| Frequency selective surfaces (FSSs) are planar, periodic arrays of conducting patches on a substrate and/or superstrate or a periodic array of apertures in a conducting sheet used to filter electromagnetic waves [1]. Many metals used in FSSs behave essentially as perfect electric conductors for microwaves, but possess finite, dispersive, complex valued conductivity at higher frequencies.; The finite difference time domain (FDTD) method is adapted to accommodate the properties of real metals in the mid-infrared and used to study several properties of FSSs. The first study demonstrates that under plane wave illumination, waves leaving a FSS are plane waves after traveling only a short distance.; Next, the effects of real metals in FSSs operating in the infrared is examined. One new finding is that the spectral properties of a FSS depend not only on the geometry of the structure and the dielectric properties of any substrates and/or superstrates that are present, but also on the metallic species used for the conductors.; FSSs with multiple elements in the unit cell are then considered. These structures have been studied previously [2], but here the role of mutual induction between the elements in determining the spectral properties is examined.; Finally, the spatial distribution of conduction current density on capacitive and inductive FSSs is examined. Conduction current density is present throughout the real metal portions of these structures. The current density on the back surface of a capacitive FSS is similar to that on the front or illuminated surface. Conduction current density is also found on the front and back surfaces of an inductive FSS, but with significant differences. Conduction current density flows in the same direction as the electric field of the illuminated or the front of the FSS, but in the opposite direction on the back and looping currents between the front and back surfaces are observed for inductive FSSs.; [1] R. Ulrich, "Far-infrared Properties of Metallic Mesh and its Complementary Structure", Infrared Physics, 7, (1967): 37-55. [2] J. A. Reed, "Frequency Selective Surfaces with Multiple Periodic Elements", (Ph.D. diss., University of Texas at Dallas, 1997). |
