Tunable high acoustic impedance alumina epoxy composite matching for high frequency ultrasound transducer

Matching layer is a critical component that determines the performance of piezoelectric ultrasound transducer. For most piezoelectric materials, their acoustic impedances are significantly higher than human tissues and organs, so a tunable matching layer with a high acoustic impedance is required for optimizing the acoustic wave transmission. In this article, a high compression fabrication method is presented, with which the acoustic impedance of alumina-epoxy composite matching layer can be tuned from 6.50 to 9.47 MRayl by controlling the applied compression pressure and ratio of the components. The maximum acoustic impedance 9.47 MRayl can be achieved by compressing a mixture of 80% alumina weight ratio under a 62.4 MPa pressure. This enhancement mainly relies on the increased acoustic longitudinal velocity which enlarged the tolerance of high to ultra-high frequency transducer fabrication using quarter wavelength matching design. Furthermore, the attenuation of the matching layer developed by this method is only -10 dB/mm at 40 MHz. The very high acoustic impedance value and very low attenuation make this matching material superior than all reported matching materials, and therefore, can enhance the performance of the ultrasound transducers, especially for medical imaging applications.