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%.

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.

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.

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.

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.

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.