Ultrasonic Hydrophone's Effective Aperture Measurements

The ultrasonic pressure waveforms produced at the output of medical ultrasound devices must be determined and strictly regulated to ensure patient safety and to ascertain whether the ultrasound devices are performing satisfactorily. However, characterization and measurements of the ultrasound fields are difficult because of the size of the hydrophones' effective aperture. Since the spatial averaging effect mainly depends on the effective diameter of the hydrophone probes, this work explains an experimental technique used to measure the size of the ultrasonic hydrophones' effective aperture. Three ultrasonic transducer sources with three different resonance frequencies, 5 MHz, 7.5 MHz, and 10 MHz were utilized with a pulse-echo technique. The measurements in this work were performed with a bilaminar PVDF membrane hydrophone probe having nominal diameter of 400 μm. The results show that the current measurement system offers the ability to effectively determine the directivity pattern and thus effective diameter for circular aperture membrane hydrophones.