A piezoelectric-sound-resonance cavity for hydrogen gas detection.

A new concept for hydrogen gas (H2) detection has been developed. This concept is based on a piezoelectric-sound-resonance cavity (PSRC). Detection uses sound resonance and the acoustic property differences of gases as a sensing mechanism in which there is a significant difference in the sound velocity and acoustic impedance between H2 and air. The PSRC sensor consists of two thin piezoelectric discs, separated by a small cavity. One disc excites a weak acoustic standing wave in the cavity, and the second senses the wave by monitoring the acoustic impedance characteristics of the cavity. Changes in H2 concentration result in a shift of the sound resonance state. Investigations of a PSRC prototype have demonstrated a sensitivity limit of <10 ppm, a fast response time approximately 1 second, and a signal (phase and voltage) in proportion to the change in H2 concentration (n) over the range of 10(-5) < n < 0.2. These performance characteristics are far superior to those of other methods.