Moiré effect studies at thermal frequencies
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Moiré patterns arise from the superposition of two (or more) periodic structures (one-dimensional or two-dimensional) defined over flat (or curved) surfaces in which one (or more) is rotated, translated, or any form of altercation from the initial position. This results in a series of periodic dark/bright fringes which characteristics are determined by the period, orientation, and shape of the patterned samples. When two arrays of similar periods are superposed, the period of the resultant pattern acts like a magnifier of the original period. The Moiré effect has been used in different areas which includes microscopy, cryptography, profilometry, and material stress evaluation. Most of the applications, however, were carried out at optical frequencies. In this work, we performed studies on the generation of Moiré patterns at thermal frequencies (f ~ 20-40 THz) using the superposition of metallic arrays of two-dimensional structures with different periods and lattice configurations. Thermal imaging experiments revealed that the period of the superposed structures can be significantly modified as the angle between patterns is varied. A combination of samples with different features and dimensions resulted in Moiré patterns with period and lattice geometries very different from the individual patterns. The obtained results can be prospectively used to deploy reconfigurable metamaterials frequency selective filters for operation at thermal frequencies.