Electronic Capacitance Research Articles

Improving vineyard irrigation efficiency with soil water sensors

Improving vineyard irrigation efficiency with soil water sensors Using soil water sensors to automatically schedule irrigation in winegrape vineyards offers the potential for growers to enhance water use productivity under warmer climate conditions. The use of electrical soil water sensors for improving crop water use efficiency is an emerging trend in agricultural regions of the world where irrigation is vital for sustainable food production. This advancement uses solar powered electronic capacitance probes to activate irrigation in real time for maintaining a desired level of soil water content needed by a particular crop.

Influence of shielding on the dependence of capacitance of planar capacitor on a distance of a measured object

This article deals with the topic of the shielding effect of electrodes in the design of capacitance sensors. The main focus of the article is the phenomenon, which occurs when placing shielding electrodes between planar capacitor electrodes. This phenomenon naturally occurs when the multi-electrode setup is being used. Such setup is used in electronic capacitance tomography (ECT). The first part of the article briefly describes the theoretical attributes of a planar capacitor. Then the model of the multi-electrode system is explained. Subsequently, the experiment during which the phenomenon was observed, is being described. The real measurement is then compared to the simulation of the equal setup. Results, implications, and possible explanations are being discussed in the conclusion.

Theory for Potential of Zero Charge and Capacitance on Metals with Nanocorrugated Steps

We develop the mean-field theory for the step density-induced anomalous variation in electronic capacitance, work function (WF), potential of zero charge (PZC), and interfacial capacitance (IC) of ...

Magnetic and electric properties of single crystal MnI2

Multiferroic materials endowed with both dielectric and magnetic orders, are ideal candidates for a wide range of applications. In this work, we reported two phase transitions of MnI2 at 3.45 K and 4 K by systemically measuring the magnetic-field and temperature-dependent magnetization of the MnI2 thin flakes. Furthermore, we observed similar temperature and field-dependent behaviours for the magnetic susceptibility of MnI2 and electronic capacitance of the Ag/MnI2/Ag devices below 3.5 K. Considering the related theory work, we discussed the relationship between the antiferromagnetic and ferroelectric orders in MnI2. Our work reveals the in-plane magnetic and electric properties of MnI2 materials, which might be helpful for the further investigation and application of MnI2 multiferroics in the future.

Interplay of negative electronic compressibility and capacitance enhancement in lightly-doped metal oxide Bi0.95La0.05FeO3 by quantum capacitance model

Light-sensitive capacitance variation of Bi0.95La0.05FeO3 (BLFO) ceramics has been studied under violet to UV irradiation. The reversible capacitance enhancement up to 21% under 405 nm violet laser irradiation has been observed, suggesting a possible degree of freedom to dynamically control this in high dielectric materials for light-sensitive capacitance applications. By using ultraviolet photoemission spectroscopy (UPS), we show here that exposure of BLFO surfaces to UV light induces a counterintuitive shift of the O2p valence state to lower binding energy of up to 243 meV which is a direct signature of negative electronic compressibility (NEC). A decrease of BLFO electrical resistance agrees strongly with the UPS data suggesting the creation of a thin conductive layer on its insulating bulk under light irradiation. By exploiting the quantum capacitance model, we find that the negative quantum capacitance due to this NEC effect plays an important role in this capacitance enhancement

Understanding the Ion-Sorption Dynamics in Functionalized Porous Carbons for Enhanced Capacitive Energy Storage.

Heteroatom-functionalized porous carbon has long been regarded as a promising electrode material to construct high-performance capacitive energy storage devices. However, the development of this field is seriously limiteddue to thelack ofan in-depth understanding of the ion-sorption dynamics. Herein, the component and structure controllable N, O, and Cl codoped bimodal (micro-to-meso) porous carbons were prepared and further used as the investigated object for exploring the intrinsic ion-sorption dynamics, which is the root of the enhanced electrochemical response in capacitive energy storage devices. Voltammetry response analysis is employed to quantify the charge storagecontributions from bothelectrostatic adsorption effect (electrical double-layer capacitance) and highly reversible redox process (pseudocapacitance). The existence of electronic capacitance enables a positive correlation between surface capacitance and the ratio of micropores. Besides, an electron-dependent correlation between theelectroactive functional groups and redox reactioninduced capacitance is also explored. This work will advance the capacitive energy storage field by presenting a clear understanding of the ion-sorption dynamics in thefunctionalized porous carbons.

Effects of Voltage Biasing on Current Extraction in Perovskite Solar Cells

AbstractThe recent rapid increase in efficiency of organic–inorganic perovskite solar cells (PSCs) has resulted in a need to develop a clear understanding of their stability and working mechanisms. In particular, it has been suggested that ion migration contributes to the commonly observed hysteresis in the current–voltage measurements of PSCs, but the rate of ion migration and its effects on the electronic properties of PSCs remain to be addressed. In this work, electron‐beam‐induced current (EBIC) is used to directly map changes in local current extraction in organic–inorganic PSCs under applied voltage. By combining EBIC mapping, standard current–voltage measurements, and external quantum efficiency measurements, it is shown that between the two potential roles that point defects play in device enhancement under voltage biasing, the effects caused by defect‐mediated ion migration outweigh the effects from the filling of trap states caused by these defects. Evidence is also provided for ion migration preferentially at local features such as extended defects. The measured timescale of tens of seconds for migration across a full device imply that ion migration contributes indirectly to the electronic capacitance of perovskite devices through interface charging.

Thermodynamics of self-oscillations in VO2 for spiking solid-state neurons

Neuron-like mechanisms under DC bias are observed in two-port VO2 pads. We investigate these self-oscillations responses for different types of VO2 and uncovered an underlying story common to all materials on how self-oscillations arise. From the electronic responses measured as a function of temperature and time, we determined three precise conditions inducing self-oscillations and very large current spikes. Rather than being caused by an electronic capacitance as previously understood, we prove that such self-oscillations are caused by thermodynamic interactions entirely predicted by material constants. These calculations should extend to other materials, enabling the design of various low-power thermoelectronic computing circuits.

Shape- and size-dependent electronic capacitance in nanostructured materials

The shape and size are the two important geometrical factors that affect the electronic screening in nano-materials. Here, we develop an analytical theory for electronic capacitance based on Thomas–Fermi screening in conjunction with ‘multiple scattering method’ for arbitrary-shaped nanostructures including electronic spillover correction. We relate the electronic capacitance of the material to the curvature correction expressed in terms of ratio of electronic screening length to principal radii of curvature. Electronic capacitance of various nanostructures is obtained showing geometrical shape- and size-dependent electronic screening in nanostructures that manifest important consequences in charge storage enhancement or reduction.

Hydrostatic pressure effects onto the electronic structure and differential capacitance profile for a metal/δ-doped-GaAs.

ABSTRACTA metal-semiconductor contact with a n-type δ-doped quantum well of impurities (metal/δ-doped GaAs) was studied numerically to extract electronic properties such as energy levels and the corresponding wave functions of each level as well as the differential capacitance for the structure. In this work we reported these properties as a function of the hydrostatic pressure (p). We used the effective mass approximation for the calculation of the electronic structure and consider the hydrostatic pressure effects on the basic semiconductor parameters as is the effective mass for the conduction electrons and the static dielectric constant, finally we also take into account an experimental expression that dependency of the Schottky barrier height as a function of this external factor, at least for values between 0 and 6 kar. We showed that the linear behavior for C−2, obtained by pervious works, is switched over a parabolic-like curve due to the δ-doped two-dimensional impurities density.

Electrosynthesis and characterization of gold nanoparticles for electronic capacitance sensing of pollutants

In the present study, gold/surfactant core/shell colloidal nanoparticles with a controlled morphology and chemical composition have been obtained via the so-called sacrificial anode technique, carried out in galvanostatic mode. As synthesized Au-NPs had an average core diameter comprised between 4 and 8 nm, as a function of the electrochemical process experimental conditions. The UV–Vis characterization of gold nanocolloids showed clear spectroscopic size effects, affecting both the position and width of the nanoparticle surface plasmon resonance peak. The nanomaterial surface spectroscopic characterization showed the presence of two chemical states, namely nanostructured Au(0) (its abundance being higher than 90%) and Au(I). Au-NPs were then deposited on the top of a capacitive field effect sensor and subjected to a mild thermal annealing aiming at removing the excess of stabilizing surfactant molecules. Au-NP sensors were tested towards some gases found in automotive gas exhausts. The sensing device showed the largest response towards NO x , and much smaller – if any – responses towards interferent species such as NH 3, H 2, CO, and hydrocarbons.

Calibração e validação de um medidor de capacitância num projecto de agriculturade precisão em pastagens

The general objective of the study was calibrate an electronic capacitance meter to estimating the pasture dry matter in a precision agriculture project. The standard method of assessing pasture requires great effort and farmers are not willing to make this effort in day-to-day management of pastures. The field tests for carrying out in different dates of 2007 and in three dairy farms, represents the typical pastures in Alentejo region (grasses; leguminous; and bio divers mixture). Regression techniques are used to relate the weight of the herbage in kg of dry matter for hectare to the meter reading of capacitance. The estimation of dry matter of the herbage mass, in kg ha-1, based in capacitance was relatively good in two sites, with overall coefficients of determination of 0,90 in grasses and 0,67 to 0,75 in bio divers mixture. In the leguminous the coefficients of determination obtained varied between 0,27 and 0,59. In 2008, the regression equations were validated in two sites and the results showed a gap between the mass effectively cut and the estimated mass of less or equal to 20%.

Effect of herbage mass on the selection and use by cattle of fine‐scale locations in a progressively grazed tropical grass pasture

AbstractThis study quantified herbage mass and feeding behavior by animals at a fine spatial scale, in a 1.1‐ha bahiagrass (Paspalum notatum Flügge) pasture progressively (4 or 5 days) grazed by a herd of 32–33 beef cows and 8–13 calves in three seasons (spring, summer and autumn). Herbage mass was nondestructively estimated every day, using an electronic capacitance probe, at 91 fixed locations (50 cm × 50 cm; approximating a feeding station scale) along a permanent line transect. At the same time, selection and use of the individual locations by cows were measured every day, in terms of the number of visits, number of bites and residence time. Vegetation of the pasture created a trade‐off between availability (herbage mass) and quality (nitrogen concentration, dry matter digestibility) in summer and autumn but not in spring. There were always considerable location‐to‐location variations in the feeding behavior of animals; that is, some locations were not visited and bitten at all or were visited infrequently (once or twice daily) and grazed only for a short time (<10 s daily) receiving relatively few bites (<10 bites daily), whereas some locations were frequently visited (5–10 times daily) and utilized for a long period (>30 s daily) receiving many bites (>30 bites daily). Although regression analysis showed a tendency for animals to select and use locations with higher herbage mass in spring and those with lower or intermediate herbage mass in autumn as a result of the seasonally different availability–quality relationships, neither herbage mass nor herbage quality was an absolute factor determining the choice and use of locations by animals. The results show that the choice and use of fine‐scale locations by animals foraging in actual grasslands are not fully explained by major forage factors such as mass, nitrogen and digestibility.

A sensitive electronic capacitance measurement system to measure the comb drive motion of surface micromachined MEMS devices

We have developed a method to measure the displacement of a MEMS comb drive using a probe station, by monitoring the minute capacitance changes between the fingers due to the motion. Probe station measurements of the capacitance changes of small comb drives are usually hampered by the relatively large parasitic capacitances present. This can be reduced by using a proper measurement layout design for minimal on-chip capacitance, in combination with a resonant LCR-circuit to counteract the effect of the probe station cable capacitance. The method results in a measurement that, after averaging, enables us to see the motion of a MEMS comb drive with 4 nm peak-to-peak noise sensitivity, corresponding to a capacitance change around 10 aF. Both the effect of comb drive lateral motion and that of levitation are observed.

Alternative Methods of Estimating Forage Height and Sward Capacitance in Pastures Can Be Cross Calibrated

Alternative Methods of Estimating Forage Height and Sward Capacitance in Pastures Can Be Cross Calibrated

Measurement of the quantum capacitance of interacting electrons in carbon nanotubes

The electronic capacitance of a one-dimensional system such as a carbon nanotube is a thermodynamic quantity that contains fundamental information about the ground state1. It is composed of an electrostatic component describing the interactions between electrons and their correlations, and a kinetic term given by the electronic density of states. Here, we use a field-effect transistor geometry to obtain the first direct capacitance measurement of individual carbon nanotubes, as a function of the carrier density. Our measurements detect the electrostatic part of the capacitance as well as the quantum corrections arising from the electronic density of states. We identify the van-Hove singularities that correspond to the one-dimensional electron and hole sub-bands and show that the measured capacitance exhibits clear electron–hole symmetry. Finally, our measurements suggest the existence of a negative capacitance, which has recently been predicted to exist in one dimension as a result of interactions between electrons2,3,4.

Variant of estimation method of above‐ground plant biomass in grassland with gamma model 1. Use of an electronic capacitance probe

AbstractWe propose the following method for estimating above‐ground plant biomass (biomass, hereafter) in grassland as a variant of Shiyomi's (1991) second method and test its accuracy of estimation. The method proceeds thus: (i) place a given number of quadrats in the grassland of interest; (ii) an electronic capacitance probe is used to provide corrected meter reading (CMR) values within each quadrat; (iii) two sampling points with a biomass of C1 g and C2 g based on CMR values are selected to allow subdivision into three approximately equal frequency classes; (iv) quadrats are placed and CMR values are measured at the two sampling points; (v) the vegetation within the two quadrats is harvested and these samples weighed after drying; (vi) each quadrat (placed in step [i]) is divided into three categories based on the CMR values – less than C1 g, more than C1 g and less than C2 g, and more than C2 g; and (vii) biomass is estimated from the data obtained by these procedures using the gamma model. Test results suggest that the accuracy of biomass estimation of our method is equivalent to that of the cutting method using several quadrats. Thus, we propose the use of an electronic capacitance probe to rank pasture biomass and the selection of only two quadrat sites for cutting as this offers labor‐saving advantages over current methods.

Adsorption of n-Butanol from Aqueous Solutions on an Sn-Ga Electrode in the Absence of a Metal-Water Chemisorption Interaction

Data on the dependence of the differential capacitance on potential at the Sn-Ga/H2O interface in 0.05 M solutions of Na2SO4 with various additives of n-butanol are obtained by a bridge method at a frequency of 420 Hz and a temperature of 32°C. In the region of potentials studied, the chemisorption interaction (Sn-Ga)-H2O is completely absent. The adsorption parameters of n-butanol are obtained by a method of a regression analysis of these data. The data obtained are compared with similar data on various hydrophobic electrodes. Shown is that, on the Sn-Ga and Pb-Ga electrodes, whose “electronic” capacitance is similar, the free energies of adsorption of n-butanol are also similar but differ from the adsorption energy on electrodes of Hg, Bi-Ga, and Tl-Ga. The results that are obtained on an Sn-Ga electrode nicely fit a general correlation dependence between the reciprocal value of the electronic capacitance of various electrodes in the absence of a metal-water chemisorption interaction, (C m −1 ), and the free energies of adsorption of molecules of n-butanol on these, ΔG A 0 . The dependence of the free energies of adsorption of molecules of n-butanol in the absence of a metal-water chemisorption interaction on the magnitude of the electronic capacitance of the metal confirms the assumption that we had put forth previously that it is necessary to introduce corrections to criteria of hydrophilicity of metals based on a comparison of quantities ΔG A 0 and potentials of cathodic peak of adsorption-desorption Edes, which are expressed in a rational scale. With the obtained correlation relationships taken into account, criteria of hydrophilicity are suggested, which take into account these correlation relationships.

Adsorption of n-Butanol on Pb–Ga in Aqueous Solutions: Effect of Metal on the Adsorption of Organic Compounds in the Absence of Metal–Water Chemisorption Interaction

The potential dependence of the differential capacitance is measured by an ac bridge at 420 Hz and 32°C at Pb–Ga/H2O interface in 0.05 M Na2SO4 solutions containing n-butanol in different concentrations. Adsorption parameters for n-butanol are determined using a regression analysis and compared with those for Hg, Tl–Ga, and Bi–Ga. As follows from this comparison, though there is no chemisorption interaction between these metals and water, the energy of n-butanol adsorption at these metals depends on the metal nature. The Pb–Ga data fit a common correlation dependence of the electronic capacitance of different electrodes (Cm–1)phys on the energy of the n-butanol molecules adsorption thereon in the absence of a metal–water chemisorption interaction. This finding evidences that the dependence of the energy parameters for the adsorption of organic compounds on the metals' electronic properties, when characterized by (Cm–1)phys, is of general nature.

Calibration of electronic capacitance and dissipation factor bridges

A new calibration procedure for electronic capacitance and dissipation factor bridges is presented. These bridges measure the ratio of their input currents. For the calibration, two sinusoidal alternating currents are synthesized with the aid of a digital, programmable two-channel AC voltage source and two AC resistors. The complex ratio of these synthesized input currents is calculated from an AC voltage ratio determined by a sampling method, together with the impedance ratio of the AC resistors. At currents of a few mA, their complex ratio in the frequency range up to 100 Hz can be measured with uncertainties (k=2) of approximately 1/spl times/10/sup -6/ and 1 /spl mu/rad, respectively.