Ultra-Miniaturized Planar Absorbing Metamaterial Structures for Millimeter Wave and Terahertz Imaging Array

In this paper two metamaterial structures are presented for the design of millimeter and terahertz (THz) bolometers. The first design is composed of U-shaped resonant structures grouped together to achieve strong absorption and wide-bandwidth properties. The second design is a hybrid between a serpentine and a spiral structure which provides strong absorption over a much wider bandwidth (> 100 GHz). The unit cell size for the U-shaped structure and the hybrid unit cell structure are 360 mm and 194 mm in size, respectively. These are much smaller than the operating wavelength (3mm at 0.1 THz). Simulations were performed using commercial finite element (FEM) method. These structures were fabricated using Nickel metal on a flexible polyether ether ketone (PEEK) substrate. Nickel has low conductivity and thus provides high conductivity loss due to skin loss effect. Bolometer pixel elements having different number of unit cells were fabricated and tested. The bolometer elements were integrated with 3D printed plastic microlens array to enhance sensitivity. It was determined that few unit cells having effective size much less than a wavelength is sufficient to design a high sensitivity bolometer when coupled with microlens. Thus, the use of large antenna sizes can be avoided in the design of THz focal plane arrays.