2.45 GHz Passive Wireless Temperature Monitoring System Featuring Parallel Sensor Interrogation and Resolution Evaluation

We report on the development of a TDMA (time division multiple access) based wireless sensor system for temperature monitoring. The transponders consisting of passive surface acoustic wave delay line sensors were designed for operation in the ISM band at 2.45 GHz and for a temperature range from -20degC to 180degC. A multi-step evaluation scheme using a combined delay and phase analysis, is introduced. A temperature resolution of 0.19 K (6sigma) was achieved at a transmission power of +2 dBm (1.59 mW), when the distance between the transceiver and sensors was about 140 cm. We also report the importance of mounting the sensors during packaging based on experimental results.