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

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