Abstract
A comprehensive model of wireless power transfer (WPT) between a pair of inductively coupled loop resonators in the vicinity of a conducting slab is developed by combining electromagnetic (EM) theory with an equivalent circuit representation of the system. The model incorporates all EM interactions occurring between the coils both directly and through the slab. The design of an optimal WPT regime for two coils in the presence of a conducting slab with variable conductivity is demonstrated by exploiting the model to predict the coil detuning produced by the slab. It is further shown that the model also constitutes an effective tool to estimate the losses in the conducting material solely in terms of the parameters of the generalised equivalent circuit and to analyse the power flow in a WPT system. The validity of the analytical results is proved by comparison with rigorous full-wave simulations. The proposed analytical method can have particular relevance in the field of wireless charging of electric vehicles and WPT for supplying implanted medical devices and body sensor networks, where it can be instrumental for the design and optimisation of the system to be compliant with existing RF exposure safety levels.
Highlights
The ubiquitous diffusion of mobile communications and computing and the expanding utilisation of electric vehicles have stimulated increasingly greater interest in wireless power transfer (WPT) technology, due to its potential of rescinding the requirement for the last remaining wired connection to power and charge portable devices
The use of wireless supply to power implanted medical devices [16,17,18,19,20] and body sensor networks for healthcare and medical research [21] are other situations where taking into account the impact of the environment is important. In these applications, substantial variations in load, coupling, and circuit parameters can be expected because the human body and biological tissues are moderately conductive; at the same time, there are strong requirements to maintain an effective power regulation to ensure that a constant power is delivered, as desirable [19], maximise transfer efficiency and thereby reduce heat dissipation in the coils, and provide compliance of WPT systems with human EM exposure limits [22]
One of the most notable advantages of the model presented in this work is that it allows framing the description of WPT in a complex environment, possibly including multiple conducting interfaces, within the same simple equivalent circuit formalism used for WPT in free space; as a result, the main parameters characterising the power link, e.g. the output power (6) and transfer efficiency (7), can be readily computed, while all relevant EM effects and interaction mechanisms are subsumed into the calculation of the inductances
Summary
The ubiquitous diffusion of mobile communications and computing and the expanding utilisation of electric vehicles have stimulated increasingly greater interest in wireless power transfer (WPT) technology, due to its potential of rescinding the requirement for the last remaining wired connection to power and charge portable devices. The use of wireless supply to power implanted medical devices [16,17,18,19,20] and body sensor networks for healthcare and medical research [21] are other situations where taking into account the impact of the environment is important In these applications, substantial variations in load, coupling, and circuit parameters can be expected because the human body and biological tissues are moderately conductive; at the same time, there are strong requirements to maintain an effective power regulation to ensure that a constant power is delivered, as desirable [19], maximise transfer efficiency and thereby reduce heat dissipation in the coils, and provide compliance of WPT systems with human EM exposure limits [22].
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