Mechanical & acoustic — overview

This section covers mechanical and acoustic-wave hydrogen sensors, which transduce a hydrogen-induced change in a thin palladium film into a shift of a mechanical or electromechanical resonance.

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1. Acoustic-wave & MEMS sensors — quartz crystal microbalances (QCM), surface-acoustic-wave (SAW) chips, film bulk acoustic resonators (FBAR), and MEMS cantilevers, which read palladium-hydride stress rather than the mass of absorbed hydrogen, through a resonance or curvature shift. No dedicated commercial hydrogen product exists yet, so it remains a watchlist item for passive-wireless downhole telemetry.

Speed-of-sound and bulk-gas acoustic analysis is a distinct principle, treated separately under thermal conductivity & acoustic sensors.