Electrowetting and Its Applications in Adaptive Electronics Cooling, Optofluidic Solar Concentrators and Agile Beam Steering for Automatic Driving

#Solar #Cells #Optofluidics #Beam #Steering

First, we introduce electrowetting-based digital microfluidics for hot spot cooling of electronics systems. In response to the rapid advances in microelectronics, novel cooling technologies are needed to meet increasing cooling requirements. As a paradigm-shifting technique, electrowetting-on-dielectric (EWOD) uses electric potential to control the movement of a liquid droplet on a dielectric surface. We have developed an EWOD-based microfluidic technique for active and adaptive thermal management of on-chip hot spots. A two-dimensional array of control electrodes was patterned on the chip surface for EWOD operations. By applying AC voltages with appropriate sequence and timing to the coplanar electrode units, we are able to transport microdroplets of tens of mL along a programmable path. Without the need of external pumps and valves, the droplets are precisely delivered to cooling targets. With the driving voltage as low as 40 VAC, we demonstrate high heat flux (7.6 W/cm²) cooling on a hot spot. The EWOD-induced internal circulation within the droplets leads to a time-averaged Nusselt number of ~45.

Next, we introduce a novel optofluidic solar concentration system based on electrowetting tracking. With two immiscible fluids in a transparent cell, we can actively control the orientation of fluid–fluid interface via electrowetting. The naturally-formed meniscus between the two liquids can function as a dynamic optical prism for solar tracking and sunlight steering. An integrated optofluidic solar concentrator can be constructed from the liquid prism tracker in combination with a fixed and static optical condenser (Fresnel lens). Therefore, the liquid prisms can adaptively focus sunlight on a concentrating photovoltaic (CPV) cell sitting on the focus of the Fresnel lens as the sun moves. Because of the unique design, electrowetting tracking allows the concentrator to adaptively track both the daily and seasonal changes of the sun’s orbit (dual-axis tracking) without bulky, expensive and inefficient mechanical moving parts. This approach can potentially reduce capital costs for CPV and increases operational efficiency by eliminating the power consumption of mechanical tracking. Importantly, the elimination of bulky tracking hardware and quiet operation will allow extensive residential deployment of concentrated

solar power. In comparison with traditional silicon-based photovoltaic (PV) solar cells, the electrowetting-based self-tracking technology will generate ~70% more green energy with a 50% cost reduction.

Last, we introduce reconfigurable beam steering components, which are indispensable to support optical and photonic network systems operating with high adaptability and with various functions. Currently, almost all such components are made of solid parts whose structures are rigid, and hence their functions are difficult to be reconfigured. Also, optical concentration beam steering is still a very challenging problem compared to radio frequency/microwave steering. Here we show a watermill-like beam steering system that can adaptively guide concentrating optical beam to targeted receivers. The system comprises a liquid droplet actuation mechanism based on electrowetting-on-dielectric, a superlattice-structured rotation hub, and an enhanced optical reflecting membrane. The specular reflector can be adaptively tuned within the lateral orientation of 360°, and the steering speed can reach ~353.5° s⁻¹. This work demonstrates the feasibility of driving a macro-size solid structure with liquid microdroplets, opening a new avenue for developing reconfigurable components such as optical switches in next-generation sensor networks and LIDAR system for automatic driving.