Lift-Off and Tilt Effect in Microwave Surface Resistance Measurement Using TE011 Mode Cylindrical Cavity

Measurement of surface resistance at microwave or higher frequency bands is needed for applications, such as accelerators, microwave systems, and integrated circuits. Cylindrical cavity resonators operating at TE
₀₁₁
mode have been applied in surface resistance measurement for decades. It is common that samples under test are usually used as one of the cavity’s endplates and contact the cylinder side wall directly, which cannot be regarded as noncontact measurement. In this article, through quantitative research on lift-off effect of samples under test, we explore the possibility of realizing noncontact surface resistance measurement by intentionally introducing an air gap (ranging from ~0 to 10 mm) between the samples and the cavity side wall. From the results of both electromagnetic simulations and experiments, it can be concluded that by taking care of the sample’s tilt effect, surface resistance can be measured in a noncontact manner. Measurement results of polished metal plates with electrical conductivity ranging from ~2 to 58 MS/m (measured with standard eddy current method) show that the relative measurement error is expected to be less than 10%. Compared with related publications, the focus of this work is put on the lift-off effect and a larger range of air gap is introduced. The obtained results indicate that the air-gap size may be an additional consideration in the design of surface resistance measurement system for special applications, such as temperature-dependent measurements in vacuum chamber,
in situ
diagnosis tools.