Development of a high temperature transducer backing element with porous ceramics

In this study, porous ceramics are introduced as a backing element suitable for high temperature transducers. Acoustic impedance and attenuation can be regulated through control of the porosity and pore size, using scattering from micropores as the attenuation mechanism. Porosity is induced by mixing the ceramic powder with polyethylene particles. The polymer component burns during the sintering process and leaves behind spherical voids. Porosity and pore size are controlled through the polymer-to-ceramic weight ratio and poltyethylene particle size, respectively. In this manner, a porous mullite material is designed and manufactured to act as the binding agent for a gallium phosphate (GaPO₄) piezocrystal; this yields our goal of a wide-band signal with center frequency of 2.8 MHz and operating temperature up to 700 - 800 °C. The design and fabrication process can be employed in manufacturing backing elements for a variety of transducers with specified center frequency and signal bandwidth.