Analytic comparison of the sensitivities of bulk-wave, surface-wave, and flexural plate-wave ultrasonic gravimetric sensors

Abstract

We show that, for small added masses, the sensitivities of bulk-mode, surface-mode, and flexural plate-mode gravimetric ultrasonic sensors are respectively 2/ρλ, ≊1/ρλ, and 1/2ρd, where ρ is the density of the sensor substrate material, λ is the wavelength, and d is the plate thickness of the flexural-mode sensor.

Thin rod flexural acoustic wave devices: a sensor candidate

“…Following the approach in [5] we assume that when the sensor is loaded, the mass per unit area, m" is changed by an amount of ~m, (= ~m/21ta) with negligible change in the rod diameter and Young's modulus, where ~m and ~m, are the mass change per unit length and area respectively. Equation (6) can then be written as…”

“…Most of these sensors operate in a gaseous medium, although a few are used with liquids or solids, to determine concentrations of chemical and biological substances, as well as viscosity, acceleration, temperature, pressure, etc. Recently, Wenzel and White [5] have found out that flexural plate wave gravimetric sensors can have higher mass sensitivity at low operating frequencies (a few MHz) than the BA W or SAW counterparts. The lowest flexural (anti symmetric) Lamb mode, Ao, was used for thin isotropic plates [5].…”

“…Recently, Wenzel and White [5] have found out that flexural plate wave gravimetric sensors can have higher mass sensitivity at low operating frequencies (a few MHz) than the BA W or SAW counterparts. The lowest flexural (anti symmetric) Lamb mode, Ao, was used for thin isotropic plates [5]. The thickness of the plates is much smaller than an acoustic wavelength.…”

“…The mass sensitivity, S!, can be defined as [5] ( 1) where .1m. is the uniformly distributed mass per unit area added to the surface of the device; .1 V = (V -Yo), Vo and V are the unloaded and loaded phase velocity respectively.…”

“…The high achievable S! relies on the fact that the thickness h can be made very small (2 ~m in [5]). …”