Ch. 6 Interaction Of Sound And Media

Question 1

Logarithm

Answer 1

A novel method of rating numbers. Logarithm or log of a number represents the number of 10s that are multiplied to create the original number.

Question 2

What is the log of 1000, 10000, & 1000000?

Answer 2

For 1000: We multiply 10 by itself 3 times to create the number 1,000, so the log is 3. For 10000: We multiply 10 by itself 4 times to create the number 10,000, so the log is 4. For 1000000: We count the zeros, there are 6 zeros, so the log is 6.

Question 3

When a wave’s intensity doubles the relative change is ________

Answer 3

Relative change is +3 dB.

Question 3

Definition of Decibel

Answer 3

A relative measurement, comparison, ratio, and logarithmic.

Question 3

What do positive decibels report?

Answer 3

Signals are increasing in strength or getting larger.

Question 4

What do negative decibels report?

Answer 4

Describe signals that are decreasing in strength, or getting smaller.

Question 4

When a wave’s intensity increases 10-fold the relative change is ________

Answer 4

Relative change is +10 dB.

Question 5

When a wave’s intensity is reduced to ½ its original value the relative change is ________

Answer 5

-3 dB

Question 6

When a wave’s intensity reduced to 1/10 its original value the relative change is ________

Answer 6

-10 dB

Question 7

Definition of attenuation

Answer 7

The decrease in intensity, power, and amplitude as sound travels.

Question 8

Attenuation is determined by

Answer 8

Path length and frequency of sound.

Question 9

Attenuation is measured by

Answer 9

In decibels and reported as a relative change, not as an absolute change.

Question 10

3 Processes that contribute to attenuation

Answer 10

Reflection, scattering, and absorbtion.

Question 11

Two types of reflection

Answer 11

Specular and diffuse

Question 12

Rayleigh Scattering

Answer 12

A special form of scattering that occurs when the structures dimensions are much smaller than the beams wavelength. This redirects the sound wave equally in all directions.

Question 13

Attenuation Coefficient

Answer 13

The number of decibels of attenuation that occurs when sound travels one centimeter.

Question 14

Attenuation Coefficient in soft tissue

Answer 14

The attenuation coefficient (dB/cm) and frequency (MHz) are directly related. The attenuation coefficient is one=half the frequency.

Question 15

What mathematical equation is used to solve for total attenuation in soft tissue?

Answer 15

Atten. Coef. (dB/cm) = frequency (MHz)/ 2; Atten. Coef. = 0.5 dB/cm/MHz

Question 16

Half – Value Layer Thickness defined

Answer 16

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

Question 17

Half – Value Layer Thickness units

Answer 17

Centimeters, or any other unit of length.

Question 18

Half – Value Layer synonyms

Answer 18

Penetration depth, depth of penetration, and half-boundary layer.

Question 19

Half – Value Layer dependent on what?

Answer 19

The medium and frequency of sound.

Question 20

Impedance defined

Answer 20

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.

Question 21

Reflection & Transmission

Question 22

Impedance units

Answer 22

Rayls, often represented by the letter z.

Question 23

Impedance determined by what?

Answer 23

Associated with the medium only. It is calculated, not measured.

Question 24

Impedance synonyms

Answer 24

Characteristic impedance

Question 25

A tissue’s impedance is ____.

Answer 25

Calculated, not measured.

Question 26

Impedance formula

Answer 26

impedance (rayls) = density (kg/m^3) x prop. Speed (m/s)

Question 27

Incidence defined

Answer 27

A sound pulse strikes many tissue interfaces as it travels in the body. The angle at which the wave strikes the boundary determines the behavior of the pulse.

Question 28

Acute angle

Answer 28

Less than 90 degrees

Question 29

Right angle

Answer 29

Exactly 90 degrees

Question 30

Obtuse angle

Answer 30

Greater than 90 degrees

Question 31

Normal Incidence defined

Answer 31

Means that the incident sound beam strikes the boundary at exactly 90 degrees.

Question 32

Synonyms for normal incidence

Answer 32

Perpendicular, orthogonal, right angle, and 90 degrees.

Question 33

Oblique Incidence defined

Answer 33

Occurs when the incident sound beam strikes the boundary at any angle other than 90 degrees.

Question 34

Oblique Incidence synonyms

Answer 34

Means not at right angles or non-perpendicular

Question 35

Incident Intensity defined

Answer 35

Is the sound waves intensity immediately before it strikes a boundary.

Question 36

Reflected Intensity defined

Answer 36

The intensity of the portion of the incident sound beam that, after striking a boundary, returns from where it came.

Question 37

Transmitted Intensity defined

Answer 37

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.

Question 38

All intensities are measured in ____________ .

Answer 38

W/cm^2

Question 39

Intensity Reflection Coefficient (IRC) defined

Answer 39

Is the percentage of the intensity that bounces back when a sound beam strikes the boundary between the two media.

Question 40

Intensity Transmission Coefficient (ITC) defined

Answer 40

The percentage of intensity that passes in the forward direction when the beam strikes an interface between two media.

Answer 41

100% = inten. Reflection coef. (IRC) (%) + intensity trans. Coef. (ITC) (%)