Abstract
In this study, we investigate the interfacial droplet jetting characteristics and thermal stability of a focused surface acoustic wave device (F-SAW). An F-SAW device capable of generating a 20 MHz surface acoustic wave by applying sufficient radio frequency power (2–19 W) on a 128°-rotated YX-cut piezoelectric lithium niobate substrate for interfacial droplet jetting is proposed. The interfacial droplet jetting characteristics were visualized by a shadowgraph method using a high-speed camera, and a heat transfer experiment was conducted using K-type thermocouples. The interfacial droplet jetting characteristics (jet angle and height) were analyzed for two different cases by applying a single interdigital transducer and two opposite interdigital transducers. Surface temperature variations were analyzed with radio frequency input power increases to evaluate the thermal stability of the F-SAW device in air and water environments. We demonstrate that the maximum temperature increase of the F-SAW device in the water was 1/20 of that in the air, owing to the very high convective heat transfer coefficient of the water, resulting in prevention of the performance degradation of the focused acoustic wave device.
Highlights
Since Faraday first discovered liquid interface oscillation due to vibrational elastic surfaces in 1831, many attempts have been made to understand this physical phenomenon
When high RF power is applied to the focused surface acoustic wave device (F-surface acoustic waves (SAWs)) device, significant acoustic heating occurs [27,28,29,30,31,32,33]
The heat measurement in the F-SAW device is important for microfluidic applications owing to its direct effect on such phenomena as acoustic streaming, pumping, and jetting
Summary
Since Faraday first discovered liquid interface oscillation due to vibrational elastic surfaces in 1831, many attempts have been made to understand this physical phenomenon Rayleigh first explained this phenomenon theoretically by publishing the main theory of elastic surface waves in 1896. SAW devices are widely used in biochemical detection, drug development, life sciences, and medical research. They have been applied for precise microfluidic control for studying sound streaming, mixing, and pumping [10,11,12]. The SAW is well known as a nozzle-less liquid jet actuator in the microscale regime [14,15,16,17]. If a nozzle or orifice is used in 3D bioprinting applications, the mortality rate of the cell within the droplet increases and clogging may occur, resulting in deterioration of the performance
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