Abstract
The Miniaturised Lab-on-a-Disc (miniLOAD) platform, which utilises surface acoustic waves (SAWs) to drive the rotation of thin millimeter-scale discs on which microchannels can be fabricated and hence microfluidic operations can be performed, offers the possibility of miniaturising its larger counterpart, the Lab-on-a-CD, for true portability in point-of-care applications. A significant limitation of the original miniLOAD concept, however, is that it does not allow for flexible control over the disc rotation direction and speed without manual adjustment of the disc’s position, or the use of multiple devices to alter the SAW frequency. In this work, we demonstrate the possibility of achieving such control with the use of tapered interdigitated transducers to confine a SAW beam such that the localised acoustic streaming it generates imparts a force, through hydrodynamic shear, at a specific location on the disc. Varying the torque that arises as a consequence by altering the input frequency to the transducers then allows the rotational velocity and direction of the disc to be controlled with ease. We derive a simple predictive model to illustrate the principle by which this occurs, which we find agrees well with the experimental measurements.
Highlights
The necessity for such a motor makes it difficult to further miniaturise the Lab-on-a-CD platform from its current benchscale dimensions to that which facilitates portable operation for true point-of-care use
This is limiting if arbitrary rotational direction of the disc is desired, which can only be effected in the miniLOAD platform by patterning and triggering a second opposing pair of offset interdigitated transducer (IDT) on the device whilst relaxing the power on the first IDT pair (Fig. 1(c))
The fixed position and aperture of these IDTs means that the disc size has to be fixed relative to these IDT positions; in other words, altering the disc dimension would require a new device with a separate IDT design patterned to match
Summary
The necessity for such a motor makes it difficult to further miniaturise the Lab-on-a-CD platform from its current benchscale dimensions to that which facilitates portable operation for true point-of-care use.
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