Inductive Link Research Articles

A Power and Data Decoupled Transmission Method for Wireless Power Transfer Systems via a Shared Inductive Link

Wireless Power Transfer (WPT) technology is gaining global popularity. However, in some applications, data transmission is also required to monitor the load states. This paper presents an alternative wireless power and data transmission method via the shared inductive link. With the method, the system presents three characteristics: (1) controllability and stability of the output voltage; (2) miniaturization in volume of the system; (3) decoupled transmission of power and data. The output voltage control is realized by a non-inductive hysteresis control method. In particular, data is transferred when the power transmission is blocked (i.e., the hysteresis switch is off). The interference between power and data transmission is very small. The signal to noise ratio (SNR) performance which is relevant to the interference from power transfer to data transfer and data transfer capacity, is studied and optimized. Both simulation and experimental results have verified the proposed method.

Efficient Modeling of Crosstalk Noise on Power Distribution Networks for Contactless 3-D ICs

An efficient and frequency-dependent model describing the crosstalk noise on power distribution networks due to inductive links in contactless 3-D ICs is presented. A two-step approach is followed to model the crosstalk effect. During the first step, the mutual inductance between the power distribution network and the inductive link is analytically determined. Due to the weak dependence of mutual inductance to frequency, a magnetostatic model is proposed for this step. The model includes the physical and electrical characteristics of both the on-chip inductor and the wires of the power distribution network. In this way, different power network topologies can be modeled facilitating noise analysis in the vicinity of the on-chip inductor. This approach is justified by the typical use of regular power network topologies in modern integrated circuits. In the second stage, the noise is assessed with SPICE simulations, considering the mutual inductance between the two structures from the first step and the resistance variations due to high frequency effects. Thus, an efficient, scalable, and accurate method for the analysis of the crosstalk effects due to inductive links is provided, without resorting on computationally expensive and time consuming full-wave simulations. Compared with the full-wave simulations, the induced noise is evaluated four orders of magnitude faster with the proposed model. The accuracy of the proposed model is within 10% of the respective noise computed with a commercial electromagnetics simulator using the finite element method. An analysis including the effect of substrate resistivity on the crosstalk noise is also presented.

Resonant Configuration Topology Exploration for Inductive Link Power Transfer

This paper investigates the performance of circuit topology used in wireless power applications to optimize the level of maximum efficiency. We analyse the series and the parallel resonant topologies for use in an inductive coupling link to derive power transfer efficiency expressions verified using MATLAB. We look into the two topologies into the link under resonant conditions for selectively supplying the device with power. The results are obtained analytically which are verified subsequently by MATLAB simulation. We then analyse the links to see how maximum power transfer efficiency for a given pair of coils can be achieved. The topology at a given tuning frequency is used for powering a selected resistive load. The method is presented using a given pair of coils simulated and the results agree well with the theoretical explanation and derivations.

Chip-Scale Coils for Millimeter-Sized Bio-Implants.

Next generation implantable neural interfaces are targeting devices with mm-scale form factors that are freely floating and completely wireless. Scalability to more recording (or stimulation) channels will be achieved through distributing multiple devices, instead of the current approach that uses a single centralized implant wired to individual electrodes or arrays. In this way, challenges associated with tethers, micromotion, and reliability of wiring is mitigated. This concept is now being applied to both central and peripheral nervous system interfaces. One key requirement, however, is to maximize specific absorption rate (SAR) constrained achievable wireless power transfer efficiency (PTE) of these inductive links with mm-sized receivers. Chip-scale coil structures for microsystem integration that can provide efficient near-field coupling are investigated. We develop near-optimal geometries for three specific coil structures: in-CMOS, above-CMOS (planar coil post-fabricated on a substrate), and around-CMOS (helical wirewound coil around substrate). We develop analytical and simulation models that have been validated in air and biological tissues by fabrications and experimental measurements. Specifically, we prototype structures that are constrained to a 4mm 4mm silicon substrate, i.e., the planar in-/above-CMOS coils have outer diameters 4mm, whereas the around-CMOS coil has an inner diameter of 4mm. The in-CMOS and above-CMOS coils have metal film thicknesses of 3- m aluminium and 25- m gold, respectively, whereas the around-CMOS coil is fabricated by winding a 25-m gold bonding wire around the substrate. The measured quality factors (Q) of the mm-scale Rx coils are 10.5 @450.3MHz (in-CMOS), 24.61 @85MHz (above-CMOS), and 26.23 @283MHz (around-CMOS). Also, PTE of 2-coil links based on three types of chip-scale coils is measured in air and tissue environment to demonstrate tissue loss for bio-implants. The SAR-constrained maximum PTE measured (together with resonant frequencies, in tissue) are 1.64% @355.8MHz (in-CMOS), 2.09% @82.9MHz (above-CMOS), and 3.05% @318.8MHz (around-CMOS).

Practical Inductive Link Design for Biomedical Wireless Power Transfer: A Tutorial.

Wireless power transfer systems, particularly those based on inductive coupling, provide an increasingly attractive method to safely deliver power to biomedical implants. Although there exists a large body of literature describing the design of inductive links, it generally focuses on single aspects of the design process. There is a variety of approaches, some analytic, some numerical, each with benefits and drawbacks. As a result, undertaking a link design can be a difficult task, particularly for a newcomer to the subject. This tutorial paper reviews and collects the methods and equations that are required to design an inductive link for biomedical wireless power transfer, with a focus on practicality. It introduces and explains the published methods and principles relevant to all aspects of inductive link design, such that no specific prior knowledge of inductive link design is required. These methods are also combined into a software package (the Coupled Coil Configurator), to further simplify the design process. This software is demonstrated with a design example, to serve as a practical illustration.

Sensitivity optimization of Printed Spiral Coil for Wireless Resistive Analog Passive (WRAP) Sensors using Genetic Algorithm.

Body-worn battery-less Wireless Resistive Analog Passive (WRAP) sensor can be unobtrusive while collecting physiological data continuously. Inductive connection between a pair of Printed Spiral Coils (PSC) eliminates the intrusive wires. Inductive connection of primary and secondary PSC enabled us to probe the body signals using the inductive link. The primary side voltage is modulated by the sensed body signal at the secondary PSC. The coil physical characteristics influence the sensitivity which is defined as observed voltage changes over the sensor variation. We have previously reported an iterative method to optimize the coil specifications for maximum sensitivity with constrained coil prof ile size by maximizing the power transfer efficiency from primary to secondary. In this study sensitivity is maximized by first, driving an analytical multivariable equation of circuit components and physical characteristics, and then using Genetic Algorithm (GA) to maximize it with considering the size and fabrication constraints. The results are compared to the other methods that shows a higher result in the range of 102 comparing to the best alternate methods (sqp). It helps us to detect smaller physiological signals in the noisy environment.

Magnetically Balanced Power and Data Telemetry for mm-scale Neural Implants.

Millimeter-sized implants for neural interface have been of great interest in the neuroengineering field due to their minimal invasiveness and great potential as an alternative to conventional bulky neural interfacing systems. However, their size poses great challenges not only on wireless power transmission, but also on uplink (implant to outside) data communication. One of most feasible data communication methods is load-shift keying based on the backscattering principle utilizing the existing inductive power link. This method consumes minimal power inherently, but its achievable modulation index is infinitesimal so that it is greatly challenging to detect the transmitted data on the outside. In this paper, we explore new schemes using a separate data reception coil that is magnetically balanced with the power coil. Due to its minimal crosstalk between the power transmission coil and data coil, a much higher data modulation index can be achieved. In addition to circular coils, we also present elliptical magnetic-balanced coil structures. According to finite element model stimulations with a realistic brain tissue model in Ansys HFSS and time domain simulation in Cadence, up to $ 15\times $ improvement in data modulation index can be achieved compared to conventional methods.

Maximum Efficiency Tracking in Inductive Power Transmission Using Both Matching Networks and Adjustable AC–DC Converters

The maximum efficiency point of an inductive power link depends on its load power consumption and the distance between the transmitter and the receiver. Matching networks (MNs) and adjustable ac–dc converters have been proposed in the literature as a means to achieve and track this maximum efficiency point. Most of the published papers in inductive power transmission only use one of these two methods without considering a joint design. In this paper, we analyze and compare both methods proposing a general joint design which exploits the advantages of each method. A proof-of-concept system was developed following the proposed flow, built and tested. This system, with a regulated output voltage, presents improvements in measured efficiencies of up to 80% (from 9.2% to 16%) at the largest distances, thus maximizing the distance range. The same approach can be used to maximize output dc voltage, instead of the link efficiency. The proposed system using our designed MN achieved a maximum output voltage that was 90% higher (from 1.36 to 2.59 V) than the case where only a step-up converter was used.

Suggested Methods to Solve the Coils Misalignment for the Biomedical Implants

One of the major problems of the inductive coupling link in the biomedical implantable devices is the misalignment between coils. This paper produces two simple suggested methods to avoid and reduce the misalignment between two coils. The first one is to split the implanted coil into two identical coils with 450 μH of inductance where the external coil was equal to them in inductance ~ 900μH. The results show that the received powers are constant and compensated by one of the coils, which provides a stable power at the implant. The second proposed suggestion is to use two separated identical coils situated in the center angles outside the human skin. The transmitting RF power of the both coils has a same resonance frequency and received with a single small implant coil, which sums the received RF signals where the amplitudes are double. The mathematical analysis of the second suggestion is introduced.

Backscatter Efficiency Modeling of Inductive Links Applied to Wireless Power Transfer Systems

In this paper, we analyze the backscatter response of inductive link-based wireless power transfer systems. This analysis leads to a model that predicts the power levels received back on the primary side of the inductive link. The proposed model considers the inductive link characteristics as the magnetic coupling factor, the quality factors of the inductors, and the impedance matching at the secondary side, but also accounts for the equivalent on-resistance of the switch used to apply the response on the secondary side. The modeling of the backscattering response can be helpful to choose design variables of the system such as the duty cycle of the response and the size of the switching transistors. Moreover, the estimation of the reflected power can be used to specify the receiver sensitivity on the primary side. The model is validated with experimental results on two different inductive links: one using only FR4-printed inductors with a PIN diode acting as backscatter switch and the other using a CMOS fully integrated wireless power receiver. The measured backscattered power in both cases agrees with the predicted values.

Toward an Energy-Efficient High-Voltage Compliant Visual Intracortical Multichannel Stimulator

We present, in this paper, a new multichip system aimed toward building an implantable visual intracortical stimulation device. The objective is to deliver energy-optimum pulse patterns to neural sites with needed compliance voltage across high electrode–tissue interface impedance of implantable microelectrodes. The first chip is an energy-efficient stimuli generator (SG), and the second one is a high-impedance microelectrode array driver (MED) output stage. The four-channel SG produces rectangular, half-sine, plateau-sine, and other types of current pulse with stimulation current ranging from 2.32 to 220 $\mu \text{A}$ per channel. The microelectrode array driver is able to deliver 20 V per anodic or cathodic phase across the microelectrode–tissue interface for ±13 V power supplies. The MED supplies different current levels with the maximum value of 400 $\mu \text{A}$ per input and 100 $\mu \text{A}$ per output channel simultaneously to 8–16 stimulation sites through microelectrodes, connected either in bipolar or monopolar configuration. Both chips receive power via inductive link and data through capacitive coupling. The SG and MED chips have been fabricated in 0.13- $\mu \text{m}$ CMOS and 0.8- $\mu \text{m}$ 5-/20-V CMOS/double-diffused metal-oxide-semiconductor technologies. The measured dc power budgets consumed by low- and mid-voltage chips are 2.56 and 2.1 mW consecutively. The system, modular in architecture, is interfaced with a newly developed platinum-coated pyramidal microelectrode array. In vitro test results with 0.9% phosphate buffer saline show the microelectrode impedance of 70 $\text{k}\Omega $ at 1 kHz.

Coil geometry models for power loss analysis and hybrid inductive link for wireless power transfer applications

This paper presents a hybrid inductive link for Wireless Power Transfer (WPT) applications. Achieving better power transfer efficiency over a relatively wider distance across coils is the prime objective in most of the WPT systems, but often suffers from power loss in the near field area of inductively coupled coils. One of the reasons for this power loss is the pattern of the magnetic field produced by the source coil used in the WPT system. Mostly the nature of magnetic field produced by the source coil is distributed radially over the coil, in which the produced magnetic field is not fully utilized. Achieving better efficiency and load current by reducing power loss is the main driving force of this work. One of the viable methods to reduce the power loss is by increasing the field intensity thereby redirecting the flux lines flow to be directional. With this aim, three coils such as solenoid, spiral and conical are designed and simulated to determine the magnetic field strength using Finite Element Method. The conical coil produces the highest self-inductance of 8.63 µH and a field strength of 1.542 Wb with the coil thickness of 3.20 mm. Then, WPT system is demonstrated with the inclusion of Maximum Power Point Tracking algorithm for improving efficiency. The schematic of flux generation of both in the transmitter and receiver sections are demonstrated and analyzed graphically. The efficiency of both simulation and experimental measurements are matched well with similar progression. The effect of parameters (angle, distance, and load resistance) on the efficiency is explored. The outcomes conclude that the inductive coupling has achieved 73% (average case) power transfer wirelessly over a distance of 5 cm with an input voltage of 5 V and 5 MHz frequency.

Design and measurement of a contactless interface between a dipole antenna and a CMOS fully integrated wireless power receiver

Here, the authors present a study on a contactless interface between a fully integrated wireless power receiver (WPR) and a dipole antenna. The authors analyse the impedance matching between the antenna and the inductive link formed by the contactless interface for providing an appropriate design methodology. Furthermore, the authors developed a measurement strategy to verify the entire system comprised by a pair of dipole antennas, the inductive link, and the CMOS WPR. The results show that the CMOS die is well coupled to the antenna, the complete system operates correctly with a source of 26.6 dBm at 987 MHz when the distance between the dipole antennas is 58 cm.

Contactless Heterogeneous 3-D ICs for Smart Sensing Systems

A heterogeneous contactless transceiver circuit is designed to provide inter-tier signalling for a 3-D system considering specific bonding constraints. The system is composed of two tiers, a 65 nm processing tier and a 0.35 µm sensing tier. Face-to-back integration is chosen to support fluidic sensing. Half duplex communication between the tiers is provided through inductive links. Each tier is considered to be fabricated in a different technology to enable low manufacturing cost and benefit from the advantages each technology offers. Both the uplink and downlink transceivers achieve data rates that reach 1 Gbps with non-return-to-zero data encoding. Energy efficiency is the predominant objective, with the uplink dissipating 5.28 pJ/b and 8.67 pJ/b for the downlink. A 6.8× power reduction is demonstrated when using heterogeneous technologies, compared to a state-of-the-art 0.35 µm transceiver, while the dissipated energy is decreased by 37.5% as compared to a state-of-the-art 65 nm transceiver. Process variation analysis is also performed to ensure the proposed circuit operates correctly across several process corners, covering a broad design space. To improve system robustness, an overhead of 2.3% on the peak power and <1% on the average power is shown, respectively.

A Comprehensive Comparative Study on Inductive and Ultrasonic Wireless Power Transmission to Biomedical Implants.

This paper presents a comprehensive comparison between inductive coupling and ultrasound for wireless power transmission (WPT) to biomedical implants. Several sets of inductive and ultrasonic links for different powering distances (d 12) and receiver dimensions have been optimized, and their key parameters, including power transmission efficiency (PTE) and power delivered to the load (PDL) within safety constraints, have been compared to find out which method is optimal for any given condition. Two design procedures have been presented for maximizing the PTE of inductive and ultrasonic links by finding the optimal geometry for the transmitter (Tx) and receiver (Rx) coils and ultrasonic transducers as well as the optimal operation frequency (fp ). Our simulation and measurement results showed that the ultrasonic link transcends the inductive link in PTE and somewhat in PDL for a small Rx of 1.1 mm3 (diameter of 1.2 mm), particularly when the Rx was deeply implanted inside the tissue (d 12 ≥ 10 mm). However, for a larger 20 mm3 Rx (diameter of 5 mm), the inductive link achieved higher PTE and PDL, particularly at shorter distances (d 12 < 30 mm). The optimal loading condition is shown to be quite different in inductive and ultrasonic links. Despite higher performance for small Rx and large d 12, the ultrasonic link is more sensitive to Rx misalignments and orientations. This led us to propose a new design procedure based on the worst-case misalignment scenario. The simulation results have been validated by measurements. The inductive and ultrasonic links, operating at 30 MHz and 1.1 MHz, achieved measured PTEs of 0.05% and 0.65% for the 1.1 mm3 Rx located 30 mm inside tissue and oil environments with optimal load resistances of 295 Ω and 3.8 kΩ, respectively.

Attachment, relationship communication style and the use of jealousy induction techniques in romantic relationships

Insecurely attached individuals are more likely to try to induce jealousy in their partners than securely attached individuals. Research more consistently links anxious attachment styles with jealousy induction, compared to avoidant attachment. The current study extends this limited research by examining how four attachment styles are indirectly related to jealousy induction through relationship communication styles. College men and women (N = 263) completed an online survey on their dating experiences, and indicated their likelihood of using jealousy induction tactics and relationship communication styles with a hypothetical partner. Path analysis revealed that fearfully attached individuals are more likely to indicate an aggressive communication style and this is linked to greater jealousy induction; whereas, preoccupied individuals are more likely to use a nonassertive communication style and this is linked to greater jealousy induction. Secure and dismissing styles were unrelated to jealousy induction. Findings support the anxious attachment-jealousy induction link. Future research should examine whether motives behind jealousy induction diverge as function of attachment style.

Impact of Coil Misalignment in Data Transmission over the Inductive Link of an EV Wireless Charger

The penetration rate of electric vehicles (EVs) will experience a relative increment in the future, so easy to use ways to recharge will be demanded. In this sense, wireless charging represents a safe charging method that minimises user intervention. In a similar way to conductive charge, wireless charging requires some information exchange between the charger primary side and secondary side (battery) for safety and operational reasons. Thus, wireless chargers depend on a communication system for their controlled and correct operation. This paper analysed the communication performance of a wireless EV charger in which the communiction device is part of the wireless power transfer system. Particularly, this work studies how the communication system reacts to power coil displacements, which commonly occur in their conventional performance. The results show that the compensation topology selected to ensure the resonant operation clearly impacts on the communication performance. In particular, the theoretical model and the simulation results demonstrate that the asymmetrical compensation topologies are more stable in terms of the wireless communication channel capacity.

A Low-Power High-Efficiency Inductive Link Power Supply for Neural Recording and Stimulation System-on-Chip

A Low-Power High-Efficiency Inductive Link Power Supply for Neural Recording and Stimulation System-on-Chip

A power conversion chain with an internally-set voltage reference and reusing the power receiver coil for wireless bio-implants

In this paper, a power conversion chain (PCC) with an internally-set voltage reference is presented. It is comprised of a power receiver coil, an active rectifier and a novel buck-boost converter. The output voltage of the PCC is set by using the parameters of a new buck-boost converter control unit in order to avoid utilizing an extra voltage reference circuit. Furthermore, the proposed PCC reuses the power receiver coil to facilitate the realization of the buck-boost converter. This way, the efficiency of the proposed PCC gets almost independent of the receiving coil voltage amplitude. In addition, the proposed buck-boost converter significantly reduces the size of the PCC and makes it suitable for wireless power transfer via inductive links in bio-implant applications. It should be noted that employing an active rectifier followed by the proposed buck-boost converter enhances the PCC end-to-end efficiency. The proposed PCC is simulated for the input received signal with a frequency of 10 MHz and an amplitude variation within 3–7 V. The simulation results show that the efficiency variation is less than 2.6% and the achieved maximum efficiency is 80.4% and 63.4% for the proposed converter and PCC, respectively. For further verification of the proposed idea, a proof-of-concept prototype is implemented and experimental results are provided.

An optimal operating frequency selection scheme for maximizing inductive power link efficiency

AbstractImproving the efficiency of the inductive wireless power transfer (WPT) is an effective way to increase the power transfer distance, reduce the power exposure, and popularize the WPT application. If the geometrical sizes of the transmitting and receiving coils and the distance between them have been determined, an operating frequency exists to maximize the power transfer efficiency. In this work, a method to find this optimal frequency is introduced by virtue of analytical models of self‐ and mutual‐inductances and parasitic resistances and capacitances of the coils, and verified via simulations and measurements.