Inductive Wireless Power Transfer Research Articles

Implantable Semi-Active UHF RFID Tag With Inductive Wireless Power Transfer

The objective of this letter was to design a compact, battery-less system for an implantable semi-active UHF radio frequency identification (RFID) tag with inductive wireless power transfer for the human body. An RFID chip of the tag, combining powering from a reader by communication and from another source through inductive wireless power transfer, was used. Tag sensitivity for communication was increased by about 21 dB with the help of wireless inductive powering when compared to tags that did not employ this system. Communication and powering circuits were integrated within compact structures on the sides of the reader and the tag. The structure for communication and powering on the side of the reader consists of a center-excised Archimedes spiral antenna and a circular loop, respectively. Similarly, the structure on the side of the tag consists of a folded dipole antenna for communication and a rectangular loop for powering.

A New Current-Fed CLC Transmitter and LC Receiver Topology for Inductive Wireless Power Transfer Application: Analysis, Design, and Experimental Results

This paper presents a new wireless power transfer topology for electric vehicle (EV) charging application. The main emphasis is given on high-frequency dc–ac and ac–dc wireless power transfer stage where the inversion stage is current-fed topology. The required resonance in transmitter side is (C) (LC) type and in the receiver-side series (LC) type. The proposed resonance tank network reduces the inverter switch stress to half of the conventional (L) (C) parallel resonance tank network. Inductor in dc-link provides natural short-circuit protection during inverter fault. The required high-transmitter coil (TC) current for air core coupled inductor circulates through parallel resonating capacitor which reduces inverter switch current stress. Resonant converter provides soft switching at device turn on which reduces switching loss. Also, soft recovery at bridge rectifier eliminates diode reverse recovery loss. The converter is analyzed and simulated using PSIM 9.3. A proof-of-concept 420-W lab-prototype is designed and developed, and hardware results are added to validate the analysis and simulation results.

Design and experimentation of two-coil coupling for electric city-car WPT charging

The article deals with the two-coil coupling of an inductive wireless power transfer system intended to charge the battery of an electric city-car. At first, two-coil coupling structures with different arrangements for the coil windings and different shapes for the magnetic core are investigated. Investigation is carried out by help of a FEM code, and encompasses the determination of (i) the inductive parameters as a function of the coil distance and axial misalignment and (ii) the nearby electromagnetic fields to verify their admissibility for the humans. Afterwards the coil coupling is designed and then set up according to the results of the investigation. Measurements executed on the set-up validate the design for both the inductive parameters and the nearby electromagnetic fields.

Optimization, design, and modeling of ferrite core geometry for inductive wireless power transfer

This paper presents a new design of ferrite core made of ferrite bars positioned in radial geometry. New core design is used in inductive wireless power transfer where the optimal design of ferrite bars was analyzed. Numerical simulations of seven ferrite bars geometries were performed in 3D models using Comsol Multiphysics in terms of the coupling coefficient. Two optimal designs of three and nine ferrite bars geometries were used for parameterization of geometric parameters. Both simu- lations of three and nine ferrite bars geometries were verified by measurements. Optimal design of nine ferrite bars geometry is proposed for use in wireless power transfer because of low consumption of ferrite material. Ferrite bars geometry was also used as a magnetic shield to reduce magnetic fields which may interfere with the electronics nearby. Magnetic flux density in ferrite bars is low enough that prevents ferrite bars from the saturation. The angular alignment of optimal design of nine ferrite bars on the transmitter and receiver side was negligible as the difference in the coupling coef- ficient was 0.13%. Advantages of using optimal design of nine ferrite bars geometry are: high value of the coupling coefficient, low consumption of ferrite material, and reduced weight.

Efficiency optimization of class-D biomedical inductive wireless power transfer systems by means of frequency adjustment.

Inductive powering for implanted medical devices is a commonly employed technique, that allows for implants to avoid more dangerous methods such as the use of transcutaneous wires or implanted batteries. However, wireless powering in this way also comes with a number of difficulties and conflicting requirements, which are often met by using designs based on compromise. In particular, one aspect common to most inductive power links is that they are driven with a fixed frequency, which may not be optimal depending on factors such as coupling and load. In this paper, a method is proposed in which an inductive power link is driven by a frequency that is maintained at an optimum value f(opt), to ensure that the link is in resonance. In order to maintain this resonance, a phase tracking technique is employed at the primary side of the link; this allows for compensation of changes in coil separation and load. The technique is shown to provide significant improvements in maintained secondary voltage and efficiency for a range of loads when the link is overcoupled.

FPGA-Based Implementation of Multiple Modes in Near Field Inductive Communication Using Frequency Splitting and MIMO Configuration

Conventional near field inductive wireless power transfer theory shows that systems suffer from splitting frequency behaviors when strong coupling condition exists between the transmitter and the receiver. However, this characteristic has not been explored for communication. Our analysis demonstrates that the splitting behaviour of frequency creates multiple frequencies that support inductive communication in MIMO configuration. As a result, we implement a binary chirp modulation on an FPGA and validate two channel communication using splitting. This paper introduces the use of chirp signals to spread data and excite inductive MIMO systems. The simulation and experiment show that the splitting frequency depends on a quality factor and the flux coupling condition between the data source and receiver. In other words, the degree of mutual coupling defines the splitting mode. This paper proves that multi-channel communication using splitting can be used for data transmission. The results show that data rates of 50 Mbps or 69 Kbps can be achieved for each channel between the transmitters and receivers when the transmitter and receiver operate at the original resonant frequency of 13.56 MHz or 28 KHz, respectively and the distance between them varies from about 1 cm to 10 cm.

Position-insensitive long range inductive power transfer

This paper presents results of an improved inductive wireless power transfer system for reliable long range powering of sensors with milliwatt-level consumption. An ultra-low power flyback impedance emulator operating in open loop is used to present the optimal load to the receiver's resonant tank. Transmitter power modulation is implemented in order to maintain constant receiver power and to prevent damage to the receiver electronics caused by excessive received voltage. Received power is steady up to 3 m at around 30 mW. The receiver electronics and feedback system consumes 3.1 mW and so with a transmitter input power of 163.3 W the receiver becomes power neutral at 4.75 m. Such an IPT system can provide a reliable alternative to energy harvesters for supplying power concurrently to multiple remote sensors.

Optimization of Resonant Inductive Wireless Power Transfer Using Multilayer Flat Spiral Coils

A method of using loading capacitors of varying sizes to experimentally determine the alternating current behavior of resistance and inductance for a multilayer flat spiral coil is presented. For the presented coil design, the Dowell method is shown to underpredict the alternating current resistance of the coil by as much as a factor of 4 for frequencies up to 10 kHz. A classical modification to the Dowell method produces improved results but still underpredicts the alternating current resistance by as much as a factor of 2. Curve fits of the form used in Dowell’s method are applied to experimentally obtained data, allowing for the identification of the frequency at which wireless power transfer efficiency is maximized. In addition, an analytical approach to predicting coil impedance vs the duty cycle of a rectangular wave applied voltage is presented and is shown to agree well with experimentally obtained results.

Analysis of in situ electric field and specific absorption rate in human models for wireless power transfer system with induction coupling

This study investigates the specific absorption rate (SAR) and the in situ electric field in anatomically based human models for the magnetic field from an inductive wireless power transfer system developed on the basis of the specifications of the wireless power consortium. The transfer system consists of two induction coils covered by magnetic sheets. Both the waiting and charging conditions are considered. The transfer frequency considered in this study is 140 kHz, which is within the range where the magneto-quasi-static approximation is valid. The SAR and in situ electric field in the chest and arm of the models are calculated by numerically solving the scalar potential finite difference equation. The electromagnetic modelling of the coils in the wireless power transfer system is verified by comparing the computed and measured magnetic field distributions. The results indicate that the peak value of the SAR averaged over a 10 g of tissue and that of the in situ electric field are 72 nW kg−1 and 91 mV m−1 for a transmitted power of 1 W, Consequently, the maximum allowable transmitted powers satisfying the exposure limits of the SAR (2 W kg−1) and the in situ electric field (18.9 V m−1) are found to be 28 MW and 43 kW. The computational results show that the in situ electric field in the chest is the most restrictive factor when compliance with the wireless power transfer system is evaluated according to international guidelines.

Aerodynamic Fluid Bearings for Translational and Rotating Capacitors in Noncontact Capacitive Power Transfer Systems

Wireless power transfer (WPT) is commonly accomplished with magnetic (inductive) techniques for a wide range of applications. Electrostatic or capacitive power transfer (CPT) approaches to WPT have had limited exposure primarily due to lower achievable power density when compared to inductive WPT techniques. Recently, high-frequency (in kilohertz to megahertz) power electronics have reintroduced capacitive techniques as an option for WPT over short distances ( <; 2 mm) for applications such as slip ring replacement. To further the practicality of CPT, capacitive coupling must be maximized in an effective manner, i.e., the volumetric capacitance density of rotating/translational capacitors must be significantly increased. This paper proposes the use of aerodynamic fluid bearings to maximize capacitive coupling between stationary and moving surfaces, by minimizing their separation distance, allowing for greater surface area per unit volume. The technique allows micrometers of separation distance between moving surfaces while maintaining manufacturability and mechanical robustness. Coupling capacitance is increased up to 100 times greater than rigid plate rotating and translational CPT systems. Additional benefits include the estimation of mechanical system parameters such as speed. Operational characteristics and design highlights are presented and corroborated with experimental results for general slip ring replacement applications.

An efficient wireless power transfer system with security considerations for electric vehicle applications

This paper presents a secure inductive wireless power transfer (WPT) system for electric vehicle (EV) applications, such as charging the electric devices inside EVs and performing energy exchange between EVs. The key is to employ chaos theory to encrypt the wirelessly transferred energy which can then be decrypted by specific receptors in the multi-objective system. In this paper, the principle of encrypted WPT is first revealed. Then, computer simulation is conducted to validate the feasibility of the proposed system. Moreover, by comparing the WPT systems with and without encryption, the proposed energy encryption scheme does not involve noticeable power consumption.

A Small Dual-Band Asymmetric Dipole Antenna for 13.56 MHz Power and 2.45 GHz Data Transmission

Despite the disparity between typical small antenna designs for wireless powering and far-field radiation, this letter proposes a single asymmetric dipole antenna for both applications on a printed circuit board (PCB) of dimension 10 × 24 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . In this design, current cancellation is applied as a technique to enhance far-field radiation efficiency while maintaining inductive wireless power transfer performance. The measured radiation efficiency at 2.45 GHz is 57%, and the power transfer efficiency at 13.56 MHz over a distance of 20 mm is 2.15 dB. The results demonstrate the feasibility of a single dual-band antenna operating at two distinct frequencies while attaining reasonable efficiencies.

Study of Coupling Factor for Wireless Power Link in Advanced Brain-Machine Interface

The inductive wireless power transfer efficiency is determined by the coupling factor and coil quality factors. This paper studies the coupling factor of an inductive power link (IPL) for wireless power transfer in advanced brain-machine interface applications. By comparison to the experimental results, the various design tools including Maxwell simulation and two analytical models are evaluated for prediction of the coupling factor. The coupling factors of IPLs with different design parameters are also analyzed. The results show that for specific wireless power transfer distances, the coupling factor of an IPL is mainly related to the size and fill ratio of the coils, while is almost independent of the coil track pitch, coil width/pitch ratio, and track thickness.

A Fully Implantable Pacemaker for the Mouse: From Battery to Wireless Power

Animal models have become a popular platform for the investigation of the molecular and systemic mechanisms of pathological cardiovascular physiology. Chronic pacing studies with implantable pacemakers in large animals have led to useful models of heart failure and atrial fibrillation. Unfortunately, molecular and genetic studies in these large animal models are often prohibitively expensive or not available. Conversely, the mouse is an excellent species for studying molecular mechanisms of cardiovascular disease through genetic engineering. However, the large size of available pacemakers does not lend itself to chronic pacing in mice. Here, we present the design for a novel, fully implantable wireless-powered pacemaker for mice capable of long-term (>30 days) pacing. This design is compared to a traditional battery-powered pacemaker to demonstrate critical advantages achieved through wireless inductive power transfer and control. Battery-powered and wireless-powered pacemakers were fabricated from standard electronic components in our laboratory. Mice (n = 24) were implanted with endocardial, battery-powered devices (n = 14) and epicardial, wireless-powered devices (n = 10). Wireless-powered devices were associated with reduced implant mortality and more reliable device function compared to battery-powered devices. Eight of 14 (57.1%) mice implanted with battery-powered pacemakers died following device implantation compared to 1 of 10 (10%) mice implanted with wireless-powered pacemakers. Moreover, device function was achieved for 30 days with the wireless-powered device compared to 6 days with the battery-powered device. The wireless-powered pacemaker system presented herein will allow electrophysiology studies in numerous genetically engineered mouse models as well as rapid pacing-induced heart failure and atrial arrhythmia in mice.

The minimization of the extraneous electromagnetic fields of an inductive power transfer system

The efficiency of inductive wireless power transfer (IPT) systems has been extensively studied. However, the electromagnetic compatibility of such systems is at least as important as the efficiency and has received much less attention. We consider the net magnetic dipole moment of the system as a figure of merit. That is, we seek to minimize the magnitude of the net dipole moment in order to minimize both the near magnetic fields and the radiated power. A 20 kHz, 3.3 kW, IPT system, representative of typical wireless vehicular battery charging systems, is considered and it is seen that one particular value of load impedance minimizes the net dipole moment while another, distinct, value maximizes efficiency. Thus, efficiency must be traded off, at least to some extent, in order to minimize extraneous electromagnetic fields.

Communication controller and control unit design for Qi wireless power transfer

Abstract Qi, the wireless power standard, has been proposed to allow low power systems to receive power through wireless inductive power transfer. The standard outlines the essential, desired and optional requirements for developing the wireless power transfer platform. In this paper, we present the design and implementation results of communication controller for guided positioning single transmitter–single receiver wireless power transfer platform. Apart from the basic design, additional processing and data storage capability is introduced to make the design adaptive in terms of response time and the size of control data transfer. The method of estimating the amount of power transfer is modified to reduce design complexity and internal power consumption of power transmitter and receiver. The implementation results help to access the ratio of power transferred to resource utilization and the ratio of power transferred to power consumed in simplistic wireless power transfer platform.

PRT 차량의 전력 공급시스템 개발

In this paper, the design of PRT vehicle power supply system is discussed. Since there is no power feeding line facilities in PRT system under development, the PRT vehicle must have its own energy storage device on board. For the energy storage device, ultra-capacitor bank is applied due to its fast charging capability and long life time. Charging the Ultra-capacitor bank is performed by wireless inductive power transfer system. The capacitor bank is charged up in less than 10 seconds when the vehicle is traveling by passenger stations. In this paper the design of the ultra-capacitor bank and the wireless inductive power transfer system for the PRT vehicle are discussed. Tests are conducted for the both system and the result shows the efficiency of the wireless inductive power transfer system is higher than 80%.

Wireless Power Transfer in Loosely Coupled Links: Coil Misalignment Model

A novel analytical model of inductively coupled wireless power transfer is presented. For the first time, the effects of coil misalignment and geometry are addressed in a single mathematical expression. In the applications envisaged, such as radio frequency identification (RFID) and biomedical implants, the receiving coil is normally significantly smaller than the transmitting coil. Formulas are derived for the magnetic field at the receiving coil when it is laterally and angularly misaligned from the transmitting coil. Incorporating this magnetic field solution with an equivalent circuit for the inductive link allows us to introduce a power transfer formula that combines coil characteristics and misalignment factors. The coil geometries considered are spiral and short solenoid structures which are currently popular in the RFID and biomedical domains. The novel analytical power transfer efficiency expressions introduced in this study allow the optimization of coil geometry for maximum power transfer and misalignment tolerance. The experimental results show close correlation with the theoretical predictions. This analytic technique can be widely applied to inductive wireless power transfer links without the limitations imposed by numerical methods.

Method of Load/Fault Detection for Loosely Coupled Planar Wireless Power Transfer System With Power Delivery Tracking

A method to determine various operating modes of a high-efficiency inductive wireless power transfer system which is capable of supporting more than one receiver is proposed. The three operating modes are no-load, safe, and fault modes. The detection scheme probes the transmitter circuitry periodically to determine the operating mode. For power saving, the transmitter is powered down when there is no valid receiver placed on the transmitting coil. If any conductive or magnetic object that can affect the total effective inductance of the transmitting coil is located nearby, the system will enter the fault mode and shut down the transmitter so that it will not be damaged. The safe mode is the nominal operation mode when the power transmission efficiency is high with minimum power loss and zero-voltage switching operation of the class-E transmitter is achieved. The determination of the operating mode is achieved by analyzing the transmitting coil voltage and supply current space, requiring no communication link between the transmitter and receiver. The linear relationship between the power delivery and the supply current can be used to calculate the power delivered to the load(s).

A wireless power supply system for robotic capsular endoscopes

In expanding capsular endoscopy from a mere passive screening tool to a multipurpose robot, batteries become inadequate. Wireless power supply overcomes the problem of power shortage and enables the integration of high-power modules. This work focuses on wireless inductive power transfer and its technology optimization in size, materials and efficiency. A user friendly and stable external unit has been developed that supports power and data transmission through the downlink (from the external world to the capsule). The possibility of using a Helmholtz coil at the primary side has been investigated and a preliminary set-up has been implemented. The ongoing development on 3D coil geometries is further refined by the introduction of a laser machined ferrite core to boost the amount of available power. It is demonstrated that 330 mW can be transferred to a capsule under all possible orientations, within a 0.48 cm 3 volume.