Performance Of Wireless Power Transfer Research Articles

Design of TE-polarized resonant Bessel-beam launchers for wireless power transfer links in the radiative near-field region

Abstract Resonant Bessel-beam launchers (BBLs)are radiating devices constituted by a cylindrical metallic cavity with a partially reflecting sheet (PRS) on top. Millimeter-wave resonant BBLs typically exhibit transverse magnetic (TM) polarization due to the use of coaxial probes as feeders and homogenized metasurfaces as PRS. Launchers showing either a purely transverse electric (TE) or a hybrid (quasi-TE) polarization have recently been proposed for realizing wireless power transfer (WPT) links in the radiative near-field region at millimeter waves. The former are obtained by means of a radial slot array as a feeder and a homogenized metasurface as a PRS. The latter are obtained by using a loop antenna as a feeder and an annular strip grating in the homogenization limit as radiating aperture. In this work, based on an original semi-analytical model, such a metasurface is demonstrated to show a dichroic behavior. This interpretation explains the improvement in terms of polarization purity with respect to more nondichroic conventional homogenized metasurfaces. The behavior of the annular strip grating under a pure TM polarization is tested with a coaxial feeder, whereas its behavior under a pure TE polarization is tested by means of the radial slot array feeder. Results confirm the validity of the proposed analysis, which is finally exploited to evaluate the WPT performance.

Joint Transceiving and Reflecting Design for Intelligent Reflecting Surface Aided Wireless Power Transfer

In an intelligent reflecting surface (IRS) aided wireless power transfer (WPT) system, a practical architecture of an energy receiver (ER) is proposed, which includes multiple receive antennas, an analog energy combiner, a power splitter and multiple energy harvesters. In order to maximise the output direct-current (DC) power, the transmit beamformer of the transmitter, the passive beamformer of the IRS, the energy combiner, and the power splitter of the ER are jointly optimised. The optimisation problem is equivalently divided into two sub-problems, which independently maximises the input RF power and the output DC power of the energy harvesters, respectively. A successive linear approximation (SLA) based algorithm with a low complexity is proposed to maximise the input RF power to the energy harvesters, which converges to a Karush-Kuhn-Tucker (KKT) point. We also propose an improved greedy randomized adaptive search procedure (I-GRASP) based algorithm having better performance to maximise the input RF power. Furthermore, the optimal power splitter for maximising the output DC power of the energy harvesters is derived in closed-form. The numerical results are provided to verify the performance advantage of the IRS-aided WPT and to demonstrate that conceiving the optimised energy combiner achieves better WPT performance than the deterministic counterpart.

Efficient Multi-Hop Wireless Power Transfer for the Indoor Environment.

With the rapid development of the Internet of Things (IoT) and wireless sensor networks (WSN), the modern world requires advanced solutions for the wireless powering of low-power autonomous devices. The present study addresses the wireless power transfer (WPT) efficiency problem by exploiting a multi-hop concept-based technique to increase the received power at the end sensor node (ESN). The current work adopts efficient multi-hop technology from the communications field to examine its impact on WPT performance. The investigation involves power transfer modeling and experimental measurements in a sub-GHz frequency range, chosen for being capable of providing a greater distance to transmit power. The paper proposes a multi-hop (MH) WPT concept based on signal amplification and demonstrates the fabricated multi-hop node (MHN) prototype. The experimental verification of the MHN is performed in the laboratory environment. The present paper examines two WPT scenarios: line-of-sight (LoS) and non-line-of-sight (NLoS). The turn-on angle of 90 degrees on MHN is used for the NLoS case. The received power and RF-DC converted voltage on the ESN are measured for all investigated scenarios. Moreover, the paper proposes an efficient simulation approach for the performance evaluation of MH WPT technology, providing an opportunity to analyze and optimize wireless sensor nodes' spatial distribution to increase the received power.

Performance analysis of wireless power transfer using series-to-series topology

Wireless power transfer (WPT) is a technology used to transmit power using air as it medium of transfer. The function of the WPT is similar to a transformer. The power provided on the primary side will be transferred through air to the secondary side. The performance of the WPT is crucially depends on the air gap length, 𝛿 that separates primary and secondary side. In this paper discusses the performance of WPT using series-to-series topology. The performance of the WPT was estimated using finite element analysis (FEA). During the study, focus was given to effect of turn ratio, a, air gap length, 𝛿 and capacitor value at primary Cp, and secondary, Cs winding to voltage ratio of the WPT. The air gap length, 𝛿 was set to 1 and 2 mm while the capacitors were set depend on the ratio of primary to secondary winding capacitor, Cp/Cs. The WPT performance also being tested under no-load and loaded operation to observed it effect. As a result, the WPT with turn ratio, a at 0.37, air gap length, 𝛿 at 1 mm and ratio of primary to secondary winding capacitor, Cp/Cs at 0.5 produce the best voltage ratio compared to other settings.

UAV-Aided Dual-User Wireless Power Transfer: 3D Trajectory Design and Energy Optimization.

Unmanned aerial vehicles (UAVs) have been widely considered to enhance the communication coverage, as well as the wireless power transfer (WPT) of energy-constrained communication networks to prolong their lifetime. However, the trajectory design of a UAV in such a system remains a key problem, especially considering the three-dimensional (3D) feature of the UAV. To address this issue, a UAV-assisted dual-user WPT system was investigated in this paper, where a UAV-mounted energy transmitter (ET) flies in the air to broadcast wireless energy to charge the energy receivers (ERs) on the ground. By optimizing the UAV's 3D trajectory toward a balanced tradeoff between energy consumption and WPT performance, the energy harvested by all ERs during a given mission period was maximized. The above goal was achieved through the following detailed designs. On the one hand, on the basis of previous research results, there is a one-to-one correspondence between the UAV's abscissa and height, so only the relationship between the height and time was focused on in this work to obtain the UAV's optimal 3D trajectory. On the other hand, the idea of calculus was employed to calculate the total harvested energy, leading to the proposed high-efficiency trajectory design. Finally, the simulation results demonstrated that this contribution is capable of enhancing the energy supply by carefully designing the 3D trajectory of the UAV, compared to its conventional counterpart. In general, the above-mentioned contribution could be a promising way for UAV-aided WPT in the future Internet of Things (IoT) and wireless sensor networks (WSNs).

A Systematic Method for Efficient Wireless Powering to Implantable Biomedical Devices

Wireless power transfer (WPT) technology has played a vital role in the rapid development of biomedical devices. While several single methods to improve WPT efficiency have been reported, the lack of integrality in these single methods limits the effect of the improvements. In this investigation, we analyze the physical process of a typical WPT scenario and find that the high propagation loss consisting of in-tissue attenuation and interface reflection degrades the WPT performance. A systematic method to comprehensively improve WPT efficiency is then proposed. Specifically, a Fresnel zone plate (FZP) is applied against the attenuation of inner biological tissue, and a practical air layer-artificial matching layer (AL-AML) is applied to decrease the reflection on the surface of biological tissue. According to a simulation of possible analytical models, the efficiency is significantly improved when using the proposed method. In an experiment with an implant depth of 20 mm, the proposed systematic method is found to enhance maximum relative received power by 12 dB, with an almost 15-fold increase in efficiency over the conventional system with just a transmitter (Tx) and a receiver (Rx). It is also verified that the improvement in efficiency is greater in the systematic method than in single methods. Also, various misalignment tolerances between the proposed structures and the Rx are determined from the coupling strength of the proposed WPT system. The results of this investigation show the potential of the proposed systematic method for further improvements in WPT efficiency.

A Comprehensive Analysis, Design, and Experimental Evaluation of Single-Loop Polygonal Slotted RF Resonators and WPT Systems

A thorough analysis of slotted ground plane (SGP)-based resonators designed for wireless power transfer (WPT) applications is reported in this paper. For the first time, some new findings that relate a resonator and WPT performance metrics to the slot shape, quality factor (Q), and radiation loss are presented in a very comprehensive manner. As a case study, a single-loop polygonal shape was considered to carry out all analyses and investigations. It has been identified that the slot shape has no impact on the performance of resonators and, hence, developed WPT. Instead, the performance is hugely dependent on Q of resonators regulated by the chosen slot area. These findings allow the conceptualization of systematic analysis of WPT systems and the development of design schemes that are readily realizable, and they also enable significant improvement in power transfer efficiency (PTE). The developed prototypes conforming to the industrial, scientific, and medical frequency bands show an enhancement in PTE to the extent of 11% during the measurements. The proposed analysis and design approach are very important steps in advancing state-of-the-art radio-frequency WPTs. In essence, this has the potential to reinvigorate the stagnated SGP-based WPT systems so as to facilitate the requirements of low-power applications.

Opportunities and Challenges for Wireless Power Transfer System

"In truth, WPT has at least 30 years of history with the term "IPT," using the same fundamental tenet that has already been established. The development of WPT technology has recently accelerated, with transmission distances at the kilowatt power level ranging from a few millimeters up to several hundred millimeters and a point loading efficiency of more than 90%, which applies to both static and dynamic charging environments. Due to this, WPT is particularly appealing for electric vehicles (EVs). However, the performance of wireless power transfer (WPT) systems in various WPT applications remains a significant design challenge. While the use of plug-in electric vehicles (PEVs) is growing, a technological advance is needed to address battery-related flaws. Even if battery technology is improving, the key growth barriers for EVs will continue to be price, dimensions, weight, delayed charge features, and low energy density. Additionally, many customers may not embrace PEVs as their preferred choice due to concerns about price. Dynamic wireless power transfer (DWPT)-enabled EVs have been offered as a solution to battery-related restrictions. The dynamic EV charging concept should be implemented using a WPT-capable infrastructure. As less energy storage is needed for operating the car wirelessly while driving, a battery pack can be lighter. WPT fixed charging refers to wirelessly charging the EV while it is parked, which is less complex in terms of design than dynamic WPT. In contrast to plug-in EVs, ordinary WPT does not extend the driving range of the vehicle. This chapter discusses cutting-edge WPT technology for future transportation and introduces performance indices for the WPT system."

Optimal transmit beamforming for near-field integrated sensing and wireless power transfer systems

The integrated sensing and wireless power transfer (ISWPT) technology, in which the radar sensing and wireless power transfer functionalities are implemented using the same hardware platform, has been recently proposed. In this paper, we consider a near-field ISWPT system where one hybrid transmitter deploys extremely large-scale antenna arrays, and multiple energy receivers are located in the near-field region of the transmitter. Under such a new scenario, we study radar sensing and wireless power transfer performance trade-offs by optimizing the transmit beamforming vectors. In particular, we consider the transmit beampattern matching and max-min beampattern gain design metrics. For each radar performance metric, we aim to achieve the best performance of radar sensing, while guaranteeing the requirement of wireless power transfer. The corresponding beamforming design problems are non-convex, and the semi-definite relaxation (SDR) approach is applied to solve them globally optimally. Finally, numerical results verify the effectiveness of our proposed solutions.

Anti-offset performance optimization of coupling coils in wireless power transfer system based on genetic algorithm

With the popularity of electric vehicles (EVs), the application of wireless power transfer (WPT) in EVs has attracted more and more attention. The coupling coil is the key component to realize the stable transmission of electric energy, but in the process of wireless charging, the position of the primary and secondary coils may be misaligned, resulting in the change of mutual inductance and the instability of output current and power. Therefore, the study of the structure of the coupling coil is helpful to improve the transmission performance of WPT. In order to improve the anti-offset ability of the coupling coil, a DS (Double tangent semicircle) coil model based on the DD (Double D) coil is proposed in this paper, which can improve the pick-up ability and anti-offset ability of the receiver coil. Through theoretical analysis, genetic algorithm (GA) optimization, simulation analysis and experiments, it is verified that DS coil is better than DD coil in horizontal offset state and rotary offset state. At the same time, the experiments show when the rotation angle is in the range of −45° to 45° and 135° to 225°, that the current at the receiving end remains stable, and the maximum change rate is only 0.3%. This paper is of great significance to the optimal design of WPT coupling coil.

Coil material and magnetic shielding methods for efficient wireless power transfer system for biomedical implant application

In this paper, a passive shielding method is presented to minimize the magnetic field around the transmitting (Tx) and receiving (Rx) coil of wireless power transfer (WPT) system for biomedical implant application. Different conductive materials for coil construction, as well as dielectric materials for shielding, are being considered to improve WPT performance. Several cases of WPT coils have been examined using the simulation approach at 800 kHz and 6.78 MHz in the existence of a pacemaker casing with and without a magnetic shield. According to simulated results, it is found that high conductivity coils and high permeability shield materials are excellent materials for increasing the WPT system's efficiency. The results of the simulation method and physical measurement in Lab are validated using an analytical method. The efficiency obtained by using simulation method is very close to that obtained using the analytical method. The voltage gain obtained using an analytical and a simulation method at 800 kHz and 6.78 MHz is very close to the actual measurement in the lab. It is found that the WPT efficiency at 6.78 MHz is higher as compare to 800 kHz.

A Circularly Polarized Implantable Rectenna for Microwave Wireless Power Transfer.

A circularly polarized implantable antenna integrated with a voltage-doubled rectifier (abbr., rectenna) is investigated for microwave wireless power transfer in the industrial, scientific, and medical (ISM) band of 2.4–2.48 GHz. The proposed antenna is miniaturized with the dimensions of 7.5 mm × 7.5 mm × 1.27 mm by etching four C-shaped open slots on the patch. A rectangular slot truncated diagonally is cut to improve the circular polarization performance of the antenna. The simulated impedance bandwidth in a three-layer phantom is 30.4% (1.9–2.58 GHz) with |S11| below −10 dB, and the 3-dB axial-ratio bandwidth is 16.9% (2.17–2.57 GHz). Furthermore, a voltage-doubled rectifier circuit that converts RF power to DC power is designed on the back of the antenna. The simulated RF-to-DC conversion efficiency can be up to 45% at the input power of 0 dBm. The proposed rectenna was fabricated and measured in fresh pork to verify the simulated results and evaluate the performance of wireless power transfer.

RC Filter Design for Wireless Power Transfer: A Fourier Series Approach

In this letter, we study the impact of the low-pass resistor-capacitor (RC) filter on radio frequency (RF) wireless power transfer (WPT). The RC filter influences both the RF bandwidth by removing the harmonics as well as the ripple voltage at the output of the rectifier. In particular, a large (small) RC time constant, reduces (increases) the ripple but decreases (enhances) the direct-current (DC) component. By following a Fourier series approach, we obtain closed-form expressions for the rectifier's output voltage, the RC filter's output as well as the DC voltage. Our analytical framework provides a complete characterization of the RC filter's impact on the WPT performance. We show that this complete and tractable analytical framework is suitable for the proper design of the RC filter in WPT systems.

Multi-Dimensional Lorenz-Based Chaotic Waveforms for Wireless Power Transfer

In this paper, we investigate multi-dimensional chaotic signals with respect to wireless power transfer (WPT). Specifically, we analyze a multi-dimensional Lorenz-based chaotic signal under a WPT framework. By taking into account the nonlinearities of the energy harvesting process, closed-form analytical expressions for the average harvested energy are derived. Moreover, the practical limitations of the high power amplifier (HPA) at the transmitter are also taken into consideration. We interestingly observe that for these types of signals, high peak-to-average-power-ratio (PAPR) is not the only criterion for obtaining enhanced WPT. We demonstrate that while the HPA imperfections do not significantly affect the signal PAPR, it notably degrades the energy transfer performance. As the proposed framework is general, we also demonstrate its application with respect to a Henon signal based WPT. Finally we compare Lorenz and Henon signals with the conventional multisine waveforms in terms of WPT performance.

A performance predictor of beamforming versus time-reversal based far-field wireless power transfer from linear array

For far-field wireless power transfer (WPT) in a complex propagation environment, a time-reversal (TR) based WPT that can overcome the drawbacks of conventional beamforming (BF) by taking advantage of multipath has been recently proposed. However, due to the WPT performance of BF and TR depending on the complexity of the propagation environment, the performance prediction between BF versus TR would be required. We present a detailed and generalized analysis of the recently proposed performance metric referred to as the peak received power ratio (PRPR) for linear array-based WPT. Here, the effectiveness of PRPR is verified via measurement for free space and indoor scenarios. The results demonstrate that PRPR is directly related to the complexity of the propagation environment and the corresponding power transmission capability of BF and TR. That is, the higher the complexity, the greater the value of PRPR and TR outperforms BF with higher peak power given the same average transmit power and vice versa. The mode decision between BF and TR based on PRPR potentially promises efficient far-field WPT even in a dynamic propagation environment.

A multimode metamaterial for a compact and robust dualband wireless power transfer system

To release more flexibility for users to charge their portable devices, researchers have increasingly developed compact wireless power transfer (WPT) systems in recent years. Also, a dual-band WPT system is proposed to transfer power and signal simultaneously, enriching the system’s functionality. Moreover, a stacked metasurface has recently been proposed for a single band near-field WPT system. In this study, a novel multimode self-resonance-enhanced wideband metasurface is proposed for a robust dual-band WPT system, which significantly improves the performance of both bands. The size of the transmitter (Tx) and the receiver (Rx) are both 15 mm × 15 mm only. The proposed metasurface can improve efficiency from 0.04 up to 39% in the best case. The measured figure of merit (FoM) is 2.09 at 390 MHz and 2.16 at 770 MHz, respectively, in the balanced mode. Especially, the FoM can reach up to 4.34 in the lower mode. Compared to the previous state-of-the-art for similar applications, the WPT performance has significantly been improved.

Multi-dimensional Lorenz-Based Chaotic Waveforms for Wireless Power Transfer

In this paper, we investigate multi-dimensional chaotic signals with respect to wireless power transfer (WPT). Specifically, we analyze a multi-dimensional Lorenz-based chaotic signal under a WPT framework. By taking into account the nonlinearities of the energy harvesting process, closed-form analytical expressions for the average harvested energy are derived. Moreover, the practical limitations of the high power amplifier (HPA) at the transmitter are also taken into consideration. We interestingly observe that for these types of signals, high peak-to-average-power-ratio (PAPR) is not the only criterion for obtaining enhanced WPT. We demonstrate that while the HPA imperfections do not significantly affect the signal PAPR, it notably degrades the energy transfer performance. As the proposed framework is general, we also demonstrate its application with respect to a Henon signal based WPT. Finally we compare Lorenz and Henon signals with the conventional multisine waveforms in terms of WPT performance.

Interference Alignment Inspired Opportunistic Communications in Multi-Cluster MIMO Networks with Wireless Power Transfer

In this work, we jointly investigate the issues of node scheduling and transceiver design in a sensor network with multiple clusters, which is endowed with simultaneous wireless information and power transfer. In each cluster of the observed network, S out of N nodes are picked, each of which is capable of performing information transmission (IT) via uplink communications. As for the remaining idle nodes, they can harvest energy from radio-frequency signals around their ambient wireless environments. Aiming to boost the intra-cluster performance, we advocate an interference alignment enabled opportunistic communication (IAOC) scheme. This scheme can yield better tradeoffs between IT and wireless power transfer (WPT). With the aid of IAOC scheme, the signal projected onto the direction of the receive combining vector is adopted as the accurate measurement of effective signal strength, and then the high-efficiency scheduling metric for each node can be accordingly obtained. Additionally, an algorithm, based on alternative optimization and dedicated for transceiver design, is also put forward, which is able to promote the achievable sum rate performance as well as the total harvested power. Our simulation results verify the effectiveness of the designed IAOC scheme in terms of improving the performance of IT and WPT in multi-cluster scenarios.

An Advanced Inductively Coupled Wireless Charging System For Electric Vehicle Applications

Any day today, the globe transitions to electrified transportation, reducing non-renewable fossil fuel pollutant emissions. Electromagnetic energy is transferred from the power source to the electrical charge without interconnection wires and the operation is carried out in every device. Electric cars are seen in the potential mobility area to be substitutions for the vehicles propelled by oil fueled internal combustion engine. In this project wireless charging technologies are examined using the inductive coupling approach. Numerous factors, including magnetic flow, inductance of the resonant bob, determine the performance of wireless power transfer and mutual inductance. The paper focuses in particular on static (stationary) charge, while dynamic loading (loading during driving) involves a dramatically different method. The Multi-Load method is modelled and the efficiency expression for each charge is determined with a different resonant frequency.

Wireless power transfer system for angled concave conditions utilizing quasi-bowl-shaped couplers

Wireless power transfer (WPT) is favored by consumers due to its convenience, safety, and flexible layout. Circular and rectangular coils are the most common coil structures in WPT systems. However, they are not suitable for installation conditions with angled groove areas such as railways, conveyors, and so on. To fully utilize installation space and to improve transfer efficiency, this paper has proposed a quasi-bowl-shaped (QBS) magnetic coupler, which can suitably fit on angled grooves. First, a QBS coupler model was presented. Second, formulas of its spatial magnetic field density were derived. Third, the influences of the bending distance and bending angle on the coupler coefficient were analyzed. Fourth, five magnetic core types were presented and analyzed for coupler optimization. Finally, QBS WPT performances were tested on a newly built experiment platform. Experimental results show that the QBS coupler can realize a constant transfer efficiency of 92.36% at an axial distance of 6 cm, and it can realize a constant transfer efficiency of 84.17% at an axial distance of 10 cm.