Optimization Design of Non­magnetic Shield for Electromagnetic Tomography

Zhang Junqing1, Wang Chao1, Xu Chuanjin1, Zhang Ming1, Yin Wuliang1

1 School of Electrical Engineering and Automation, Tianjin University, Tianjin, China, wangchao@tju.edu.cn

ABSTRACT

The measured signal of electromagnetic tomography (EMT) systems is the secondary signal produced by conductivity objects or permeability objects in the sensing field, which is much weaker than the original excitation signal and easier to be disturbed by capacitive couplings of the system itself and external magnetic fields. So an external shield is added to effectively reduce capacitive couplings of the system and avoid the influence of external fields. In this paper, the development of the non­magnetic shield for EMT systems is introduced. According to the skin depth of the shielding material, the thickness of the shield is designed. Based on the determination of simulation models and the optimization criterion, influences of the material, height and inner radius of the shield to the shielding effect are investigated. Using the criterion of uniformity of sensitivity maps, the orthogonal table with three factors is designed via orthogonal test which reduces the workload. The relatively optimal parameters of the shield which are used in practical systems are intuitionally analyzed and determined by results of the orthogonal test.

Keywords Electromagnetic tomography, non­magnetic shield, orthogonal test, optimal parameters