- 54 - OMNIVERSA
®
ULTRASOUND / ELECTROTHERAPY SYSTEM USER MANUAL
COPYRIGHT © 2017-2020, ACCELERATED CARE PLUS CORP., ALL RIGHTS RESERVED
Pulsed Wave Output
Ultrasound devices may also produce pulsed waveforms. These outputs are generally square wave in shape as is the
case with the Omnisound. 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). Duty factor is the ratio of on time to total time for pulsed
waveforms. Decreasing duty factor will reduce the average ultrasonic power, which will lower the thermal effect of
the beam on the tissue.
Beam Characteristics, Power, and Intensity Measurement
Intensity is a quantity used to establish exposure level to the ultrasound beam. Ultrasonic output power or intensity
can be measured in watts or watts per square centimeter. Watts are a measure of the total power emitted in the form
of ultrasonic radiation by the applicator, averaged over each cycle of the ultrasonic radiation carrier wave. However,
ultrasound applicators do not generally produce beams of perfectly uniform intensity over the surface of the transducer.
When the power is expressed in watts/cm
2
, it provides the output in watts for each square centimeter of effective
radiating area on the transducer surface. The effective radiating area (ERA) 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. Thus the measurement represents an average for the effective radiating surface area.
Beam Non-Uniformity Ratio (BNR)
Ultrasound has an excellent ability to penetrate deeply, primarily due to its small beam divergence (Schwan, 1958).
A typical beam scan of an applicator is presented below.
Model Number: Omnisound
®
Pro
Serial Number: 11.529
Frequency: 1 & 3 MHz
Test Date: 11/19/2015
ERA: 5.0 cm
2
BNR: < 5:1
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