Development of a PVDF membrane hydrophone for use in air-coupled ultrasonic transducer calibration

This work describes the use of a polyvinylidene fluoride (PVDF) membrane hy drophone for application in air-coupled transducer calibration. A one-dimen sional theoretical analysis is used to demonstrate the potential and perfor mance of PVDF as a hydrophone material over the frequency range 100 kHz to 5 MHz Included in the evaluation is the influence of deposited metallic ele ctrode layers on the sensitivity of the material. Experimental validation o ver the restricted range 400 kHz to I MHz is provided by a coplanar 0.028 m m thick membrane hydrophone in conjunction with a custom built 1-3 piezocom posite transmitter. Calibration of the membrane hydrophone is performed by employing a standard hydrophone that has been calibrated to a primary stand ard in a water medium. Justification for such an approach is presented with in the theoretical analysis which provides a close correlation with experim ental data. The generation of Lamb waves at critical angles in the PVDF and their subsequent influence on the directional response of membrane hydroph ones operating in air is also addressed. A method for partial suppression o f the Lamb waves, based around perforation of the membrane (either in whole or in part), is evaluated experimentally with reasonable results.