Ejection of small objects in a noncontact ultrasonic transporter

2017

Self Cite

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.

Section: Introductionmentioning

confidence: 99%

Ejection of small droplet from microplate using focused ultrasound

Tanaka

2017

Self Cite

“…We can utilize a variety of ultrasonic technologies to handle small objects in air. [15][16][17][18][19][20][21][22][23] Although linear transport, [24][25][26] direction switching, 27) mixing, 28) and ejection 29) have already been demonstrated, the other procedures need to be studied to accomplish the goal.…”

Section: Introductionmentioning

confidence: 99%

Effect of holed reflector on acoustic radiation force in noncontact ultrasonic dispensing of small droplets

Tanaka

Wada

2016

Self Cite

We investigated the fundamental aspects of droplet dispensing, which is an important procedure in the noncontact ultrasonic manipulation of droplets in air. A holed reflector was used to dispense a droplet from a 27.4 kHz standing-wave acoustic field to a well. First, the relationship between the hole diameter of the reflector and the acoustic radiation force acting on a levitated droplet was clarified by calculating the acoustic impedance of the point just above the hole. When the hole diameter was half of (or equal to) the acoustic wavelength λ, the acoustic radiation force was ∼80% (or 50%) of that without a hole. The maximal diameters of droplets levitated above the holes through flat and half-cylindrical reflectors were then experimentally investigated. For instance, with the half-cylindrical reflector, the maximal diameter was 5.0 mm for a hole diameter of 6.0 mm, and droplets were levitatable up to a hole diameter of 12 mm (∼λ).

“…When the materials to be transported are liquids (or droplets), mixing of multiple droplets is also essential. Up to now, linear transport, [23][24][25] direction switching, 26) and ejection 27) have been successfully demonstrated, but other procedures need to be developed to achieve our aim.…”

Section: Introductionmentioning

confidence: 99%

Demonstration of Noncontact Ultrasonic Mixing of Droplets

2013

The noncontact ultrasonic mixing of two droplets is demonstrated, for the first time, by controlling the acoustic field using the following two methods: (1) by changing the distance between the vibrator and the reflector and (2) by modulating the driving voltage amplitude applied to the vibrator. The operating principle is confirmed by measuring the acoustic pressure distribution and the temporal change in the acoustic pressure near the mixing position. We also show that the stable mixing of droplets with high repeatability is feasible by method (2), which does not involve the use of mechanically moving parts.