PERIOD
is the length of time that it takes to complete a single cycle.
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.
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.
INTENSITY
relates to the strength of the sound beam. It is the concentration of energy in a sound beam.
WAVELENGTH
the distance or length that one complete cycle occupies: the cycle length.
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
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.
Power/Amplitude/Intensity Relationship
• Power is proportional to the amplitude squared.• Intensity is proportional to the amplitude squared.• Power is proportional to intensity.
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.
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)
Period (Units)
Seconds
Frequency (units)
Hz
Amplitude (Units)
Pascal's (Pa)
Power (Units)
Watts (W)
Intensity (Units)
Watts/cm2
Wavelength (Units)
meters
Propagation Speed (Units)
Meters/seconds
Period (normal)
0.1-0.5 us
Frequency (normal)
2-10 MHz
Amplitude (normal)
1-3 MPa
Power (normal)
0.004 to .090 watts (4 to 90 mwatts)
Intensity (normal)
0.01 mW/cm2 to 300 W/cm2
Wavelength (normal)
0.15-0.8 mm
Propagation Speed (normal)
1.54 km/s1,540 m/s1.54 mm/us
Determined by Source
Period, Frequency, Power, Amplitude, Intensity
Determined by Source and medium
Wavelength
Determined by medium
Propagation Speed
Cannot be changed by user
Wavelength, Propagation Speed, Period
Can be changed by user
Power, Intensity
Can be changed only if transducer is changed
Frequency
Can be changed after its initial presentation
Amplitude
Period (measure)
Time
Frequency (measure)
1/Time
Amplitude (measure)
Acoustic Velocity
Power (measure)
Work/time
Intensity (measure)
Power/area
Wavelength (measure)
Distance
Propagation Speed (measure)
Distance/Time
Longer period lower pitch
Period
determined by the period of a single cycle in the wave.
Frequency
decreases as sound propagates through the body.
Amplitude
decreases as ultrasound travels through the body.
Power
decreases as ultrasound propagates through the body
Intensity
detail that is displayed in an image is substantially influenced by wavelength because wavelength determines longitudinal resolution.
Wavelength