Recent advancements in the semiconductor integrated circuits and functional materials technologies have accelerated the demand of electronic and biomedical devices such as internet of things (IoT) and wearable sensors, which have low power consumption, miniature size and high data transfer efficiency. Wireless power transfer (WPT) has become the alternative solution to current electronic devices that rely on bulky batteries to supply the power and energy. Near Field Communication (NFC) technology is extensively used for wireless power transfer, where devices communicate through inductive coupling via induced magnetic fields between transmit and receive coils (loop antennas). Thin NFC sheets made of soft magnetic materials are inserted between antennas and metal case of wireless gadgets, such as mobile phones or tablets, to reduce the degradation of antenna gain and radiation efficiency due to generation of eddy currents. To enhance the efficiency of wireless power transfer, magnetic materials with superb properties such as high permeability, low magnetic loss and high resistivity are highly desirable. In this chapter, we will provide an overview of the current state of the art, recent progress and future directions in NFC based wireless power transfer, with the special focus on near field communications operating at 13.56 MHz.

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Novel soft magnetic ferrite materials will play a crucial role in next-generation trillion-dollar sensor technologies related to 5G communications and internet of things as these materials can achieve improved wireless power/signal transfer efficiency with high operation frequency. In this work, Ni 0.4 Co 0.25 Zn 0.35 Fe 2 O 4 ferrites with high permeability and low magnetic loss were prepared for RF and microwave device applications. Composition and microstructure control is crucial to obtain the desired magnetic and loss properties. CuO dopant (x = 0 wt% to 20 wt%) were employed during the synthesis of Ni 0.4 Co 0.25 Zn 0.35 Fe 2 O 4 ferrite specimens to modify the microstructures, thus improving the magnetic properties of the ferrites. High value of measured relative permeability (μ' of 4-10) and relatively low magnetic loss tangent (𝑡𝑎𝑛𝛿 𝑚 of 0.01-0.1) has been achieved at frequency range between 100 and 800 MHz. Addition of CuO, especially up to 3 wt%, can cause a significant increase in permeability. Real part of the permeability of 3.87 and 10.9 has been achieved for undoped and 3 wt% CuO doped specimens, while noticeable reduction in magnetic losses has been observed for the doped sample measured at 400 MHz. The resonance frequency of synthesized ferrites has also been shifted into GHz range, when higher concentration of CuO dopants (>5 wt%) were employed.