Sheet Resistance Non-destructive Test of Coated Glass Using Air-Gapped Microwave Cylindrical Resonator

Coated glass has been used for many applications, such as electromagnetic shielding/absorbing, green architecture, antennas and solar cells. Sheet resistance is one of the important parameters of coated glass. This paper, based on the end-wall replacement cavity technique, used four resonators in the TE₀₁₁ mode to observe the relationship between the measurement performance of sheet resistance and the design of the resonator. An air gap was introduced to achieve true non-contact non-destructive testing, and the effects of the air gap between the cavity sidewall and the sample (0–15.5 mm), the sample’s tilt (0–10 degrees), and the substrate thickness were studied. The results show: (1) The air-gapped microwave cylindrical resonator is suitable for the R_□ evaluation of coated glass, and its measurement range and accuracy are closely related to the design of the resonator. When the air gap is between 0 and 15.5 mm, the sapphire filled resonator can extend the measurable sheet resistance to approximately 1000 Ω/sq; (2) For samples with R_□ < ~ 49.33 Ω/sq, the air filled resonator has higher precision than the sapphire filled resonator; (3) The sample tilt has a small effect on the resonant frequency but a significant effect on the Q-factor; Potential advantages of the air-gapped method include: (1) it realize real non-contact test, which may protect the sample from damage/contamination, or be convenient for multi-physics test such as high temperature, photo excitation; (2) the air gap size can be used as an additional parameter for measurement performance optimization.