title: Ultramultiple roundtrips of surface acoustic wave on sphere realizing innovation of gas sensors.
abstract: A thin beam of wave usually diverges due to diffraction, which is a limitation of any device using such waves. However, a surface acoustic wave (SAW) on a sphere with an appropriate aperture does not diverge but is naturally collimated, realizing ultramultiple roundtrips along an equator of the sphere. This effect is caused by the balance between diffraction and focusing on a spherical surface, and it enables realization of high-performance ball SAW sensors. The advantage of ball SAW is most fully appreciated when applied to a very thin sensitive film for which the multiple-roundtrip enhances the sensitivity, but the attenuation loss is not very large. It is exemplified in a hydrogen gas sensor that realizes a wide sensing range of 10 ppm to 100% for the first time, and realizes relatively fast response time of 20 s without heating the sensitive film.
authors.affiliation: Tohoku University, Aoba 02, Sendai, Japan. yamanaka@material.tohoku.ac.jp
authors.forename: Kazushi
authors.initials: K
authors.lastname: Yamanaka
authors.forename: Satoru
authors.initials: S
authors.lastname: Ishikawa
authors.forename: Noritaka
authors.initials: N
authors.lastname: Nakaso
authors.forename: Nobuo
authors.initials: N
authors.lastname: Takeda
authors.forename: Dong Youn
authors.initials: DY
authors.lastname: Sim
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Mihara
authors.forename: Akio
authors.initials: A
authors.lastname: Mizukami
authors.forename: Ichitaro
authors.initials: I
authors.lastname: Satoh
authors.forename: Shingo
authors.initials: S
authors.lastname: Akao
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tsukahara