Collaborative Research: Liquid Metal Tuned Flexible Metasurfaces

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Nontechnical:Optical windows such as lenses in prescription glasses are reasonably customizable. Lenses can vary in size, shape, curvature, or design. In addition to aesthetic features, the functionalities and overall packaging can also be modified or upgraded. For example, anti-reflective coatings can be added to reduce glare and photochromic lenses suppress light transmission on exposure to ultraviolet radiation. These optional features have minimal impact on physical properties since such coatings add less than a millimeter of thickness. Microwave windows can be considered as a type of optical window that functions in the microwave spectrum. As with optical windows, microwave windows are made to transmit, reflect, or absorb electromagnetic waves. Microwave windows are indispensable components in systems such as radomes (enclosures that protect a radar antennas) and shields that reduce electromagnetic interference. Unlike optical windows, current design techniques do not lend much freedom to customize both functional and physical characteristics of the microwave windows. For example, practical microwave windows that are flexible, thickness customizable, and can tune the transfer response on-demand in real-time remain to be realized. This project will exploit new techniques that can be applied to realize liquid metal enabled tunable and mechanically flexible multi-layered microwave windows. The proposed device will be made by integrating movable liquid metals that can provide a wide tuning range with minimal loss. The resulting concept can be adapted to all types of filters, delivering unprecedented design control in the implementation of multi-layered tunable/flexible microwave windows. The educational and outreach plan focuses on students from underrepresented groups, integrating research findings into classroom courses taught by the PIs and developing active collaboration with industry.Technical:The objectives of this proposal are to study new theoretical foundations and explore the potentials and limitations of liquid metal tuned mechanically flexible (bendable/foldable) metasurfaces. The technical approach relies on adopting a multi-layer metasurface synthesis technique based on thickness customizable intercoupling layers that behave as admittance inverters. The proposed liquid metal tuned mechanically flexible metasurfaces consist of gallium-based liquid metal slugs in polydimethylsiloxane (PDMS) microfluidic channels as moveable tuning elements and another gallium alloy filled in specific metasurface pattern as fixed metal. These liquid metal slugs will be made oxide free and freely movable in the microfluidic channel. Thus, the position of the moveable liquid metal slug train in a large 2D array metasurface can be tuned pneumatically with high precision. The reconfigurable property makes microwave windows attractive for a wide range of applications that demand controllable/stable high-frequency response when operated under a dynamic EM environment. When combined with the flexibility feature, the new technology can revolutionize the use of next-generation microwave windows by enabling deployable, transportable, and conformable metasurfaces that can be tuned on-demand, in real-time. The end result is a significant scientific leap in metasurface technology and establishment of the principles and the feasibility of new technologies for future metasurface-based devices and systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.