Interaction of Sound and Media

Question 1

as sound waves propagate, what happens to attenuation

Answer 1

it increases

Question 2

term describing weakening of sound waves as they travel in media

Answer 2

attenuation

Question 3

decibel notation is described as ___ because it reports relative changes in signal strength

Answer 3

logarithmic

Question 4

effect of 3dB

Answer 4

doubles

Question 5

effect of 6dB

Answer 5

4x

Question 6

effect of 9dB

Answer 6

8x

Question 7

effect of 10dB

Answer 7

10x

Question 8

effect of 20dB

Answer 8

100x

Question 9

effect of -20dB

Answer 9

1/100

Question 10

effect of -10dB

Answer 10

1/10

Question 11

effect of 9dB

Answer 11

1/8

Question 12

effect of 6dB

Answer 12

1/4

Question 13

effect of -3dB

Answer 13

1/2

Question 14

Sound waves weaken as they propagate. This decrease in intensity, power, and amplitude as sound travels is called

Answer 14

attenuation

Question 15

attenuation is determined by 2 factors

Answer 15

path length

frequency

Question 16

how are distance and attenuation related

Answer 16

directly

Question 17

how are frequency and attenuation related

Answer 17

directly

Question 18

3 processes that contribute to attenuation

Answer 18

reflection
scattering
absorption

Question 19

as sound strikes a boundary, a portion of the wave’s energy may be redirected, or __

Answer 19

reflected

Question 20

two forms of reflection

Answer 20

specular

diffuse / backscatter

Question 21

type of reflection that happens when it hits a smooth boundary and the sound is reflected in only one direction, in an organized manner

Answer 21

specular

Question 22

type of reflection that happens when a wave reflects off an irregular surface and radiates in more than one direction

Answer 22

diffuse reflection or backscatter

Question 23

random redirection of sound in many directions is called

Answer 23

scattering

Question 24

how is scattering related to frequency

Answer 24

directly

Question 25

do high frequency sound beams scatter more or less than low frequency beams?

Answer 25

high frequency beams scatter more

Question 26

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)

Answer 26

Rayleigh scattering

Question 27

Rayleigh scattering relationship with frequency

Answer 27

Rayleigh scattering is directly proportional to frequency^4

Question 28

___ occurs when ultrasonic energy is converted into another energy form such as heat

Answer 28

absorption

Question 29

attenuation coefficient formula

Answer 29

frequency (MHz) / 2 = atten. coeff. (dB / cm)

Question 30

total attenuation formula

Answer 30

total atten. (dB) = atten. coeff. (dB/cm) x distance (cm)

Question 31

Media in which attenuation is the highest

Answer 31

air

Question 32

media in which attenuation is the lowest

Answer 32

water

Question 33

the distance sound travels in a tissue that reduces the intensity of sound one-half its original value

Answer 33

half value layer thickness penetration depth half boundary layer

Question 34

half-value layer thickness depends on 2 factors

Answer 34

medium | frequency

Question 35

acoustic resistance to sound traveling in a medium

Answer 35

impedance

Question 36

how do we calculate impedance

Answer 36

impedance (rayls, Z) = density (kg/m3) x propagation speed (m/s)

Question 37

normal incidence is also called

Answer 37

perpendicular orthogonal right angle 90 degrees

Question 38

oblique incidence occurs at the incident sound beam strikes a boundary at what angle

Answer 38

any angle other than 90 degees

Question 39

units for intensity

Answer 39

w/cm2

Question 40

intensity of the portion of the incident intensity AFTER striking a boundary

Answer 40

transmitted intensity

Question 41

sound waves intensity BEFORE striking a boundary is called

Answer 41

incident intensity

Question 42

conservation of energy equations

Answer 42

incident intensity = reflected intensity + transmitted intensity 100% = IRC% + ITC%

Question 43

what happens when there is a change in impedances between media

Answer 43

reflection

Question 44

at an oblique incidence, these two things are always true

Answer 44

conservation of energy | incident angle = reflection angle

Question 45

change in direction of a wave propagation when traveling from one medium to another

Answer 45

refraction

Question 46

refraction occurs only under two conditions...

Answer 46

oblique incidence | different propagation speeds between 2 media