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.

The objective of the presented work is to take advantage of the precision capabilities of tailor-fiber-placement (TFP) embroidery processes in order to qualify carbon-fiber parts as viable antennas for wireless power transfer applications in multifunctional carbon-fiber-reinforced plastic (CFRP) composites. The solution comes first from a literature study of electrical, high-frequency, and textile engineering concepts. This review built familiarity with the technological challenges and state-of-the-art of the presented technology. Next step was iterative experimentation of machine capabilities for the production of carbon-fiber antennas. Finally, antenna prototypes were produced and their physical and electrical characteristics were evaluated through several test methods. The results showed that TFP embroidery machines were capable of producing quality, carbon antennas. Induction values of the antennas from 0.5 to 3.5 ‘H were achieved. Signal transfer efficiencies from carbon-antenna transmitters to an aftermarket receiver show promise in commercial application.

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.

This article experimentally explores the use of ferrite cores to miniaturize the receivers used for inductive wireless power transmission. A variety of receivers were designed and fabricated using cylindrical ferrite cores, ranging in total size from 47 to 687 mm3. The receivers were tested with a commercially available transmitter operating under the Rezence (Air Fuel Alliance) standard at 6.78 MHz. Experiments measured performance of the receivers in terms of their maximum power draw and efficiency as functions of the receiver load and transmission distance. Experimental results showed that ferrite-core receivers could draw multiple watts of power with end-to-end efficiencies in excess of 50%. While the efficiencies are less than a commercially planar coil receiver, the ferrite-core receivers offer a >50% reduction in mass and >90% reduction in footprint. As a result, the receiver power densities reach up to 17.6 W/cm3, which is a 25× improvement over previously reported work. This effort confirms the viability of ferrite-core receivers for size- and weight-constrained applications.

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.

Wireless power transmission (WPT) systems with moveable mechanical parts have been acquired more and more attention during the past decade. However, due to the moveable feature of transmitting coil and receiving coil, misalignment issue lead to extra power loss, decrease in efficiency, increase in control complexity, and unwanted performance degradation of the whole system. Moreover, it happened frequently than those traditional planar coils systems. The motivation for this paper is trying to have a deep understanding of quantitative relationship between ball-shaped coils mutual inductance and misalignment. Based upon that, engineers would know more detail of the coils position and mutual inductance. So, optimized design might be achieved. On considering that, this paper presents a WPT system with a ball-shaped coil for robot joints. A mutual inductance calculation based on filament method aimed at ball-shaped coil is proposed. Based on these, nine different ball-shaped coil solutions are calculated. Then, model with a minimized change rate of mutual inductance against the angular misalignment is chosen as the optimized design. Circuit analysis of the WPT system with the series–series resonant topology is conducted to choose a proper working frequency and load. Finally, an experimental platform is established. It demonstrates the feasibility of the proposed calculation method and the feasibility of the WPT prototype.

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.

Advances in material science and semiconductor technology have enabled a variety of inventions to be implemented in electronic systems and devices used in the medical, telecommunications, and consumer electronics sectors. In this paper, a wireless charging system is described as a wearable body heater that uses a chair as a transmitter (Tx). This system incorporates the widely accepted Qi wireless charging standard. Alignment conditions of a linear three-element coil arrangement and a 3 × 3 coil matrix array are investigated using voltage induced in a coil as a performance indicator. The efficiency obtained is demonstrated to be up to 80% for a voltage of over 6.5 Volts and a power transfer of over 5 Watts. Our results and proposed approach can be useful for many applications. This is because the wireless charging system described herein can help design seating areas for the elderly and disabled, commercial systems, consumer electronics, medical devices, electronic textiles (e-textiles), and other electronic systems and devices.

Microwave power transfer (MPT) can solve certain types of problems. For example, Internet of Things requires a flexible configuration of sensor networks, which is hindered by wired-charging sensors. This problem can be overcome by MPT techniques. However, the transmission efficiency of MPT is lower than that of wired transmission. This study focuses on the operation of rectifiers having a pulse-modulated input signal. Although a pulse-modulated wave is effective for improving the RF-DC conversion efficiency, the output voltage waves of rectifiers have a high ripple content. Moreover, the harmonic balance method cannot be used to simulate the operation of a pulse-modulated rectifier. To reduce the ripple content, a smoothing capacitor should be connected in parallel to an output load. We investigated the influence of a smoothing capacitor, the general characteristics of rectifiers under pulse-modulated waves, and the effectiveness of using pulse-modulated waves for improving RF-DC conversion efficiency. In conclusion, we reveal a necessary condition of the smoothing capacitor for improvement, demonstrate the effectiveness of pulse modulation, and show that the optimum impedance with a pulse-modulated wave input is an inverse of duty ratio times as compared to that with continuous wave input.

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.

More mobile devices such as mobile phones and robots are wirelessly charged for convenience, simplicity, and safety, and it would be desirable to achieve three-dimensional (3D) wireless charging with high spatial freedom and long range. This paper proposes a 3D wireless charging cube with three orthogonal coils and supporting magnetic cores to enhance the magnetic flux outside the cube. The proposed system is simulated by Ansoft Maxwell and implemented by a downsized prototype. Both simulation and experimental results show that the magnetic cores can strengthen the magnitude of B-field outside the cube. The final prototype demonstrates that the power transfer distance outside the cube for getting the same induced electromotive force in the receiver coil is extended approximately by 50 mm using magnetic cores with a permeability of 2800. It is found that the magnitude of B-field outside the cube can be increased by increasing the width and the permeability of the magnetic cores. The measured results show that when the permeability of the magnetic cores is fixed, the induced electromotive force in the receiver coil at a point 300 mm away from the center of the cube is increased by about 2V when the width of the magnetic cores is increased from 50 to 100 mm. The increase in the induced electromotive force at an extended point implies a greater potential of wireless power transfer capability to the power pickup.

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.