Wireless SAW Temperature Sensor System for High-Speed High-Voltage Motors

This paper gives an overview on the system development of a wireless surface acoustic wave (SAW) temperature measurement application in high-speed high-voltage motors. The measurement location of interest is on the rotor in the vicinity of the copper squirrel cage. To fit the sensor in a 4 mm bore, a custom packaging with outer dimensions of 10.0 × 3.1 × 2.0 mm³ has been developed. For the purpose of interrogation a mechanically robust metal slot antenna has been designed to withstand rotation speeds up to 15 000 rpm. As the sensor interacts only during a very short time of a few 100 μs with the reader antenna a fast frequency modulated continuous wave (FMCW) reader was developed. The reader operates in the ISM band of 2.4 GHz and achieves a typical sweep time for data acquisition of 100 μs. The sensor system has been tested both in test bed and real engine conditions and performed stable read outs, although in the real engine signal behavior is disturbed by reflections and possibly electromagnetic field bursts caused by the power converter.