Intensity transmission coefficient ITC
Percentage of the intensity that bounces back when a sound beam strikes the boundary between 2 media
Intensity reflection coefficient IRC
If the IRC and ITC are added, the result must equal
100%
Transmission with a bend is called
refraction
With normal incidence, reflection depends on
impedance difference
With oblique incidence, the angle of reflection is equal to
angle of incidence
What is an oblique incidence with different speeds required
refraction
When speed 2 = speed 1, what is the refraction
No refraction
When speed 2 is > speed 1 the tranmission angle is ___ than incident
greater than
When speed 2 is < speed 1 the transmission angle is ___ than incident angle
less than
Impedence is calculated with what 2 things
density x speed
To calculate acoustic impedance do
density x prop speed
To calculate attenuation do
Min value - max value / 2
When a sound strikes a boundary between media at exactly 90 degrees
Orthogonal, perpendicular, right angles, normal
A sound strikes a boundary between 2 media at a 60 degree angle. this is ____ incidence
oblique
Units for intensity transmission coefficient and intensity reflection coefficient
none
Intensity reflection coefficient formula
Reflected intensity / incident intensity
Intensity transmitted intensity formula
Transmitted intensity/ incident intensity
What is the max permissible value for both the IRC and ITC
1 or 100%
What is the min permissible value for the IRC and ITC
0
