This paper presents the design and fabrication of a broadband microstrip attenuator, operating at 1-20 GHz, based on few layer graphene flakes. The RF performance of the attenuator has been analyzed ...in depth. In particular, the use of graphene as a variable resistor is discussed and experimentally characterized at microwave frequencies. The structure of the graphene-based attenuator integrates a micrometric layer of graphene flakes deposited on an air gap in a microstrip line. As highlighted in the experiments, the graphene film can range from being a discrete conductor to a highly resistive material, depending on the externally applied voltage. As experimental evidence, it is verified that the application of a proper voltage through two bias tees changes the surface resistivity of graphene, and induces a significant change of insertion loss of the microstrip attenuator.
This letter presents a voltage-controlled tunable attenuator based on few layer graphene flakes. The proposed structure exploits the variation of graphene resistance with an applied bias voltage. The ...attenuator consists of a microstrip line, connected to grounded metal vias through graphene pads: when no bias voltage is applied, the resistance of graphene is high and the pads behave as open circuits, causing minimum attenuation. By increasing the bias voltage, the resistance of the graphene pads decreases, connecting the metal vias to the microstrip, thus increasing the attenuation. A prototype operating in the frequency band from dc to 5 GHz has been designed and tested. The measured attenuation ranges from 0.3 to 15 dB at 3 GHz, with a bias voltage ranging from 0 (minimum attenuation) to 6.5 V (maximum attenuation).
In recent years, the ENEA has introduced a novel methodology based on motion magnification (MM) into the Italian cultural heritage protection and monitoring field. It consists of a digital video ...signal processing technique able to amplify enormously the tiny movements recorded in conventional videos, while preserving the general topology of the acquired frames. Though the idea of such a methodology is not new, it has recently been provided with an efficient algorithm that makes possible a viable and low-cost magnification. Applications are extremely varied in almost every field of science and technology; however, we are interested in its application to the safeguarding of architectural heritage, a sector of the utmost importance for Italy. As ancient buildings can be extremely sensitive to even minimally invasive instrumentation, most common monitoring sensors can be replaced by contactless tools and methods, such as video-based techniques like MM. It offers many advantages: easy to use, contactless devices, virtual sensors, reusability of the videos, practicality, intuitive graphical results, quantitative analyses capability and low costs. These characteristics are well suited to the monitoring of large ancient monuments; on the other hand, historical sites have peculiarities of their own, requiring careful approaches, proper tools and trained personnel. Moreover, outdoor applications of MM present quite notable difficulties from a practical point of view, e.g., the dimensions of the studied objects, uncontrolled environmental conditions, spurious vibrations, lighting change/instability, etc. Here we give a general idea of the potential of MM and related issues, using some relevant in-the-field case studies in Italian heritage protection.
Thermal diffusivity of
(graphene nano-platelets) is an important thermo-physical property as it is useful to predict the material behavior in many heat transfer applications.
samples were pressed at ...different loads to obtain different densities, and then thermal diffusivity was measured with the flash method. All samples were coated with a thin layer (~1 µm) of colloidal graphite (Aquadag
) on both sides to reduce reflectance of their surfaces and consequently increase the emissivity. Carrying out measurements on both samples with and without coating, a difference between the two series of measurements was found: This is attributed to a non-negligible transmittance of the uncoated samples due to the porosity of
. Furthermore, assuming a spatial distribution of the light within the samples according to the Lambert-Bougert-Beer law, the extinction coefficient of
at different densities has been evaluated processing experimental data with a nonlinear least square regression, (
, nonlinear least square fitting), whose model contains the extinction coefficient as unknown. The proposed method represents a further improvement of thermal diffusivity data processing, crucial to calculate the extinction coefficient when data with and without coating are available; or to correct biased thermal diffusivity data when the extinction coefficient is already known. Moreover, reflectance effects have been highlighted comparing asymptotic temperature reached during the tests on coated and uncoated samples at different densities. In fact, the decrease of asymptotic temperature of the uncoated samples gives the percentage of the light reflected and consequently an estimate of the reflectance of the
surface.
This paper explores the potential of a low-cost, advanced video-based technique for the assessment of structural damage to buildings caused by seismic loading. A low-cost, high-speed video camera was ...utilized for the motion magnification processing of footage of a two-story reinforced-concrete frame building subjected to shaking table tests. The damage after seismic loading was estimated by analyzing the dynamic behavior (i.e., modal parameters) and the structural deformations of the building in magnified videos. The results using the motion magnification procedure were compared for validation of the method of the damage assessment obtained through analyses of conventional accelerometric sensors and high-precision optical markers tracked using a passive 3D motion capture system. In addition, 3D laser scanning to obtain an accurate survey of the building geometry before and after the seismic tests was carried out. In particular, accelerometric recordings were also processed and analyzed using several stationary and nonstationary signal processing techniques with the aim of analyzing the linear behavior of the undamaged structure and the nonlinear structural behavior during damaging shaking table tests. The proposed procedure based on the analysis of magnified videos provided an accurate estimate of the main modal frequency and the damage location through the analysis of the modal shapes, which were confirmed using advanced analyses of the accelerometric data. Consequently, the main novelty of the study was the highlighting of a simple procedure with high potential for the extraction and analysis of modal parameters, with a special focus on the analysis of the modal shape's curvature, which provides accurate information on the location of the damage in a structure, while using a noncontact and low-cost method.
One of the most appealing properties of carbon nanotube (CNT) interconnects is the possibility of exhibiting, under certain circumstances, a negative temperature coefficient of the electrical ...resistance, i.e., a resistance that decreases as temperature increases. In the past, this behavior has been theoretically predicted and experimentally observed, but only for a certain class of CNTs, with short lengths (up to some micrometers) and in a limited range of temperature. This paper demonstrates the possibility of obtaining such a desirable behavior in a larger scale (up to fractions of millimeters). An accurate electrothermal model is used to define the conditions under which a negative derivative of the resistance may be observed. Then, a novel bottom-up technique is proposed to realize the interconnect, by self-assembly of short CNTs. The experimental results of an electrothermal characterization demonstrate the possibility of obtaining a negative temperature coefficient of the resistance and confirm the validity of the theoretical model.
The blood-brain barrier (BBB) bypass of dopamine (DA) is still a challenge for supplying it to the neurons of
mainly affected by Parkinson disease. DA prodrugs have been studied to cross the BBB, ...overcoming the limitations of DA hydrophilicity. Therefore, the aim of this work is the synthesis and preliminary characterization of an oxidized alginate-dopamine (AlgOX-DA) conjugate conceived for DA nose-to-brain delivery.
A Schiff base was designed to connect oxidized polymeric backbone to DA and both AlgOX and AlgOX-DA were characterized in terms of Raman, XPS, FT-IR, and
H- NMR spectroscopies, as well as in vitro mucoadhesive and release tests.
Data demonstrated that AlgOX-DA was the most mucoadhesive material among the tested ones and it released the neurotransmitter in simulated nasal fluid and in low amounts in phosphate buffer saline. Results also demonstrated the capability of scanning near-field optical microscopy to study the structural and fluorescence properties of AlgOX, fluorescently labeled with fluorescein isothiocyanate microstructures. Interestingly, in SH-SY5Y neuroblastoma cell line up to 100 μg/mL, no toxic effect was derived from AlgOX and AlgOX-DA in 24 h.
Overall, the in vitro performances of AlgOX and AlgOX-DA conjugates seem to encourage further ex vivo and in vivo studies in view of nose-to-brain administration.
The use of carbon nanomaterials (CNMs) in sensors and biosensor realization is one of the hottest topics today in analytical chemistry. In this work, a comparative in-depth study, exploiting ...different nanomaterial (MWNT-CO
H, -NH
, -OH and GNP) modified screen-printed electrodes (SPEs), is reported. In particular, the sensitivity, the heterogeneous electron transfer constant (k
), and the peak-to-peak separation (ΔE) have been calculated and analyzed. After which, an electrochemical amperometric sensor capable of determining uric acid (UA), based on the nano-modified platforms previously characterized, is presented. The disposable UA biosensor, fabricated modifying working electrode (WE) with Prussian Blue (PB), carbon nanotubes, and uricase enzyme, showed remarkable analytical performances toward UA with high sensitivity (CO
H 418 μA μM
cm
and bare SPE-based biosensor, 33 μA μM
cm
), low detection limits (CO
H 0.5 nM and bare SPE-based biosensors, 280 nM), and good repeatability (CO
H and bare SPE-based biosensors, 5% and 10%, respectively). Moreover, the reproducibility (RSD%) of these platforms in tests conducted for UA determination in buffer and urine samples results are equal to 6% and 15%, respectively. These results demonstrate that the nanoengineered electrode exhibited good selectivity and sensitivity toward UA even in the presence of interfering species, thus paving the way for its application in other bio-fluids such as simple point-of-care (POC) devices.
Nowadays, a deep knowledge of procedures of synthesis of nanostructured materials plays an important role in achieving nano-materials with accurate and wanted properties and performances. ...Carbon-based nanostructured materials continue to attract a huge amount of research efforts, because of their wide-ranging properties. Using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy in the soft X-ray regime, by the synchrotron radiation, we studied the L3,2 absorption edges of iron (Fe) nanoparticles, when they are embedded in oriented Multi Wall Carbon Nanotube (MWCNTs) layers grown by thermal Chemical Vapor Deposition (CVD) technique catalyzed by this transition metal. This could allow us to understand the valence state and role of catalysts and thus their electronic and magnetic structures. It is important to note that the control of the size of these tethered nanoparticles is of primary importance for the purpose of tailoring the physical and chemical properties of these hierarchical materials. The MWCNTs samples used in XAS and XMCD measurements were synthesized by the CVD technique. The actual measurements were carried out by the group NEXT of the INFN- LNF with the logistic experimental support of the INFM-CNR and the Synchrotron Elettra Trieste.
As part of a biopolymer matrix, pectin was investigated to obtain an engineered jam, due to its biodegradability. Only a few examples of pectin-based nanocomposites are present in the literature, and ...even fewer such bionanocomposites utilize nanocarbon as a filler-mostly for use in food packaging. In the present paper, ecofriendly nanocomposites made from household reagents and displaying multiple properties are presented. In particular, the electrical behavior and viscoelastic properties of a commercial jam were modulated by loading the jam with carbon nanotubes and graphene nanoplates. A new nanocomposite class based on commercial jam was studied, estimating the percolation threshold for each filler. The electrical characterization and the rheological measurements suggest that the behavior above the percolation threshold is influenced by the different morphology-i.e., one-dimensional or two-dimensional-of the fillers. These outcomes encourage further studies on the use of household materials in producing advanced and innovative materials, in order to reduce the environmental impact of new technologies, without giving up advanced devices endowed with different physical properties.
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