Relay Resonators Research Articles

Surface Routing for Wireless Power Transfer Using 2-D Relay Resonator Arrays

Wireless power transfer via magnetic resonance coupling offers the prospect of autonomously charging connected devices. Previous work demonstrated that the system deployment can be facilitated by “routing” power on 2-D relay resonator arrays, using the multi-hop phenomenon. Power propagates through untethered relay resonators in such systems, and the routing strategy significantly affects the power transfer efficiency. However, most previous studies limit the routing to line-shaped routes, which compromises power transfer efficiency to preserve the simplicity of analysis. Here we show a surface routing approach, which can be orderly generated and is more efficient than linear routing. The confronting challenge is the complex representation of cross-coupled relays, which this work overcomes by conditioning the resonators’ current by appending additional loading conditions to the relays. Simulation-based evaluations show that the proposed approach improves the efficiency by up to 10% in 1.5 m range power delivery.

Analysis and Performance Enhancement of Wireless Power Transfer Systems With Intended Metallic Objects

While detection of foreign or unintended metallic objects is an important topic for wireless power transfer (WPT), operation of WPT systems with intended metallic objects is largely an unchartered territory. This article presents a methodology for analyzing the effects of intended metallic object on a WPT system through the study of the magnetic field distribution and the use of a reduced-order equivalent model of the systems for comparing the WPT system with and without the metallic object. The methodology is applied to a metallic corona ring of low resistance used with a WPT system. The analysis quantifies how an intended metallic object could change the magnetic coupling between the transmitter and receiver coils, and alter the equivalent resonant tank parameters of the WPT system. Recompensation of the resonant tank can only enhance the power transfer capability but not the energy efficiency. The theory and practical verification of a new performance-enhancement method based on a combination of recompensating the resonant tanks and maximizing the equivalent mutual inductance of the Tx and Rx coils is presented. Such methodology provides a general approach to analyze WPT systems with or without relay resonators in the presence of intended metallic objects.

Range-extended wireless food spoilage monitoring with a high energy efficient battery-free sensor tag

In this study, we developed a smart sensor tag without a battery for monitoring spoilage in packaged foods. To give our smart sensor tag a compact structure for inserting into food packaging, we designed a double PCB structure with two 6-turn rectangular antennas. The first PCB includes several low power sensors for monitoring food spoilage, a transceiver IC for communication with a reader, a microcontroller for the smart sensor tag operations, and a 6-turn rectangular antenna at the edge of the PCB. The second relay PCB contains another 6-turn rectangular antenna (that is the same size as the first antenna) and is parallel to the first board. This second PCB is designed as a relay resonator to improve the RF energy harvesting efficiency from the reader side. The antenna on the first board transmits data to the reader and simultaneously operates as a receiver resonator for RF energy harvesting. To evaluate the food spoilage, the proposed smart sensor tag was designed to have several low power sensors that monitor factors including humidity, temperature, total volatile organic compounds, and equivalent carbon dioxide. Validation results showed that the proposed smart sensor tag with the sensor module is able to collect the sensing data on food spoilage without a battery, at a maximum distance of 50 cm from a reader. The collected sensing data were analyzed with a personal computer to evaluate spoilage level in food packages.

An Enhanced Multiplication of RF Energy Harvesting Efficiency Using Relay Resonator for Food Monitoring.

Recently, radio frequency (RF) energy harvesting (RFEH) has become a promising technology for a battery-less sensor module. The ambient RF radiation from the available sources is captured by receiver antennas and converted to electrical energy, which is used to supply smart sensor modules. In this paper, an enhanced method to improve the efficiency of the RFEH system using strongly coupled electromagnetic resonance technology was proposed. A relay resonator was added between the reader and tag antennas to improve the wireless power transmission efficiency to the sensor module. The design of the relay resonator was based on the resonant technique and near-field magnetic coupling concept to improve the communication distance and the power supply for a sensor module. It was designed such that the self-resonant frequencies of the reader antenna, tag antenna, and the relay resonator are synchronous at the HF frequency (13.56MHz). The proposed method was analyzed using Thevenin equivalent circuit, simulated and experimental validated to evaluate its performance. The experimental results showed that the proposed harvesting method is able to generate a great higher power up to 10 times than that provided by conventional harvesting methods without a relay resonator. Moreover, as an empirical feasibility test of the proposed RF energy harvesting device, a smart sensor module which is placed inside a meat box was developed. It was utilized to collect vital data, including temperature, relative humidity and gas concentration, to monitor the freshness of meat. Overall, by exploiting relay resonator, the proposed smart sensor tag could continuously monitor meat freshness without any batteries at the innovative maximum distance of approximately 50 cm.

Wireless power transfer using relay resonators

This paper presents an advanced design configuration of a wireless power transfer system using overlapping relay coil techniques for free loading position. The work undertaken investigates the tuning position of prototype relay coils in a horizontal configuration in order to evaluate power transfer efficiency versus increasing operating distance between the transmitter and receiver coils. A prototype relay coil system was evaluated to determine the optimum distance between the transmitter and receiver. Finite element magnetic simulation was used to appraise the magnetic field distribution and power transfer efficiency with respect to a strongly coupled magnetic resonance condition. Experimental and simulation results analysis suggest that the proposed design could achieve 85%–90% efficiency within a 4 cm operational distance. Finally, the experimental results were analyzed and compared with the simulation results.

An investigation on frequency characteristics of wireless power transfer systems with relay resonators

PurposeThis paper aims to analyze the frequency characteristics of wireless power transfer (WPT) systems with relay resonators in terms of the power delivered to the load and system efficiency. Based on the analytical results, system parameters can be optimized to achieve maximum power transfer and higher system efficiency.Design/methodology/approachBased on Kirchhoff’s voltage law equations, WPT systems with relay resonators are described by the coupled linear second-order differential equations. Splitting frequencies are estimated by using the matrix theory. In addition, critical coupling conditions are demonstrated based on discriminant analysis.FindingsIt was found that multi-maximum values exist for the power delivered to the load and total system efficiency owing to multiple eigenfrequencies of the system. Also, frequency conditions of maximum power transfer and system efficiency, as well as their critical coupling conditions, were quantitatively estimated.Research limitations/implicationsDuring our analytical process, we assume that quality factors of resonators in the system are high and the crossing coupling between resonators is negligible.Originality/valueIn previous works, the exact analysis of frequency characteristics is limited to WPT systems with two resonators. The appealing feature of this work lies in its ability to present a simplified analytical method with negligible approximation errors for WPT systems with relay resonators.

Stability Improvement of Transmission Efficiency Based on a Relay Resonator in a Wireless Power Transfer System

We investigate the stability of the transmission efficiency (TE) in nonradiative wireless power transfer (WPT) using a relay resonator. An equivalent circuit model is used to show mathematically that two suppositions are satisfied in an overcoupled region: first, the TE of relay-based WPT systems is always larger than that of conventional two-coil-based WPT systems, and second, as the coupling coefficient increases, the TE of two-coil-based WPT systems decreases severely, while the TE of relay-based WPT systems increases slightly. Consequently, we surmise that an intermediate relay can be used to achieve higher TE and stability, compared with conventional two-coil-based WPT systems. We verify that our analytical results are in good agreement with the experimental ones.

Two‐port network approach for a wireless power transfer link using a cascade of inductively coupled resonators

SummaryA wireless power transmission link consisting of a transmitting and a receiving resonator wirelessly connected by means of N relay resonators is investigated, and a 2‐port network approach is proposed. The presented approach exploits the properties of periodic networks to derive useful closed‐form formulas that can be used to match the wireless energy link with respect to generic reference impedances.

A Network Approach for Wireless Resonant Energy Links Using Relay Resonators

In this paper, a network approach for the analysis of a wireless resonant energy link consisting of $N$ inductively coupled $LC$ resonators is proposed. By using an artificial transmission line approach, the wireless link is modeled as a transmission line described by effective parameters. It is shown that the analyzed system exhibits a passband filter behavior. More specifically, the reported results demonstrate that in the wireless link passband the effective parameters assume negative values resulting in a negative phase delay. Useful design formulas are derived and validated by comparisons with the experimental data.

Design of Asymmetrical Relay Resonators for Maximum Efficiency of Wireless Power Transfer

This paper presents a new design method of asymmetrical relay resonators for maximum wireless power transfer. A new design method for relay resonators is demanded because maximum power transfer efficiency (PTE) is not obtained at the resonant frequency of unit resonator. The maximum PTE for relay resonators is obtained at the different resonances of unit resonator. The optimum design of asymmetrical relay is conducted by both the optimum placement and the optimum capacitance of resonators. The optimum placement is found by scanning the positions of the relays and optimum capacitance can be found by using genetic algorithm (GA). The PTEs are enhanced when capacitance is optimally designed by GA according to the position of relays, respectively, and then maximum efficiency is obtained at the optimum placement of relays. The capacitance of the second resonator tonth resonator and the load resistance should be determined for maximum efficiency while the capacitance of the first resonator and the source resistance are obtained for the impedance matching. The simulated and measured results are in good agreement.

Near field wireless power transfer using curved relay resonators for extended transfer distance

This paper investigates the performance of a near field wireless power transfer system that uses curved relay resonator to extend transfer distance. Near field wireless power transfer operates based on the near-field electromagnetic coupling of coils. Such a system can transfer energy over a relatively short distance which is of the same order of dimensions of the coupled coils. The energy transfer distance can be increased using flat relay resonators. Recent developments in printing electronics and e-textiles have seen increasing demand of embedding electronics into fabrics. Near field wireless power transfer is one of the most promising methods to power electronics on fabrics. The concept can be applied to body-worn textiles by, for example, integrating a transmitter coil into upholstery, and a flexible receiver coil into garments. Flexible textile coils take on the shape of the supporting materials such as garments, and therefore curved resonator and receiver coils are investigated in this work. Experimental results showed that using curved relay resonator can effectively extend the wireless power transfer distance. However, as the curvature of the coil increases, the performance of the wireless power transfer, especially the maximum received power, deteriorates.

Auxiliary Circuits for Power Flow Control in Multifrequency Wireless Power Transfer Systems With Multiple Receivers

This paper describes a technique for multifrequency wireless power transfer systems in which the wireless power can be transmitted through the wireless power transfer channel or channels from the transmitter to the targeted loads with receiver coils specifically tuned for energy reception. Auxiliary circuits comprising bandpass and/or bandstop circuits are proposed for incorporation into the receiver circuits and optional relay circuits so as to facilitate the selection and enhancement of the wireless power transfer to the designated load without causing significant cross interference due to the use of multifrequency wireless power flow control. A unique feature of this technique is that the nontargeted receiver will automatically act as a relay resonator to enhance 1) magnetic coupling, and thus, 2) the power transfer between the power transmitter and the targeted receiver. A second novel feature is that the chosen operating frequencies for the tuned receivers need not be widely apart because the auxiliary circuits consist of bandpass and/or bandstop filters to reduce any cross interference from the nontargeted frequency. The proposed technique has been practically verified in experimental prototype.

Wireless Power Transfer to Multiple Loads Over Various Distances Using Relay Resonators

Resonant wireless power transfer has attracted much attention in recent decades. In some practical applications such as wireless sensor networks, multiple-load transfer over various distances is required. In this letter, the intermediate-coil structure is utilized to transfer the same power to multiple loads over various distances, which indicates that the intermediate coils work both as relay resonators and as power receivers. The mathematical model is built and in-depth analysis is conducted. Four important factors, namely the source matching factor, the load matching factor, the transfer quality factor, and the reflected impedance factor, are employed to build the mathematical model of n-load transfer. The conditions to transmit the same power to all the loads attached in each relay resonator are investigated. The optimal load resistance and the highest efficiency with the same load resistance are derived. The theoretical calculations and the experimental results of double-load and three-load transfer confirm the analysis.

A Methodology for Making a Three-Coil Wireless Power Transfer System More Energy Efficient Than a Two-Coil Counterpart for Extended Transfer Distance

A new methodology for ensuring that a three-coil wireless power transfer system is more energy efficient than a two-coil counterpart is presented in this paper. The theoretical proof and the conditions for meeting the objective are derived and practically verified in a practical prototype. The key features of the magnetic design are to: 1) shift the current stress from the primary driving circuit to the relay resonator; and 2) generate a large relay current for maximizing magnetic coupling with the receiver coil for efficient power transfer. Consequently, the current rating and cost of the driving circuit can be reduced and the overall quality factor and system energy efficiency are improved. This approach utilizes the combined advantages of the maximum efficiency principle and the use of relay resonator to overcome the energy efficiency problem for applications with extended energy transfer distances.

Flexible Design Method for Multi-Repeater Wireless Power Transfer System Based on Coupled Resonator Bandpass Filter Model

It has been verified that wireless power transfer (WPT) system with multiple relay resonators (repeaters) inserted properly between the transmitter and the receiver can increase the transmission distance significantly. Based on the coupled resonator bandpass filter model, a flexible design method for wireless power transfer system with arbitrary number of repeaters is proposed in detail. The transmission efficiency and the transferred power of the proposed wireless power transfer system are derived under the design theory of filters. It is illuminated the reason that Butterworth type is preferred type for designing WPT with multi-repeater. Moreover, the relation between transmission distance and bandwidth is examined and a technique is further introduced to increase the transmission distance. An RS=50 Ω WPT system with three repeaters is tested and another RS=0 Ω WPT system with one repeater is simulated, and the effectiveness of the proposed method is confirmed as well.

A Critical Review of Recent Progress in Mid-Range Wireless Power Transfer

Starting from Tesla's principles of wireless power transfer a century ago, this critical review outlines recent magneto-inductive research activities on wireless power transfer with the transmission distance greater than the transmitter coil dimension. It summarizes the operating principles of a range of wireless power research into 1) the maximum power transfer and 2) the maximum energy efficiency principles. The differences and the implications of these two approaches are explained in terms of their energy efficiency and transmission distance capabilities. The differences between the system energy efficiency and the transmission efficiency are also highlighted. The review covers the two-coil systems, the four-coil systems, the systems with relay resonators and the wireless domino-resonator systems. Related issues including human exposure issues and reduction of winding resistance are also addressed. The review suggests that the use of the maximum energy efficiency principle in the two-coil systems is suitable for short-range rather than mid-range applications, the use of the maximum power transfer principle in the four-coil systems is good for maximizing the transmission distance, but is under a restricted system energy efficiency (<;50%); the use of the maximum energy efficiency principle in relay or domino systems may offer a good compromise for good system energy efficiency and transmission distance on the condition that relay resonators can be placed between the power source and the load.

Efficiency Improvement of Underwater Midrange Inductive Contactless Power Transmission Via a Relay Resonator

AbstractInductive contactless power transmission (ICPT) offers a safe and convenient means of delivering energy underwater. However, ICPT is capable of transferring power effectively only within a near-distance range (millimeters). In recent years, magnetic resonance coupled power transmission (MRCPT), which can wirelessly deliver power across a distance of meters, has been introduced and studied. Nevertheless, MRCPT is usually operated at a very high resonance frequency (MHz) and is unavailable for underwater applications because of the considerable power loss in water. In this paper, we present an ICPT system with a relay resonator for a midrange efficiency improvement. The proposed system is based on an (inductor-capacitor) LC resonance circuit, rather than magnetic resonance. The system operates at a lower resonance frequency than the typical MRCPT system. A theoretical model is introduced for the proposed system using coupled mode theory. Theoretical treatments and an analysis of the system parameters are presented for improving the efficiency in underwater environments. The inductance and stray capacitance of a relay coil with a flat spiral profile are calculated. The experimental results indicate that the proposed system can substantially enhance the power transmission efficiency under water in midrange distances (≥10 cm) compared with the ICPT system without a relay resonator.

New Analysis Method for Wireless Power Transfer System with Multiple n Resonators

This paper presents a new method for analyzing the maximum efficiency of a wireless power transfer (WPT) system with multiple n resonators. The method is based on ABCD matrices and allows transformation of the WPT system with multiple n resonators into a single two-port network system. The general maximum efficiency equation of a WPT system with multiple n resonators is derived using the ABCD matrix. Use of this equation allows placement of the relay resonators for maximum efficiency even though they are asymmetrical. The general maximum efficiency equation and the method of the optimum placement are verified by a full wave simulation. The results show that the method is useful for the analysis of a WPT system with relay resonators.

General Analysis on the Use of Tesla's Resonators in Domino Forms for Wireless Power Transfer

In this paper, we present a brief overview of historical developments of wireless power and an analysis on the use of Tesla's resonators in domino forms for wireless power transfer. Relay resonators are spaced between the transmitter and receiver coils with the objectives of maximizing energy efficiency and increasing the overall transmission distance between the power source and the load. Analytical expressions for the optimal load and maximum efficiency at resonance frequency are derived. These equations are verified with practical measurements obtained from both coaxial and noncoaxial domino resonator systems. To avoid the use of high operating frequency for wireless power transfer in previous related research, the technique presented here can be used at submegahertz operation so as to minimize the power loss in both the power supply and the output stage. We demonstrated both theoretically and practically that unequal spacing for the coaxial straight domino systems has better efficiency performance than the equal-spacing method. Also, the flexibility of using resonators in various domino forms is demonstrated.

Quantitative Design and Analysis of Relay Resonators in Wireless Power Transfer System

Wireless power transfer systems are finding increasing applications which can enhance the living standard of the general public. Typical examples are wireless charging of mobile phone batteries and car batteries. Thanks to the advent of power electronics in the past few decades, some wireless charging systems are now emerging in the commercial sector. However, the transfer efficiency and transfer distance of these chargers are limiting the technology to a few specific applications only. In order to increase the transfer distance, some researchers have successfully proposed to use relay coils to improve their wireless power transfer efficiency. In this paper, the role of relay resonator is examined critically. The reported findings indicate that it is not always desirable to have relay coils in wireless charger as the relay resonator may increase, or sometimes reduce, the overall power transfer efficiency. The findings also reveal that there is an optimal position for the designer to locate the relay resonator to maximize the power transfer efficiency.