Fuzzy logic based ELF magnetic field estimation in substations

This paper examines estimation of the extremely low frequency magnetic fields (MF) in the power substation. First, the results of the previous relevant research studies and the MF measurements in a sample power substation are presented. Then, a fuzzy logic model based on the geometric definitions in order to estimate the MF distribution is explained. Visual software, which has a three-dimensional screening unit, based on the fuzzy logic technique, has been developed.     

Assessment of ELF magnetic fields produced by independent power lines

In this paper, the problem of assessing the ELF (extremely low-frequency) magnetic fields produced, in a certain area characterised by the presence of more than one independent power line, is faced. The use of the incoherent summation of the single contributions, as an advantageous estimator of the total magnetic field, is proposed and justified by means of a heuristic procedure. This kind of approach can be seen as a useful and practical tool to be employed in environmental impact analysis and in assessing long-term human exposure to ELF magnetic fields.     

基于主磁场不均匀的分数域磁共振成像方法

现有核磁共振设备面对主磁场不均匀多是采取贴磁片等补偿磁场不均匀等硬件方法,但这给成像带来图像伪影,图像模糊等不良影响。针对磁共振成像中磁场不均匀的问题,提出了一种主磁场不均匀下的分数域磁共振成像方法。首先选择待成像活体组织的某一层,在该层上选择若干个点,测量该层面上的磁场强度大小,在磁共振成像原理的基础上,建立成像区域磁场强度分布模型,然后建立磁场的多项式模型,按照测量的磁场中是否存在明显的二阶分量可以将该多项式模型分为二阶多项式模型和高阶多项式模型;之后,将这两个模型分别代入磁共振的自由感应衰减(FID)信号中,对于二阶模型可以用分数阶傅里叶变换工具进行求解成像物体某一层上的自旋密度函数,对于高阶模型需要通过求解代数方程的方法得到成像物体某一层面上的自旋密度函数,这样便建立了主磁场任意不均匀下的磁共振信号模型。实验结果表明,该方法达到与均匀主磁场下近似同样的效果。     

Hall sensor response to an inhomogeneous magnetic field

The response of a Hall-effect sensor to a spatially dependent magnetic field is of importance for many applications such as magnetic microscopy and nondestructive testing. Using the analytical expression of the response of a Greek cross Hall sensor response to an ideal field dot published a few years ago, we have calculated its sensitivity and its full width at half maximum for the field produced by a magnetic dipole and by two coplanar lines. The experimental results are in good agreement with theory. They show that the spatial resolution is roughly equal to the dimension of the central part of the Greek cross and that a flux-meter approximation is not appropriate for modeling such Hall-effect sensors for very close field sources.     

On the motion of macroparticles in inhomogeneous magnetic field

The behavior of macroparticles that form a near-wall dust in tokamaks is described with allowance for the force of gravity, force of entrainment by plasma ion flux, and Lorentz force acting on the motion of charged macroparticles in an inhomogeneous magnetic field. It is shown that, in some cases, the effect of induced currents that arise in the particles during this motion must in some cases be taken into account.     

The hall cross in a perpendicular inhomogeneous magnetic field

Equations are derived which give the voltage that is generated in a Hall conductor when an inhomogeneous magnetic field is applied normal to the plane of the Hall conductor. These equations are used to solve a specific example of a Hall cross in such a field, using finite difference techniques. The results are shown to be in excellent agreement with measured data.     

The gain in the plane wiggler with inhomogeneous magnetic field

We calculate the gain in a plane wiggler (undulator) with inhomogeneous magnetic field and in the external electromagnetic wave. The electromagnetic field-induced corrections to electron trajectories are found. The linear (field-independent) gain is calculated using these corrections to complex motion of electrons, which was described in previous paper, without electromagnetic field. This complex motion arises because of magnetic field inhomogeneity. It is shown that the account of inhomogeneity of the magnetic field leads to appearance of additional peaks in the gain of usual wiggler with uniform magnetic field.     

Survey of ELF magnetic field levels in households near overhead power lines in Serbia

During the last eight years, 'VIN?A' Institute--Radiation and Environmental Protection Laboratory has performed environmental 'spot' broadband measurements of extremely low frequency (ELF-50 Hz) electric and magnetic fields and RF (100 kHz-3 GHz) electromagnetic fields in over 35 municipalities in Serbia. These investigations were motivated by the local population requesting information about levels of general public exposure to time-varying electric and magnetic fields in living spaces. This paper presents a summary of values measured in households under overhead power lines. These measurements will be useful in determining the exposure levels of the general public, which in turn determines whether the exposure levels are within reference levels recommended by International Commission on Non-Ionizing Radiation Protection (ICNIRP) Guidelines. It has turned out that measured values are far below the recommended safe levels.     

Output microwave radiation power of low-voltage vircator with external inhomogeneous magnetic field

Dependence of the power of a broadband microwave radiation generated by a low-voltage oscillator with virtual cathode (vircator) on the parameters of an external inhomogeneous magnetic field has been studied by numerical simulations using a two-dimensional model. It is established that there are optimum parameters of the generator (configuration of the external magnetic field, electron beam current) for which the output radiation power is maximum. A relationship between the optimum conditions of virtual cathode formation in the electron beam and the microwave generation regime is established.     

Formation of coulomb clusters from charged diamagnetic microparticles in inhomogeneous magnetic field

The possibility of levitating Coulomb clusters formed by charged diamagnetic microparticles in an inhomogeneous magnetic field has been theoretically substantiated and experimentally confirmed. An experimental setup is described, in which the Coulomb clusters can be formed from charged graphite particles 100–300 μm in size and maintained stable between the poles of an electromagnet generating a magnetic field with induction B ∼ 10⁴ G and gradient |∂B| ∼ 10⁵ G/cm.     

Nonlinear dynamics of electron beam with virtual cathode in external inhomogeneous magnetic field

Nonlinear dynamics of virtual cathode (VC) formed in electron beam in a strongly inhomogeneous external magnetic field generated by a ring magnet has been numerically simulated using a two-dimensional model. It is established that the field characteristics strongly influence the VC dynamics. Physical processes responsible for this strong dependence are considered. The output power of generation in a model system with VC is determined as a function of the field parameters.     

The harmonic oscillator equation for ultracold neutrons moving in an inhomogeneous magnetic field

The motion of ultracold neutrons in a magnetic field featuring a quadratic inhomogeneity is considered. A partial solution to the stationary Schrödinger equation is found, which leads to a harmonic oscillator equation for the X coordinate. It is demonstrated that, under certain conditions, it is basically possible to provide for a spatial focusing of neutrons with the formation of either a single point focus or two side foci. Dependence of the focusing on the degree of monochromaticity of the neutron beam is considered.     

Superconducting gap function and upper critical field in the presence of inhomogeneous magnetic order

Rare earth ternary superconductors are known to exhibit oscillatory magnetic orders below their superconducting transition temperatures. The study of behaviour of superconducting electrons in an inhomogeneous magnetic field is therefore important for such systems. We report here the results of our theoretical study of superconducting gap function Δ(T) and upper critical fieldH _c2 (T). The results are applied to analyse and explain the variation of Δ(T) andH _c2 (T) in case of NdRh₄B₄.     

Investigation of the propagation of microwave beams in an inhomogeneous plasma in a magnetic field

An analysis is made of the propagation of microwave beams in an inhomogeneous magnetized plasma. It is shown that the presence of a plasma increases the astigmatism of the beams, increases the amplitude of the beam compared with vacuum conditions, and reduces the curvature of their phase fronts compared with vacuum. Pis’ma Zh. Tekh. Fiz. 25, 67–71 (December 12, 1999)     

Exposure to inhomogeneous static magnetic field beneficially affects allergic inflammation in a murine model

Previous observations suggest that static magnetic field (SMF)-exposure acts on living organisms partly through reactive oxygen species (ROS) reactions. In this study, we aimed to define the impact of SMF-exposure on ragweed pollen extract (RWPE)-induced allergic inflammation closely associated with oxidative stress. Inhomogeneous SMF was generated with an apparatus validated previously providing a peak-to-peak magnetic induction of the dominant SMF component 389 mT by 39 T m⁻¹ lateral gradient in the in vivo and in vitro experiments, and 192 mT by 19 T m⁻¹ in the human study at the 3 mm target distance. Effects of SMF-exposure were studied in a murine model of allergic inflammation and also in human provoked skin allergy. We found that even a single 30-min exposure of mice to SMF immediately following intranasal RWPE challenge significantly lowered the increase in the total antioxidant capacity of the airways and decreased allergic inflammation. Repeated (on 3 consecutive days) or prolonged (60 min) exposure to SMF after RWPE challenge decreased the severity of allergic responses more efficiently than a single 30-min treatment. SMF-exposure did not alter ROS production by RWPE under cell-free conditions, while diminished RWPE-induced increase in the ROS levels in A549 epithelial cells. Results of the human skin prick tests indicated that SMF-exposure had no significant direct effect on provoked mast cell degranulation. The observed beneficial effects of SMF are likely owing to the mobilization of cellular ROS-eliminating mechanisms rather than direct modulation of ROS production by pollen NAD(P)H oxidases.     

Mixed magnetooptical contrast induced by an inhomogeneous magnetic field in metal films with planar anisotropy

Magnetooptical (MO) images induced by a strongly inhomogeneous external magnetic field in magnetic metal films with planar anisotropy have been studied. In the polar Kerr effect geometry, MO images created by the normal magnetization component is observed. In the meridional Kerr effect geometry, a superposition of the MO images (mixed MO contrast) is observed, which is determined by the distribution of the normal and horizontal magnetization components. Calculation of distribution of magnetization in a film is carried out, a field of magnetic system corresponding to coordinate dependence and are simulated corresponding MO images and the corresponding MO images have been simulated, which demonstrate satisfactory agreement between the theory and experiment.     

Microwave generation features in a vircator with an inhomogeneous magnetic field in the interaction region

A vircator with an inhomogeneous external magnetic field superimposed onto the cathode-anode-virtual cathode potential well was studied by methods of computer modeling. It is shown that the application of such additional field allows a significant (almost fivefold) increase in the microwave generation efficiency, which is explained by the gyrotron effect development.     

Magnetic field analysis by edge elements of magnetic components considering inhomogeneous current distribution within conductor windings

For magnetic field analysis by edge elements of the magnetic components, the method considering inhomogeneous current distribution within the conductor windings is investigated. To consider the inhomogeneous current distribution within the windings, we utilized the magnetic vector potential represented by edge elements and the current conservation equation represented by nodal elements in the region of the windings. In the first application, the eddy-current model, which has the conventional wire winding, was analyzed. For correct analysis using our method, it is required that all turns of the wire winding be divided into meshes. However, if the region of the wire winding does not exceed the winding window of the magnetic core, even the combination of our method and the solidly modeled wire winding enables us to correctly analyze the transformer and the inductor with conventional wire winding. In the second application, a flat transformer with conductor winding, such as a copper foil or sheet, was analyzed. The magnetic flux densities within the flat core and the inductance calculated by our method were in good agreement with the experiments. Thus, we confirmed the effectiveness of our method considering inhomogeneous current distribution within the conductor windings.     

Outdoor background ELF magnetic fields in an urban environment

Classification of 'exposed/non-exposed' subjects in epidemiological studies concerning the possible cancer risk associated with ELF magnetic field exposure is based on the a priori assumption of magnetic field value cut-off points that, often, are defined equal to minimum exposure levels typical of a population residing near high voltage facilities (0.1-4.2 microT), but in some cases an environmental magnetic field level not associated with transmission lines can exist. The results of an ELF magnetic field survey in an Italian urban area (about 1 million inhabitants) are presented: average field levels are correlated with population density of different districts. Exposure indexes are obtained, which are compared with those evaluated in studies regarding domestic exposure: background average levels result in comparable to cut-off points in epidemiological studies, but in some districts with high population density, they are much higher. This shows that knowledge of background magnetic field level in urban areas can assume a significant role in exposure assessment.