Biological effects of ultrasound : mechanisms and clinical by National Council on Radiation Protection and Measurements

By National Council on Radiation Protection and Measurements

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Sample text

We consider the field to arise from a source-transducer generating continuous ultrasound of frequency f, the characteristic amplitude of the source being A. Then the characteristic magnitude of each contribution is proportional to A", where n is the order of the contribution. Thus zero-order terms are, of course, independent of A (proportional to A0 = 1)while firstorder terms are proportional to A and second-order terms proportional to A2. 2 are first-order contributions to the acoustic pressure and particle velocity.

A common type of unit is a disc (or rectangle or ring) of piezoelectric material with area electrodes (of gold or other electrical conductor) on both faces, to which electrical connections are made. The unit, with attached electrical leads, is often embedded in epoxy or other material to provide damping and/or impedance matching and positioned in a housing; the latter provides mechanical protection as well as acoustic damping, and also facilitates cable connections. 1. Ultrasound is generated from a source transducer by applying a suitable input voltage.

6 dB/cm. 6 dB. 8. 01 for this fraction. 04 dB. 3. 36 x 10' g/s cmZ. F/M: fat/muscle. 5-Reported attenuation between the abdominal surface and the uterine cavity in early pregnancy from Stewart and Stratmeyer (1982) No. 25 Takeuchi et d, 1977 2 Momhashi and Iizuka, 5 Morohashi and Iizuka. 5 MHz ultrasound from transducer to gestational sac. 5 from t h e compilation of Stewart and Stratmeyer (1982). 5 MHz. 5. From the calculation and experiments, a realistic estimate of the minimum expected attenuation in early pregnancy is, in dB, one or two times the frequency in megahertz.

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