A method of measuring complex ermittivity of nonmagnetic materials and selecting its initial value based on iterative inversion

Abstract

Complex permittivity is an important parameter to reflect the macroscopic electromagnetic properties of materials. The selection, design, and application of related materials and devices in the electromagnetic field must be based on the electromagnetic parameters of materials in the working frequency band. The numerical iterative method is an important method to inverse and calculate the complex permittivity of materials. But there has always existed a difficult problem that the initial values of iterations are difficult to be given accurately. Based on the relationship between the complex permittivity and the reflectivity of absorbing materials, an initial value selecting method for iteration to invert permittivity of absorbing material is proposed. For absorbing materials with arbitrary thickness at a certain frequency, the complex permittivity must be near the complex permittivity of perfect matching layer. Therefore, the permittivity of perfect matching layer can be used as the initial value of the iterative algorithm. On this basis, a method for calculating the complex permittivity of monolayer absorbing materials by reflection parameter is constructed. The experimental results show that the complex permittivity of lossy materials can be calculated more accurately in the frequency with absorbing performance. It will cause great error in the frequency where the reflectivity is close to zero. Based on the iterative solution of the complex permittivity of single-layer absorbing materials, a new method for measuring the complex permittivity of materials is constructed by combining multi-layer absorbing materials to enhance full-band reflectivity. When the electromagnetic parameters of other layer materials are clear, the permittivity of absorbing materials and low-loss materials can be obtained accurately.