ON THE MASS SENSITIVITY OF ACOUSTIC-PLATE-MODE SENSORS

The mass sensitivity of acoustic plate modes (APMs) in general and in particular APMs on ZX-LiNbO3 is investigated for gas and liquid phase- sensing applications. It is shown that, unlike pure shear horizontal A PMs, the modes on ZX-LiNbO3 consist of both propagating bulk-wave comp onents (with a linear frequency dependence of mass sensitivity) and ev anescently trapped surface components from the pseudo surface acoustic wave (PSAW) (with f(2) frequency dependence of mass sensitivity). Thu s, for a given plate thickness, the overall frequency dependence of ma ss sensitivity depends on the frequency range of operation. Theoretica l and experimental results are in good agreement. Results are also giv en for actual immunosensor experiments. The results show that, in sens or applications, an f(2) dependence at relatively high frequencies, an d hence higher mass sensitivity, is achievable. This will require usin g thinner plates and the dominant PSAW-derived APM.