Mechanical Engineering

October 9, 2025 (Thursday) 4:00pm-5:00pm
Improving indoor air requires addressing source control, ventilation, and filtration. This presentation explores filter performance from both aerosol science and building science perspectives with a focus on how theoretical and laboratory-tested filtration efficiencies translate to filtration performance in real buildings. The removal of particulate matter is only part of the filtration story. Filters also have a variety of secondary consequences including emissions of gas-phase compounds and complicated impacts on energy use. Some of these secondary effects may have a positive impact, including the ability of filters to offer insight on air quality through filter forensics, the analysis of the particles that accumulate on the filter. Several examples of filter forensics for disease surveillance, exposure assessment, and ambient air quality are used to illustrate the hidden value in used filters. The COVID-19 pandemic further increased the attention paid to central and portable filtration in buildings and this presentation assesses new challenges and opportunities that arise from this renewed focus.

June 27, 2025 (Friday) 4:30pm-5:30pm
This talk will present the latest advancements from Professor Chan’s research team and his startup company Brainsmart, dedicated to developing minimally invasive brain-computer interface (BCI) technologies for stroke rehabilitation and neurological recovery. His team focuses on flexible neural probes and high-density ECoG arrays that can be implanted without craniotomy, offering safer options for high-risk patients. Professor Chan will highlight their recent results in decoding neural signals related to hearing perception and motor intentions, and discuss how these findings contribute to future neuroprosthetic applications. The talk will also cover our pathway from technology development to clinical translation, aiming to enhance functional recovery and quality of life for patients.

December 19, 2024 (Thursday) 4:30-5:30pm
To enhance the thermoelectric conversion efficiency of materials, the thermal conduction needs to be suppressed, and the lattice dynamics and the thermal transport mechanisms must be better understood. Lattice thermal conduction of conventional solids is dominated by phonon propagation; however, diffuson-like thermal transport can become predominant in materials with ultralow thermal conductivity. New strategies for a simultaneous suppression of both propagative and diffusive thermal transports will be discussed in this talk based on state-of-the-art theories. Zintl compounds were recently found to exhibit exceptional thermoelectric properties. A thorough experimental study of the thermoelectric transport and carrier properties of Zintl compounds will be discussed. It will be shown that a high figure of merit over a broad temperature range can be realized through the suppression of the intrinsic carrier excitation.

November 28, 2024 (Thursday) 4:30-5:30pm
Structural colors use nanostructured building blocks or thin films to resonantly reflect or scatter light to generate colors and can exhibit higher resolution, saturation, and durability than pigment-based colors. To create structural color based paintings, it is essential to develop a capability of spatially varying the dimensions of these nanosized structures. Recently we reported a high-throughput and wafer-scale nanopatterning method by combining interference lithography and grayscale-patterned secondary exposure (IL-GPSE) to spatially modulate nanostructure feature sizes on large scale while maintaining sufficiently high resolution. Here, we employ the IL-GPSE method in the fabrication of wafer-scale structural color paintings, which can improve the patterning efficiency by orders of magnitude when compared with e-beam lithography. The fabrication techniques developed in this work have unique potentials for broader applications in biomedical sensing, spectral filtering, anti-counterfeiting or encryption, etc.

January 9, 2024 (Thursday) 2:30-3:30pm
We demonstrate that grain boundaries (GBs) behave as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under oscillatory driving forces or cyclic thermal annealing. We observed these phenomena for nearly all nonsymmetric GBs but not for symmetric ones. Our observations build on molecular dynamics and phase-field crystal simulations for a wide range of GB types and driving forces in both bicrystal and polycrystalline microstructures. We corroborate these simulation results through in situ experimental observations. We analyze these results with a Markov chain model and explore the implications of GB ratchet behavior for materials processing and microstructure tailoring.

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.