Ch.3 Describing Sound Waves Flashcards
What are the seven parameters that describe sound waves?
Period
Frequency
Amplitude
Power
Intensity
Wavelength
Propagation Speed
Period
is the time it takes a wave to vibrate a single cycle, or the time from the start of one cycle to the start of the next cycle
Period:
Units
Typical values
units of time
microseconds (us),
0.06 to 0.5 us
Period:
Determined by
Adjustable
Sound Source ONLY
NOT medium
No
Frequency
is the number of particular events that occur in a specific duration of time
Frequency:
Units
Typical Values
units of per second
(1/sec, hertz, Hz)
(1 cycle/second = Hertz)
Approx. 2MHz to 15 MHz
Frequency:
Determined by
Adjustable
Sound Source ONLY
No
Sound Wave Spectrum:
Infrasound (infrasonic)
Less than 20 Hz
(NOT Audible)
Sound Wave Spectrum:
Audible Sound
Between 20 Hz and 20 kHz
Sound Wave Spectrum:
Ultrasound (ultrasonic)
Greater than 20 kHz
(Greater than 20,000 Hz)
(In audible to humans)
What is the relationship between frequency and period?
are inversely related
(Reciprocal = 1/f )
if one remains constant that the other remains the unchanged
What are the three bigness parameters?
Amplitude
Power
Intensity
Amplitude
is the “bigness” of a wave. It is the difference between the maximum value and the average or undisturbed values of an acoustic variable
Amplitude:
Units
Typical Values
any units from the acoustic variable
pascals
density
cm, inches
decibels (dB)
1 million pascals (MPa)
to 3 MPa
Amplitude:
Determined by
Adjustable
Sound Source only
Yes, a control on the system allows the sonographer to alter initial amplitude of a wave
What is the difference between amplitude and peak-to-peak amplitude?
Amplitude: is measured from the baseline to the maximum value or minimum value
Peak-to-Peak: is difference between maximum and minimum value of an acoustic variable. (Twice the value of the amplitude)
Power
is the rate of energy transfer or the rate at which work is performed
Power:
Units
Typical value
watts
0.004 to 0.090 watts
(4 to 90 milliwatts)
Power
Determined by
Adjustable
Sound Source ONLY
Yes, initial power like amp can be changed
Power decreases as _____ propagates through the body.
The rate at which power decreases as sound propagates depends on the characteristics of the _____ and the _____ .
sound
amplitude and wave
How are amplitude and power related?
power is proportional to the wave’s amplitude squared
If a sonographer increases the amplitude of a wave by a factor of 3. How has the power changed?
3 x 3 = 9
power increased by 9
If a sonographer decreases the amplitude of a wave to 1/2 of its original value, how has the power changed?
1/2 x 1/2 = 1/4
power decreases to 1/4th or 25% of its original value
Intensity
is the concentration of energy in a sound beam.
to calculate divide the beam’s power by the beam’s cross-sectional area.
relates to how the power in a wave spreads or is distributed in space
-depends on power and area
Intensity:
Units
Typical Values
Watts/square centimeter
W/cm^2
0.01 to 300 W/cm^2
Intensity:
Determined by
Adjustable
Sound Source ONLY
(intensity changes as sound propagates thru body)
Yes allowed to alter the initial intensity of a wave
The rate at which intensity changes as sound propagates depends on the characteristics of both the _____ and the ______
sound wave
medium
How is intensity related to power?
proportional to power
How is intensity and amplitude related?
proportional to the wave’s amplitude squared
Wavelength
units
is the distance or length of one complete cycle
mm, meters, or other unit of length
Wavelength:
Typical Values
Determined by
Adjustable
0.1 to 0.8 mm
By BOTH source and medium (only parameter)
NO
What is the difference between wavelength and period?
Wavelength refers to the length or distance of a single cycle
Period refers to the time that it takes to complete a single cycle
What is the relationship between wavelength and frequency?
As long as a wave remains in one medium, wavelength and frequency are inversely related
As frequency increases , wavelength ________ .
The lower the frequency, the _____ the wavelength.
decreases
longer
What is the wavelength of 1 MHz sound in soft tissue?
Has a wavelength of 1.54 mm
If sound has a frequency of 2 MHz, which is the wavelength in soft tissue?
1.54 mm / 2
= 0.77 mm
Why is wavelength important in diagnostic ultrasound?
Wavelength plays an important role in image quality
-Shorter wavelengths are created by high frequency sound, which usually produces higher quality images with great detail
Propagation Speed
units
is the rate at which a sound wave travels through a medium
-meters per second
-mm/us
Propagation Speed:
Typical Values
Determined by
Adjustable
500 m/s to 4000 m/s
depending on the tissue
Medium ONLY
NO (Speed changes only when the wave travels from one medium to a different medium
What is the speed of sound in soft tissue?
1,540 m/s
(1.54 mm/us)
Sound travels fastest in what materials?
Solids
Liquids
Gases (slowest)
What is the formula for the speed of sound in other media?
Speed (m/s) = frequency (Hz) x wavelength (m)
What characteristics of a medium determine the speed of sound in that medium?
Stiffness and Density
Stiffness
describes the ability of an object to resist compression
-retain its shape
Density
describes the relative weight of a material.
How does stiffness affect speed?
Stiffness and speed are directly related
-As materials become stiffer, the speed of sound in the material increases
How does density affect speed?
Density and speed are inversely related
-As materials become more dense (heavier), the speed of sound decreases
If two media are equally stiff, the dense medium will have a _____ speed.
lower
Stiffness increases, Speed ____
Increases
Density increases, speed _____
Decreases
Materials that are stiff but not dense will have the ____ speed.
fastest
Ex: Bone
Materials that are not stiff and very dense will have the ________ speed.
slowest
Although both stiffness and density affect propagation speed, _______ has the greatest influence on speed
Stiffness
Ex: Air has an exceedingly low stiffness, so sound travels slowly in it.
Period:
Adjustable
Units
Determined by
Typical value
NOT adjustable
seconds, us
source
0.06 to 0.5 us
Frequency:
Adjustable
Units
Determined by
Typical Value
NOT adjustable
per second, Hz
source
2 to 15 MHz
Amplitude:
Adjustable
Units
Determined by
Typical Value
Yes adjustable
pascals, cm, g/cm^3, dB
source
1 MPa to MPa
Power:
Adjustable
Units
Determined by
Typical value
Yes adjustable
Watts, dB
Source
4 to 90 mW
Intensity:
Adjustable
Units
Determined by
Typical value
Yes adjustable
Watts/cm^2, dB
Source
0.01 to 300 W/cm^2
Wavelength:
Adjustable
Units
Determined by
Typical value
NOT adjustable
mm, distance
BOTH source & medium
0.1 to 0.8 mm
Speed:
Adjustable
Units
Determined by
Typical value
NOT adjustable
m/s
medium
1,500 to 1,600 m/s
What three parameters can be adjusted by the sonographer?
Amplitude
Power
Intensity
