The Development of a Shield of Amorphous Soft Magnetic Alloy to Reduce the Effect of the Earth’s Magnetic Field on the Sensitive Element of a Photoelectronic Spectrometer

Abstract

The results of calculations of the effi ciency of the shielding of a photoelectronic spectrometer by amorphous alloys, designed to protect the instrument from the Earth's magnetic fi eld, are presented. The distribution of the magnetic induction inside the shield for different positions of the instrument is measured. The anisotropy of the shielding properties of a magnetopolymer shield is investigated. An analysis of modern trends in investigating the effect of physical fi elds, in particular, the Earth's magnetic fi eld, on technical devices shows that most attention is being devoted to fi nding optimal methods of shielding (1-4). There are a number of instruments available at present, the readings of which are sensitive to the Earth's magnetic fi eld. These include instruments which use the physical laws of motion of charged particles in magnetic and electric fi elds: mass spectrometers, scanning electron microscopes, x-ray fl uorescent spectrometers, etc. Both static and variable magnetic fi elds of different fre- quency can defl ect particles from their normal trajectories of motion and thereby distort the readings of such instruments. Another form of magnetically sensitive devices is systems by means of which one can measure extremely small magnetic fi elds. For example, the magnetocardiograph, designed to carry out medical diagnostics, detects magnetic fi elds, the source of which is the heart. These fi elds are very weak, and hence it is important to eliminate the effect of induced external magnetic fi elds on the results of the measurements. An electromagnetic shield is a necessary part of the cabinet containing the magnetic tomography apparatus. If its integrity is disturbed or there is no shielding, extensive techniques cannot be correctly used, in view of the magnetic interference produced by surrounding electronic equipment and the geomagnetic fi eld. Standards in the area of the electromagnetic compatibility of technical instruments lay down the requirements for stability to electromagnetic interference, the quality of the electric power in the networks, and new methods of testing (5, 6). In practice, one cannot always transport the technical equipment a distance at which the fi eld is reduced to the thresh- old limit value. In this case, it is necessary to use shielding materials. The shielding of constant and low-frequency magnetic fi elds is the most complicated operation. For such purposes, one requires materials possessing high magnetic permeability and saturation induction, and low coercive force. They should remain capable of operating in diffi cult working conditions: they must be insensitive to mechanical and dynamic disturbances (deformations and vibrations), they must operate over a wide temperature range, and must have highly reproducible properties. To protect measuring instruments from the effect of extraneous physical fi elds, they are often placed in massive closed casings made of ferromagnetic material - usually permalloy. However, these shields have considerable drawbacks: the high shielding factor is not retained under mechanical actions, which inevitably arise during the manufacture and assembling the