**Conflict of interest**

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

MTSs. We obtained the measured transfer efficiency of LTSR case of 51,5%, 50.1%, 48.3%,43.2%, 39.5% and 26.6% at the receiver positions of No. 1 to No. 6, respectively. Contrastingly, for the uniform MTS, the efficiency decreases obviously, when the receiving positions are moved far away from the center since the intensity of magnetic field at the edge is lower than at the center for the uniform MTS.

*Measured and simulated results of the transfer efficiency with the uniform or defected metasurface (a) LTLR* 

In this chapter, we propose the defected MTS for enhancing transferred efficiency and reducing the EMF. The MTS is based on a defected unit cell at the desired receiving position formed two-dimensional cavity. It can improve the localization of the magnetic field; thus, the strong confinement of the receiving location can be realized. Compared to previous defected MTSs especially in case of the small transmitter, using this proposed method, it is a simple way to create the cavity of twodimension area because the single unit cell is only used and controlled in contrast of the series of an array of the defected unit cells via hopping or MIW route. The power transfer efficiency of the proposed defected MTS increases significantly from 1.9% (free space case) and 38% (uniform MTS) to 60% with the size ratio between transmitter and receiver is 4:1. Moreover, the confinement can reduce the leakage EMF around the surrounding system without additional shielding box. It can reduce EMF leakage about 10 to 15 dB at 13.56 MHz with the defected MTS. When the defected MTS is integrated in the WPT system, however, the size of the receivers is affected of the overall efficiency. If the size of the receiver is comparable compared with the unit cell size, it gets better efficiency than the larger receivers. Consequently, the defected MTS is not suitable for the case of the large transmitting and receiving coils due to splitting frequency effect. We hope that thought the proposed defected MTS operates in low frequency, the proposed structure can be easily scaled and tuned by

adjusting the geometry of the coil and changing the capacitor value.

This work was supported by the Thailand Research Fund under Grant

**158**

RSA6280056.

**Acknowledgements**

**4. Conclusions**

**Figure 9.**

*and (b) LTSR.*

The authors declare no conflict of interest.
