Investigation of Robust Flexible Conformal THz Perfect Metamaterial Absorber J.H. Kim, M. P. Hokmabadi, S. Balci, E. Rivera, D. S. Wilbert, P. Kung, and S. M. Kim * Department of Electrical and Computer Engineering, University of Alabama, Tuscaloosa, AL 35487, USA * Corresponding author: seongsin@eng.ua.edu Abstract-The flexible metamaterials have promised to greatly expand our ability to realize a wide range of novel applications including new methods of sensing and cloaking. Although a few work related to the flexible metamaterials with THz frequency selective surfaces already have been reported, their ability as a thin film absorber needs to be verified in the real world application. Thus, we performed a new experiment for the robust flexible THz frequency perfect absorber, which was fabricated as a combination of multilayer polyimides and multilayer frequency selective surfaces, which works for dual-band absorption, on various 3D printed conformed surfaces. The Terahertz (THz) spectral region remains a scientifically rich but yet technologically underdeveloped research area. An unfortunate hurdle is the difficulty to efficiently generate, detect, and control the propagation of radiation at THz frequencies. An emerging class of materials, consisting of an effective medium made of arrays of subwavelength elements carefully engineered to exhibit a desired electromagnetic response, known as metamaterials, shows great promise for improving our ability to utilize THz frequency radiation [1]. In particular, flexible metamaterials offer many benefits, including the ability to be conformed on non-uniform surfaces while maintaining a high degree of functionality, which makes them suitable for a wide variety of sensing applications such as cloaking [2]. In this work, we intended to have a robust and flexible perfect absorbent metamaterials that works for semi-realistic rough (conformal) surface at THz frequency. To do that, we have fabricated a frequency selective surfaces (FSS) unit cells consisted of two different sized, nonconcentric, out of plane copper rings using standard photolithography, and achieved different resonant frequencies depending on the position of the rings Detailed of the simulation, fabrication and measurement has been reported in our previous work [3]. Those are separated by a dielectric spacer on a 50m thick polyimide film on top of a conduction ground plane as shown in the Fig. 1 (a), (b), (c). Inset for Fig. 1.shows actual thin and flexible devices fabricated. To describe the semi-rough surface, we have attached this device on top of three-dimensional conformal surface by using specially designed holder to use vacuum force. To realize the micro-scale 3D conformal structure, 3D printing technology was used to design and create hemisphere and cylindrical features, on which the flexible THz metamaterials were conformed to, thereby creating 3D metamaterials structures as shown in the Fig. 2. Characterization of the flexible absorbers was accomplished through terahertz time domain spectroscopy to determine the change in operation of the device during its deformation. The absorbers exhibited strong absorption at the targeted resonance frequency both when planar and non-planar surfaces, while showing some tenability after deformation. The design and fabrication method is applicable for any desired frequency. Our finding promises applications in electromagnetically shielding of devices or objects and can be utilized to design Radar Absorbent Materials (RAM).