Rotary scanning wireless temperature measurement method for hyperthermia using ferromagnetic implants

Recently, the use of a ferromagnetic material in a soft‐heating method has garnered much attention as a novel method for cancer treatment. By concurrently using this material as a thermal probe, we are currently developing a minimally invasive heating and wireless temperature measurement system. To make the approach feasible in a clinical setting, it is vital to overcome the key challenge of heating the local tumor at a constant temperature. In previous conventional approaches, it was necessary to switch the induction‐heating power supply on/off after the target tumor temperature was reached. However, it cannot determine the temperature of the material during the power‐off period. Therefore, we changed this approach and found that by adjusting the distance between the heating coil and the material while maintaining a constant current flow in heating coil, the drift problem, which happened just after power is supplied during the on/off operation, did not occur any longer. Accordingly, it was not required to use multiple sensors to reduce the drift, thereby minimizing the cost. This study verifies the validity of our wireless thermometry approach while performing rotary scanning and proposes a technique for determining achievement of the target temperature. This knowledge complements other approaches for cancer treatment utilizing hyperthermia. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

外加应力与残余应力对低碳钢Q235矫顽力的影响

由U型铁芯和构件的被测部分构成了一个闭合磁路,在U型铁芯上缠绕激励线圈和感应线圈,由激励线圈中的电流信号与感应线圈中的电压信号测绘出不同应力条件下被测试样的未饱和磁滞回线,得出试样矫顽力H_c与外加拉应力、由塑性变形引起的残余应力之间的关系.外加拉应力使材料的矫顽力Hc减小,而残余应力在材料内部产生位错的钉扎效应使矫顽力H_c增大.冷作硬化过程中,材料矫顽力H_c的变化为外加应力与残余应力综合作用的结果.     

三维正交线圈磁通信信道稳定性分析

针对无线磁感应通信系统中因接收端线圈姿态变化而导致通信不稳定的问题,提出接收端采用三个相互正交的线圈的方法,以弥补单个线圈通信波动性较大的缺点。首先建立了单个线圈和全向线圈的数学模型,对磁场大小和接收端感应电压进行规律分析,最后通过仿真和试验验证了接收线圈为三维正交线圈的方法可行性。仿真和试验结果表明,三维正交线圈作为接收线圈可以有效提高无线磁感应通信系统中的感应电压值,并提升通信信道稳定性,波动性减小了95%。     

A novel method applicable to large-scale active magnetic shielding system which effectively compensates gradient magnetic fields originated from the surrounding buildings

We propose the novel magnetic compensation method which is suitable to compensate gradient magnetic fields. The method is to be applied to a conventional large-scale, tri-axial active magnetic shielding system such as a spacecraft magnetic testing facility. The essences of this method are the adoption of compensation coils which have degrees of freedom in their coil orientations, and their installation position, which is chosen to have certain distances from the center of the shielding area. The method works with at least four compensation coils. In this research, we actually demonstrated the method with a scaled-down experiment. Disturbance magnetic field (B) at the target zone was suppressed from 21.33 nT to −1.54 nT and magnetic field uniformity (ΔB) within the test zone was improved from 2.3 nT to 0.015 nT. In terms of magnetic field gradient, improvement from over 4 nT/m to below 0.5 nT/m was achieved.     

微纳米磁性材料在肿瘤磁感应热疗中的应用

磁感应加热肿瘤治疗与超声、微波、容性射频等其它热疗手段相比具有靶向性强、可自动控温、生物相容性好等优点。它是利用铁磁性物质在交变磁场中升温的物理特性,将磁性物质作为热介质引入肿瘤组织,将肿瘤组织加热到治疗温度。本文主要阐述了微纳米级磁性材料在交变磁场下的产热原理和应用特点,简要介绍了微纳米磁性材料在磁感应治疗技术中的研究现状,并提出尚需解决的问题和发展方向。     

MRI and implanted medical devices: basic interactions with an emphasis on heating

There are three principal magnetic fields in magnetic resonance imaging (MRI) that may interact with medical implants. The static field will induce force and torque on ferromagnetic objects. The pulsed gradients are of audio frequency and the implant may concentrate the induced currents, with a potential for nerve stimulation or electrical inference. The currents induced in the body by the radio frequency (RF) field may also be concentrated by an implant, resulting in potentially dangerous heating of surrounding tissues. This paper presents basic information about MRI interactions with implants with an emphasis on RF-induced heating of leads used for deep brain stimulation (DBS). The temperature rise at the electrodes was measured in vitro as a function of the overall length of a DBS lead at an RF frequency of 64 MHz. The maximal temperature rise occurred for an overall length of 41 cm. The method of moments was used to calculate the current induced in the lead. From the induced currents, the RF power deposition near the electrodes was calculated and the heat equation was used to model the temperature rise. The calculated temperature rises as a function of lead length were in good agreement with the measured values.     

Recording brain activity wirelessly

The continuous monitoring of electrical brain activity with implanted depth electrodes is essential for understanding the neural substrates of many physiological and pathological brain functions, such as emotion and epilepsy. Existing instrumentation uses wires to power and record directly from the brain. This article describes the theory involved in every aspect of the design of an inductively powered system with emphasis on the trade-offs involved. A complete inductive powering system consists of two major parts - a drive coil and a pickup coil, and their associated impedance matching networks. The drive coil is designed to maximize the magnetic field within the desired enclosure at the drive frequency. Similarly, the pickup coil is designed to maximize the amount of magnetic flux density converted to power for the implant, while minimizing it's own dimensions. A specific real-world application of inductive powering is detailed, illustrating how many of the design decisions were made to develop a successful system for recording neural signals from awake and freely behaving animals.     

电力变压器磁屏蔽模型涡流场和损耗的计算与测量

大型电力变压器铁磁结构件中产生的电磁损耗会导致局部过热并使相关的绝缘部件受到损害,进而危及整个变压器的正常运行,对面向工程的国际TEAM(Testing Electromagnetic Analysis Methods)Problem 21的磁屏蔽基准模型的涡流场和损耗进行了计算和试验测量研究,考虑了模型中铁磁材料的非线性、各向异性及磁滞等特性,提出了用于分离激励线圈电阻损耗和涡流损耗的测量方法(漏磁通补偿线圈测量装置),并用MagNet软件进行了数值计算.基准模型的计算和测量结果相吻合,验证了计算方法和软件的有效性.     

基于磁轭结构的脉冲涡流热成像激励效果比较

针对目前脉冲涡流感应热成像无损检测中激励线圈加热不均匀、受提离影响大的问题,将导线缠绕在磁轭装置上加载电流,分析其激励效果。为确定线圈缠绕位置对激励效果的影响,比较了不同装置激励时裂纹两端和底部的涡流分布及温度分布。结果表明,引入磁轭装置后系统的能量传递效率得到很大提高,同时激励的不均匀性减弱。激励线圈均匀分布在磁轭装置横梁及两极靴时激励效果最好。利用最优激励模型对不同方向的裂纹进行检测,结果表明,铁磁材料表面各个方向角的裂纹都可以被检测到,非铁磁材料方向角较小的裂纹不能被检测到。根据试件表面最高温度随裂纹方向角增大而线性增加的特点可以识别裂纹的方向角。     

含金属异物的无线充电系统场域等效建模分析

无线充电系统中,电能传输遵循发射线圈和接收线圈之间的磁耦合关系。当发射线圈和接收线圈之间存在金属异物时,异物的涡流或聚磁效应将会影响无线充电系统的传输性能与运行稳定性,严重时还会危害充电安全。为了厘清不同材质金属异物对无线充电系统性能的影响机理,有效分析异物的影响规律,迫切需要一种精确的金属异物建模方法,提高金属异物的检测精度。为此,文中计及金属的材质、位置、等效面积等关键因素,提出一种金属异物场域等效建模方法,通过构造金属异物影响下的无线充电系统耦合方程,对比得到异物引入前后发射线圈电流和接收线圈电流间的相位差表达式。在此基础上,进一步提出了铁磁性金属与非铁磁性金属的等效线圈模型及其参数配置方法,可精确得到金属异物介入条件下的电流相位差值。最终通过仿真与实验验证了建模方法的准确性与有效性,为无线充电系统中引入金属异物的特性分析与在线检测提供了一种新思路。     

开放式磁共振系统中梯度磁场的快速计算方法

梯度线圈是磁共振系统的核心部件之一,其产生的梯度磁场是成像空间定位的物理基础。在开放式磁共振系统中,大量铁磁介质会导致实际梯度磁场偏离设计值,因此需要对实际梯度磁场进行校验。本文针对开放式磁共振的结构特点,提出了一种基于扇环形状单元的积分方程法,可以计算二维/三维模型中的梯度磁场。针对两种常见的开放式磁共振结构,通过将本文方法的计算结果与其他三种方法(直接法、镜像法和有限元法)进行对比,证明了本文方法在保证计算精度的同时,可以大幅减少计算时间,在重复计算和迭代优化中具有显著优势。实验结果证明了该算法具有良好的可靠性。     

Three-dimensional magnetic field analysis of a system containing coil currents and iron elements using the virtual current method

This paper proposes a method of analyzing the three-dimensional magnetic field of a system containing coil currents and magnetic substances using virtual currents. Various methods have been presented for analysis of a three-dimensional static field in an open boundary space; however, in a large-scale problem, the computational size easily exceeds the acceptable limit of computing time and machine capacity. The basic idea of the proposed method is to divide the whole region into interior and exterior regions with an artificial boundary and to substitute virtual currents for source currents and magnetic substances within the boundary. The use of virtual currents reduces the number of elements to be analyzed and shortens computing time while maintaining accuracy of analysis. In this paper, a method of determining virtual current is proposed and principal parameters of virtual currents that affect accuracy of analysis are examined. The conditions under which the virtual current method can be applied are examined through analysis of errors introduced by the virtual current method. This method has been applied to analyze magnetic shielding of a magnet for magnetic resonance imaging. This example proves that the proposed method is effective in reducing the scale of analysis and computing time.     

Capacitor-less induction heating system with self-resonant bifilar coil

In this work, a capacitor-less self-resonating coil-based induction heating (IH) system with magnetic resonant coupling has been proposed. In the conventional heating system, the inclusion of additional capacitor for creating the resonance results in poor efficiency of overall system. To overcome this issue, a bifilar coil system is implemented, which leads to series resonance at a particular frequency. The key mechanism is self-resonance wireless power transfer concept to IH system; hence, no capacitor is needed in the system. The coil has a series association of the coil inductance and capacitance at the resonant operating condition. A mathematical modeling and steady state analysis is performed for the conventional (solenoidal) coil and bifilar coil to estimate the actual value of the capacitance and inductance of the coil. The performance of the bifilar coil system is tested through COMSOL multiphysics simulation tool and parameters like eddy current, magnetic flux, and temperature distribution in the work piece are analyzed. The experimental setup of the bifilar coil-aided IH system is implemented with PIC16F877A microcontroller, and FLIR thermal imager is used to analyze the temperature distribution on the work piece. The experimental results are compared with the simulation results, and the bifilar coil system provides a promising solution.     

Design of a coil geometry for generating magnetic field to evaluate biological effects at 85 kHz

In recent years, the use of induction‐heating systems has increased and wireless power transmission (WPT) systems have been discussed. These applications are installed close to a human body. Therefore, it is important to discuss the effects of alternating magnetic fields and to evaluate electromagnetic interference. This paper discusses the design procedure of a magnetic field generator to evaluate the electromagnetic interference at 85 kHz that is being studied in WPT systems for EV and HEV. The magnetic field generator presented in this paper consists of a single‐phase inverter circuit that uses SiC‐MOSFETs and an air–core inductor that is used as the coil for generating a magnetic field. In particular, this paper shows that the coil used for generating magnetic field needs to reduce the winding voltage to generate higher magnetic flux. In addition, this paper presents the design procedure of the proposed coil structure that can satisfy some limited conditions. The experimental results of the proposed system rated at 82 kHz and 100 A are presented.     

基于主动磁检测技术的车辆检测新方法

为了给智能交通管理系统提供交通信息,提出了一种车辆检测的新方法.主动磁检测器包括一个发射线圈和一个接收线圈,发射线圈持续地辐射交流磁场,当车辆从检测器上方通过时,车辆的金属外壳中就会产生涡电流,从而产生涡流二次场,那么接收线圈周围的磁场就会发生改变.通过测量接收线圈周围的磁场是否改变来达到检测车辆的目的.检测概率为96...     

Noncontact energy transfer system using immittance converter

Noncontact energy transfer systems are widely used in industrial material handling systems. This paper proposes a new noncontact energy transfer system using a tuned pickup coil and an immitance converter inductively coupled to a parallel transmission line excited by a high‐frequency constant‐current source. In a noncontact energy transfer system which supplies continuous energy to movers by electromagnetic induction, the efficiency is low owing to low excitation impedance because of the wide air gap of the magnetic core in the pickup coil. The excitation impedance can be increased by the resonance with a capacitor connected parallel to the pickup coil. The resonant pickup coil works as a high‐frequency constant‐current source for the load. We propose using an immittance converter to transform the high‐frequency constant‐current source into a high‐frequency constant‐voltage source. Then, the high‐frequency constant‐voltage source is rectified into a constant‐voltage dc source, and supplies power to an inverter for motor driving. In this paper, the configuration of this new noncontact energy transfer system and its characteristics are described. The experimental results and simulation waveforms are also described. © 2001 Scripta Technica, Electr Eng Jpn, 136(4): 58–64, 2001     

电力变压器磁屏蔽模型损耗三维有限元分析及实验研究

针对大型电力变压器铁磁结构件中(例如油箱)产生的电磁损耗导致局部过热,使相关的绝缘部件受损,进而危及整个变压器的正常运行现象,笔者提出以国际TEAM Problem 21基准磁屏蔽(简称为板式和立式屏蔽)模型为例,采用分离激励线圈电阻损耗和涡流损耗的测量方法(漏磁通补偿线圈测量装置),对变压器取向硅钢叠片中的磁通和损耗进行计算和试验测量。其计算与测量结果表明,该方法较好地解决了线圈损耗和结构件损耗分离的问题。同时,也验证了三维非线性涡流场分析和损耗模拟方法的有效性。     

正方形亥姆霍兹线圈三维磁场及其均匀性分析

为研究光纤陀螺的磁敏感性,利用三个正方形亥姆霍兹线圈构建三维匀强磁场,并分析其匀强磁场区域特性。将正方形亥姆霍兹线圈视为四段载流导线,采取分段计算然后进行矢量叠加的方法,分析了正方形亥姆霍兹线圈三维空间磁场强度及其均匀性,并给出仿真结果。最后给出了正方形亥姆霍兹线圈三维匀强磁场的结构模型及相关数据分析。     

胶囊内窥镜新型外磁场驱动系统模型与仿真

为了克服传统推进式和被动式内窥镜在医用检查时存在的不足,提出了一种由三个同轴圆线圈和两对平行鞍线圈组成的胶囊内窥镜新型外磁场驱动模型。胶囊内窥镜内部嵌入NdFeB永磁体,通过控制外部线圈的电流来驱动永磁体,带动内窥镜在体内运动。在实验过程中,运用ANSOFT电磁场仿真软件分别对三个同轴圆线圈和鞍线圈的磁场分布进行了分析,结果表明,该模块能够产生三维匀强磁场,符合驱动无线胶囊内窥镜在体内运动的要求,并且结构简单紧凑,可控性高,有利于提高检测效率。     

带有大中继线圈的无线充电磁耦合器抗偏移特性研究

感应式电能传输技术在电动汽车实际应用中不可避免地出现原副边线圈相对位置错位,这会导致系统效率下降、线圈过流等一系列问题。针对这些问题,提出一种带大中继线圈的三线圈磁耦合器结构用于提升系统抗偏移能力。结合解析法和有限元法,分析了影响系统效率的关键因素,研究了不同补偿参数下三线圈磁耦合器传输性能以及不同偏移程度下两线圈和三线圈的互感和损耗的变化规律,并验证了含大中继线圈的三线圈磁耦合器在提升抗偏移能力方面的独特优势。在此基础上,提出基于两线圈和三线圈切换的具有强抗偏移能力的磁耦合器优化设计方法。设计并研制了线圈尺寸为400 mm×400 mm的磁耦合器样机,实验结果表明在偏移尺寸达到线圈尺寸50%、输出功率为3 kW的情况下,磁耦合器效率可达95 %,相比传统两线圈磁耦合器效率提升5 %。