A Broadband, Nondestructive Microwave Sensor for Characterizing Magnetic Sheet Materials

Full-wave analysis of a two-port, broadband, nondestructive microwave sensor for characterizing magnetic sheet materials is presented. The sensor, called a clamped dual ridged waveguide (CDRWG) probe, consists of two DRWGs connected to metal flange plates, which sandwich the unknown magnetic material. Prior CDRWG probe work considered only the dominant DRWG mode. This paper significantly extends and effectively completes the prior work by considering all DRWG modes. The theoretical development of the CDRWG probe, including all higher-order DRWG modes, is presented and discussed. A physical discussion of the higher-order modes, in particular, why they are or are not excited, is included. Finally, experimental results of a lossy magnetic material are presented and analyzed to determine what impact higher-order modes have on CDRWG probe accuracy. The probe's errors in determining the permittivity and permeability of the material are estimated, considering uncertainties in measured scattering parameters and specimen thickness.