We present the design, fabrication, and characterization of a metamaterial absorber which is resonant at terahertz frequencies. We experimentally demonstrate an absorptivity of 0.97 at 1.6 terahertz. Importantly, this free-standing absorber is only 16 microns thick resulting in a highly flexible material that, further, operates over a wide range of angles of incidence for both transverse electric and transverse magnetic radiation.

We demonstrate reconfigurable anisotropic metamaterials at terahertz frequencies where artificial "atoms" reorient within unit cells in response to an external stimulus. This is accomplished by fabricating planar arrays of split ring resonators on bimaterial cantilevers designed to bend out of plane in response to a thermal stimulus. We observe a marked tunability of the electric and magnetic response as the split ring resonators reorient within their unit cells. Our results demonstrate that adaptive metamaterials offer significant potential to realize novel electromagnetic functionality ranging from thermal detection to reconfigurable cloaks or absorbers.

We have fabricated resonant terahertz metamaterials on free standing polyimide substrates. The low-loss polyimide substrates can be as thin as 5.5 µm yielding robust large-area metamaterials which are easily wrapped into cylinders with a radius of a few millimeters. Our results provide a path forward for creating multi-layer non-planar metamaterials at terahertz frequencies. PACS numbers:The advent of metamaterial composites has given rise to numerous electromagnetic functionalities previously unimagined. This includes negative refractive index, superlensing, cloaking, and quite generally, the fabrication of metamaterials which have been designed using coordinate transformation approaches [1,2,3, 4,5]. Many of these ideas were initially implemented at microwave frequencies where fabrication of multilayer composites has become increasingly sophisticated during the past several years. This has resulted in dramatically reduced times from conceptualization and electromagnetic simulation to, ultimately, fabrication and characterization. However, the fabrication of subwavelength unit cells becomes increasingly challenging in moving from the microwave to visible region of the electromagnetic spectrum though important progress has been made [6,7,8,9]. To date, the majority of this work has been on planar composites. At terahertz (THz) frequencies and above, creating multiple unit cell structures in the direction of propagation and taking full advantage of coordinate transformation MM design to realize non-planar MM composites requires the development of new fabrication strategies.The far-infrared, or terahertz, is a promising region to investigate novel approaches to metamaterials fabrication. First, the unit cells are on the order of tens of microns which is amenable to novel microfabrication approaches. Second, and perhaps of greater importance, there is a strong technological impetus to create sources, detectors, and components at terahertz frequencies to realize the unique potential of THz radiation [10,11,12,13]. Metamaterials are expected to play an important role in this regard as evidenced by recent demonstrations of MM-based modulators and frequency tunable filters [14,15,16]. An important step in the progression of functional THz MM composites is the fabrication of multilayer structures. For example, a strongly resonant THz MM absorber consisting of two layers spaced by approximately six microns [24] was recently demon- * Electronic address: xinz@bu.edu † Electronic address: raveritt@physics.bu.edu strated (see also [17] for the microwave perfect absorber). The entire structure, however, was on top of a thick GaAs supporting substrate. There has also been other work at THz frequencies using polymer spin-coating based techniques to fabricate metamaterials, but the focus of this work was not on ultrathin flexible substrates [18,19]. FIG. 1: (Color) Photographs of the free standing electric metamaterials fabricated on polyimide substrate. The thin samples naturally roll up into a cylinder unless supported on a fra...

We have designed, fabricated, and characterized metamaterial enhanced bimaterial cantilever pixels for far-infrared detection. Local heating due to absorption from split ring resonators (SRRs) incorporated directly onto the cantilever pixels leads to mechanical deflection which is readily detected with visible light. Highly responsive pixels have been fabricated for detection at 95 GHz and 693 GHz, demonstrating the frequency agility of our technique. We have obtained single pixel responsivities as high as 16,500 V/W and noise equivalent powers of 10(-8) W/Hz(1/2) with these first-generation devices.