Noncontact Sheet Resistance Measurement Using Open-Ended Waveguide Probe

Accurate measurement of sheet resistance (R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub>) is crucial for evaluating the infrared reflectance and transmittance of coated glass, which is vital for enhancing thermal management efficiency of green building. It is also important for applications like film strain gauges, optoelectronics and attenuators. This study explores the feasibility of assessing R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> using open-ended rectangular waveguide, including both low-frequency and highfrequency experimental setups, covering working frequency bands from 3 to 40 GHz. Using 14 indium tin oxide (ITO) conductive glasses with R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ranging from ∼3 to 500 Ohm/sq as samples under test. Compared to existing waveguide methods, this work offers three advantages: 1, a low-cost setup for practical applications in low-frequency range is developed; 2, non-contact setups in high-frequency range are also developed and impact of air gap between waveguide flange and sample under test is studied; 3, effect of working frequency on measurement performance is mentioned. In the cost-effective setup, Radio Frequency (RF) circuits and microcontroller unit (MCU) modules are used. For this setup, with suitable air gap, the measured direct-current (DC) voltage increases linearly with R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub>. For the high-frequency setup, a vector network analyzer (VNA) is used to obtain R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> by mathematic fitted relationship between S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> at specific frequencies. This research provides valuable insights for evaluating R<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> of conductive materials using waveguide technology