摘要
The crystal langasite manifests its unique advantages and potentials for high temperature applications due to a high electromechanical coupling coefficient, temperature compensated orientations for surface acoustic wave （SAW）, and temperature stability. In order to analyze the pressure-induced frequency shift in SAW resonator type sensors at high temperature, this paper presents the electroelastic wave equations employing the effective material constants for small vibrations superimposed on biases originated from homogeneous temperature and external pressure fields in the Lagrangian description. Incorporated with the first-order perturbation integration, a model including both the mechanical and electrical perturbation items originating from thermal biases and small pressure fields is proposed. This universal model is suitable for substrate with high piezoelectricity and can be applied at either room temperature or high temperature circumstance. The criteria of optimal cuts for SAW pressure sensitivity, i.e., high electromechanical coupling coefficient and low temperature coefficient of delay, are proposed. A thorough investigation in trebly rotated cuts has shown that optimal pressure sensitive crystallographic areas can be obtained. The areas suitable for pressure sensors at room temperature are defined with Euler angles Ω1： φ=0°-0.6°, θ=144.4°-145.8°, ψ =23.2°-24.1°,Ω2： φ=59.4°-61.°, θ=34.2°-36.2°, ψ =24.1°-22.3°,Ω3： φ=119°-120°, θ=143.8°-145.5°, ψ =22.3°-23.5° The areas suitable for pressure sensors at high temperature are defined with Euler angles Ⅰ： φ=8°-30°, θ=24°-36°, ψ =4°-25°Ⅱ： φ=30°-55°, θ=144.4°-158°, ψ =4°-28° A set of experiments employing LGS （0, 150°, 22°） and （0, 90°, 0） has been performed to check the validity of the proposed calculation. The experimental relative sensitivity is in excellent agreement with the theoretical results.
The crystal langasite manifests its unique advantages and potentials for high temperature applications due to a high electromechanical coupling coefficient, temperature compensated orientations for surface acoustic wave （SAW）, and temperature stability. In order to analyze the pressure-induced frequency shift in SAW resonator type sensors at high temperature, this paper presents the electroelastic wave equations employing the effective material constants for small vibrations superimposed on biases originated from homogeneous temperature and external pressure fields in the Lagrangian description. Incorporated with the first-order perturbation integration, a model including both the mechanical and electrical perturbation items originating from thermal biases and small pressure fields is proposed. This universal model is suitable for substrate with high piezoelectricity and can be applied at either room temperature or high temperature circumstance. The criteria of optimal cuts for SAW pressure sensitivity, i.e., high electromechanical coupling coefficient and low temperature coefficient of delay, are proposed. A thorough investigation in trebly rotated cuts has shown that optimal pressure sensitive crystallographic areas can be obtained. The areas suitable for pressure sensors at room temperature are defined with Euler angles Ω1： φ=0°-0.6°, θ=144.4°-145.8°, ψ =23.2°-24.1°,Ω2： φ=59.4°-61.°, θ=34.2°-36.2°, ψ =24.1°-22.3°,Ω3： φ=119°-120°, θ=143.8°-145.5°, ψ =22.3°-23.5° The areas suitable for pressure sensors at high temperature are defined with Euler angles Ⅰ： φ=8°-30°, θ=24°-36°, ψ =4°-25°Ⅱ： φ=30°-55°, θ=144.4°-158°, ψ =4°-28° A set of experiments employing LGS （0, 150°, 22°） and （0, 90°, 0） has been performed to check the validity of the proposed calculation. The experimental relative sensitivity is in excellent agreement with the theoretical results.
基金
supported by the National Natural Science Foundation of China(Grant Nos.60274062 and 10304012).
