**7. Conclusions**

*Wireless Power Transfer – Recent Development, Applications and New Perspectives*

wireless information transfer (WIT) for several decades.

have been widely adopted in the literature [35].

(RFID) tags), as it is a cost-effective solution. Radio Frequency (RF)-based wireless power transfer (WPT) can provide continuous and controllable power supply, and thus is applicable to more energy-demanding applications [35]. Radio frequency (RF) signals have been widely used in wireless communications as the carrier for

A query thus arises that whether we can utilize RF signals more efficiently for both WPT and WIT at the same time with a new technique called simultaneous wireless information and power transfer (SWIPT) [35]. The SWIPT is developed by considering a single-antenna point-to-point channel, where the trade-off between the achievable rate for WIT and the received energy for WPT is investigated that the single-antenna receiver can utilize the same received RF signals for both information decoding (ID) and energy harvesting (EH) at the same time without any loss. However, this assumption is difficult to realize in practice since existing information receivers (IRs) and energy receivers (ERs) are separately designed with distinct circuit structures, and as a result, each of them cannot be used to decode information as well as harvest energy at the same time. The two basic receiver structures

Time-Switching receiver (TS) switches between an information decoder and an energy harvester over time. This technique is the simplest way to implement SWIPT by using off-the-shelf commercially available circuits for information decoding (ID) and energy harvesting (EH), respectively. It is crucial to determine their operation modes (ID or EH) over time for TS receiver. This is based on their communication and energy requirements, as well as the channel conditions [36]. Power-Splitting receiver (PS) splits its received signal into two portions with one for information decoding (ID) and the other for energy harvesting (EH). In this technique, it is important to determine the power splitting ratio at each antenna to balance the rate-energy tradeoff between the information decoding (ID) and energy harvesting (EH) receivers. Note that time-switching and power-splitting receiver can be regarded as a special and low-complexity realization of power-splitting receiver with only binary (0 or 1) power splitting ratio at each receiving antenna. They are implemented by different

hardware circuits (time switcher versus power splitter) in practice [36].

sion channels and enhancing security of energy transmission.

There are miscellaneous issues investigated by many researchers on wireless power transfer. A. M. Azman et al., investigated superimposition technique in wireless power transfer for enhancing the distance of transmission of the transmission coil [37]. This technique resulted in incrementation of the distance by up to 2 times compared to the system without superimposed technique. Yunfei Chen et al., investigated interference analysis in wireless power transfer [38]. They studied the co-channel interference (CCI) generated by wireless power transfer. They considered the effect on information delivery for three widely used setups of simultaneous wireless information and power transfer (SWIPT), hybrid access point (HAP) and power beacon (PB). In the book on Wireless Power Transfer edited by Johnson I. Agbinya, various innovative techniques for design of Optimal Wireless Power Transfer Systems are discussed [39]. The authors present new methods of delivering flux efficiently using the inductance-based transmitter to an inductance-based receiver by using either flux concentrator or separator. The flux coupling coefficient can be increased by the concentrator. This leads to increased flux delivered to the receiver by a large order of magnitude. Whereas the separator helps in reducing the crosstalk between two identical types of nodes and also leads to significant increase in power delivery. In another paper, Zhen Zhang et al., investigated energy encryption for wireless power transfer [40]. They studied the improved security performance of wirelessly transferred energy as an attempt to switch off other unauthorized energy transmis-

**22**

This chapter has presented brief outline of the state-of-the-art and developments in wireless power transfer using solar energy. The harvesting technologies of ambient solar radiation like solar photovoltaic, kinetic, thermal or electro-magnetic (EM) energy can be used to recharge the batteries and power various electronic gadgets. Brief on Radio frequency (RF) harvesting technologies is also presented. The energy converted to useful DC energy which can be used to charge electrical devices which need low power consumption. The chapter has also presented analysis of the parallel plate photovoltaic amplifier connected to a potentiometer as a Resistance-Capacitance (RC) circuit power amplifier. The effect of inductance and resulting power transfer was theoretically determined in the RC amplifier circuit. The electrical and thermal properties and measurements from a parallel plate photovoltaic amplifier were collected to analyze the unbalanced power transfer and inductance in a nonlinear RC circuit amplifier using equivalent transfer functions. The concept of Wireless Information and Power Transfer using Electromagnetic and Radio Waves of Solar Energy Spectrum is also briefly outlined. The chapter has also presented miscellaneous issues pertaining to wireless power transfer such as superimposition technique, interference, and security issues. Appendix has presented Equations for transmitter and receiver using mutual inductance of the magnetic resonance between transmitter and receiver.
