Development of a Theoretical Model for Membrane Hydrophone Transfer Characteristics Pierre Gélat 3 April 2003

Background Bilaminar hydrophones are extensively used to measure and characterise medical ultrasound fields Developing a hydrophone model would enable users to improve the accuracy of their measurements in the field of medical ultrasound (phase response, deconvolution) Type of hydrophone initially modelled: 25 m film thickness 0.5 mm diameter bilaminar membrane hydrophones Need to generalise model to simulate the response of the new generation of Precision Acoustics bilaminar membrane hydrophones (15 m film thickness, 0.4 mm diameter)

A bilaminar membrane hydrophone

Diagram of a bilaminar membrane hydrophone

Hydrophone model assumptions 25 m pvdf film thickness, 0.5 mm diameter bilaminar Assume plane wave incidence on hydrophone Use transfer matrix formulation to evaluate pressure and particle velocities at extremities of pvdf layers Account for secondary piezoelectric effects Model pvdf layers as equivalent voltage sources in series with capacitance Model leg as distributed series resistance shunt capacitance network Model coaxial cable as transmission line Account for electrical loading on cable (e.g. oscilloscope, amplifier, arbitrary load)

Bilaminar Hydrophone Equivalent Electrical Circuit

Model input parameters   Model input parameters  

Open-circuit sensitivity

Predicted phase response

Prediction of pressure waveform

Conclusions Validation of a model for predicting the transfer characteristics of membrane hydrophones Can be used to estimate true pressure waveform