Compact Wireless Power Transfer Research Articles

Intelligent wireless power transfer via a 2-bit compact reconfigurable transmissive-metasurface-based router

With the rapid development of the Internet of Things, numerous devices have been deployed in complex environments for environmental monitoring and information transmission, which brings new power supply challenges. Wireless power transfer is a promising solution since it enables power delivery without cables, providing well-behaved flexibility for power supplies. Here we propose a compact wireless power transfer framework. The core components of the proposed framework include a plane-wave feeder and a transmissive 2-bit reconfigurable metasurface-based beam generator, which constitute a reconfigurable power router. The combined profile of the feeder and the beam generator is 0.8 wavelengths. In collaboration with a deep-learning-driven environment sensor, the router enables object detection and localization, and intelligent wireless power transfer to power-consuming targets, especially in dynamic multitarget environments. Experiments also show that the router is capable of simultaneous wireless power and information transfer. Due to the merits of low cost and compact size, the proposed framework may boost the commercialization of metasurface-based wireless power transfer routers.

Self-tuning approach for metasurface-based resonators for one-to-many wireless power transfer

One-to-many wireless power transfer (WPT) is one of the leading directions in WPT systems development due to the rapid growth of consumer devices. The most challenging task is to ensure high efficiency for free-positioned receivers and provide low-cost compact WPT systems. In this paper, a transmitting metasurface-based resonator for one-to-many WPT systems is proposed and experimentally studied. The resonator design and matching method provides the self-tuning ability and allows to simplify the control and communication units of WPT systems. The resonator is composed of periodically arranged unit-cells, implemented as two crossed conductors separated by a thick substrate with a 330 pF capacitor mounted at the cross-hair of the conductors. The prototype of the proposed metasurface-based resonator is fabricated and experimentally studied for free-positioned single- and multi-receivers. The WPT efficiency to a free-positioned receiver varies from 19.7% to 84.8%. The overall efficiency for a three-receiver case reaches 83.2% which is suitable for one-to-many WPT systems.

A Compact Duplexing Rectenna With Wireless Power Transfer and Harmonic Feedback Capabilities

A compact duplexing rectenna with wireless power transfer (WPT) and harmonic feedback capabilities is proposed in this work. It can not only convert the radio frequency (RF) power to the direct current (DC) power at the fundamental frequency, but also feedback the second harmonic signal from power limited receiver side (Rx) to transmitter side (Tx), for the purpose of stabilizing the DC outputs when the dedicated power source is moving. To this end, the duplexing antenna working at 0.915 GHz and 1.83 GHz with good isolation is designed at first. Then, a rectifier with second harmonic signal output is integrated on the ground of the duplexing antenna for a compact size. The rectifier exhibits a measured maximum power conversion efficiency (PCE) of 58% (at 5 dBm input power) and peak second harmonic signal power of -11 dBm with economic Schottky diodes SMS7630-005LF. Finally, the WPT experiment is carried out. It is demonstrated that the received feedback power increases from -66 dBm to -44.8 dBm monotonically when Tx transmit power varies from 15 dBm to 30 dBm, which proves an effective solution for compact WPT terminal.

Inductive Coupler Analysis Based on Scattering Parameters With Nonstandard Terminal Impedance

A higher frequency helps to design a compact wireless power transfer system. Due to the parasitic effects and component nonlinearity, the increased frequency would depreciate the accuracy of the circuit model (CM). The scattering parameters (SPs) are powerful to avoid this issue and helpful to study the efficiency and voltage gain. However, the existing SP-based analysis would fail when the nonstandard terminal impedance is used. This article explores the limitation of the original SP-based analysis and, then, proposes a modified one with the help of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bm{ABCD}$</tex-math></inline-formula> and impedance matrices. For a system with a clear model, the modified SP-based analysis can get exactly the same results as the CM-based one in terms of calculation. In the experiment, a 1-MHz inductive power transfer system is built to show the benefit of the SP-based analysis with increased model uncertainty. Compared to the CM-based one, the largest error reduction is 17% for the efficiency and 8% for the voltage gain.

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.

High-efficiency and compact WPT receiving antenna design using simulation optimization method

In this paper, a high-efficiency and compact wireless power transfer (WPT) receiving antenna using an flexible printed circuits board (FPCB) with high-Q factor is proposed. The proposed high-efficiency and compact WPT receiving antenna consists of a spiral structure, a lumped element and via through the ground structure. In this paper, in order to design a miniaturized high-efficiency WPT receiving antenna, machine learning technology was used to optimally design the antenna pattern that affects the Q factor. The designed receiving antenna has improved wireless power transmission efficiency with high Q characteristics. The power transfer efficiency is above 88% from distance 10 mm and the resonant frequency is 110 MHz. The sizes of the receiving antenna and the NFC antenna are 30 × 40 mm and 20 × 30 mm, respectively. Machine learning was used to design and fabricate the composite module of a WPT receiving antenna and NFC antenna. Comparison of the experimental results of the proposed receiving antenna with a general receiving antenna confirms the improvement in transmission efficiency.

A polymer membrane electrolysis micropump powered by a compact wireless power transmission system

In this study, a polydimethylsiloxane (PDMS) membrane electrolysis micropump activated by a miniaturized wireless power transfer (WPT) system is introduced. The micropump system has total dimensions of 20 × 14 × 8.2 mm3. Combined with a compact WPT system, the micropump enables the delivery of drugs to the treatment area on demand. The WPT system consists of an impedance matching network and a two-stage voltage multiplier. Voltages ranging from 0.8 V to 1.3 V can be generated at different operating distance of 8 cm to 20 cm away from the RF source. The micropump is capable of delivering liquid continuously over a flow ranging from 0.11 µL/min to 4.84 µL/min. This micropump demonstrates a maximum cumulative released drug volume of up to 100.8 µL and was able to produce a pressure that is higher than the intraocular pressure. The results can be used for the study of age-related macular degeneration, diabetic retinopathy, and other ophthalmic diseases.

Dual-Band Free-Positioning Transmitting Coil for Multiple-Receiver Wireless Power Transfer

In recent years, the requirement for a compact wireless power transfer (WPT) system that can supply power to multiple devices in various practical usage scenarios has been attracted many researchers. The receiver (Rx) misalignment problem is contributory to the power transfer efficiency (PTE) degradation. Moreover, in a multiple-output WPT system, the overall system efficiency is also affected by cross-coupling between receivers. This paper proposes a dual-band free-positioning transmitting coil (FPDB-Tx) for multiple-receiver WPT. A three-dimensional Tx structure is modeled by investigating the current direction on each coil loop to adapt the Rx angular and axial misalignment. The Tx configuration is designed following a wireless charging box concept, where multiple Rx devices can receive energy freely without a null efficiency point. The mutual inductance is examined by a mathematical method in various Rx orientations to verify the free-positioning characteristic. Furthermore, an equivalent circuit model of the WPT system is theoretically analyzed to obtain dual operating frequency bands and then maximized the PTE. The experimental results show that the proposed WPT system achieves a stable PTE in various Rx positions. Especially, the WPT system has a maximum PTE of 97.27% and 91% at 6.78 MHz and 13.56MHz, respectively.

Compact wireless power transfer system with microstrip-driven coupled dielectric resonators

A compact, low-cost, and highly efficient wireless power transfer (WPT) system is presented. Besides transferring power, this system provides the required bandwidth for data communication; thus, it can be exploited as a wireless digital connector. It utilizes two off-the-shelf cylindrical dielectric resonators with a dielectric constant of 33 and a loss tangent of 2.5×10-4. The mutually coupled dielectric resonators operate in their magnetic-dipole mode. The resonance frequency of this mode determines the optimum operating frequency of the system which is approximately 7 GHz. The power transfer efficiency of more than 43% is maintained for distances up to four times the resonator radius. The maximum power transfer efficiency as a function of distance and misalignment is computed and experimentally verified. Its relative bandwidth renders the proposed WPT system appropriate for high-rate data transmission.

Wireless Electric Vehicle Charger With Electromagnetic Coil-Based Position Correction Using Impedance and Resonant Frequency Detection

Wireless power transfer (WPT) is an enabling technology for electric vehicles (EV), as it eliminates driver intervention during charging. Major challenges to the adoption of WPT systems include coil misalignment and large air-gap WPT, both of which degrade the transfer efficiency. To address these issues, this article presents a compact WPT charger for the rear of an EV, capable of correcting lateral misalignment $\Delta$ x using two integrated electromagnetic coils. The air-gap $\Delta$ y is reduced due to the rear placement of the charging pads. The variation in $\Delta$ y , however, increases due to vehicle parking accuracy, which impacts the operation of the electromagnetic coils. This article proposes a closed-loop three-stage position-correcting control algorithm capable of detecting the impedance and resonant frequency of the system, which, in conjunction with the electromagnetic coils, results in improved vehicle alignment. The experimental prototype achieves a peak dc–dc efficiency of 90.1% at 5 kW WPT. With $\Delta$ y = 50 mm, the electromagnetic coils laterally align the pads within 1.75 s and correct $\Delta$ x as large as 240 mm. The position-correcting control was successfully demonstrated in four parking scenarios with the charging pads being corrected to within a 10-mm radius of perfect alignment.

Experiments With a Compact Wireless Power Transfer System Using Strongly Coupled Magnetic Resonance and Metamaterials

The technology for inductive wireless power transfer (IWPT) by using strongly coupled magnetic resonance has been applied successfully to supply energy to several applications such as biomedical implants, radio frequency identification systems, Internet-of-Things sensors, and battery chargers for personal devices. In order to attain high values of efficiency and reach, the technology requires the employment of coils with high values of quality factor. However, this feature can only be found by using large wire coils. A compact IWPT system composed of printed coils, which typically have low values of quality factor, is proposed in this paper. An evolutionary algorithm is used to optimize the printed coil geometry so that it presents the greatest value of quality factor possible, according to the imposed restrictions. With the aim to improve the system efficiency and reach, the effect of metamaterial surfaces inclusion is investigated. In addition, in order to increase the amount of power processed by the system, a low-cost self-oscillating electronic converter is proposed to power it.

Wireless Power Transfer Technology Using Resonant Technique

Wireless power transfer (WPT) is a kind of technology by transferring the electrical energy from a power source to an electrical load without the use of wire or conductor. Nowadays, electricity power is very important in our daily life. People use portable electronic devices to improve their routine work. The portable electronic devices are connected to power socket for their power supply. However, it is not convenient to people due to the length of the wire and they are unable to move far from the power socket. Therefore, the main objective of this project is to investigate a wireless power transfer technology using resonant technique. The proposed model was designed and pre-tested by Multisim. An efficient and compact wireless power transfer using resonant technique was proposed and a wireless power supply system for low power electronic devices was developed. The design of the system is to transfer the low power for electronic devices from transmitter to receiver coils. The input DC power is 12 V and the magnetic field passes through resonator and causes the energy to build up. As the result, the voltage and current of LED (acts as load) are 0.668 V and 0.01 mA respectively with the distance of 5 cm. In order to smoothen the peak voltages, a capacitor and a diode were used as a filter and rectifier respectively in the circuit. Resonance inductive coupling is widely used for mid-range transmission distance due to its simplicity in system design. The optimum distance for harvesting the highest voltage is 3.5 cm apart. The efficiency of power transmitted was 41.6 %. The transmission of power is only affected by the metal made component which is placed near to it. Wireless power transfer is convenient, reliable, low cost, safer and environmentally sound. In conclusion, the wireless power transfer using resonance induction coupling is more efficient if compared with inductive coupling and electromagnetic wave. The power can transfer with a longer distance and safely by using this technique.

A compact wireless power transfer system at 915 MHz with supercapacitor for optogenetics applications

To facilitate sophisticated optogenetics research with minimal disruption to animal’s behavior, a fully wireless optical stimulator module is desirable. This paper presents a compact wireless power transfer (WPT) system for optogenetics applications that is adapted to work in implanted condition with unstable and insufficient ambient RF energy field. The scope of this work is to design and implement a power transfer system architecture that is able to: 1) work over long distance, 2) achieve high power conversion efficiency and 3) provide stable output power for sufficient time duration. The designed WPT circuit operates at 915 MHz and achieves maximum power conversion efficiency of 50% at −15 dBm input power. With a compact circuitry design (12.20 × 13.22 mm), the obtained full power transmission efficiency was 0.329% at 20 dBm (100 mW) transmission power. Ex-vivo experiments indicated that when the WPT system was located 10 cm from the source, it retrieved a maximum of 0.324 mW in free space, and 0.112 mW if inserted inside porcine cadaver meat with 4 cm of thickness. At a distance of 1 m from the source, the system retrieved 17 μW in free space, and 1 μW in porcine meat. Furthermore, to sufficiently drive the LED, an advanced supercapacitor was utilized as an energy storage element. When fully charged, the system can supply the LED over 75 s with a total power of 2.45 W. The developed WPT system can be a viable solution to be applied in optogenetic experiments on laboratory animals for preclinical studies.

Accurate Position Detection in Wireless Power Transfer Using Magnetoresistive Sensors for Implant Applications

Recently, the utilization of magnetic resonant coupling (MRC) mechanism for wireless power transfer (WPT) has been actively investigated. Among numerous applications of WPT technology, the energization of implanted biomedical devices wirelessly and uninterruptedly from external supply is important because it can eliminate possible device replacement due to battery depletion. Given the implanted receiver is invisible from the external transmitter, the coil misalignment occurs easily which results in low transfer efficiency and high magnetic field leakage, and consequently endangers the human health [1]. Thus, the development of accurate position detection of the implanted receiver from the external transmitter is highly desirable. Presently, most studies of the position detection in WPT are focused on the application of electric vehicles. Although the corresponding technologies such as coil sets [2] or auxiliary multi-coils [3] have achieved fruitful outcome, they are too bulky and complicated to be used in implant applications. Due to the advantages of high stability, small size, low power consumption and high precision, the magnetoresistive (MR) sensor has been widely used in many industrial applications [4]. Generally, they are arranged in an array style to measure the magnetic field vector [5] or a moving magnetic object [6]. To the best of authors' knowledge, the application of MR sensors in WPT is absent in literature. In this paper, a new position detection approach in WPT is proposed and implemented, which is particularly suitable for implant applications. The key is to use a MR sensor array to directly measure the variation of magnetic field so as to precisely detect the relative position of the implanted receiver from the external transmitter. Therefore, the advantages of efficient and compact WPT for implant applications can be achieved.

Analysis of efficiency improvement in wireless power transfer system

Recently, efficiency improvement of wireless power transfer (WPT) systems has been the focus of research. Conventional methods of DC-DC converters are employed for load modulation to achieve high efficiency over large variations in mutual inductance and load. However, these additional circuits degrade the performance due to their inherent losses. To address this problem, this study presents a dual-side phase shift control method for load modulation and voltage regulation in a compact WPT system. The key features of the proposed work are: attaining load modulation and voltage regulation with reduced size of the system; elimination of communication between active bridges and simple control logic. Mathematical expression of equivalent resistance versus the phase shift angles (PSAs) is deduced and the optimal PSAs for maximum efficiency are presented. Utilisation of local control, stability analysis and fault detection method are included. MATLAB/Simulink simulation and experimental results are carried out to validate the proposed method.

1.06 FoM and Compact Wireless Power Transfer System Using Rectangular Defected Ground Structure Resonators

This letter proposes a wireless power transfer (WPT) system using coplanar waveguide fed rectangular defected ground structure (DGS) resonators. One of the advantages of rectangular DGS resonator is that it has higher quality (Q-) and coupling (K-) factor compared to the H-shape or semi-H-shape DGS resonators. When two DGS resonators are coupled back-to-back, it transforms to a bandpass filter with tight coupling, resulting in the transfer of power wirelessly. The fabricated WPT system of size $35.8~\text {mm} \times 20$ mm achieves, for the first time, a figure of merit of more than one at a WPT distance from 40 to 44 mm.

Compact Wireless Power Transfer System Using Defected Ground Bandstop Filters

This letter presents a new design for wireless power transfer (WPT) applications using two coupled bandstop filters (BSF). The stopband is created by etching a defected structure on the ground plane, and the power is transferred through electromagnetic (EM) resonant coupling when the two BSFs are coupled back to back. An equivalent circuit model of the proposed WPT system is extracted. Verification of the proposed design is performed through a good agreement between the EM simulation, circuit simulation, and measurement results. The proposed system achieves a measured WPT efficiency of 68.5% at a transmission distance of 50 mm using a compact size ( $40\times 40$ mm $^{2})$ . This results in a figure of merit of the proposed system to be 0.856 and the ratio of transmission distance/lateral size is 1.25 that is the highest among the WPT systems proposed so far using planar structures.

A Compact 60-GHz Wireless Power Transfer System

The first reported full-system 60-GHz wireless power transfer (WPT) solution that can power batteryless and charge coil-free compact WPT devices is presented. The system is fabricated in a 40-nm digital CMOS process and an inexpensive packaging material. In the rectenna (RX), a grid antenna is integrated with a complementary cross-coupled oscillator-like rectifier. At a 4-cm spacing from the transmitter (TX), the RX harvests energy at a rate of 1.22 mW with a 32.8% efficiency, which is significantly higher than the prior state of the art. A novel theoretical analysis of the rectifier operation is presented that formulates all key specifications. The TX is equipped with a quad-core PA that produces a saturated output power ( $P_{\mathrm{ sat}}$ ) of 24.6 dBm, which is the highest power delivery in digital CMOS at millimeter-wave bands. The TX peak power-added efficiency is 9.4%. In the TX, a $4 \,\, \times \,\, 8$ -way differential power combining and a binary-tree architecture are implemented. The designed $2 \times 2$ grid array antenna helps the TX produce 35.3-dBm peak equivalent isotropically radiated power. The results of the performance characterizations of the full-system and all individually fabricated blocks are reported. The quad-core PA supports power control and beam steering. A four-port TX antenna is designed that shows a 70° steering range in simulations.

A UHF Near-Field Link for Passive Sensing in Industrial Wireless Power Transfer Systems

This paper presents an innovative nonconventional exploitation of a self-resonant capacitive near-field link at UHF, for data communication, to be combined in a compact wireless power transfer (WPT) system. At UHF, an increased channel transfer efficiency is made possible by exploiting two faced auto-resonant structures, such as split-ring resonators (SRRs), one at each far-end side of the link. Their physical layouts are designed to ensure accurate prediction of both the resonant frequency and the resulting frequency-variable behavior of the two-port arrangement. This network is then used in a passive sensing system, based on a smart exploitation of the dc-power dc-load relationship of a standard RF identification (RFID) rectifier, to convert the data of a remote sensor, representing the system variable load. The reflected power variations at the transmitter side, due to the dc load variations, are successfully used to perform the sensor readout. The entire sensing system is first optimized by means of nonlinear circuit and electromagnetic (EM) simulations. Experimental data, compared to prior results, demonstrate the strength of the adopted approach.

Design and implementation of compact WPT system using printed spiral resonators

A planar wireless power transfer (WPT) system with printed square spiral resonators is reported. To facilitate its fabrication, both the spiral resonator and its coupling loop are printed on the top and bottom layer of a single FR4 substrate, such that the spiral resonator is driven by the magnetic field of the coupling loop. The utilised coupling loop along with the appropriate matching circuit will improve the overall efficiency. The proposed WPT system which features a measured efficiency of more than 40% is not only compact but also low cost.