This study investigated MXene ink as the absorbing material in a wideband millimeter wave (MMW), metasurface absorber and applied the ink in a periodic array. The MXene ink was characterized in the Ka-band, and a Debye permittivity model was found that accurately described the highly frequency-dependent properties. A 1-bit coding-metasurface algorithm was used to discover an optimized design that minimized the average reflectance at normal incidence, utilizing the unique properties of the materials. The absorber was fabricated using hybrid processing techniques and measured at multiple incident angles to compare against the simulated design. The absorber demonstrated a wideband response (i.e., 14 GHz bandwidth) at normal incidence with a greater than 93% absorptance from 26 GHz to 40 GHz and an average reflectance of 2% over the entire band. Furthermore, the absorber tested at a 10-deg incident angle demonstrated a greater than 91% absorptance at the Ka-band and an average reflectance of 3.4% across the band; Tested at a 20-deg incident angle, the absorber demonstrated a greater than 88.5% absorptance and an average reflectance of 3.9% across the band. The study established the value of using MXene ink in metasurface absorbers for wideband applications in MMW frequencies.
Recent improvements in microparticle synthesis and handling have prompted new research into the engineering and fabrication of single and multilayered microspheres through traditional physical and chemical vapor depositions. At the University of Delaware, we have developed a custom batch coating process utilizing a vibro-fluidized mixing vessel to deposit thin-films onto the surface of microparticle substrates through R.F. magnetron sputtering. This process opens up a number of design possibilities for single and multilayered microsphere technologies that can be used to improve the optical performance of several optical filtering applications. Through the use of custom design and simulation software, we have optimized a number of filter designs and validated these findings through commercial software. Specifically, we have aimed to improve upon the mass extinction performance seen by traditional materials in the long wave infrared spectrum (LWIR, λ=8-12μm). In order to do this, we have run a series of experiments aimed at creating ultra-lightweight metallic hollow-spheres. Aluminum thin-films have been successfully deposited onto a number of substrates including hollow glass microspheres, high density polyethylene microspheres, and polystyrene foam spheres. By depositing the thin-films onto polymer substrates we have been able to remove the solid core after deposition through a thermal decomposition or chemical dissolution process, in an effort to reduce particle mass and improve mass extinction performance of the filter. A quantum cascade laser measurement system has been used to characterize the optical response of these fabricated aluminum hollow-spheres and have largely agreed with the expected simulated results.
As infrared (IR) imaging technologies improve for the commercial market, optical filters complementing this technology are critical to aid in the insertion and benefit of thermal imaging across markets of industry and manufacturing. Thermal imaging, specific to shortwave infrared (SWIR) through longwave infrared (LWIR) provides the means for an observer to collect thermal information from a scene, whether being temperature gradients or spectral signatures of materials. This is beneficial to applications such as chem/bio sensing, where the identification of a chemical species being present or emitted could compromise personnel or the environment. Due to the abundant amount of information within an environment, the difficulty lies within the observer’s ability to extract the information. The use of optical filters paired with thermal imaging provides the means to interrogate a scene by looking at unique infrared signatures. The more efficient the optical filter can either transmit the wavelengths of interest, or suppress other wavelengths increases the finesse of the imaging system. Such optical filters can be fabricated in the form of micro-spheres, which can be dispersed into a scene, where the optical filter’s intimate interaction with the scene can supply information to the observer, specific to material properties and temperature. To this extent, Lumilant has made great progress in the design and fabrication of such micro-sphere optical filters. By engineering the optical filter’s structure, different optical responses can be tuned to their individual application.
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