A miniaturized wireless and passive antenna sensor with meandering structure for integrated multi-directional strain and temperature sensing

To meet the demand for real-time synchronous monitoring of multidirectional mechanical states and temperature in complex working environments such as new energy fields, high-speed rotating machinery, large-scale building structures, and special enclosed systems, where space is limited, wiring is restricted, and power supply is difficult, this paper proposes a wireless, passive, and miniaturized integrated sensor for multidirectional strain and temperature sensing. The sensor adopts a novel stepped trapezoidal three-dimensional layout to reduce mutual coupling effects and integrates three patch antennas for strain sensing at 0°, 45°/135° directions and temperature sensing, respectively. By introducing T-shaped slots on the patch surfaces through meandering technology to extend the equivalent current paths, the sensor achieves miniaturization, resulting in a reduction of radiation area by 53%, 29.3%, and 42.3% for the three patches compared with conventional designs of the same resonant frequency and material, and an overall size reduction of 59.7%. Additionally, a high-temperature resistant broadband coplanar waveguide antenna is designed to replace the traditional horn antenna as the interrogation antenna, enabling signal transmission in high-temperature environments. To comprehensively evaluate the sensor performance, three test systems were established: a room-temperature strain test system, a temperature test system, and a variable-temperature strain test system. The room-temperature strain test system measures strain in the 0°, 45°, and 135° directions within the range of 0-500 με. The temperature test system monitors temperature in the range of 15-800 °C. The variable-temperature strain test system characterizes strain in the same temperature zone for the three aforementioned directions within 0-500 με, based on which a temperature correction algorithm for strain signals is proposed to decouple strain signals under varying temperatures. Experiments show that the measured results agree well with simulations, and the sensor is capable of synchronous monitoring of multidirectional strain and temperature. The average strain sensitivity reaches up to 26.14 kHz/με, with measurement errors ≤5%, and the maximum temperature sensitivity is 341.67 kHz/°C. The fitting errors for both room-temperature strain and temperature tests are below 0.1%. In repeatability tests, the standard deviations for room-temperature strain and temperature monitoring are less than 0.1 MHz and 0.9 MHz, respectively. This sensor provides an effective integrated solution for multi-parameter monitoring under complex working conditions.