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49 Cards in this Set
- Front
- Back
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What is energy?
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The ability to do work.
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What is the unit for energy?
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Joule or J
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What is power?
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The rate of energy.
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What is the unit of power?
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Joule/s or J/s
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What is intensity?
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The power per unit area.
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What is the unit for intensity?
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W/m2
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How is intensity measured?
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On the dB scale.
dB = 10 log Intensity/ Reference Intensity |
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Define compression.
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Density of a molecule is greater when no sound is preseent.
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Define rarefaction.
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A lower density of molecules when sound is present compared to the density when no sound is present.
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Define nodes.
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No displacement of a sine wave.
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Define antinodes.
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Maximum displacement of a since wave.
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The Acoustic Spectrum
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< 20 Hz Infrasound
20-20,000 Hz Audible Sound 20,000-1,000,000 Hz Ultrasound 1,000,000-30,000,000 Diagnostic Medical Ultrasound |
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tera/T
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10^12
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giga/G
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10^9
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mega/M
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10^6
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kilo/k
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10^3
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hecto/h
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10^2
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deca/da
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10^1
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pico/p
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10^-12
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nano/n
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10^-9
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micro/u
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10^-6
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milli/m
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10^-3
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centi/c
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10^-2
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deci/d
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10^-1
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How is something polarized?
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A temperature is applied above the Curie Point which allows the movement of the dipoles within the crystal.
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Voltage + Dipoles
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The voltage aligns the dipoles; it polarizes them. The voltage is kept on the crystal and it is cooled to a point below the Curie Point. The voltage is removed at this point.
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What is the driving characteristic of a medium?
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Compressibility.
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What is the relationship between compressibility and velocity?
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They are inversely proportional.
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Is density a factor compared to compressibility?
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No.
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Is there a reference intensity for ultrasound?
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No, there is no reference intensity per se for ultrasound; the transmitted intensity is used instead.
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What must there be in order for sound waves to occur?
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A medium.
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Are sound waves mechanical?
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Yes.
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Mechanical Sound Waves
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If sound waves are mechanical, they are traveling through a medium and producing vibrations. A medium must be present for this to occur.
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Ultrasound Problem
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If the problem is related to ultrasound, the reference intensity is the transmitted intensity.
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Why are the echoes received smaller than what is transmitted?
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This is due to attenuation.
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What is the bulk modulus?
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The BM is the measure of the stiffness of a material.
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Compressibility + Sound
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It is not the density of the material that drives the velocity of the sound but rather the compressibility of the medium.
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What is the relationship between compressibility and velocity?
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They are inversely proportional.
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If compressibility increases...
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...velocity decreases.
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If velocity increases...
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...compressibility decreases.
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What is the average speed of sound in soft tissue?
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1540 m/s
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What is the threshold for hearing?
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10^-12 W/m2
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How is a mechanical wave illustrated?
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They are illustrated by sine wave, graphing the pressure variation.
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When is a transducer most efficient at converting its energy?
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At its resonance frequency.
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What is the most efficient thickness of a crystal?
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1/2 of the wavelength.
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What purpose does the backing material serve?
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Backing material dampens the crystal.
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Where is the backing material located?
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It is located behind the crystal.
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Acoustic Impedance (Z)
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Z = p x c
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Angle + Refracted Beam
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When we go from fast to slow, the angle of the refracted beam is smaller than the angle of the incident beam.
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