Experimental determination of the impulse response of axisymmetric focused ultrasonic transducers

The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. One of the advantages of this approach is an easy understanding of the diffraction phenomena in the time domain; moreover, it allows the prediction of diffraction effects on the pressure field by a simple temporal convolution between the impulse response for the potential and the acceleration of the surface transmitter. An experimental evaluation of the impulse response for the potential in the case of focused transducers is proposed using a deconvolution of two pressure signals detected by a small hydrophone. One of these two signals corresponds to a measurement at the focus since at this particular point the pressure is directly proportional to the acceleration of the surface source. Because of the finite bandwidth of the measurement system the deconvolution is not an easy operation. In order to restore the missing low-frequency components, a polynomial extrapolation of the transfer function is used to improve the deconvolution results.