A highly efficient 20 MHz piezo-composite transducer for nondestructive characterization of multilayer plastics

Fabrication of piezo-composite transducers over 20 MHz by the dice-and-fill method is a challenge to the industry. This paper reports a newly developed 20 MHz single element composite transducer using the dice-and-fill method. The transducer exhibited significant improvement in sensitivity of more than 10 dB in measurement of plastics as compared to standard piezo-ceramic transducers having similar size and electrical impedance. The high efficiency of the composite transducer was achieved by optimizing composite design to a configuration with maximum thickness coupling coefficient of the material. Meanwhile, the polymer and ceramic phases of the composite efficiently oscillate in phase. This design also allows the piezo-composite to be fabricated for frequencies higher than 20 MHz with a low aspect ratio where lateral modes usually dominate. However, with the optimized design, lateral modes are suppressed and almost invisible within usable bandwidths up to 40 MHz. Measurement of thin barrier layer samples using the 20MHz composite transducer demonstrated consistent results for a thickness of 0.084 mm, while the standard 20 MHz transducers are only able to resolve thickness above 0.100 mm.