Temporal Variation Of Ultrasonic Output - Accelerated Care Plus OMNISOUND 3000C PRO User Manual

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OMNISOUND 3000C PRO USER MANUAL 19

Temporal Variation of Ultrasonic Output

Continuous Wave Output
Ultrasonic output may be produced on a continuous basis or may be pulsed. Ultrasonic power is measured in watts,
which are a measure of the total power emitted in the form of ultrasonic radiation by the applicator, averaged over
2
each cycle of the ultrasonic radiation carrier wave. The power may also be expressed in watts/cm , which gives the
output in watts for each square centimeter of effective radiating area on the transducer surface. The effective
radiating area is a measurement of the surface area of the transducer, which produces more than 5 percent of the
maximum intensity in the near ultrasound field measured at 5mm from the transducer surface. It should be noted
that the effective radiating area does not generally cover the entire surface area of the transducer (effective radiating
surface) and varies with the crystal frequency when operated at different crystal harmonics.
In continuous wave mode (cw) the time average power is defined as the temporal average power and is 50 percent of
the peak instantaneous power. When the ultrasound unit is calibrated with a power measurement device it is
generally measured in the continuous wave mode.
Pulsed Wave Output
Ultrasound devices may also produce pulsed or discontinuous waveforms. These outputs are generally square wave
in shape. The output of pulsed ultrasound is defined as the average output over one cycle of the carrier, rather than
the average over time (time average). This measurement is referred to as the Temporal Maximum power. By
defining the output in this way, Average power (temporal average) may be calculated by multiplying the Temporal
Maximum by the duty factor. Duty factor is the ratio of on time to total time for pulsed waveforms.
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