Abstract
When a surface acoustic wave (SAW) is excited on a spherical surface, a naturally collimated SAW propagates around the equator hundreds of times. The propagation characteristics such as the velocity and amplitude are affected by adsorbed and/or reacted molecules on the surface, and the changes are accumulated by multiple turns of propagation. This enables highly sensitive detection of adsorbed molecules including water vapor. In this paper, the development and testing of a 1 mm diameter spherical SAW sensor, which is capable of measuring water vapor at concentrations well below 1 μmol · mol−1H2O in N2, are reported. The rise time from 10% to 90% of the spherical SAW sensor to a step change from dry N2 to 1 μmol · mol−1H2O in N2 was approximately 15 s.
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Takeda, N., Motozawa, M. Extremely Fast 1 μmol · mol−1 Water-Vapor Measurement by a 1 mm Diameter Spherical SAW Device. Int J Thermophys 33, 1642–1649 (2012). https://doi.org/10.1007/s10765-012-1223-z
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DOI: https://doi.org/10.1007/s10765-012-1223-z