Abstract
Dispersion equation is an important tool for analyzing propagation properties of acoustic waves in layered structures. For Love wave (LW) sensors, the dispersion equation with an isotropic-considered substrate is too rough to get accurate solutions; the full dispersion equation with a piezoelectric-considered substrate is too complicated to get simple and practical expressions for optimizing LW-based sensors. In this work, a dispersion equation is introduced for Love waves in a layered structure with an anisotropic-considered substrate and an isotropic guiding layer; an intuitive expression for mass sensitivity is also derived based on the dispersion equation. The new equations are in simple forms similar to the previously reported simplified model with an isotropic substrate. By introducing the Maxwell-Weichert model, these equations are also applicable to the LW device incorporating a viscoelastic guiding layer; the mass velocity sensitivity and the mass propagation loss sensitivity are obtained from the real part and the imaginary part of the complex mass sensitivity, respectively. With Love waves in an elastic SiO2 layer on an ST-90°X quartz structure, for example, comparisons are carried out between the velocities and normalized sensitivities calculated by using different dispersion equations and corresponding mass sensitivities. Numerical results of the method presented in this work are very close to those of the method with a piezoelectric-considered substrate. Another numerical calculation is carried out for the case of a LW sensor with a viscoelastic guiding layer. If the viscosity of the layer is not too big, the effect on the real part of the velocity and the mass velocity sensitivity is relatively small; the propagation loss and the mass loss sensitivity are proportional to the viscosity of the guiding layer.
Highlights
INTRODUCTIONThe waveguide layer’s characteristics, such as density, velocity of shear acoustic wave, viscoelasticity, and thickness
Since Love wave (LW) based sensors were reported in 1992,1,2 they have been attracting the interest of many researchers
If the viscosity of the layer is not too big, the effect on the real part of the velocity and the mass velocity sensitivity is relatively small; the propagation loss and the mass loss sensitivity are proportional to the viscosity of the guiding layer
Summary
The waveguide layer’s characteristics, such as density, velocity of shear acoustic wave, viscoelasticity, and thickness. In the theoretical part of this study, a detailed inducing process is presented to obtain another form of the dispersion equation for LWs in a layered structure with an anisotropic-considered substrate and an isotropic guiding layer. A comparison is carried out between the propagation velocities and mass sensitivities, which prove that the new method can bring accurate solutions close to those of the complicated method with a piezoelectric-considered substrate. Another numerical calculation is carried out for the case of a LW sensor with a viscoelastic guiding layer. If the viscosity of the layer is not too big, the effect on the real part the velocity and the mass velocity sensitivity is relatively small; the propagation loss and the mass loss sensitivity are proportional to the viscosity of the guiding layer
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