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sensors can be powered by conventional smartphones at a depth up to 16 mm and

Measured average magnetic field as a function of the mobile to skin distance for an implanted tag in a phantom at different depths between 4 and 16 mm for the two-coil system (a) and the three-coil system with a resonant

The availability in the market of low-cost near-field communication devices with energy-harvesting capabilities allows to feed small sensors enabling the development of low-cost battery-less sensors. One important advantage over other

smartphones incorporate NFC readers. The limited read range for a selected number of applications is an advantage rather than a drawback because it ensures the privacy and improves the security under undesired access to sensible information by nearby third parties. In this chapter, an overview of recent advances in the field of battery-less NFC sensors at 13.56 MHz is provided, and it also briefly compares these sensors to other short-range RFID technologies. After reviewing power transfer in NFC, recommendations are made for the practical design of NFC-based sensor tags and NFC readers. A list of commercial NFC integrated circuits with energy-harvesting capabilities is also provided. A survey of recent battery-less NFCbased sensors for different applications has been done showing that conventional low-power sensors can be integrated within NFC tags for the new generation of

This work was supported by grant BES-2016-077291 and Spanish Government

RFID is that additional readers are not required since most of the modern

read at distance between 1 and 2 cm from the skin.

relay loop on the skin (b). The threshold Hmin is shown in dashed line.

Recent Wireless Power Transfer Technologies

4. Conclusion

Figure 20.

IoT devices.

42

Acknowledgements

Project RTI2018-096019-B-C31.

Antonio Lazaro\*, Marti Boada, Ramon Villarino and David Girbau Department of Electronic, Electric and Automatic Control Engineering, Rovira i Virgili University, Tarragona, Spain

\*Address all correspondence to: antonioramon.lazaro@urv.cat

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
