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Tuesday, October 29th, 3:30-4:30 PM

Physics Building, Room 104

Richard Zihao Zhang

University of North Texas

Abstract

Under the duress of extreme environments, radiative heat transfer coatings can serve as thermal regulators of habitats, vehicles, electronics, and personal comfort devices. With advancements in nanomaterials and micromanufacturing, high performance, tunable, and resilient coatings can be made possible. Using electromagnetic wave calculation methods, frontier optical materials properties, and state-of-the-art microfabrication and synthesis techniques, we present ways to create multi-functional thin films and periodic metasurfaces that simultaneously passively regulate radiative thermal transport and provide protection in real-world environments.

We showcase diverse works of at- and sub-wavelength gratings that trigger plasmonic or guided mode resonances. In early works, we investigated theoretical formulations of a folding ‘origami’ graphene sheet over narrowband emission metal gratings that are narrow and deep to support magnetic plasmon-polaritons. This work led to a new LC circuit model analogy and morphology-tunable resonance emission frequency peak shifts. We also identified aligned nanowire arrays of a reversible near-room temperature metal-insulating phase transition Vanadium Dioxide (VO2) to produce record-high passive infrared emissivity contrast. Other phase transition oxides studied that are electrically or thermally tunable include Nb2O5, MoO3, and Ti2O3. These phase transition oxides can switch on-and-off between narrowband emission and broadband reflection by a Bloch mode Zero-Contrast Grating design. This concept of Contrast Gratings, including High-Contrast and Zero-Contrast Gratings, has been identified as a secondary Fabry-Perot round-trip interference mode for broadband infrared reflectance and transmittance. We combined a Fabry-Perot multilayer thin film with Contrast Gratings to achieve broadband and hemispherical reflectance exceeding that of underlying metal mirrors. This ‘super mirror’ can be applied to superior thermal radiative insulation, especially in spacecraft blanket insulation. We recently showcased Bayesian optimization, genetic algorithms, and deep neural network AI/ML schemes to obtain best grating and materials parameters for achieving optimal high performance thermal radiative coatings. Our research and educational activities can impact the development of safe and energy-efficient thermal regulation surfaces used in not only spacecraft devices, but also for buildings, automobiles, clothing, and the environment.

 Bio

Dr. Richard Zihao Zhang is an Associate Professor of Mechanical Engineering at the University of North Texas specializing in nano/micro-technology thermal management, materials synthesis, device fabrication, and spectroscopic measurement. Dr. Zhang received his S.B. in Mechanical Engineering from Massachusetts Institute of Technology, and M.S. and Ph.D. in Mechanical Engineering from Georgia Institute of Technology. Prior to UNT, he was a Member of Technical Staff at the Aerospace Corporation in El Segundo, California. His research has been sponsored by the U.S. Air Force Office of Scientific Research, U.S. Army Research Office, Los Alamos and Sandia National Research Laboratories’ Center for Integrated Nanotechnology, and National Aeronautical and Space Administration (NASA). He was a faculty fellow at Air Force Research Laboratory. Dr. Zhang is an organizing member of the American Society of Mechanical Engineers (ASME).

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