Wireless langasite resonator as a force sensor

Langasite (La₃Ga₅SiO₁₄), a promising new piezoelectric crystal, has attracted interest from piezoelectric communities around the world for its superior behavior such as having a high Q, stable frequency-temperature behavior, high electrical-mechanical coupling coefficient and no phase transition to a high temperature form. The combination of these superior properties makes it ideal for high temperature sensor applications. This article presents a system for a wireless langasite resonator force sensor. The system uses frequency conversion techniques to convert the sensor´s ultrasonic signal to a microwave signal in order to transmit the signal wirelessly without digitization. The sensor is able to transmit the ultrasound signal by using passive components that modulate and transmit the full waveform. A specially designed loading device is constructed in order to measure the frequency shifts of the langasite resonator caused by a pair of diametric forces. The wireless transmission system was tested using a doubly rotated plano-plano langasite resonator (YXlw)θ/Φ 45°/85° operating on its third overtone (6.304844 MHz) as its sensor. Wireless system data obtained using a network analyzer was compared with similar wired system data. The force-frequency effect at different azimuth angles was measured for both wired and wireless configurations as well. The result shows a good agreement between the wired and wireless signals. The wireless langasite resonator force sensing system has a large variety of possible applications, and the wireless transmission system has the potential to be used with other types of sensors as well.