# US Vocabulary

## Terms

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Pressure
Concentration of force in an area (units = pascals)
Density
The relative weight of a material
Distance
Measure of particle motion (units = cm, feet, mile)
Transverse Waves
Particles move in a direction that is PERPENDICULAR (at right angles) to the direction that the wave propogates
Longitudinal Waves
Particles move in the same direction that the wave propogates
In-Phase Waves
When peaks (maximum values) occur and the same time and at the same location
Out-of-Phase Waves
When peaks (maximum values) occur at different times and so do their troughs
Constructive Interference
Resultant wave is larger than its components
Destructive Interference
Resultant wave is smaller than one of its components
Period
The time it takes a wave to vibrate a single cycle
Frequency
The number of events that occur in a specific duration of time
Amplitude
The "bigness" of a wave
Power
The rate of energy transfer
Intensity
The concentration of energy in a sound beam
Wavelength
The distance or length of one complete cycle
Propogation Speed
The distance that a sound wave travels through a medium in one second
Stiffness
The ability of an object to resist compression
Pulse Duration
The actual time from the start of a pulse to the end of that pulse
Spatial Pulse Length
The distance thta a pulse occupies in space from the start to the end of a pulse
Pulse Repetition Period
The time from the start of one pulse to the start of the next pulse.
Pulse Repetition Frequency
The number of pulses that an US system transmits into the body each second
Duty Factor
The percentage or fraction of time that the system is transmitting a pulse
Intensities
Spatial - refers to space
Peak - maximum value
Average - middle value
Temporal - refers to time
Pulsed - transmit time only
Beam Uniformity Coefficient
Describes the spread of a beam in space
Attenuation
Weakening of a sound beam in intensity, power and amplitude
Amplification
Strengthening of a sound beam
Decibel Notation
Standard measurement tool used to report changes in two intensities
Logarithms
A novel method of rating numbers, which represents the number of 10's that are multiplied to create the orignal number.
Reflection
The portion of a sound beam that is redirected back to the source after striking a boundary
Specular Reflection
The sound beam is reflected in only one direction in an organized manner after striking a smooth boundary
Diffuse Reflection
The sound beam is reflected in many directions after striking an irregular surface (backscatter)
Scattering
The random redirection of sound in many directions
Raleigh Scattering
A special form of scattering that occurs when the structure's dimensions are much smaller than the beam wavelength
Absorption
US energy is converted into another energy form, such as heat
Attenuation Coefficient
The number of decibels of attenuation that occurs when sound travels one centimeter.
Impedance
The acoustic resistance to sound traveling in a medium, measured in rayls
Half-value layer thickness or penetration depth
The distance sound travels in a tissue that reduces the intensity of sound to one-half its original intensity
Three Types of Angles
Acute - less than 90 degrees
Right - equal to 90 degrees
Obtuse - greater than 90 degrees
Normal Incidence
The incident sound beam stikes a boundary at exactly 90 degrees
Oblique Incidence
The incident beam striks a boundary at any angle other than 90 degrees
Incident Intensity
The sound wave's intensity immediately before striking a boundary
Reflected Intensity
The sound wave's intensity after striking a boundary that returns back in the direction from which it came
Transmitted Intensity
The sound wave's intensity after striking a boundary as it continues forward
Intensity Reflection Coefficient
Percentage of the intensity that bounces back after striking a boundary

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