1,721,002 research outputs found
Effective inductances of periodic perforated metal plates for predicting microwave shielding effectiveness
No full textThis paper presents new analytical expressions for the effective inductances of perfectly conductive metal screens that are made up of periodic sub-wavelength circular or square apertures. These expressions are applied to the prediction of the shielding effectiveness (SE) of arrays when excited by oblique incidence plane waves below the cut-off frequency, while taking into account the effect of plate thickness. A new transformation model of two arrays with different hole shapes, assuming the SE as a constraint is proposed. The inductance-based modeling is applied to circular and square pattern configurations in the gigahertz frequency range. The good accuracy of the proposed formulations is demonstrated by comparing the obtained shielding performances with the reference values given by numerical codes or experimental tests. These formulations are easy to use and can provide reliable predictions of the SE of metal screens with periodic sub-wavelength apertures
Closed-form analytical design of optically transparent wideband absorbers for 5G technology
No full textThe design of new transparent absorbers for the upcoming fifth-generation (5G) technology is investigated. The absorbers consist of a matching layer, a lossy sheet, a spacer, and a back conducting layer (BCL). Both the matching layer and the spacer are one-quarter-wavelength thick and made of polyethylene terephthalate (PET). The lossy sheet and the BCL consist of indium tin oxide (ITO) thin films or graphene-PET laminates in order to avoid the use of any metal and to guarantee the optical transmittance. An innovative closed-form formulation is developed with the aim of evaluating the optimal values of sheet resistances of the lossy layers through analytical expressions. The absorption performances are investigated considering impinging plane waves with an incidence angle between 0° and 30°. The computed absorption coefficients in transverse magnetic (TM) or transverse electric (TE) modes are greater than 0.8, and the transmission coefficient is lower than 0.1 in the 5G frequency range from 25 up to 47 GHz, assuming that the matching layer and the spacer are 1.3 mm thick. The optical transmittance of the absorbers is evaluated in the wavelength range from 400 up to 700 nm by means of an accurate matrix simulation model, considering both optical polarizations, S (i.e., TE) and P (i.e., TM) for different incidence angles. The computed average optical transmittances of the designed absorbers are greater than 80% at 550 nm, i.e., at the wavelength corresponding to the maximum eye sensitivit
Oblique incidence optimal design of microwave dielectric-magnetic absorbing composites
No full textThe impedance matching equation of a single-layer dielectric-magnetic absorber excited by an oblique incidence plane wave is resolved with an expression providing the optimal thickness and highlighting the composite crucial parameters. The effective propagation constant of the nonuniform refracted plane wave into the absorber is represented by a new formulation as a function of the true refraction angle which is a real number unlike the complex quantity resulting from the Snell's law, usually applied in the literature. The proposed design process is applied to compute microwave absorption performances of different dielectric-magnetic materials, considering both normal and oblique incidence. Furthermore, the incidence angle effect is investigated
Literal Solutions for Optimal Design of Microwave Absorbing Composites
No full textThis paper proposes a new approach for the optimal design of microwave absorbing composites backed by a PEC layer and characterized by frequency dependent permeability and permittivity. The reflection coefficient is expressed as a function of the difference between the absorber hyperbolic input impedance and the free space wave impedance, considering an impinging plane wave with either normal or oblique incidence angle. The impedance matching condition for the selected frequency and incidence angle is solved in terms of literal expression of the optimal thickness, which is compared with the one quarter wavelength thickness given by a new accurate expression. The optimal thickness is used for the design of microwave absorbers made by dielectric-magnetic and dielectric composite materials. The frequency spectra of the absorber input impedances and reflection coefficients are computed in the frequency range from 2 GHz up to 18 GHz and for an incidence angle ranging between 0° and 30°. The obtained results prove the validity of the literal expression of the composite optimal thickness which explicitly shows the crucial parameters for the absorbing performances, obscured in common numerical procedure
Coaxial waveguide methods for shielding effectiveness measurement of planar materials up to 18 GHz
No full textThe issue concerning the measurement of the shielding effectiveness (SE) of planar materials over a wide frequency range is of crucial relevance in several EMC applications. This paper describes three different coaxial specimen holders for the measurement of the SE of thin metallic films over a non-conducting substrate or sandwiched between two insulating layers from a few kHz up to 18 GHz. Besides the well-known ASTM D4935 flanged coaxial cell, two novel versions of coaxial fixtures with an interrupted and continuous inner conductor are presented and compared. Their limits of applicability, advantages and drawbacks are discussed with respect to frequency, sample characteristics and test procedure. The analysis is performed by the use of simple equivalent circuit models, experimentally validated measuring thin copper films of different thicknesses which are deposited on kapton substrates by magnetron sputtering. It is demonstrated that the use of the three methods, properly combined, provides reliable SE results in the overall considered frequency range. It is also shown that the measurement of conducting films between two dielectric layers is critical at frequencies lower than some tens of MHz
Effective medium model of periodic nanolayered transparent shields
No full textAn innovative effective medium model based on the transfer matrix method is proposed for the simulation of 1D-periodic subwavelength metal-dielectric laminated structures excited by TM- or TE-polarized plane wave with oblique incidence angles. The homogeneous medium of each period is characterized by TM or TE complex effective permeability and conductivity. The resulting effective single layer (ESL), having the same total thickness of the multilayer laminate, is represented by a transfer matrix given by the product of the transmission matrices of the periods composing the structure. Notice that this model allows the homogenization of n-layer periods, while the effective medium approximation method is formulated for only two-layer periods. The ESL is used to compute the transmission and reflection coefficients and the shielding effectiveness of 1D-periodic nanolayered transparent coatings made by alternating layers of silver, zinc oxide, or titanium dioxide films, in the frequency range from 100 MHz up to 10 THz. The propagating wave performances of the ESL are compared with the ones given by the rigorous multilayer model. Finally, two different screens made of transparent coatings over glass are proposed and analyzed
Flexible ecoflex®/graphene nanoplatelet foams for highly sensitive low-pressure sensors
Get PDFThe high demand for multifunctional devices for smart clothing applications, human motion detection, soft robotics, and artificial electronic skins has encouraged researchers to develop new high-performance flexible sensors. In this work, we fabricated and tested new 3D squeezable Ecoflex® open cell foams loaded with different concentrations of graphene nanoplatelets (GNPs) in order to obtain lightweight, soft, and cost-effective piezoresistive sensors with high sensitivity in a low-pressure regime. We analyzed the morphology of the produced materials and characterized both the mechanical and piezoresistive response of samples through quasi-static cyclic compression tests. Results indicated that sensors infiltrated with 1 mg of ethanol/GNP solution with a GNP concentration of 3 mg/mL were more sensitive and stable compared to those infiltrated with the same amount of ethanol/GNP solution but with a lower GNP concentration. The electromechanical response of the sensors showed a negative piezoresistive behavior up to ~10 kPa and an opposite trend for the 10–40 kPa range. The sensors were particularly sensitive at very low deformations, thus obtaining a maximum sensitivity of 0.28 kPa−1 for pressures lower than 10 kPa
Production and characterization of Graphene Nanoplatelet-based ink for smart textile strain sensors via screen printing technique
Get PDFWearable systems are becoming highly attractive in different application areas. Recently, particular attention has been focused on the development of personal portable devices for monitoring occupational safety and health. Smart clothes based on strain sensors integrated on fabric seem to be a promising solution for real-time measurement of physiological endpoints. However, the development through a simple and cost-effective process of smart textiles characterized by high sensitivity, wearability and stable response even during physical activity, in case of exposition to environmental conditions and after washing is still challenging. In this work, the authors have developed a novel strain sensor made of graphene nanoplatelets (GNPs) properly dispersed into a water-based transparent ink, then deposited via screen printing technique on a synthetic fabric. Rheological investigations of the GNP-filled inks, morphological characterization of coated fabrics, electrical measurements of films obtained with different GNPs concentrations were performed. Smart textile specimens loaded with 3%wt and 3.8%wt of GNP-based inks were characterized through quasi-static tensile tests to investigate the electromechanical response, even after a washing cycle. Specimens have shown a sensitivity of about 30 for a strain of 5%. This performance is interesting for different applications such as monitoring of respiratory and heart rates
Optimal design of microwave absorbers based on high-impedance surfaces
No full textThe simulation model and the optimal design methodology for absorbers consisting of metallic patches on a dielectric substrate backed by a perfectly conductive layer, have been developed. New expressions for the real and imaginary parts of the substrate permittivity are proposed to achieve a desired reflection coefficient at a specified resonance frequency. This analytical formulation is then utilized to predict the absorbance performance of various structures under both normal and oblique incidence plane waves up to 10 GHz. Validation of the obtained results is conducted by comparing them with those obtained from CST full-wave numerical simulations
Transparent graphene-based absorber for next generation wireless 5G technology
No full textThe design of new transparent and metal-free absorbers for the upcoming wireless fifth-generation (5G) technology is investigated. To this purpose, innovative absorbers made of graphene-polyethylene terephthalate (PET) laminates separated by PET spacers are proposed. The graphene-PET laminates are modelled as homogeneous single layers characterized by effective conductivities whose values are obtained by means of a new analytical procedure with the aim of optimizing the absorption performances. Reflection, transmission and absorption coefficients of designed absorbers are computed considering optimum theoretical or feasible values of effective conductivities for graphene-PET laminates in order to achieve the best absorbing performance between 24.25 GHz and 42.5 GHz, i.e. in the 5G next generation bandwidth
- …
