ACOUSTIC-WAVE LIQUID-PHASE-BASED MICROSENSORS

The responses of acoustic wave liquid-phase-based microsensors can be expressed in terms of the mass sensitivity, viscoelastic stiffening effect, and the sensitivity of the sensing modes to electrical loading. Two examples of sensitivity studies for two acoustic modes used for sensing in liquids are presented. A theoretical calculation of the mass sensitivity of a pseudo surface acoustic wave-acoustic plate mode (PSAW-APM) on ZX-LiNbO3 obtained by the perturbation method is presented. The results are used to derive design guidelines for practical sensors in liquid environments based on mass loading. In a second example, the sensitivity to electrical loading of a quartz-crystal resonator (QCR) in conductive liquid media is analyzed. By modifying the size and/or shape of the grounded electrode (the electrode in contact with the solution) relative to the 'hot' electrode, it is shown that, in addition to being a well-known mass and viscosity detector, a QCR can be used as an effective detector of conductivity and permittivity in liquid environments. Applications are suggested.