Enhancement of Wireless Power Transfer Efficiency Using Higher Order Spherical Modes

The use of resonant magneto-inductive links is an efficient technique to transfer power over midranges in the field of wireless power transfer (WPT). Power transfer efficiency (PTE) and power delivered to the load (PDL) are two important indicators of power transmission for a WPT system. A predetermined amount of PDL need be generated at maximum PTE for practical application in a WPT system; thus, the authors focus on maximising PTE and a predetermined amount of PDL for transfer in this study. First, load-matching conditions are presented for maximum PTE transfer though circuit theory-based analyses. Then, a new tuning method is proposed to transfer a predetermined amount of PDL which can be controlled by source-matching distance at maximum PTE. The relations between the loss of a load-matching resonator and the PTE (or PDL) of a correspondingly unmatched system are derived though analyses as well. Finally, the calculated results of the design examples are verified through electromagnetic simulations and experimental measurements.

Maximum power transfer and maximum efficiency are two important design constraints in wireless power transfer applications. Several works have investigated the proper load and impedance match conditions to optimize either efficiency or power transfer. In this paper we show that the optimal load for maximum power transfer and maximum efficiency is the same (a conjugate matched load) when the source resistance is zero. This is important, as many WPT systems have a relatively low, unknown source impedance. Since the optimal load for both efficiency and power is the same as the source impedance approaches zero, the designer can use a bi-conjugate load for a near optimal design for both maximum power and efficiency. As the source impedance becomes significant, the bi-conjugate matched system provides higher power, but at the expense of lower efficiency. Maximum efficiency is achieved with a non-bi-conjugate load, when the source impedance is non-negligible.

With the extensive applications of magnetically coupled resonant wireless power transfer (WPT), improving the power transfer efficiency (PTE) of WPT systems is critical. Magnetic metamaterials (MTMs) can effectively improve the PTE. However, currently the design of MTMs is mainly based on microwave or optical theory, and their applicability in low-frequency WPT systems needs to be further explored. In this paper, a fast and effective method for the design and optimization of low-frequency MTM is provided. Firstly, based on circuit theory and mutual inductance calculation, the PTE of WPT systems is concluded in an equation that concerns the position of a 2-D MTM slab and compensation capacitance of MTM unit coils. Two WPT systems with large differences in coil size of the transmitter (Tx) and receiver (Rx) and the same size are considered. In addition, a directly separating variables method is proposed to optimize the MTM slab position and the compensation capacitance of unit coils to maximize PTE when the MTM slab position changes axially between Tx and Rx. It is found that the optimal MTM slab positions for the two systems are remarkably different, and the PTE impressively presents a capacitance splitting phenomenon with the change of compensation capacitance. Finally, two MTM-enhanced WPT systems are established to verify the theoretical calculation. The experiments show that the maximum PTE is significantly increased by 144% and 31% respectively by adopting optimized compensation capacitance compared with that without MTM for the two systems with different or same transceiver coil size.

Since the concept of wireless power transfer has been proposed and implemented by Tesla over a hundred years ago, it has obtained lots of breakthroughs and applied in many potential fields especially in implantable biomedical devices [1–2]. The implantable biomedical devices are surgically introduces into the human body to rebuild body function, achieve a better quality of life, and expand longevity. With the development of microelectronics, biotechnology, and materials, the industry of implantable biomedical devices grows up quickly. The researches show that in America 8% to 10% of the people have experienced an implantable medical device, while in industrialized countries 5% to 6% of population have consumption demand in implantable medical devices. How to provide a constant power supply, for implantable medical devices, becomes a restricted problem. In order to guarantee the implanted medical devices to work normally, the energy storage or harvesting components should be included in these devices. In the traditional implantable medical devices, there are two ways to provide power for the devices. The common method is the implantable batteries are used to be as a power supply, and the other method is to transfer the power in vitro to the devices with the lead wires through the skin. For implantable batteries, their lifetime, size and toxic composition will lead to potential hazard to the patients. The transcutaneous wires, as well, will bring infection and reliability problems. In order to address above problems, the technology of wireless power transfer is used in the biomedical devices. The system has two parts in which one part including power supply and the transmitter coil is placed outside the patients’ body, and the other part including the receiver coil is placed in the patients’ body. For this system, the receiver coil should be limited as small as possible and the power transfer efficiency should be as high as possible. Different from the traditional two-coil wireless power transfer system, a novel three-coil system is proposed in this paper. In the novel system, there are two rectangular transmitter coils and one circular receiver coil. To obtain the maximum power transfer efficiency, the system is optimal designed according to the following step as shown in Fig. 1. Firstly, the size and the geometry of the receiver coil are determined. A circular coil with a radius of 10mm is chosen as the receiver coil. Secondly, the distribution of the magnetic field generated by the rectangular coil is analyzed based on the Biot-Savart’s law. Then the relationship between the distance and the magnetic field intensity will be obtained and expressed as a formula according to the analysis result. Finally, the above formula is chosen as the optimization constrains and the power transfer efficiency is chosen as the optimization objective function. After the optimal designing, the optimal parameters of the transmitter coils are obtained and verified through the experimental system as shown in Fig. 2. The power transfer distance is about 30cm, and the power received by the receiver coil can achieve about 5W. The detailed results will be given in the full paper.

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).

In this paper, we propose an efficient wireless power transfer (WPT) system at 1050 kHz for an active capsule endoscope. The performance of the proposed WPT system is evaluated by placing a capsule receive coil in a hollow body phantom as well as that filled with colon-equivalent liquid. The power transfer efficiency has been studied with respect to the operating frequency and the load resistance. The measured results show that the maximum power transfer efficiency of 20.4% and 17.47% can be achieved in a hollow and a liquid phantom, respectively.

The power transfer efficiency of magnetic-resonance coupled wireless power transfer (WPT) systems is sensitive to the alignment of coils. In this paper, a novel multi-coil WPT system is proposed to enhance power transfer efficiency. It can overcome the misalignment problem and maintain high power transfer efficiency. The proposed coil loop structure can provide a strong magnetic resonance coupling between the Tx and Rx coils. There are four induvial resonators applied in the system and it demonstrates that at least a pair of coupled resonators in several misaligned conditions could realize high power transfer efficiency over a misaligned distance. The experimental results show that the proposed multi-loop WPT system can achieve 90.2% peak efficiency when the coils are well aligned. Mean-while, this WPT system maintains over 70% efficiency over a misalignment distance from 0 to 55 mm, which is about 66% of the length of the Rx board. The proposed WPT system could be used either in implant devices for biomedical healthcare and treatment or for electric vehicles charging systems.

This study investigates the enhancement of power transfer efficiency (PTE) in wireless power transfer (WPT) systems for electric vehicles (EVs) through simulations and experimental evaluations using metamaterial (MTM) configurations. The MTM model, validated against existing research, was designed for operation at 85 kHz. The influence of MTM on the magnetic field alignment and flux density at the receiver coil significantly improved PTE compared to systems without an MTM configuration. We tested various arrangements of three, six, and nine MTM cells positioned at left, right, top, bottom, and combined locations across coil distances of 0–5.0 cm. The results showed that a nine-cell MTM arrangement yielded greater PTE than a three-cell arrangement because of improved electromagnetic flux distribution. However, the T-shaped arrangement of six MTM cells achieved the maximum PTE at a 2.0 cm coil distance. This performance exceeded that of the configuration with 3 × 3 MTM cells, indicating that the T-shaped design optimizes electromagnetic flux distribution. The six-cell T-shaped arrangement boosted the PTE by 7.7% compared to the nine-cell version, demonstrating its potential as an innovative and efficient WPT system for future EV applications.

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.

A technique for wireless power transfer (WPT) efficiency improvement by a proper design of the excitation waveform is presented. This improvement is obtained on the one hand by a combined‐harmonics excitation, and on the other hand by exploiting multiple‐resonance coupled resonators. In contrast to wireless communications, there is no constraint on the linearity of the transmitter and receiver in a WPT system. Therefore, the impact of the excitation waveform on the power transfer efficiency with the help of an analytical model is investigated. An optimum excitation waveform is determined to maximise the power transfer efficiency. Thereafter, the authors concentrate on designing a multiple‐resonance coupled resonator system that is consistent with the determined excitation waveform. This work introduces a non‐uniform spiral resonator for controlling the self‐resonant frequencies, which is consistent with the required excitation waveform. The performance of the designed coupled resonators is then evaluated using a 3D finite‐element method and experiments. The numerical simulation and experimental results are in good agreement, verifying the validity of our design.

The electromagnetic Halbach array (EHA) for wireless power transfer (WPT), designed to improve the transferred power and power transfer distance, has been proven to be effective and can be applied in various consumer applications. This paper presents a hybrid form of the EHA, aimed at improving the quality of power generated and transmitted. The expression for the determination of the magnetic field of a variable pitch flat coil for wireless power transfer and other uses has been derived. The average magnetic field, magnetic flux, and power transfer efficiency are investigated. The power transfer efficiency and the average magnetic field generated by four different design considerations were compared. The hybrid electromagnetic Halbach array wireless power transfer system (HEHA‐WPTS) has also been studied and results are compared with the conventional arrangements. Simulations and experiments were carried out to verify the analytical results obtained. According to the results obtained, the HEHA‐WPTS, with a base coil with variable pitches and uniform side coils, produces a more uniform average magnetic field and a better average power transfer efficiency over a longer power transfer distance.

This article presents a simultaneous wireless power and data transfer (SWPDT) system based on double-sided inductor-capacitor-capacitor compensation topology and frequency-shift keying. A simplified method to analyze the power transfer, data transfer, and interference between them is proposed. To obtain higher data transfer gain and lower bit error rate, the data injection and extraction transformers are optimized. A laboratory prototype was built to verify the correctness of the analysis and the methodology. The proposed SWPDT system is less susceptible to interference between the power and data transfer. This is experimentally proven by high signal-to-noise ratio of 47 dB in the worst case. The power transfer efficiency is 90.5% under nominal conditions, and the data rate is 150 kb/s. The proposed system is robust against coupling variations, with effective data transfer even though the coupling coefficient is decreased by 95.3%.

Simultaneous power distribution to multiple loads using a single source in the wireless power transfer (WPT) system is a challenging issue due to cross-coupling between the load coils, which reduces the power transfer efficiency. In a resonant WPT system, when two or more coils operated under over coupled condition, the original operating resonant frequency gets bifurcated, and thereby reduction in the power transfer efficiency. Different techniques are investigated in the literature to mitigate the frequency bifurcation phenomena in the resonant WPT system. However, the utilization of frequency bifurcation approach for the simultaneous power transfer to multiple loads is not addressed. This paper proposes a simultaneous power transfer approach using frequency bifurcation for the multiple load system designed with different operating frequency. Mathematical, simulation, and experimental studies performed for dual, triple, and four coil WPT systems with multiple loads. In addition, an automatic power flow control method is implemented to estimate the load current from the source, which helps to select a new set of load coils to be charged. The experimental results confirm the proposed power transfer, helps to attain higher power transfer efficiency of 39.34%, 49.31%, 68.22% and cross interference of -31.2 dBV, -36.2 dBV, -41.2 dBV for dual, triple, and four coil WPT system, respectively.

This article introduces an innovative approach integrating machine learning (ML) methods into a far-field wireless power transfer (WPT) system. Within this system, a radar is employed to detect the presence and height of individuals. These data, combined with information on the location of nodes, as well as the propagation channel between transmitters and nodes, are fed into the proposed ML algorithm. The ML model aims to predict the optimal power level for each transmitter, effectively establishing a safe 3-D zone around people while also maximizing power transfer efficiency. The advantages of using ML are the realization of a real-time system, which is crucial in indoor applications, keeping dangerous radiation at a safe level with a very low risk of harmful exposure, and simultaneously enhancing efficiency. Three ML models are evaluated, namely the random forest (RF), support vector machine (SVM), and neural network (NN). Simulation results highlight the superior performance of the NN model, demonstrating its ability to effectively capture the complex nonlinear characteristics of indoor propagation environments, with only approximately 6% of its predictions exceeding the predefined safety threshold. The experimental results show that NN-based WPT can maintain the electric field amplitude (EFA) below a defined threshold for multiple indoor experimental scenarios over the person’s height. In addition, the proposed approach outperformed the maximum ratio transmission (MRT) approach in terms of radio frequency–radio frequency (RF–RF) transmission efficiency in 21.43% of the measurements conducted with multiple people present in the testbed.

A Wireless Power Transfer (WPT) system, known for its contactless power delivery, is extensively used for power supply in spacecraft applications. Achieving efficient and stable power transfer necessitates the integration of DC/DC converters on both the primary and secondary sides of WPT systems for power conversion and control. Traditional efficiency optimization methods primarily focus on impedance matching within the wireless power resonance network, often neglecting the overall efficiency optimization of multi-stage DC-DC and WPT systems. This oversight results in suboptimal overall system efficiency despite optimal efficiency in the wireless transmission segment. Additionally, the time-varying nature of mutual inductance and load parameters during power transmission in WPT systems presents challenges for maximum efficiency tracking and power control. This paper introduces a multi-level coordinated control efficiency optimization method for WPT systems utilizing the particle swarm optimization (PSO) algorithm. This method takes into account the transmission losses across all power conversion units within the WPT system, establishing a mathematical model for the joint optimization of overall system transmission efficiency and power. The PSO algorithm is then employed to solve this optimization model using estimated mutual inductance and load values. By adjusting the DC/DC converters on both sides, the method ensures optimal overall system efficiency and consistent power transmission. Experimental results indicate that under varying load and mutual inductance conditions, a Series–Series (SS) compensated WPT system using this method achieves a 200 W power output with maximum efficiency tracking, a power output error of 0.63%, and an average transmission efficiency of 86.2%. This demonstrates superior power transmission stability and higher efficiency compared to traditional impedance matching methods.