Ch 1-4 8 Flashcards
The molecules vibrate in the same direction as the sound travels. I.e, sound waves.
Longitudinal Wave
When one value increases, and so does the other value, the two values are said to be ___________.
Directly Proportional
The molecules vibrate at 90 degrees to the direction of energy travel. i.e. Water ripples
Transverse Wave
concentration of force
units: lb/sq inch, Pascals Pa
Pressure
concentration of mass or weight
units: kg/cubic cm
Density
measure of particle motion
units: cm, feet, miles
Distance
The distance of one wave cycle.
Wavelength
•The length of time it takes to complete one single cycle of sound or to one complete single wavelength.
Units: seconds, msec, hours – all units of time
=1/frequency
Period
The # of wave cycles per second.
1 cycle per second = 1 hertz Hz
Frequency
The speed at which wave cycles travel.
Propagation Speed
(Sin Angle of Incidence)/(Sin Angle of Refraction)= c1/c2
Where c1 & c2 are the speeds of sound in the two mediums
Snell’s Law
Z=P/V Where P = excess pressure and V=the particle velocity. OR Z=P x c Where c=speed of light
Acoustic Impedance
The dominant factor in attenuation (80%).
-conversion of sound to heat
Absorption
Occurs at a boundary between 2 different media with different impedances.
-the sound bounces back (toward transducer)
Reflection
z=P x V , measured in Rayls. (z=Density x Prop Speed)
Impedance
Smooth surface that causes sound to bounce back toward the transducer.
Specular Reflector
Scatter returning in the same general direction as the transducer.
BackScatter
Interface has irregularities one wavelength or smaller.
Non-specular scattering.
Sound scatters symmetrically in all directions. Not related to incidence angle. Increase frequency, and increase this.
Rayleigh scattering.
%R=Reflected Intesity/Incidence Intensity=((z2-z1)/(z2+z1))^2
Intensity Reflection Coefficient
90 degrees. (Porn)
Normal Incidence
not 90 degrees
Oblique Incidence
a bending from a straight line or path or a change in direction of a wave travelling from one medium to another. Must have two things: an Oblique Incidence, and2 media with different propagation speeds. Related to the change in acoustic velocity. (If medium 2 is faster, then it will increase the transmit angle.
Refraction
Sin (angle of transmit)/ sin (angle of incidence)=prop speed 2/prop speed 1
Snell’s Law
“bulk modulus.” The extent to which a material cannot be compressed. To increase this will increase propagation speed.
Stiffness
aka Harmonics
Non-linear Propagation
Pulse, then listen for echo
Puled Ultrasound
Time from the start of one pulse to the end of the same pulse. THis can only be changed by changing the transducer.
Pulse Duration
% of the time that the system is transmitting a pulse and not “listening.” Determined by the sound source.
Duty Factor
of pulses that occur in a single second(Hz/sec). Determined by the sound source.
Pulse Repetition Frequency (PRF)
Time from the start of a pulse to the start of the next pulse (includes “listening time”).
Determined by the sound source. CAN be changed by the sonographer by changing the listening time.
= 1/PRF
Pulse Repetition Period (PRP)
The distance a pullse occupies in space. # of cycles in a pulse x wavelength. Determined by the sound source and the medium. Cannot be changed by the sonographer.
Increase freq, Increase this
Spatial Pulse Length
Weakening of a sound wave as it travels through media. Decrease in amplitude and decrease in intensity. Increase frequency and increase this
Attenuation
+3 Db doubles the sound
+10 dB ten times the sound
Decibels
value that expresses how different materials attenuate the sound beam per unit length (dB/cm). The average attenuation coefficient in soft tissue is 1/2 the transducer frequency.
Attenuation Coefficient
The distance the sound beam travls when its intensity is reduced to 1/2 its original value.
Half-Value Layer
The fraction of the original intensity after attenuation.
Intensity Ratio
a peak aligns with a peak; increase in amplitude
Constructive Interference
a peak aligns with a trough; decrease in amplitude
Destructive Interference
Distance to Boundary = (go-return time x speed)/2
d=ct/2
Range Equation
Every 13 microseconds of go-return time means the reflector is 1 cm deeper in the body
13 microsecond rule
when wave peaks and troughs continue to line up.
In-Phase Wave
When troughs from one wave continually line up with the peaks from another wave.
Out-of-Phase Wave
The strength of the sound beam, maximum variation from the baseline (dB)
Amplitude
The rate that work is performed, rate of energy transfer in the entire beam. Measured in watts.
P=I x CS
P is proportional to Amplitude squared
Power
Concentration of energy in certain areas of the sound beam
I=P/CS (watts/cm^2)
Intensity
The highest intensity area or time of the sound beam
Peak
(Peak + low + medium)/3
Average Intensity
Greatest at the center and in focal zone of the sound beam
Spatial Intensities
Occurs with Time
Temporal non-uniformity
Is greatest at the center of the beam
Spatial non-uniformity
Related or proportional
Related, Proportional, Directly Proportional
As one value increases, the other value decreases.
Inversely proportional.
The effects that are made on the human body
Biological Effects
The thing that is creating the sound wave
Source
The material that the sound wave is traveling through
medium
