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Evanescent microwave principles of operation are based on the papers described by Kumar and Smith  and Kumar . They described that when a dielectric/semiconductor/biological material is placed in the vicinity of the evanescent waveguide (which is connected to a cavity resonator), the reflection coefficient of the resonator changes. Both the resonance frequency and the quality factor of the cavity resonator are affected by the presence of the material. The amount of change in the resonance depends primarily on the microwave properties of the sample as well as on the distance between the wall (resonator iris to the evanescent waveguide) and the sample, and the effective area of sample in the waveguide. It was also shown that microwave properties of a material are a function of permittivity and permeability. The authors of the above paper have used the same principle, where a microstrip type resonator and an evanescent probe have been used instead of a waveguide resonator and an evanescent waveguide. Therefore, they should have referenced the original papers in their article.