OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Integrated Sensing and Cyber OBJECTIVE: Design and build an electrically thin electromagnetic (EM) skin to absorb, scatter, and change the polarization of undesirable radio frequency (RF) radiation providing spectrum camouflage for Army antennae and radar systems. The objective of this SBIR is to utilize novel EM skins by adding RF functionality to create a Smart Radome surface to apply to airborne platforms or Smart Munitions. DESCRIPTION: We define an Electromagnetic (EM) skin as a thin layer of radio frequency (RF) components and/or periodic structures conformed to an Army platform that manipulate radiation or scattering parameters. Thin EM skins will occupy areas designed and shaped primarily for mechanical and environmental functions. One example is an antenna radome which is a protective enclosure surrounding an antenna. The radome is made of a material that minimally attenuates transmit and receive signals from the enclosed antenna. Many applications, such as airborne platforms or Smart Munitions, use curved radomes and must maintain performance under extremely harsh environments (i.e., high velocity and high acceleration conditions). Application requirements will impact the size and geometrical shape of the radome, and these requirements may cause a noticeable radar cross section (RCS) signature. An EM Skin can exist on the surface of such a radome as a frequency selective surface that allows desirable frequencies to penetrate the radome while absorbing undesirable bands to greatly reduce undesirable RF scattering. Additional functions these EM skins may perform include beamforming, transceiver operation, deception through signal polarization conversion, transmit signal coding, and anti-jamming operations. The added functionality creates a SMART Radome which performs important RF functions in addition to its original purpose of protecting the enclosed antenna. This can't be done with conventional materials while maintaining the mechanical and aerodynamic properties of Army platforms. This SBIR will address two important topics to produce a functional Smart Radome utilizing an EM skin. First is the design of electronic RF components and subsystems that produce the EM skin's required RF functionality. These RF components must fit within the thin bounds of the skin which will be on the order of 5 mm or less. The second topic of study is the mechanical, thermal, and environmental aspects of integrating the EM skin onto selected Army platforms. A major concern is the stability of EM performance on conformal platforms, airborne drag effects, and the extreme thermal and high-G conditions of munitions. Both topics must be addressed before considering the integration of SMART Radomes onto airborne platforms or munitions. PHASE I: In Phase I, the investigation shall explore the underlying technologies used to enable an EM skin within the frequency range of 2-18 GHz. The EM skin should enhance EM radiation while mitigating internal reflections for desirable frequency bands, and act as a scatterer or absorber of undesirable frequencies. The end of Phase I should produce several outcomes in the range of TRL 2-3. (1) Simulation study of the interactions and coupling between different RF components/subsystems in both planar and conformal aspects of an EM skin. (2) Determine how the chosen RF components affect the conformal, mechanical, thermal and environmental aspects of integrating the EM skin onto an airborne radome. (3) Full system simulation of the EM skin design on a representative Smart Radome surface including S-parameter performance and transmit/receive radiation performance of the EM skin. (4) A proof-of-concept prototype of a single unit cell of the EM skin with measured S-parameter and radiation performance. (5) The performer will provide a final report detailing the technology developed and its performance based on simulation and measured results. PHASE II: The end of Phase II should produce several outcomes in the range of TRL 4. (1) Prototype a flat EM skin prototype based on the unit cell demonstrated in Phase I. The performer should measure the S-parameter and radiation performance of the EM skin. (2) Integrate a conformal EM skin prototype onto a representative curved Smart Radome surface. The performer should measure the S-parameter and radiation performance of the EM skin. (3) Determine the feasibility of integrating multiple layers of EM skins on top of one another either to enable two separate RF functionalities or to extend the bandwidth of the original EM skin design. Provide simulation results demonstrating the increased functionality of a multi-layer EM skin. (4) Prototype a flat EM skin unit cell incorporating the multi-layer configuration. The performer should measure the S-parameter and radiation performance of the EM skin. (5) The performer will provide a final report detailing the technology developed and its performance based on simulation and measured results. PHASE III DUAL USE APPLICATIONS: At the end of the SBIR, the performer should be well positioned to transfer their EM skin and Smart Radome technology to both military and commercial applications. An electrically thin surface with built-in RF functionality would be of great interest to both military and commercial airborne applications. Replacing large radiating structures on the surface of an airborne platform has mitigating effects on drag reducing fuel consumption and lowering the overall cost of air flight. For military applications there is also the possibility to control out of band RF absorption. For SMART Munitions, the EM skin design would be easy to alter to provide geolocation and or RF sensing. REFERENCES: 1. Nguyen, Q. and Zaghloul, A.I., 2020, July. Design of beam steering patch arrays using self-phased metasurface pixels. In 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting (pp. 909-910). 2. Hodge, J.A., Nguyen, Q.M. and Zaghloul, A.I., 2020. Reflective beam steering of metasurface using circular inter-digitated self-phased pixels/cells. In 2020 General Assembly and Scientific Symposium of the International Union of Radio Science (pp. 1-4). 3. Hu, J., Bandyopadhyay, S., Liu, Y.H. and Shao, L.Y., 2021. A review on metasurface: from principle to smart metadevices. Frontiers in Physics, 8, p.586087. 4. Tahseen, H.U., Yang, L. and Zhou, X., 2021. Design of FSS-antenna-radome system for airborne and ground applications. IET Communications, 15(13), pp.1691-1699. KEYWORDS: Electromagnetic (EM) skins, Smart Radome, metamaterials/metasurfaces, RF scattering
