Strain Measurements With Langasite SAW Resonators at High Temperature

The strain sensitivities of the langasite surface acoustic wave resonators are strongly dependent on the temperature, which causes measurement strain to shift greatly at high temperature. To cancel the effect of temperature, a surface acoustic wave strain sensor which consisted of three langasite surface acoustic wave resonators was presented in this work. The surface acoustic wave resonators are configured to ensure that the propagation directions of the surface acoustic wave in the three surface acoustic wave resonators are parallel, perpendicular and at an orientation of 30 degrees to the applied strain. The strain sensitivities of the three surface acoustic wave resonators from room temperature to 250 degrees C were investigated. Functional relationships of the resonance frequency shifts of the three surface acoustic wave resonators due to both the temperature and applied strain were established. It was deduced that the strain was linearly represented by the resonance frequency shifts of the three surface acoustic wave resonators. Experimental results demonstrated that the langasite surface acoustic wave strain sensor was well worked within the temperature range from room temperature to 250 degrees C. The average values of the calculated strains were in agreement with the practical applied strains. There was a little fluctuation between the calculated and preset strains. The measurement error was about 1%. The maximal standard deviation was about 18.5 mu epsilon.