SOFT-FOCUSING IN ANISOTROPIC INDEFINITE MEDIA THROUGH HYPERBOLIC DISPERSION

Abstract

Materials that exhibit negative refraction may have many novel applications. We seek to evaluate the possibility of soft-focusing of microwave signals using a medium with an indeflnite (hyperbolic) anisotropic permittivity tensor. We fabricated a 147mm thick and 220mm wide Styrofoam sample with an embedded array of 12-gauge brass wires of 6.35mm lattice spacing. Two single-loop antennas were used to approximately generate a transverse magnetic (TM) point source and the associated detector. Using an Agilent 8510C Vector Network Analyzer (VNA), the frequency spectrum was scanned between 7 and 9GHz. Relative gain or loss measurements were taken at equal spatial steps behind the sample. A scanning robot was used for automatic scanning in the x, y, and z directions, in order to establish the focusing patterns. The signal amplitudes measured in the presence and absence of the sample were compared. The robot was controlled using LabVIEW y , which also collected the data from the VNA and passed it to MATLAB z for processing. A soft focusing spot was observed when the antennas were placed in two difierent symmetric conflgurations with respect to the sample. These results suggest a method for focusing electromagnetic waves using negative refraction in indeflnite (hyperbolic) anisotropic materials.