Design and Fabrication of a Radio Frequency GRIN Lens Using 3D Printing Technology

Abstract

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information SPONSORING/MONITORING AGENCY ACRONYM(S)AFRL/RYMH SPONSORING/MONITORING AGENCY REPORT NUMBER(S)AFRL-RY-WP-TR-2013-0059 DISTRIBUTION/AVAILABILITY STATEMENTApproved for public release; distribution unlimited. SUPPLEMENTARY NOTESPAO Case Number 88ABW-2013-1345, Clearance Date 20 March 2013 . Report contains color. ABSTRACTElectromagnetic media and metamaterials have been explored in frequency regimes ranging from the acoustic to the visible domain over the past decade. Here we present the design of a focusing GRadient INdex (GRIN) lens to operate at RF frequencies that is not polarization constrained. We compare theoretical and experimental results from this lens designed to operate at X-band and fabricated using 3D printing technology. The lens with radially varying refractive index gradient was designed, optimized and analyzed by conducting full-wave simulations finite-element method based software Ansoft HFSS®. The design was fabricated and experimentally results are compared to the performance of the theoretical design. SUBJECT TERMS List of FiguresFigure Page SUMMARYElectromagnetic media and metamaterials have been explored in frequency regimes ranging from the acoustic to the visible domain over the past decade. A large part of the design, fabrication and prototyping of such materials has focused on planar structures and devices have been demonstrated primarily for certain propagation directions and/or defined polarization. Here, we present the design of a focusing GRadient INdex (GRIN) lens that operates at radio frequency (RF) frequencies and is not polarization constrained. We compare the theoretical and experimental results from this lens designed to operate at X-band and fabricated using three dimensional (3D) printing technology to implement the effective medium. The lens with radially varying refractive index gradient was designed, optimized and analyzed by conducting full-wave simulations finite-element method based software. The permittivity was estimated by effective medium theory and calculated using HFSS®. The optimized design was used to fabricate the GRIN lens with isotropic, inhomogenous dielectric material. The refractive index was designed to match the theoretical results using mixing ratio of air/voids and a polymer. Further, we used the refractive index profile to predict the rays' trajectories and focus length to compare them to those predicted by the finite element method (FEM) simulations. The field distributions were also analyzed to compare performance of the theor...