A Microwave Sensor Based on Interdigital Capacitors and Electrodes for Solid Dielectric Measurement

In this letter, a microwave sensor designed for the measurement of the dielectric constant of solid materials is proposed. Compared to a traditional interdigital capacitor (IDC), the annular IDC (AIDC) used in this study is used to effectively reduce the dimension of the sensor, offering a compact solution for microwave sensor design. By integrating interdigital electrodes (IDEs) within the AIDC, the electric-field concentration is enhanced, achieving high-sensitivity measurements while maintaining miniaturization. The dimension of the sensor is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20 \times 15 \times 0.762$</tex-math> </inline-formula> mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>, with a sensing area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.4 \times 8.4$</tex-math> </inline-formula> mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The test results indicate that the unloaded resonant frequency of the sensor is 2.373 GHz, with an average measurement sensitivity of 6.744% and an average resolution of 160 MHz. The sensor is designed to exhibit high measurement nonlinear correlation and potential material identification capabilities, demonstrating significant potential for precise characterization of permittivity in solid materials.