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30 Cards in this Set

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Acoustic Propagation Properties

the effects of the medium upon the sound wave

Biological Effects

the effects of the sound wave upon the biologic tissue

Sound

A type of wave that carries energy, not matter, from place to place

How sound travels

Vibration of a moving object


Compression (increase pressure/density)


Rarefactions (decreased pressure/density)


Travels in a medium


Straight line


Mechanical and longitudinal

Three acoustics variables

Pressure


Density


Distance

Pressure

Concentration of force within an area


Force/area. Pascals (Pa)

Density

Concentration of mass within a volume


kg/cm3

Distance

Measure of particle motion


cm, feet, miles

Parameters describe sound waves

Period Speed


Frequency



Amplitude


Power


Intensity Wavelength

Period

Time required to complete a single cycle


Seconds, Mses, hours


Sound source

Frequency

Number of certain events that occur in a particular time duration (# cycles per second)


Per second, 1/second, hertz, Hz


Hertz=per second


Sound source


2 MHz-15 MHz


Affects penetration and axial resolution (image quality)

Ultrasound

A wave with a frequency exceeding 20,000Hz (20kHz)


Too high and is not audible to man

Audible sound

Frequencies between 20Hz and 20,000Hz. Heard by man

Infrasound

Frequencies less than 20Hz. Too low for man to hear.

Frequency and Period

Are reciprocals



Equation


Frequency (Hz) x period (sec) =1


Period (sec) = 1/frequency (Hz)


Frequency (Hz) = 1/ period (sec)

Three Bigness Parameters

Amplitude


Power


Intensity

Amplitude

The difference between the average value and the maximum value of an acoustic variable.


Pressure-Pascals


Density-grams/cubic cm


Particle motion-cm, inches, unit of distance


Can be expressed in decibels,dB


Sound source

Power

The rate that is performed or rate of energy transfer.


Watts


Sound source


Power proportional (Amplitude)2

Intensity

Concentration of energy in a sound beam


= power (watts)/


beam area(cm2)


Sound source


Proportional or directly related to the power


proportional to amplitude2

Wavelength

The length or distance of a single cycle


Meters, mm


Source and medium


= propagation speed (mm/Ms)/


Frequency (MHz)

Propagation speed

The rate that sound travels through a medium also called velocity or speed


Meters per second, mm/Ms


Medium only


= frequency (Hz)


x wavelength (meters)

Speed and wavelength are directly related.


Sound in a slow medium has a short wavelength.


Sound in a fast medium has a long wavelength

Average speed of sound

Soft tissue = 1.54km/s = 1,540m/s = 1.54mm/Ms


Lung (air) << fat < soft tissue <

Average speed of sound

Soft tissue = 1.54km/s = 1,540m/s = 1.54mm/Ms


Lung (air) << fat < soft tissue <

Rule of thumb


propagation speed

Stiffness ⬆️and speed⬆️ - same direction


Density ⬆️and speed⬇️ - opposite direction


Bulk modulus is the same as stiffness. When bulk modulus increases speed increases


Compressibility and elasticity are opposites of stiffness

Parameters of continuous waves

Back (Definition)

Parameters of continuous waves

Back (Definition)

Continuous wave


Cheat sheet

Back (Definition)

Phase relationships

Interference


-in phase


-out of phase


Constructive interference


Destructive interference

Constructive interference

Occurs when the amplitude of the new, combined wave is greater than the original two waves. In-phase waves interfere constructively.

Destructive interference

The amplitude of the new wave is less than one of the original waves. Out-of-phase waves interfere destructively. Out-of-phase waves are said to have a phase difference