Comparison of ultrasonic phased array probes based on PMN-PT and PZT 1-3 composites

The using of PZT composite is very common in manufacturing ultrasonic probes for nondestructive evaluations (NDE). This paper describes the manufacturing of PMN-PT composites and the using as a new material for NDE ultrasonic probes. The manufacturing process of phased array probes with the PMN-PT single crystal was investigated. PMN-PT based composites were directly used in the acoustic stack manufacturing process (matching layer, etc.) similar to conventional the PZT based composite. Therefore a PMN-PT single crystal wafer was diced mechanical to manufacture a 1-3 piezo composite, filled with epoxy and grinded to a thickness of about 210 micrometer. The polarization process was performed after the metallization of the final composite and then the electromechanical parameters were measured. The performance of the phased array probes was measured then by a so called PCUS® pro phased array electronic front end from Fraunhofer and compared with a PZT-based phased array probe. Therefore a 16 element linear array with an active aperture of 12mm x 12,75mm in a Fraunhofer IKTS standard housing was manufactured. The PMN-PT phased array probe shows a significant improvement of the sensitivity and a higher bandwidth. Until now the advantages of PMN-PT are used in medical applications, but are not implemented in NDE applications. But because of its high sensitivity and broad frequency spectrum, PMN-PT transducers can be advantageous compared to conventional PZT transducers for special applications in NDE. A very high sensitivity is needed when the test object shows a very high damping and scattering of ultrasonic waves, for example investigations on fibre reinforces plastics. Additionally techniques like the sampling phased array require very small apertures and therefore need a very high sensitivity.