Preliminary analysis and simulation of the influence of radiations from the rim of therapeutic transducers in the irradiated acoustic field

In this work, the radiation behavior of two ultrasonic therapy applicators (working around 1 MHz range) is investigated when they are radiating into water media having acoustic impedance similar to that being encountered in biological tissues. Several experimental plots of field patterns generated by both therapy transducers are gate-detected and accurately evaluated in laboratory. One very serious problem observed in many real ultrasonic patterns emitted at the very near field is the influence of non-ideal housing radiation in the effectively radiated acoustic energy patterns. This measuring fact is shown in some detail and its causes are theoretically analyzed here. These additional radiation effects perturb the desired spatial uniformity in the emitted ultrasonic field and could change the beam path causing that therapeutic radiation outside the treatment field should be heating neighbor tissues. A preliminary analysis to check in the practice these possible real radiation problems, associated with such type of ultrasonic therapeutic devices, is presented. And a computer simulation, using Zemanek method, of the influence of anomalous & unexpected radiations, originated by aperture rim and housing of a typical therapy transducer, in the effective acoustic field, is presented here, comparing it with experimental results.