An Improved Two-Coil Configuration for Low-Frequency Magnetic Field Immunity Tests and Its Field Inhomogeneity Analysis

The low-frequency magnetic field immunity test usually requires a homogenous magnetic field inside a cubic space to demonstrate the interference field. However, the 3-dB homogenous magnetic field region generated by the commonly used the Helmholtz coil is not a cubic space, which indicates a suboptimal design. This paper proposes an improved two-coil configuration for low-frequency magnetic field immunity tests and other similar applications, and discusses two key issues related to its field inhomogeneity, namely winding cross section and installation misalignment. Three simple formulas are concluded to establish a relationship between the parameters of the improved coil and the required homogenous magnetic field. These formulas enable the parametric and fast design of the improved coil. A comparison with the Helmholtz coil shows that the improved coil can reduce over 10% conductor mass cost when the same homogenous magnetic field is required. In addition, the effects of winding cross section and installation misalignments on the field homogeneity are analyzed, and valuable suggestions are provided for the design of a practical coil system. At last, an experimental test and a finite-element analysis are performed. The results are compared with the theoretical analysis, and the validity of the main conclusions in this paper is proved.