Principle and application of ball surface acoustic wave (SAW) sensor

Abstract

Detection of hydrogen gas is a crucial task for establishing safety and reliability of fuel cells, a key technology for the environment and our society. However, hydrogen is difficult to detect and various hydrogen sensors have many drawbacks. Here we report a novel hydrogen gas sensor, the ball surface acoustic wave (SAW) sensor, using Pd or PdNi sensitive film. The ball SAW sensor is based on a novel phenomenon, diffraction-free propagation of collimated beam along an equator of sphere. The resultant ultra-multiple roundtrips of SAW makes it possible to achieve highest sensitivity among SAW sensors. Moreover, it enables to use a very thin sensitive film, and consequently the shortest response time (2 s) was realized. In terms of the sensing range, it has the widest range of 10 ppm to 100% among any hydrogen sensors including FET or resistivity sensors. The response time was less than 1 s for 3.0% hydrogen concentration in nitrogen gas, evaluated by using a newly developed digital quadrature detector.

Laser-grown ZnO nanowires for room-temperature SAW-sensor applications

“…Beyond these numbers, our experimental results showed that the nanowire sensors could be used effectively to measure concentrations on the order of ∼0.01%, close to the performance demonstrated by spherical sensors requiring sophisticated fabrication techniques [33]. In the same experiments, the thin film could actually be used for only about one order higher H 2 concentration.…”

Ultrathin-film hydrogen gas sensor with nanostructurally modified surface

“…[21][22][23] Pd is a hydrogen storage material, and therefore resistance increases when exposed to hydrogen because of the crystal lattice expansion of the crystal lattice by hydride formation. Surface acoustic wave sensors [24][25][26][27][28] are based on surface wave propagation caused by changes in electrical properties such as conductivity, permittivity, and carrier concentration. Thermoelectric sensors using a thermocouple device 29,30) detect heat generated by catalytic reactions.…”

A study on gas sensors using a SAW device

“…The phthalocyanine compounds absorb various chemical substances and are chemically stable. Therefore, phthalocyanine films have been utilized in gas sensors [4][5][6][7].…”