集束超音波を用いたマイクロウェルからの液滴の打ち上げに関する田中（OB）の論文がJapanese Journal of Applied Physics に掲載されました。
Hiroki Tanaka, Yosuke Mizuno, Kentaro Nakamura, “Ejection of small droplet from microplate using focused ultrasound,” Japanese Journal of Applied Physics, vol. 56, no. 8, 087202, Jul. 2017.
We discussed an ultrasonic system for single-droplet ejection from a microplate, which is one of the basic and important procedures in the noncontact handling of droplets in air. In this system, a 1.5 MHz concave transducer located below the microplate is used for chasing the liquid surface through a pulse echo method, and also for the ejection of a 1 µL single droplet by the burst of focused ultrasound. We investigated the relationship between the droplet ejection characteristics, the distance from the transducer to the surface of liquid, the material property, and the excitation condition of the focused ultrasonic transducer. It was verified that the optimal position of the transducer was off the focal point of sound pressure by ±1 mm, because the sound intensity had to be controlled to eject a single droplet. Subsequently, we confirmed experimentally that the ejected droplet volume linearly depended on the surface tension of the liquid, and that the droplet volume and ejection velocity were determined by the Webber number, Reynolds number, and Ohnesolge number. In addition, by optimizing the duration of the burst ultrasound, the droplet volume and ejection velocity were controlled.