Wireless Power Transfer Applications Research Articles

Demonstration of topological wireless power transfer

Recent advances in non-radiative wireless power transfer (WPT) technique essentially relying on magnetic resonance and near-field coupling have successfully enabled a wide range of applications. However, WPT systems based on double resonators are severely limited to short- or mid-range distance, due to the deteriorating efficiency and power with long transfer distance. WPT systems based on multi-relay resonators can overcome this problem, which, however, suffer from sensitivity to perturbations and fabrication imperfections. Here, we experimentally demonstrate a concept of topological wireless power transfer (TWPT), where energy is transferred efficiently via the near-field coupling between two topological edge states localized at the ends of a one-dimensional radiowave topological insulator. Such a TWPT system can be modelled as a parity-time-symmetric Su-Schrieffer-Heeger (SSH) chain with complex boundary potentials. Besides, the coil configurations are judiciously designed, which significantly suppress the unwanted cross-couplings between nonadjacent coils that could break the chiral symmetry of the SSH chain. By tuning the inter- and intra-cell coupling strengths, we theoretically and experimentally demonstrate high energy transfer efficiency near the exceptional point of the topological edge states, even in the presence of disorder. The combination of topological metamaterials, non-Hermitian physics, and WPT techniques could promise a variety of robust, efficient WPT applications over long distances in electronics, transportation, and industry.

Modelling and improvement of oscillation problem in a double-sided LCC compensation network for electric vehicle wireless power transfer

The double-sided LCC compensation network shows high performances in electric vehicle wireless power transfer (EV WPT) applications owing to its constant output current, low voltage stress and other good characteristics. In order to achieve full power and high-efficiency energy transmission within the specified range of coupling and battery voltage, a controlled rectification scheme became a trend in EVs manufacturers and standards. However, a current oscillation problem emerges in a double-sided LCC system when employing a circulating current control method for the controlled rectifier. This paper proposes a mechanism to understand the oscillation phenomenon caused by the inter-harmonics and a positive feedback scheme. The amplification effect of circuit admittance is believed to be the key cause of the inter-harmonics. Therefore, an oscillation improvement is proposed in this paper by adding an inductor and a capacitor to the secondary LCC network, minimizing the admittance amplification effect. A comprehensive simulation and experimental validations under different rectifier duty cycles, coupling positions and load resistances, confirmed the effectiveness of the proposed method. Interestingly, the optimized system expanded the safe operating region and reduced the oscillating operating points from 18 to 8 out of the 27 possible conditions. • This paper clearly reveals the cause of current oscillation in an EV-WPT system. • Interharmonics were grabbed and analyzed in an LCC-LCC circuit for the first time. • Additional LC is first introduced into the system, suppressing oscillation greatly.

Capacitive Power Transfer System with Double T-type Resonant Network for Mobile Devices Charging/Supply

In the applications of wireless power transfer for mobile devices, the pick-up of the wireless power transfer system often needs to be moved in and moved out. A sudden change in the system structure will cause high transient voltages or currents, which could damage the power electronic device of the capacitive power transfer (CPT). In addition, the standby power of the system will be too high to work after removing the pick-up. A CPT system with double T-type resonant networks has been proposed to address these problems. The steady-state models of the system without the pick-up and normal state conditions of it are established. The relationships between the resonant network parameters are analyzed, and a systematic circuit parameter design method is provided. The proposed CPT topology and the parameter design method have been verified by simulation and experiment. The system not only achieved self-protection under severe load change but also entered standby mode automatically after the pick-up was moved out. Besides, the system is restored to the normal state condition when the pick-up is moved in without additional detection and control circuitry.

Dual-Polarized Wearable Antenna/Rectenna for Full-Duplex and MIMO Simultaneous Wireless Information and Power Transfer (SWIPT)

Owing to the mobility of a wearable antenna and the unpredictable body-centric communications environment, dual-polarization antennas are essential for both communications and energy harvesting. This paper presents a dual-polarized four-port textile antenna/rectenna for wearable simultaneous wireless information and power transfer (SWIPT) applications. The proposed antenna utilizes dual ports for both off-body communication and energy harvesting from horizontal and vertical polarizations. The antenna maintains a 100 MHz bandwidth with an S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> under -10 dB around 2.4 GHz in the presence and absence of the human body, and at least 10 dB small-signal and large-signal isolation between all ports. The antenna maintains a 70-88% measured total efficiency and 8.4-9.6 dBi gain for various on-phantom positions across both communication ports. The measured mutual coupling is under -10 dB between co-polarized rectenna/antenna ports, and under -16 dB between orthogonally-polarized ports. A high RF to DC peak power conversion efficiency of over 70% (±5%) is achieved with a broadside harvesting pattern. Based on the proposed antenna's performance, SWIPT microstrip antennas can be adopted for both full-duplex and MIMO applications, significantly reducing the complexity of future battery-free networks for both wearable and non-wearable applications.

Bessel–Gauss Beam Launchers for Wireless Power Transfer

In this work, we study the use of Bessel–Gauss beam launchers for wireless power transfer (WPT) applications. The power transfer efficiency between two radiating apertures is investigated in the radiative near field. A spectral Green’s function approach is used to derive the power efficiency under a simultaneous conjugate impedance match. The transverse electromagnetic (TEM) mode of a coaxial cable, as well as Bessel beam (BB) and Bessel–Gauss beam (BGB) field distributions, are considered as aperture distributions. Numerical results demonstrate that a BGB field distribution is the optimal choice for WPT due to its limited spectrum and reduced diffraction of the radiated beam. We synthesized a Bessel–Gauss launcher that exhibits power efficiency exceeding 50% for distances larger than $30\lambda $ . These results show that non-diffracting beams can pave the way toward efficient near-field WPT systems with extended operating ranges.

Design of Unlicensed Dual Band Quasi-Yagi Antenna Using Semi-Bowtie for Indoor Wireless Power Transfer Application

This paper focuses on antenna for harvesting energy from a dedicated transmitter. The potential novel quasi-Yagi antenna with semi-bowtie driven element can be used as part of rectenna due to its characteristic of having directional properties and considerably wide bandwidth covering the Industrial, Scientific, and Medical (ISM) band consists of 863-870 MHz band and 902-928 MHz band. The modified quasi-Yagi is designed on a low-cost FR4 substrate with a physical size of 130 x 100 mm2 equivalent to 0.35λo x 0.27λo. The antenna has a peak directivity of 2.7 dBi and peak gain of 2.2 dBi in the targeted unlicensed bands with bandwidth of 14.4% for the range between 0.820-0.944 GHz. The shift in the resonant frequency is achieved by varying the phase shifter length and maintaining the same width for consistency. The antenna's operating frequency range varies between 0.8 GHz until 1 GHz which is less than 1 GHz by using semi-bowtie as driven element with a specific 7.22⸰ flare angle. The phase shift arm length of the antenna has been studied and simulated by using Computer Simulation Technology (CST) software and verified by using analytical equations. The simulated results are in accordance with the results obtained using analytical method. The same antenna geometry except variation in phase shifter arm length has been used throughout the study for consistency. The proposed antenna is promising to be used as part of rectenna for powering power management chip such as BQ25570 in a smart house environment operating at the indicated ISM bands.

Second Harmonic Exploitation for High-Efficiency Wireless Power Transfer Using Duplexing Rectenna

In this article, a novel duplexing rectenna with harmonic feedback capability is proposed for efficient wireless power transfer (WPT) applications. The proposed duplexing rectenna can harvest the incoming radio frequency (RF) energy efficiently and also make use of an inherent harmonic signal, which is sent back to the RF transmitter (Tx) for positioning in order to guide the radiation patterns from Tx antenna array for optimum WPT. A novel duplexing dipole antenna is designed based on the top loading and capacitive gap effects. It is used to receive RF power at fundamental frequency 0.915 GHz and transmit the second harmonic signals at 1.83 GHz as a feedback. Experimental validation of a complete WPT system with beam-scanning capability has been carried out. It is shown that the fabricated rectifier has realized a maximum RF-dc conversion efficiency of 71% (at 15-dBm input power) and a measured peak second harmonic power of −1 dBm. Thus, the proposed duplexing rectenna can form a closed-loop system by providing its location information for efficient WPT applications.

An OOK Chirp Spread Spectrum Backscatter Communication System for Wireless Power Transfer Applications

In this work, a general-purpose wireless energy receiving unit with improved backscatter (BS) communications capabilities assisted by far-field wireless power transfer (WPT) techniques is proposed. The unit employs an auxiliary RF-to-dc converter circuit which is used to simultaneously power and tune a low-power voltage controlled oscillator (VCO). By doing so, a relation between its frequency of oscillation and the instantaneous available RF input power is established. It is shown that by adding a small amplitude modulation to the wireless power carrier, the device can generate a linear frequency modulated signal which is used to provide low-power and long-range ON–OFF keying (OOK) chirp spread spectrum (CSS) BS communications. Experimental validation in real scenarios is provided, showing its superiority against the well-known conventional BS amplitude shift-keying (ASK) modulation scheme. Moreover, contrary to other designs, it is demonstrated that the proposed design does not need a dedicated processing unit to generate the required baseband signals, allowing to save power and complexity.

Space-Vector Based Excitation of a Bipolar Transmitter for Wireless Power Transfer Applications

A space-vector (SV) based excitation method for wireless power transfer systems with a bipolar transmitter is introduced in this article. Unlike traditional bipolar excitation techniques that rely on fixed transmitter current distributions, this SV approach provides an elegant analytical method of redistributing a greater magnitude of current to the transmitter coil, which is closer to a misaligned receiver. This method is shown to require a smaller transmitter current vector magnitude for a required output power compared to all other bipolar coil excitation schemes over a broad range of receiver misalignments, thereby reducing conduction losses within the system. Additionally, the gradual redistribution of transmitter current as a function of receiver misalignment achieved by the SV method causes it to be less influenced by errors in receiver position sensing compared to conventional methods. Experimental results shows that the proposed method in conjunction with single coil operation at extreme misalignments was able to achieve a coil efficiency profile with minimal variation due to misalignment (93.2% at perfect alignment to 92.7% at a misalignment of 20 cm, for 2 kW power transfer into a 200 V battery load.)

Trends in Wireless Power Transfer: WPT Technology for Energy Harvesting, Mllimeter-Wave/THz Rectennas, MIMO-WPT, and Advances in Near-Field WPT Applications

Wireless power transfer (WPT) technology gained wide recognition over a decade ago following a resonance coupling WPT study conducted by a group at the Massachusetts Institute of Technology (MIT) [1]. WPT was originally proposed by Nicola Tesla at the end of the 19th century [2] based on a study of near-field inductive-coupling WPT and far-field WPT via radio waves. The first patent involving inductive WPT as a wireless charging system was granted in 1894 for the earliest electric vehicle (EV) [3]. Inductive WPT technology is based on a transformer and was commercialized as a wireless charger for an electric toothbrush in 1981 by Panasonic Corporation and as a power source for an integrated circuit (IC) card in 1995 by Sony Corporation. Daifuku Corporation produces many systems for material handling in stockroom and clean room applications [4]. From the 1970s through the 1990s, several research projects on wireless chargers for EVs were undertaken in New Zealand, the United States, and Europe. Advances in microwave technology led to improvements in WPT via radio waves, with many field experiments on microwave power transfer (MPT) conducted from the 1960s through the 1970s by William C. Brown in the United States [4]. The commercialization of RFID at the 920-MHz band started recently, and the proliferation of mobile rechargeable batteries since 2010 accentuates the need for a wireless charger in, e.g., mobile phones, EVs, and sensors for the Internet of Things (IoT).

Analysis and design of a S/PS compensated IPT system with constant current output

Load-independent constant current (CC) output with high-system efficiency is required in many cases of Wireless power transfer (WPT) applications. However, the existing topologies with CC output are hard to achieve both simple structure and enough design freedom. In this study, the series/parallel–series (S/PS) topology, which has three compensation capacitors, is presented to achieve CC output. The constant output current of the proposed S/PS topology is free from the constraint of the coils' self-inductance of the loosely coupled transformer (LCT). A thorough analysis of the proposed S/PS topology that implements CC and ZPA is provided. Besides, ZVS can also be obtained by reasonably setting the value of compensation capacitors. An experimental prototype with 50 V input voltage and 3 A output current is fabricated to validate the practicability and rationality of the proposed topology, and 92.18% power transfer efficiency is achieved. Furthermore, a design example with 2 A output current and the corresponding experimental results are provided to verify that the CC output of the proposed S/PS topology is free from the constraint of the LCT parameters. Finally, a comprehensive comparison with several existing topologies for CC output is conducted to reveal the advantages of the proposed S/PS topology.

Multiband asymmetric radio frequency to direct current converter circuit for wireless power transfer

AbstractThis article presents the multiband asymmetric radio frequency (RF) to direct current (DC) converter circuit for the wireless power transfer (WPT) applications. The proposed circuit is composed of a power divider, novel asymmetric multiband matching circuit and RF Schottky diode quadrupler voltage rectifier circuit. Unlike the conventional narrow band quadrupler using two Greinacher cells with opposite polarities, the proposed circuit aims to cover the multifrequency bands, which are the cell phone 1.8–2.1 GHz, the industrial, scientific, and medical (ISM) bands 2.4–2.5 GHz and 5.725–5.875 GHz. The interested RF input power range of −10 to 20 dBm for the WPT application is focused. The measured RF‐to‐DC conversion efficiency (η) of 50–65% at 1.8–2.1 GHz, 65% at 2.45 GHz and 16% at 5.8 GHz are obtained at 10 dBm optimal input power.

Multiphysics modeling of ultrasonic elastic wave attenuation for wireless power transfer including viscoelasticity and acoustic emission

A COMSOL Multiphysics model is developed to computationally predict power attenuation in an ultrasonic elastic wave wireless power transfer application. This model invokes the complete equations of elastodynamics, coupled electric field and piezoelectric elastic response, and coupled transmitter and receiver circuits. Structural damping is captured in the adhesive layers by treating them as isotropic viscoelastic media with complex valued elastic moduli. Structural damping is captured in the parent structure by modeling the acoustic emission from the exposed surfaces which couples the displacement field of the parent structure with the surrounding fluid medium. This model quantitatively predicts the electrical power transduction efficiency to within 5% over a range of excitation frequencies. This model is also able to predict the voltage gain to between 10 and 25% over the same range of excitation frequencies.

A High Power, High Quality Single-Phase AC-DC Converter for Wireless Power Transfer Applications

A High Power, High Quality Single-Phase AC-DC Converter for Wireless Power Transfer Applications

A wide input power range rectenna for energy harvesting and wireless power transfer applications

This article describes a novel rectifying-antenna design with extended input power range operating at 2.4 GHz for both ambient wireless energy harvesting and wireless power transmission (WPT) systems. The rectenna consists of a 2 × 2 fractal antenna array and a rectifier circuit with a high-power conversion efficiency (PCE) in a wide input power range. This circuit contains two conversion stages based on two different Schottky diodes, and a third stage that dissipates the unconverted input power, which can disturb the harvesting process. These three stages are controlled by a power management block based on circulators, that direct the input power to the adequate stage according to its power range. A prototype of the proposed harvesting system is fabricated and experimentally validated. The measurement results confirm the wide input power range behavior of the designed rectenna with a relatively constant and high PCE (between 58% and 67%) for a power density ranging from 4 to 252 μW/cm2. The proposed solution can be successfully used for both ambient energy harvesting and WPT systems.

Misalignment Resilient Anchor-Shaped Antennas in Near-Field Wireless Power Transfer Using Electric and Magnetic Coupling Modes

In this article, we propose a new antenna geometry for near-field magnetoelectric wireless power transfer (ME-WPT) application, where the antenna geometry is found to be resilient to misalignment between the receiving and the transmitting antennas. The proposed geometry is simple to fabricate and is planar, and therefore it can be easily integrated with various platforms suitable for wearable applications. The proposed structure is demonstrated to show improved WPT efficiency under different forms of misalignment between the transmitting and receiving antennas by the virtue of miniaturization and the fringing fields. Specifically, a central bar structure is added in the traditional loop antenna to provide dipole-like and miniaturized performance. Concurrently, a discontinuity in the loop is introduced to enable fringing fields beyond the aperture of the antenna. Investigations are conducted to conclude that a superiority in the performance is associated with these fringing fields. Design-optimization, simulation, and measurement investigations are conducted to estimate the WPT performance under various forms of misalignment. Notably, the proposed structure shows an increase as high as 65% in power transfer efficiency within the range of misalignment considered in this work.

Self-Resonant Antisymmetric Planar Coil for Compact Inductive Power Transfer System Avoiding Compensation Circuits

Compensation circuits, the unavoidable components of the traditional inductive power transfer (IPT) systems for high efficiency, not only increase the circuit complexity, but also reduce the system reliability. Self-resonant coils are promising in capacitorless IPT systems. A high-efficiency novel antisymmetric planar coil (APC) is proposed to improve the performance of self-resonant coils. The APC consists of two antisymmetric planar windings that are arranged in two parallel layers, and exhibits an intrinsic parasitic series capacitor. Possessing the simplest configuration, the APCs IPT system is only composed of two APCs, an ac source and a load. Based on analysis and simulations, the design guidelines for developing transmitting and receiving APCs according to the maximum power transfer principle and the maximum energy efficiency principle with given voltage transfer ratio are derived, respectively. The novel APC, the corresponding compact IPT system and the design guidelines are validated by design examples with experimental tests and a demonstration. Avoiding the compensation circuits, the APCs IPT system has compact configuration, high reliability, and proves to be a good candidate in wireless power transfer applications.

A Universal Optimal Drain–Source Voltage Tracking Scheme for Synchronous Resonant Rectifiers in Megahertz Wireless Power Transfer Applications

For wireless power transfer (WPT) in mobile applications, the receiving side is usually embedded inside the devices, which makes the heating issue quite challenging, especially at high operating frequency (such as 6.78 MHz) and high power levels. High-frequency synchronous resonant rectification is expected to significantly reduce the power loss on the receiving side and thus improve the rectifier power density. This article proposes a universal optimal drain–source voltage (ODSV) tracking scheme for synchronous resonant rectifier in megahertz (MHz) WPT applications. The ODSV tracking enables the switches in the synchronous rectifiers work at the same switching operation with that of the diodes in the passive rectifiers. Thus, the soft-switching operation can be maintained with minimized body-diode conduction. A tracking algorithm is then developed to adaptively achieve the optimal operation of the synchronous rectifier under varying loading conditions. Finally, the proposed ODSV tracking scheme is implemented in a GaN-based Class E full-wave synchronous rectifier and tested in an experimental 6.78-MHz WPT system. A dc–dc efficiency of 91.6% is achieved under the output power of 120 W. The efficiency of the synchronous rectifier is 97.0% and the rectifier power density can be as high as 1212 W/in $^{3}$ .

Rectennas for Radio-Frequency Energy Harvesting and Wireless Power Transfer: A Review of Antenna Design [Antenna Applications Corner

Radio-frequency (RF) energy harvesting (RFEH) and radiative wireless power transfer (WPT) have attracted significant interest as methods of enabling battery-free sustainable wireless networks. Rectifying antennas (rectennas) are the cornerstone of WPT and RFEH systems and critically affect the amount of dc power delivered to the load. The antenna element of the rectenna directly impacts the radiation-to-ac harvesting efficiency, which can vary the harvested power by orders of magnitude. In this article, antenna designs employed in WPT and ambient RFEH applications are reviewed. Reported rectennas are categorized based on two main criteria: the antenna-rectifier impedance bandwidth and the antenna's radiation properties. For each criterion, the figure of merit (FoM) is identified for different applications and reviewed comparatively.

On the Design of Planar Arrays of Nonresonant Coils for Tunable Wireless Power Transfer Applications

In this article, we introduce a novel array-based system for inductive wireless power transfer (WPT) applications and a procedure for its design, which can be interpreted as a generalization of the traditional three-coil systems where the intermediate passive resonant coil (i.e., the transmitter) is replaced with an array of nonresonant concentric loops. We demonstrate that the new WPT array system provides flexibility with respect to the characteristic parameters of the inductive link (i.e., efficiency and gain), thus allowing for their optimal tradeoff depending on the specific WPT application: this is achieved by controlling the current amplitude flowing in each element of the array through the addition of an appropriately selected reactive load. Furthermore, we demonstrate that it is possible to obtain, with the WPT array, focused magnetic field distributions, leading to a potential reduction in the receiver dimensions. Such configuration can be made effectively equivalent to a traditional three-coil system in terms of physical dimensions and performance, through the addition of an appropriate reactance to each loop of the array. To demonstrate the validity and usefulness of the proposed system and design procedure, we first performed extensive numerical simulations of a traditional three-coil system and compared its performance with different array configurations. We then fabricated and experimentally characterized several prototypes, observing an excellent agreement between the measurements and simulations. The innovative features of the proposed design can be extremely useful in many WPT applications requiring a fine optimization in efficiency, gain, and field distribution.