Determinação da sensibilidade de transdutores ultrassônicos para fisioterapia pelo método da autorreciprocidade

Abstract

Ultrasonic irradiation is frequently used in physiotherapy to treat soft tissue injuries. It must be pointed however that physiotherapists have no means to know exactly the amount of energy emitted from the transducers of such equipments because of limitations in their calibration. The objective of the present study is to show one possible way to perform sensitivity calibration of ultrasonic physiotherapy transducers by a self-reciprocity method. As exemplification the method was tested in the calibration of 3 transducers for an excitation voltage varying from 3.5 to 10.5 Vpp and the results show a relative error of less than 6%. It was observed that, on their respective frequency band, one transducer was linear and two were not linear, for the same excitation voltage. This indicates that for some transducers a linear increase in excitation voltage may not correspond to a proportional increase in the ultrasonic output energy. Such information must be taken into account in the electronics project of the equipment in order to ensure that the nominal scale is a reliable indicator of the acoustic power generated. The experimental procedures were based on international standards (IEC 60866). The following step is to adapt this method to characterize ultrasound beams with exciting tensions capable to generate acoustic intensities in therapeutic levels.