**2. Experimental**

The commercial piezoelectric bimorph is used for basic operations in the power management circuit. And the piezoelectric unimorph were fabricated by remodeling the commercial bimorphs. The experimental setup for measuring the unimorph generator is shown in **Figure 6**. Details were described in our previous study [16]. Commercial bimorph was produced by using a patterned fiber-reinforced plastic (FRP) plate (105 mm × 10 mm × 1.6 mm) that was used as the base beam. Piezoelectric ceramics was adhered to both the side of the beam. The unimorph structure was fabricated by removing the piezoelectric ceramics from both the side and adhering PZT- or BT-based ceramics (10 mm × 18 × 0.5 mm) to one side of the FRP beam. The unimorph was attached to the vibration generator and oscillated with various frequencies and accelerations. And the characteristic frequency of the beam was 57

**Figure 6.** The experimental setup for measuring the unimorph generator. The unimorph constructed by the piezoelec‐ tric ceramics and FRP beam was attached to the vibration generator and oscillated with various frequencies and accel‐ erations. The displacements and accelerations of the unimorph were monitored by the acceleration sensor attached to the other end during measurement [16].

Hz. An acceleration sensor was attached to the other end, and the displacements of the unimorph were monitored during measurement. The beam vibrated with the tip as a node at 60 Hz.

In the case of the unimorphs, commercial bulk PZT ceramic disks were used. The PZT-based ceramic disks were hard PZT ceramics with Tc of 325°C, soft PZT ceramics with Tc of 145, 190, or 330°C (hereafter PZTh325, PZTs145, PZTs190, or PZTs330, hereafter, respectively, NEC Tokin) of 0.5 mm thickness were used [15]. As lead-free ceramics, nondoped BaTiO3 (BT) ceramics, manganum-doped BaTiO3 (BT-Mn), and (Ba0.85Ca0.15)(Ti0.95Zr0.05)O3 (BCCZ5) sintered at 1400°C, 1300°C, and 1350°C, respectively, were used. The dielectric and piezoelectric properties of these ceramics are shown in **Table 2** and were reported in detail in our previous study [16, 18].


**Table 2.** Voltage, power, and material parameters of the piezoelectric samples [16].

In order to evaluate the performance as an energy source, a piezoelectric energy-harvesting power supply integrated circuit (LTC3588-1, Linear Technology Corp.) that integrates a lowloss full-wave bridge rectifier with a high efficiency buck converter was employed [19]. The bimorphs were oscillated for 45 sec. In this power supply circuit, *V*in, voltage rectified by a fullwave bridge rectifier that rectifies AC input from piezoelectric elements, and Pgood, power good output signal signing that the output voltage produced by the converter in the power supply exceeding 92% of the programmed output voltage of 3.6 V, were outputted.
