Wireless Power Transfer Link Research Articles

An NFC on Two-Coil WPT Link for Implantable Biomedical Sensors under Ultra-Weak Coupling.

The inductive link is widely used in implantable biomedical sensor systems to achieve near-field communication (NFC) and wireless power transfer (WPT). However, it is tough to achieve reliable NFC on an inductive WPT link when the coupling coefficient is ultra-low (0.01 typically), since the NFC signal (especially for the uplink from the in-body part to the out-body part) could be too weak to be detected. Traditional load shift keying (LSK) requires strong coupling to pass the load modulation information to the power source. Instead of using LSK, we propose a dual-carrier NFC scheme for the weak-coupled inductive link; using binary phase shift keying (BPSK) modulation, its downlink data are modulated on the power carrier (2 MHz), while its uplink data are modulated on another carrier (125 kHz). The two carriers are transferred through the same coil pair. To overcome the strong interference of the power carrier, dedicated circuits are introduced. In addition, to minimize the power transfer efficiency decrease caused by adding NFC, we optimize the inductive link circuit parameters and approach the receiver sensitivity limit. In the prototype experiments, even though the coupling coefficient is as low as 0.008, the in-body transmitter costs only 0.61 mW power carrying 10 kbps of data, and achieves a 1 × 10 bit error rate under the strong interference of WPT. This dual-carrier NFC scheme could be useful for small-sized implantable biomedical sensor applications.

Conditions for a Load-Independent Operating Regime in Resonant Inductive WPT

This paper provides a rigorous theoretical formulation to obtain an inductive resonant wireless power transfer (WPT) link with load-independent output voltage or current. This is a crucial working condition for wireless battery recharging, where there is no deterministic knowledge of load variation with respect to the battery charging level. The ideal lossless and the realistic lossy configurations are considered for both voltage- and current-excited WPT links. The link transfer matrix ( ABCD matrix) is used to determine the operating frequencies where a load-independent output voltage or current can be obtained. It is shown that in the lossy cases that an almost load-independent behavior can be achieved, provided that the load resistance lies in a suitable range and analytical conditions on the load resistance value have been derived. The analytical relationships obtained by this theory are validated by means of both circuit simulation and experimental data at 13.56 MHz.

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 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.

Conjugate Image Theory Applied on Capacitive Wireless Power Transfer

Wireless power transfer using a magnetic field through inductive coupling is steadily entering the market in a broad range of applications. However, for certain applications, capacitive wireless power transfer using electric coupling might be preferable. In order to obtain a maximum power transfer efficiency, an optimal compensation network must be designed at the input and output ports of the capacitive wireless link. In this work, the conjugate image theory is applied to determine this optimal network as a function of the characteristics of the capacitive wireless link, as well for the series as for the parallel topology. The results are compared with the inductive power transfer system. Introduction of a new concept, the coupling function, enables the description of the compensation network of both an inductive and a capacitive system in two elegant equations, valid for the series and the parallel topology. This approach allows better understanding of the fundamentals of the wireless power transfer link, necessary for the design of an efficient system.

Ultrahigh-Data-Rate Communication and Efficient Wireless Power Transfer at 13.56 MHz

Wireless power transfer (WPT) has gained renewed interest due to emerging low-power applications and high efficiency. Coupled with power in many applications is the need for communication, whether for regulation of power transfer or for transfer of information between the source and the load. Several communication methods have been proposed for use with WPT, including adjacent channel communication (non-WPT), as well as WPT-based methods, such as load modulation and passive backscattering. However, approaches using the WPT link have historically been low-speed (<;400 kb/s). In this letter, we report on an ultrahigh data-rate (3.39 Mb/s) communication method that utilizes the WPT link for both power and data transfer, operating at 13.56 MHz, capable of 3.39 Mb/s data transfer with an efficiency reduction of only <;2%.

Inductive Wireless Power Transfer and Uplink Design for a CMOS Tag With 0.01 mm2Coil Size

This work introduces the smallest inductive wireless power transfer and backscattering communication link to date, with tag coil only of 0.01 mm2. The CMOS tag, operated at 4.7 GHz, generates a 0.1-mW dc power under a coupling distance of 1.2 mm and reader power of 31.4 dBm. The on-off keying back-scattering uplink is demonstrated with data rate of 20 kb/s.

An improved resonant wireless power transfer system with optimum coil configuration for capsule endoscopy

Resonant wireless power transfer is a prominent method of powering a biomedical capsule endoscope, in which the high efficiency of an inductive power link and the electromagnetic safety of biological tissues are greatly important. This paper presents a complete analytical model of a resonant wireless power transfer link, where the efficiency is remarkably increased with the improved power transmission coil configuration. This configuration involves two outer coils and one middle coil. The separation and turn ratios between the outer coils and the middle coil are 0.4 times of the coil radius and 3:2, respectively. An analysis of and comparison with the existing coil configuration show that the proposed configuration relatively attains higher Q-factor, coupling coefficient, and H-field uniformity, which lead to improvement in power transfer efficiency, stability, and electromagnetic safety. The analysis is validated through experiments. With a power receiving coil of Ø11mm×8mm, the proposed power transfer coil attains a minimum efficiency of around 36.6% at the worst position of the power-receiving coil. The attained efficiency was 156% higher than the efficiency of 14.62% obtained by the best of existing coil at the same level of H-field uniformity. Incorporating high permeability core, up to 200mW of power is transferred with the proposed coil at 300kHz in accordance with the electromagnetic safety guideline.

Optimal design of a wireless power transfer link using parallel and series resonators

The optimal design problem for a wireless power transfer link based on a resonant inductive coupling is addressed in this paper. It is assumed that the magnetic coupling coefficient and the inductor quality factors are known. By employing the conjugate image impedances, the values of the inductances realizing the optimal design with respect to given values of the network input and load impedances are derived. It is demonstrated that there is just one optimal design maximizing both the power delivered to the load and the power transfer efficiency of the link. The four possible schemes corresponding to the use of a parallel or a series arrangement for the two coupled resonators (Parallel-Parallel, Series-Series, Parallel-Series, and Series-Parallel) are considered and discussed. Closed form analytical formulas are derived and validated by circuital simulations.

Modelling of wireless power transfer links based on capacitive coupling

SummaryBy using network theory, a wireless power transfer network based on coupled capacitance, that is, on electric field coupling, is numerically investigated. Three possible solutions of interest are considered: one that maximizes efficiency, one that maximizes the power delivered to the load and one that realizes power matching (conjugate matching). In each case, at a selected frequency, the optimal source/load impedances are derived in closed form. It is shown that maximum efficiency solution has the possibility of achieving almost unitary efficiency. It is also shown that, as the efficiency is increased, the power delivered to the load is decreased. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Enhancing the versatility of wireless biopotential acquisition for myoelectric prosthetic control

Objective. A significant challenge in rehabilitating upper-limb amputees with sophisticated, electric-powered prostheses is sourcing reliable and independent channels of motor control information sufficient to precisely direct multiple degrees of freedom simultaneously. Approach. In response to the expressed needs of clinicians, we have developed a miniature, batteryless recording device that utilizes emerging integrated circuit technology and optimal impedance matching for magnetic resonantly coupled (MRC) wireless power transfer to improve the performance and versatility of wireless electrode interfaces with muscle. Main results. In this work we describe the fabrication and performance of a fully wireless and batteryless EMG recording system and use of this system to direct virtual and electric-powered limbs in real-time. The advantage of using MRC to optimize power transfer to a network of wireless devices is exhibited by EMG collected from an array of eight devices placed circumferentially around a human subject’s forearm. Significance. This is a comprehensive, low-cost, and non-proprietary solution that provides unprecedented versatility of configuration to direct myoelectric prostheses without wired connections to the body. The amenability of MRC to varied coil geometries and arrangements has the potential to improve the efficiency and robustness of wireless power transfer links at all levels of upper-limb amputation. Additionally, the wireless recording device’s programmable flash memory and selectable features will grant clinicians the unique ability to adapt and personalize the recording system’s functional protocol for patient- or algorithm-specific needs.

Rigorous design of matched wireless power transfer links based on inductive coupling

AbstractThis paper focuses on a near‐field wireless power transmission link consisting of two magnetically coupled inductances. The case of a resonant coupling realized by adding appropriate compensating capacitances is solved. By using a network formalism, the link is modeled as a two‐port network and rigorously analyzed in the case where both the input impedance and the load are specified. In particular, it is demonstrated that there is just one optimum design of the network that allows maximizing both the efficiency and the active power on the load. Closed‐form design formulas for the optimum design are presented and validated by circuital simulations.

Simple compensation for lateral misalignments in resonant inductive coupling links

This Letter describes a simple compensation method to reduce the transfer efficiency variation in a resonant inductive coupling (RIC) wireless power transfer link subject to lateral misalignment. The technique is based on impedance matching an RIC link such that the link operates at either over-coupling or critical coupling within the extents of lateral misalignment. Applying the method in a test scenario led to a reduction in the range of obtained transfer efficiency values, from 45% of peak value in a conventional arrangement, to 5%. The proposed method has a potential for application in the design of free-positioning planar wireless chargers.

A Computational Approach for a Wireless Power Transfer Link Design Optimization Considering Electromagnetic Compatibility

This paper presents an electromagnetic-artificial intelligence design optimization approach of a wireless power transfer link (WPTL). Electromagnetic solutions from a 3-DFE model of the WPTL were utilized to minimize the field signature around each design while maintaining high efficiency. The reduced field signatures around the WPTL would enable the achievement of designs that are in accordance with international electromagnetic compatibility (EMC) standards such as international commission on non-ionizing radiation protection guidelines with respect to public exposure levels of EM signatures below 27 $\mu \text{T}$ . As the optimization process involved utilizing a large number of fitness function evaluations, numerous 3-DFE solutions were required increasing the computational burden. Artificial neural networks were developed, trained, and used to produce the required equivalent 3-DFE solutions to evaluate the fitness function. As a result, this process significantly reduced the computational time by nearly 90%. The genetic algorithm-based optimization process yielded the desired results of electromagnetically compatible WPTL designs at the early development stage satisfying EMC standards.

Unidirectional wireless power transfer using near-field plates

One of the obstacles preventing wireless power transfer from becoming ubiquitous is their leakage of power: high-amplitude electromagnetic fields that can interfere with other electronic devices, increase health concerns, or hinder power metering. In this paper, we present near-field plates (NFPs) as a novel method to tailor the electromagnetic fields generated by a wireless power transfer system while maintaining high efficiency. NFPs are modulated arrays or surfaces designed to form prescribed near-field patterns. The NFP proposed in this paper consists of an array of loaded loops that are designed to confine the electromagnetic fields of a resonant transmitting loop to the desired direction (receiving loop) while suppressing fields in other directions. The step-by-step design procedure for this device is outlined. Two NFPs are designed and examined in full-wave simulation. Their performance is shown to be in close agreement with the design predictions, thereby verifying the proposed design and operation. A NFP is also fabricated and experimentally shown to form a unidirectional wireless power transfer link with high efficiency.

Design of magnetic-resonant wireless power transfer links realized with two coils: comparison of solutions

A novel approach for the rigorous design of magnetic resonant wireless power transfer links is introduced. We show how, starting from two coupled inductors and making use of general network theory, it is possible to derive analytic rules for designing the source and load terminations which provide the maximum power transfer efficiency or maximize the received power. We also show that, by adding suitable matching networks to two coupled inductors we can realize a wireless link acting as a 1:n transformer and having the all required tunable reactive elements on the primary side. The proposed topology greatly simplifies the design, since only an inductive coil and a fixed capacitance are required on the secondary side; in addition, when tuning is required due to coils misalignment or to link distance variation, it can be attained by acting on the transmitter side without the need for a feedback communication through the link. Moreover, when the load resistance is designed for maximum output power, its value is fixed and does not depend on the coupling. A numerical and experimental verification of the proposed approach is also presented.

Rigorous Network and Full-Wave Electromagnetic Modeling of Wireless Power Transfer Links

The proposed approach makes use of full-wave electromagnetic modeling of wireless power transfer links in order to derive the network characterization, e.g., in terms of scattering or impedance matrix. Once the latter is obtained, we show that network theory provides the appropriate matching impedances for achieving either maximum efficiency, maximum power on the load, or conjugate matching. The proposed approach also permits to derive closed-form matching networks and expressions for power and efficiency. An example of full-wave numerical electromagnetic modeling of a wireless power transfer link is presented. The selected example, which is similar to the experiment published by Kurs , shows the importance of selecting the appropriate source/load impedance for obtaining significative results.

Electromagnetic Energy Harvesting and Wireless Power Transmission: A Unified Approach

In this paper, a rigorous procedure for the circuit-level analysis and design of entire systems, developed to provide power wirelessly, is presented. A unified theoretical approach is first introduced, based on a two-port-equivalent circuit representation, to describe the wireless power transfer link when the transmitter and the receiver are either in the near-field or in the far-field region reciprocally. This approach allows one to compute in a straightforward manner the system figure of merit, namely the power transfer efficiency. Specific guidelines for the two configurations are then intensively discussed together with the adopted software tools based on the combination of full-wave analysis and nonlinear harmonic balance techniques. Several practical examples based on this design procedure are presented, demonstrating predicted and experimental behavior of unconventional devices for both near-field and far-field power transfer usage.

A 1-kW Contactless Energy Transfer System Based on a Rotary Transformer for Sealing Rollers

This paper introduces an innovative contactless energy transfer system for power supplying rotatable parts of automatic machineries as a robust alternative to sliding contacts. The design procedure of the key system devices, such as the dc/ac converter and the rotary transformer with its windings, is discussed. Different configurations in terms of switching network, number of turns, wire, and compensation are discussed with respect to their impact on the system efficiency and power factor. A thermal model to account for the core temperature is also introduced. Two setups, operating at 50 kHz and able to transfer up to 1.3 kW in a contactless fashion, are realized and tested to supply sealing roller resistors of automatic machineries. The system prototypes are then experimentally tested to validate the analytical models and the finite element simulations of the entire wireless power transfer link. Trade-offs emerge from the setups, in particular concerning efficiency, power factor, and electro-magnetic compatibility. As a consequence, we discuss the choice of the optimal configuration depending on the final application.

Design and Characterization of Wireless Power Links for Brain–Machine Interface Applications

In this paper, the design of an inductive power link (IPL) for wireless power transfer (WPT) in brain–machine interface (BMI) applications is thoroughly studied. The constraints and requirements of BMI applications are analyzed. By theoretical derivations, the relationships between the IPL performances and its electrical parameters are determined. The design guidelines for the IPL physical parameters are then obtained through experimental characterizations. Experimental results show that with proper IPL design, the efficiency can be improved from the previously reported values of 29.9% and 4.3% to 33.1% and 9.2% for BMI WPT distances of 5 and 12.5 mm, respectively.