Self‐Powered Wireless Sensor Networks in Cyber Physical System

With the advancements in wireless communication, cyber physical system (CPS) has originated as a leading technology to support interactions among humans and objects by integrating abstract computations and physical processes. CPS has raised the demand for interconnected devices with physical input and output. Sensors, actuators, and embedded devices are the key components required for sensing, monitoring, and controlling the physical world. If wireless sensors are not deployed in CPS development, real-time decision making becomes difficult, and this leads to unreliable and unpredictable CPS design. The sensors are usually power driven. But usage of a wired power supply is not preferable as it increases the complexity and leads to resource wastage. The power supply lines will also cause possible hazards and limit the growth of the wireless sensor network. As an alternative, battery driven sensors can be used. But it demands maintenance and recharge issues. The energy storage unit comes with the constraint of having a set lifetime; the sustainable operation of the sensors becomes the major challenge faced by the CPS systems. The wide spread distribution of the sensors, their mobility, and wireless operations also add to the drain of the storage unit. This necessitates for a self-powered sensor system that is either capable of harvesting ambient energy in order to sustain continuous operation without relying on external power sources or by using a power source that is self-generated. Therefore, a self-sustaining, maintenance-free power source needs to be integrated inside an individual sensor node for powering it by harvesting energy from its operational environment. There is an abundance of energy available in nature in different forms like thermal energy, mechanical energy, solar energy, chemical energy, and many more. The conversion and harvesting of such energies can be used to build self-powered devices and also to develop clean renewable energy sources. The widely available form of energy at any place and time is mechanical energy that includes mechanical vibration, air flow, raindrops, and hydraulic pressure. It is available specifically in the household, industrialized, and transport sectors where there is huge scope for the application of sensor networks. Hence, the focus will be on harvesting of mechanical energy. The two popular energy-harvesting devices that transform mechanical energy into electrical energy are piezoelectric nanogenerators and triboelectric nanogenerators. Utilizing these devices, self-powered sensors can be built. This chapter gives an overview of how utilization of nanogenerators can lead to development of self-powered sensors and its applications.