# Shared Flashcard Set

## Details

US Physics (Edelman)
Chapter 6 Ineraction of Sound and Media
51
Physics
Professional
06/20/2011

Term
 The logarithm or log of a number represents
Definition
 the number of 10's that are multiplied to create the original number
Term
 The common method of measuring the electrical signal strength and the brightness of images of sound beams is the
Definition
 decibel dB
Term
 Decibel notation does not report absolute numbers it reports
Definition
 relative changes
Term
 Positive decibels report signals
Definition
 that are increasing or getting larger
Term
 When a wave's intensity doubles, the relative change is
Definition
 + 3 dB
Term
 When a waves intensity increases 10 fold the relative change is
Definition
 + 10 dB
Term
 Negative decibels describe signals that are
Definition
 decreasing or getting smaller
Term
 When the intensity is reduced to 1/2 of its original value the relative change is
Definition
 - 3 dB
Term
 When the intensity is reduced to 1/10 of its original value the relative change is
Definition
 - 10 dB
Term
 Sound waves decrease in intensity, power and amplitude as they propagate through the body. This is called
Definition
 attenuation
Term
 Attenuation is determined by
Definition
 path length and frequency of sound
Term
 Distance and attenuation are related
Definition
 directly
Term
 Frequency and attenuation are related
Definition
 directly
Term
 Three processes contribute to attenuation
Definition
 reflection, scattering and absorption
Term
 Two forms of reflection are created in soft tissue they are
Definition
 specular and diffuse
Term
 Scattering is directly related to
Definition
 frequency
Term
 Scatter that redirects the sound wave equally in all directions is called
Definition
 Rayleigh scattering
Term
 Raleigh scattering is proportional to
Definition
 frequency to the 4th power
Term
 When frequency doubles Raleigh scattering is
Definition
 16 times greater
Term
 Organized sound back to the transducer is
Definition
 specular reflection
Term
 Disorganized reflection back to the transducer is
Definition
 diffuse or backscatter
Term
 Absorption occurs when
Definition
 ultrasonic energy is converted into another energy form such as heat.
Term
 Attenuation coefficient is
Definition
 the number of decibels of attenuation that occurs when sound travels one centimeter.
Term
 The units of attenuation coefficient are
Definition
 dB/cm
Term
 Attenuation Coefficient in Soft Tissue
Definition
 the attenuation coefficient is 1/2 of the frequency
Term
 Half-Value Layer Thickness is
Definition
 the distance that sound travels in a tissue that reduces the intensity of sound to 1/2 its original value.
Term
 The units for half value layer are
Definition
 centimeters or any other unit of length
Term
 Typical values for half-value layer
Definition
 ranges from 0.25 to 1.0cm
Term
 The half-value layer thickness depends on two factors
Definition
 the medium and the frequency of sound
Term
 Impedance is
Definition
 the acoustic resistance to sound traveling in a medium
Term
 Impedance is calculated by
Definition
 multiplying the density of a medium by the speed that sound travels in the medium
Term
 Impedance is measured with units of
Definition
 rayls Z
Term
 In biologic media, typical values for impedance range from
Definition
 1,250,000 rayls to 1,750,000 rayls
Term
 Impedance is a characteristic of
Definition
 the medium only, it is calculated not measured
Term
 Acoustic impedance is also called
Definition
 characteristic impedance
Term
 An acute angle is
Definition
 less than 90 degrees
Term
 A right angle is
Definition
 exactly 90 degrees
Term
 An obtuse angle is
Definition
 greater than 90 degrees
Term
 Normal incidence means that the incident sound beam strikes the boundary at
Definition
 exactly 90 degrees
Term
 Normal incidence is also called
Definition
 perpendicular, orthogonal, right angle or 90 degrees
Term
 Oblique incidence occurs when the incident sound beam strikes the boundary at
Definition
 any angle other than 90 degrees
Term
 Incident intensity is
Definition
 the sound wave's intensity immediately before it strikes a boundary
Term
 Reflected intensity is the intensity of the portion of the incident sound beam that after striking a boundary
Definition
 returns back in the direction from which it came
Term
 Transmitted intensity is the intensity of the portion of the incident beam that, after striking a boundary
Definition
 it continues forward in the same general direction that it was traveling.
Term
 Intensity Reflection Coefficient is
Definition
 the percentage of the intensity that bounces back when a sound beam strikes the boundary between two media.
Term
 The intensity transmission coefficient is
Definition
 the percentage of ultrasound intensity that passes in the forward direction when the beam strikes an interface between two media.
Term
 Two principles apply to reflection with oblique incidence
Definition
 conservation of energyandreflection angle = incident angle
Term
 Refraction is
Definition
 a change in direction of wave propagation when traveling from one medium to another.
Term
 Refraction occurs only if two conditions are satisfied
Definition
 oblique incidenceandpropagation speed of the two media are different
Term
 Refraction is transmission with
Definition
 a bend
Term
 The physics of refraction are defined by what law?
Definition
 Snell's Law
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