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This study aims to assess the levels of extremely low frequency magnetic fields (ELF-MF) emitted from portable hand-held fans (HHFs) and their principal frequency and to identify factors influencing these levels. We collected a total of eleven models of HHF and monitored the ELF-MF as a function of fan speed and distance from the fan. EMDEX II was used to monitor the ELF-MF. An SMP2 EMF-meter equipped with a P400 field probe was used to determine the levels of ELF-MF and the frequency spectrum. Ten of the fans, excluding only one bladeless-fan model, emitted a high level of ELF-MF near the source of the HHF direct-current motor. The maximum measured level of ELF-MF ranged from 14.07 to 218.7 µT. All measurements of the ELF-MF taken within 10 cm from the HHFs showed values higher than 1.0 µT. ELF-MF levels were found to decrease markedly with distance, regardless of the HHF product. The level of ELF-MF rose noticeably with increased fan speed. The speed of and distance from the HHF significantly influenced the level of ELF-MF. All principal frequencies ranged from 1 to 300 Hz, which falls in the typical range of ELF. Bioelectromagnetics. 2019;40:569-577. © 2019 Bioelectromagnetics Society., (© 2019 Bioelectromagnetics Society.)

We assessed the exposure of semiconductor workers to extremely low frequency-magnetic fields (ELF-MF) and identified job characteristics affecting ELF-MF exposure. These were demonstrated by assessing the exposure of 117 workers involved in wafer fabrication (fab) and chip packaging wearing personal dosimeters for a full shift. A portable device was used to monitor ELF-MF in high temporal resolution. All measurements were categorized by operation, job and working activity during working time. ELF-MF exposure of workers were classified based on the quartiles of ELF-MF distribution. The average levels of ELF-MF exposure were 0.56 µT for fab workers, 0.59 µT for chip packaging workers and 0.89 µT for electrical engineers, respectively. Exposure to ELF-MF differed among types of factory, operation, job and activity. Workers engaged in the diffusion and chip testing activities showed the highest ELF-MF exposure. The ELF-MF exposures of process operators were found to be higher than those of maintenance engineers, although peak exposure and/or patterns varied. The groups with the highest quartile ELF-MF exposure level are operators in diffusion, ion implantation, module and testing operations, and maintenance engineers in diffusion, module and testing operations. In conclusion, ELF-MF exposure among workers can be substantially affected by the type of operation and job, and the activity or location., Competing Interests: The authors declare no conflict of interest.

Objectives Peak exposure to extremely low-frequency magnetic fields (ELF-MF) among semiconductor workers was characterized by type of factory, operation, and job. Methods A portable EMDEX meter was used to monitor the ELF-MF exposure of 117 semiconductor workers who are involved in wafer fabrication (fab) and assembly operations. ELF-MF measurements were logged every 3 s and categorized by process and job or activity during working hours. Two values of 0.5 and 1 μT were adopted subjectively as cutoff values of peak exposure levels based on a literature review. Results All semiconductor workers who were involved in diffusion, ion implanter operation, module, and chip test were exposed to ELF-MF higher than 0.5 μT during their entire working time. Engineers who maintained electric facilities in the semiconductor operations were exposed to the highest ELF-MF peak levels (2.5 μT on average above 0.5 μT and 3.6 μT on average above 1 μT). Operators working in chip testing showed the highest daily contribution of their peak levels to their daily average ELF-MF exposure levels (98.1% and 83.9%). In contrast, chemical mechanical planarization engineers, wafer test operators, and administrative workers outside clean rooms showed average exposure to less than 0.5 μT and a low proportion of duration of time exposed above either the 0.5 μT or 1 μT peak level points, along with a low daily contribution of peak exposure levels (16.0, 11.9, and 18.7%). Conclusions Most of the activities and working locations next to machines generating ELF-MF in semiconductor operations showed high contributions of ELF-MF peak exposure to daily exposure dose despite their relative minor fraction of workers' daily time. [ABSTRACT FROM AUTHOR]

ABSTRACT We demonstrate that electrically small ferrite antenna gain is significantly increased with a small dc magnetic field of compact Nd-Fe-B permanent magnet (9.5 × 4.6 × 1.5 mm3). The experimental magnetic tangent loss of the Ni-Mn-Co ferrite decreased by about 62%, which was from 0.509 with 0 Gauss to 0.192 with 750 Gauss. The antenna gain increased by 54% (from −10.58 to −4.81 dBi) when the magnetic field of 1600 Gauss was applied to the antenna. The ferrite antenna has the volume of 0.346 cm3 and shows omnidirectional patterns, which are suitable for hand-held mobile device applications. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1531-1534, 2014 [ABSTRACT FROM AUTHOR]

The scaling effect of permalloy s-shaped element, a rectangular element with appendages, on operating fields, Hx and Hy, was investigated by micromagnetic computer simulations for and or or logic. The optimized combination of operating fields (Hx, Hy) was found to be (27.7 \pm 9.9, -16.7 \pm 8.8), (37.9 \pm 12.4, -25.9 \pm 6.0), and (42.2 \pm 8.8, -23.9 \pm 4.0) in kA/m for the 100, 50, and 30 nm long s-shaped elements, respectively. As the s-shaped element is scaled down, the allowable deviation from the optimized operating fields becomes smaller and optimized operating fields shift to higher field. [ABSTRACT FROM AUTHOR]

• High quality LTP MnBi powders with enhanced magnetic properties were successfully synthesized by "induction melting" process. • The effects of heat treatments, ball milling and chemical compositions were finely optimized to enhance magnetic properties. • The high purity MnBi powders in this work show remarkably high saturation magnetization (M s) of up to 74.8 Am2/kg. • After ball milling, Mn 56 Bi 44 powders showed (BH) max of 11.7 MGOe at room temperature, close to 70% of the theoretical value, making rare-earth free MnBi promising candidate for applications. High purity MnBi magnetic low temperature phase (LTP) were prepared via induction melting, annealing and low energy ball milling. The effects of synthetic parameters and chemical compositions on phase purity and magnetic properties were systematically investigated. A homogenization heat treatment process was employed to increase the fraction of LTP MnBi, which showed notably high saturation magnetization (M s) of up to 74.8 Am2/kg with the purity of 97 wt% LTP MnBi. The purity of MnBi is strongly related to the amount of Mn and residual Bi in the annealed ingot. By controlling the residue, the highest phase fraction was obtained with the atomic ratio of Mn 56 Bi 44. The maximum energy product (BH) max was recorded 11.7 MGOe under an applied magnetic field of 1.5 T at room temperature, making MnBi a promising rare-earth-free permanent magnet. [ABSTRACT FROM AUTHOR]

Rare-earth-free permanent magnets have attracted considerable attention due to their favorable properties and applicability for cost-effective, high-efficiency, and sustainable energy devices. However, the magnetic field annealing process, which enhances the performance of permanent magnets, needs to be optimized for different magnetic fields and phases. Therefore, we investigated the effect of composition on the crystallization of amorphous MnBi to the ferromagnetic low-temperature phase (LTP). The optimal compositions and conditions were applied to magnetic field annealing under 2.5 T for elemental Mg- and Sb/Mg pair-substituted MnBi. The optimum MnBi composition for the highest purity LTP was determined to be Mn56Bi44, and its maximum energy product, (BH)max, was 5.62 MGOe. The Mg-substituted MnBi exhibited enhanced squareness (Mr/Ms), coercivity (Hc), and (BH)max values up to 0.8, 9659 Oe, and 5.64 MGOe, respectively, whereas the same values for the Sb/Mg pair-substituted MnBi were 0.76, 7038 Oe, and 5.60 MGOe, respectively. The substitution effects were also investigated using first-principles calculations. The density of states and total magnetic moments of Mn16Bi15Mg and Mn16Bi15Sb were similar to those of pure Mn16Bi16. Conversely, the Sb-substituted MnBi resulted in a dramatic enhancement in the anisotropy constant (K) from a small negative value (−0.85 MJ/m3) to a large positive value (6.042 MJ/m3). [ABSTRACT FROM AUTHOR]

The magnetostatic exchange length is an important parameter in magnetics as it measures the relative strength of exchange and self-magnetostatic energies. Its use can be found in areas of magnetics including micromagnetics, soft and hard magnetic materials, and information storage. The exchange length is of primary importance because it governs the width of the transition between magnetic domains. Unfortunately, there is some confusion in the literature between the magnetostatic exchange length and a similar distance concerning magnetization reversal mechanisms in particles known as the characteristic length. This confusion is aggravated by the common usage of two different systems of units, SI and cgs. This paper attempts to clarify the situation and recommends equations in both systems of units. [ABSTRACT FROM PUBLISHER]

We demonstrate that magnetic loss tangent of M-type hexaferrite can be controlled by a small dc magnetic field, thereby improving radio frequency (RF) antenna radiation efficiency and realizing antenna miniaturization. Magnetic loss tangent (tan δμ) of the M-type BaFe9.6Co1.2Ti1.2O19 hexaferrite at 200 MHz decreased significantly from 11.8% to less than 1% as the applied dc magnetic field increased from 0 to 400 Oe. This is because the contribution of domain wall motion to permeability dispersion is decreased, and the ferromagnetic resonance frequency increases with the magnetic field. Antenna simulation results showed that radiation efficiency of the designed ferrite helical antenna increased from -22.9 to -9.2 dB with dc magnetic field of 400 Oe. Therefore, the small dc magnetic field played a key role in reduction of tan δμ of hexaferrite and improvement of antenna performance in the RF range. [ABSTRACT FROM AUTHOR]