感应式磁声耦合成像脉冲磁场激励源的设计

目的：脉冲磁场激励源是感应式磁声耦合成像系统激发声振动信号的关键部分,为了提高成像质量及成像分辨率,对脉冲磁场激励源进行参数设计及模拟实验验证。方法：选用正弦脉冲作为激励信号,对脉冲磁场放电电路参数进行了仿真设计,通过实验测量磁激励线圈产生的空间磁场信号,验证仿真结果。结果：实验结果表明,利用正弦脉冲对设计制作的线圈进行放电,磁感应强度信号中心频率为0.8MHz,频带宽度为1.2MHz,此参数下成像分辨率理论上可达1.9mm,脉宽达1.27μs。结论：利用设计的脉冲磁场激励源参数,通过功率放大即可实现感应式磁生耦合成像系统的脉冲磁场激励。     

新型功率可调MIT激励源设计及其磁场分析

目的：设计输出功率可调的MIT激励源和3种类型的激励线圈,以提高MIT相位检测的精度。方法：通过选取PA19放大器芯片,设计200 kHz工作频率下可调输出的功率放大电路;通过计算,设计制作了螺线管线圈和2种聚焦线圈;最终测试比较各激励线圈的磁场分布,并在不同激励线圈的磁场下对圆柱形铁块进行相位测试。结果：激励源输出峰值电流大于1 A,圆形螺旋聚焦线圈的磁场由线圈轴线向两边衰减斜率最大,约为0.06 T/cm,且在该激励线圈磁场中,对铁块的相位检测结果最大。结论：该激励源输出功率可调范围大,采用圆形螺旋聚焦线圈磁场聚焦效果最佳、相位检测效果最好。     

磁致热疗肿瘤用磁场发生装置的研制

目的:设计一种磁感应致热疗肿瘤用的正弦波形磁场发生装置。方法:电路采用555时基芯片为核心,利用单运放与RC组成的电路,将脉冲波形信号转换为正弦波形信号,然后通过放大电路进行电流放大,加负载线圈后产生所需磁场。结果:所研制的磁场发生装置可调节产生频率范围为50～150 kHz的正弦波形磁场,加入微量纳米磁性粒子集合体后发生磁致产热现象。结论:所研制的磁场发生装置具有成本低,精度高,性能稳定,参数调整方便等优点,为研究磁致热疗肿瘤提供必要的手段。     

改进型BMIT激励源设计及磁场分析

目的：设计一种符合人体电磁暴露安全标准要求的脑磁感应成像激励源,以满足临床应用中人体安全性的需要。方法：在该课题组前期工作的基础上,采用有源晶体振荡器作为振荡源,参照IEEEStdC95.1人体电磁暴露安全标准,计算、设计和实现3种激励线圈和激励电路,以产生符合安全标准的激励磁场,并对所产生的激励磁场进行初步测量和评估。结果：平面矩形聚焦线圈在线圈中心处10MHz、1MHz、200kHz最大磁感应强度分别为0.005、0.057、0.189T,沿着轴线方向磁场逐步衰减,且磁场由轴线方向两侧也逐步衰减,斜率分别约为0.0002、0.002、0.007T/cm。结论：测量区域内的场强均满足安全性要求。安全性激励源的实现为临床安全应用打下了良好的基础。     

一种便携式医用磁感应测量装置的设计

目的:设计一种便携式高精度的磁感应相位检测装置。方法:设计一种基于梯度线圈主磁场抵消技术以及新型鉴相芯片SYPD-1的便携式医用磁感应测量装置。整个系统包括梯度线圈结构、差动放大器、鉴相器、单片机处理电路和显示电路。SYPD-1是新上市的无源鉴相芯片,鉴相带宽1～100 MHz,灵敏度8 mV/(°),相位差分辨率不超过0.03°,是当前分辨率最高的鉴相芯片,使用方便。结果 :该装置可以分辨出电导率为0.5、1.3、7.8 S/m的3种同体积NaCl溶液,且具有较好的线性度。结论:该磁感应测量装置实现了高精度和便携式的要求,具有一定的实用价值和很大的改进空间。     

基于单片机的交变磁治疗床的设计与实现

本文介绍了一种新型交变磁治疗床的设计与实现。该系统采用飞利浦单片机LPC2214为核心控制芯片，控制安装于床体上的线圈产生脉冲磁场，利用磁场的主要物理性质以及磁场与器官组织发生交互作用治疗疾病，控制脉冲磁场频率产生不同的磁场强度，使得不同的患者、不同的病情可以选择最佳的交变磁强度治疗方案，同时具备穿透力强的特点。本仪器包括床体以及安装于床体上用于产生脉冲磁场的线圈、用于控制线圈输出的控制装置、为控制装置供电的电源电路等。本文以如何设计交变磁治疗床的控制系统为切入点，阐述整个控制系统的设计过程和调试过程。该仪器已在生物医学领域成功应用。     

医用高强度磁场的磁场线圈散热结构设计

该研究设计了一种新型磁刺激线圈,并利用COMSOL软件对线圈的散热性能和磁场分布情况进行分析。将普通的矩形线缆线圈作为对照组,在第1组散热分析中,采用简化设计的散热模型对新型磁刺激线圈和对照组线圈的散热情况进行分析,结果显示,简化模型中新型磁刺激线圈的散热效果优于对照组,两者均可将线圈的周边温度降至41℃以下;在第2组散热分析中,对整个散热模型进行了结构优化,优化后的散热模型可将线圈的周边温度降至30℃以下;同时,模型中新型磁刺激线圈的散热效果优于对照组;另外,该研究还分析了两种不同线圈的磁场分布,结果显示,两种线圈产生的磁场强度差异较小,新型磁刺激线圈的磁场分布情况与对照组持平,可满足正常的使用需求。     

外磁场驱动无线胶囊式内窥镜的电路设计与操作

目的：利用外磁场驱动无线胶囊式内窥镜,可以使患者吞服的无线肠胃内窥镜在医生的控制下做多自由度的移动,使内窥镜的摄像头直接在可疑区域做有针对性的检查,大大增加了检查的成功率。方法：依靠3组线圈产生的磁场可以对处在任意位置、任意方向的附带有磁性材料的无线胶囊式内窥镜产生作用力。通过改变线圈内电流的大小和方向,操控胶囊内窥镜在人体内的位置以及指向。结果：设计出简单的操作装置,实现线圈的操作,进而实现对无线胶囊式内窥镜的控制。结论：外磁场驱动的无线胶囊式内窥镜减小了内窥镜的整体体积和质量,减轻了肠胃检查时的痛苦,缩短了医生的检查时间,使医生控制其移动更为容易和灵活。     

基于亥姆霍兹线圈的均匀磁场发生器设计分析及应用

目的:根据亥姆霍兹线圈原理设计、制作大尺寸均匀磁场发生器,用于大鼠磁场辐射干预实验,研究磁场对生物生理及病理机能的影响.方法:用计算机、功率放大器、亥姆霍兹线圈组成均匀磁场发生器,利用Matlab软件编程,将产生的正弦波音频信号传送到功率放大器,驱动亥姆霍兹线圈产生均匀的磁场,利用有限元分析软件ANSYS的电磁分析模块对亥姆霍兹线圈产生的磁场进行有限元分析,并与实测结果进行对比.结果:实验证明,均匀磁场发生器能在亥姆霍兹线圈15％的空间内产生误差小于10％的均匀磁场,能够满足医学实验的要求.结论:该装置结构简单、成本低、控制精度高,具有重要的理论和实用价值.     

经颅磁刺激器的设计及磁场分布的测量

提出了设计磁刺激器一般原则,包括基本理论、硬件及其构成,分析磁刺激器的RLC模型,给出模型参数的计算方法,讨论了决定磁场强度的各种因素;设计制作了一套磁刺激系统,绕制了圆形线圈和8字形线圈,并用这2种线圈进行实验,用特斯拉计检测线圈产生的磁场;实验数据显示,这2种线圈的磁场分布和目前已有的研究方法所作的理论计算对照,是相吻合的。在此基础上,进行了一个测量头部磁场的模拟实验。     

Characterization of the magnetic fields around walk-through and hand-held metal detectors

Magnetic field strength measurements were made around eight hand-held and 10 walk-through metal detectors. The method was similar to that used in previous research for Electronic Article Surveillance units except a Cartesian rather than cylindrical coordinate system was used. Special magnetic field probes specifically designed for metal detector measurements were used. A non-metallic positioning apparatus was designed and fabricated. Magnetic field strength measurements were collected on one hand-held metal detector in the laboratory. The remaining data were collected at airport terminals, federal and state government buildings, and a local high school. Walk-through metal detectors had considerably higher magnetic field strengths [up to 299 Am(-1) p-p (3,741 mG)] than hand-held metal detectors [up to 6 Am(-1) p-p (76 mG)]. The frequencies of the magnetic field signal for walk-through detectors were between 0.1 kHz and 3.5 kHz while those for hand-held detectors were between 89 kHz and 133 kHz. Waveforms for all hand-held metal detectors were sinusoidal; those for walk-through metal detectors varied with most being saw-toothed or pulsed. Due to their higher field strengths and the pulsed nature of their magnetic fields, walk-through metal detectors likely pose a higher risk for medical device electromagnetic interference than do hand-held units. Root mean squared magnetic field strengths were calculated from the peak-to-peak values and compared to occupational and general public exposure limits. None of these limits were exceeded. Measurement repeatability was examined for one hand-held and two walk-through metal detectors. For the hand-held metal detector measurements at the location of the maximum magnetic field strength, measurements by three individuals had a repeatability (percent standard deviation) of 5.9%. Limited repeatability data were collected for on-site measurements of walk-through detectors. One unit showed repeatability of 0.1 to 4.5%; a multi-zone unit showed repeatability of 2.7 to 67.5%.     

Assessment of complex EMF exposure situations including inhomogeneous field distribution

Assessment of exposure to time varying electric and magnetic fields is difficult when the fields are non-uniform or very localized. Restriction of the local spatial peak value below the reference level may be too restrictive. Additional problems arise when the fields are not sinusoidal. The objective of this review is to present practical measurement procedures for realistic and not too conservative exposure assessment for verification of compliance with the exposure guidelines of ICNIRP. In most exposure situations above 10 MHz the electric field (E) is more important than the magnetic field (B). At frequencies above 500 MHz the equivalent electric field power density averaged over the body is the most relevant indicator of exposure. Assessment of specific absorption rate (SAR) is not needed when the spatial peak value does not exceed by 6 dB the average value. Below 50 MHz down to 50 Hz, the electric field induces currents flowing along the limbs and torso. The current is roughly directly proportional to the electric field strength averaged over the body. A convenient way to restrict current concentration and hot spots in the neck, ankle and wrist, is to measure the current induced in the body. This is not possible for magnetic fields. Instead, for a non-uniform magnetic field below 100 kHz the average magnetic flux density over the whole body and head are valid exposure indicators to protect the central nervous system. The first alternative to analyze exposure to non-sinusoidal magnetic fields below 100 kHz is based on the spectral comparison of each component to the corresponding reference level. In the second alternative the waveform of B or dB/dt is filtered in the time domain with a simple filter, where the attenuation varies proportionally to the reference level as a function of frequency, and the filtered peak value is compared to the peak reference level derived from the ICNIRP reference levels.     

Measurements of extremely low-frequency magnetic fields around video display terminals

The extremely low-frequency (ELF) magnetic field emissions of seven video display terminal (VDT) models were measured. A measuring coil with a linearized frequency response (50 Hz to 25 kHz) was used. The dominating ELF magnetic field around the terminals was the 50 or 60 Hz asymmetric triangular waveform from the vertical deflection coil of the cathode ray tube. At the distance of 50 cm, the magnetic field strength was still slightly higher than the background level in usual office rooms, but several orders of magnitude lower than the thresholds of known interaction mechanisms. Some recent experiments suggest that certain biological effects may occur at field strengths only a few times higher than those found at the position of VDT operators, but the significance of these effects to human health is not known.     

Measurements of electromagnetic emissions from video display terminals at the frequency range from 30 Hz to 1 MHz

Electric (E) and magnetic field (B) strengths or flux densities were measured at distances of 30 and 50 cm from the screen of video displays at a frequency range from 30 Hz to 1 MHz. The measurement system consisted of an optically coupled active dipole for E-fields, a magnetic field meter, a digital oscilloscope, a portable computer for data storage and a laboratory computer for Fourier analysis of the recorded signals. Comparison of measurement results with available broadband exposure standards or proposed standards indicated that magnetic flux density should be measured at both the (ELF) frequency range from 30 Hz to 300 Hz and at the (RF) frequency range from 10 kHz to 500 kHz. Alternatively, time derivative of magnetic flux density may be measured. Nor should the measurement of the electric field strength at the RF range be neglected. These conclusions, however, are valid only in relative terms. In all cases the exposure is at least one decade below the most stringent exposure limit. The maximum relative exposure 0.077 was obtained by applying the ACGIH standard for magnetic fields at a distance of 30 cm from the screen. The field strengths decrease by a factor varying from 2.5 to 3.5 at a distance of 50 cm, which is a more realistic distance when considering actual working conditions.     

脉冲磁场刺激仪的研制

研制的脉冲磁场刺激仪主要指标是：最大磁感应强度0．01-2T，频率0．2-100Hz，脉冲宽度0．01～1ms。仪器的工作方式分为手控、脚控和自控，可显示刺激强度和刺激次数，并可输出不同波形的触发信号，使检测仪器同步工作。     

磁感应强度测量仪的研制

目的：研制一种用于脉冲磁场强度测量的仪器。方法：采用单片机和霍耳集成传感器测量磁感应强度，并给出了相关硬件电路和软件流程，其测量范围是0～50mT。结果：仪器结构简单，性能安全可靠，测量精度高。结论：可用于各类电磁场发生仪磁感应强度的检测。