ULTRASONIC PRESSURE FIELDS DUE TO RECTANGULAR APERTURES

The linear pressure fields generated by rectangular apertures at ultra sonic frequencies are considered, experimental results and theoretical predictions are presented both for focused and unfocused cases. Measu rements were made in water using a circular transducer (38 mm in diame ter) with various rectangular apertures in front of it. Focusing was a chieved by the addition of perspex lenses. The aperture dimensions and focal lengths were chosen to be comparable with those encountered in medical ultrasound systems. The pressure field generated by the apertu re was sampled using a 1-mm-diam bilaminar polyvinylidene difluoride ( pvdf) hydrophone. Predictions for diffraction losses due to a rectangu lar transmitter and a circular receiver of finite size are also shown. The general behavior of the pressure field of a rectangular aperture is discussed and good agreement is shown between experimental measurem ents and theoretical predictions within the known limitations of both.