Room-Temperature Surface Acoustic Wave Gas Sensors: Sensing Mechanisms, Functional Materials, and Performance Benchmarking

Room-temperature surface acoustic wave (SAW) gas sensors respond through several transduction mechanisms, but published analytical figures of merit are rarely directly comparable. This critical, non-systematic review examines mass, acoustoelectric, elastic and viscoelastic loading across hydrogen, methane, ammonia, nitrogen oxides, hydrogen sulfide, carbon oxides and selected vapors. The review draws on 32 selected study records and compares 16 configurations in detail, retaining native readout units, calibration definitions, minimum tested concentrations, author-reported limits of detection (LODs), humidity and optical activation. Studies were selected to illustrate the diversity of materials, acoustic architectures and analytical reporting practices rather than to provide exhaustive literature coverage. The analysis identifies inconsistent LOD arithmetic, conflicting sensitivity statements and substantial gaps between estimated thresholds and experimentally tested concentrations. Humidity-dependent polarity changes and aging further limit simple performance rankings. Calculated LODs, measured concentration boundaries and experimentally determined sensitivities are treated as distinct quantities. Further development requires direct low-concentration validation, reproducible noise statistics, mechanism-resolved measurements, matrix testing and system-level energy accounting.