Capacitor Research Articles

Crack sensor based on patch antenna fed by capacitive microstrip lines

When sensors based on a single patch antenna are used to monitor crack width, the issues of incomplete strain transfer ratio, insufficient bonding strength, and randomness of crack propagation will inevitably compromise sensor sensitivity and make the calibration uncontrollable. To circumvent these difficulties, this study presents a novel crack-measuring sensor based on a rectangular patch antenna fed by a pair of microstrip lines, which form a parallel plate capacitor as a crack-sensing unit. The sensing mechanism was analyzed using the transmission-line model. Then two crack sensor prototypes were designed and the dimensions were optimized. A crack opening simulator was customized to test the sensors by using different width resolutions. The experiment results validated that the resonant frequency shifts are linearly proportional to the applied crack width; moreover, the crack sensor proved capable of detecting crack widths as small as one-hundredth of a millimeter in an object.

A COMPARATIVE STUDY: VOLTAGE MULTIPLIERS FOR RF ENERGY HARVESTING SYSTEM

Voltage multipliers are widely used for energy harvesting processes to convert the received AC signal to DC signal, also enhanced the low level received signal. In this study, Villard, Dickson and Greinacher type voltage multipliers are analyzed without impedance matching and substrate materials to decide the effective voltage multiplier type depend on the inputs of the harvester. So, load resistance, input power and input frequencies’ effects are analyzed and compared with each other. Agilent Advanced Design System (ADS) is used for simulations. HSMS 2852 Schottky diode and capacitors are used for these voltage multipliers. Results show that, determining load resistance is important for evaluating high efficiency, e.g. efficiency differences are reached 33% between 2kΩ and 20 kΩ for Dickson voltage multiplier at 100 MHz input frequency. Furthermore, the best efficiency is obtained by Greinacher voltage multiplier for low input frequencies which is lower than 1 GHz but there are no significant differences are observed for high frequencies. This study shows that load resistance, input frequency and input power are important parameters for voltage multiplier selection and Greinacher voltage multiplier is the best choice to obtain high efficiency for low frequency application of RF harvesting.

An SVC based Power Quality Improvement Model for Consumers Connected to Weak Busses in Distribution Systems

Power quality is a major concern considering weak bus systems. In order to improve power quality, residential consumers go with voltage stabilizers as a cheap solution consequently overstressing weak busses. Industrial consumers use other alternatives like switched capacitor banks to cope with low power factor but the limitation is step-wise reactive power injection which does not meet the changing load requirements. Real time improvement requires constant monitoring and real-time injection of Volt-Ampere-Reactive (VAR) which is possible with the help of a Static VAR Compensator (SVC). An SVC based Power Quality Improvement (PQI) is proposed in this paper which addresses the real time varying reactive VAR requirement with reduced harmonic content.

Understanding Dielectrics: Impact of External Salt Water Bath.

As predicted by the theory of super dielectric materials, simple tests demonstrate that dielectric material on the outside of a parallel plate capacitor dramatically increases capacitance, energy density, and power density. Simple parallel plate capacitors with only ambient air between the plates behaved as per standard theory. Once the same capacitor was partially submerged in deionized water (DI), or DI with low dissolved NaCl concentrations, still with only ambient air between the electrodes, the capacitance, energy density, and power density, at low frequency, increased by more than seven orders of magnitude. Notably, conventional theory precludes the possibility that material outside the volume between the plates will in any fashion impact capacitive behavior.

Fractional model of the electrochemical capacitor relaxation phenomenon

Fractional model of the electrochemical capacitor relaxation phenomenon

Correction: Nilsson, J. et al. Maximal Q Factor for an On-Chip, Fuse-Based Trimmable Capacitor. Electronics 2019, 8, 62

The authors wish to make the following correction to our published paper [...]

Vertically Aligned Carbon Nanotubes Capacitive Sensors

Capacitive sensors are key components in a wide range of sensing applications, such as gas detectors and safety systems. While the mainstream silicon sensors demonstrated good performances, vertically aligned carbon nanotubes (VA-CNTs) outperform them and, therefore, are an attractive candidate material for capacitive applications owing to their extremely high surface area. Specifically, their top (crust) layer is characterized by a porous and dense morphology that further enhances the capacitive area and, consequently, induces an electrostatic fringe field and an enhancement of the capacitance. In this paper, we study how the porosity of VA-CNTs determines their electrostatic behavior. We observed that the porous surface of the crust layer generates a significant enhancement of the capacitance comparing to parallel plate capacitors. The rough surface of the crust layer results in amplification of the VA-CNT effective capacitor area, which further increases with the electrostatic gap. As-grown VA-CNTs with lower porosity demonstrate higher capacitance; however, densified samples and samples reinforced with conductive nano-particles did not show an enhancement of the capacitance, due to a significant change in their CNT formation. Thus, this paper emphasizes the influence of the morphological structure of VA-CNTs on their capacitance and enriches the material library that can be used for capacitive sensing.

Design of capacitance based on interdigitated electrode for BioMEMS sensor application

In this paper present, an electrostatic actuation mechanism based on the interdigitated electrode for the Biomedical Micro Electro Mechanical Systems (Bio-MEMS) sensors was mainly used for sensing or actuation in analytical and different detection applications. One of the main things interdigitated electrode (IDE) for capacitance derived from multiple electrode pairs has been connected in parallel with wide proof mass, folded spring beam attached as anchor in the sensor construction. The total capacitance was a sum of capacitance contributed by neighbouring electrodes. Hence the opposite walls of comb electrodes in the overlapping region form a parallel plate capacitor and contribute a capacitance C easily analyzed with fringe capacitance can be estimated to analytically difficult one. However, the nearly accurate way to estimate for the fringe capacitance is by using the finite element method (FEM). The major importance of the geometric dimensions on interdigitated electrode sensors are studied with an analytical model. The design of capacitive based IDE sensors are simulated and demonstrated on visualizing of the electrical properties by COMSOL Multiphysics software.

Measurement and regulation of saturated vapour height level in VPS chamber

Purpose The purpose of this paper is to investigate measurement and regulation of saturated vapour height level in vapour phase soldering (VPS) chamber based on parallel plate capacitor and retaining a stable saturated vapour level above the boiling fluid, regardless of the quantity and size of assembled components. Design/methodology/approach Development and realisation of capacitance sensor that sensitively senses the maximum height level of saturated vapour above the boiling fluid in the VPS chamber was achieved. Methodology of measurement is based on capacitor change from single air to a parallel plate, filled with two dielectric environments in a stacked configuration: condensed fluid and vapour (air). Findings An easy air plate capacitor immersed in the saturated vapour above the boiling fluid can serve as a parallel plate capacitor owing to the conversion of the air to the parallel plate capacitor. A thin film of fluid between the two capacitor plates corresponds to the height of the saturated vapour, which changes the capacity of the parallel plate capacitor. Originality/value Introducing the capacitive sensor directly into the VPS work space allows to achieve a constant height level of saturated vapour. Based on the capacity change, it is possible to control the heating power. There is a lack of information regarding measurement of stable height of vapour in the industry, and the present article shows how to easily improve the way to regulate the bandwidth of saturated vapour in the VPS process.

An Ultra-Wideband Measurement Method for the Dielectric Property of Rocks

Dielectric properties of rocks are the important indicators of subsurface formations when electromagnetic sensing methods are applied. Interpreting those in situ measurements relies on characterizing the dielectric permittivity of rock samples in the laboratory. For solid phase samples, the parallel-plate capacitance method (PCM) serves as one of the most accurate and feasible methods for charactering electrical properties. Low-frequency (~kilohertz) PCM measurements are most common; extending the PCM to an ultra-wideband measurement will establish a general framework for measuring both low-frequency and high-frequency (~gigahertz) properties (e.g., permittivity and conductivity). Major challenges of ultra-wideband measurements using the PCM are: 1) at high frequency, the measurement apparatus may introduce errors due to reflection and dissipation of the electromagnetic waves and 2) resonance caused by impedance mismatching in the apparatus design can occur at higher frequency, which will significantly compromise the accuracy of this method. Thus, the optimization and modification of the method is needed. In this letter, we: 1) show the validity and accuracy of the PCM for permittivity measurement by comparing numerical simulation and experiments; 2) propose a practical geometric parameter to conduct system-level optimization under giving constrains; 3) perform the optimization for the sample holder to increment the measurement accuracy at higher frequency without downsizing the sample. The results show that a satisfactory accuracy and stability can be achieved in an ultra-wide range of frequency spectrum from 100 kHz to 1.5 GHz with the improved PCM apparatus design.

A New Hybrid Unit Operation for Gas Separation Membranes Application

An innovative membrane-based process for the separation of gaseous streams has been developed and tested at lab-scale. The new process can be conveniently carried out on the same modules currently employed for conventional gas separation membrane systems, and it relies on periodic swing of the downstream pressure, while upstream conditions are kept constant. Such new unit operation is run with no need of switching streams, and it allows to process constant flow rate and composition of both feed and retentate, while permeate is collected at assigned frequency, resulting in an overall on-average steady state process. An on-off control strategy over time of permeate collection produces alternate sorption/desorption steps in the membrane, associated to increase/decrease cycles of downstream pressure in the process, in a similar fashion to pressure swing adsorption (PSA). Indeed, consistently with the hybrid nature of the new process, the specific dynamic control of downstream pressure allows the exploitation of both resistive (permeation) and capacitive (adsorption) properties of the membrane, and the associated characteristics in terms of selectivity. By changing the duration of pressure swing period, the resistive or capacitive properties of the membrane can be conveniently tuned in order to explore different performances of the process, in terms of key component recovery and separation factor.

Performance of Lithium-ion Capacitors Using Pre-lithiated Multi-walled Carbon Nanotube Composite Anode

Performance of Lithium-ion Capacitors Using Pre-lithiated Multi-walled Carbon Nanotube Composite Anode

Structural changes of cerium doped copper ferrites during sintering process and magneto-electrical properties assessment

Abstract Crystalline CuCexFe2-xO4 nanoparticles with different rare earth metal content (x = 0.00, 0.03, 0.05, 0.08 and 0.10) were synthesized using a co-precipitation technique that involves a 600 °C calcination treatment. The newly obtained powders were pressed into pellets and heated up to 950 °C in order to form a compact and less porous material, ideal for dielectric measurements. X-ray investigations revealed a structural modification from typical cubic system to a tetrahedral spinel form, accompanied by Ce3+ cations exclusion and formation of secondary phases. The amount of phases and cations distribution were determined by Rietveld refinement method. A degradation process of cerium doped copper ferrite was proposed based on X-ray analysis and Rietveld refinement. Furthermore, the magnetic behavior of both 600 °C and 950 °C samples was investigated from the hysteresis loops recorded from a vibrating sample magnetometer (VSM) in a ±10 kOe range. Room temperature dielectric values for the 950 °C samples were determined using the parallel-plate capacitor configuration in a frequency range of 10 Hz – 1 MHz.

Conduction and Excess Charge in Silicate Glass/Air Interfaces.

The glass/air interface shows electrical properties that are unexpected for a widely used electrical insulator. The mobility of interfacial charge carriers under 80% relative humidity (RH) is 4.81 × 10-5 m2 s-1 V-1, 3 orders of magnitude higher than the electrophoretic mobility of simple ions in water and less than 2 orders of magnitude lower than the electron mobility in copper metal. This allows the glass/air interface to reach the same potential as a biased contacting metal quickly. The interfacial surface resistance R increases by more than 5 orders of magnitude when the RH decreases from 80 to 2%, following an S-shaped curve with small hysteresis. Moreover, the biased surfaces store charge, as shown by Kelvin potential measurements. Applying an electric field parallel to the surface produces RH-dependent results: under low humidity, the interface behaves as expected for an ideal two-dimensional parallel-plate capacitor, while under high RH, it acquires and maintains excess negative charge, which is lost under low RH. The glass surface morphology and potential distribution change on the glass/air interface under high RH and applied potential, including the extensive elimination of nonglass contaminating particles and potential levelling. All these surprising results are explained by using a protonic-charge-transfer mechanism: mobile protons dissociated from silanol groups migrate rapidly along a field-oriented adsorbed water layer, while the matrix-bound silicate anions remain immobile. Glass may thus be classified as the ionic analogue of a topological insulator but based on structural features and charge-transfer mechanisms different from the chalcogenides that have been receiving great attention in the literature.

Electrical Properties of Thiol-ene-based Shape Memory Polymers Intended for Flexible Electronics.

Thiol-ene/acrylate-based shape memory polymers (SMPs) with tunable mechanical and thermomechanical properties are promising substrate materials for flexible electronics applications. These UV-curable polymer compositions can easily be polymerized onto pre-fabricated electronic components and can be molded into desired geometries to provide a shape-changing behavior or a tunable softness. Alternatively, SMPs may be prepared as a flat substrate, and electronic circuitry may be built directly on top by thin film processing technologies. Whichever way the final structure is produced, the operation of electronic circuits will be influenced by the electrical and mechanical properties of the underlying (and sometimes also encapsulating) SMP substrate. Here, we present electronic properties, such as permittivity and resistivity of a typical SMP composition that has a low glass transition temperature (between 40 and 60 °C dependent on the curing process) in different thermomechanical states of polymer. We fabricated parallel plate capacitors from a previously reported SMP composition (fully softening (FS)-SMP) using two different curing processes, and then we determined the electrical properties of relative permittivity and resistivity below and above the glass transition temperature. Our data shows that the curing process influenced the electrical permittivity, but not the electrical resistivity. Corona-Kelvin metrology evaluated the quality of the surface of FS-SMP spun on the wafer. Overall, FS-SMP demonstrates resistivity appropriate for use as an insulating material.

Demonstration of Microwave Multiplexed Readout of DC-Biased Superconducting Nanowire Detectors

Superconducting nanowires are widely used as sensitive single photon detectors with wide spectral coverage and high timing resolution. We describe a demonstration of an array of DC biased superconducting nanowire single photon detectors read out with a microwave multiplexing circuit. In this design, each individual nanowire is part of a resonant LC circuit where the inductance is dominated by the kinetic inductance of the nanowire. The circuit also contains two parallel plate capacitors, one of them is in parallel with the inductor and the other is coupled to a microwave transmission line which carries the signals to a cryogenic low noise amplifier. All of the nanowires are connected via resistors to a single DC bias line that enables the nanowires to be current biased close to their critical current. When a photon hits a nanowire it creates a normal hot spot which produces a voltage pulse across the LC circuit. This pulse rings down at the resonant frequency of the LC circuit over a time period that is fixed by the quality factor. We present measurements of an array of these devices and an evaluation of their performance in terms of frequency and time response.

Further Study of the Sensing Ring Position on the Orifice-Type Capacitive Flow Sensor

The flow head of an orifice-type capacitive flow sensor for a conducting liquid consists of a vertically mounted metallic orifice plate in a horizontal pipeline made of insulating material and a rigidly grounded metallic ring or sensing ring placed surrounding the pipeline at a small distance from the orifice plate where the capacitance between the orifice plate and the sensing ring follows a linear relationship with flow rate as reported in the literature. In this paper, a further study on the effect of position of the sensing ring on the sensor capacitance has been carried out along with the modification of the simple parallel plate capacitance principle described in the earlier work by the real disk-type capacitance principle. From this paper, it has been observed that for any position of the sensing ring near the orifice plate, the sensor capacitance decreases linearly with the increase of flow rate and follows the modified capacitance principle similarly as that observed in earlier work. It has also been observed that the sensing ring distance-sensor capacitance product increases almost linearly with the increase of sensing ring distance. From the experimental study of the proposed orifice type capacitive flow sensors installed on two different pipelines, the said modified theory of the sensor appears to be verified in the present paper where the experimental results are reported.

Controlled Growth of Metal Nanoparticles on Multi-Walled Carbon Nanotubes for Chemical Sensing Applications

We have grown nanoparticles of gold, silver, copper, cobalt and nickel on the surface of carbon nanotubes which are deposited by CVD on gold wires bearing a nickel catalyst layer. A study of the CVD reaction as a function of time revealed that one-minute and ten-minute deposition times yielded qualitatively similar coatings. Metal nanoparticles were grown from electroplating solutions by using the nanotube-coated wire as the working electrode and running a galvanostatic, electrochemical deposition. For gold depositions, we were able to show that varying the conditions of current, plating bath concentration and deposition time allowed control of the size of the deposited nanoparticles within the range of 10 – 150 nm. The morphology of the gold nanoparticles was approximately spherical, except under unique conditions where spiked spheroids, also known as nano-urchins, were observed. By using the gold nanoparticle-decorated CNT electrode as one plate in a parallel-plate capacitor, we were able to show a change in electrical properties, such as capacitance, by comparing voltammograms before and after exposure of the electrode to a dilute solution of organic thiols. This demonstrates the potential utility of the electrode structure as a chemical detector. The two SEM images below show typical results. On the left, CVD carbon nanotube growth prior to electrodeposition of metal nanoparticles; note the presence of nickel catalyst particles at nanotube tips. On the right, carbon nanotube sample after electrodeposition of gold nanoparticles. Figure 1

(Invited) Mechanical Forces Around the Diffuse Double Layer

Our group has recently fleshed out a general theoretical framework applicable to problems where electricity induces mechanical responses within electrolytic media. We take a continuum approach, rooted in classical thermodynamics and irreversible thermodynamics, which extends Newman's concentrated-solution theory by accounting for mechanical dynamics via a coupled momentum balance. This talk will focus on an application of coupled electrochemical/mechanical transport theory to ideal parallel-plate electrolytic capacitors. A classical Poisson-Boltzmann model of the diffuse double layer within the electrolytic separator is augmented to include space charging within the conductive capacitor plates, which are modelled as Sommerfeld-Fermi electron gases. When accounted for in this way, the electrodes are found to contribute significantly towards the double-layer capacitance, as well as exerting a substantial compressive force on the electrolyte's boundary. This toy problem may help to clarify modelling approaches to piezoelectric materials with substantial electrochemical activity. Both nonlinear and linear versions of the theory will be explored, the former around a single plate and the latter for the entire capacitor. The linear model holds when the electrolyte's Debye length far exceeds the plate separation, allowing the mechanical forces to be studied in the well-understood limit where the separator is an ideal dielectric.

High Q-factor near infrared and visible Al2O3-based parallel-plate capacitor kinetic inductance detectors.

We designed, fabricated and characterized parallel-plate capacitor lumped-element kinetic inductance detectors (LEKIDs) to operate at near-infrared and optical wavelengths (0.3 -1 μm). The widely used interdigitated capacitor is replaced by a parallel-plate capacitor which, for a given resonance frequency, has a larger capacitance value within a much smaller space allowing to strongly reduce the size of the pixels. The parallel-plate capacitor LEKID array comprises 10 × 10 pixels. The inductive meander is patterned from stoichiometric 52 nm-thick TiN film (Tc ≈4.6 K). The parallel-plate capacitor is made of a TiN base electrode, Al2O3 dielectric and Nb upper electrode. More than 90 resonances out of 100 within the 0.994-1.278 GHz band were identified. The resonances exhibit internal Q-factors up to ∼370 000 at 72 mK. The array was illuminated using a white light and 890 nm monochromatic near infrared LEDs. The estimated quasiparticle lifetime is τqp≈13 µs.