2D measurement of airborne ultrasound using thermography
In recent years, technology using aerial ultrasound has been attracting attention as an example of aerial haptics, which is expected to be used in VR and AR. On the other hand, the current situation is that a high-speed measurement method for airborne ultrasonic fields, which is essential for practical use, has not yet been established. For example, microphone scanning, which is the most common method so far, takes an enormous amount of time to measure a three-dimensional sound field. In this research, we demonstrated that a thermography camera can instantaneously measure the sound pressure distribution on any two-dimensional surface in a three-dimensional space. Using a thermal image of a mesh screen surface transparent to ultrasound, we were able to visualize the ultrasound field in 0.5 seconds. Furthermore, we were able to visualize focal positions and interference patterns from surface temperature information, even for objects that mostly reflect ultrasonic waves, such as hands. It is a measurement technology that can be expected to be put into practical use soon because it is easy to set up and can measure high sound pressure that cannot be measured with a microphone.
- Using thermal images of the mesh screen surface, a two-dimensional ultrasonic field can be visualized in real time.
Sound field features such as (a) the focal point and its side lobes and (b) the pressure nodes and antinode of the standing wave are clearly visualized.
- Furthermore, we confirmed that even objects that completely reflect ultrasonic waves, such as a hand or an acrylic plate, can visualize the focal point and interference patterns from surface temperature information.
(a) The temperature distribution on the palm surface revealed a concentric pattern corresponding to the sound field. (b) An image sequence showing the temperature distribution at the fingertip revealed that the focal point moved in 2 mm steps every 0.4 seconds.
Ryoya Onishi, Takaaki Kamigaki, Shun Suzuki, Tao Morisaki, Masahiro Fujiwara, Yasutoshi Makino, and Hiroyuki Shinoda, “Two-Dimensional Measurement of Airborne Ultrasound Field Using Thermal Images” Phys. Rev. Applied 18, no. 4 (2022) 044047 (Open Access)
Onishi, R., Kamigaki, T., Suzuki, S., Morisaki, T., Fujiwara, M., Makino, Y., & Shinoda, H. (2022). “Visualization of airborne ultrasound field using thermal images”. arXiv preprint arXiv:2203.07862.
小丹枝 涼哉, 神垣 貴晶, 鈴木 颯, 森崎 汰雄, 藤原 正浩, 牧野 泰才, 篠田 裕之, “熱画像を用いた強力空中超音波の音場分布計測,” 第38回センシングフォーラム計測部門大会, pp. 141-145 オンライン開催, Sep. 30・Oct 1, 2021 *SICE センシングフォーラム研究奨励賞 受賞