Mechanical transmission loss of the sole Bragg reflector by GHz pulse echo technique with thick SiO₂delay line

Extraction of the experimental data of the sole Bragg reflector is complicated compared to the theoretical prediction of mechanical transmission loss of the sole Bragg reflector. This is because the property of a piezoelectric layer on Bragg reflector and that of the sole Bragg reflector is measured simultaneously in the standard impedance measurement. In this study, the method to evaluate the acoustic transmission loss of the sole Bragg reflector by using pulse echo technique with SiO2 delay line is proposed. A Sc0.40Al0.60N piezoelectric transducer whose acoustic conversion loss is 3.2 dB and fractional bandwidth is 56% was employed with two pairs Ta/SiO2 Bragg reflectors as a test sample. As a result, the experimental transmission loss of the sole Bragg reflector less than -20 dB was obtained. Experimentally extracted mechanical transmission loss agrees with the theoretical one.