The characteristic transfer parameters of inductive power transfer systems highly depend on the relative position of the coils to each other. While translational offset has been investigated in the past, the effect of rotatory offset on the transfer parameters is widely unclear. This paper contains simulation results of an inductive power transfer system with a rotatory offset in three axes and shows the possible improvements in the coupling coefficient. As a result, rotation angles can be used as control parameters and thereby increase the system efficiency. Alternatively, the allowed misalignment area of the secondary coil can be increased while maintaining the functionality and same dimensions.

This paper presents a comparative study on three types of slim coil structures used as a three-dimensional (3-D) receiver in a wireless power transfer system with a planar transmitter coil. The mutual coupling values and their variations between the receiver structures and the transmitter coil are compared under different distances and angular orientations with respect to the transmitter coil. The merits of performance are related to the consistency of the mutual coupling values under different orientations in a range of distances from the transmitter coil. The practical results show that slim 3-D receiver coil structures can be compatible with a planar transmitter coil with reasonably high-mutual coupling.

In this paper, possible coupling configurations of a four-plate capacitive power transfer system are studied by varying the combinations of its input and output ports. A voltage source is applied between two of the four plates, and a load is connected to the other two to form different circuit topologies. A mathematical model based on a 4 × 4 mutual capacitance matrix is established for equidistantly placed four identical metal plates. Based on the proposed model, four separate circuit topologies are identified and analysed in detail and described in a general form. The electric field distributions of the coupling configurations are simulated by ANSYS Maxwell. The theoretical modeling and analysis are then verified by a practical system, in which four aluminum plates of 300 mm × 300 mm are used and placed with a gap of 10 mm between adjacent plates. The experimental results show that the measured output voltage and power under the four coupling configurations are in good agreement with the theoretical results. It has found that the voltage gain is the highest when the two inner plates are connected to the source, and this coupling configuration also has the lowest leakage electric field.

A novel, dual-band, voltage-multiplying (RF-DC) rectifier circuit with load-tuned stages resulting in a 50 Ω input-impedance and high RF-DC conversion in 2.4 and 5.8 GHz bands for wireless energy-harvesting is presented. Its novelty is in the use of optimal-length transmission lines on the load side of the 4 half-wave rectifying stages within the two-stage voltage multiplier topology. Doing so boosts the rectifier's output voltage due to an induced standing-wave peak at each diode's input, and gives the rectifier a 50 Ω input-impedance without an external-matching-network in the 2.4 GHz band. Comparisons with other rectifiers show the proposed design achieving a higher DC output and better immunity to changing output loads for similar input power levels and load conditions. The second novelty of this rectifier is a tuned secondary feed that connects the rectifier's input to its second stage to give dual-band performance in the 5.8 GHz band. By tuning this feed such that the second stage and first stage reactances cancel, return-loss resonance in the 5.8 GHz band is achieved in addition to 2.4 GHz. Simulations and measurements of the design show RF-DC sensitivity of −7.2 and −3.7 dBm for 1.8V DC output, and better than 10 dB return-loss, in 2.4 and 5.8 GHz bands without requiring an external-matching-network.

This paper presents an effective and time saving procedure for designing a three-coil resonant inductive wireless power transfer (WPT) link. The proposed approach aims at optimizing the power transfer efficiency of the link for given constraints imposed by the specific application of interest. The WPT link is described as a two-port network with equivalent lumped elements analytically expressed as function of the geometrical parameters. This allows obtaining a closed-form expression of the efficiency that can be maximized by acting on the geometrical parameters of the link by using a general purpose optimization algorithm. The proposed design procedure allows rapidly finding the desired optimal solution while minimizing the computational efforts. Referring to the case of an application constraining the dimensions of the receiver, analytical data are validated through full-wave simulations and measurements.

Radiofrequency surface coils used as receivers in magnetic resonance imaging (MRI) rely on cables for communication and power from the MRI system. Complex surface coil arrays are being designed for improving acquisition speed and signal-to-noise ratio. This, in-turn makes the cables bulky, expensive, and the currents induced on cables by time-varying magnetic fields of the MRI system may cause patient harm. Though wireless power transfer (WPT) can eliminate cables and make surface coils safer, MRI poses a challenging electromagnetic environment for WPT antennas because the antennas made using long conductors interact with the static and dynamic fields of the MRI system. This paper analyses the electromagnetic compatibility of WPT antennas and reveals that commercially available antennas are not compatible with MRI systems, presenting a safety risk for patients. Even when the risk is minimized, the antennas couple with surface coils leading to misdiagnosis. This paper presents an approach to eliminate safety risks and minimize coupling using a filter named “floating filter.” A WPT antenna without a filter has a distortion of 27%, and floating filters reduce the distortion to 2.3%. Secondly, the floating filter does not affect the power transfer efficiency, and the transfer efficiency of 60% is measured with and without filters.

Space probes suffer from a fundamental problem, which is the limited energy available for their operation. Energy supply is essential for continuous operation and ultimately the most important sub-system for its sustainable functioning. Considering, for instance, the last space probe put on Comet 67P/Churyumov–Gerasimenko, called “Philae”, which was sent by Rosetta (http://www.esa.int/Our_Activities/Space_Science/Rosetta), to operate and to monitor comet activity, its operation was jeopardized due to the fact that it landed on a shadowed zone (no direct sunlight). Since its operational energy was only based on solar harvesters, the energy for its operation was limited by solar energy availability. In this paper a study on a viable alternative based on wireless power transmission is presented and discussed at the system level. It is proved that, using current technology, it is possible to create alternatives or supplement to existing power sources such as solar panels to power up these important space probes and to secure their operation.

The changes in physical environmental parameters have severe impacts on food safety and security. Therefore, it is important to understand micro-level physical parameter changes occurring inside food packages to ensure food safety and security. The emergence of smart packaging has helped to track and inform the specific changes such as a change in humidity, temperature, and pH taken place in the microenvironment in the food package. Moreover, these key physical parameters help determine the freshness of the food as well. Radio-frequency identification (RFID)-based sensors are an emerging technology that has been used in smart packaging to detect changes in the physical stimuli in order to determine food freshness. This review looks at the key environmental factors that are responsible for food safety and food freshness, the role of smart packaging with sensors that can measure changes in physical stimuli in the microclimate and the detailed review of RFID-based sensors used in smart packaging for food-freshness applications and their existing limitations.

Advances in technology have seen mobile robots becoming a viable solution to many global challenges. A key limitation for tetherless operation, however, is the energy density of batteries. Whilst significant research is being undertaken into new battery technologies, wireless power transfer may be an alternative solution. The majority of the available technologies are not targeted toward the medium power requirements of mobile robots; they are either for low powers (a few Watts) or very large powers (kW). This paper reviews existing wireless power transfer technologies and their applications on mobile robots. The challenges of using these technologies on mobile robots include delivering the power required, system efficiency, human safety, transmission medium, and distance, all of which are analyzed for robots operating in a hazardous environment. The limitations of current wireless power technologies to meet the challenges for mobile robots are discussed and scenarios which current wireless power technologies can be used on mobile robots are presented.

An internal wireless system (IWS) for satellites was proposed in a previous study to reduce the weight of satellites. It is a system that uses wireless communication modules to communicate between the satellite's subsystems. We proposed a complete IWS that employs microwave wireless power transmission technology, and we proposed a design of GHz band high efficiency rectifier based charge pump rectifiers with a class-f filter called class-f charge pump rectifiers. We theoretically compare the diode losses in a charge pump and single shunt rectifier, and experimentally verify the results. Apart from this, we consider that the class-f charge pump rectifiers will be used for a rectenna array. In order to know the direct current (DC) load change of class-f charge pump circuits is connected as a rectenna array, we measured the conversion efficiencies of a 2 by 2 rectenna array, connected in series and in parallel. The results of the experiment indicate that the optimum load of the rectifier changes to four times DC load when connected in series, and to 1/4 the DC load when connected in parallel.