1,720,968 research outputs found
Design and analysis of an ultra-thin dual-band metamaterial absorber for THz applications
No full textIn this paper, we consider the design and analysis of an ultra-thin dual-band metamaterial absorber in the THz regime with a thickness of about lambda_0/16 where lambda_0 is the free-space wavelength, at the higher operating frequency. We have observed both a narrowing of the frequency response and a broadening of the angular response obtained through the insertion of a conducting ground plane.
To retrieve the effective electromagnetic parameters of the structure, we have applied a homogenization technique to extract the relative electric permittivity, magnetic permeability and wave impedance
Wideband equivalent-circuit model analysis, realization and time-domain spectroscopy characterization of terahertz periodic metamaterial devices
Full text linkIn my PhD thesis, I have thoroughly researched THz periodic metamaterial devices by dealing with all the phases of their development: electromagnetic analysis, design, fabrication, characterization, and data post-processing. Initially, for the analysis and design phases, I have adopted an analytical/numerical perspective for the retrieval of the devised circuit topologies. In particular, I have developed and applied equivalent circuit models and parametric macromodels for the physical investigation and optimization of the devices; these methods have been validated by proving their efficiency and effectiveness through the comparison with finite-element method based simulations. Also, they guarantee a wider range of applications in terms of frequency spectra, complexity of geometrical shapes, and material characteristics. For the realization phase, I have used a heuristic procedure of micro-fabrication and after evaluating possible non-idealities, I have made tolerance studies in order to obtain a stable electromagnetic performance. For the characterization of the flexible devices, I have used custom THz-TDS setups for both reflection and transmission-modes; the resulting configurations have proved to be compact and interesting also for further integration in embedded measurement systems. For the data analysis phase, I have post-processed the acquired measurements by implementing retrieval procedures of the constitutive parameters of the samples. Other than topics specifically related to the THz field, I have developed some models of analytical/numerical character for the study of scatterers with discontinuous impedance boundary conditions
Broad-band terahertz metamaterial absorber with stacked electric ring resonators
No full textIn this paper, we propose an ultra-thin broad-band metamaterial absorber composed of a periodic array of three-layered electric ring resonators (ERRs) within a dielectric spacer and backed by a metallic ground plane for THz applications. The overlapping of the resonance peaks relevant to the ERRs leads to a broad spectral absorption bandwidth over a wide range of incidence angles under both transverse electric and transverse magnetic polarizations. We analyze the effect of different physical properties on the absorption spectra in order to estimate the dielectric and Ohmic losses in the metamaterial structure. In addition, the Nicolson, Ross, and Weir algorithm is adopted as homogenization technique to retrieve the effective electromagnetic parameters, while the interference theory is employed to compare the simulated and analytical results for the multi-layered absorber
Narrow-band and dual-band metamaterial absorbers in the THz regime
No full textIn this paper, we consider the analysis and design of narrow-band and dual-band metamaterial absorbers in the THz regime. We observe a broadening of the angular response obtained through absorbers backed by a conducting ground plane and we apply a homogenization technique to calculate the effective electric and magnetic properties of the structures
Efficient design of metamaterial absorbers using parametric macromodels
No full textMetamaterial absorbers have recently attracted a lot of interest for applications spanning from microwave to terahertz, near infrared and optical frequencies, such as electromagnetic compatibility, thermal emitters, solar cells and micro-bolometers. In this paper, a procedure for the efficient design of metamaterial absorbers based on parametric macromodels is presented. These models are used to describe the frequency-domain behaviour of complex systems as a function of frequency and design parameters (e.g., layout features). Parametric macromodels are very efficient and can be used to speed up the design ow in comparison with using electromagnetic simulators for design tasks. The use of quasi-random sequences for the sampling of the design space and of radial basis functions and polynomial functions for the model construction is proposed. Numerical results validate the efficiency and accuracy of the proposed technique for multiple optimizations
Polarization-maintaining reflection-mode THz time-domain spectroscopy of a polyimide based ultra-thin narrow-band metamaterial absorber
Full text linkThis 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
Frequency domain behavior of S‐parameters piecewise‐linear fitting in a digital‐wave framework
Full text linkThis paper describes PWLFIT+, an extension to the frequency domain of PWLFIT, a new paradigm in time-domain macromodeling for linear multiport systems, based on a piecewise-linear (PWL) behavioral representation of the S-parameters step response. While the impulse response of each S-parameter is approximated as sum of delayed rectangles (rect) functions, its spectrum is interpolated as sum of the corresponding delayed cardinal sine (sinc) functions. Exploiting this correspondence, the model building is performed by an iterative procedure where the PWL macromodels can be determined in order to meet defined accuracy goals on the spectrum. At runtime, waves at macromodels ports are calculated using the Segment Fast Convolution (SFC) algorithm within the Digital Wave Simulator (DWS) framework. The proposed method is characterized by its simplicity, stability, speed and scalability, all features that are emphasized when it is used in the DWS framework. After an analysis of the excellent numerical features of SFC in the Z-domain, clearly differentiated with respect conventional macromodeling methods based on poles and residues, two suitable application examples are presented to demonstrate the unique features of PWLFIT+
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