Describing Sound Waves Flashcards
Name the seven acoustic parameters
Frequency/Period, Amplitude/Power/Intensity, Wavelength/Propagation Speed
Define period
Time necessary to complete a single cycle
What are the units of period?
any time units
What are the typical values of period?
0.06 - 0.5 microseconds
0.00000006 - 0.0000005 seconds
6x10^-8 - 5x10^-7 seconds
Period is determined by?
the sound source
Is period adjustable by the sonographer?
No
Define Frequency
The number of cycles that occur in one second
What are the units of frequency?
Hz (1 cycle per second)
What are the typical values of frequency?
2-15 MHz
2 million - 15 million cycles per second
What is the frequency determined by?
the sound source
Is the frequency adjustable by the sonographer?
No (assuming everything remains constant)
Infrasound is less than _______ Hz
20
Range of frequencies for audible sound
20 Hz - 20,000 Hz (20 MHz)
Ultrasound has frequencies higher than ______.
20,000 Hz (20 MHz)
Frequency and period have an ________ and _______ relationship.
Inverse; reciprocal
Period x frequency = ?
1
What are the bigness parameters?
Amplitude, Power, Intensity
What do the bigness parameters describe?
The size, magnitude, or strength of sound waves
What is amplitude?
The difference between the maximum/minimum value and the average of an acoustic variable
What are the units for amplitude?
any of the acoustic variable units (Pa, g/cm^3, cm)
What are the typical values of amplitude?
1 million pascals - 3 million pascals
1MPa - 3 MPa
What is amplitude determined by?
the sound source
What is amplitude determined by?
the sound source and eventually the medium
Can amplitude be adjusted by the sonographer?
Yes
Define power
the rate of energy transfer
What are the units of power?
watts
What are the typical values of power?
0.004 - 0.090 watts
4 - 90 milliwatts
What is power determined by?
sound source
Is power adjustable by the sonographer?
Yes
Amplitude and power have a _______ relationship
direct
Power is proportional to amplitude ______.
squared
If amplitude was increased by a factor of 3, the power would be increased by a factor of?
9 (3 x 3)
If the amplitude is decreased by a factor of 1/2, the power is decreased by a factor of?
1/4 (1/2 x 1/2)
Define intensity
The concentration of energy in a sound beam
What are the units of intensity?
watts/cm^2
What are the units of intensity?
watts/cm^2
What are the typical values of intensity?
0.01 - 300 W/cm^2
What are the typical values of intensity?
0.01 - 300 W/cm^2
What is intensity determined by?
The sound source
Is intensity adjustable by the sonographer?
Yes (b-mode or TGCs)
Intensity is ______ to power
Proportional
When a waves power doubles, intensity will _____.
double
Intensity is proportional to amplitude ______.
squared
When a wave’s amplitude is increased by a factor of 2, the intensity is increased by ______.
4
Define wavelength
the distance or length of one complete cycle
What are the units of wavelength?
mm, cm, m
What are the typical values of wavelength?
0.1 - 0.8 mm (in soft tissue)
What is the wavelength determined by?
the source and medium
Which is the only parameter determined by both the source and medium?
wavelength
Is the wavelength adjustable by the sonographer?
no
Wavelength and frequency have an _______ relationship.
inverse
In soft tissue, sound with a frequency of 1 MHz has a wavelength of ________.
1.54 mm
Propagation speed in soft tissue is?
1,540 m/s, 1.54 km/s, 1.54 mm/microsec
True or False: A sound wave with a short wavelength and a high frequency produce high quality images
True
Define Propagation speed
The rate at which a sound wave travels through a medium
What are the units of propagation speed?
m/s, mm/ms
What are the typical values of propagation speed?
1.54 mm/microsec
range: 500 m/s - 4000 m/s
Propagation speed is determined by?
the medium only
Is propagation speed adjustable by the sonographer?
No
When does propagation speed change?
Only when going from one medium to the next
What is the speed of sound in air?
330 m/s
What is the speed of sound in metals?
2,000 - 7,000 m/s
What two characteristics of the medium affect speed?
stiffness, density
Define stiffness?
The ability of an object to resist compression
Stiffness is also called?
bulk modulus
Stiffness and speed have a _______ relationship
direct
What is the opposite of stiff?
Elasticity or compressibility
What is density?
the relative weight of a material
Density and speed are ______ related.
inversely
What is the formula for frequency?
prop. speed / wavelength
What is the formula for wavelength?
prop. speed / frequency
What is the formula for prop. speed?
wavelength x frequency
