Direct Capacitance Research Articles

Relative Permittivity Measurements of Carbon Dioxide + Ethanol Mixtures

The relative permittivities (εr) of carbon dioxide (CO2) + ethanol mixtures (0.050, 0.100, 0.152, and 0.212 mass fractions of ethanol) were measured at (303 to 333) K in the pressure range (7.2 to 30.8) MPa using a direct capacitance method.

Determination of space charge distributions in highly segmented large volume HPGe detectors from capacitance–voltage measurements

The space charge distribution of a large volume highly segmented HPGe detector was determined by a non-destructive capacitance–voltage measurement. The capacitances between the 36 segments and the core were measured simultaneously with a precision pulser which was implemented in the core preamplifier. The pulser measurement was compared to and validated by direct capacitance measurements. The three-dimensional doping profile was reconstructed using analytical and numerical methods. Consistent values for the impurity concentration in the range of 0.5 and 1.5×10 10 cm −3 were obtained.

A Comparative Study on Two Kinds of 3D Direct Capacitance Imaging Sensors

Two kinds of sensor structures for 3D direct capacitance imaging are presented. 12 electrodes are arranged in three planes each with four electrodes. Every four electrodes on each plane are rotated 45° (sensor 1) or 0° (sensor 2) with reference to the previous. A comparative study between the two sensors shows that although the difference in sensor’s sensitivities and outputs is obvious, the difference in reconstruction images isn’t apparent, at least for some permittivity distribution. The output range of sensor 1 is smaller than that of sensor 2, thus sensor 1 is better than sensor 2 in terms of the design of a capacitance measuring circuit. Both sensors can achieve 3D direct capacitance imaging with a good axial resolution.

Miniature Implantable Pressure Sensors for Medical Applications

Pressure sensors are requisite for many medical implantable devices to monitor physiological pressures or fluid pressure and flow from a subsystem. Size, power consumption, accuracy, sensitivity, stability, and biocompatibility are all key considerations in the design and fabrication of such sensors. Conventional designs, based on piezoresistive technologies, are power consuming with significant drift and temperature error, whereas capacitive solutions are often cumbersome when packaged for biocompatibility. Tronics Microsystems has developed absolute pressure sensors, which achieve the benefits of both technologies. Miniaturization is achieved using a MEMS sensing element and a multifunction ASIC with small form factors. Low power consumption, low drift, high resolution, and waveform capture capability are obtained by using a capacitive MEMS coupled with a sigma-delta, direct capacitance to digital converter. Biocompatibility is achieved with grade II titanium packaging in two form factors (“tubular” or “pancake”) for incorporation into various applications. These sensors have been fabricated, calibrated, and tested extensively over physiologic temperature ranges. The design has achieved power consumption lower than 500 ÂμW at 100 Hz and a drift lower than 0.5% full scale per year. An accuracy of +/−1% full scale, over the temperature range is obtained by on-ASIC nonlinearity and temperature compensation. The two packaging configurations allow analysis of the trade-offs on the temperature range, sensitivity, volume, sterilization, etc. Different feed-through materials permit optimization of the form factors for the tube and the flat sensor and wired or wireless communication.

Development of a DNA probe using barium strontium titanate

In this paper we report on the development of an electronic DNA sensor probe assembly using barium strontium titanate (BST) applied by pulsed laser deposition in conjunction with optical spectroscopy and impedance spectroscopy methods. To verify the binding of the probe to the BST, Fourier transform infrared (FTIR) spectroscopy and attenuated total reflectance (ATR) techniques were employed. FTIR and ATR were employed to verify the hybridization of the probe to an oligonucleotide target. In addition to the FTIR technique, direct capacitance and impedance spectroscopy measurements were used to verify the ability of the probe binding to the ceramic substrate and also the hybridization of the target DNA strand to the probe DNA strand. The proposed design has the advantages of label-free detection and large detectable capacitance changes upon hybridization, and does not require the application of a gold electrode layer.

Development of a capacitive mass measuring system

The paper deals with the theory, design, fabrication and test results of a robust, linear and accurate capacitive mass sensor. The change in capacitance, with increased mass, takes place due to the shielding effect of a conducting cylinder which moves in between the stationary concentric co-axial cylinders. A direct capacitance measuring system, developed by the authors, is used in the calibration of the mass sensor. Presented sensor is linear, immune to temperature errors, highly flexible in the design and can cover different weighing ranges by selecting proper springs only. For the spring, used in the system, mass sensor can weigh up to 4 kg.

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

In gas-solid fluidized beds, the distribution of the particles typically varies both in time and space. Since the gas-solids distribution and its variation have a strong influence on the performance of a fluidized bed for a given process, it is very important to accurately measure the gas-solids or voidage distribution. This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. We will treat subsequently direct visualisation, tomography, optical probes, capacitance probes, and pressure measurements.Dense gas-solids flows are typically opaque to visible light. This makes optical techniques only of limited use in dense gas-solids flow. However, direct visualization can be useful for very dilute systems, pseudo 2-D beds, and the outer layer of dense, 3-D systems. Tomography is frequently used to obtain the voidage distribution in a horizontal cross-section of the bed. Electric capacitance tomography is fast, but its spatial resolution is limited and image reconstruction is still troublesome. Although some steps forward have been made, research is continuing at this point. For nuclear (X-ray and gamma-ray) tomography, the image reconstruction is much easier and the spatial resolution better, but its temporal resolution is typically much lower. Therefore, research efforts for nuclear tomography are mainly aimed at increasing the measurement frequency. Optical probes determine the voidage as a function of time in a small measurement volume, either by the degree of reflection or by the degree of transmission of a light bundle. Capacitance probes determine the voidage as a function of time in a small measurement volume by measuring the dielectric permittivity of the gas-solids suspension in the measurement volume. Both optical and capacitance probe techniques are reasonably well-developed; the current research effort spent at improving them seems limited, especially for capacitance probes. Time-averaged pressure measurements are commonly used to determine the average bed density and bed height. By sampling the local pressure at a sufficiently high frequency (typically in the order of 200 Hz), much more information can be obtained about the fluidized bed hydrodynamics. However, obtaining quantitative voidage data from pressure fluctuations measurement remains a difficult task; in-bed pressure fluctuation (and acoustic) measurements are mostly used to determine changes in the voidage dynamics and distribution.

Dielectric properties of 1,1,1-trifluoroethane (HFC-143a) in the liquid phase

The relative permittivity ( ɛ r) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ɛ r measurements is estimated to be better than ±1.2 × 10 −2. A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ɛ r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase ( μ*). The apparent dipole moment obtained was μ* = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements.

Influence of heat treatment on magnetostrictions and electrical properties of (Fe 1Co 1) 76Mo 8Cu 1B 15

The investigation of magnetostriction of (Fe 1Co 1) 76Mo 8Cu 1B 15 metallic glass upon structural changes has been performed on samples with different thermal history. The samples have been annealed for 0.5 h at different temperatures ranging from 573 to 973 K. Measurements of saturation magnetostriction λ S, volume magnetostriction ω and forced magnetostriction ∂ ω/∂H have been performed using direct capacitance method. For the set of annealed samples, the temperature dependence of lambda(s) exhibits local maximum at 828 K. Above 828 K, there is a decrease of lambda(s) by about 1/3 of its maximal value. The dependence of the value of ∂ ω/∂H on the annealing temperature exhibits local minima at 573 and 923 K and local maximum at 678 K. These extremes in λ S and ∂ ω/∂H are related to the changes in CSRO and TSRO, to relaxation processes and to internal stresses. The transformation process has been monitored by temperature dependencies of electrical resistivity. Amorphous samples crystallized after annealing at temperatures above 678 K into nanocrystalline supersaturated solid solution bcc-Fe(Co, Mo) and above 873 K into B 24Fe 84Mo 8, CoMoB and traces of B 2Mo 2Fe and tetragonal Fe 3B. As-quenched samples exhibit the Curie temperature at around 600 K, in the vicinity of the glass transition temperature. At room temperatures, the ribbon exhibits isotropic characteristics. Thermal treatment induces magnetic anisotropy formed in the direction parallel to the ribbon axis during relaxation annealing while during crystallization its direction becomes perpendicular to the ribbon axis. Remanence appears after heat treatment above 920 K.

Measurement of Carrier Mobility in Silicon Nanowires

We report the first direct capacitance measurements of silicon nanowires (SiNWs) and the consequent determination of field carrier mobilities in undoped-channel SiNW field-effect transistors (FETs) at room temperature. We employ a two-FET method for accurate extraction of the intrinsic channel resistance and intrinsic channel capacitance of the SiNWs. The devices used in this study were fabricated using a top-down method to create SiNW FETs with up to 1000 wires in parallel for increasing the raw capacitance while maintaining excellent control on device dimensions and series resistance. We found that, compared with the universal mobility curves for bulk silicon, the electron and hole mobilities in nanowires are comparable to those of the surface orientation that offers a lower mobility.

Relative Permittivity and Dipole Moments of Replacement Refrigerant Mixtures (R408A and R409A) in the Liquid State

This paper provides reliable dielectric property information on two refrigerant mixtures regarded as replacements for chorodifluoromethane (CAS no. 75-45-6) (HCFC22) and R502 (CHClF2 + CClF2CF3) (w1 = 0.49; w2 = 0.51). Liquid phase relative permittivity measurements are reported for R408A (CHF2CF3 + CF3CH3 + CHClF2) (w1= 0.07; w2= 0.46; w3= 0.47) and R409A (CHClF2 + CHClFCH3 + CClF2CH3) (w1 = 0.60; w2 = 0.25; w3 = 0.15). The measurements were performed by using a direct capacitance method at temperatures from T = (233 to 303) K under pressures up to 16 MPa. A complete set of tables of experimental data, covering dielectric property needs for most engineering applications, is provided. The data obtained was correlated as a function of density, pressure, and temperature. The apparent dipole moments (μ∗) of R408A and R409A in the liquid state were obtained from the Kirkwood modification of the Onsager equation for the variation to the modified molar polarization with temperature and density. The μ∗ value fou...

Relative Permittivities of 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-Hexafluoropropane (HFC-236ea), and 1,1,1,3,3-Pentafluorobutane (HFC-365mfc) in the Liquid Phase

Relative permittivity measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), and 1,1,1,3,3-pentafluorobutane (HFC-365mfc) in the liquid phase are reported. Measurements were performed by using a direct capacitance method at temperatures from 223 K to 303 K and pressures up to 16 MPa for HFC-227ea and HFC-236ea and at temperatures from 263 K to 303 K up to 16 MPa for HFC-365mfc. The uncertainty of the relative permittivity measurements is estimated to be better than ±1.1·10-2. The theory developed by Vedam et al., and adapted by Diguet, and the Kirkwood modification of the Onsager were applied to obtain the apparent dipole moment of HFC-227ea, HFC-236ea, and HFC-365mfc in the liquid state, found to be 2.356 D for HFC-227ea, 2.624 D for HFC-236ea, and 4.917 D for HFC-365mfc. The effective dipole in the liquid state of HFC-236ea predicted by the Kirkwood−Frölich theory is 2.065 D. Density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment are reported for HFC-227ea.

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.

A microfabricated wall shear-stress sensor with capacitative sensing

A silicon-based micromachined, floating-element sensor for low-magnitude wall shear-stress measurement has been developed. Sensors over a range of element sizes and sensitivities have been fabricated by thin-wafer bonding and deep-reactive ion-etching techniques. Detailed design, fabrication, and testing issues are described in this paper. Detection of the floating-element motion is accomplished using either direct or differential capacitance measurement. The design objective is to measure the shear-stress distribution at levels of O(0.10 Pa) with a spatial resolution of approximately O(100 /spl mu/m). It is assumed that the flow direction is known, permitting one to align the sensor appropriately so that a single component shear measurement is a good estimate of the prevalent shear. Using a differential capacitance detection scheme these goals have been achieved. We tested the sensor at shear levels ranging from 0 to 0.20 Pa and found that the lowest detectable shear-stress level that the sensor can measure is 0.04 Pa with an 8% uncertainty on a 200 /spl mu/m/spl times/500 /spl mu/m floating element plate.

Methodology for characterization of high-speed multi-conductor metal interconnections and evaluation of measurement errors

Analysis and design of interconnects in high speed integrated circuits and systems involves models in the form of multiconductor transmission lines. The fundamental parameters of those models are matrices of capacitance, (C), inductance, (L), resistance, (R), and conductance (G). We present a methodology for measurement of entries in capacitance matrix. The entries of capacitance matrices can be calculated using numerical solvers of electrostatic fields established under the assumption of suitable biasing of interconnect structures. Numerical calculations of complete field equations are very complex and expensive in terms of computer time, therefore several approximations are made in constructing interconnect dedicated software packages available on the market. Because of these approximations it is necessary to validate the calculations via measurements. Calculation of the off-diagonal entries of capacitance matrix from measurements of two-terminal capacitances is strongly corrupted by the measuring errors. The method involves direct capacitance measurement in multi-conductor structures and provides analysis of accuracy.

Characterisation of high-speed multiconductor interconnections

The paper presents a method for the determination of the capacitance matrix needed in modelling and simulation of signal transmission in multiple coupled interconnecting lines. The method utilises capacitance measurements and thus one of its useful application areas is in the validation of numerous previously published algorithms based on various approximations to field equations, originally developed for the computation of capacitance matrices. The technique described is based on the active separation of the capacitance network, achieved through the use of a unity-gain amplifier. Thanks to the circuit configurations introduced with a unity-gain amplifier it is possible to make direct capacitance measurements in the multiconductor interconnecting structures. Measurement procedures are described and analysis of errors in measured quantities caused by the imperfections of measuring equipment is discussed. A sample of results obtained in measuring manufactured test structures is included for illustration of the method and measuring procedures.

Dielectric Properties of 1,1,1,3,3-Pentafluoropropane (HFC-245fa)

The relative permittivity of 1,1,1,3,3-pentafluoropropane (HFC-245fa), a liquid hydrofluorocarbon developed as a blowing agent for plastic foams, is reported. This fluid is being evaluated as a potential replacement for HCFC-141b (1,1-dichloro-1-fluoroethane). The relative permittivity of HFC-245fa in the liquid phase was measured using the direct capacitance method at temperatures from (217 to 303) K and at pressures up to 16 MPa, for a frequency of 10 kHz. The uncertainty of the dielectric constant measurements is estimated to be ±0.88 × 10-2. A complete set of values of the relative permittivity as a function of temperature, pressure, and density is presented that covers the needs for most engineering applications. The results were correlated by polynomial equations as a function of density and temperature and also as a function of pressure and temperature. To study the dependence of relative permittivity on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyze the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase. The apparent dipole moment obtained was μ* = 2.688 D.

Dielectric Properties of Liquid Pentafluoroethane (HFC-125)

This paper reports measurements of the static relative permittivity of HFC-125 in the liquid phase, performed by using the direct capacitance method at 10 kHz, for temperatures from 214 to 304 K and pressures up to 16 MPa. The repeatability of the measurements was found to be of the order of ±0.7×10−3and the uncertainty is estimated to be better than ±0.72×10−2. We provide a complete set of tables of experimental data as a function of temperature, pressure, and density, which cover the dielectric property needs for most engineering applications. The data obtained were used to establish dielectric equations of state as a function of density and temperature and as a function of pressure and temperature. To study the dependence of the relative permittivity on temperature, pressure and density, we have applied various molecular theories of polar liquids. The apparent dipole moment obtained wasμ*=2.482 D.

Dielectric constant and dipole moment of hydrofluorocarbon refrigerant mixtures R404A, R407C, and R507

Reliable dielectric property information about three HFC mixtures currently regarded as replacements for R22 and R502 is given. The static dielectric constants of the ternary systems HFC125/143a/134a (R404A), HFC32/125/134a (R407C), and of the binary system HFC125/143a (R507) in the liquid phase were measured by the direct capacitance method at temperatures from 217 to 303 K and under pressures up to 16 MPa. The uncertainty of the measurements is estimated to be within 0.1% and the repeatability 0.01%. A complete set of tables is given of experimental data as a function of temperature, pressure, and density, which covers dielectric property needs for most engineering applications. The data obtained were correlated as a function of density and temperature by polynomial equations. In order to study the dependence of dielectric constant on density and temperature on a molecular basis, the theory developed by Vedam and Chen and adapted by Diguet was applied to analyse the data. Estimates for the dipole moments of the mixtures based on dielectric constant measurements are given. The Kirkwood theory was used to obtain the values of apparent dipole moments of R404A, R407C, and R507 in the liquid phase.

Dielectric Constant of the Nearly Azeotropic Mixture R410A 1

The purpose of this paper is to present dielectric constant measurements of R410A, a chlorine-free refrigerant, which is a 50/50 (mass %) mixture of R32/125. The measurements on R410A were performed as a function of pressure and temperature ranging from 2 to 16 MPa and from 217 to 304 K, respectively, by using a direct capacitance method. The values of dielectric constant have an estimated repeatability of ±0.01% and an accuracy of ±0.1%. The data were correlated as a function of density and pressure. The theory developed by Vedam et al., and adapted by Diguet, and the Kirkwood modification of the Onsager equation for the variation of the modified molar polarization with temperature and density were applied to analyze the data and to obtain the dipole moment of R410A in the liquid state. This was found to be 3.31 Debye.