An approach for correcting magnitude and phase distortion in wideband piezoelectric transducer systems

Acoustic ultrasonic measurements are widespread and commonly performed using sensitive piezoelectric sensors. An accurate transducer system response to investigate pressure fluctuations in water and their subsequent detection remains a challenge. Typically, these sensors exploit the resonant behaviour of the piezoelectric active element, being designed to give maximum sensitivity in the bandwidth of interest. Calibration of such transducers can provide both magnitude and phase information describing the way in which the sensor responds to a surface displacement over its frequency range. Such resonant sensors are widely used for ultrasonic applications. The resonant nature of the sensors leads to the use of narrowband signals with central frequencies close to the resonant frequency of the piezoelectric element. Consequently, such devices work efficiently and linearly over only a narrow band of their overall frequency range. This causes phase and magnitude distortion of any linear broadband signal being transmitted through such a transmitter-receiver acoustic system. In the present work, we describe a software calibration technique to correct for distortion in a wideband piezoelectric transducer system. We consider only the input and the final output signals of the whole system. Compensating for the distortion of the magnitude and phase responses, we ensured the signal seen at the receiver represents a good replica of the desired signal. A Gaussian, linear, chirp signal was used to demonstrate our approach. This method may be applied to correct system distortion in a wide variety of ultrasonic applications.