Interaction of Sound and Media

Question 1

Sound _______ as it propagates through the body

Answer 1

weakens

Question 2

The weakening of sound as it travels through tissues is called?

Answer 2

attenuation

Question 3

When sound waves are sent back to the system they are ______.

Answer 3

amplified

Question 4

What is used to report a change in intensity?

Answer 4

decibels

Question 5

The log of 1000 is?

Answer 5

3

Question 6

The log of 100 is?

Answer 6

2

Question 7

Decibal notation is?

Answer 7

a relative measurement, a comparison, a ratio, logarithmic

Question 8

Decibels require _____ intensities

Answer 8

2

Question 9

Positive decibels signify?

Answer 9

an increase or amplification

Question 10

+3dB means the intensity _______.

Answer 10

doubles

Question 11

+10 dB means the intensity ________.

Answer 11

increases by ten times

Question 12

Negative decibels signify?

Answer 12

a decrease in intensity or attenution

Question 13

-3dB means the intensity _______

Answer 13

reduces to 1/2 its value

Question 14

-10 dB means the intensity _______

Answer 14

reduces to 1/10 it’s original value

Question 15

If the original intensity is 2 watts/cm2, and it reduces by 3 dB, what is the final intensity?

Answer 15

1 watt/cm2

Question 16

If the original intensity is 20 watts/cm2, and it reduces by 10 dB, what is the final intensity?

Answer 16

2 watts/cm2

Question 17

Attenuation is determined by?

Answer 17

path length (depth) and frequency

Question 18

Attenuation and path length are _______ related

Answer 18

directly

Question 19

Attenuation and frequency are _________ related

Answer 19

directly

Question 20

What three things contribute to attenuation?

Answer 20

reflection, scattering, absorption

Question 21

Reflection occurs when a boundary is _____

Answer 21

large

Question 22

What are the two types of reflection?

Answer 22

specular and diffuse

Question 23

What are the two types of reflection?

Answer 23

specular and diffuse

Question 24

What is specular reflection? When does it occur?

Answer 24

sound reflects in one direction; boundary is smooth

Question 25

What is diffuse reflection? When does it occur?

Answer 25

Sound is reflected in more than one direction; boundary is irregular

Question 26

What is scattering? When does it occur?

Answer 26

random redirection of sound in many directions; boundary is small

Question 27

Frequency and scattering are _______ related

Answer 27

directly

Question 28

What is an example of rayleigh scattering?

Answer 28

interaction with red blood cells

Question 29

What is absorption?

Answer 29

Ultrasonic energy is converted into another energy form, like heat

Question 30

Absorption is _______ related to frequency

Answer 30

directly

Question 31

What does the attenuation coefficient represent?

Answer 31

the number of decibels of attenuation that occur when sound travels 1 cm

Question 32

Unit of the attenuation coefficient?

Answer 32

dB/cm

Question 33

Unit of attenuation?

Answer 33

dB

Question 34

Formula for total attenuation

Answer 34

attenuation coefficient x distance

Question 35

Attenuation coefficient and frequency are _______ related

Answer 35

directly

Question 36

The attenuation coefficient is _____ the frequency

Answer 36

half

Question 37

Define half value layer thickness

Answer 37

the distance sound travels to reduce the intensity to 1/2 it’s original value (-3dB)

Question 38

The HVL depends on?

Answer 38

medium and frequency

Question 39

Define impedance

Answer 39

the resistance to sound traveling in a medium

Question 40

What are the units of impedance

Answer 40

rayls (Z)

Question 41

What is the typical value of the HVL?

Answer 41

0.25-1.0 cm

Question 42

What can lead to a thin HVL?

Answer 42

high frequency sound or medium with high attenuation rate

Question 43

What can lead to a thick HVL?

Answer 43

low frequency sound or a media with a low attenuation rate

Question 44

Define incidence

Answer 44

the angle at which a wave strikes a bondary

Question 45

What are the three types of incident angles?

Answer 45

acute/oblique, right, obtuse/oblique

Question 46

Define normal incidence

Answer 46

beam strikes boundary at 90 degrees

Question 47

Normal incidence is also called?

Answer 47

perpendicular, **orthoganal**, right angle

Question 48

Define oblique incidence

Answer 48

Sound beam strikes boundary at angle other than 90 degrees

Question 49

What is the intensity before a wave strikes a boundary?

Answer 49

incident intensity

Question 50

What is the intensity of the portion of the wave that bounces back after striking a boundary?

Answer 50

reflected intensity

Question 51

What is the intensity of the portion of the wave after striking a boundary that continues forward?

Answer 51

Transmitted Intensity

Question 52

The Incident intensity equals?

Answer 52

Reflected intensity + Transmitted intensity

Question 53

What is the intensity reflection coefficient (IRC)?

Answer 53

the percentage of intensity that bounces back after striking a boundary

Question 54

What is the intensity transmission coefficient?

Answer 54

the percentage of intensity that continues forward after striking a boundary

Question 55

True or False: The IRC is usually larger than the ITC

Answer 55

False; ITC is larger (more transmission than reflection)

Question 56

IRC + ITC =?

Answer 56

100%

Question 57

Reflection only occurs when with normal incidence ?

Answer 57

When media have different impedances

Question 58

True or False: If impedances are identical with normal incidence there is reflection

Answer 58

False; All transmissio

Question 59

If there are slightly different impedances, there is a _______ amount of reflection

Answer 59

small

Question 60

If there are largely different impedances, there is a _______ amount of reflection

Answer 60

large

Question 61

With normal incidence, if two media have identical impedances, all sound is?

Answer 61

Transmitted

Question 62

With normal incidence, reflection and transmission depends on?

Answer 62

the impedences

Question 63

True or False: Reflection and transmission cannot be predicted with oblique incidence

Answer 63

True

Question 64

With oblique incidence, what two principles always apply?

Answer 64

conservation of energy; reflection angle = incident angle

Question 65

With an oblique incidence, the direction of the reflected echo is?

Answer 65

equal and opposite to the direction of the incidence

Question 66

What is refraction?

Answer 66

When a beam strikes a boundary at oblique incidence and transmits but changes direction (does not travel straight)

Question 67

Refraction only happens under what two conditions?

Answer 67

oblique incidence and different propagation speeds of two media

Question 68

True or False: Refraction can occur with normal incidence

Answer 68

False; only oblique incidence

Question 69

True or False: Refraction occurs when the speeds of two media are identical

Answer 69

False; different speeds

Question 70

When the speed of medium 2 is is greater than medium 1, the transmission angle will be ______ than the incident angle

Answer 70

greater

Question 71

When the speed of medium 2 is less than medium 1, the transmission angle will be______ than the incident angle

Answer 71

less