Week 2 Assessment (6,7,8) Flashcards

1
Q

logarithms

A

Count the zeros.Ex.log of 100 is 2.

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2
Q

Positive decibels and negative decibels

A

Positive:Intensity doubles for every 3bD
Ex. 9dB (two 3s to get 9 so 2 x 2= 4 times larger)
Negative: -3dB:1/2 ..example—6dB=1/2x1/2=1/4
-10dB: 1/10…ex.9dB=1/2x1/2x1/2=1/8

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3
Q

Attenuation is directly related to

A

Distance and frequency
longer distances, higher frequencies= more attenuation

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4
Q

3 components of attenuation

A

Absorption, scattering and reflection

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5
Q

Media with least attenuation

A

water

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6
Q

Media with most attenuation

A

Air

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7
Q

what’s the conversion of acoustic energy into heat?

A

Absorption

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8
Q

Primary cause of attenuation in soft tissue (80%)

A

Absorption

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9
Q

Absorption is_________related to distance and frequency

A

directly

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10
Q

Sound that returns back to the transducer after striking a boundary

A

Reflection

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11
Q

The 2 forms of reflection are

A

Specular:
(smooth reflector, one direction, smaller wavelength than boundary irregularities)
Diffuse/backscatter:
(rough reflector, random directions, wavelength same size as boundary irregularities)

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12
Q

Boundary’s irregularities are same size to bit smaller than wavelength, wave redirected in all directions.High frequencies have more …ex.Red blood cells are this

A

Rayleigh scattering

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13
Q

Thin half value layer

A

Bone
high freq,high attenuation rate

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14
Q

thick half value layer

A

Fluids
low freq,low attenuation rate

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15
Q

what other names half value layer known by

A

penetration, depth of penetration, half boundary layer

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16
Q

sound beam strikes boundary exactly at 90 degrees

A

Normal incidence

17
Q

Any angle other than 90 degrees is

A

Oblique incidence
acute<90
Obtuse >90

18
Q

Formula for incident intensity

A

Reflected intensity + Transmitted intensity

19
Q

% reflected for soft tissue,bone and air

A

soft tissue: less than 1%
Bone : 50%
Air : 99%

20
Q

Formula for IRC(%)–reflection with normal incidence

A

(Z2-Z1/Z2+Z1)^2
Z1= reflection #
Z2= Transmission #

21
Q

Reflection with normal incidence (90 degrees) occurs when (IRC)

A

there are different impedances on either side of the boundary

22
Q

Transmission with normal incidence occurs (ITC)

A

When the Two media have same impedance
% from reflected sound - 100%= ITC

23
Q

Transmission with oblique transmission

A

100% IRC +ITC
transmission difficult to predict

24
Q

Refraction cannot occur with

A

Normal incidence or with identical propagation speeds.

25
Refraction is and requires
when the direction of wave propagation is changed from 1 medium to another requires : Oblique incidence and diff propagation speeds of 2 media
26
Snell's slaw is the reason
-Refraction occurs. -Greater the change in the speeds of the media the greater the change in the angle of refraction sin(transmission angle)/sin (incident angle)=propagation speed 2/propagation speed 1
27
medium 1 and medium 2 refraction (oblique angle)
If md 1 is > md 2 travel in same direction md 1 < md 2 ,md 2 is faster,shorter md 1 > md 2 ,md 2 is slower, longer
28
Thickness of matching layer
1/4
29
thickness of active element (pzt)
1/2
30
3 consequences of using backing material
decreased sensitivity wide bandwidth low quality factor
31
Resonant frequency
ringing at single frequency
32
Main frequency of transducer known as
center, resonant,primary or natural frequency
33
Quality factor
Main frequency/ bandwidth ex.7hz/8hz-6
34
transducer that has Low Q due to backing material
Imaging transducers
35
therapeutic imagining has
HIGH Q
36
Speed of sound in PZT and frequency are
directly related
37
Thickness in PZT and frequency are
inversely related