7 Parameters of Sound
Power (normal)
0.004 to .090 watts (4 to 90 mwatts)
Intensity (normal)
0.01 mW/cm2 to 300 W/cm2
Period (normal)
0.1-0.5 us
Wavelength (normal)
0.15-0.8 mm
Amplitude (normal)
1-3 MPa
Propagation Speed (normal)
1.54 km/s 1,540 m/s 1.54 mm/us
Frequency (measure)
1/Time
Frequency (normal)
2-10 MHz
Amplitude (measure)
Acoustic Velocity
Can be changed after its initial presentation
Amplitude
decreases as sound propagates through the body.
Amplitude
Wavelength (measure)
Distance
Propagation Speed (measure)
Distance/Time
Can be changed only if transducer is changed
Frequency
determined by the period of a single cycle in the wave.
Frequency
Frequency (units)
Hz
decreases as ultrasound propagates through the body
Intensity
Propagation Speed (Units)
Meters/seconds
Amplitude (Units)
Pascal's (Pa)
Longer period lower pitch
Period
Determined by Source
Period, Frequency, Power, Amplitude, Intensity
decreases as ultrasound travels through the body.
Power
Can be changed by user
Power, Intensity
Intensity (measure)
Power/area
Determined by medium
Propagation Speed
Period (Units)
Seconds
Period (measure)
Time
Power (Units)
Watts (W)
Intensity (Units)
Watts/cm2
Determined by Source and medium
Wavelength
detail that is displayed in an image is substantially influenced by wavelength because wavelength determines longitudinal resolution.
Wavelength
Cannot be changed by user
Wavelength, Propagation Speed, Period
Power (measure)
Work/time
PERIOD
is the length of time that it takes to complete a single cycle.
Wavelength (Units)
meters
INTENSITY
relates to the strength of the sound beam. It is the concentration of energy in a sound beam.
AMPLITUDE
relates to the strength of the sound wave. Amplitude describes the magnitude of a wave. Amplitude is the maximum variation of a variable from its mean value.
POWER
relates to the strength of the sound wave. It is the rate in which work is performed or energy is transferred from the entire sound beam.
WAVELENGTH
the distance or length that one complete cycle occupies: the cycle length.
FREQUENCY
the number of certain events that occur in a specific duration of time. The frequency of a wave is the number of vibrations that a molecule in it makes per second or the number of times the cycle is repeated per second.
PROPAGATION SPEED
the speed at which sound moves through a medium -- also called sound's speed, velocity of sound, or acoustic velocity.
Three parameters relate to the strength of a sound wave. They are:
• Amplitude dB Magnitude (volume) • Power Watts Work • Intensity Watts/cm2 Work per unit area
Power/Amplitude/Intensity Relationship
• Power is proportional to the amplitude squared. • Intensity is proportional to the amplitude squared. • Power is proportional to intensity.
Propagation speed/wavelength Relationship
• This means that sound with a frequency of 3 MHz will travel with different speeds in different mediums. If the acoustic velocity is high in a medium the sound will have a higher speed and travel a greater distance. (this will be an increased wavelength) • If the acoustic velocity is slow in a medium the sound will travel at a lower speed and travel less distance. (this will be a decreased wavelength)
Wavelength/Frequency Relationship
• Wavelength is inversely related to frequency. o Higher frequency waves have shorter wavelengths. o Lower frequency waves have longer wavelengths. • Shorter wavelengths generally produce higher quality images. This explains why higher frequency transducers create better quality clinical images.
Period/Frequency Relationship
• period (sec) x frequency (Hz) = 1 • period (sec) = 1 / frequency (Hz) • frequency (Hz) = 1 / period (sec) • Remember to use complementary units for period and frequency; such as sec & Hz, or msec & kHz.
