We investigate graphene-based optical absorbers that exploit guided mode resonances (GMRs) attaining theoretically perfect absorption over a bandwidth of few nanometers (over the visible and ...near-infrared ranges) with a 40-fold increase of the monolayer graphene absorption. We analyze the influence of the geometrical parameters on the absorption rate and the angular response for oblique incidence. Finally, we experimentally verify the theoretical predictions in a one-dimensional, dielectric grating by placing it near either a metallic or a dielectric mirror, thus achieving very good agreement between numerical predictions and experimental results.
We propose an innovative approach for the realization of a microwave absorber fully transparent in the optical regime. This device is based on the Salisbury screen configuration, which consists of a ...lossless spacer, sandwiched between two graphene sheets whose sheet resistances are different and properly engineered. Experimental results show that it is possible to achieve near-perfect electromagnetic absorption in the microwave X-band. These findings are fully supported by an analytical approach based on an equivalent circuital model. Engineering and integration of graphene sheets could facilitate the realization of innovative microwave absorbers with additional electromagnetic and optical functionalities that could circumvent some of the major limitations of opaque microwave absorbers.
A one-dimensional dielectric grating, based on a simple geometry, is proposed and investigated to enhance light absorption in a monolayer graphene exploiting guided mode resonances. Numerical ...findings reveal that the optimized configuration is able to absorb up to 60% of the impinging light at normal incidence for both TE and TM polarizations resulting in a theoretical enhancement factor of about 26 with respect to the monolayer graphene absorption (≈2.3%). Experimental results confirm this behavior showing CVD graphene absorbance peaks up to about 40% over narrow bands of a few nanometers. The simple and flexible design points to a way to realize innovative, scalable and easy-to-fabricate graphene-based optical absorbers.
In this paper, we numerically and experimentally demonstrate how to modulate the amplitude and phase of a microwave ring resonator by means of few-layers chemical vapour deposition graphene. In ...particular, both numerical and experimental results show a modulation of about 10 dB and a 90 degrees-shift (quadrature phase shift) when the graphene sheet-resistance is varied. These findings prove once again that graphene could be efficiently exploited for the dynamically tuning and modulation of microwave devices fostering the realization of (i) innovative beam-steering and beam-forming systems and (ii) graphene-based sensors.
We investigate the linear response of single and multiple graphene sheets embedded in quarter-wave one-dimensional photonic crystals (PhCs) in terms of absorption and losses. In particular, we show ...that it is possible to achieve near-perfect narrowband absorption when a single monolayer graphene is sandwiched between two PhC mirrors with optimized pair numbers. The simulations reveal that the resonant wavelength and the total absorption frequency may be tuned by tilting the angle of incidence of the impinging source. We also show that the losses, related to the dielectric materials constituting the one-dimensional PhC, can degrade the optical performance of the device. Conversely, by arranging the same dielectric slabs in a different order (supercell), it is possible to achieve a broadband absorption that is almost constant over a wide range of angle of incidence. In this configuration, the absorption and the bandwidth can be tuned by varying the supercell geometry. These features make these devices attractive for different applications ranging from tunable and saturable absorbers for short-pulse lasers to graphene-based photodetectors.
A GHz Transverse Electromagnetic (GTEM) cell is proposed to investigate the arising of biological effects due to electromagnetic signals at the typical frequencies of mobile phone communications. The ...proposed GTEM cell, placed within a commercial incubator, has been ad hoc designed and fabricated to expose in vitro samples. The electromagnetic and the thermal analyses of the GTEM cell are reported. In particular, the inner electromagnetic field and the Specific Absorption Rate of the exposed sample (saline solution having 9 g/l concentration) have been evaluated by a homemade computer code based on the transmission line matrix method. Furthermore, the thermal analysis of the exposure arrangement has been carried out by the finite difference time domain algorithm.
In this paper the performance of an optical organic sensor based on a plasmonic grating immersed in an asymmetric dielectric environment is investigated. Metal gratings offer the possibility to ...tailor the spectral response, in dependence of the geometrical parameter settings and variation of the refractive index of the surrounding media. It is then possible to obtain a reflection spectrum displaying a sharp dip that can be efficiently exploited to improve the detection of small quantities of organic materials. In particular, using a finite difference time domain (FDTD) based method, we demonstrate that the designed plasmonic grating, made of gold strips placed on a silicon substrate and covered by a generic organic material (analyte), exhibits an improved sensitivity for the detection of the overlayer thickness (analyte quantity). Nevertheless, this plasmonic sensor can also be used to determine the typology of the generic organic layer in dependence of the refractive index change.
Recycled waste porous glass (RWPG), from municipal solid wastes (MSW) sorting operations, may be used as a sorbent for lead ion removal from industrial wastewaters. To the purpose, dynamic ...(laboratory columns) operations were carried-out by the use of differently sized glass beads in the range 0.35–1.25
mm which were eluted with lead ion containing synthetic solutions (2–9.5
mg/L). Temperature was kept constant (298
K), whereas column flow-rates varied in the range 0.20–0.75
L/h. Lead ion retention mechanism was associated to the adsorption/ion exchange phenomena. Best column performance was obtained at 0.5–1
mm bead size range, influent concentration 2
mgPb
2+/L and column flow-rate 0.20
L/h. In the reference conditions lead ion retention capacity exceeded 1.10
mg/g. Kinetic analysis of the experimental data was also carried-out and film interdiffusion of the involved ions in the Nernst stationary liquid around the particle was identified as the rate controlling step.
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