EFFECT OF LOW-FREQUENCY ELECTROMAGNETIC FIELD ON THE AS-CASTING MICROSTRUCTURES AND MECHANICAL PROPERTIES OF HDC 2024 ALUMINUM ALLOY

The influences of the low frequency electromagnetic field on the horizontal direct chill casting process were investigated experimentally. Ingots of 2024 aluminum alloy with a cross size of 40 mm× 200 mm were produced by the conventional horizontal chill casting process and low frequency electromagnetic horizontal chill casting processre- spectively. The as-cast structures and the mechanical property of the ingots were examined. The results showed that the low frequency electromagnetic field could sub- stantially refine the microstructures and pronouncedly reduce the macrosegregation in the horizontal direct chill casting process. Moreover, the surface quality of the ingot was prominently improved by the low frequency electromagnetic field. The fracture strength and elongation percentage of the ingot was increased with the low frequency electromagnetic field.

Effect of low-frequency electromagnetic field on the as-cast microstructure of a new super high strength aluminum alloy by horizontal continuous casting

The super high strength aluminum alloy ingots with 100 mm in diameter were cast by the process of low-frequency electromagnetic horizontal continuous casting (LFEHC) and the effect of electromagnetic field on the as-cast microstructure was studied. Results show that microstructure of the sample prepared by the LFEHC process was greatly refined. Microstructures at the border and the center of the ingots were fine, uniform and rosette-shaped. Electromagnetic frequency plays a key role in microstructure refining. Fine and uniform microstructures can be obtained with optimal electromagnetic frequency. In this experiment, under a frequency of 30 Hz the microstructure was the finest and the most uniform.

Low-frequency pulsed electromagnetic field pretreated bone marrow-derived mesenchymal stem cells promote the regeneration of crush-injured rat mental nerve

Bone marrow-derived mesenchymal stem cells （BMSCs） have been shown to promote the regeneration of injured peripheral nerves. Pulsed electromagnetic field （PEMF） reportedly promotes the proliferation and neuronal differentiation of BMSCs. Low-frequency PEMF can induce the neuronal differentiation of BMSCs in the absence of nerve growth factors. This study was designed to investigate the effects of low-frequency PEMF pretreatment on the proliferation and function of BMSCs and the effects of low-frequency PEMF pre-treated BMSCs on the regeneration of injured peripheral nerve using in vitro and in vivo experiments.In in vitro experiments, quantitative DNA analysis was performed to determine the proliferation of BMSCs, and reverse transcription-polymerase chain reaction was performed to detect S100 （Schwann cell marker）, glial fibrillary acidic protein （astrocyte marker）, and brain-derived neurotrophic factor and nerve growth factor （neurotrophic factors） mRNA expression. In the in vivo experiments, rat models of crush-injured mental nerve established using clamp method were randomly injected with low-frequency PEMF pretreated BMSCs, unpretreated BMSCs or PBS at the injury site （1 × 106 cells）. DiI-labeled BMSCs injected at the injury site were counted under the fluorescence microscope to determine cell survival. One or two weeks after cell injection, functional recovery of the injured nerve was assessed using the sensory test with von Frey filaments. Two weeks after cell injection, axonal regeneration was evaluated using histomorphometric analysis and retrograde labeling of trigeminal ganglion neurons. In vitro experiment results revealed that low-frequency PEMF pretreated BMSCs proliferated faster and had greater mRNA expression of growth factors than unpretreated BMSCs. In vivo experiment results revealed that compared with injection of unpretreated BMSCs, injection of low-frequency PEMF pretreated BMSCs led to higher myelinated axon count and axon density and more DiI-labeled neurons in the trigeminal ganglia, contributing to rapider functional recovery of injured mental nerve. These findings suggest that low-frequency PEMF pretreatment is a promising approach to enhance the efficacy of cell therapy for peripheral nerve injury repair.

Effect of low frequency electromagnetic field on microstructures and macrosegregation of horizontal direct chill casting aluminum alloy

The influences of low frequency electromagnetic field on cast surface, microstructures and macrosegregation in horizontal direct chill(HDC) casting process were investigated experimentally. The cast surfaces, microstructures and macrosegregation of the ingots manufactured by conventional HDC and low frequency electromagnetic HDC casting were compared. The results show that low frequency electromagnetic field significantly improves the surface quality, refines the microstructures and reduces macrosegregation. Further more, increasing electromagnetic intensity or decreasing frequency is beneficial to the improvement. In the range of ampere-turns and frequency employed in the experiments, the optimum ampere-turns is found to be 10 000 A·turn and the frequency to be 30 Hz.

Temperature field in the hot-top during casting a new super-high strength Al-Zn-Mg-Cu alloy by low frequency electromagnetic process

The billets of a new super-high strength Al-Zn-Mg-Cu alloy in 200mm diameter were produced by the processesof low frequency electromagnetic casting (LFEC) and conventional direct chill (DC) casting, respectively. The effects of lowfrequency electromagnetic field on temperature field of the melt in the hot-top were investigated by temperaturemeasurement method. Temperature curves were measured from the surface to the center of the billets by locating type Kthermocouples into the casting during the processes. The results show that during LFEC process the temperature field inthe melt applying the hot-top is very uniform, which is helpful to reduce the difference of thermal gradients between thesurface and the center, and then to reduce the thermal stress and to eliminate casting crack.

Effect of Low Frequency Electromagnetic Field on Macrosegregation of Horizontal Direct Chill Casting Aluminum Alloys

The horizontal direct chill (HDC) casting process is a well-established production route for aluminum alloy ingot but the ingot may suffer from macrosegregation sometimes. In order to control the defect, a low frequency electromagnetic field has been applied in HDC casting process and the relevant influence has been studied. The results show that application of low frequency electromagnetic field can reduce macrosegregation in HDC casting process; and two main parameters of electromagnetic field density and frequency, have great influences on the solution distribution along the diameter of ingot. Moreover, the mechanisms of reduction of macrosegregation by electromagnetic field have been discussed.

Production of super-high strength aluminum alloy billets by low frequency electromagnetic casting

The effects of low frequency electromagnetic field on the macro-physical fields in the semi-continuous casting process of aluminum alloys and the microstructure and crack in the billets were studied and analyzed by the numerical and experimental methods.Comparison of the results for the macro-physical fields in the low frequency electromagnetic casting（LFEC） process with the conventional DC casting process indicates the following characters due to the application of electromagnetic field：an entirely changed direction and remarkably increased velocity of melt flow;a uniform distribution and a decreased gradient of temperature;elevated isothermal lines;a reduced sump depth;decreased stress and plastic deformation.Further,the microstructure of the billets is refined remarkably and the crack in the billets is eliminated in LFEC process because of modification of the macro-physical fields induced by the application of low frequency electromagnetic field.

Efects of low frequency electromagnetic ield on surface quality, microstructure and hot-tearing tendency of semi-continuous casting ZK60 magnesium alloy billets

The low frequency electromagnetic field was applied during direct chill(DC) semi-continuous casting of the ZK60 magnesium alloy billets. Effects of low frequency electromagnetic field on surface quality, microstructure and hot-tearing tendency of Φ500 mm ZK60 magnesium alloy billets were investigated. The results showed that with the application of the low frequency electromagnetic field, the surface quality of the ZK60 magnesium alloy billets is markedly improved and the depth of cold fold is decreased. The microstructure of the billets is also significantly refined. Besides, the distribution of the grain size is relatively uniform from the billet surface towards its center, where the average grain size is 42 μm at surface and 50 μm at center. It also shows that the hot-tearing tendency of DC semi-continuous casting ZK60 magnesium alloy billets is significantly reduced under low frequency electromagnetic field.

Analysis and Simulation of the Influence of Electromagnetic Fields on Living Beings near HV Power Lines Using the FDTD Method

Recent decades have seen rapid advances in the field of electrical engineering, such that our environment has become a sea of electrical and magnetic signals, raising questions about the possible effects of low-frequency electromagnetic fields on the environment and which are capable of modifying and destroying our ecosystem. Particular interest was given in this article due to a massive influx of population living near high voltage lines. The analysis and simulation of the influence of low frequency electromagnetic fields on living beings in the vicinity of high voltage sources 132 kV and 220 kV in urban areas in DR Congo is the subject of our research with a view to estimating the level of exposure of humans to low frequency electromagnetic fields. To carry out our research, we used the classic method of analyzing the field produced near a high voltage line based on Maxwell’s image theory, the Maxwell-Gauss theorem and Maxwell-Ampère theorem to model and quantify low-frequency electromagnetic fields in the vicinity of high-voltage lines. The 2D FDTD numerical formulation was developed from telegraphers’ equations and allowed us to obtain models of current and voltage induced by electromagnetic fields on living beings below and near HV lines. The different simulations carried out on the proposed models illustrate the effects of the electrical and geometric parameters of the pylons on the distribution of the electromagnetic field in the vicinity of the HV lines. The results obtained were compared to the safety limits recommended by the standards.

Effects of low-frequency magnetic field on grain boundary segregation in horizontal direct chill casting of 2024 aluminum alloy

Effects of low frequency electromagnetic field on grain boundary segregation in horizontal direct chill (HDC) casting process was investigated experimentally. The grain boundary segregation and microstructures of the ingots, which manufactured by conventional HDC casting and low frequency electromagnetic HDC casting were compared. Results show that low frequency electromagnetic field significantly refines the microstructures and reduces grain boundary segregation. Decreasing electromagnetic frequency or increasing electromagnetic intensity has great effects in reducing grain boundary segregation. Meanwhile, the governing mechanisms were discussed.

EXTREMELY LOW FREQUENCY MAGNETIC FIELD SUSCEPTIBILITY OF VISUAL DISPLAY UNITS

Extremely low frequency (ELF) magnetic field susceptibility is an index of visual display unit (VDU) quality and performance. This paper provided field measured data on the susceptibility for a large variety of VDUs. A test rig was built to study the susceptibility of VDUs to magnetic fields at fundamental and third harmonic frequencies. It was found that the susceptibility level is largely dependent on refresh rate of the VDU and the orientation of the external ELF field. It was also found that the VDU susceptibility is significantly increased in the presence of harmonic frequency magnetic fields. About 30% of the tested samples have susceptibility levels higher than that stated in IEC 1000-4-8 standard.

Direct-chilling casting of Mg alloy under electromagnetic and ultrasonic combined field

The effects of low frequency electromagnetic (LFEC) field and ultrasonic (US) field on the microstructures, macrosegregation of alloying elements and the mechanical properties of DC cast AZ80 alloy were studied. The results show that both LFEC and US fields can refine the grains of the billets, which results in the increase in mechanical properties and uniformity of alloying element distribution. The effective refinement takes place on the edge of ingots when LFEC field is applied, while in the center of billets when field US is adopted. Combined the characteristics of LFEC and US fields, a new process for direct-chilling (DC) casting of Mg-electromagnetic-ultrasonic (ECUS) casting is developed, by which the grains are refined significantly and are more uniform in the whole ingots, and the mechanical properties of the ingots are improved.

Favourable and Unfavourable EMF Frequency Patterns in Cancer:Perspectives for Improved Therapy and Prevention

Carcinogenesis fits in a frequency pattern of electromagnetic field (EMF) waves, in which a gradual loss of cellular organization occurs. Such generation of cancer features can be inhibited by adequate exposure to coherent electromagnetic frequencies. However, cancer can also be initiated and promoted at other distinct frequencies of electromagnetic waves. Both observations were revealed by analyzing 100 different EMF frequency data reported in a meta-analyses of 123 different, earlier published, biomedical studies. The studied EM frequencies showed a fractal pattern of 12 beneficial (anti-cancer) frequencies, and 12 detrimental (cancer promoting) frequencies, that form the central pattern of a much wider self-similar EMF spectrum of cancer inhibiting or promoting activities. Inhibiting of the cancer process, and even curing of the disease, can thus be considered through exposure to the coherent type of EM fields. Stabilization of the disease can be understood by constructive resonance of macromolecules in the cancer cell with the externally appied coherent EMF field frequencies, called solitons/polarons. The latter, for instance, have been shown earlier to induce repair in DNA/RNA conformation and/or epigenetic changes. The field of EMF treatment of cancer disorders is rapidly expanding and our studies may invite further experimental and clinical studies in which systematically various potential EMF treatment protocols could be applied, with combined and modulated frequencies, to obtain even more efficient EMF anti-cancer therapies.

Coupled Modeling of Electromagnetic Fleld,Fluid Flow,Heat Transfer and Solidification During Conventional DC Casting and Low Ftequency Electrmagnetic Casting of 7xxx Aluminum Alloys

A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.

Effects of Different Electromagnetic Fields on Circadian Rhythms of Some Haematochemical Parameters in Rats

Objective To investigate the effects of different electromagnetic fields on some haematochemical parameters of circadian rhythms in Sprague-Dawley rats. Methods The study was carried out in 18 male and 18 female rats in good health conditions exposed to 50 Hz magnetic sinusoid fields at the intensity of 1000 μT, 100 μT, and 0 μT （control group） respectively, and in 18 male and 18 female rats in good health conditions exposed to 1.8 GHz electromagnetic fields at the intensity of 50 V/m, 25 V/m and 0 V/m （control group）, respectively. Following haematochemical parameters for glucose, triglycerides, and total cholesterol were measured. Results Different effects of electromagnetic fields on circadian rhythms of both male and female rats were observed. Different changes occurred in some haematochemical parameters for glucose, triglycerides, and total cholesterol （P〈0.05）. Conclusion Exposure to different electromagnetic fields is responsible for the variations of some haematochemical parameters in rats.

Effects of electromagnetic field intensity on as-cast microstructures and mechanical properties of Al-Zn-Mg-Cu-Zr alloy

Al-Zn-Mg-Cu-Zr ingots with diameter of 200 mm were made by low frequency electromagnetic casting (LFEC) and conventional direct chill (DC) casting process. The results show that under the low frequency electromagnetic field (25 Hz, 32 mT) the microstructures of LFEC ingot from the border to the center on the cross section are all equiaxed grains, and the grains are much finer and more uniform than that of DC ingot. The magnetic flux density plays an important role in the microstructure formation of LFEC ingots. With increasing the magnetic flux density from 0 mT to 32 mT, grains become finer (from about 120 urn to 30 urn) and more uniform. While, with increasing the magnetic flux density from 32 mT to 46 mT, the grains change much slowly. In the range of experimental parameters, the optimum magnetic flux density for LFEC process is found to be 32 mT.

地中电偶极源极低频电磁场的分布与传播特征

利用层状大地中偶极源响应的正演算法,计算地中电偶极源激发的极低频地震电磁场并分析其在地球环境下的传播特征.设计了多个水平层状地球模型,分别模拟和展示了深埋地中的电偶极源的响应和空间分布特征.重点分析了含地壳波导+LAI波导模型的高阻大地中,倾斜电偶极源激励响应随观测点的偏移距和垂直位置、激励源深度、地壳波导结构和参数变化时各场量响应的幅频特征.研究表明,用倾斜电偶极源模拟和分析高阻大地中孕震电磁辐射的响应及在大地电磁系统中的传播特性是可行的;模拟的高阻大地中的电磁辐射在地壳波导和LAI波导中均表现有慢衰减或幅值增强特性,但两个波导效应具有不同的频率选择性;高阻大地中的电磁辐射在波导的高阻介质中具有幅值强、衰减慢的特点.建议在高阻地层出露的地表、井中或海底的高阻岩层中以及大气层中布设测站.

基于里德伯原子天线的低频电场波形测量

里德伯原子的高极化率可以实现电磁场的多维度参数测量.本文利用室温里德伯原子构建原子天线,基于原子天线将低频电场幅度信息转化为强度信息,从而实现低频电场的参数测量.实验采用双光子激发制备铯原子里德伯态,通过阶梯型电磁感应透明(electromagnetically induced transparency,EIT)光谱实现里德伯原子量子态的检测,基于内置电极技术在室温原子气室导入k Hz频段低频电场.电场中里德伯原子的Stark频移会在EIT过程导致双光子失谐,从而引起EIT光谱频移和强度变化.在弱电场条件下,EIT光谱频移可以忽略,EIT透射强度与输入低频电场强度近似为线性关系,基于该效应可以实现低频电场的波形、幅度、频率等参数测量.

基于原子天线的低频电场量子精密测量和应用

基于原子系综的量子精密测量体系具有高准确和高稳定的特点,是未来先进测量体系的发展方向之一。其中,基于里德堡原子的电场测量具有高灵敏、超宽带以及优异的电气隔离等特性,近年来受到广泛关注。然而,当前基于里德堡原子的电场量子精密测量研究多集中于微波频段,GHz以下的低频电场测量研究较少。鉴于DC~MHz频段电场的高灵敏探测在地球物理、生物传感、国防通信、太空探索等方面具有重要的科学意义和应用价值,本文梳理了DC~MHz频段的新型天线研究进展,综述了近年来原子天线技术的发展趋势,概述了基于里德堡原子的低频电场测量原理,并分析讨论了原子天线在灵敏度、瞬时带宽等关键性能指标方面的提升方案及在未来低频探测领域的潜在应用。

基于层次分析模型的潜艇极低频电磁场贡献率评估方法研究

潜艇极低频电磁场作为目标探测的关键特征,其形成机制复杂多样,平台工况以及在水下所处位置都会对其产生很大影响。有效操控以降低潜艇的磁特征对于提升其磁隐身性能具有重要的意义。然而,当前各种因素对电磁场影响程度的研究尚不充分。为此该文提出一种基于层次分析模型的贡献率评估方法,旨在为有效操控提供理论依据。首先深入分析潜艇极低频电磁场的威胁成因,并建立相应的威胁层次结构模型。其次,通过仿真手段获取由不同成因产生的电磁场信号特征,并构建威胁矩阵和特征矩阵。最后,计算得到不同成因电磁场对总电磁场的贡献率,在尾部测线上,尾流磁场的贡献率占比最高,达到0.7649;径向测线上轴频磁场贡献率占比最高,并逐渐衰减,最终在150 m处低于尾流电磁场,并保持在占比0.5左右。仿真结果验证了该方法的有效性,可为潜艇极低频电磁场的综合主动控制策略研究奠定技术基础。