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US physics > Sound Chapter 2 > Flashcards

Sound Chapter 2 Flashcards

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1
Q

What are acoustic propagation properties?

A

The effects of the medium upon the sound wave

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2
Q

What are biologic effects?

A

The effects of the sound wave upon the biologic tissue

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3
Q

How would you describe sound?

A

A type of wave that carries energy, not matter, from place to place. Created by the vibrating object

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4
Q

What are sound waves made up of? What are these best described?

A

Series of compressions (areas of increased pressure and density) and rarefactions (areas of decreased pressure and density)

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5
Q

What are three important descriptors of sound waves?

A
  1. Sound is a mechanical, longitudinal wave
  2. Sound travels in a straight line
  3. Sound must travel through a medium, it cannot travel through a vacuum
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6
Q

What are the three acoustic variables? Why are these important?

A

Pressure, density, distance. Used to identify which waves are sound waves.

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7
Q

What is the definition of pressure? Units?

A

Concentration of force within an area. Force/area. Pascals (Pa)

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8
Q

What is the definition of density? Units?

A

Concentration of mass within a volume. Mass/volume. Kg/cm^3

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9
Q

What is the definition of distance? Units?

A

Mesure of particle motion. Distance mm or cm.

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10
Q

How do particles move in a transverse wave?

A

Particles move in a perpendicular direction (right/ 90 degree angles) to the wave’s direction

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11
Q

How do particles move in a longitudinal wave? What are found within these waves?

A

Particles move back and forth in the same direction as the wave. Compression and rarefactions.

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12
Q

What are acoustic parameters? Name all 7 of them.

A

Describe the features of a particular sound wave.
1. Period
2. Frequency
3. Amplitude
4. Power
5. Intensity
6. Wavelength
7. Speed

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13
Q

What is the definition of period? Units? Typical values? What is this determined by? Can it be changed by the sonographer? What kind of relationship does it have with the other parameters?

A

Time required to complete a single cycle. Microseconds (time). 0.06-0.5 microseconds. Determined by the sound source. No it is a fixed period. Inverse relationship to frequency, they are reciprocals of each other.

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14
Q

What is the definition of frequency? Units? Typical values? What is this determined by? Can it be changed by the sonographer? What kind of relationship does it have with the other parameters?

A

Number of cycles of an acoustic variable that occur in one second. Per second (Hertz). 2MHz - 15 MHz. Sound source. No.

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15
Q

What does higher frequency mean? Lower frequency? Why is this?

A

Higher= better resolution Lower = better penetration. This is because higher frequencies attenuate more.

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16
Q

What are the frequencies of audible, ultra, and infrasound? Can these be heard?

A
  1. Audible = b/w 20 Hz and 20,000 Hz.
  2. Ultrasound = greater than 20,000 Hz. No frequency too high
  3. Infrasound = less than 20 Hz. No frequency too low
17
Q

What are the 3 bigness parameters? What are these used for?

A

Amplitude, power, and intensity. Describes a sound beam’s strength.

18
Q

What do the 3 bigness parameters have in common?

A

Determined initially by the sound source, can be adjusted by the sonographer, and decreases as sound travels (propagates)

19
Q

What is amplitude? Units?

A

The difference between/w the average and the max value of an acoustic variable (variation). Units are those of the acoustic variables: pascals (pressure), grams/cubic cm (density), cm/ inches (particle motion) and decibels.

20
Q

What is power? Units? Relationship b/w other variables?

A

The rate that work is preformed, or the rate of energy transfer. Watts. Power is proportional to amplitude squared.

21
Q

What is intensity? Equation/ units? Relationship to other parameters?

A

The concentration of energy in a sound beam. Intensity = power/ beam area. Watts/cm squared. Intensity is proportional to power. Intensity is also proportional to the amplitude squared.

22
Q

What is wavelength and what does it influence? Units/ equation? What is it determined by? Can it be changed? What are the typical values? What is its relationship to the other parameters?

A

Distance of a single cycle; influences image quality (axial resolution) short wavelength = better resolution. Length (mm or meters); wavelength= propagation speed/frequency. Both source and the medium. No. 0.1-0.8mm in soft tissue. Higher frequency=shorter wavelengths.

23
Q

In soft tissue what is the wavelength of a sound with a frequency of 1 MHz? So what’s the equation now?

A

1.54 mm. In SOFT TISSUE wavelength (mm)= 1.54mm/us / frequency (MHz)

24
Q

What is propagation speed? Units? Typical values? Can it be changed? What is this determined by and what does this mean? Relationship between the other parameters?

A

Rate that sound travels through a medium (velocity/speed). mm/us. In soft tissue 1.54 mm/us. No. Medium only (density and stiffness) all sound (no matter the frequency) travels at the same speed thru the SAME medium. Directly related to wavelength sound in a slow medium= short wavelength.

25
Q

What is the general rule of speed when considering mediums? AKA?

A

Gas (slower) < liquid < solid (faster). Lung (air) &laquo_space;fat < soft tissue &laquo_space;bone.

26
Q

What is the propagation speed of the following tissues? Air, soft tissue/blood, tendon, bone.

A

0.33 mm/us, 1.54 mm/us, 1.85 mm/us, 2.0 - 4.0 mm/us

27
Q

What is a general room of thumbs when considering speed and the characteristics of a medium? What has the greater effect on speed? What is bulk modulus?

A

Stiffer medium= faster speed, Denser medium= decreased speed. Changes in stiffness have greatest effect on speed. Bulk modulus= same as stiffness, so when this increases so does speed.

28
Q

What happens when two waves overlap at the same location and time? What is this called? What are the two different types?

A

They combine into a single new wave- interference. Constructive and destructive.

29
Q

What happens in constructive interference? Destructive?

A

2 in-phase waves combine into one bigger wave. 2 out-of-phase waves combine into a smaller wave.

US physics (5 decks)

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