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

2. 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)

3. A bilaminar membrane hydrophone

4. Diagram of a bilaminar membrane hydrophone

5. 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)

6. Bilaminar Hydrophone Equivalent Electrical Circuit

7. Model input parameters
Model input parameters

8. Open-circuit sensitivity

9. Predicted phase response

10. Prediction of pressure waveform

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