Mechanical Engineering

TechTalk – Toward A Self-Chargeable Power Module for the Internet of Things

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.

Young Scholar TechTalk – On Causality and the Upper Limit of Sound Absorption

April 30 2024 (Tuesday) 4:30-5:30pm
Sound absorption across a wide range of frequencies is a focus in contemporary acoustics. Recently, integral bounds of absorption or reflection coefficients were introduced as a guide of design optimization following the footsteps of electromagnetics, where integral relations were derived based on system causality considerations. This talk carefully examines the proper formulation of physical causality and its implications on the scattering properties of the system. Taking into consideration the effects of different physical boundary conditions and the bulk absorber material, a more generalized integral bound is derived. It becomes evident that, while the bound exists, it is governed by system stiffness rather than the causality constraint. By studying the effects of various approximations made during mathematical derivations, the physics of the bound is thoroughly discussed, and the limitations in utilizing integral bounds as reference for design optimization are highlighted. The findings are expected to have significant implications for the development of effective noise reduction strategies and the advancement of smart acoustic design.

TechTalk – UAV Navigation and Mapping with Light Detection and Ranging (LiDAR) Sensors

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.

TechTalk – The World at the Microscale: From Swimming Microorganisms to Artificial Microrobots

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.

Young Scholar TechTalk – Customizable Acoustic Metamaterials on Frequency and Spatial Dimensions

March 12 2024 (Tuesday) 4:30-5:30pm
Acoustic metamaterials are artificially designed structured ‘atoms’. Initially, scientists discovered that these meta-atoms can exhibit extraordinary properties beyond those found in natural materials, such as negative density and negative modulus, through localized resonance, which sparked significant interest in the academic community. Subsequently, it was confirmed that these unique narrow-band frequency responses can be extended to broadband impedance designs, leading directly to the emergence of absorption metamaterials and opening up large-scale applications in noise reduction. In recent years, the potential of customizable metamaterials has gradually been realized. We will present our latest works from two complementary perspectives: customized frequencies and spatial non-uniformity, which may open up new applications such as directional emission, stealth cloaking and automotive acoustics.

TechTalk – Nature-Inspired Fluidics

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.

TechTalk – Biomimetic Soft Materials for Bio-Integrated Smart Devices

Biological tissues are soft, dynamic, and water-rich, while abiotic tools are typically rigid, static, and dry. These differences in physical properties have presented challenges for the development of advanced biomedical systems that require interfacing with the human body. In this presentation, I will introduce our recent work on biomimetic soft composites as a platform for engineering bio-integrated devices that can potentially bridge this gap. These synthetic materials capture important structural features of natural soft tissues and exhibit tissue-mimetic reconfigurability, robustness, and functionality, making them advantageous for constructing bio-interfaces. Soft electronic components were also integrated into the biomimetic materials platform, enabling multifunctional systems for physiological sensing and targeted stimulation. Examples of these smart biomedical tools include artificial cartilage and tendons, electroconductive hydrogels, and organ-integrated 3D electronics, which create exciting opportunities in advanced biomedicine.

TechTalk – A “Programmable” Cell Niche Engineering Platform – Multiphoton Microfabrication and Micropatterning (MMM) Technology

In native tissues, cells reside in a complex microenvironment (niche) consisting of factors including neighbor cells, soluble factors, extracellular matrices, topological and mechanical signals. Cell niche is critical in maintaining their phenotype and determining their fates and functions. Reconstituting complex cell niche factors in vitro, either individually or in combinations, in a quantitatively and spatially controllable manner, is critical for investigating the interactions between cells and their niches and hence deriving designing strategies for optimal conditions during cell culture applications and optimal scaffolds for tissue engineering applications. Our lab has developed a multiphoton microfabrication and micropatterning (MMM) technology. Here, the technical capability of the MMM platform in fabricating complex protein microstructures and micropatterns with pre-designed topological features, mechanical properties, extracellular matrix, cell interaction molecules and soluble factors, and biomedical applications including cell niche factor screening for phenotype maintenance and engineering cell niche for cell fate determination will be discussed.

Young Scholar TechTalk – High-throughput Cell Mechanics Characterization with Microfluidics

Cells can sense mechanical stimuli and convert them to biochemical signals for various specific cellular responses, such as stem cells differentiation, initiation of transcriptional programs, and cell migration. Cell mechanics focuses on the mechanical properties and behaviours of living cells and how cell mechanics relates to various cell functions. Currently, traditional cell mechanics measurement methods are cumbersome, low-throughput, and expensive to deploy. By exploiting microfluidic technology, Dr. Johnson Cui is investigating the cancer cell mechanics and developing an accurate, easy-to-use cell mechanics measurement platform for cell mechanics research and also for cancer diagnosis and therapeutics in the future.

TechTalk – Scalable Nanoprinting for Nanophotonics Computing Platform

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.