In this thesis a model is developed to characterise the behaviour of layered SAW 2- port resonator sensors operating in liquid media. In the critical review of literature, it is found that methods based on the periodic Green's function combined with the COM model are best suited to this task. However, an important deficiency of this approach is the lack of a good model for electrodes buried within layered media. This deficiency is resolved in this thesis by the formulation of a periodic matrix eigen-operator, using a phase-shifted Fourier series representation. This model is then utilised in the study of resonator behaviour as a function of guiding layer thickness, including the mass sensitivity. Based on this modelling work, a SAW resonator structure is designed, and its frequency response is found to be in generally good agreement with theoretical predictions. The mass sensitivity of this device is then analysed using both theoretical and experimental means. In contrast to the sensitivity analyses found in the literature, sensitivity variation across the device surface is considered in this work. For the resonator structure it is found that sensitivity is greatest at the device centre, with the ends of the device making negligible contribution to the complete device response. The result is that the sensitive material may be deposited only in a small region in the centre of the device, with minimal reduction in device response.