Flashcards in Physics Review Ch. 5, 6, 7 Deck (63)
How do you calculate intensity?
a beam's power divided by its area.
What are other names for normal incidence?
Difference between normal and oblique incidence
normal incidence strikes the boundary at exactly 90 degrees
oblique incidence strikes the boundary at any angle other than 90 degrees (acute and obtuse)
Define incidence intensity
The sound waves intensity immediately before it strikes a boundary
Define reflected intensity
Is the intensity of the portion of the incident sound beam that, after striking a boundary, returns back from where it came
Define transmission intensity
Is the intensity of the portion of the incident beam that, after striking a boundary, continues forward in the same general direction that it was traveling
Intensity Reflection Coefficient; the percentage of intensity that bounces back, after it strikes the boundary between 2 media. (1%)
Intensity Transmission Coefficient; the percentage of intensity that passes in the forward direction between 2 media. (99%)
The acoustic resistance to sound traveling in a medium. Calculated by multiplying the density of a medium by the speed at which sound travels in the medium.
Units: rayls; Z
Impedance-what is takes to achieve reflection
Reflection of an ultrasound wave depends upon the difference in acoustic impedances of the two media at a boundary.
Define specular reflectors
When the boundary is smooth, the sound is reflected in only on direction in an organized manner
Conservation of energy
Applies at the boundary between two media.
IRC + ITC = 100%
Reflection and transmission with oblique incidence
We cannot predict; it's too complex
Is a change in direction of wave propagation when traveling from one medium to another
Refraction occurs only when there is what?
1. Oblique Incidence. (not normal)
2. Different Propagation speeds between the media.
What is refraction associated with?
The decrease in intensity, power, and amplitude as sound travels.
Attenuation is determined by?
1. Path length
2. Frequency of sound
What three processes contribute to attenuation?
What is impedance determined by?
Is the random redirection of sound in many directions. (Disorganized and chaotic)
Define Rayleigh scattering
Is a special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength. (Organized and omnidirectional)
*omnidirectional-in all directions
Relationship between scattering and frequency
directly related; Rayleigh scattering is proportional to frequency^4
Formula for Impedance
Impedance (rayls) = density (kg/m^3) * prop. speed (m/s)
Formula for IRC and ITC
100% = IRC + ITC
What are other names for decibel notation?
Is the depth of tissue that results in 3 dB of attenuation to the intensity.
May be called: penetration depth, depth of penetration, and half-boundary layer
Half-value layer thickness depends on what two factors?
1. The medium
2. The frequency of sound
Half-Value Layer conditions
Thin Half Value:
-High frequency sound
-Media with high attenuation rate
Thick Half Value:
-Low frequency sound
-Media with low attenuation rate