Search results for "MICROWAVE"

Assessing the relationship between microwave vegetation optical depth and gross primary production

2018

At the global scale, the uptake of atmospheric carbon dioxide by terrestrial ecosystems through photosynthesis is commonly estimated through vegetation indices or biophysical properties derived from optical remote sensing data. Microwave observations of vegetated areas are sensitive to different components of the vegetation layer than observations in the optical domain and may therefore provide complementary information on the vegetation state, which may be used in the estimation of Gross Primary Production (GPP). However, the relation between GPP and Vegetation Optical Depth (VOD), a biophysical quantity derived from microwave observations, is not yet known. This study aims to explore the …

Microwave-assisted catalytic esterification of α-glucoisosaccharino-1,4-lactone with tall oil fatty acids

2016

Background: Carbohydrates-rich materials are partly degraded during alkaline kraft pulping into a complex mixture of aliphatic carboxylic acids consisting of α-glucoisosaccharinic acid as one of the main acids. On the other hand, crude tall oil, containing significant amounts fatty acids, is obtained as a by-product from kraft pulping. One interesting novel approach is to utilize chemically both these side-streams by producing renewable surfactants from aliphatic carboxylic acids and fatty acids via esterification. Results: In this paper, lauric (C12:0) and oleic (C18:1) acids as well as a mixture of tall oil fatty acids were esterified with α-glucoisosaccharino-1,4-lactone in a microwave-a…

High-sensitivity narrow-band CSRR-based Microwave Sensor for Monitoring Glucose Level

2022

In this paper, a high-sensitivity narrow-band microwave sensor based on a complementary split-ring resonator (CSRR) to detect glucose concentrations in an aqueous solution is presented. The sensor consists of three CSRR cells engraved on the bottom level of a 59 mm x 20 mm x 0.8 mm FR4 (εr=4.3) dielectric substrate with a sensing area of 36 x 20 mm2. The cells operate over the 2.3 - 2.4 GHz band and are powered by a 50 Ω microstrip waveguide at the bottom of the substrate. A sensitivity analysis, starting from an optimization of the thickness of the glass layer added to the cells to avoid short circuits between the sample solution and the CSRRs rings, is performed. The sensitivity analysis …

Electrical and optical properties of Graphene Field-Effect Transistors (GFETs) fabricated on sapphire

Fabrication and analysis of the layout impact in Graphene Field Effect Transistors (GFETs)

2016

In this work we focused on the analysis of Graphene Field Effect Transistor (GFET) microwave parameters dependence on geometries. In particular, a statistical, experimental investigation of the cut-off frequency (ft) dependency on both the gate-drain/source distance (Δ) and the gate length (Lg) was carried out. 24 GFET families on the same chip were fabricated, each one made of 10 identical (same geometry) devices. The analysis of the measured data shows that ft is both Δ and Lg dependent, and that there exists an optimal region in Δ and Lg design space.

Impact of GFETs geometries on RF performances

2016

Graphene is a relatively new material whose unique properties have attracted significant interest for its use in electronic and photonic applications. In particular, field effect has been proved in graphene samples and the observed high carrier mobility makes graphene an interesting solution for high frequency electronics. In this work, we focused on the analysis of microwave parameters dependence on geometries in Graphene Field Effect Transistors (GFETs). In particular, a statistical, experimental investigation of the cut-off frequency (fT) and of the output impedance (Zout) dependency on both the gate-drain/source distance (Δ) and the gate length (Lg) was carried out. 24 GFET families wer…

Radiofrequency performances of different Graphene Field Effect Transistors geometries

2016

In this work, we investigated on microwave parameters geometry dependence in Graphene Field Effect Transistors (GFETs). A DC and RF characterization of the fabricated GFETs has been performed. The parametric analysis was carried out on 24 GFET families fabricated on the same chip and differing only for the channel length (Δ) and the gate length (Lg). In order to obtain a statistical average, each family included ten devices with the same geometry.Our study demonstrates that the output resistance and the cut-off frequency depend on both Δ and Lg. As expected, Rout increases with the graphene channel surface thus confirming the good quality of the fabrication procedures. An optimum region whi…

Efficient microwave-assisted synthesis of glycerol monodecanoate

2017

International audience; Solvent-free microwave-assisted synthesis was carried out to prepare 2,3-dihydroxypropyl decanoate, by esterification of decanoic acid in the presence of two distinct glycerol derivatives, glycidol, and glycerol carbonate, respectively. The process described is based on microwaves heating source with electrical power in the range of 200–400 W, involving stoichiometric proportions of decanoic acid and glycerol derivatives, and using catalytic amounts of TBAI used as organocatalyst. Conversion and selectivity rates of esterification reactions were monitored by 1H and 13C{1H} NMR spectroscopy. The predominantly formed ester, 2,3-dihydroxypropyl decanoate was fully chara…

Green Synthesis, Molecular Characterization and Associative Behavior of Some Gemini Surfactants without a Spacer Group.

2013

A series of new gemini surfactants without a spacer group, disodium 2,3-dialkyl-1,2,3,4-butanetetracarboxylates, were synthesized in a green chemistry context minimizing the use of organic solvents and applying microwaves (MW) when activation energy was required. Once the desired architecture was confirmed by means of the nuclear magnetic resonance technique (1H-NMR, 1H-1H COSY) for all the studied surfactants, the critical micellization concentration was determined by conductance measurements. The diffusion coefficient of micelles formed by the four compounds was characterized using pulsed field gradient (PFG)-NMR. Diffusion coefficients were found to be dependent on the concentration and …

Microwave Response of Ceramic MgB2 Samples

2009

The microwave response of ceramic MgB2 has been investigated as a function of temperature and external magnetic field by two different techniques: microwave surface impedance and second-harmonic emission measurements. The measurements of the surface resistance have shown that microwave losses in MgB2 are strongly affected by the magnetic field in the whole range of temperatures below Tc, even for relatively low field values. The results have been accounted for in the framework of the Coffey and Clem model hypothesizing that in different temperature ranges the microwave current induces fluxons to move in different regimes. In particular, the results at temperatures close to Tc have been quan…