A Miniaturized Integrated Wireless Passive Antenna Sensor Based on Meandering Technology for Multi-Directional Strain and Temperature Sensing

To address the pressing demands for real-time, wireless, and multi-dimensional monitoring of mechanical states in high-speed rotating machinery, large-scale architectural structures, and specialized enclosed systems under complex operating conditions, as well as temperature sensing requirements in new energy applications, this paper proposes a wireless, passive, and miniaturized multi-directional strain/temperature integrated sensor. Featuring a compact structure and weldable/adhesive mounting capabilities, the sensor is particularly suitable for applications with wiring constraints, power supply challenges, and requirements for synchronous multi-directional strain monitoring. To reduce mutual coupling between patch antennas, a novel stepped structure integrates three patch antennas into a single unit. Furthermore, by employing meandering technology with T-shaped slots etched on the patch surface to extend the equivalent current path, sensor miniaturization is achieved. Experimental results demonstrate significant reduction in radiating patch area, with the three patches achieving area reductions of 53.0%, 29.3%, and 42.3% respectively compared to conventional designs of the same resonant frequency and material, while the overall sensor area is reduced by 59.7%. A strain measurement system was set up with a horn antenna as the interrogator to test the sensor under 0–500 με along 0°, 45°, and 135° directions. Additionally, a high-temperature-resistant, miniaturized broadband coplanar waveguide antenna was designed to replace the horn antenna as the interrogator for temperature sensing, thereby forming a temperature measurement system capable of testing the sensor over a range of 50 to 800 °C. The measured results show good agreement with the simulations, indicating that the sensor is capable of either effectively characterizing temperature variations in high-temperature environments or performing simultaneous strain measurements in multiple directions, with a strain sensitivity of up to 32.27 kHz/με and a temperature sensitivity of 341.67 KHz/℃. Under all tested conditions, the fitting error was less than 0.1%, while the standard deviation of repeatability was below 0.1 MHz for strain measurements and below 0.9 MHz for temperature measurements.