Identification of Material Properties and Optimal Design of Magnetically Shielded Rooms

Abstract

In this paper, we propose an optimal design procedure for magnetically shielded rooms. Focusing on multi-layer ferromagnetic structures, where inner layers operate at very low magnetic field, we propose an identification method of the magnetic material characteristic in the Rayleigh region. A numerical model to simulate the shielding efficiency of a multi-layer ferromagnetic structure is presented and experimentally tested on different geometries and layer configurations. The fixed point iterative method is adopted to handle the nonlinearity of the magnetic material. In conclusion, the optimization of the design parameters of a MSR is discussed, using the Vector Immune System algorithm to minimize the magnetic field inside the room and the cost of the structure. The results highlight that a linear magnetic characteristic for the material is sufficient to identify the suitable geometry of the shield, but the nonlinear model in the Rayleigh region is of fundamental importance to determine a realistic shielding factor.

Analytical model and precise evaluation of multi-layer magnetic shielding performances considering ultra-weak magnetic properties

“…Li et al [20] measured an initial permeability (15 000) at the applied magnetic field as low as 4 × 10 −5 A m −1 , which is much lower than the initial permeability of 36 000 corresponding to 0.08 A m −1 , based on the principle of the soft magnetometer test by changing the turns of a large-size permalloy sample ring. Canova et al [21] proposed a method for identifying magnetic material properties in the Rayleigh region for the phenomenon of multi-layer structures in which the inner layer operates in the ultra-weak magnetic field and solved the nonlinear problem of permeability with the fixed-point iteration method. Researchers have obtained the permeability of materials in the ultra-weak magnetic field through various methods but have not applied it to evaluate the shielding performance of multi-layer structures.…”

A Method to Measure Permeability of Permalloy in Extremely Weak Magnetic Field Based on Rayleigh Model

“…British physicist Lord John Rayleigh [ 24 ] proposed that the parabolic dependence between the magnetic flux density of ferromagnetic materials and the magnetization field can be used to describe the hysteresis phenomenon of iron and steel under the low magnetizing fields (called the Rayleigh model). Since then, some scholars used the Rayleigh model to obtain the initial permeability of magnetic materials [ 25 , 26 ]. They established a shielding factor test system with Helmholtz coils applied for generating a 5 Hz and low-amplitude homogeneous magnetic field and finite element analysis applied for identifying the two important parameters in the Rayleigh model.…”

Special Issue: Advances in Computational Electromagnetics

“…Recent advances in computational electromagnetics (CEMs) have made the full characterization of complex magnetic materials possible, such as superconducting materials, composite or nanomaterials, rare-earth free permanent magnets, etc. Such advances are found in the collection of papers from this Special Issue, where vector properties and the non-linearity of ferromagnetic materials are investigated in [1][2][3][4], while new composite materials for automotive and aircraft are envisaged in [5,6], respectively. Finally, novel deposition techniques for nanomaterials using nonuniform magnetic fields are addressed in [7].…”

“…The comparison between calculated and measured loops evidenced the capability of the model in both the reconstruction of the magnetic field trajectory and the prediction of the power loss under various excitation waveforms. To finish the characterization of ferromagnetic materials, Aldo Canova and co-workers [4] proposed an optimal design procedure for magnetically shielded rooms (MSRs) made of grain-oriented (GO) electrical steel. A numerical model based on fixed point iterative method to simulate the shielding efficiency of a MSR was presented and experimentally tested.…”