Dual-band Wireless Power Transfer Research Articles

Novel design of a compact tunable dual band wireless power transfer (TDB-WPT) system for multiple WPT applications

Novel design of a compact tunable dual band wireless power transfer (TDB-WPT) system for multiple WPT applications

Design and analysis of compact dual‐band WPT system using capacitively loaded interdigital capacitor

SummaryIn this paper, a noteworthy compact dual‐band wireless power transfer (DB‐WPT) system is presented and studied. This DB‐WPT system is proposed using a capacitively loaded interdigital capacitor which reduces the size of the whole system, lessens the number of the attached surface mount elements, and accomplishes high efficiencies. An interdigital capacitor is printed in the ground plane of the design and loaded with a chip capacitor to produce dual bands. The operation of the system is verified by fabricating the proposed DB‐WPT system, which shows measured coupling efficiencies of 96% and 98.8% at 0.53 and 1.1 GHz, respectively at a transfer space of 12 mm. The fabricated structure has dimensions of 13.5 mm × 20 mm. The results show good agreement between the circuit model and the measurements. The idea of this design makes it applicable for compact near‐field WPT applications.

Hybrid SRR-Based Stacked Metamaterial for Miniaturized Dual-Band Wireless Power Transfer System

A novel stacked wideband metamaterial is proposed for a robust and compact dual-band wireless power transfer (WPT) system. The proposed metamaterial employs split ring resonator (SRR) unit cells loaded by non-uniform capacitors. First, two types of unit cells that exhibit two resonance frequencies are analyzed. The results show that it can only improve the coupling between the transmitter (Tx) and the receiver (Rx) at the single band. Then each unit cell is sandwiched with each other, and a hybrid unit cell that indicates three resonance frequencies is finally proposed. The hybrid SRR exhibits near-zero permeability within the wide frequency range of interest. Therefore, the proposed metamaterial is effective at both bands simultaneously. The system was fabricated and tested, including a compact dual-band WPT system. The size of the Tx (Rx) and the metamaterial are 15 × 15 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 20 × 20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. The measured figure of merits (FOMs) are 0.92 at 390 MHz and 0.85 at 770 MHz, respectively, at a power transfer distance of 20 mm, which is a significant improvement over recently proposed dual-band WPT systems with metamaterials.

Tunable Dual Band Wireless Power Transfer (TDB-WPT) System for Short Range Applications

This brief introduces a novel design to transfer wireless power in dual bands with reconfiguration operation. The idea is obtained by transferring power through one fixed band at 190 MHz and the second band is tuned from 1.1 GHz to 1.4 GHz. The top layer is constructed of a spiral resonator coupled with the feed line. The bottom layer contains a spiral resonator. The varactor diode is attached to the spiral at the top layer which is responsible for the tuned band. Further, a surface mounted (SMD) capacitor is added to the spiral at the bottom layer for getting a fixed band. The system has a size of 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 20 mm2 and the transmission distance between the coupled resonators is 10 mm. The system achieved an efficiency of 97 % at the fixed band of 190 MHz while the average efficiency is 95 % over the tuned band. A good agreement between the measurement and the simulation is achieved.

Electrochromic soft contact lenses with built-in non-interfering, high-efficient dual-band wireless power transfer system

Color contact lenses attracts considerable attention for vision management and cosmetic applications nowadays. However, they require a wired power supply system because positive and negative voltages need to be applied for color modulation of electrochromic coating on the lens. This study demonstrates a wireless-powered electrochromic soft contact lens that modulates color using a dual-band wireless power transfer (WPT) system. The stretchable and conductive electrochromic film is the result of fabrication by spin-coating a mixed solution comprising PEDOT:PSS for the electrical conductor, polyurethane for the stretchable supportive layer, ethylene glycol, and dodecylbenzene sulfonic acid as conductivity enhancers. The dual-band system for negative voltage at 13.56 MHz and positive voltage at 28.4 MHz consists of two resonators using semi-loop antennas connected in parallel with capacitors. The dual-band resonators and electrochromic films are electrochemically bonded onto a commercially available soft contact lens. The proposed lens is capable of reversibly and wirelessly modulating the color from transparent to dark blue for several tens of seconds and usable as wireless color filters and Morse code transmitters.

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.

Dual-Band RF Wireless Power Transfer System with a Shared-Aperture Dual-Band Tx Array Antenna

In this paper, a dual-band RF wireless power transfer (WPT) system with a shared-aperture dual-band Tx array antenna for 2.4 and 5.8 GHz is proposed. The final configuration of the Tx array, which is made up of 2.4 GHz right-handed circular polarization (RHCP) patches and 5.8 GHz RHCP patches, is derived from the optimization of 2.4 and 5.8 GHz thinned arrays, ultimately to achieve high transmission efficiency for various WPT scenarios. The dual-band RF WPT Tx system including the Tx array antenna and a Tx module is implemented, and Rx antennas with a 2.4 GHz patch, a 5.8 GHz patch, and a dual-band (2.4 and 5.8 GHz) patch are developed. To validate the proposed dual-band RF WPT system, WPT experiments using a single band and dual bands were conducted. When transmitting RF wireless power on a single frequency (either 2.482 GHz or 5.73 GHz), the received power according to the distance between the Tx and Rx and the position of the Rx was measured. When the distance was varied from 1 m to 3.9 m and the transmitted power was 40 dBm, the received power value at 2.482 GHz and 5.73 GHz were measured and found to be 24.75–13.5 dBm (WPT efficiency = 2.985–0.224%) and 19.25–6.8 dBm (WPT efficiency = 0.841–0.050%), respectively. The measured results were in good agreement with the calculated results, and it is revealed that the transmission efficiency when wireless power is transmitted via beam-focusing increases more than that with conventional beam-forming. Furthermore, the dual-band WPT experiment proves that 2.482 GHz beam and 5.73 GHz beams can be formed individually and that their wireless power can be transmitted to a dual-band Rx or two different Rx.

Efficiency Improvement of Dual-Band Wireless Power Transfer (DB-WPT) System with U-shape Resonator and Capacitively Loaded E-shape Defected Ground Structure (DGS)

This paper suggests a design for dual-band wireless power transfer systems that use E-shape defected ground structure resonator loaded with a 1.5 pF capacitor and U-shape resonator at the top layer. When the two resonators of the proposed design are coupled back-to-back, it transfers to a dual band-pass filter leading to an efficient WPT system working at 0.9 GHz and 1.4 GHz. A compact size of 20 mm × 20 mm is fabricated achieving a WPT efficiency of more than 97% at a distance of 16 mm for both bands. Good concurrences among the equivalent circuit model (ECM), the theoretical studies, and the measurements have been attained.

Design of Dual Frequency Coupled Resonators Using DGS and Microstrip Resonators for Dual Band WPT Applications

This paper introduces a new design for a highly efficient and more compact size dual frequency wireless power transfer (WPT) system, which can operate at both 0.65 GHz and 1.56 GHz bands. The idea of the structure depends on designing a symmetrical system containing Tx and Rx. Each Tx and Rx has a feed line on the top layer with two stubs; each stub has different dimensions than the other one. The bottom layer contains two C-shaped defected ground structures (DGS). By changing the dimensions of one stub, the frequency resonance corresponds to this stub is changed without any change on the other resonance. The system has a size of 20 × 20 mm2. Further, the system achieves efficiencies of 72 % and 89 % at 0.65 GHz and 1.56 GHz, respectively with a transmission distance of 8 mm. The proposed dual frequency WPT is implemented and verified. Good concurrences among electromagnetic (EM) simulations and the measurements have been attained. The system is suitable for recharging shortrange applications.

Design and Analysis of an Omnidirectional Dual-Band Wireless Power Transfer System

The wireless power transfer system (WPT) is becoming increasingly important for smart home automation, in which an array of wireless sensors is used to monitor and manage smart devices and furniture. Charging the sensors, which may require different frequencies, at any position in the home is a challenge. In this article, a dual-band omnidirectional 3-D WPT system is introduced for the sensors in a smart home. The power transmitted by the transmitter can be received by any receivers operating at 13.56 and 27.12 MHz located at any position. The dual-band 3-D square and circular transmitters are designed and demonstrated. In particular, an equivalent circuit model of the proposed system is derived and numerically analyzed. In addition, the efficiency of the dual-band 3-D WPT system is evaluated based on the receiving angle through simulation and measurement. At a 16 cm distance, the system can achieve efficiencies of 61.6% and 65.4% (57.15% and 61.2%) for rotating 360° at 13.56 and 27.12 MHz without a null value in the square (circular) system. Furthermore, the effect of the angular misalignment of the receiver on efficiency is also analyzed. Finally, the performance of the WPT system in a concrete structure is validated for practical scenarios.

A Dual-Band Wireless Power Transfer System With Efficiency-Boosting Converter

A dual-band wireless power transfer (WPT) system is proposed to satisfy multiple distinct-band WPT demands. A power amplifier combined with a dual-band output matching coil, which is relatively compact, is adopted to enable asynchronous two-band power transfer for multiple single-band receivers (RXs). The measurement results revealed that the efficiency reached 71% for both 6.78 and 13.56 MHz when the transmitter (TX) coil and RX coil were in alignment. However, the efficiency of a dual-band WPT system decreases when the spacing between the TX coil and RX coil deviates from its optimal distance. To address this concern, boost converters were used in the RX ends to achieve higher efficiency under coil misalignments. Efficiency improvement of 14% was obtained when the deviation of the RX coil from the alignment center of the TX coil was 5 cm.

Impedance matching and efficiency improvement of a dual-band wireless power transfer system using variable inductance and coupling method

This paper proposes a dual-band wireless power transfer (DWPT) system which can deliver more power compared to a single-band WPT within the electromagnetic field constraints. Moreover, one of its channels can be applied to increase the data transfer rate compared to a single-band WPT. In this work because of less crosstalk between distinct frequencies, a dual-resonant single-coil is used similarly as a transmitter and receiver. The main challenge in the design of conventional DWPT systems is the simultaneous impedance matching at the different resonant frequencies. In the proposed method, this problem has been solved by varying the coupling factor between the source (load) and the dual-band internal resonator. Moreover, we analytically investigate the influence of the different values of the source(load) inductance on impedance matching. The system equivalent circuit model is presented, and the voltage transfer function and the matching condition for transmitting maximum power are extracted. To evaluate the system performance, the power transfer efficiency is simulated by HFSS software and validated by experimental results. The measurement results show the efficiency of 71% and 56% at frequencies of 6.78 MHz and 13.56 MHz, respectively.

Design and Implementation of Dual-Mode Inductors for Dual-Band Wireless Power Transfer Systems

We propose a dual-band wireless power transfer (WPT) system employing a dual-mode inductor. The dual-mode inductor is possible through enforcing a self-resonance condition by loading an inductor in series by a tank circuit. In return, two distinct resonances are achieved, simultaneously, utilizing a single compensation capacitor as the inductance of the dual-mode inductor appears with a smaller value after its self-resonance. Also, by maintaining the same mutual coupling, the coupling coefficient becomes larger at the higher resonance, which allows for the employment of the same source/load admittance inversion network to achieve maximum power transfer at both of the operating frequency bands, concurrently. We verify the operation by fabricating a dual-band WPT system, which shows measured efficiencies of 70% and 69% at 90.3 MHz and 138.8 MHz, correspondingly. The size of the WPT system is $\boldsymbol {50} \boldsymbol {\times } \boldsymbol {50}$ mm $^{\boldsymbol {2}}$ and has a transfer distance of 40 mm.

A New Compact Dual-Band Wireless Power Transfer System Using Interlaced Resonators

This letter presents a new compact dual-band wireless power transfer (DB-WPT) system. The proposed system is based on two individual transmitting (TX) and receiving (RX) structures. Each structure consists of two interlaced resonators to achieve compact size. A single microstrip line loaded by a surface mounted capacitor (SMD) is used for power feeding. Moreover, high miniaturization of the TX/RX structures is achieved by SMD capacitor loading. In the proposed DB-WPT system, power is transferred from/to the source/load through electromagnetic resonant coupling between the TX and the RX structures. An equivalent circuit of the proposed DB-WPT system is extracted, and then the optimized structures are fabricated and measured. The measured results are in good agreement with the simulated ones. The proposed DB-WPT system has a peak efficiency of 80% and 73% at a transmission distance of 17 mm for frequency 300 and 675 MHz, respectively.

Dual-Band Wireless Power Transfer With Reactance Steering Network and Reconfigurable Receivers

Wireless power transfer (WPT) via near-field magnetic coupling is an enabling technology for many applications. A few WPT standards are under development with frequencies ranging from kilohertz (kHz) to megahertz (MHz). Operation in kHz offers a higher power rating and that in MHz offers a smaller size. This paper presents a dual-band WPT architecture with novel transmitter and receiver topologies that can achieve high performance at both 100 kHz and 13.56 MHz with low component count and decoupled power delivery at different frequencies. On the transmitter side, we introduce an enhanced push–pull Class-E topology together with a reactance steering network (RSN), which can seamlessly compensate the load impedance variation for MHz wireless power transmitters. On the receiver side, we present a reconfigurable dual-band rectifier that can achieve a power density of 300 W/in $^3$ with low component count and low total harmonic distortion. A complete dual-band WPT system comprising an RSN-based dual-band transmitter and multiple reconfigurable receivers has been built and tested. The WPT system can simultaneously deliver a total of 30 W of power to multiple receivers (15 W maximum each) with 82.5% efficiency at 100 kHz and 74.8% efficiency at 13.56 MHz with 2.8 cm of coil distance and up to 5 cm of coil misalignment.

Novel and compact design of capacitively loaded C-shaped DGS resonators for dual band wireless power transfer (DB-WPT) systems

This paper proposes a new dual band coupled resonators band pass filter that employs two C-shaped defected ground structures (DGSs) loaded with lumped capacitors for dual band wireless power transfer (DB-WPT) applications. The proposed resonators produce two independent frequency bands for dual band operations of the WPT system. When the two C-shaped DGS are coupled back-to-back, it transfers to a dual band pass filter leading to compact and efficient WPT system working at 0.3 GHz and 0.9 GHz. The system has been analyzed using the J-inverter method for verification. A compact prototype with a size of 20 mm × 20 mm is fabricated, tested, and measured. The fabricated prototype achieves coupling efficiencies of 99% and 91% at a transmission distance of 10 mm for both operating bands at 0.3 and 0.91 GHz, respectively. Good agreements between the equivalent circuit model (ECM) and the measurements have been achieved.

Dual-Band Coil Module With Repeaters for Diverse Wireless Power Transfer Applications

Dual-band coil modules facilitate efficient access to distinct-band, high-power, or rapid-charging wireless power transfer (WPT) systems. However, they do not function efficiently when the frequency ratio between two operating frequencies is large. To overcome this problem, we propose enhanced dual-band coil modules that adopt repeaters in the WPT system. We present a circuit-based analysis of repeaters in various dual-band coil modules compared with those in a single-band WPT system. The analytical results provide a design methodology applicable to diverse types of dual-band coil modules with a repeater in the WPT system. Our experimental results are consistent with the circuit-based analysis: coil power transfer efficiencies of 55% at 200 kHz and 74% at 6.78 MHz were obtained concurrently in the dual-band WPT system with a dual-band repeater. This paper reduced the application constraint of dual-band coil modules and facilitated the realization and application of multiband WPT systems.

Dual-Band Defected Ground Structures Wireless Power Transfer System With Independent External and Inter-Resonator Coupling

This brief proposes a design methodology based on the admittance ( ${J}$ -) inverters for a dual-band wireless power transfer (WPT) system that employs two cascaded circulars defected ground structure (DGS) resonators with different capacitive loading to guarantee distinct resonances. A single microstrip line excites the two DGSs, and when two DGS resonators are coupled back to back, it transforms to a dual band pass filter leading to WPT at both bands. Each of the DGS resonators has independent coupling. Thus, the realized ${J}$ -Inverters are designed independently. Also, we employ a single stub for the matching. This stub appears with a different length according to the operating frequency; hence, an independent external coupling is achieved at both frequencies. A compact size of 30 mm ${\times } \,\, 15$ mm is fabricated achieving a WPT efficiency of more than 71% at a power transfer distance of 16 mm for both bands (0.3 and 0.7 GHz).

A Dual-Band Wireless Power Transfer and Backscatter Communication Approach for Real-Time Neural/EMG Data Acquisition

We present a dual-band approach for HF wireless power delivery and UHF backscatter communication in implanted biomedical devices. A testbed is described including a custom implant device as well as an external system based around the USRP B210 software defined radio platform. The implant integrates a binary phase shift keying backscatter uplink rate of 5 Mb/s, with an HF wireless power transfer link delivering 1.33 mW at an efficiency of 17%. The implant is 25 mm in diameter and 2.8 mm thick, including the printed circuit substrate, dual-band antenna, all circuitry, and biocompatible silicone encapsulation. It supports up to ten neural and four electromyogram (EMG) channels with a sampling rate of 26.10 kHz for the neural channels and 1.628 kHz for the EMG channels. The communication link is shown to have 0% packet error rate at an implant depth of up to 2.5 cm.

Design of dual-band coil for wireless power transfer system via magnetic resonant coupling

For wireless power transfer (WPT) systems, communication between the two terminals of power transfer system is also an important problem to be solved. This paper proposes a design method of multi-turn dual-band coil for implementing synchronous transfer of power and data in WPT system with one set of WPT coils. An extra compensation circuit is inserted into the multi-turn spiral coil, so the new coil has two resonant frequencies that lie on both sides of the original resonant frequency of the multi-turn coil. Just one set of dual-band coils is used to provide the data and power transfer via two different resonant frequencies, so the undesirable interference in multi-coil WPT system is avoided. The equivalent circuit model is built to analyze the characteristic of the dual-band WPT system. The data pickup circuit is analyzed and designed for the receiver of WPT system. Finally, a dual-band WPT prototype with data pickup circuit is built to demonstrate the effectiveness of the proposed dual-band WPT system.