In a wireless power transfer system via coupled magnetic resonance, the power transfer efficiency (PTE) drastically decreases with the transfer distance and the changing load. To solve this problem, an automatic impedance matching system is usually embedded in an intelligent algorithm. However, the traditional algorithm cannot dynamically track the impedance due to its slow matching speed. In this paper, an automatic impedance matching method based on adaptive network based fuzzy inference system (ANFIS) is proposed to overcome this disadvantage. A simulation system is constructed, and results show that the efficiency of the proposed ANFIS method is 80.26% higher than that of the genetic algorithm. Moreover, an automatic impedance matching prototype is built and dynamic matching experiments are carried out, showing that the PTE is up to 84.76% when the distance increases from 4.5 to 50 cm. The simulation and experimental results are basically consistent, which prove the validity of the novel method.

The improvement of effective transfer distance is significant for wireless power transfer (WPT) via coupled magnetic resonances, with coil radius being the most important influencing factor. To study the relationship between effective transfer distance and coil radius, a model of WPT is established at first. Based on analyses of circuit and magnetic field, the influencing factors for effective transfer distance are obtained. Second, the models of WPT are constructed using software COMSOL, and the influences of Tx and Rx coil radius on the effective transfer distance are studied in detail. In addition, they are not proportional and the coil impedance is the most important factor. On this basis, a coil design method is proposed. Finally, an experiment device was built, and experimental results were well consistent with the theoretical analysis, showing the rationality and effectiveness of the proposed method.

The technology of wireless power transfer via coupled magnetic resonances (CMR-WPT) has a good transfer performance in the “middle range”, but it is far from satisfying the application requirements in practice. To achieve a longer transfer distance, coils are usually complicatedly designed, making the system unwieldy and costly. Based on the intuitive and easily adjustable coil parameters, a design and optimization method was proposed in this paper, which can realize the minimum size coil that meets the requirements at 6.78 MHz. First, an equivalent model of the CMR-WPT system was developed, and the influences of coil parameters on the effective transfer distance and power transfer efficiency (PTE) were analyzed, indicating that the effective transfer distance and PTE were not always proportional to the coil radius, the number of turns or the pitch. Then, the coil impedance and the quality factor of different coils were calculated. In addition, the influence degree of coil parameters on the transfer performance was also compared using variable control. Finally, an experimental platform was built, and experimental results agreed well with the simulation results.

Aiming at the risk of electricity theft of wireless power transfer (WPT) technology due to its untargeted and non-directional characteristics, a novel method of identification and resonance decoupling based on frequency hopping communication is proposed. The basic principle of the identification method is to make the resonant frequency of transmitter coil and receiver coil jump synchronously and randomly according to the pseudo-random code sequence, which can identify the load in single-source single-user mode and single-source multi-user mode respectively by calculating energy consumption ratio. And if user is illegal, then the resonant frequency of system jumps randomly to cut off the power, which is named resonance decoupling. The experimental circuit is designed on the basis of theoretical analysis and the method is verified. The test results are consistent with theoretical analysis, which has proved the validity of the method. This paper not only provides a solution to the power management of WPT system, but also is a support for the measurement of electricity, moreover, it is conducive to the further application and promotion of WPT technology.

Two kinds of electrical models for concrete have been used to calculate the transmission loss, propagation loss and total loss of normal incidence and oblique incidence of wave. The value of these losses depends on the electrical properties of the concrete, frequency of wave and the incidence angle. When the wave is normal incident and the frequency is between 20-80 MHz, the sensor will receive significantly larger power than the other cases we examined. Also, an optimum frequency range (corresponding to minimum transmission losses) has been identified for the cases we have examined. Detailed comparison between powering techniques that use RF signals versus low frequency inductive coupling will be presented at the conference. Also, the effects of rebars will be considered.