A High-Sensitivity Microwave Sensor With Split-Ring Resonator Structure for Force and Bending Measurement

In the fields of biological and medical research, precise detection of microscale structural changes is crucial. This article presents a microwave sensor based on a microstrip line (MSL)-coupled split-ring resonator structure for detecting structural bending changes and force conditions. The sensor is composed of Flame-Retardant 4 (FR4) epoxy resin, copper foil, and an organic protective layer, with a resonant frequency of 3.60801 GHz. Detection of bending and microforces is achieved through the shift in resonant frequency. When the bending angle is between 0.1° and 1°, the sensor’s resonant frequency shift range is from 3.60771 to 3.60280 GHz; when the bending angle is between 5° and 90°, the resonant frequency shift range is from 3.60801 to 3.60126 GHz, with a sensitivity of 74.916 kHz/°. Additionally, the sensor can measure forces in the range of 0–20 N, and for microforces within the range of 0.1–1 mN, the resonant frequency shift range is from 3.56256 to 3.56219 GHz, with a sensitivity of 372 hertz (Hz)/ $\mu $ N. The sensor has the advantages of high resolution, high sensitivity, and a broad measurement range. Validated by pulse measurement, it successfully measured the wrist arterial pulse force of approximately 1.5 mN, providing a new perspective for the fields of biological and medical monitoring.