2F-6 Properties and Application-Oriented Performance of High Frequency Piezocomposite Ultrasonic Transducers

Routine high frequency piezocomposite fabrication is now becoming possible. However, specialized characterisation techniques and reference results are absent from the literature and there is an urgent demand for characterisation to support the use of this material in transducers for biomedical diagnosis and non-destructive evaluation. In this paper, we report on a novel procedure for high frequency piezocomposite fabrication and results of intensive characterisation based on electrical impedance spectroscopy and other techniques. 1-3 composite structures have been made with circular PZT pillars with diameter and kerf down to 12 mum and 6 mum respectively, aspect ratio > 3, volume fractions around 40% and active area of around 4 mm using a process which is capable of scalable commercial production. Experimental electrical impedance measurements have proved to be closely matched to one-dimensional models and piezocomposite material performance greatly exceeds that of other materials such as PVDF and LiNbO₃. Comprehensive characterization of practical performance has been carried out including both through-transmission and pulse-echo measurements, generating single point results and high resolution 1D and 2D scans to produce 2D and 3D data sets, including tungsten wires test objects to determine axial and lateral resolution and transducer sensitivity. A typical prototype focused transducer is described here, with f- number of 4 and centre frequency of 37 MHz. Performance investigation yielded a through-transmission -3 dB bandwidth of 24 MHz, pulse-echo -6 dB bandwidth of 22 MHz, and lateral and axial resolutions of 250 mum and 150 mum respectively.