Resonant Inductive Link Research Articles

Design and miniaturization of a microsystem to power biomedical implants using grey wolf optimizer-based cuckoo search algorithm

<p>One of the greatest techniques, inductive coupling is frequently utilized in the biomedical sector for wireless energy transfer to implants. The aim of this article is to develop and analyze the effect of inductor geometrical characteristics, distance between transmitter (TX) and receiver (RX) and also the operating frequency on the wireless power transfer system, using grey wolf optimizer-based cuckoo search (GWO-CS) algorithm. Power transfer efficiency (PTE), power provided to load, and other critical components must all be improved or maximized and miniaturaze the microsystem proposed. The invention, design, and optimization of coils square spirals in a wireless energy transfer system using a resonant inductive link are the emphasis of this paper. The GWO-CS approach is evaluated to existing methods, demonstrated by simulations and to demonstrate the effectiveness of the suggested strategy.</p>

Improving Wireless Power Transfer Efficiency Considering Rectifier Input Impedance and Load Quality Factor

This paper presents a method to maximize power transfer efficiency (PTE) in wireless power transfer (WPT) systems with low-quality factors merely based on tuning the receiver-side components. The paper also suggests an algorithm to find the optimum components values considering the effect of input impedance of receiver-side rectifier at high-frequency (MHz) applications such as portable electronic devices. Existing methods often consider the input impedance of the full-bridge rectifier as a pure resistance at low frequencies. However, at high frequencies, the complex impedance of the rectifier should be taken into account since it impacts on the components optimum values to maximize PTE. Despite conventional maximizing PTE methods for series-series and series-parallel topologies, this paper shows that a series-parallel WPT system with low load quality factor requires adjusting the resonant capacitor in addition to resistive load. The validity of the proposed method is verified based on numerical simulations and experiment tests using a 100 mW cm-scale prototype of a resonant inductive link at 6.78 MHz with varying distance between coils. The test results show a PTE improvement up to 40% in a series-parallel WPT compared with the methods that only tune the load equivalent resistance.

Multiple Input Multiple Output Resonant Inductive WPT Link: Optimal Terminations for Efficiency Maximization

In this paper a general-purpose procedure for optimizing a resonant inductive wireless power transfer link adopting a multiple-input-multiple-output (MIMO) configuration is presented. The wireless link is described in a general–purpose way as a multi-port electrical network that can be the result of either analytical calculations, full–wave simulations, or measurements. An eigenvalue problem is then derived to determine the link optimal impedance terminations for efficiency maximization. A step-by-step procedure is proposed to solve the eigenvalue problem using a computer algebra system, it provides the configuration of the link, optimal sources, and loads for maximizing the efficiency. The main advantage of the proposed approach is that it is general: it is valid for any strictly–passive multi–port network and is therefore applicable to any wireless power transfer (WPT) link. To validate the presented theory, an example of application is illustrated for a link using three transmitters and two receivers whose impedance matrix was derived from full-wave simulations.

Simultaneous Power Feedback and Maximum Efficiency Point Tracking for Miniaturized RF Wireless Power Transfer Systems.

Near-field interfaces with miniaturized coil systems and low output power levels, such as applied in biomedical sensor systems, can suffer from severe efficiency degradation due to dynamic impedance mismatches, reducing battery life of the power transmitter unit and requiring to increase the level of electromagnetic emission. Moreover, the stability of weakly-coupled power transfer systems is generally limited by transient changes in coil alignment and load power consumption. Hence, a central research question in the domain of wireless power transfer is how to realize an adaptive impedance matching system under the constraints of a simultaneous power feedback to increase the system’s efficiency and stability, while maintaining circuit characteristics such as small size, low power consumption and fast reaction times. This paper presents a novel approach based on a two-stage control loop implemented in the primary-side reader unit, which uses a digital PI controller to maintain the rectifier output voltage for power feedback and an on-top perturb-and-observe controller configuring the setpoint of the voltage controller to maximize efficiency. The paper mathematically analyzes the AC and DC transfer characteristics of a resonant inductive link to design the reactive AC matching network, the digital voltage controller and ultimately the DC-domain impedance matching algorithm. It was found that static reactive L networks result in suitable efficiency levels for coils with sufficiently high quality factor even without adaptive tuning of operational frequency or reactive components. Furthermore, the regulated output voltage of the rectifier is a direct measure of the DC load impedance when using a regular DC/DC converter to supply the load circuits, so that this quantity can be tuned to maximize efficiency. A prototype implementation demonstrates the algorithms in a 40.68 MHz inductive link with load power levels from 10 to 100 mW and tuning time constants of 300 ms, while allowing for a simplified receiver with a footprint smaller than 200 mm2 and a self-consumption below 1 mW. Hence, the presented concepts enable adaptive impedance matching with favorable characteristics for low-energy sensor systems, i.e., minimized footprint, power level and reaction time.

Resonant Inductive WPT Link in MISO Configuration

Resonant Inductive WPT Link in MISO Configuration

Optimal Terminations for a Single-Input Multiple-Output Resonant Inductive WPT Link

This paper analyzes a resonant inductive wireless power transfer link using a single transmitter and multiple receivers. The link is described as an (N+1)–port network and the problem of efficiency maximization is formulated as a generalized eigenvalue problem. It is shown that the desired solution can be derived through simple algebraic operations on the impedance matrix of the link. The analytical expressions of the loads and the generator impedances that maximize the efficiency are derived and discussed. It is demonstrated that the maximum realizable efficiency of the link does not depend on the coupling among the receivers that can be always compensated. Circuital simulation results validating the presented theory are reported and discussed.

Additional Two-Capacitor Basic Compensation Topologies for Resonant Inductive WPT Links

The letter reveals two additional basic compensation topologies for resonant inductive wireless power transfer links (supplementary to the existing four) created by placing both compensation capacitors either on primary or secondary side, leaving the opposite coil uncompensated. This produces parallel-series/none and none/series-parallel topologies, with the latter being more practical due to its suitability to operation with typically utilized voltage-source inverters.

A High-Q Resonant Inductive Link Transmit Driver With Adaptive-Predictive Phase-Continuous Tuning and Deviation Frequency Calibration for Enhanced FSK/PSK Modulation and Power Transfer

Inductively coupled power transfer systems often use high- $Q$ antenna circuits to reduce losses and increase transmission range. However, the narrow bandwidth due to the high $Q$ -factor conventionally constrains the modulation rate on the carrier, creating a tradeoff between power transfer efficiency and data rate. In this article, we show how instantaneous tuning of the antenna can permit frequency and phase modulation data rates beyond the $Q$ -factor limitations, provided that the drive and antenna resonance frequencies are kept the same at all times. It is also necessary to ensure that the modulation symbol boundaries are precisely aligned with the tracking of the resonance tuning to ensure phase continuity and optimum power transfer. With instantaneous tuning, phase modulation can be implemented by defined numbers of cycles at an offset frequency, provided the offset is precisely controlled. We describe how the required instantaneous resonance tuning can be achieved using a switched fractional capacitor technique and present a system architecture that can follow abrupt frequency changes due to the modulation while tracking changes to the resonant condition due to environmental detuning effects at each modulation frequency. An integrated mixed-signal driver/modulator/tuner demonstrator system is presented, operating from 10 kHz–2 MHz using a 0.18- $\mu$ m 1.8–50-V CMOS/laterally-diffused metal-oxide semiconductor (LDMOS) process. The system maintains phase continuity in the antenna current throughout frequency shift keying (FSK) and phase-shift keying (PSK) modulation and employs self-calibration of the PSK modulation frequencies to achieve precise angles of phase rotation for QPSK. The antenna tuning, modulation, and frequency calibration are verified with experimental results.

Compensation Capacitors Sizing for Achieving Arbitrary Load-Independent Voltage Gain in Series-Series Inductive WPT Link Operating at Fixed Frequency

The letter reveals that for a given operating frequency, infinite amount of compensation capacitor pairs exists, yielding load independent voltage gain of a typical series-series compensated resonant inductive wireless power transfer link (WPTL). Closed-form analytical expression is derived, linking the values of compensating capacitors with the desired load independent voltage gain based on given coil inductances, coupling coefficient and operating frequency. Feasible range of achievable voltage gains is shown to be bounded by the value of coupling coefficient based on a novel 4-parameter generalized loosely coupled transformer model. Experimental results are given to validate the presented findings.

A Splitting Frequencies-Based Wireless Power and Information Simultaneous Transfer Method

A splitting frequencies-based wireless power and information simultaneous transfer (SF-WPIT) method is proposed, and its power and information transfer performances are investigated theoretically and experimentally. First, the power and information transfer characteristics, including transmitting power, power efficiency, frequency bandwidth, and effective operating range, are investigated theoretically on the splitting frequencies of strongly coupled region in symmetric series-series resonant inductive link. The investigation result shows that the splitting frequencies have a good potential of realizing a high-performance power and information transfer. Second, the SF-WPIT system is configured and the factors that influence on the performance of this system are investigated theoretically. A method of tracing two splitting frequencies is presented. A response time calculation method of splitting frequencies is presented, and the influence of response times on the performance of the SF-WPIT system is clarified. Finally, an experimental prototype is constructed with a pair of planar coils of 75-mm mean radius, and the proposed theory and system performance are verified by experimental results. This prototype exhibits a 15 kb/s of data rate and a stable power transfer irrespective of distance change in its operating range of 0-120 mm.

Selection of maximum power transfer region for resonant inductively coupled wireless charging system

In order to uphold the maximum power transfer in a resonant inductively coupled wireless power transfer system, an operating region has been proposed based on the coupling coefficient, frequency and electric load. The effectiveness of the proposed condition has been examined both theoretically and experimentally. The obtained results are in well agreement with each other. It has been seen that the operating frequency region is different for different electric loads corresponding to the coupling coefficient between the transmitter and receiver coils of the resonant inductive link. The operating frequency region shifts to lower frequency side for lower value of electric load at larger value of coupling coefficient even maintaining the optimum power transfer. The obtained knowledge reveals the design modus operandi through which an effective wireless charging system can be intended not only for low power device applications but also for high power EV charging.

Inductive link for power and data transfer to a medical implant

This paper presents a resonant inductive link for power and data transfer to a pulse generator implanted in the chest. The proposed link consists of two planar resonators and has been optimized for operating in the MedRadio band centered at 403 MHz. The wireless power/data link occurs between an external resonator operating in direct contact with the skin and a receiving resonator integrated in the silicone header of a pulse generator implanted in the chest. Numerical and experimental results are presented and discussed. From measurements performed by using minced pork to simulate the presence of human tissues, an efficiency of about 51% is demonstrated. The feasibility of using the proposed link for recharging the battery of the medical device in compliance with safety regulations is also verified and discussed.

A Review of Optimal Conditions for Achieving Maximum Power Output and Maximum Efficiency for a Series–Series Resonant Inductive Link

This paper presents the conditions for achieving maximum power output and maximum efficiency in a series–series (SS) resonant inductive link. It has been shown that output power depends on the nature of supply: current source or voltage source, resulting in different values for the same resonant link setup. For both types of sources, conditions for maximum power transfer with respect to different parameters have been derived. Efficiency, on the other hand, is independent of the nature of supply; it depends only on circuit parameters. Conditions for maximum efficiency with respect to circuit parameters have also been derived. It has been shown that an SS resonant inductive link is best suited for current-sourced input, since a voltage-sourced link behaves poorly when deviated from ideal tuning conditions. Moreover, for a voltage-sourced link, there exists an optimum value of mutual inductance at which maximum power transfer occurs. However, for a current-sourced link, output power increases with increase in coupling coefficient. The modeling and analysis has been supported with detailed simulation and experimental results.

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.

Resonant Inductive Link for Remote Powering of Pacemakers

This paper presents a wireless power link for powering implantable medical devices. The proposed link operates at 403 MHz and exploits magnetic coupling between an external resonator and an implanted resonator to wirelessly provide power to implantable devices. Experimental results for remote powering of pacemakers are reported and the compliance with safety guidelines is discussed. It is demonstrated that the proposed wireless link is able to deliver up to 1 mW with an induced 10-g average specific absorption rate lower than 1.08 W/kg. This value is significantly below the 2-W/kg recommended limit, thus proving the suitability of the proposed system to be used to energize modern pacemakers.

Electronic Tuning of Misaligned Coils in Wireless Power Transfer Systems

The misalignment and displacement of inductively coupled coils in a wireless power transfer system (WPT) can degrade the power efficiency and limit the amount of power that can be transferred. Coil misalignment leads the primary coil driver to operate in an untuned state which causes nonoptimum switching operation and results in an increase in switching losses. This paper presents a novel method to electronically tune a Class-E inverter used as a primary coil driver in an inductive WPT system to minimize the detrimental effects of misalignment between the inductively coupled coils which may occur during operation. The tuning method uses current-controlled inductors (saturable reactors) and a variable switching frequency to achieve optimum switching conditions regardless of the misalignment. Mathematical analysis is performed on a Class-E inverter based on an improved model of a resonant inductive link. Experimental results are presented to confirm the analysis approach and the suitability of the proposed tuning method.

Tuning Class E Inverters Applied in Inductive Links Using Saturable Reactors

This paper investigates the performance of Class E inverters used in wireless power transfer applications based on resonant inductive coupling. The variations in the load and the distance between the coils cause Class E inverters to operate under nonoptimal switching conditions, which result in inefficient operation and can lead to permanent damage to its switching transistor. Therefore, a novel approach to tune Class E inverters electronically is proposed. The tuning method relies on saturable reactors to ensure that the inverter operates under optimal switching conditions regardless of variations in the load and the distance between the coils. In addition, a more accurate model of inductive links is presented in order to provide a better understanding of the major power losses in resonant inductive links. Experimental results are presented to confirm the improved accuracy of the inductive link model and the validity of the tuning method.

Wireless Energy and Data Transfer for In-Vivo Epileptic Focus Localization

This paper presents a wireless energy transfer and a wireless data communication link for neural signal monitoring-more specifically, fast ripple detection for epilepsy patients. Wireless data are transferred on the same channel as the wireless energy transfer link by shifting resonance frequency of the implanted part. The remote powering link consists of a four-coil resonant inductive link structure and a power management unit on the implant side. Modulated information on the implant is demodulated using an envelope detector type amplitude shift keying demodulator in the external unit. Power transfer efficiency in air without data communication is measured as 36% for 10 mW output power at 8.4 MHz excitation frequency, while the external and the implanted coils are separated by 10 mm. Under the same experimental conditions, 1 Mbit/s data communication is achieved while maintaining a power transfer efficiency of 33%. Moreover, in-vitro tests employing mock cerebrospinal fluid are performed and 1 Mbit/s data communication is performed with an efficiency of 33% while all other parameters are preserved. Finally, hermetical sealing capability of the packaging that is composed of epoxy and Parylene-C is successfully tested for one month to evaluate the implant's short-term performance.