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Barriers against radiated disturbances
Published in Mark van Helvoort, Mathieu Melenhorst, EMC for Installers, 2018
Mark van Helvoort, Mathieu Melenhorst
A steel box with dimensions 11.5 × 9.2 × 5.1 cm and a wall thickness of 2 mm has a shielding effectiveness of 12.5 dB, which means that 50 Hz fields are reduced with a factor of 4. If a larger reduction factor is needed we can increase the wall thickness, or use mu-metal. Mu-metal is nickel-iron alloy with a very high relative permeability up to 50,000. In contrast to steel, the permeability rapidly drops with increasing field strength and, at increasing frequency, even at 50/60 Hz (Luker 1998).
7 Electromagnetic Interference
Published in C. Sankaran, Power Quality, 2017
One problem due to low-frequency electromagnetic fields and observed often in commercial buildings and healthcare facilities is the interaction between the fields and computer video monitors. Such buildings contain electrical vaults, which in some cases are close to areas or rooms containing computer video monitors. The net electromagnetic fields due to the high current bus or cable contained in the vault can interact with computer video monitors and produce severe distortions. The distortions might include ghosting, skewed lines, or images that are unsteady. For personnel that use computers for a large part of the workday, these distortions can be disconcerting. In the high-current electrical vault, it is almost impossible to balance the wiring or bus so that the residual magnetic field is very low. A practical solution is to provide a shielding between the electrical vault and the affected workspaces. The shielding may be in the form of sheets of high conductivity metal such as aluminum. When a low-frequency magnetic field penetrates a high-conductivity material, eddy currents are induced in the material. The eddy currents, which set up magnetic fields that oppose the impinging magnetic field, create a phenomenon called reflection. When a material such as low carbon steel is used for shielding low-frequency magnetic fields, the magnetic fields are absorbed as losses in the ferrous metal. High-permeability material such as Mu-metal is highly effective in shielding low-frequency magnetic fields; however, such metals are very expensive and not very economical for covering large surfaces.
Soft Magnetic Materials
Published in David Jiles, Introduction to Magnetism and Magnetic Materials, 2015
The nickel-iron alloys in general have very high permeabilities, as shown in Tables 12.4 and 12.5. The maximum permeability of the polycrystalline alloys occurs in those alloys for which the anisotropy and magnetostriction are small. The value of the anisotropy constant K1 is zero at a nickel content of 78%. The addition of 5% copper to permalloy produces the alloy known as mu-metal, although commercial mu-metal also contains 2% Cr. Its magnetic properties are no better than permalloy but mu-metal is rather more ductile than permalloy and is therefore used in the form of thin sheets in magnetic shielding in order to prevent stray magnetic fields from affecting sensitive components.
Optimization of magnetic field assisted finishing process during nanofinishing of titanium alloy (grade-5) implant using soft computing approaches
Published in International Journal of Modelling and Simulation, 2022
Anwesa Barman, Manas Das, Vimal Kumar Pathak
The MFAF in comparison to other finishing processes provides better finishing, facilitates enhanced geometry consistent capability for external as well as internal part features and for freeform surface [6,7]. Kim et al. mixed abrasives with magnetorheological (MR) fluid to be effectively utilized as a polishing tool for improving finishing performance during polishing 3-dimensional silicon microchannel [8]. Recently, Guo et al. applied MFAF process for polishing of injection molded insert of microfluidic chips having curved surfaces [9]. Kum et al. in their study investigated the effect of MFAF polishing media properties and developed a material removal rate model based on contact mechanics [10]. Yamaguchi et al. in their work achieved finishing of cobalt-chromium alloy knee implant magnetic abrasive finishing with control over the surface lay [11]. Fan et al. performed surface finishing of titanium alloy using MFAF process with shear thickening media combining carbonyl iron particle (CIP) and SiC particles with shear thickening fluids combining as MR fluid [12]. Guo et al. realized surface integrity and material removal rate in microfinishing of aluminium alloy RSA 905 in relation to MFAF process parameters [13]. Wang et al. also performed polishing of various freeform surfaces and used finite element analysis for determining the material removal rate in case of magnetic field assisted mass polishing (MAMP) [14]. Barman and Das developed a new MFAF tool made of mu-metal and abrasives mixed with MR fluid for creating different finishing media in FE simulation run showing nanofinishing of bio-titanium alloy [15]. In a similar study, Singh et al. utilized magnetic abrasive finishing for producing précised surface finish and improved hardness of Aluminium 6060 workpiece. The results provide an improvement in surface finish and hardness of material by 6.67 and 5.37%, respectively [16]. Sidpara and Jain applied magnetorheological fluid-based finishing (MRFF) process for showing the influence of two different forces under magnetic field resulting in abrasive particle indentation on workpiece surface [17].