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CMI 350 > Ch.3 Describing Sound Waves > Flashcards

Ch.3 Describing Sound Waves Flashcards

1
Q

What are the seven parameters that describe sound waves?

A

Period
Frequency
Amplitude
Power
Intensity
Wavelength
Propagation Speed

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2
Q

Period

A

is the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle

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3
Q

Period:
Units
Typical values

A

units of time
microseconds (us),
0.06 to 0.5 us

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4
Q

Period:
Determined by
Adjustable

A

Sound Source ONLY
NOT medium
No

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5
Q

Frequency

A

is the number of particular events that occur in a specific duration of time

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6
Q

Frequency:
Units
Typical Values

A

units of per second
(1/sec, hertz, Hz)
(1 cycle/second = Hertz)
Approx. 2MHz to 15 MHz

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7
Q

Frequency:
Determined by
Adjustable

A

Sound Source ONLY
No

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8
Q

Sound Wave Spectrum:
Infrasound (infrasonic)

A

Less than 20 Hz
(NOT Audible)

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9
Q

Sound Wave Spectrum:
Audible Sound

A

Between 20 Hz and 20 kHz

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10
Q

Sound Wave Spectrum:
Ultrasound (ultrasonic)

A

Greater than 20 kHz
(Greater than 20,000 Hz)
(In audible to humans)

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11
Q

What is the relationship between frequency and period?

A

are inversely related
(Reciprocal = 1/f )
if one remains constant that the other remains the unchanged

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12
Q

What are the three bigness parameters?

A

Amplitude
Power
Intensity

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13
Q

Amplitude

A

is the “bigness” of a wave. It is the difference between the maximum value and the average or undisturbed values of an acoustic variable

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14
Q

Amplitude:
Units
Typical Values

A

any units from the acoustic variable
pascals
density
cm, inches
decibels (dB)
1 million pascals (MPa)
to 3 MPa

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15
Q

Amplitude:
Determined by
Adjustable

A

Sound Source only
Yes, a control on the system allows the sonographer to alter initial amplitude of a wave

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16
Q

What is the difference between amplitude and peak-to-peak amplitude?

A

Amplitude: is measured from the baseline to the maximum value or minimum value
Peak-to-Peak: is difference between maximum and minimum value of an acoustic variable. (Twice the value of the amplitude)

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17
Q

Power

A

is the rate of energy transfer or the rate at which work is performed

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18
Q

Power:
Units
Typical value

A

watts
0.004 to 0.090 watts
(4 to 90 milliwatts)

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19
Q

Power
Determined by
Adjustable

A

Sound Source ONLY
Yes, initial power like amp can be changed

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20
Q

Power decreases as _____ propagates through the body.

The rate at which power decreases as sound propagates depends on the characteristics of the _____ and the _____ .

A

sound
amplitude and wave

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21
Q

How are amplitude and power related?

A

power is proportional to the wave’s amplitude squared

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22
Q

If a sonographer increases the amplitude of a wave by a factor of 3. How has the power changed?

A

3 x 3 = 9
power increased by 9

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23
Q

If a sonographer decreases the amplitude of a wave to 1/2 of its original value, how has the power changed?

A

1/2 x 1/2 = 1/4
power decreases to 1/4th or 25% of its original value

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24
Q

Intensity

A

is the concentration of energy in a sound beam.
to calculate divide the beam’s power by the beam’s cross-sectional area.
relates to how the power in a wave spreads or is distributed in space
-depends on power and area

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25
Intensity: Units Typical Values
Watts/square centimeter W/cm^2 0.01 to 300 W/cm^2
26
Intensity: Determined by Adjustable
Sound Source ONLY (intensity changes as sound propagates thru body) Yes allowed to alter the initial intensity of a wave
27
The rate at which intensity changes as sound propagates depends on the characteristics of both the _____ and the ______
sound wave medium
28
How is intensity related to power?
proportional to power
29
How is intensity and amplitude related?
proportional to the wave's amplitude squared
30
Wavelength units
is the distance or length of one complete cycle mm, meters, or other unit of length
31
Wavelength: Typical Values Determined by Adjustable
0.1 to 0.8 mm By BOTH source and medium (only parameter) NO
32
What is the difference between wavelength and period?
Wavelength refers to the length or distance of a single cycle Period refers to the time that it takes to complete a single cycle
33
What is the relationship between wavelength and frequency?
As long as a wave remains in one medium, wavelength and frequency are inversely related
34
As frequency increases , wavelength ________ . The lower the frequency, the _____ the wavelength.
decreases longer
35
What is the wavelength of 1 MHz sound in soft tissue?
Has a wavelength of 1.54 mm
36
If sound has a frequency of 2 MHz, which is the wavelength in soft tissue?
1.54 mm / 2 = 0.77 mm
37
Why is wavelength important in diagnostic ultrasound?
Wavelength plays an important role in image quality -Shorter wavelengths are created by high frequency sound, which usually produces higher quality images with great detail
38
Propagation Speed units
is the rate at which a sound wave travels through a medium -meters per second -mm/us
39
Propagation Speed: Typical Values Determined by Adjustable
500 m/s to 4000 m/s depending on the tissue Medium ONLY NO (Speed changes only when the wave travels from one medium to a different medium
40
What is the speed of sound in soft tissue?
1,540 m/s (1.54 mm/us)
41
Sound travels fastest in what materials?
Solids Liquids Gases (slowest)
42
What is the formula for the speed of sound in other media?
Speed (m/s) = frequency (Hz) x wavelength (m)
43
What characteristics of a medium determine the speed of sound in that medium?
Stiffness and Density
44
Stiffness
describes the ability of an object to resist compression -retain its shape
45
Density
describes the relative weight of a material.
46
How does stiffness affect speed?
Stiffness and speed are directly related -As materials become stiffer, the speed of sound in the material increases
47
How does density affect speed?
Density and speed are inversely related -As materials become more dense (heavier), the speed of sound decreases
48
If two media are equally stiff, the dense medium will have a _____ speed.
lower
49
Stiffness increases, Speed ____
Increases
50
Density increases, speed _____
Decreases
51
Materials that are stiff but not dense will have the ____ speed.
fastest Ex: Bone
52
Materials that are not stiff and very dense will have the ________ speed.
slowest
53
Although both stiffness and density affect propagation speed, _______ has the greatest influence on speed
Stiffness Ex: Air has an exceedingly low stiffness, so sound travels slowly in it.
54
Period: Adjustable Units Determined by Typical value
NOT adjustable seconds, us source 0.06 to 0.5 us
55
Frequency: Adjustable Units Determined by Typical Value
NOT adjustable per second, Hz source 2 to 15 MHz
56
Amplitude: Adjustable Units Determined by Typical Value
Yes adjustable pascals, cm, g/cm^3, dB source 1 MPa to MPa
57
Power: Adjustable Units Determined by Typical value
Yes adjustable Watts, dB Source 4 to 90 mW
58
Intensity: Adjustable Units Determined by Typical value
Yes adjustable Watts/cm^2, dB Source 0.01 to 300 W/cm^2
59
Wavelength: Adjustable Units Determined by Typical value
NOT adjustable mm, distance BOTH source & medium 0.1 to 0.8 mm
60
Speed: Adjustable Units Determined by Typical value
NOT adjustable m/s medium 1,500 to 1,600 m/s
61
What three parameters can be adjusted by the sonographer?
Amplitude Power Intensity

CMI 350 (11 decks)

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