We demonstrate a new method for realizing modified Luneburg lens antennas with nearly continuously graded permittivity profiles in three‐dimensions. The method used a quasi‐conformal transformation optics (QCTO) approach to modify the geometry and permittivity of a spherical Luneburg lens to have a flat surface for convenient integration of antenna feeds. The modified lens was then fabricated using Fused Deposition Modeling (FDM) printing with an effective media approach that employs space‐filling curves. The method was validated by designing and fabricating a modified Luneburg lens antenna designed to operate in the Ka‐band. The antenna performance of the sample was measured experimentally and shown to compare well to predicted results using full wave simulations. The device was able to achieve a reasonably high degree of beam steering (ie, −55° to +55°) over the entire Ka‐band. We believe this new approach provides a cost‐effective and scalable means of realizing practical passive beam steering lenses that operate over a broad range of frequencies.
Conjugated polymers (CPs) undergo a wide range of reversible intrinsic property changes including electrical conductivity, electromagnetic absorption, volume, and charge mobility upon electrochemical oxidation/reduction, which has made them popular as ON/OFF organic-based switchable materials. Recent studies on the insulating-to-conductive transition within CPs have paved the way for a next generation of flexible switches that permit the creation of “dynamic” electric circuits. Here, we present an approach to a low-voltage, low-power electrochemically controllable, switchable, and printable CP-based conductive element that acts as a platform for the configuration of frequency-reconfigurable radiative antennas. We demonstrate that the DC conductivity of a soluble PEDOT derivative, PE2, film can be switched electrochemically by 4 orders of magnitude across large insulating gaps up to 15 mm within 20 s. Its integration in a DC switching element that is incorporated along the poles of a half-wave dipole antenna structure is able to generate an AC resonant frequency switch, and thus a radiation frequency shift, in the microwave (i.e., 1–2 GHz) range. This type of printable antenna fills an important need for the demand of bandwidth that is growing beyond the crowded frequency spectrum, by relying on the development of frequency-reconfigurable antenna systems capable of dynamically tuning their spectral properties when desired.
Previous electromagnetic computations of multilayered dielectric/metallic spheres identified the ideal dimensions and composition for achieving optimized mass extinction coefficients ( m 2 / g ). A hollow metallic sphere, with a thin metallic shell, is one such example of a spherical structure that can theoretically achieve high mass extinction coefficients in the long wave infrared (LWIR) region (8–12 µm). To this end, we endeavored to demonstrate a cost-effective and scalable manufacturing approach for synthesizing and experimentally validating the mass extinction coefficients of hollow metallic spheres. Specifically, we detail a novel approach for fabricating hollow aluminum spheres using radio frequency (RF) magnetron sputter deposition. Sacrificial high-density polyethylene polymer microspheres were used as substrates for the deposition of thin layers of aluminum. The core shell structures were subsequently thermally processed to form the hollow micron sized aluminum shells. The mass extinction coefficients of the hollow aluminum spheres were subsequently measured and compared to computational results. A strong agreement between experimental and theoretical predictions was observed. Finally, the LWIR mass extinction coefficients of the hollow spheres were compared to high aspect ratio brass flakes, a common pigment used for LWIR attenuation, and other materials and geometries that are used for LWIR filtering applications. This comparison of both performance and availability revealed that the fabricated hollow aluminum spheres exhibited competitive LWIR properties using a more scalable and cost-effective manufacturing approach.
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