Abstract
This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements.
Highlights
Terahertz (THz) technology has recently received growing attention, enabling it to overcome the so-called “ THz gap” connecting the fields of electronics and optics[1]
The ultra-thin narrow-band MMA27 is realized with a three-layer metal-dielectric-metal configuration consisting of a patterned frequency-selective surface (FSS)[27,30] inspired by ref.[23], a highly flexible insulating polyimide spacer, and a metal ground plane on a silicon substrate
Polyimide PI-2611 from HD MicroSystems[31] with nominal dielectric constant ε′ = 2.9, loss tangent tan δ = 0.002, and thickness of 5.4 μm, has been chosen as middle dielectric layer for its high electrical and thermal stability, low refractive index, low absorption, and flexibility[32,33,34,35,36,37,38,39,40]. It is a well-established material within the micro-fabrication processes, and it is used in applications of electronics on plastic and in photonic devices[41,42]
Summary
Terahertz (THz) technology has recently received growing attention, enabling it to overcome the so-called “ THz gap” connecting the fields of electronics and optics[1]. THz devices have been successfully applied in security detection[7,8,9], because non-conductive and non-polar materials, such as packaging, plastics, paper and ordinary clothes, show low absorption at these frequencies In this context, the THz regime represents a fertile area for the development of metamaterial absorbers (MMAs)[10,11,12,13], which are manmade devices designed to absorb specific bands of the incident electromagnetic radiation and generally constituted of periodic structures with sub-wavelength unit cells[14]. The quality of the experimental results critically depends on alignment errors of THz optical components which might alter the measured signals due to differences in THz pulses path length and phase errors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
