Numerical and Experimental Investigation of Time-Domain-Reflectometry-Based Sensors for Foreign Object Detection in Wireless Power Transfer Systems.

Foreign object detection (FOD) is considered a key method for detecting objects in the air gap of a wireless charging system that could pose a risk due to strong inductive heating. This paper describes a novel method for the detection of metallic objects utilizing the principle of electric time domain reflectometry. Through an analytical, numerical and experimental investigation, two key parameters for the design of transmission lines are identified and investigated with respect to the specific constraints of inductive power transfer. For this purpose, a transient electromagnetic simulation model is established to obtain and compare the sensor impedance and reflection coefficients with experimental data. The measurement setup is based on parametrically designed sensors in laboratory scale, using an EUR 2 coin as an exemplary test object. Consequently, the proposed simulation model has been successfully validated in this study, providing a comprehensive quantitative and qualitative analysis of the major transmission line design parameters for such applications.

Optimal Frequency and Wireless Power Budget for Miniature Receivers in Obese People.

This study investigates wireless power transfer for deep in-body receivers, determining the optimal frequency, power budget, and design for the transmitter and receiver. In particular, the focus is on small, in-body receivers at large depths up to 20 cm for obese patients. This enables long-term monitoring of the gastrointestinal tract for all body types. Numerical simulations are used to investigate power transfer and losses as a function of frequency and to find the optimal design at the selected frequency for an obese body model. From all ISM-frequencies in the investigated range (1 kHz-10 GHz), the value of 13.56 MHz yields the best performance. This optimum corresponds to the transition from dominant copper losses in conductors to dominant losses in conductive tissue. At this frequency, a transmitting and receiving coil are designed consisting of 12 and 23 windings, respectively. With a power transfer efficiency of 2.70×10-5, 18 µW can be received for an input power of 0.68 W while still satisfying exposure guidelines. The power transfer is validated by measurements. For the first time, efficiency values and the power budget are reported for WPT through 20 cm of tissue to mm sized receivers. Compared to WPT at higher frequencies, as commonly used for small receivers, the proposed system is more suitable for WPT to large depths in-body and comes with the advantage that no focusing is required, which can accommodate multiple receivers and uncertainty about receiver location more easily. The received power allows long-term sensing in the gastrointestinal tract by, e.g., temperature, pressure, and pH sensors, motility sensing, or even gastric stimulation.

Foreign object detection considering misalignment effect for wireless EV charging system.

Foreign object detection (FOD) is crucial to preventing wireless electric vehicle charging (WEVC) systems from thermal risk caused by intruded metals in the charging area. In practice, the spatial misalignment between EV and ground-assembled power transmitter is evitable. Unfortunately, according to our quantitative analysis based on conventional voltage-difference-based method, a misalignment of merely tens of mm has been enough to severely deteriorate the FOD accuracy. To combat this misalignment effect, a FOD strategy based on passive sensing coils utilizing voltage vector decomposition (VVD) is proposed in this paper. The proposed strategy can be invariant to misalignment in an automatic manner, during the whole charging process, and regardless of the resonance state of charging circuit. To facilitate VVD implementation, a method called inductance-misalignment mapping (IMM) is devised to obtain the spatial misalignment of EV in real time, and it can be executed by reusing the sensing coils without introducing extra cost. The effectiveness of optimized sensing coils with the proposed FOD method is validated successfully using a commercialized 3-kW prototype working from light load to rated load.

Miniature Coil for Wireless Power and Data Transfer through Aluminum.

This paper presents the design and development of miniature coils for wireless power and data transfer through metal. Our coil has a total size of 15 mm × 13 mm × 6 mm. Experimental results demonstrate that we can harvest 440 mW through a 1 mm-thick aluminum plate. Aluminum and stainless-steel barriers of different thicknesses were used to characterize coil performance. Using a pair of the designed coils, we have developed a through-metal communication system to successfully transfer data through a 1 mm-thick aluminum plate. A maximum data rate of 100 bps was achieved using only harvested power. To the best of our knowledge, this is the first report that demonstrates power and data transfer through aluminum using miniature coils.

Ironsand (Titanomagnetite-Titanohematite): Chemistry, Magnetic Properties and Direct Applications for Wireless Power Transfer.

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ∼100 µm to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage.

Frequency bifurcation in a series-series compensated fractional-order inductive power transfer system.

This paper reveals and analyzes the frequency bifurcation phenomena in the fractional-order inductive power transfer (FOIPT) system with series-series compensation topology. Using fractional calculus theory and electric circuit theory, the circuit model of the series-series compensated FOIPT system is first proposed, then taking the case of a single variable fractional order as an example, three frequency analytical solutions of frequency bifurcation equation are solved by using Taylor expansion method. By analyzing the three bifurcation frequencies solved, it can be found that the frequency bifurcation phenomenon can be effectively eliminated by controlling the fractional order, and the boundary of critical distance and critical load is reduced, thereby expanding the working range of the conventional inductive power transfer (IPT) system. Furthermore, the output power and transfer efficiency at the three bifurcation frequencies are analyzed, it can be observed that the output power and transfer efficiency at the high bifurcation frequency and low bifurcation frequency are close and basically keep constant against the variation of transfer distance, and the output power is obviously higher than that at the intrinsic frequency. In addition, the output power at the three bifurcation frequencies can be significantly improved by adjusting the fractional order. Finally, the experimental prototype of FOIPT is built, and the experimental results verify the validity of theoretical analysis.

Wireless Pacing Using an Asynchronous Three-Tiered Inductive Power Transfer System.

Despite numerous advancements in pacemaker technology for the treatment of cardiac arrhythmias and conduction disorders, lead-related complications associated with these devices continue to compromise patient safety and survival. In this work, we present a system architecture that has the capacity to deliver power to a wireless, batteryless intravascular pacer. This was made possible through a three-tiered, dual-sub-system, four-coil design, which operates on two different frequencies through intermittent remote-controlled inductive power transfer. System efficiency was enhanced using coil design optimization, and validated using numerical simulations and experimental analysis. Our pacemaker design was concepted to achieve inductive power transfer over a 55 mm range to a microscale pacer with a 3 mm diameter. Thus, the proposed system design enabled long-range wireless power transfer to a small implanted pacer with the capacity for intravascular deployment to the anterior cardiac vein. This proposed stent-like fixation mechanism can bypass the multitude of complications associated with pacemaker wires while wireless power can eliminate the need for repeated procedures for battery replacement.

A Power-Efficient Wireless System With Adaptive Supply Control for Deep Brain Stimulation.

A power-efficient wireless stimulating system for a head-mounted deep brain stimulator (DBS) is presented. A new adaptive rectifier generates a variable DC supply voltage from a constant AC power carrier utilizing phase control feedback, while achieving high AC-DC power conversion efficiency (PCE) through active synchronous switching. A current-controlled stimulator adopts closed-loop supply control to automatically adjust the stimulation compliance voltage by detecting stimulation site potentials through a voltage readout channel, and improve the stimulation efficiency. The stimulator also utilizes closed-loop active charge balancing to maintain the residual charge at each site within a safe limit, while receiving the stimulation parameters wirelessly from the amplitude-shift-keyed power carrier. A 4-ch wireless stimulating system prototype was fabricated in a 0.5-µm 3M2P standard CMOS process, occupying 2.25 mm². With 5 V peak AC input at 2 MHz, the adaptive rectifier provides an adjustable DC output between 2.5 V and 4.6 V at 2.8 mA loading, resulting in measured PCE of 72 ~ 87%. The adaptive supply control increases the stimulation efficiency up to 30% higher than a fixed supply voltage to 58 ~ 68%. The prototype wireless stimulating system was verified in vitro.