Sensing and Wireless Powering Performance Assessment of Magnetic Resonance-Based Bioelectronic Sensors

Achieving high stable Power Transfer Efficiency (PTE) in Wireless Power Transfer (WPT) systems remains challenging due to the nonlinear, multimodal nature of the optimization space. Conventional algorithms such as Genetic Algorithms (GA), Differential Evolution (DE), and Simulated Annealing (SA) often face premature convergence, sensitivity to parameter settings, and inconsistent performance across runs. To overcome these issues, this study introduces the Evolutionary-Swarm Hybrid Algorithm (ESHA), which integrates DE for directional exploration, GA crossover for population diversity, SA for adaptive convergence, and Lévy Flights for stochastic global search. ESHA was implemented on a WPT system with a fixed 20 cm transmission distance and compared with GA, DE, and SA using three performance indicators: PTE, convergence speed, and computational efficiency. Results show that ESHA achieved a maximum PTE of 97.18%, surpassing GA (96.81%), DE (96.65%), and SA (96.19%), while maintaining zero variance across independent runs. It converged in an average of 31.2 iterations, slightly faster than GA (33.15) and SA (32.1), and comparable to DE (31.3). Execution time was 0.4738 s, close to GA (0.4654 s) and only marginally higher than DE (0.4262 s) and SA (0.4329 s). Statistical validation confirmed significant improvements in PTE (p < 0.05).

The following topics are dealt with: inductive power transmission; coils; microwave power transmission; rectifiers; rectennas; energy harvesting; rectifying circuits; radiofrequency power transmission; DC-DC power convertors; resonators.

Miniature bioelectronic implants promise revolutionary therapies for cardiovascular and neurological disorders. Wireless power transfer (WPT) is a significant method for miniaturization, eliminating the need for bulky batteries in today's devices. Despite successful demonstrations of millimetric battery-free implants in animal models, the robustness and efficiency of WPT are known to degrade significantly under misalignment incurred by body movements, respiration, heart beating, and limited control of implant orientation during surgery. This paper presents an omnidirectional WPT platform for millimetric bioelectronic implants, employing the emerging magnetoelectric (ME) WPT modality, and "magnetic field steering" technique based on multiple transmitter (TX) coils. To accurately sense the weak coupling in a miniature implant and adaptively control the multi-coil TX array in a closed loop, we develop an Active Echo (AE) scheme using a tiny coil on the implant. Our prototype comprises a fully integrated 14.2mm3 implantable stimulator embedding a custom low-power System-on-Chip (SoC) powered by an ME film, a transmitter with a custom three-channel AE RX chip, and a multi-coil TX array with mutual inductance cancellation. The AE RX achieves -161dBm/Hz input-referred noise with 64dB gain tuning range to reliably sense the AE signal, and offers fast polarity detection for driver control. AE simultaneously enhances the robustness, efficiency, and charging range of ME WPT. Under 90° rotation from the ideal position, our omnidirectional WPT system achieves 6.8× higher power transfer efficiency (PTE) than a single-coil baseline. The tracking error of AE negligibly degrades the PTE by less than 2% from using ideal control.

The low efficiency of far-field wireless power transfer (WPT) limits the fundamental rate-energy (R-E) performance trade-off of the simultaneous wireless information and power transfer (SWIPT) system. To address this challenge, we propose in this letter a new SWIPT system aided by the emerging intelligent reflecting surface (IRS) technology. By leveraging massive low-cost passive elements that are able to reflect the signals with adjustable phase shifts, IRS achieve a high passive beamforming gain, which is appealing for drastically enhancing the WPT efficiency and thereby the R-E trade-off of SWIPT systems. We consider an IRS being deployed to assist a multi-antenna access point (AP) to serve multiple information decoding receivers (IDRs) and energy harvesting receivers (EHRs). We aim to maximize the weighted sum-power received by EHRs via jointly optimizing the transmit precoders at the AP and reflect phase shifts at the IRS, subject to the individual signal-to-interference-plus-noise ratio (SINR) constraints for IDRs. Since this problem is non-convex, we propose efficient algorithms to obtain suboptimal solutions for it. In particular, we prove that it is sufficient to send information signals only at the AP to serve both IDRs and EHRs regardless of their channel realizations. Moreover, simulation results show significant performance gains achieved by our proposed designs over benchmark schemes.

To further improve the power efficiency of wireless power transfer(WPT) systems, a hybrid metamaterial slab (HMS) consisting of the 3rd-order Hilbert fractal spiral resonator with magnetic permeability tending to 0 and -1 is proposed. The HMS is applied to a WPT system with an operating frequency of 6.78 MHz. The effect of the Hilbert fractal-based hybrid metamaterial on the WPT system is explored through theoretical analysis and simulation verification. The simulation results show that the incorporation of the Hilbert fractal-based HMS can improve the power efficiency of the WPT system with a transmission distance of 0.4m by 17.57%.

Improvements in performance of resonant coils are important for the range and efficiency of wireless power transfer (WPT); however, these improvements are difficult to measure using the conventional figure-of-merit (FoM), which is the product of quality factor and coupling factor. The conventional FoM does not account for important WPT system performance parameters such as coil size and range of power transfer; furthermore, it requires information which is not commonly reported. In this paper, we propose a new FoM that is the ratio of the loss fraction of a reference system and and the system-under-test. The reference system models two-loops of solid wire that are scaled to the same overall size as the system-under-test. The FoM is an indication of the performance of a WPT coil technology independent of a specific implementation, and can be calculated using commonly reported parameters: coil diameter, transmission range, and coil-to-coil efficiency. We computed the FoM for a few WPT systems in the literature, and found the highest FoM to be 3.4, achieved using a self-resonant structure.

An adaptively smart wireless power transfer (WPT) system is proposed by using a 2-bit programmable metasurface (PMS), in which an indoor dynamic charging application scenario is described and near-field focused (NFF) technique is adopted to transmit wireless powers. Theoretical analyses of NFF PMS are presented to illustrate its WPT capabilities. To implement dynamic WPTs, digital phase-shift quantization of PMS element is investigated, indicating that 2-bit quantization scheme is a preferred solution. As experimental demonstrations, a 2-bit 12 × 12 PMS operating at 5.8 GHz is designed, fabricated, and tested. High-power focal spots that can be regulated to focus at different near-field positions are measured in an anechoic chamber. We conduct multiple WPT experiments by using the 2-bit PMS as the transmitter and a 4 × 4 microstrip array antenna as the receiver. Experimental results show that the proposed 2-bit PMS can continuously transmit the wireless powers to the receiver even though the target is moving, and the WPT efficiency is maintained over 9.1%, which has about 16.3 dB improvement at the end of the trajectory compared to the fixed NFF beam. This work is one of the first attempts to thoroughly examine the possibility of the dynamic WPTs using PMS, offering a brand-new manner for the adaptively smart WPT systems.

Output voltage regulation is an essential technology for achieving stable wireless power supply. A receiver-side switching voltage regulator is useful for realizing output voltage regulation. However, this paper shows that the switching voltage regulator degrades the transfer efficiency to below 50% in a wireless power transfer system that consists of a class-D power inverter and series-resonant transmitting and receiving resonators. Such efficiency degradation is caused by the instability of an operating point where the efficiency is >50%. The input resistance value of the switching voltage regulator at a stable operating point is much higher than the optimum value for maximizing the efficiency. To stabilize the high-efficiency operating points, this paper formulates a stability condition and derives its sufficient condition. The sufficient condition facilitates a system design method using a K-impedance inverter that allows for the optimum input resistance value to lie in the range of allowable input resistance values. In addition, we introduce an input-voltage-based efficiency maximization method for the system with the receiver-side switching voltage regulator. By combining these two methods, efficiency maximization is realized with the receiver-side switching voltage regulator. The proposed methods were verified by both simulations and measurements.

Recently, metamaterials have been developed for wireless power transfer applications. It has been shown that the near-field electromagnetic coupling between two resonant coils can be enhanced by a slab of metamaterial. With the assist of the metamaterial, the efficiency of wireless power transfer between the resonant coils can be greatly improved. In this paper, recent progress in this area will be presented: theoretical development of enhanced coil coupling with metamaterial will be briefly discussed; the design of metamaterial slabs for near-field wireless power transfer will be shown; recent experimental results on wireless power transfer efficiency improvement with metamaterial will also be presented.

In this paper, we provide a holistic overview of the aspect of electromagnetic radiation (EMR) and its efficient control in wireless communication networks. Especially, we focus on the emerging technology of wireless power transfer (WPT). Our global perspective is to suggest methods for the effective control of EMR while keeping at high levels the QoS experienced by users as well as the charging efficiency of WPT. First, we provide formal definitions of EMR in wireless communications and propose related performance metrics and EMR evaluations in wireless communication networks. Then, we focus on EMR control in efficient wireless power transfer, under different WPT models. For the well-known scalar model, we assume finite energy reserves and batteries, and introduce the low radiation efficient charging problem. For this problem, we identify its computational complexity and provide efficient algorithms and heuristics. A vectorial model of WPT is then employed, allowing a more precise management of radiation, via directly exploiting interesting super-additive and cancellative phenomena of received power; we provide algorithms which achieve satisfactory tradeoffs of charging efficiency and radiation. Then, we present a more futuristic model and the method of peer-to-peer wireless power transfer where no strong, central charger stations are used, thus keeping radiation at almost zero levels. Another method of controlling EMR in the case of mobile nodes is adapting the charger change in a dynamic, on-line way so as to avoid unnecessarily large fixed changing ranges. Finally, we discuss some future challenges and related research directions, toward efficiently combining high WPT provisioning and low EMR. Such directions include the effective management of mobility in the network, the use of diverse WPT signal phase-configuration as well as efficient chargers’ scheduling strategies.

<pre>This paper derives an expression of efficiency of wireless power transfer on a situation that there are two devices towards one AC power supply. The interaction between a power supply and load is paid attention on a conventional wireless power transfer system, in contrast, the interaction between loads must be taken account of on the situation too. This is attributed to a possibility that a load disturbs the energy transmitted from a power supply to another load. Moreover each load needs different frequency of power supply for the ideal transfer since they have different natural frequencies on many situations. This paper models a circumstance that there are a power supply and two loads with a state space equation, and proposes how to decide a frequency of power supply to realize efficient transfer for each load.</pre>

Networks of miniature implants could enable simultaneous sensing and stimulation at different locations in the body, such as the heart and central or peripheral nervous system. This capability would support precise disease tracking and treatment or enable prosthetic technologies with many degrees of freedom. However, wireless power and data transfer are often inefficient through biological tissues, particularly as the number of implanted devices increases. Here we show that magnetoelectric wireless data and power transfer supports a network of millimetre-sized bioelectronic implants in which system efficiency improves with additional devices. We demonstrate wireless, battery-free networks ranging from one to six implants, where the total system efficiency increases from 0.2% to 1.3%, with each node receiving 2.2 mW at 1 cm distance. We show proof-of-concept networks of miniature spinal cord stimulators and cardiac pacing devices in large animals via efficient and robust wireless power transfer. These magnetoelectric implants provide a scalable network architecture of bioelectronic implants for next-generation electronic medicine.

In magnetic resonance-based wireless power transfer (WPT), any misalignment between resonators degrades the strength of the magnetic coupling, and the use of a relay does not always improve performance if it is misaligned with a transmitter or a receiver. It is therefore necessary to determine the proper activation of a relay depending on the degree of misalignment. In this paper, we analyze the effect of a misaligned relay on two important performance metrics in WPT, namely output power and efficiency. In particular, we derive the achievable output power and efficiency with optimal load resistance based on an equivalent circuit model, and determine whether it is beneficial to utilize the relay for a given lateral and angular misalignment. By simulation and experimental verifications under various environments, we validate the exactness of our analysis, and we also confirm two interesting observations, namely 1) with regard to performance improvement in terms of output power and efficiency, it is better to deactivate the relay if it is seriously misaligned with the other resonators and 2) output power is more vulnerable to the misalignment of a relay than efficiency.

Wireless power transfer (WPT) is the technology that forces the power to transmit electromagnetic field to an electrical load through an air gap without interconnecting wires. This technology is widely used for the applications from low power smartphone to high power electric railroad. In this paper, the model of wireless power transfer circuit for the low power system is designed for a resonant frequency of 13.45 MHz. Also, a feedback WPT circuit is proposed, and the methodology for power efficiency improvement is studied as the coupling coefficient increases above 0.01, at which the split frequency is made.

In this study, an advanced wireless power transfer (WPT) system of two coils with the artificial magnetic conductors (AMC) is explored through simulations and experiments. The AMC structure is added on the transmitter coil, and the multiple resonant modes on the surface of the AMC can be energized. On the other hand, the AMC structure act as a magnetic field shield, which leads to the magnetic field above AMC structure is localized. Therefore, the localized resonant magnetic field enhance the transmission coefficient of the WPT system. The results show that the WPT transmission coefficient is increased from 16% to 35% in the experiment at 26.2 MHz resonant frequency when transmission distance is 3 cm. The experimental results agree with the simulation results. Additionally, AMC has the advantages of low-cost and can easily be installed on the WPT system.