  Acoustic matching layers are widely employed in high-frequency transducers
which are excited by different signal types depending on applications. In this
study, a theoretical method has been proposed to investigate the dependence of
functional mechanism of matching layer on excitation signal types, i.e., short
pulse and long pulse. The results indicate that the matching layer acts as a
bandpass frequency filter under the two excitation signal types. In the short
pulse excitation case, the matching layer can improve bandwidth and
transmitting voltage response simultaneously, whereas for the case of long
pulse excitation, the increased bandwidth is at the expense of transmitting
voltage response. To verify our theoretical results, underwater acoustic
transducers with and without matching layer were fabricated and tested. The
thickness design principle of matching layer was modified due to the
frequency-dependent acoustic radiation impedance. The experimental results
verified the theoretical prediction. Our results provide a deep insight into
the fundamental principle of matching layer design according to practical
applications.
