Graduate Seminar – Rabin Dhakal

Abstract: Scientists and engineers have often been fascinated by the nature for its optimal way of evolutionary development and often take them as an inspiration in the improvement of engineering discipline. The main challenge in the process of mimicking the nature is their compact and complex soft structures. Progress in micro-fabrication technology has pushed forward biomimetic research in materials, structures, sensors and applications.

One example that can imitate nature’s compact and complex design such as the compound eyes of insects is wide field of view design in efficient solar concentrator that does not require solar trackers for continuous compensation of the solar motion in both azimuthal and elevation directions. We designed miniaturized thin and flat solar concentrators (TFSCs) where the sunlight impinging normally on their upper surface is condensed and launched into lateral propagation along a lightguide using light redirection elements (LRE) towards the edge where PV cells are installed. Such TFSCs not only integrates PV conversions into everyday life but also achieves wide acceptance angle with static structures. Through design optimizations, we could achieve optical concentration factors up to 39 and acceptance angle up to ±15° while maintaining the thickness of the concentrator under 1.1 cm for a length of 20 cm.

As an extension to the TFSCs design we propose to deliver sunlight directly to the indoorlamp fixtures to improve the overall lighting efficiency, as it is the major area of electricity consumption in both residential and commercial sectors. Making the solar indoor lighting comfortable to human eyes requires additional processes since the light level must be kept constant and uniform through active control. We designed and fabricated autonomous, self-powered light control using opto-thermo-mechanical actuation whereby the IR portion of the sunlight focused into the micro chamber containing paraffin to cause its volume expansion and produce the pneumatic force. This force is translated to close the cantilever against the lightguide operating in the guiding mode and the visible light in the lightguide is leaked into the cantilever using principles of frustrated-TIR.

We finally made used the nano imprinting based surface patterning of biodegradable polymer, PLLA, to modify its surface structure for potential use as a platform as a template to cell growth or drug eluting stents (DESs). Nanoscale patterns in the PLLA surface for use in DES can tailor the drug elution profile to maintain the optimum release kinetics and drug concentration in the affected tissues.