This paper discusses novel methodologies for the characterization of harmonic signals generated by wireless powered devices, i.e. passive ultra-high frequency (UHF) radio frequency identification (RFID) tags, due to the wireless power transferred from reader to tag. Theoretical aspects, as well as measurements to characterize these non-linear phenomena are exposed. Particular care is taken to explain the analysis methodology and setup for two kinds of characterization measurements: radiated and conducted. The existence of harmonic signals carrying information is exploited in an advanced application example. A dual-band RFID tag is designed to increase the backscattered harmonic level in the tag-to-reader link. Measurement of this dual band tag demonstrates the exploitation of the hitherto neglected harmonic power; it also opens the door to more advanced applications exploiting the harmonic-link communication.

We propose a wireless power distribution system (WPDS) operating at 2.45 GHz CW in buildings instead of wired power distribution in order to reduce the initial cost of the building. Required technologies for the WPDS are (a) low-cost and low-loss deck plate waveguide, (b) variable microwave power distributor for the waveguide, and (c) high-power (>100 W) rectifier at the outlet. We developed and tested the deck plate waveguide, power distributor, and high-power rectenna consisting of 256 Si Schottky barrier diodes and newly developed GaN diodes. Finally, a test WPDS was built and microwave power transmission experiments were conducted. The total efficiency of the test WPDS was estimated to be 52%.

A method of power transmission is proposed that delivers power through the resonance of a helical receiver with its surrounding stray capacitance. The system operates in a quasi-wireless state where power is transferred over a single connection to a surface much larger than the dimensions of the receiver. This ensures high-efficiency energy transfer over large areas without the need of strong coupling electromagnetic fields. Standard power connectors such as tracks, plugs, and cords may be easily replaced with conductive surfaces or objects such as foil sheets, desks, and cabinets. Presently, the method is experimentally demonstrated at the small scale using loads of up to 50 W at an efficiency of 83% with both bare and insulated surfaces. Simple circuit modeling of the system is presented which shows close agreement with experimental results.

This paper is dedicated to the extensive review of state-of-the-art contactless energy transfer (CET) systems that are gaining increasing interest in the automatic machinery industries. We first introduce the circuit equivalent networks considered in the literature, and discuss the main operating principles. Possible circuital resonant solutions are also discussed together with the required compensating networks. Then we focus on the problem of transferring, at the maximum efficiency, high-power levels (of the order of 1 kW or higher), showing that highly coupled inductive links are needed, requiring to refrain from the resonance condition. These systems are usually referred to as CET systems, since the link distances are negligible with respect to the coils dimensions. The operating frequencies are of the order of tens to hundreds of kilohertz. The fundamental figures of merit are analytically defined and used to measure the actual limitations involved in this class of systems, including aspects related to realization feasibility with respect to voltages and currents limitations. Finally, state-of-the-art CET works are surveyed, and realistic applications for different operating frequencies are considered and critically compared.

This study presents a method of determining the magnetic coupling coefficient of inductive power transfer (IPT) systems under real-time operating conditions by measuring the open-circuit voltage and short-circuit current of coupled coils. Besides the theoretical analysis, the proposed method is verified by finite elements simulation and practical evaluation. Both simulation and experimental results have demonstrated that the proposed method can determine the coupling coefficient of both closely and loosely coupled coils with high-quality factors. The method can be used for online monitoring of the coupling condition and real-time power flow controller design of IPT systems.

The wireless efficiency of the strongly coupled magnetic resonance (SCMR) method greatly depends on the Q-factors of the TX and RX resonators, which in turn are strongly dependent on the geometrical parameters of the resonators. This paper analytically derives the equations that can be used to design optimal spiral resonators for SCMR systems. In addition, our analysis illustrates that under certain conditions globally maximum efficiency can be achieved.

Magnetic-resonant wireless power transfer (MRWPT) has been typically realized by using systems of coupled resonators. In this paper, we introduce a rigorous network modeling of the wireless channel and we introduce several viable alternatives for achieving efficient MRWPT. Ideally, the wireless channel should realize a 1:n transformer; we implement such transformer by using immittance inverters. Examples illustrate the proposed network modeling of the magnetic-resonant wireless power channel.

Electric vehicles (EVs) are becoming more popular due to concerns about the environment and rising gasoline prices. However, the charging infrastructure is lacking, and most people can only charge their EVs at home if they remember to plug in their cars. Using the principles of magnetic inductance and magnetic resonance, wireless charging (WC) could help significantly with these infrastructure problems by making charging secure and convenient. WC systems also have the potential to provide dynamic charging, making long road trips with EVs feasible and eliminating range anxiety. In this paper, we review the companies available in the literature that have developed electric vehicle wireless charging systems, automobile manufacturers interested in such technology, and research from universities and laboratories on the topic. While the field is still very young, there are many promising technologies available today. Some systems have already been in use for years, recharging public transit buses at bus stops. Safety and regulations are also discussed.

This paper addresses low-power, low-voltage electronic circuit requirements for wireless sensors with energy harvesting. The challenges of start-up for micro-controller unit (MCU)-based energy-harvesting platforms is discussed where a transient, low-voltage (20–1000 mV), low-power (<100 μW) source having a relatively high source impedance (possibly >500 Ω) is used. Efficient converter circuitry is required to transform the low-voltage output from the source to a level suitable for typical electronic devices, 1.8–5 V, and a prototype is demonstrated in the paper. Owing to the limited energy available to deliver to the storage element, the converter output voltage typically has a slow rising slew rate that can be a problem for MCUs. This necessitates a reset circuit to hold-off operation until a level high enough for reliable operation is achieved. Once operational, Maximum Power Point Tracking (MPPT) extracts peak power from the harvester while simultaneously tracking the transient nature of the source. In this low-power application, MCU programming needs to be efficient, while otherwise keeping the MCU in the lowest power standby mode possible to conserve energy. In a fully integrated design, a single MCU may be used for the sensor application, power management, power conversion, and MPPT functions.

Wireless power transfer (WPT) technology using the resonant coupling phenomenon has been widely studied. However, possible relationships between WPT exposure and human health have not been experimentally evaluated. In this study, we developed a new in vitro exposure system to evaluate the biological effects of magnetic resonant coupling WPT. The WPT was carried out using a self-resonant helical coil, which was designed to transfer the power with 85.4% efficiency at a 12.5 MHz resonant frequency. The magnetic field at the positions of the cell culture dishes is approximately twice the reference level for occupational exposure as stated in the International Commission on Non-Ionizing Radiation Protection (ICNIRP) guidelines. The specific absorption rate (SAR) at the positions of the cell culture dishes match the respective reference levels stated in the ICNIRP guidelines. In this paper, the coil design for the magnetic resonant coupling in the in vitro exposure system and characteristics, such as power transfer efficiency, electric field and magnetic field distributions, and SAR of the exposure system, are described.

In this paper, a hybrid solar/electromagnetic (EM) energy harvester that operates at 2.45 GHz is presented. The proposed harvester integrates the solar cells in the same area as the rectenna element obtaining a compact implementation. The radiating element that forms part of the rectenna is a cavity-backed slot antenna based on substrate-integrated waveguide technology, which allows for a compact, single substrate implementation. The radiating element is connected to a circuit that provides both the rectification of the incoming EM signals and the collection of DC energy coming from solar cells. A single-substrate prototype has been implemented, demonstrating an overall power conversion efficiency up to 30%, depending on the incoming radio frequency signal level and the ambient light conditions.

A survey of the regulatory framework pertinent to wireless power transfer (WPT) systems is given. Both technical (power and frequency) considerations along with health safety radiation compliance are examined. A primer on regulatory processes is also included to facilitate the understanding of the developments. The current state is analyzed and ongoing regulatory activities across the globe are discussed. Furthermore, a review of recent radiation safety studies of WPT systems is included.

To date, the technique of inductive power transfer has found applications in industry including two-dimensional battery charging. However, this restricts any load to planar movements. This paper proposes custom designed magnetic structures of a loosely magnetically coupled three-dimensional inductive power transfer system. This is done via computational software utilizing the finite-element-method. More specifically, single-phase and multi-phase primary magnetic structures are proposed to distribute a power transfer window along three orthogonal axes. Next, a secondary magnetic structure is custom designed to induce electromotive force in three-dimensions. The proposed system is simulated to demonstrate power transfer for charging an AA-battery cell. Finally, the thermal effects upon the secondary load are considered.