#### 7 Parameters of Sound

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