The paper presents a simplified analysis of harmonically terminated rectifier circuit and experimental results of a Schottky diode rectifier with even and odd harmonic terminations. The analysis is based on the Fourier series expansion of the voltage and current across the diode circuit. Harmonic terminations similar to the techniques used for power amplifiers are studied. A maximum efficiency of 84% at 30 dBm is obtained with second- and third-order harmonics terminated. The optimum value of dc load to maximize efficiency is obtained by sweeping the load. An optimal operating range of 28–35 dBm is obtained. The applications of the rectifier in wireless charging and power transfer systems are discussed.

Resonant Inductive Coupling Wireless Power Transfer (RIC-WPT)is a key technology to provide an efficient wireless power channel to consumer electronics, biomedical implants and wireless sensor networks. Due to its non radiative nature, RIC Wireless Power Transfer has been considered safe for humans when adhered to magnetic health radiation safety regulations (Christ et al., 2013), unveiling a large range of potential applications in which this technology could be used. However, current deployments are limited to point-to-point links and do not explore the capabilities of Multi-Node RIC-WPT Systems. In such a system, the multi-path relaying effect between different nodes could effectively improve the performance of the link in terms of power transferred to the load and power transfer efficiency. However, depending on the impedance and resonant frequency of the nodes that generate the multi-path effect, these nodes could also act as interfering objects, therefore (a) making the transmitter and/or receiver act as a pass-band filter and (b) losing part of the transmitter magnetic field through coupling to the interfering node. In this paper, a circuit-based analytical model that predicts the behavior of a Multi-Node Resonant Inductive Coupling link is proposed and used to perform a design-space exploration of the multi-path relaying effect in RIC Wireless Power Transfer Systems.

Battery-powered wireless sensor networks have been extensively deployed in condition monitoring and structural health monitoring systems, but the performance of wireless sensors are limited by battery capacity and difficulty of application in rotating machines. In this paper, a variety of commercial wireless charging solutions and coil-shaft configurations for magnetic coupling are compared, having in mind of the application of continuously charging wireless sensors on rotating machines. For the co-axial configuration of the transmitter coil and the receiver coil, a Qi standard compliant wireless charging kit and a custom charging circuit are successfully applied to charge wireless sensors on small rotating test rigs. In order to harvest and store intermittent energy input from the wireless power source, a prototype receiver circuit using a supercapacitor and low-dropout regulator is designed and validated. Based on the prototype circuit, the radial configuration of single transmitter coil and multiple receiver coils is demonstrated for wireless power transfer to the sensor nodes on the drivetrain of a small wind turbine test rig.

The optimal design problem for a wireless power transfer link based on a resonant inductive coupling is addressed in this paper. It is assumed that the magnetic coupling coefficient and the inductor quality factors are known. By employing the conjugate image impedances, the values of the inductances realizing the optimal design with respect to given values of the network input and load impedances are derived. It is demonstrated that there is just one optimal design maximizing both the power delivered to the load and the power transfer efficiency of the link. The four possible schemes corresponding to the use of a parallel or a series arrangement for the two coupled resonators (Parallel-Parallel, Series-Series, Parallel-Series, and Series-Parallel) are considered and discussed. Closed form analytical formulas are derived and validated by circuital simulations.

Here we demonstrate wireless energy transfer that exploits the conductivity and permittivity of soil to create a potential gradient on the surface around an earthed electrode, distributing electrical energy over the area. This generated surface potential can be amplified using a special standing-wave receiver for harnessing the distributed energy. We have experimentally mapped the surface potential around the electrode and plotted the received energy covering an area of 1200 m2. Key operating parameters are determined with a discussion on optimizing the system efficiency. This technique could address the challenge of distributing electrical energy to many low power devices over large outdoor areas without the use of wires.