that can power any form of the device [17]. In this context, the semi-conducting materials

play a crucial role, as they can serve as means that can make the energy conversion

possible. Today, most PV cells are fabricated from the monocrystalline or polycrystalline

Si in the form of a PN-junction diode. The current research scenario has shown that the

PV cells’ efficiency based on the Si has reached a level of 18% for polycrystalline Si to 24%

for monocrystalline Si. The I V

–

characteristics and the output power generated from the

PV cells can be described by the following equations [17]:

I V

I

I

V

I V R

R

(

) =

+

(

)

SC

d

s

sh

(20.7)

P

I

V

FF

=

·

·

out

SC

OC

(20.8)

where Rs is the series resistance of PV cell, Rsh is the shunt resistance of the PV cell, ISC is

the short-circuit current, is the dark current of the PV cell, VOC is the open-circuit voltage,

and FF is the fill factor. It must be mentioned here that for implantable device applica­

tions, the PV cells are required to be encapsulated in a particular arrangement that will

protect the PV cells and, at the same time, save the body from any toxicity [17]. The

details of some of the devices that use these PV cells and, in general, all the aforemen­

tioned technologies shall be done in the subsequent section.

20.4 Self-Powered Devices Based on the New Technologies

In biomedical applications of the technologies described previously, many factors need

special attention. The implantable devices need to be miniaturized and have a long

lifetime, both of which are contradictory under the purview of the current technology.

This has encouraged researchers to invent technologies that do not require batteries to

power devices. We have presented a discussion on the possible technologies that can be

used instead of batteries. In the present section, we shall discuss some of the devices

based on these technologies that have been used in the biomedical market.

20.4.1 Self-Powered Cardiac and Pulse Sensors

Ma et al. first proposed the first cardiac sensor in 2016 based on the TENG technology used

for real-time monitoring of the vital signals [18]. The device was based on nanostructured

PTFE and Kapton film that served as the primary friction materials for the triboelectric

sensor. The intelligent design of the sensor with flexible packaging enables the sensor to

monitor even tiny changes in the signals originating from the vital organs together with

incredible biocompatibility and enhanced durability. It has been reported that the device

could generate an output voltage of Voc ~ 10 V, and Isc ~ 4 µA when the sensor is used to

monitor the pericardium model of the living porcine model (Figure 20.3). Further, the

device could also achieve the added advantage like the monitoring of the blood pressure

and the velocity of the blood flow in the subject with fair degree of accuracy [18].

Ouyang et al. in 2017 proposed a wearable ultrasensitive pulse sensor (SUPS) based on

a TENG, having a commendable signal-to-noise ratio of 45 dB and long durability of 10⁷

cycles (Figure 20.4) [19]. By using Bluetooth, this sensor showed the capability of

Self-Powered Devices

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