Ultrasound radiation from a three-layer thermoacoustic transformation device

• Published in: Ultrasonics Vol. 57; pp. 84 - 89
• Main Authors: Nishioka, Takuya, Teshima, Yu, Mano, Takashi, Sakai, Ken, Asada, Takaaki, Matsukawa, Mami, Ohta, Tetsuo, Hiryu, Shizuko
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.03.2015
• Subjects: Aluminum Oxide - chemistry; Broadband; Devices; Electrically conductive; Equipment Design; Glass; Glass - chemistry; Lead - chemistry; Models, Theoretical; Silver; Silver - chemistry; Sound; Surface Properties; Thermoacoustic transformation; Thermoacoustics; Thermophone; Three-layer structure; Transducers; Ultrasonics - instrumentation; Ultrasound; Ultrasound emission; Vibration; Thermophone; Three-layer structure; Thermoacoustic transformation; Broadband; Ultrasound emission
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2014.10.019

•An Ag–Pd conductive film on a glass substrate can produce ultrasound.•The directivity was in good agreement with predictions, assuming a rectangular diaphragm.•Broadband sound wave emission was achieved up to 100kHz. A thermophone is a thermoacoustic transducer, which generates sound via time-varying Joule heating of an electrically conductive layer, which leads to expansion and contraction of a small pocket of air near the surface of the film. In this work, a 10-μm-thick Ag–Pd conductive film was coupled with heat-insulating and heat-releasing layers to fabricate a three-layer thermophone for generating ultrasound. The heat-insulating layer was 47μm thick, and was made of glass. The heat-releasing layer was 594μm thick, and was made of 94% alumina. Because of the simple sound-generation mechanism, which does not require mechanical moving parts, the Ag–Pd conductive film on the glass substrate can produce ultrasound radiation with broadband frequency characteristics, where exiting commercial electrode materials were used. We also demonstrate that the measured directivity patterns are in good agreement with theoretical predictions, assuming a rectangular diaphragm with the same size as the metallic film.