battery powering such devices occupies almost two-thirds of the volume of the entire

device [4]. One of the significant hurdles towards the miniaturization of devices is the

battery size, which can be realized in the immediate future with the advent of self-

powered devices.

20.3 Emergent Technologies for Self-Powered Generators

In this section, a summary of the various new generation technologies available for

powering the self-powered devices is discussed in sufficient detail.

20.3.1 Nanogenerators

Four technologies associated with nanogenerators are identified, and the first two types

are the PENGs and TENGs. These devices have the capacity to harvest the mechanical

energy generated from the human body. The different mechanical energy sources are the

heart beating, internal movement of the organs, breathing, exhalation, and acoustic en­

ergy. The other nanogenerator categories focus on converting the power generated from

the heat gradient between the body and the environment while performing various

functions. These devices are the PyNG and TEG that have the adequate technologies to

harvest the energy wasted due to temperature gradients. A broad description of such

devices’ workings will be presented in the following sections.

20.3.1.1 PENG

The piezoelectric nanogenerators are based on the piezoelectric effect, related to the

generation of voltages upon applying mechanical stress to a particular class of crystals [7].

The direct piezoelectric effect and the PENG are based on this principle. Piezoelectric

materials have been shown to generate continuous and alternating pulsed electric signals

for responding to dynamic mechanical stimuli. This effect has tremendous potential in

biomedical applications, from bone regeneration to self-powered devices. However, the

primary concern that limits the direct use of these classes of materials is the issues con­

cerning biocompatibility [8]. There have been a lot of advances made in developing

FIGURE 20.1

A schematic of the energy associated with various motions

related to the different movements of the body. Adapted

with permission [ 4], Copyright (2021), American Chemical

Society.

Self-Powered Devices

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