piezoelectric that are biocompatible, and it is not far from now when such biocompatible

piezoelectric will be a reality.

For a PENG, as shown in Figure 20.2, the open-circuit voltage (VOC) and the short circuit

current (ISC) can be expressed mathematically according to the following equations:

V

k

h

d

=

×

×

×

.

OC

T

1

33

33

(20.1)

I

k

A

t

d

=

×

×

×

.

SC

2

33

(20.2)

where k1 and k2 are two constants, d33 denotes the piezoelectric coefficient (CN

)

1 , and h is the

thickness of the (piezoelectric material used in) PENG. ^T

33 ^{Is the permittivity of the material of}

the PENG when constant stress is applied along the direction of polarization, A denote the

area of the opposite faces of the piezoelectric material, and

indicates the magnitude of the

applied mechanical stress. The equations described above are related to the piezoelectric

material used in manufacturing the PENG. Wang et al. reported a remarkable discovery on

FIGURE 20.2

Illustration of the different sources of energy that can be harvested to power the self-powered devices. Each

illustration represents the mechanism by which other physical and biological processes can be utilized to

harvest the energy for running the self-powered devices. Adapted with permission [ 8]. Copyright (2021), The

Authors, some rights reserved; exclusive licensee John Wiley & Sons. Distributed under a Creative Commons

Attribution License 4.0 (CC BY).

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