Abstract
Langasite (LGS) surface acoustic wave (SAW) temperature sensors have a large second order temperature coefficient of frequency, which leads to their non-linear and non-monotonic responses in a wide temperature range and possibly makes the measured temperatures non-unique for a specific sensor response. Here, we propose a high-temperature Pt/LGS SAW sensor with linear frequency–temperature behavior in a wide temperature range, which was fabricated on a LGS (0°, 138.5°, 72°) substrate. The sensor has a single acoustic mode, but dual resonances with similar second- and third-order temperature sensitivities that were utilized for achieving a linear frequency–temperature response by a method of difference. A linear relationship between the measured sensor output (Δfm21) and temperature was obtained in the range of −60 °C to 700 °C, consistent with the theoretical analysis. The sensor has a high sensitivity of −167 ppm/K for the whole temperature range. All the results demonstrated exciting prospects of the sensor for wide temperature monitoring in harsh environments.
Highlights
IntroductionSurface acoustic wave (SAW) devices have been intensively explored for sensing applications due to their attractive merits such as low cost, compact size, and passive wireless operation capability. Among them, high temperature surface acoustic wave (SAW) sensors have attracted great interest because of the great demands for wireless sensing in harsh environments such as in gas turbines so as to conduct real-time remote monitoring of the machine operation conditions. Langasite (LGS) has been the most extensively studied material for fabricating harsh environment SAW sensors owing to its high phase-transition temperature (up to 1470 ○C), large scale production, and easy accessibility. it was revealed in many publications that LGS SAW temperature sensors have a parabolic response to temperature variation due to the large second order temperature coefficient of frequency (TCF2), which could contribute to the non-linear even non-monotonic response in a wide temperature range, and non-unique sensing outputs exist on the two sides of the turn-over temperature
Langasite (LGS) surface acoustic wave (SAW) temperature sensors have a large second order temperature coefficient of frequency, which leads to their non-linear and non-monotonic responses in a wide temperature range and possibly makes the measured temperatures nonunique for a specific sensor response
It was revealed in many publications that LGS SAW temperature sensors have a parabolic response to temperature variation due to the large second order temperature coefficient of frequency (TCF2),11,12 which could contribute to the non-linear even non-monotonic response in a wide temperature range, and non-unique sensing outputs exist on the two sides of the turn-over temperature
Summary
Surface acoustic wave (SAW) devices have been intensively explored for sensing applications due to their attractive merits such as low cost, compact size, and passive wireless operation capability. Among them, high temperature SAW sensors have attracted great interest because of the great demands for wireless sensing in harsh environments such as in gas turbines so as to conduct real-time remote monitoring of the machine operation conditions. Langasite (LGS) has been the most extensively studied material for fabricating harsh environment SAW sensors owing to its high phase-transition temperature (up to 1470 ○C), large scale production, and easy accessibility. it was revealed in many publications that LGS SAW temperature sensors have a parabolic response to temperature variation due to the large second order temperature coefficient of frequency (TCF2), which could contribute to the non-linear even non-monotonic response in a wide temperature range, and non-unique sensing outputs exist on the two sides of the turn-over temperature. Giving several commonly used LGS cuts as examples, LGS (0○, 138.5○, 27○) SAW temperature sensor has a turn-over point near ambient temperature, which means that the sensor is not suitable for measurement in the sub-zero to positive temperature range; LGS (0○, 138.5○, 117○) SAW temperature sensor features a turn-over point at about 200 ○C,14 that is to say, the sensor response is not monotonic in the range from the ambient temperature to temperatures higher than 200 ○C Piezoelectric materials such as LiNbO3, quartz, and LiTaO3 are good choices for fabricating scitation.org/journal/adv linear SAW temperature sensors, their properties deteriorate seriously at temperatures above 500 ○C due to phase-transition or chemical decomposition.
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