Surface Acoustic Wave (SAW) Sensors: Physics, Materials, and Applications

Abstract

Surface acoustic waves (SAWs) are the guided waves that propagate along the top surface of a material with wave vectors orthogonal to the normal direction to the surface. Based on these waves, SAW sensors are conceptualized by employing piezoelectric crystals where the guided elastodynamic waves are generated through an electromechanical coupling. Electromechanical coupling in both active and passive modes is achieved by integrating interdigitated electrode transducers (IDT) with the piezoelectric crystals. Innovative meta-designs of the periodic IDTs define the functionality and application of SAW sensors. This review article presents the physics of guided surface acoustic waves and the piezoelectric materials used for designing SAW sensors. Then, how the piezoelectric materials and cuts could alter the functionality of the sensors is explained. The article summarizes a few key configurations of the electrodes and respective guidelines for generating different guided wave patterns such that new applications can be foreseen. Finally, the article explores the applications of SAW sensors and their progress in the fields of biomedical, microfluidics, chemical, and mechano-biological applications along with their crucial roles and potential plans for improvements in the long-term future in the field of science and technology.

Recent Progress in the Topologies of the Surface Acoustic Wave Sensors and the Corresponding Electronic Processing Circuits

“…Irregular IDT configurations, which can be split or floating, have been applied to reduce reflection of the SAW toward the periphery of the substrate, out of the zone of the sensing-layer location [37]. The splitting period is related to the wavelength (respectively to the frequency) and can be calculated by sub-dividing the wavelength (Figure 5a).…”

Recent Progress on Nanomaterials for NO2 Surface Acoustic Wave Sensors

“…The IDTs can have several configurations, such as bi-directional electrodes, split electrodes, Single Phase Unidirectional Transducer (SPUDT) electrode configuration, etc. [17]. The performances of the NO 2 SAW sensors strongly depend on the IDTs configurations, and a number of fingers, but at the same time on the properties of the piezoelectric substrate or the coating material.…”

“…The operating principle of these sensors relies on changes in the propagation characteristics of the mechanical wave due to the interaction between the waves and gas molecules. The process implies three main stages: (i) excitation of the acoustic wave in the piezoelectric substrate, (ii) modulation of both amplitude and phase characteristics as an effect of the sensing process, and (iii) re-conversion of the acoustic wave into an electrical signal for successful detection [16][17][18][19]. The acoustic waves' penetration depth is of the order of the wavelength, so that most of the energy density is confined to the near-surface region, resulting in high sensitivity to surface perturbation.…”

Coupled Multiphysics Modelling of Sensors for Chemical, Biomedical, and Environmental Applications with Focus on Smart Materials and Low-Dimensional Nanostructures

“…Among other coupled effects we will also mention here those induced by nonlinear acoustoelectric transport where we have to model, for example, the interactions between surface acoustic waves (SAWs) and carriers in low-dimensional nanostructures. In such cases, we can utilize the fact that electrons can be carried by sound waves for future device implementations and designs while bearing in mind that the range of applications of SAW sensors is already very impressive [ 77 ].…”