Mass sensitivities of shear horizontal waves in three-layer plate sensors

Abstract

Absfracf-Explicit velocity and mass sensitivity formulas for shear-horizontal (SH) plate wave sensors loaded symmetrically on both sides of a plate are presented. The sensor geometry is a composite plate which consists of a central isotropic plate sandwiched symmetrically between two identical layers of isotropic solids. It is demonstrated that if the side layers are considered as the mass loading, for the lowest SH mode (S&) the sensitivity decreases by a factor of (I -%) due to the elasticity and by a factor of (1 + S)-' due to the inertia of the mass loading layers, where p1, p~; PI. PZ and 2d, h are the shear moduli, densities and thickness of the central plate and of the side layers, respectively. For higher order modes, the behavior of sensors which are operated near cutoff frequency is analyzed. The mass loading decreases the cutoff frequencies of the higher order modes and near the cutoff frequencies the mass sensitivities are very high but decrease dramatically as the mass loading increases. Specific examples are given for the case of a fused silica plate sandwiched between two thin lucite layers. S

Theory of Chemical Sensors Using Surface Acoustic Waves

“…Sensors of chemical composition and concentration using surface acoustic waves have been in focus of attention for the last several years [1][2][3][4][5][6][7]. The working principle of chemical sensors considered here is based on changes in surface acoustic wave velocities under the in uence of molecules of the surrounding gas or liquid interacting speci cally with the specially prepared sensitive surfaces.…”

“…The difference in the last case, which is related mainly to the control of chemical reactions, is an increased radiation of Rayleigh wave energy into sound waves in liquid, that requires additional compensation of associated energy losses by means of an electric ampli er. To reduce these losses in sensors of chemicals in liquids one often uses shear surface waves propagating in thin plates or layered stmctures (SH-or Love type waves), instead of Rayleigh surface waves (see, e,g., [7]).…”

“…These involve ultrasonic nondestructive testing, portable radio communication systems (including mobile telephones), and different types of sensors. A special very important application of surface acoustic waves propagating along inhomogeneous subsurface layers is chemical sensors used for detecting and measuring concentrations of surrounding gases or liquids [1][2][3][4][5][6][7]. The work of these devices is usually based on change in velocities of surface acoustic waves as a result of their interaction with liquid or gas molecules adsorbed by specially deposited selective thin lms.Despite a number of success rl experimental investigations of surface acoustic wave chemical sensors, their current theoretical description is far from satisfactory.…”