Mechanical Engineering

May 16, 2024 (Thursday) 4:30-5:30pm
In the era of the Internet of Things, portable electronic technology can help citizens to avail advanced features and characteristics in different facets of their daily life. These electronics powered by energy storage devices need regular recharging, but the increasing demand for continuous operation is driving research into new power supplies that can deliver stable electricity. One major development has been a conceptual shift away from grid supply charging toward self-charging. Triboelectric nanogenerators (TENGs) are emerging as a power supply for self-charged electronics due to their lightweight, simple fabrication, diversity in material selection, and high energy conversion efficiency, but the power output of TENGs needs to be trimmed to stably power the electronics. In this talk, I will address several strategies for power management of TENGs to achieve high-performing self-chargeable electronics, including current output boosting, ion-assisted contact electrification, and energy storage control.

March 28 2024 (Thursday) 4:30-5:30pm
Over the last decades, small-size multi-copter unmanned aerial vehicles (UAVs) have received intensive research interests. These UAVs have shown promising potential for various applications, including aerial photography, farming, delivery, mapping, and surveying. However, for these applications to be successful, autonomous flights in unknown environments are necessary. In this talk, we will discuss our work on developing autonomous UAVs using lidar navigation. Specifically, we will explore recent advancements in lidar technologies and focus on navigation algorithms, including localization, mapping, planning, and control. We will showcase how lidar sensors can be utilized on small UAVs to enable complex navigation tasks, such as high-speed flight navigation, environment exploration, and estimation of agile UAV motion.

March 14 2024 (Thursday) 4:30-5:30pm
Swimming at microscales encounters stringent physical constraints due to the dominance of viscous forces over inertial forces. Swimming microorganisms have evolved their flexible appendages to overcome these constraints to swim effectively. These natural swimmers also developed versatile navigation strategies to explore their surroundings and search for specific targets. Extensive efforts in the past few decades have sought to elucidate underlying physical principles for cell motility, which has inspired a variety of designs for artificial microrobots. In this talk, I will discuss two problems of microswimmers in biological and artificial systems. I will first discuss the biophysical mechanisms through which swimming microorganisms sense and navigate their surroundings. I will then discuss the application of artificial intelligence in the development of intelligent microrobots that can self-learn how to swim and navigate at the microscale.

February 29 2024 (Thursday) 4:30-5:30pm
Fluids are ubiquitous in nature and transport of fluids plays an essential role in sustaining many activities across multiple scales. The mode of fluidic transport therefore also spans multiple length scales. Moreover, despite largely aqueous in nature, natural fluids exhibit complexity, dynamics and structures that have yet to be replicated synthetically. In this talk, I will share our works in designing approaches to form, manipulate and direct aqueous solutions. In particular, I will focus on unique properties of aqueous multiphase systems that may serve as model systems for understanding their natural counterparts. I will conclude by discussing how these systems can potentially inspire biomimetic and biomedical applications.

Photonic platforms with multiplexing capabilities are of profound importance for high-dimensional information processing. In this talk, Professor Nicholas X. Fang will present their recent effort on advancing scalable nanoprinting methods compatible with nanophotonic computing platforms. In the first part, Professor Nicholas X. Fang will discuss an efficient and cost-effective grayscale stencil lithography method to achieve material deposition with spatial thickness variation, for spatially resolved amplitude and phase modulation suitable for flat optics and metasurfaces. The design of stencil shadow masks and deposition strategy offers arbitrarily 2D thickness patterning with low surface roughness. The method is applied to fabricate multispectral reflective filter arrays based on lossy Fabry–Perot-type optical stacks with dielectric layers of variable thickness, which generate a wide color spectrum with high customizability. Grayscale stencil lithography offers a feasible and efficient solution to overcome the thickness-step and material limitations in fabricating spatially thickness-varying structures. In the second part, they show that selective ion doping of oxide electrolyte with electronegative metals shows promise to reproducible resistive switching that are critical for reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. They validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of alumina and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.