SAW temperature sensors on LiNbO3 substrate for high voltage equipment

This paper describes a temperature sensor for high-voltage equipment. The sensor contains a delay line on surface acoustic waves, which contains narrow-band thinned-out inter-digital transducers located on the surface of the piezo substrate of the YX/128 degrees-cut lithium niobate, having a large temperature delay coefficient. The sensor is interrogated by a reader based on a differential transformer and a voltage-controlled generator (VCO). With a generator power of 10mW, it is possible to confidently interrogate the sensor at 4m. To control the temperature in a three-phase circuit, three surface acoustic waves (SAW) delay lines are used, tuned to different frequencies and one reference delay line is combined in a reader with a semiconductor temperature sensor. The temperature measurement is based on measuring the average distance between the maxima (minima) of the signal at the output of the detector reader. With this approach, cheaper analog generators can be used as VOC, rather than frequency synthesizers. The measurement accuracy is +/- 2 degrees C, and the sensitivity is 80ppm/degrees C.