12.7 A power-management ASIC with Q-modulation capability for efficient inductive power transmission

In this article, we propose a new antenna geometry for near-field magnetoelectric wireless power transfer (ME-WPT) application, where the antenna geometry is found to be resilient to misalignment between the receiving and the transmitting antennas. The proposed geometry is simple to fabricate and is planar, and therefore it can be easily integrated with various platforms suitable for wearable applications. The proposed structure is demonstrated to show improved WPT efficiency under different forms of misalignment between the transmitting and receiving antennas by the virtue of miniaturization and the fringing fields. Specifically, a central bar structure is added in the traditional loop antenna to provide dipole-like and miniaturized performance. Concurrently, a discontinuity in the loop is introduced to enable fringing fields beyond the aperture of the antenna. Investigations are conducted to conclude that a superiority in the performance is associated with these fringing fields. Design-optimization, simulation, and measurement investigations are conducted to estimate the WPT performance under various forms of misalignment. Notably, the proposed structure shows an increase as high as 65% in power transfer efficiency within the range of misalignment considered in this work.

In present days, wireless power transfer systems are more popular for its application like wireless charging devices such as cell phones, laptops, electric vehicles, underwater vehicles and medical devices. In an inductively coupled battery charging system, for better power transfer capability, a high efficiency and attaining required power level, compensation is required. This paper focused on designing and analysis of series-series (S-S) compensation topologies to minimize impedance and increase efficiency of Inductive wireless power transfer (IWPT) of electric vehicle (EV) battery charging systems. First, the designing formulas are derived for S-S compensated Inductive power transfer (IPT) system from that bifurcation issue, gain, dual side control and maximum efficiency conditions are achieved. Based on formulas, equivalent electrical circuits parameters are calculated for designing a 1.5 kW output power and the resonance frequency 85 kHz. The results convey that the maximum efficiency and zero power angle (ZPA) are achieved. A simulation system is made in the MATLAB/SIMULINK, from which performance of the system results are verified.

Unmanned Underwater Vehicles (UUVs) are pivotal for underwater exploration and maintenance. Autonomous Underwater Vehicles (AUVs), with their potential to reduce operational time and environmental impact, are gaining increased interest. However, they face important technological challenges, particularly in power supply. This study focuses into the application of Inductive Wireless Power Transfer (IWPT) for continuous AUV operation, employing tightly coupled split core transformers (SCT) designed for near-field power transfer. Robust isolation and alignment mechanisms are proposed to overcome the effects of seawater environment. An IWPT device with an SCT and resonant LLC circuit is simulated and experimentally tested. Finite Element Method studies highlight the advantage of isolating the device from the seawater environment, especially at high frequencies. LLC simulation and experimental results demonstrate an efficiency in power transfer of 93.2 % and 87.1 %, respectively, transferring up to 312 W. However, global efficiency of the experimental device drops to 76.4 %, highlighting the need for optimizations in circuit design. Keywords. Inductive Wireless Power Transfer, Autonomous Underwater Vehicles, Resonant Converters, Finite Element Analysis.

Inductive power transfer (IPT) and capacitive power transfer (CPT) are two basic near-filed approaches for efficient wireless power transfer. Although they share similar system configurations, it is the coupler that determines power transfer characteristics and coupling efficiency. Given the same coupling space (i.e., coupler size constrains), this paper would study and compare the coupler characteristics for the inductive and capacitive coupler. The uniform induced voltage source is applied for both couplers, and the influence of the coupler size parameters and resonance frequencies are evaluated and used to optimize the coupler model parameters. The peak efficiency of the different couplers and their corresponding series-series compensated systems are used to judge the coupler performance. Finally, the design constrain is proposed to show the performance boundary of inductive and capacitive coupler.

An inductive link, driven by a Class-E power amplifier (PA), is the most widely used method to transfer power to medical implants. Frequency-shift keying (FSK) is a robust data modulation scheme with negligible sensitivity to amplitude noise and movements of the transmitter and receiver coils of an inductive link. However, implementing FSK modulation on a Class-E PA has been a daunting task as high-Q Class-E PAs used for remote powering are narrowband circuits, while high data rate FSK modulation demands a wideband amplifier. In this paper, we propose a Class-E PA which uses wideband FSK modulation to transfer power and data to a medical implant. In the proposed circuit, the PA is effectively switched between two load networks that keep the amplifier tuned at both carrier frequencies used for data modulation. Using this approach and with carrier frequencies of 2 and 4 MHz, we have implemented a wireless power and data transfer link which can transmit data at a rate of 1 Mbps and with a bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> . The power transfer efficiency and the power delivered to the load, with a 7.1-μH transmitter coil and a 1.2-μH receiver coil, separated by a 6-mm air gap, were measured to be 25% and 126 mW, respectively.

The next-generation retinal prostheses feature high image resolution and chronic implantation. These features demand the delivery of power as high as 100 mW to be wireless and efficient. A common solution is the 2-coil inductive power link, used by current retinal prostheses. This power link tends to include a larger-size extraocular receiver coil coupled to the external transmitter coil, and the receiver coil is connected to the intraocular electrodes through a trans-sclera trans-choroid cable. In the long-term implantation of the device, the cable may cause hypotony (low intraocular pressure) and infection. However, when a 2-coil system is constructed from a small-size intraocular receiver coil, the efficiency drops drastically which may induce over heat dissipation and electromagnetic field exposure. Our previous 2-coil system achieved only 7% power transfer. This paper presents a fully intraocular and highly efficient wireless power transfer system, by introducing another inductive coupling link to bypass the trans-sclera trans-choroid cable. With the specific equivalent load of our customized 512-electrode stimulator, the current 3-coil inductive link was measured to have the overall power transfer efficiency around 36%, with 1-inch separation in saline. The high efficiency will favorably reduce the heat dissipation and electromagnetic field exposure to surrounding human tissues. The effect of the eyeball rotation on the power transfer efficiency was investigated as well. The efficiency can still maintain 14.7% with left and right deflection of 30 degree during normal use. The surgical procedure for the coils' implantation into the porcine eye was also demonstrated.

This paper presents the design considerations to improve the power transfer efficiency (PTE) of ultrasonic power transmission links for wireless powering of millimeter (mm)-sized implantable microelectronic devices (IMDs). We have shown by the ultrasound theory that the diameter of the transmitter (Tx) and receiver (Rx) ultrasonic transducers, operation frequency, and powering distance have significant effect on the sound beam profile and, therefore, PTE of the link. The proposed design guideline, which has been verified by measurement results, suggests that the Rx diameter should be maximized to the extent that the application allows, and then the Tx diameter and operation frequency should be carefully chosen such that the IMD locates inside the focal zone of the Tx transducer for a given powering distance. The PTEs of ultrasonic and optimized inductive links with 2 mm Rx have also been compared that suggests the use of ultrasound when the powering distance is larger than 45 mm.

Inductive power transfer (IPT) systems are transforming railway infrastructure by enabling efficient, wireless energy transmission for electric locomotives equipped with Li-ion batteries. This technology eliminates the need for overhead power lines and third rails, offering financial and operational advantages over conventional electric propulsion systems. Despite its potential, IPT deployment in rail applications faces significant challenges, including the fragility of materials (i.e., ferrite and Litz wires), thermal management during high-power transfers, and electromagnetic interference (EMI) on the transmitter side. This study discusses several factors affecting IPT efficiency and introduces magnetic concrete as a durable and cost-effective material solution for IPT systems. Magnetic concrete combines soft ferrite powder with water and coarse aggregates to enhance magnetic functionality while maintaining structural strength comparable to conventional concrete. Its durability and optimized magnetic properties promote consistent power transfer efficiency, making it a viable alternative to traditional ferrite cores. A comparative study has been performed on non-magnetic and magnetic concrete (with 33% ferrite powder) using both permeability tests and finite element analysis (FEA). The FEA includes both thermal and electromagnetic simulations using Ansys Maxwell (v.16), revealing that magnetic concrete can improve temperature management and EMI mitigation, and the findings underscore its potential to revolutionize IPT technology by overcoming the limitations of traditional materials and enhancing durability, cost-efficiency, and power transfer efficiency. By addressing the challenges of fragility, thermal management, and shielding of the unique coil topology design presented, this study lays the groundwork for improving IPT infrastructure in sustainable and efficient rail transport systems.

IPT (Inductive Power Transfer) is an approach based on magnetic coupling to realize a wireless power transfer (WPT) system. In applications using IPT as a mean for transferring power, like RFID, it is of great interest to have a free positioning system, meaning with fewer constraints on relative positioning and orientation between the sender and the receiver. One of the problems which face the free positioning WPT by using IPT is the great sensitivity of the system to lateral and orientational misalignment between the sender and the receiver of power. This could hugely reduce the efficiency of the whole system for certain lateral and orientational misalignments, resulting in null points for the coupling coefficient, therefore no power transfer or no detection in case of RFID. In this work, we propose a reconfigurable antenna which changes its structure by turning on and off specific parts of itself. This will guarantee the effective power transfer in the range of interest, regardless of the lateral and orientational misalignments between the sender and the receiver. The same system can be used to increase the RFID read range by steering the magnetic field in certain direction. In general, the steering of the magnetic field could be used to achieve more efficient power transfer.

Nowadays, near-field wireless power transfer is realized by inductive or capacitive coupling. Power transmission is respectively accomplished by a time-varying magnetic or electric field as medium. Recently, mixed or hybrid near-field wireless power transfer is being developed as a possible mean to increase the power density of the system by utilizing both the magnetic and the electric near-field. The fundamental basics of mixed coupling are well understood. However, the implications of the mixed coupling theory on wireless power transfer applications is not rigorously described. Moreover, no general description is available that allows for a detailed comparison between current hybrid systems, especially for a series topology of inductive and capacitive coupling. In this work, we analytically solve a general mixed wireless power transfer configuration with series topology. We determine the optimal load to maximize the amount of power transfer and calculate the maximum achievable output power. The analytical derivation is validated by numerical simulation in SPICE. Our solution provides insight in the mixed wireless link and can serve as a reference point to evaluate the performance of mixed systems with regard to power transfer.

Recent research in wireless power transfer (WPT) using resonant inductive coupling has demonstrated very high efficiencies at large distances compared to the transmitting element dimensions, thereby increasing the number of potential applications of WPT. Since resonant inductive coupling is a very multidisciplinary field of research, different approaches have been proposed to predict the behaviour of these systems from the physical theory of resonators (coupled-mode theory) and circuit theory. Although the equivalence of these models for a point-to-point link has already been studied together with the performance metrics Power Transferred to the Load (PTL) and Power Transfer Efficiency (PTE), the new challenges and applications of this technology emphasize the necessity of analytical models to predict and assess the behavior of Multiple Input - Multiple Output (MIMO) links. In this article we revisit the current analytical models from the MIMO perspective, derive the analytical equations for the equivalent performance metrics PTE and PTL and demonstrate how to maximize them in a non-radiative resonant wireless power transfer link from a circuit-centric point of view, providing design guidelines in terms of optimal source and load impedances. This work concludes with a prospective discussion on open challenges of WPT. © 2014 IEEE.

With the development of inductive wireless power transfer technology (IPT), electromagnetic compatibility (EMC) of the IPT system has attracted much attention. In this paper, the equivalent AC impedance model of LCC/S topology is established, and the conclusion that the output characteristics and power transfer efficiency (PTE) are related to mutual inductance M is obtained. To solve the problem of excessively large magnetic flux leakage of loosely coupling transformer (LCT), magnetic coupler with vertical and horizontal shielding is designed based on the method of magnetic flux constraint, and its finite element analysis (FEA) 3D model is established. A prototype is built for experiments. The maximum transmission efficiency of the prototype is 90.33%, and the minimum transmission efficiency is 88.20%. The FEA simulation and experimental results verify the feasibility of the magnetic shielding structure design method. The results show that the novel proposed magnetic shielding structure increases the strength of magnetic field, effectively reduces the eddy current loss caused by magnetic field leakage, and increases the anti-misalignment ability of the system.

In an inductive wireless power transfer (IWPT) system, an “I” type magnetic shielding structure was proposed to simultaneously reduce the air-gap center region magnetic and electric fields without degrading the coil-to-coil efficiency. However, the proposed structure is difficult to implement due to the requirement of enormous ferrite materials. In this paper, the “I” type magnetic shielding design is optimized for the reduction of ferrite usage, cost, weight, and easy implementation, while maintaining nearly the same field distributions and power transfer efficiency. The optimized designs can reduce the ferrite usage by nearly 70% with nearly the same performance. The proposed methods are evaluated with a 2 kW, 30 cm transfer distance design example using finite element analysis (FEA).

This paper proposes the design of an engineered Wireless Power Transfer circuit for a 13.56 MHz miniaturized Inductive Resonant Wireless Power Transfer (IR-WPT) link for medical applications. The IR-WPT system is composed of a miniaturized receiver realized through three orthogonal coils winded up around a 3D-printed spherical structure. In order to create a compact system and maximize the EM coupling all the rectification circuitry needs to be placed inside the geometrical sphere. Thus, the PCB dimensions and arrangement are limited by the small volume available inside the plastic structure, less then 1 cm3, and by the 3D shape of the system, which forces the PCB layout to exploit an orthogonal arrangement with separated blocks. The circuitry component packages are chosen in order to minimize the encumbrance and ease the connection with each orthogonal coil. The equivalent circuit model is optimized with respect to the Power Transfer Efficiency (PTE) at a 5 cm Tx-Rx distance. To investigate the effect of the human body on the system performance, simulations are carried out exploiting an equivalent model of the human body tissues inside which the receiver is placed, at the same reference distance. The system performance is comparable for both cases: a 15 % average PTE and dc-output voltage exceeding 1.5 V are calculated for a 10 V input source.

Inductive power transfer (IPT) is gaining popularity across a wide range of battery charging applications like biomedical, consumer electronics and electric vehicle (EV) charging. One of the major challenges in designing IPT charge pads is determining the optimal physical sizes of the magnetic couplers resulting in efficient power transfer and low cost of materials. In EV applications, it is especially difficult due to the variation in nominal air gap, required power levels associated with different vehicle classes, and charging locations that may be encountered. This paper aims to determine the relationship between optimal coupler sizes and the nominal air gap of an IPT system. Finite element analysis (FEA) is used to model the electromagnetic behavior of the magnetic couplers. A multi-objective optimization framework is built to reveal the Pareto fronts which show the trade-offs between the power transfer efficiencies and the coupler power densities at different air gaps. This method is applied on polarized double-D (DD) couplers for a 5 kW IPT system at different air gaps. Analyzing the power densities of the Pareto Optimal designs an approximate relation between optimal pad sizes and the air gap is derived. Results show that there is an exponential relationship between the optimal coupler sizes and the nominal air gap.