Wireless Power Transfer Applications Research Articles

Adaptive Wireless Power Transfer via Resonant Laser Beam Over Large Dynamic Range

Wireless power transfer (WPT) via resonant laser beam from a spatially-distributed laser resonator not only benefits the instinct safety, but also has important potential of adaptive operation without positioning and aiming when retroreflectors are used to enable the alignment-free operation of the laser. Despite the intense theoretical modeling and experimental efforts with different laser schemes, the adaptive resonant beam WPT across large dynamic range -including both working distance and field of view (FoV) -has never been demonstrated, due to the absence of true alignment-free laser. In this work, we summarized the requirements on the dynamic range and discussed the optimization criteria of dynamic range and laser safety, including the telescope in the laser resonator, the resonator stability, coupled-resonator scheme, and influences of the optical aberrations. The analysis indicated that loss induced by optical aberrations is the main issue limits the dynamic range. In the experiment, alignment-free laser with large dynamic range for WPT application was demonstrated with improved resonator design and optical design to compensate the aberrations. Efficient multiwatt optical output was obtained across a working distance of 1-5 m, a receiver FoV of ±30∘, and a transmitter FoV of 4.6∘; and over 1.3 W electrical output was obtained via an InGaAs photovoltaic cell, with DC-DC WPT efficiency being 4%. Our work proved the feasibility of large-dynamic-range alignment-free laser with distributed-resonator, which paves the way for practical resonant beam charging and communication applications based on it for the internet of things devices.

Wearable Directional Button Antenna for On-Body Wireless Power Transfer

For the future application of wireless power transfer on the human body, a wearable directional button antenna, composed of 2×3 artificial magnetic conductor (AMC) cells, is proposed, where the kinetic energy antenna is put on the elbow, which then charges the receiving communication antenna on the upper arm. The radiator of the button antenna is a monopole antenna, which is top-loaded by two cylindrical substrates with different radii to achieve a low profile, and it is fed by the microstrip line made by textiles, including 100% cotton substrate and conductive textile. The AMC cells are put close to the feeding microstrip line in order to realize directional radiation to the other side. Meanwhile, a real human arm model of a Chinese women is built to accurately analyze the corresponding wave propagations. Consequently, two identical antenna prototypes are fabricated, and the corresponding measurements are implemented, where an on-arm approximate measurement method for the radiation pattern is proposed. The measurements agree well with the simulations. Additionally, the influence of the communication antenna on the kinetic energy antenna and the interactions between the antenna and the arm are analyzed. Finally, the transmission efficiency and the SAR values are investigated.

Leakage Power Canceling Module with a Negative Capacitor for a Circulator’s Isolation

In this study, we developed a leakage power canceling module (LPCM) incorporating a negative capacitor (NCAP). The NCAP provided the circulator with a wide bandwidth, rendering it suitable for retrodirective short-range wireless power transfer applications. The proposed LPCM consisted of a directional coupler, a hybrid coupler, and a low-pass filter network with an NCAP that exhibited the frequency response required to realize leakage power cancellation from the transmitter output to the receiver input. The two couplers were fabricated in an FR4 printed circuit board, and the NCAP was implemented using Samsung LR6LP 65 nm RF CMOS IC technology. The NCAP chip provided a capacitance of -2 pF and consumed a DC voltage and current of 3 V and 13 mA, respectively. The size of the fabricated LPCM was 41 mm × 37 mm. The application of the proposed LPCM was demonstrated with a commercial circulator. The S-parameter measurements indicated that the leakage cancellation was 20‒46 dB at a frequency range of 2.29–2.515 GHz. The bandwidth was defined considering a leakage cancellation of more than 20 dB, and the actual and fractional bandwidths were 222 MHz and 9.25%, respectively.

Novel coil design and analysis for high-power wireless power transfer with enhanced Q-factor

The power transfer efficiency (PTE) is a crucial aspect for effective wireless power transfer (WPT) applications. The quality factor (Q) of the WPT coil plays a critical role in ensuring higher PTE. In this paper, a novel method of improving the Q of a WPT coil is proposed. Resistance reduction techniques are presented which involves variation of the trace pitch, width, and thickness. This approach targets the high AC losses centered in the inner turns, which subsequently results in an increased Q. Numerical analysis with respect to the inductance and resistance models are presented, analyzed, and compared to that of the EM simulation results. To verify the efficacy of the proposed coil structure, a prototype is fabricated where good agreement is achieved between the measured and simulated results. The proposed coil attained a quality factor increment of about 19.24% at 85 kHz in comparison to the conventional one. The proposed technique can be used to optimize planar spiral coils to attain higher Q.

A new capacitive coupler design for wireless capacitive power transfer applications

Capacitive power transfer (CPT) technology has become a promising alternative solution for wireless charging applications. This paper proposes a novel coupler design to form a resonant capacitor by inserting dielectric material between two bent metal plates for each primary and secondary circuit. The main purpose of the proposed coupler is to eliminate the external capacitors and solve the low coupling capacitance for CPT applications. A comparison to the conventional four-plate coupler is presented, which shows specifically higher coupling capacitance, lower required inductance, and lower cost. Finally, the effectiveness of the proposed coupler structure is verified by simulation and experimental results.

A Miniaturized Multi‐Frequency Wide‐Band Leaky Wave Button Antenna for ISM/5G Communications and WBAN Applications

AbstractA low‐profile multi‐frequency leaky wave button antenna for body‐centric communications is presented. A leaky wave antenna loaded with U‐slots (a combination of U‐slots and slits) and tapered slot structures to improve the radiation efficiency, broadside radiation pattern, and widen the steering range is designed. Furthermore, it comprises a whole ground to meet the Specific Absorption Rate standard requirements based on the known standards. The antenna's performances are examined for on and off‐body conditions. For demonstration, a prototype is implemented, and the measurement is performed on the chest. The antenna operates at multi bands of 1.7–3.3 GHz (Industrial, Scientific, and Medical and 5G communication) and 4.15–10 GHz (sub‐6 GHz and X‐band communications). The peak gains of 6.9 and 8.2 dBi were obtained for on and off‐ body conditions, respectively. Furthermore, the antenna offers maximum radiation efficiencies of 89.3% and 99.3% for on‐body and free‐space conditions. The specific absorption rate (SAR) values obtained for body‐centric communications meet the regulation requirements (e.g., on body tissue at 3.2 GHz, it is 0.78 (1 g) and 0.44 (10 g) W/kg). With an overall miniaturized size, the proposed button antenna could be integrated with clothes. In addition, a multi‐wide bandwidth, circularly polarized radiation, a small size, high efficiency and gain, and low SAR values prove that the proposed antenna can be a potential candidate for wireless body area network and simultaneous wireless information and power transfer applications.

Investigation of resonant tank topologies performance in wireless power transfer applications

ABSTRACT Wireless power transfer (WPT) has been developed as a suitable candidate for energy transfer in various applications, recently. Resonant tank is the main passive part of such systems and various topologies are introduced to improve WPT systems performance. Characteristics of these topologies definitely affect system overall performance. Therefore, each topology’s specification and performance indexes should be evaluated and compared to choose a suitable one for a required application. In this paper, the characteristics and behaviour of voltage gain, input admittance and efficiency of well-known compensation topologies are thoroughly investigated for the first time. By calculating the voltage gain sensitivity, some analysis are performed on typical compensation including SS, SP, LCL-S, LCL-P, LCC-S, LCC-P and double-sided LCC under key parameter variations such as load resistance, switching frequency and coupling coefficient. In addition, by introducing a new formula for efficiency, the effect of resonant tank elements on efficiency is studied analytically which has not been performed before. In order to evaluate the theoretical analysis, the performance of all compensation topologies is investigated in MATLAB environment. By employing prototype SS and SP compensated inductive power transfer (IPT) test-bed system, some experimental verification are performed and the results confirm the analytical and numerical simulation findings.

Analysis of Coil-Thickness-Variation Technique for Q-Factor Enhancement of Rectangular Planar Coils

For wireless power transfer (WPT) applications, such as battery charging, the attainment of a high coil quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> ) becomes prudent to ensure a high-power transfer efficiency (PTE). In this article, we demonstrate an effective method to enhance <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> by employing different thicknesses for each trace of the coil. The thickness of the inner turns of the coil, where high alternating current (ac) losses are concentrated, is relatively smaller compared to the outer coil turns. This technique realizes a reduction in the ohmic resistance, thereby increasing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of the coil. Furthermore, we present the analysis on the performance of the conventional coils with the same turn thicknesses compared to the proposed coil. To validate this technique, the prototypes of both the proposed and conventional coil structures are fabricated, where good agreement is achieved between the simulation and measurement results. The proposed coil realizes an increment of about 11.54% in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> compared to the conventional coil.

An Independent Dual-Coil Driving Topology for Wireless Power Transfer

The existing dual-coil driving topology mostly adopts two inverters or additional switching circuit, which increases the cost and size, and the complexity of the wireless power transfer (WPT) system. In this letter, a novel inverter topology with independent dual-coil driving capability is proposed for WPT applications, where the main switch and auxiliary switch can drive two independent coils. Moreover, this topology not only offers wide zero voltage switching range and compact size, but also improves the output power and coil utilization. Meanwhile, a quadruple D square (QDS) coil with uniform magnetic field is discussed with the dual-coil driving topology. The detailed parameters design of the proposed topology is discussed and the QDS coil is compared with other coils in terms of magnetic flux intensity. Finally, a 1MHz and 220W wireless power transfer system is built to verify the proposed topology and coil structure.

Spatial filtering magnetic metasurface for misalignment robustness enhancement in wireless power transfer applications

In this paper, we present the design of spatial filtering magnetic metasurfaces to overcome the efficiency decay arising in misaligned resonant inductive Wireless Power Transfer systems. At first, we describe the analytical framework for the control of currents flowing on a finite-size metasurface, avoiding classical truncation effects on the periphery and opportunely manipulating, at the same time, the spatial magnetic field distribution produced by the closely placed RF driving coil. In order to validate the theoretical approach, we conceive a numerical test case consisting of a WPT system operating at 12 MHz. By performing accurate full-wave simulations, we prove that inducing a uniform current in the metasurface results in a more robust WPT system in terms of misalignment with respect to conventional configurations, also including standard metasurfaces. Therefore, while the use of metasurfaces in WPT systems has been already demonstrated to be beneficial in terms of efficiency enhancement, we confirmed that a proper control of the metasurfaces field filtering response can be advantageous also for the misalignment issue. Notably, the free space wavelength at the operating frequency (12 MHz) is 25 m, whereas the proposed metasurface dimensions are only 0.0024λ × 0.0024λ. Despite the extremely reduced dimensions, the spatial magnetic field distribution produced by the closely placed RF driving coil can be nevertheless opportunely manipulated. Finally, experimental measurements conducted on fabricated prototypes validated the numerical results, demonstrating the effectiveness of the proposed approach. These achievements can be particularly helpful in WPT applications where the position of driving and receiving coils frequently changes, as in consumer devices and biomedical implants.

High-Sensitivity Detection Method for Metal Foreign Objects Based on Frequency Optimization in Wireless Electric Vehicles Charging

Metal foreign objects will not only reduce the output power and efficiency of the wireless power transfer (WPT) system, but also will be heated under the eddy current effect. The method based on the detection coil array has been wildly adopted for foreign object detection (FOD), especially in high-power level WPT applications. However, the problems of low sensitivity or misjudgment still exist which leads to a safety hazard. Therefore, high sensitivity of the foreign object-detection method based on the excitation frequency optimization has been proposed in this paper. Based on the impedance change of the detection coil caused by the foreign object coupling, the frequency characteristics of detection sensitivity were analyzed under the conditions of different self-inductance detection coils. Then, the detection coil was designed and its corresponding optimal excitation frequency was selected to achieve the optimal detection effect to eliminate the area of low detection sensitivity. Finally, an FOD experimental prototype was established to verify the proposed frequency optimization strategy. The results show that the sensitivity of the FOD system is up to 97.56%. With the optimal excitation frequency of 6.22 MHz, as for 1-yuan coin in the center position and corner position of the detection coil, the detection sensitivity is 92.89% and 40.16%, respectively, which is 22.13% and 23.89% higher than that of the excitation frequency is 1 MHz. The improvement of detection sensitivity is helpful to detect accurately and eliminate the detection blind area.

Precise Modeling for Reducing Output Voltage Control Error of RX-Sensorless IPT System

This paper presents RX-Sensorless technologies required in a self-induced type of low power wireless power transfer system. Recently, apart from the fields of smartphone and electrical vehicles which have been arduously studied for application of wireless power transfer, wireless power transfer technologies are being applied to various fields. Among them, there is a very rapidly increasing demand for low power systems in displays, body implant medical devices, drones, electrical kickboards and so on. In order to acquire portability of RX side of low power systems, the most critical factors are power density and efficiency. For this purpose, there have been very much ongoing studies to improve the power density on the RX side. Among various research, most frequently used types of methods involve derivation of output voltage using the physical quantity on the TX side while removing sensors on the RX side. However, in the modeling process to derive output voltage, they fail to properly reflect the parasite components of wireless power transfer and also due to the lack of measures in case of being out of the range of resonance frequency, there tends to be a high error in the output voltage which raises an issue. Therefore, this paper aims to suggest a model which reflects the parasite resistance components and the permeability rate of medium for the TX/RX pads of wireless power transfer systems. By reflecting winding losses and eddy current losses of TX/RX pads to a model, it is possible to reflect the parasite resistance components and using the Neumann formula, it is possible to reflect it to the medium between RX/TX pads. As a result, based on the derived model, it is possible to control the output voltage. Prototypes of hardware are designed and implemented for verifications. According to the computer simulation results and test results, output voltage estimates yield an error in the range of less than or equal to 8% and model-based output voltage control also shows the control range with errors of less than or equal to 5%.

A High Angular Stability, Single-Layer Transmission Linear-to-Circular Polarization Converter for Dual ISM-Band Operation

This paper presents a planar metasurface structure for linear to circular polarization (CP) conversion at the industrial, scientific, and medical bands of 2.4 GHz and 5.8 GHz. The new unit-cell structure consists of two loaded symmetric cross-shaped stubs with a size of 0.26 λ × 0.26 λ in a single thin substrate with a thickness of 0.0064 λ. The design process and parametric study are presented to clarify the operating mechanism for each frequency. The unit-cell element is analyzed and simulated, which exhibits an axial ratio (AR) bandwidth of 15.8% and 12.6% at a 3-dB criterion with the same polarization mode at 2.4 GHz and 5.8 GHz, respectively. The proposed LP-to-CP converter achieves a stable AR bandwidth with an oblique incident angle up to 45°. Moreover, a dual-band linear polarization (LP) antenna is combined with an array of 4 × 4 unit cells to validate the polarization converting ability of the proposed metasurface. The LP-to-CP converter and the antenna are fabricated and measured. The measurement results show that the antenna obtains a good impedance matching and CP waves radiation at 2.33–2.51 GHz and 5.55–5.89 GHz. The integrated antenna with dual-band CP waves radiation is suitable for improving the transmission efficiency in communication and wireless power transfer applications.

Rectifier Circuits for RF Energy Harvesting and Wireless Power Transfer Applications: A Comprehensive Review Based on Operating Conditions

Low-power wireless sensors will play a big role in smart city applications. These sensors require a power supply to function. Batteries are not optimal for such numerous sensor networks because of their limited life and need for regular maintenance; hence, they are not a universal solution. RF energy harvesting (RFEH) and wireless power transfer (WPT) techniques have the potential to be a green and sustainable solution for supplying power to various low-power devices by capturing ambient RF energy. The ubiquitous nature of RF energy makes it available to exploit and reutilize in power wireless sensor nodes, wireless body area networks, wireless charging systems, RFID tags, and the Internet of Things <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> , <xref ref-type="bibr" rid="ref2" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[2]</xref> . <xref ref-type="fig" rid="fig1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Figure 1(a)</xref> displays a conceptual diagram of an RFEH/WPT system. To capture power from free space that is transmitted by the base station, the harvesting node needs a receiving antenna and rectifier to convert the power into dc signals. This dc output is then further utilized to feed a low-power device. <xref ref-type="fig" rid="fig1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Figure 1(b)</xref> shows that at 10-m distance from the cellular tower, a digital batteryless watch was powered by a rectenna operating at 1.8 GHz. This LCD watch (low-power device) required 1.5 V to function and was successfully powered up using the RFEH system <xref ref-type="bibr" rid="ref3" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[3]</xref> .

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.

Applications of Microwaves in Medicine

Advances and updates in medical applications utilizing microwave techniques and technologies are reviewed in this paper. The article aims to provide an overview of enablers for microwave medical applications and their recent progress. The emphasis focuses on the applications of microwaves, in the following order, for 1) signal and data communication for implants and wearables through the human body, 2) electromagnetic energy transfer through tissues, 3) noninvasive, remote or <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> physical and biochemical sensing, and 4) therapeutic purposes by changing tissue properties with controlled thermal effects. For signal and data communication and wireless power transfer, implant and wearable applications are discussed in the categories of pacemakers, endoscopic capsules, brain interfaces, intraocular, cardiac and intracranial pressure sensors, neurostimulators, endoluminal implants, artificial retina, smart lenses, and cochlear implants. For noninvasive sensing, remote vital sign radar, biological cell probing, magnetic resonance and microwave imaging, biochemical, blood glucose, hydration and biomarker sensing applications are introduced. For therapeutic uses, the developments of microwave ablation, balloon angioplasty, and hyperthermia applications are reviewed. The scopes of this article mainly concentrate on the research and development efforts in the past 20 years. Recent review articles on specific topics are cited with accomplishment highlights and trends deliberated. At the end of this article, a brief history of the IEEE Microwave Theory and Techniques Society (MTT-S) Biological Effects and Medical Applications committee and the contributions by its members to the promotion and advancement of microwave technologies in medical fields are chronicled.

A Single-Stage Regulating Voltage-Doubling Rectifier for Wireless Power Transfer

In this letter, a 6.78-MHz single-stage regulating voltage-doubling rectifier is presented for biomedical wireless power transfer (WPT) applications. Derived from a full-wave voltage doubler, a theoretical voltage conversion ratio (VCR) of 2 can be achieved, which benefits the end-to-end voltage gain of a biomedical WPT system with varying link conditions. As a result, a wider WPT operational range and less coil-link loss can be achieved. To avoid efficiency loss due to cascading, the rectifier output is in-situ regulated in a sub-50-mV hysteresis window by pulse-skipping control. To ensure a high power conversion efficiency (PCE), adaptive delay-compensated active diodes are adopted with an offset locking technique. The input/output capacitors of the rectifier are fabricated on-chip, achieving a fully integrated design. The rectifier was fabricated in a 180-nm BCD process, occupying a silicon area of 0.3/2.7 mm2 without/with on-chip capacitors. The measurements show that the rectifier can realize a peak PCE at 90.6% when the output power is 79.8 mW. The PCE and VCR are achieved higher than 86.4% and 1.6, respectively, over a large loading range (from 1 to 40 mA). The rectifier can output a maximum power of 159.2 mW, satisfying most biomedical implants.

Low Frequency Magnetic Metasurface for Wireless Power Transfer Applications: Reducing Losses Effect and Optimizing Loading Condition

Low Frequency Magnetic Metasurface for Wireless Power Transfer Applications: Reducing Losses Effect and Optimizing Loading Condition

Design and Development of High Frequency Inverter for Wireless Power Transfer Application

A number of power electronics converter topologies are implemented as Wireless Power Transfer (WPT) systems applications expand. In these applications, the optimal converter design is essential for handling the high power and frequency operation. In this paper, Simulation &amp; Hardware development of High frequency Inverter with 90KHz frequency with Pulse Width Modulation switching strategy is presented. The inverter topology is simulated in 2021a version MATLAB/Simulink with R and RL loads and its conversion ability is proven through relevant waveforms. Simultaneously designed and developed prototype model of power rating 100watt with Mosfet as switches at output voltage of 230V with R load and analyse the output behaviour of voltage waveforms at various loads. The outcomes show effective enhancements for the proposed design.

Design of Dual ISM Bands Low Power Rectenna for Indoor Wireless Power Transfer Application

The paper concentrates on the design of a dual-band rectenna which consists of a receiving antenna, impedance matching, single-stage voltage doubler rectifier as well as a load. The rectenna is designed using HSMS 280C Schottky diodes as its main component and combined with the lumped elements, microstrip lines as well as quasi-Yagi with semi-bowtie as the driven element. The quasi-Yagi antenna with a semi-bowtie driven element is designed using Computer Simulation Technology (CST) and its Touchstone file is imported into the Advanced Design System (ADS) for simulation with the other components of the rectenna. The rectenna with an input power of −6dBm has an optimal Power Conversion Efficiency (PCE) of 32.1% while receiving a signal from the ISM 0.868GHz band transmitter and 18.8% using the input power of −7dBm at ISM 0.915GHz band. Both PCEs are obtained using 700Ω and 900Ω as load and producing minimum output voltage (Vo) of 0.3V and 0.28V respectively. The rectenna operates in both Industrial, Scientific, and Medical (ISM) 0.868GHz and 0.915GHz bands since both are unlicensed bands. The ISM 0.868GHz band is normally used in Europe while ISM 0.915 GHz band is widely used in the United States as well as Japan. The dual-band rectenna can be used for powering a power management unit such as EM8500 or AEM30300 in an indoor environment.