Xiu Zhang

Quantitative Design and Analysis of Relay Resonators in Wireless Power Transfer System

Wireless power transfer systems are finding increasing applications which can enhance the living standard of the general public. Typical examples are wireless charging of mobile phone batteries and car batteries. Thanks to the advent of power electronics in the past few decades, some wireless charging systems are now emerging in the commercial sector. However, the transfer efficiency and transfer distance of these chargers are limiting the technology to a few specific applications only. In order to increase the transfer distance, some researchers have successfully proposed to use relay coils to improve their wireless power transfer efficiency. In this paper, the role of relay resonator is examined critically. The reported findings indicate that it is not always desirable to have relay coils in wireless charger as the relay resonator may increase, or sometimes reduce, the overall power transfer efficiency. The findings also reveal that there is an optimal position for the designer to locate the relay resonator to maximize the power transfer efficiency.

An Improved Artificial Bee Colony Algorithm for Optimal Design of Electromagnetic Devices

Optimal design problems of electromagnetic devices are generally multimodal, nondifferentiable, and constrained. This makes metaheuristic algorithm a good choice for solving such problems. In this paper, a newly developed metaheuristic algorithm is presented to address the aforementioned issues. The proposed algorithm is based on the paradigm of artificial bee colony (ABC). A drawback of the original ABC algorithm is because its solution variation is only 1-D, as this decreases its convergence speed. In this paper, a one-position inheritance scheme is proposed to alleviate this drawback. An opposite directional (OD) search is also proposed to accelerate the convergence of the ABC algorithm. The novel algorithm is applied to both TEAM Workshop problem 22 and a loudspeaker design problem. Both discrete and continuous cases of problem 22 are tested. The effectiveness and efficiency of the proposed algorithm are demonstrated by comparing its performance with those of the original ABC, an improved ABC known as Gaussian ABC, and differential evolution algorithms.

Quantitative Analysis of a Wireless Power Transfer Cell With Planar Spiral Structures

An emerging technology of wireless power transfer technique based on electromagnetic resonant coupling, also known as witricity, has been drawing a lot of attention from academia as well as from practitioners since it was reported in 2007 by a group of researchers from the Massachusetts Institute of Technology (MIT). In this paper, a prototype with square planar spiral structure based on witricity is proposed. To compute the resonant frequency, an equivalent circuit model is presented and simulated. The impedance matrix is computed by using a formula method and a 3-D finite-element method (FEM) of eddy-current magnetic field. The results indicate that the numerical method has a better accuracy. In order to reduce the resonant frequency, different conditions are analyzed quantitatively to study the relationship between the parameters and the relation of the prototypes with their resonant frequencies. The findings are found to offer a solid foundation for the optimization of witricity prototypes.

A Modification of Artificial Bee Colony Algorithm Applied to Loudspeaker Design Problem

The design of electromagnetic devices is generally multimodal, multidimensional, and constrained. Its simulation-based feature makes traditional optimization algorithms unsuitable to use; whereas metaheuristic approaches are good choices for tackling such problems. Since many electromagnetic design problems require excessive computer resources even on modern computers, attempts to improve the efficiency and effectiveness of metaheuristic approaches are very challenging for designers. This paper proposes a modification of artificial bee colony (ABC) algorithm. The design philosophy of this algorithm is to promote the convergence rate of ABC. The properties of the modified ABC algorithm are analyzed by testing, first, on two mathematical functions. The proposed algorithm is then applied to solve a loudspeaker design problem using FEM. Promising performance is obtained when compared with those using original ABC, genetic algorithm, particle swarm optimization, and differential evolution algorithms.

Analysis and Optimization of Magnetically Coupled Resonators for Wireless Power Transfer

The technology of wireless power transfer has made a great contribution to the quality of life of many people, especially to those relying on implantable devices in the past decades. In order to improve the performance of wireless power transfer systems, a dual-layer nested optimization method using differential evolution (DE) algorithm is proposed in this paper. In contrast to previous methods to derive the compensated capacitance, this proposed method determines the capacitance values using optimization method. By testing a prototype, it is found that the proposed design can have much higher power transfer efficiency when compared to that of traditional method. The dual-layer nested optimization method, based on the design constrains, is also used to determine the parameters of the coils to obtain the maximum power transfer efficiency of the whole system. The result is validated using finite element method (FEM).

A Novel Hybrid Resonator for Wireless Power Delivery in Bio-Implantable Devices

Magnetic resonant wireless power transfer (MRWPT) is a developing technology to transfer power over a relatively long distance. It offers a promising solution in avoiding costly and risky battery replacement surgery in bio-implantable devices. One of the obstacles of the application of this transfer technique is that its efficiency is not satisfactory and the design method has not been presented systemically. In this paper, a design method of MRPWT system with a novel hybrid resonator for deep brain stimulation (DBS) device is proposed. A new formula to determine the diameter of the resonators according to the power transfer distance is presented. The merit of the proposed design is that the transmitter coil of the MRPWT system is modulated precisely with improved magnetic coupling towards the target coil while minimizing the power loss in the coils; hence the power transfer efficiency can be improved. Experiment is carried out to verify the validity and effectiveness of the proposed design method.

A Fast Algorithm for Frequency-Domain Solutions of Electromagnetic Field Computation of Electric Devices Using Time-Domain Finite-Element Method

A fast algorithm for finding the frequency-domain solutions of electromagnetic field computation using time-domain finite-element method (FEM) is presented. Base solutions, which are time-domain solutions when the excitations are substituted by step functions, are computed first using time-stepping FEM in time domain. Then, based on these base solutions in time domain, all solutions in frequency domain at different operating frequencies can be easily and quickly obtained by simple addition and subtraction operations. It can be seen, from a numerical experiment on the performance analysis of a magnetic-resonant wireless power transfer system, that the computing time of the proposed time-domain method is less than 5% of that required if conventional frequency-domain method is used. The proposed method can be generalized and extended to any linear systems.

Complexity Analysis of Magnetic Stimulation at the Acupoint of Zusanli (St36) on EEG

Magnetic stimulation has become a very topical research area in brain studies because of its non-invasiveness, painlessness and security. It is well known that acupuncture has many varied physiologic effects on a number of functional systems of human subjects. In this paper, the EEG is recorded while the acupoint of Zusanli (St36) is stimulated by excitations of the same magnitude at different frequencies (0.5 Hz, 1 Hz, 3 Hz). Differences of EEG on the pre- and post-stimulation of the acupoint with magnetic field based on complexity analysis are reported. The data are analyzed with sample entropy (SampEn) and illustrated using brain information mapping (BIM). The results indicate that the SampEn of all the data can be used to distinguish the magnetically stimulated states from the normal state. It is also observed that while all frequencies can induce increases of SampEn over the whole brain, with the most obvious changes being found in the temporal lobe. This observation is consistent with the responses of human to acupuncture. The change of SampEn has significant statistical significances with a stimulation at 3 Hz, even though the effect is less obvious with other frequencies, when compared with the brain activities in normal state (p<0.05).

Analysis of Wireless Power Transfer System Based on 3-D Finite-Element Method Including Displacement Current

With the advent of electronic technology, researchers are devoting increasing interests to wireless power transfer methods. Generally finite-element method (FEM) is a powerful tool for numerical simulation of such systems. Due to the relatively high operating frequency, the presence of inductance and distributed capacitance in the system as well as eddy current and displacement current become two essential issues in the study of electromagnetic field distribution in wireless power transfer systems. One of the major problems to be addressed is the gap between low and high frequencies as conventional low frequency methods cannot include displacement current, while common high frequency methods focus mainly on the ultrahigh frequencies, such as in antenna studies. In this paper, a 3-D FEM including displacement current is developed to model wireless power transfer system to include displacement current and eddy current and close the gap of high and low frequency modeling methods. No frequency sweeping, which is required in conventional studies, is necessary in the proposed algorithm. Hence the computing time of the proposed algorithm requires only 1.5% of the normal time domain FEM method and this is a significant accomplishment for the electromagnetic community.

Complexity Analysis of EEG Under Magnetic Stimulation at Acupoints

A large number of studies reveal that repetitive TMS (rTMS) can have strong influences on cortical functions, even though the effect is very dependent on the stimulation parameters. At the same time, it is commonly acknowledged that acupuncture plays an important role in traditional Chinese medicine, and it is indeed receiving more and more attentions from the world. It is likely that a combination of acupuncture and magnetic stimulation which is non-invasive, painless and secure could give rise to treatments with substantial medical significance. This study discusses (a) the difference of EEG with pre- and post-stimulations at two different acupoints including Zusanli (St36) and Hegu (LI4) with three different frequencies (0.5 Hz, 1 Hz and 3 Hz) based on complexity analysis; (b) the character of the somatosensory evoked potentials(SEPs) in response to acupoint stimulation (Hegu) and mock point stimulation. The result indicates that different acupoints can induce different brain activity under the same stimulation correlated with the physical properties of the acupoints; and P150 can be observed after acupoint stimulation whereas mock point stimulation does not produce the same effect.