2.1.2. Displacement

Piezoelectric ceramics (PC) can be used to convert electrical energy into mechanical energy and to transfer energy to the metal foil. The experiment of displacement used a clamp to secure the device of PAJ and sensor head. The high-frequency current flowing through the sensor head coil generates a high-frequency magnetic field, which interferes with the degree of the impedance of the sensor head and is converted into a voltage output. While the voltage signal is being transferred to the digital oscilloscope to generate waveforms, it can be calculated into the displacement or amplitude of the metal sheet as shown in Figure 3. The sensing head named EX-305 (KEYENCE, Co., Ltd., Taipei, Taiwan) has a frequency response of 18 kHz and resolution of 0.4 μm. The distance between the sensing head and piezoelectric patches is 1 mm and the operating temperature is between −10 ◦C and 60 ◦C.

**Figure 3.** Schematic diagram of jet path.
