Vibration Energy Harvesting System - Energy Harvesting Autonomous Sensor Systems - page 126

TABLE 4.1
Technical Specifications of TH7R

TH7R Dimensions and Physical Properties

Weight g 18

Dimensions mm 95.3 × 73.4 × 0.53

PZT thickness mm 0.25

Static capacitance nF 166

Maximum voltage V 300

Vertical displacement mm 9.55

it on a shoe. Danak et al. [120] also researched ways to optimize the design of
an initially curved PZT unimorph power harvester. A mathematical model
was created that predicts the power output of the device. From this model,
relationships between generated charge and initial dome height, substrate
thickness, PZT thickness, and substrate stiffness were established.
THUNDER transducers are commercially available in a variety of sizes and
force displacement characteristics, each with very different electromechani-
cal characteristics. According to Danak et al. [120], the power available from
a flat piezoelectric transducer under 31-mode bending excitation is gener-
ally proportional to the volume of the material and the vertical displacement
induced. Therefore, while constrained by the size, comfort, and vertical dis-
placement experienced by the human pressing, the volume of PZT piezo-
ceramic is maximized when selecting the appropriate transducer. Hence, the
TH7R piezoelectric device is chosen, and its technical specifications are shown
in Table 4.1 .

4.2.2 Characteristics and Performance of THUNDER

Lead-Zirconate-Titanate Unimorph

The unique prestressed characteristic and convex shape of the THUNDER
piezoelectric material is used as a natural “press-and-release” mechanical
switch. The natural “press-and-release” process of the piezoelectric material
illustrated in Figure 4.17 consists of displacing the transducer from its equi-
librium position, reaching maximum displacement (stress), before allowing

Zero Voltage
State

Positive Voltage
State

Negative Voltage
State

+

-

- +

1 2 3

FIGURE 4.17
A depressing cycle of the prestressed piezoelectric diaphragm material.