methods In this study, the sound component of Murata ManufacturingCo., Ltd. [30] with known parameters (see Table 1) was used fortesting the system, namely 7BB-20-6. The diaphragm structure ofthe PCD is made by adhering of PZT to a metal plate of brass. PCDis used as a sound component. The drawing of the PCD is shown in Fig. 1.