Ch. 3 - Describing Sound Waves Flashcards
Wavelength is determined by what?
SS and medium
Period and frequency are determined by what?
SS
Amplitude, power, and intensity are determined by what?
SS
Speed is determined by what?
Medium
Which/what acoustic parameter(s) is/are determined by medium only?
Speed
Which/what acoustic parameter(s) is/are determined by SS only?
Period, Frequency
Amplitude, Power, and Intensity
Which/what acoustic parameter(s) is/are determined by SS and medium?
Wavelength
The time required to complete a single cycle is
Period
Give an example of period.
The period of class in hs is 50 minutes.
Can period be changed by the sonographer?
No
Period is determined by what?
SS
Typical values of a period are
0.06 - 0.5 microseconds (less than 1-millionth of a second)
Frequency is defined as
Number of certain events that occur during a particular time period.
Give an example of frequency
The frequency of presidential elections is once per four years
In US, the frequency of a wave is…
the number of cycles of an acoustic variable that occur in one second.
The unit for frequency is
Hertz (meaning “per second”)
Can frequency be changed by the sonographer?
No
What are the typical values of frequency?
2 MHz - 15 MHz
What does frequency affect in Us?
Penetration and axial resolution
A wave with a frequency exceeding 20,000Hz (so high it isn’t audible) is
Ultrasound
Sound heard by man between 20Hz and 20,000Hz
Audible sound
Sound with frequencies less than 20Hz are _____. And can they be heard by man?
Infrasound. No, so low it is inaudible.
Frequency and ______ are reciprocals.
Period
Frequency and period have a(n) _____ relationship.
Inverse
With frequency and period, units to be used are (2 examples)
Sec and Hz or microseconds and MHz
When period increases, frequency _________.
Decreases
What are the 3 bigness parameters (define and list)?
3 parameters that describe a sound wave.
Amplitude
Power
Intensity
What is defined as the difference between the average value and the max value of an acoustic variable?
Amplitude
List the 3 acoustic variables and their units.
Pressure - Pascals
Density - grams/cubic cm
Particle motion - m/s, mm/microsecond
The unit for amplitude is
Acoustic variables
Pressure - Pascals
Density - grams/cm^3
Particle motion - cm, m, distance
(And Decibels (dB))
Can amplitude be changed by the sonographer?
Yes
Amplitude ________(increases/decreases) as sound propagates through the body.
Decreases
The difference between max and min values of an acoustic variable is called
Peak-to-peak amplitude
Amplitude is ______ (fraction) of the peak-to-peak amplitude.
Half
The rate of work performed, or the rate of energy transfer is
Power
What is the unit for power?
Watts
Can power be changed by the sonographer?
Yes
Power ______(increases/decreases) as it propagates through the body.
Decreases
Why are power and amplitude often described similarly?
Because they both describe “bigness”
What is the relationship between power and amplitude?
Power is proportional to the wave’s amplitude squared
If the amplitude is tripled, the power is
Increased by a factor of 9
The concentration of energy in a sound beam is the definition of what?
Intensity
The beam’s power divided by the beam’s cross-sectional area is another description of what?
Intensity
Power (watts)
_____________
Beam area (cm^2)
is an equation for what?
Intensity
What is the unit for intensity?
Watts/cm^2
Can intensity be changed by the sonographer?
Yes
Since amplitude and power can be changed, the intensity can too
Intensity _____ (increases/decreases) as sound propagates through the body.
Decreases
What is the relationship between intensity and power?
Proportional or directly-related
Intensity is proportional to the _______ of the wave (value).
Amplitude
Squared
If amplitude is doubled, the intensity is
Increased by a factor of 4
2 x 2 = 4
The length or distance of a single cycle is
Wavelength
This is similar to a boxcar in a long train
Wavelength
What is wavelength determined by?
SS and the medium
Can wavelength be changed by the sonographer?
No
What does wavelength influence in an US?
Axial resolution (image quality)
What are the typical values of a wavelength?
0.1 - 0.8mm
What is this equation of?
Propagation speed (mm/microseconds)
____________________________________
Frequency (MHz)
Wavelength
What are the units for wavelength?
m, mm, or any measurement of length
Do higher frequency waves have longer OR shorter wavelengths?
Shorter
Do high frequency wavelengths have longer OR shorter periods?
Shorter
In soft tissue, sound with a frequency of 1 MHz has a wavelength of _____.
In soft tissue, sound with a frequency of 2 MHz has a wavelength of _____.
- 54mm
0. 77mm
This equation is for what?
1.54mm/microsecond
____________________
Frequency (MHz)
Wavelength
The rate of sound travels through a medium is a definition for what? What is it also called?
Propagation speed
Velocity or speed
What are the units for propagation speed?
m/s or mm/microsecond
Propogation speed is determined by what?
Medium - density and stiffness
Can propagation speed be changed by a sonographer?
No
What are the typical values for propagation speed?
Average speed of sound in biologic tissue.
1,540m/s = 1.54km/s = 1.54mm/microseconds
Lung, fat, soft tissue (incl. blood), air, bone, tendon - put these in order of slowest to fastest speed.
Air, lung, fat, soft tissue (incl. blood), tendon, bone
Rule of thumb is
Stiffness and speed - same direction
Density and speed - opposite direction
Stiffness is related to ________, Density is related to ________.
Change in shape/”squishability”
Weight
What is the range for audible sound?
20Hz - 20,000Hz
What are the typical values for power in US?
0.004 watts - 0.090 watts
What are the typical values of intensity in US?
0.01 W/cm^3 - 300 W/cm^3
