氮化铝声表面波器件表面微液滴的声表面波操控研究

Microdroplets manipulation using surface acoustic waves on the hydrophobic surface of AlN-based devices

声学操控是实现芯片级微流体操控的重要方法之一,如何实现在新型压电器件表面用声表面波有效驱动操控微升量级流体是该方法中一个非常关键的问题。通过在氮化铝薄膜声表面波器件表面滴放不同体积微液滴,在微尺度下利用高速摄相机和红外热像仪研究分析了声表面波操控雷诺数较小的液滴流体力学特征和声波热效应。结果显示在较低加载功率条件下观察到声波激发液滴内粒子流场轨迹呈现出典型稳定的双涡旋蝶形结构;而加载功率继续增大时,液滴定向输运过程中输运速率随加载功率增加而增大,进一步在较高功率下液滴出现了喷射现象,进而从理论上讨论了上述特征中的耦合操控机理。同时,观察到微液滴操控过程中的声波加热效应,液滴温度变化量随加载功率呈正比线性增大趋势,但在较高功率时出现偏离。对比分析了器件表面特定位置滴放微液滴前后器件表面温度和液滴温度变化量分别随加载功率线性增大的特点,提出液滴内热量的来源以液滴内的声波因克服流体粘滞阻力做功产生的贡献占主导。

The acoustic manipulation is one of the important methods to control the microfluid on a chip.It is also a vital problem how to realize the effective control of the micro-liter fluid on the surface of the novel piezoelectric device.The microfluidics of the microscale droplet with different volumes on the hydrophobic surface of the AlN-based surface acoustic wave(SAW)device was investigated using a high-speed camera.The heating effect of the SAW on the droplet and surface of the device was observed and analyzed using an infrared thermal camera.The results showed that the flow pattern had a butterfly microstructure with double vortex in the droplet interacting with the acoustic wave when the device was applied with a relatively low power.The pumping speed of the droplet along the SAW propagation direction was increased with the applied power growing,resulting in the jetting at a relatively high power.The coupling mechanism of the above manipulation was discussed using the reported microfluidic theory.The heating effect of the SAW on the droplet was analyzed.The temperature variation of the droplet was proportional to the applied power;however,the relation was deviated at a relatively large power.The linear characteristic of the variation of the temperature with the increased power on the surface of the device was compared with that in the droplet.The heat was proposed that mainly originated from the work produced against the viscous force of the fluid in the droplet coupled with the SAW.