5 Sound + Media

Question 1

What is attenuation?

Answer 1

Decrease in intensity, power and amplitude of a sound wave as it travels

Question 2

What occurs the further US travels?

Answer 2

More attenuation

Question 3

What is associated with less attenuation?

Answer 3

Lower frequency

Shorter path length

Question 4

What is associated with more attenuation?

Answer 4

Higher frequency

Longer path length

Question 5

What are the 3 components of attenuation?

Answer 5

Absorption
Scattering
Reflection

Question 6

List the following in greatest to least attenuation.
Water
Bone & Lung
Air
Soft tissue

Answer 6

Air&raquo_space; Bone & Lung > Soft tissue&raquo_space; Water

Question 7

What does attenuation ultimately limit?

Answer 7

Max depth from which meaningful reflections are obtained

Question 8

When does reflection occur?

Answer 8

Propagating sound energy strikes a boundary between 2 media and some returns to the transducer

Question 9

What is specular reflection?

Answer 9

Reflections from a smooth reflector (mirror) and return in one direction

Question 10

What is diffuse reflection or backscatter?

Answer 10

Reflection of sound in all directions

Question 11

When does backscatter occur?

Answer 11

When the boundary has irregularities that are approx the same size as the sound’s wavelength

Question 12

What is Rayleigh scattering?

Answer 12

When a reflector is much smaller than the wavelength of sound, sound is uniformly distributed in all directions (omnidirectional)

Question 13

What is Rayleigh scattering related to?

Answer 13

Frequency^4

Question 14

What is the attenuation coefficient?

Answer 14

Amount of attenuation per centimeter (dB/cm)

Question 15

What is the relationship between frequency and attenuation coefficient?

Answer 15

Proportional

Question 16

List the equation for total attenuation.

Answer 16

Total attenuation (dB) = path length (cm) x attenuation coefficient (dB/cm)

Question 17

What is the attenuation coefficient in soft tissue?

Answer 17

Approx 1/2 of the the frequency (MHz)

Question 18

What is impedance?

Answer 18

A number associated with a medium - it is calculated, not measured
Opposition (density) that the medium offers

Question 19

What is the unit for impedance?

Answer 19

Rayls (Z)

Question 20

What is the equation for impedance?

Answer 20

Impedance (rayls) = density (kg/m^3) x propagation speed (m/s)

Question 21

What does the reflection of an ultrasound wave depend upon?

Answer 21

Different acoustic impedances of the media on either side of the boundary

Question 22

What is normal incidence?

Answer 22

"PORNN'
Perpendicular
Orthogonal
Right angle
Ninety degrees

Question 23

What is incident intensity?

Answer 23

Intensity of the sound wave at the instant prior to striking a boundary

Question 24

What is reflected intensity?

Answer 24

Portion of the incident intensity that, after striking a boundary, changes direction and returns back from where it came

Question 25

What is transmitted intensity?

Answer 25

Portion of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling

Question 26

List the equation for incident intensity.

Answer 26

Incident intensity = reflected intensity + transmitted intensity

Question 27

What is the intensity reflection coefficient?

Answer 27

The percentage of the US intensity that bounces back when the sound strikes a boundary

Question 28

What is the intensity transmission coefficient?

Answer 28

The percentage of the incident intensity that, after striking a boundary, continues on in the same general direction that it was originally traveling

Question 29

What occurs at the boundary between 2 media?

Answer 29

"Conservation of energy" When IRC and ITC are added, the result is 100% When reflected and transmitted intensities are added, the result is the incident intensity

Question 30

What is the % reflection of the following biologic media? Soft tissue - air Soft tissue - bone Soft tissue - soft tissue

Answer 30

99% 50% <1%

Question 31

What is needed for reflection of normal incidence?

Answer 31

Reflection occurs only if the 2 media at the boundary have different acoustic impedances

Question 32

List the equation of the intensity reflection coefficient.

Answer 32

Intensity Reflection Coefficient (%) = [(Z2-Z1)/(Z2+Z1)]^2

Question 33

What is transmission with normal incidence?

Answer 33

Whatever is not reflected in normal incidence

Question 34

What occurs with reflection & transmission with oblique incidence?

Answer 34

Extremely complex physics regarding transmission & refection with obliquity

Question 35

What occurs with the Law of Conservation of Energy?

Answer 35

Reflection angle = Incident angle

Question 36

What is refraction?

Answer 36

Transmission with a bend | Change in direction as sound transmits from 1 medium to another

Question 37

What does refraction require?

Answer 37

Oblique incidence | Different speeds

Question 38

What does Snell's Law describe?

Answer 38

Physics of refraction

Question 39

What is Snell's law equation?

Answer 39

sin (transmission angle)/sin (incident angle) = propagation speed 2/propagation speed 1

Question 40

What is required for reflection with normal incidence?

Answer 40

Look for different impedances

Question 41

What is required for reflection with oblique incidence?

Answer 41

We do not know

Question 42

What is required for transmission?

Answer 42

Derive this from reflection information

Question 43

What is required for refraction?

Answer 43

Look for oblique incidence and different speeds