TEMPERATURE EFFECT AND CHEMICAL RESPONSE OF SURFACE-ACOUSTIC-WAVE (SAW) SINGLE-DELAY-LINE CHEMOSENSORS

The effects of temperature and chemical vapour absorption on the frequ ency shift of coated and uncoated SAW single-delay-line oscillators ar e reported. It is found that the temperature-induced frequency-shift f unction depends on the nature of the coating of the delay-line surface . It changes from the flat parabolic temperature dependence of an unco ated ST-quartz delay line near room temperature, to a steep, almost li near, curve for polymer-coated delay lines in the same temperature ran ge. The slope of the curves depends on the nature of the polymers. The dual-delay-line concept, where an uncoated SAW delay line is used as a reference element to compensate for the ambient temperature variatio ns, is therefore not universal and should be implemented with great ca ution. The response of an array of four different SAW delay-line senso rs to various chemical vapours is represented by pie charts, visualizi ng chemical pattern variability that can be used for pattern recogniti on. The frequency shifts are correlated with calculated theoretical pa rtition-coefficient values, based on thermodynamic parameters and regu lar solution theory. It is shown that this approach may be used to pre dict the interaction between the polymer and a specific target chemica l vapour. A simple method for a preliminary design of a SAW chemosenso r is thus suggested.