Far-infrared properties of metallic mesh and its complementary structure

The optical properties of thin metallic mesh (“inductive” grids) are compared theoretically and experimentally with the properties of the complementary structure (“capacitive” grids). Close interrelations are found. In the non-diffraction region (wavelength > grid constant), the optical properties of both types of grids can be described by simple transmission line equivalent circuits. The circuit parameters are determined as functions of the dimensions of the grids. This representation allows a fairly accurate calculation of interference filters consisting of two or more grids of either type. The new capacitive grids may be used advantageously in interference filters with non-harmonic lying orders, in filters with strongly differing peak transmissions, and in effective low-pass filters in the very far-infrared.