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Fall '23 Echo > Physics Exam #1 > Flashcards

Physics Exam #1 Flashcards

1
Q

what is wavelength? what’s parameters? what’s wavelength equation?

A

wavelength = propagation velocity / frequency

it is a distance so it is in mm
*or any other distance related unit

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2
Q

what is period? what’s parameters? what’s equation for period?

A

period equals 1 over the frequency

5 Hz = 1/5Hz = 1 / 5 = .2 seconds

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3
Q

what is frequency? what’s parameters?

A

it is a rate so needs a _______per________.
ex. cycles per second.

cycles per second is a Hertz, or Hz. Hz is the unit in US.

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4
Q

how does wavelength, period, and frequency affect the wave?

A
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5
Q

what’s difference between rarefactions and compressions?

A
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6
Q

what determines propagation speed of sound in the medium?

A
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7
Q

what’s propagation velocity for soft tissue

A
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8
Q

how do the properties of the medium affect the speed of sound: density, stiffness, compressibility, bulk modulus…

A
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9
Q

define density

A
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10
Q

define stiffness

A
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11
Q

define compressibility

A
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12
Q

define bulk modulus

A
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13
Q

explain: what is propagation through a medium and what determines the speed?

A
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14
Q

speed of sound order of various media

A

A Little Fat White Liar Bullies Kids… My Son

Air, Lung, Fat, Water, Liver, Blood, Kidneys, Muscle, Skull

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15
Q

what is attenuation

A

attenuation is
defined as a decrease in wave
amplitude (or intensity) due to
the mechanical interaction with
the medium

represents a transfer
of energy through absorption and
scattering represented by
reflection and refraction.

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16
Q

what is attenuation coefficient for soft tissue

A

the degree of sound beam attenuation in
a tissue is usually given in decibels per
centimeter (dB/cm)
Soft Tissue Attenuation Rate:
0.5dB/cm/MHz
attenuation coefficient is one half of the frequency (0.5)
Attenuation coefficient is the amount of attenuation per
centimeter per MHz

Attenuation coefficient is the # of decibels
of attenuation that occurs when sound
travels one centimeter.

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17
Q

what affect does increasing the frequency of a sound wave have on attenuation?

A

Attenuation coefficient is the # of decibels
of attenuation that occurs when sound
travels one centimeter.
For each centimeter that sound travels more
energy is lost from high frequency sound than
from low frequency sound.
Its units are dB/cm

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18
Q

what is the biggest factor in attenuation?

A

absorption

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19
Q

the foundation for US is

A

reflection

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20
Q

high frequency =

A

high attenuation

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21
Q

low frequency =

A

low attenuation

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22
Q

The angle that a sound wave
approaches the boundary
between two different types of
mediums helps determine
whether __________, ___________, or _________ will occur.

A

transmission, reflection, or refraction

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23
Q

what is the angle of incidence?

A

The angle at which a
sound wave approaches a boundary

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24
Q

what is the angle of transmission?

A

The angle at which it continues on
past the boundary

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25
what is the angle of reflection?
The angle at which the sound wave reflects back to the transducer (after striking the boundary)
26
"normal incidence" of an angle is exactly equal to how many degrees
90 degrees
27
The angle at which the wave strikes the boundary determines
the behavior (of the pulse)
28
Oblique incidence
occurs when the incident sound beam strikes the boundary at any angle other than 90º
29
If reflection occurs the incident angle equals the
reflected angle, WHATEVER IS NOT TRANSMITTED MUST BE REFLECTED
30
The strongest echoes are produced when the
angles of incidence approach the angle of reflection.
31
define acoustic impedance
property of tissues that influences the strength or amplitude of reflected echoes in a quantity
32
Z=ρc
ACOUSTIC IMPEDANCE The acoustic impedance of a material is equal to the product of the medium’s density and its speed of sound
33
(Acoustic impedance is a measure of the ease or difficulty with which a sound wave propagates through a particular medium) the unit for acoustic impedance is called
1 Rayl = kg/m²sec
34
2 media have identical impedances...
NO or LITTLE reflection
35
2 media have substantially different impedances...
LARGE reflection
36
explain acoustic impedance in a paragraph
Lets take 100 (we will call this our “incident” marbles) marbles throw them at a paper wall, while the marbles are rolling through the air there is no reflection. Air is homogenous therefore there is no change in impedance, no reflection Now we will throw them at a hard paper wall hard enough that 20 of the marbles come back toward us (Our reflected marbles) and 80 go through the paper. (Our transmitted marbles) This represents a difference (a mismatch) in impedance relative to the air
37
incident Intensity is (marble idea approach here)
the sound waves intensity immediately before it strikes a boundary
38
Reflected Intensity (marble idea approach here)
is the intensity of the portion of the incident sound beam that after striking a boundary returns back where it came from.
39
transmitted intensity (marble idea approach here)
is the intensity of the portion of the incident beam that after striking a boundary continues forward in the same direction that it was traveling
40
acoustic impedance media from smallest to highest air lung fat water liver blood kidney muscle skull bone
air lung fat water liver blood kidney muscle skull bone A Little Fat White Liar Bullies Kids My Son
41
Reflection Coefficient
% REFLECTED = (Z2-Z1) ² X 100 (Z2+Z1) ² if the answer is 10% reflected also means (90% was transmitted)
42
what is the need for a coupling medium such as gel between the transducer and the patient
The complete reflection at air to (other medium) interface is almost at 100% very large acoustic impedance
43
The % of the intensity that bounces back when a sound beam strikes the boundary between two media is the
intensity coefficient A greater % of the wave is reflected when sound strikes a boundary such as between soft tissue and bone or between soft tissue and air
44
Reflection and Transmission are
both reported as percentages
45
acoustic impedance can be caused by
change in speeds of sound, a change in densities or both
46
refraction is (2 things must happen for something to be considered refraction)
the “bending” of the wave at a interface of two media 1. oblique incidence 2. different propagation speeds of the two media
47
Snells Law
The rule that governs and predicts the amount of refraction is called helps to predict the magnitude of the refracted wave. It predicts direction of the transmitted beam The transmission angle will be greater than the incident angle when the speed of Medium 2 is greater than the speed of Medium 1
48
diffraction
causes the US beam to diverge or spread out as the waves move farther from the sound source
49
power equals
amplitude squared ex. 2x the power = 4x the amplitude just take the power value and square it for amplitude
50
strength of wave are all proportional with this acronym
IPA intensity, power, amplitude
51
diffuse reflection.. aka...? what kind of surface?
irregular surface, sound travels back to transducer aka BACKSCATTER more hypoechoic image
52
specular reflection
specular means mirror, even surface reflection. more hyperechoic image
53
scattering aka
speckle
54
what is Rayleigh scattering
scattering of the sound wave in all directions, occurs with very small structures ex caused by RBC's
55
attenuation rate low to high... start with WATER!
Water Brings Beautiful Life... Fill My Beer Last Water, Blood, Brain, Liver, Fat, Muscle, Bone, Lung, (Air)
56
Repetitious waves are a _____ transfer of _______.
cyclical, energy
57
cyclical means
periodic or repetitive
58
the major classification of waves are
electromagnetic and mechanical
59
A _____ wave needs a medium to propogate
mechanical
60
A vacuum is the absence of a _______.
medium
61
Two classifications of mechanical waves are
transverse and longitudinal
62
In a _____ wave, particle motion is perpendicular to the wave direction.
Transverse... particle motion is perpendicular or TRANSVERSE to the wave direction
63
In a _____ wave, the particle motion is back and forth in the same direction as the wave propagation
longitudinal
64
Sound is a _______, mechanical wave
longitudinal
65
A longitudinal wave has areas of _____ and compression.
rarefaction
66
An area of rarefaction is
where the particles are farther apart than the normal state, low pressure
67
_______ is a way of specifying how fast a wave is cyclically varying
frequency
68
The unit for frequency is _____ which is an abbreviation for cycles per _____.
Hertz, second.
69
Frequency has units which are the inverse of _____, or one divided by seconds, also called _____.
time, Hz.
70
The number of times longitudinal wave reaches maximum compression and rarefaction per time is called the
frequency
71
the reciprocal of frequency is the
period
72
The period has units of
time
73
The _____ is the time between cycles of peak compression in a longitudinal wave such as sound.
period
74
a shorter period means a higher
frequency
75
propagation velocity is a measure of
how fast a wave will travel
76
the unit for propagation velocity is
m/s
77
frequency and wavelength have an _____ relationship.
inverse
78
changes in acoustic variables are the result of the mechanical interaction of the acoustic wave and the
medium
79
sound, human audible range
20 Hz to 20 kHz
80
ultrasound... "ultra" means
above so any ultrasound is "above" human hearing
81
Diagnostic Sound
2 MHz - 12 MHz
82
elasticity is
ability of a solid object to return to its original shape after distortion by a force
83
compressibility is
how much the volume of the material changes for a given distorting force (pressure)
84
stiffness is
opposite of elasticity or compressibility. not much compression here. it is inelastic. "in" meaning "not." so not elastic.
85
bulk modulus is
ratio... stress:strain. stiff materials have high bulk modulus. it is the inverse of compressibility. Ex: a low compressibility material would have a high bulk modulus.
86
it the amplitude is DECREASED by a factor of 3, what happens to the power?
take the value 3 and square it... because it says DECREASE... you put it in fraction form. It is 1/9th the power.
87
intensity equals
power divided by beam area
88
if the beam area is doubled, what happens to the intensity?
it is 1/2 the original intensity
89
small units... deci, centi, milli, micro
deci 1/10 centi 1/100 milli 1/1000 micro 1/1,000,000
90
big units... deca, kilo, mega
deca 10 kilo 1000 mega 1,000,000
91
Transmit power, attenuation receiver gain, and compression all measured in
decibles or dB any parameter which results in a change of POWER.
92
the simplified rule of 3dB
with each 3dB gain there must be an additional doubling of power delivered. Thus, a 3dB gain requires twice the power, a 6dB gain requires four times the power, and a 9dB gain requires eight times the power. example if the original intensity produced at some point in the beam of the transducer is 20mW/cm², a 3dB increase in the output of the machine results in a new intensity of 40 mW/cm², another 3dB increase results in an intensity of 80 mW/cm² When intensity increases, ten- fold the relative change is +10 dB When the intensity is reduced to ½ its original value, the relative change is -3dB  When the intensity is reduced to 1/10 its original value, the relative change is -10dB When dB increase by +3 dB, the intensity increases by a factor of 2  When the dB increase by +10db, the intensity increases by a factor of 10
93
10 dB increase =
sound energy is increased by a factor of 10
94
10 dB decrease =
sound energy is decreased by a factor of 10
95
3 dB increase =
double
96
3 dB decrease =
half
97
in terms of INTENSITY, an increase of power by a factor of 2 is equivalent to ______dB?
3 db an increase by a factor of 10 would be 10 dB an increase by a factor of 20 would be 100 dB an increase by a factor of 30 would be 1000 dB a decrease by a factor of 1/2 would be -3dB a decrease by a factor of 1/10 would be -10dB a decrease by a factor of 1/100 would be -20dB etc
98
a gain ratio of 1 would affect the dB by how much?
0 dB
99
For every positive 10dB change this means that the intensity will
increase 10x
100
ultrasound travels very slow in air due to
air is very low in STIFFNESS
101
Speed of sound in soft tissue
1540 m/s 154,000 cm/s 1.54 km/s 1.54mm/μs= 0.154cm/μs KNOW THIS- KNOW ALL CONVERSIONS
102

Fall '23 Echo (19 decks)

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