Schematic drawing of interaction between surface acoustic wave and a liquid droplet and defining the Rayleigh angle, .
Acoustic force as a function of rf signal voltage acting on a water droplet for both a (Ref. 42) and ZnO SAW device. The device uses a Rayleigh mode wave, while the ZnO device uses a Sezawa mode wave. Both devices have 60 finger pairs in the IDT.
Photos of a droplet on an untreated and an OTS treated ZnO surface. The contact angle increased from to 110° after OTS SAM layer formation.
Variation in minimum acoustic force, , required to move a water droplet of volume on a surface as a function of contact angle calculated from Eqs. (6) and (7).
Photos of a droplet movement on an OTS treated ZnO SAW device before (a) and after (b) being driven by a rf signal at a frequency of 178.7 MHz.
Sezawa wave driven droplet velocity as a function of rf signal voltage applied on the SAW for a ZnO SAW device.
Total distance moved by a water droplet as a function of pulse number for a rf signal of 40 V and a pulse width of 100 ms.
Schematic drawing of the proposed SAW structure with ZnO on the wave path being removed compared with the standard SAW device structure where the ZnO is not patterned.
Comparison of transmission spectra for SAW devices before and after removal of the ZnO from the propagation area using (a) the Rayleigh wave from a thick ZnO thin film and (b) the Sezawa wave from a thick ZnO thin film.
Streaming velocity induced by acoustic waves from the SAW devices where there is no ZnO in the propagation region. Results for both Sezawa (s) and Rayleigh (r) mode devices are presented.
Temperature change as a funciton of time with rf signal voltage as a parameter. The temperature rises rapidly at the initial 20 s, and then increases slowly thereafter.
Extracted parameters for the acoustic force extraction.
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