Simulating the performance of SAW-based gas sensors
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Date
2026-03-31
Authors
Acharya, Suman
Journal Title
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Publisher
University College Cork
Published Version
Abstract
Surface Acoustic Wave (SAW) devices offer a promising route for compact, sensitive, and low-power gas sensors suitable for real-time greenhouse gas monitoring. This thesis investigates the design and optimization of piezoelectric SAW resonators for the detection of methane (CH₄) and nitrous oxide (N₂O), with particular focus on lithium niobate (LiNbO3) and lithium tantalate (LiTaO₃) substrates.
The work first examines the acoustic behavior of 128°-YX LiNbO₃ resonators, a material orientation known for strong electromechanical coupling and large surface displacement. 3D Finite Element Analysis (FEA) were carried out in COMSOL Multiphysics to study the influence of interdigitated transducers (IDTs) geometry, aperture, delay-line length, metallization ratio, and electrode configuration across different operating frequencies. The results show that 128°-YX LiNbO₃ can support closely spaced Rayleigh and shear-horizontal modes, with their relative dominance depending strongly on device frequency and geometry. At lower frequencies, careful optimization of the IDT design suppresses unwanted modes and promotes Rayleigh-wave operation, which is favorable for surface-sensitive gas sensing. At higher frequency, however, the shear-horizontal mode remains dominant, indicating that 128°-YX LiNbO₃ requires careful design consideration for high-frequency gas sensing applications.
The thesis also investigates spurious-mode suppression in 42°-YX LiTaO₃ devices using tilted IDT configurations. Both simulation and experimental results show that electrode tilt can reduce unwanted modes, although this improvement is accompanied by a reduction in electromechanical coupling. A modified Butterworth–Van Dyke equivalent circuit model was further developed to extract device parameters from measured admittance responses and support comparison between simulation and experiment.
Finally, optimized SAW structures were evaluated for CH₄ and N₂O sensing using metal–organic frameworks (MOFs) sensing layers, including Zeolitic Imidazolate Framework-8 (ZIF-8) and Zirconium based MOF (UiO-66). Frequency-domain simulations confirm that gas adsorption produces measurable resonance shifts through mass-loading effects, with ZIF-8 showing stronger sensitivity than UiO-66 under the investigated conditions. Overall, this work provides a systematic understanding of material orientation, acoustic mode behavior, electrode design, and sensing-layer effects in LiNbO₃- and LiTaO₃-based SAW devices, supporting their further development for compact greenhouse gas sensing platforms.
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Controlled Access
Keywords
Surface acoustic wave (SAW) , MEMS , 3D , FEA , CH4 , N2O , Quality factor , ppm , Lithium niobate , Lithium tantalate , COMSOL Multiphysics
Citation
Acharya, S. 2026. Simulating the performance of SAW-based gas sensors. MRes Thesis, University College Cork.