Screening of magnetic fields by superconducting and hybrid shields with a circular cross-section

Abstract

The use of superconducting (SC) materials is crucial for shielding quasi-static magnetic fields. However, the frequent requisite of space-saving solutions with high shielding performance requires the development of a 3D modelling procedure capable of predicting the screening properties for different orientations of the applied field. In this paper, we exploited a 3D numerical model based on a vector potential formulation to investigate the shielding ability of SC screens with cylindrical symmetry and a height/diameter aspect ratio close to unity, without and with the superimposition of a ferromagnetic (FM) circular shell. The chosen materials were MgB2 and soft iron. First, the calculation outcomes were compared with the experimental data obtained on different shielding arrangements, achieving a notable agreement in both axial-field (AF) and transverse-field (TF) orientations. Then, we used the thus validated modelling approach to investigate how the magnetic mitigation properties of a cup-shaped SC bulk can be improved by the superimposition of a coaxial FM cup. Calculations highlighted that the FM addition is very efficient in enhancing the shielding factors (SFs) in the TF orientation. Assuming a working temperature of 30 K and using a layout with the FM cup protruding over the SC one, shielding factors up to 8 times greater than those of the single SC cup were attained at low applied fields, reaching values equal or higher than 102 in the inner half of the shield. In the AF orientation, the same FM cup addition costs a modest worsening at low fields, but at the same time, it widens the applied field range, where SF ≥ 104 occurs near the close extremity of the shield, up over 1 T.

Cobalt‐Based Metallic Glass Microfibers for Flexible Electromagnetic Shielding and Soft Magnetic Properties

“…Considering that the microfibers are homogeneously distributed, and their amount is the same for both screens, the higher SF reached in transverse field orientation confirms the ability of high‐permeability material‐based shields' ability to mitigate transverse magnetic fields more effectively than axial ones. [ 40 ] In all the cases, above the applied field H appl = 60 Oe, the shielding factor curves can be considered flat and close to unity.…”

“…The probe was consistently aligned to measure the magnetic flux density component parallel to the field direction being applied, termed the z‐direction. [ 39,40 ]…”

“…The probe was consistently aligned to measure the magnetic flux density component parallel to the field direction being applied, termed the z-direction. [39,40] The high-frequency EMI shielding efficiency can be studied in terms of the attenuation constant of electromagnetic radiation [35] Springer Nature Limited).…”

Modelling and Performance Analysis of MgB2 and Hybrid Magnetic Shields

“…Therefore, we would like to note that the physical meaning of this parameter is not the same as the criterion conventionally assumed to identify the value of the critical current density from the I-V experimental curves [33]. The chosen value E 0 = 10 −4 Vm −1 gives a good compromise between the computation performance and the accuracy for the presented superconducting object, considering the chosen range of applied magnetic field and its growth rate [44]. However, in case of other configurations it may require additional verification and adjustment of E 0 value.…”

“…To this aim, this formulation, recently extended to solve 3D magnetic problems [41], was implemented in the commercial software COMSOL Multiphysics ® [42]. A preliminary validation of this modeling approach for shielding applications was already carried out via the comparison between experimental and computed data achieved on open and single-capped MgB 2 tubes in both Axial Field (AF) and Transverse Field (TF) orientations [43,44]. Here, the model viability of evaluating the magnetic flux density values inside an SC tubular shield independently from the applied field orientation is addressed by comparing the results obtained with the A-and H-formulations.…”