Capacitor Research Articles

Barium ions in liquid helium

We discuss the properties of barium clusters (neutral or charged) implanted into liquid helium and propose a model where individual barium atoms cannot form negative ions, whereas a barium cluster composed of many barium atoms can. This property is important from the standpoint of applications involving laser ablation of barium metal surfaces in liquid helium. We note the qualitative differences in the mechanisms of formation of quasi-one-dimensional chains of metal or dielectric dust during its implantation into superfluid helium. A likely scenario for a dispersed metal is the dendritic breakdown in a parallel plate capacitor filled with metal dust and a finite potential difference between the plates. It is not possible to use the dendritic mechanism of cluster evolution for the dielectric problem and the details of this mechanism do not agree well with existing observations. We outline a scenario alternative to the vortex formation of long chains with dielectric links.

Preparation and Properties of N-Doped Carbon Microtubes as the Electrode Material in Electrochemical Capacitor

Preparation and Properties of N-Doped Carbon Microtubes as the Electrode Material in Electrochemical Capacitor

Nanostructured Iron-Substituted Lithium-Manganese Spinel as an Electrode Material for Hybrid Electrochemical Capacitor

Nanostructured Iron-Substituted Lithium-Manganese Spinel as an Electrode Material for Hybrid Electrochemical Capacitor

Improved Capacitance Model Involving Fringing Effects for Electret-Based Rotational Energy Harvesting Devices

Electret-based rotational energy harvesting (EBREH) technology is promising to overcome the electrostatically converted power limitation of velocity-damped resonance generators. Its structural parameter-dominated capacitance variation and parasitic capacitance should be correctly evaluated for the optimal design of EBREH devices regarding the high power output implement. Basically, finite-element analysis (FEA) seems the only access to predict capacitances across the complicated interdigitated electrodes in 3-D space because of partially or completely neglected fringing effects in currently available theoretical models. In this paper, we proposed a more efficient model for the capacitance of EBREH devices based on four-positioned capacitors, i.e., coplanar, parallel-plate, flat-plate nonparallel, and sector coplanar capacitors. Distinctively differing from other models, our model takes 3-D fringing effects associated with fringing fields into account properly in each type of the capacitor. In addition, the accuracy of the proposed model was much improved by combining parallel-wire capacitance theory and Schwarz–Christoffel mapping. Our model was verified through both the FEA and practical measurements with a fabricated EBREH structure. The measurement indicated that this novel capacitance model can be readily applicable to rotary and linear motion-driven EBREH devices and electrostatic sensors for further design optimizations with device parameters.

Highly Sensitive Microwaves Sensors for Fluid Concentration Measurements

Although electromagnetic-stored energy of planar electrically-small resonators is mostly concentrated in an electrically small volume, most of the energy, however, is concentrated in the host substrate, thus limiting the sensitivity to detect changes in the material under test which is different from the host substrate. In this letter, a sensor design for enhancing the electromagnetic stored energy in the sensing volume is presented. The design concept is based on using a 3-D parallel-plate capacitor to enhance the stored electric energy in the sensing volume that is exposed to the material under test. For validation, a resonator based on a complementary electric-LC resonator was utilized to design the sensor. Using simulations, the sensor demonstrated a sensitivity enhancement of more than 400% when detecting changes in a dielectric material over the relative permittivity range of 1 to 1.2. To validate the concept experimentally, the sensor was utilized to detect changes in the concentration of two fluids, which makes it suitable for a host of emerging micofludic applications including lab-on-a-chip.

A Real‐Time Electrochemical Impedance Analysis for Water‐In‐Oil Emulsions of Bitumen Diluted with Naphtha

AbstractIn this paper, water‐in‐oil (W/O) emulsions of bitumen diluted with naphtha were characterized by a novel impedance technique in real time. Nyquist diagrams of electrochemical impedance spectra obtained for different systems present different spectra. For the system of bitumen in naphtha, only one semi‐circle is observed, and the resistance (RO) and capacitor (CO) are connected in parallel. Impedance measurement shows that the conductivity of bitumen results from the conductive components, asphaltenes. For the system containing W/O emulsions, Nyquist diagram is presented in two semicircles with different diameter, indicating different relaxation times corresponding to bitumen in naphtha and W/O emulsions respectively. The RO and CO are in parallel combination and then connect in series with the resistance (RW/O) and capacitor (CW/O) of W/O emulsions. The value of RW/O reduces with the decrease of volume fraction of W/O emulsions, which can be used to characterize the stability of emulsions. At the same time, the impedance spectra analysis plays an important role in the study of demulsification of W/O emulsions by comparing the RW/O after adding demulsifier ethylcellulose (EC). With the increase of EC concentration, the RW/O reduces and eventually disappears due to the decrease of volume fraction of emulsions. Further work needs to be studied to establish the relationship between dielectric constant and volume fraction of emulsions.

Excitation performance of fabricated PMN–BFO relaxor through electric field

The lead magnesium niobate (PMN; PbMg1/3Nb2/3O3) and bismuth ferrite (BFO; BiFeO3) electronic compound has been fabricated and its excitation through electric field has been experimentally investigated. The unveiled excellent material properties like frequency independent and temperature dependent high dielectric constant and low dielectric loss substantiate the relaxor behavior of the processed material. A parallel plate capacitor structure is designed in order to reveal the material’s excitation through the generated internal electric field which has also been affirmed. The experimental results exhibit the dependence of excitation intensity on the material properties, driving frequency, relative position and generated electric field strength. The intensity of excitation attains its peak when the driving frequency is synchronized with the mechanical resonant frequency of the fabricated relaxor dielectric component.

Retracted: Placement of combined photovoltaic and shunt capacitor to minimize power loss using heuristic quadratic curve fitting technique

Power loss minimization is crucial for reliable electrical power transmission and delivery. Numerous ways have been implemented to reduce power loss including photovoltaic and shunt capacitor installation. Nonetheless, improper allocation of these devices cause unstable voltages and increase power losses. Therefore, this research highlights placement of combined photovoltaic and shunt capacitor to minimize power losses using quadrature curve fitting rule. First, Fast voltage stability index (FVSI) is employed to determine the location of PV and shunt capacitor. Next, quadratic curve fitting rule is used to compute the size of the devices. The correct sizing of PV also influenced by Tenaga Nasional Berhad (TNB), Malaysian energy company guideline. Simulation results indicates the effectiveness of the techniques in minimizing power loss.

Development and characterization of a 140-element MEMS deformable mirror

For satisfying the boarder application requirement of adaptive optics (AO) and solving the problem of large volume and high cost of conventional deformable mirrors (DM), micro DM based on micro-electro-mechanical system (MEMS) technology is developed and measured. The developed DM has 140 hexagonal parallel plate capacitor electrostatic actuators. The actuators are arranged as a square array and the pitch is 400 μm. A DM prototype is fabricated by MEMS surface micromachining process and packaged by a ceramic pin grid array (CPGA). A miniaturization multi-channel high voltage driver for the DM is developed too. The measurement results show that the prototype has a surface PV value of 411 nm, RMS value of 78 nm, reflectivity of about 80% in 600 nm to 900 nm wavelength, stroke of 1.8 μm, actuator coupling of 15%, working bandwidth of 13 kHz and step response time of 23 μs. Thus the DM has the advantages of small volume, low cost and fast response. Besides the measurement of single element, the whole DM is controlled open loop to fit Zernike aberration and its fitting capability is demonstrated. Above results indicate that the DM prototype can satisfy initially the requirement of AO system.

Large anisotropy of ferroelectric and pyroelectric properties in heteroepitaxial oxide layers

Epitaxial PbZr0.52Ti0.48O3 (PZT) layers were integrated on Si(001) with single PZT {001} orientation, mosaïcity below 1° and a majority of a-oriented ferroelectric domains (∼65%). Ferroelectric and pyroelectric properties are determined along both the out-of-plane and in-plane directions through parallel-plate capacitor and coplanar interdigital capacitor along the <100>PZT direction. A large anisotropy in these properties is observed. The in-plane remnant polarization (21.5 µC.cm−2) is almost twice larger than that measured along the out-of-plane direction (13.5 µC.cm−2), in agreement with the domain orientation. Oppositely, the in-plane pyroelectric coefficient (−285 µC.m−2.K−1) is much lower than that measured out-of-plane (−480 µC.m−2.K−1). The pyroelectric anisotropy is explicated in term of degree of structural freedom with temperature. In particular, the low in-plane pyroelectric coefficient is explained by a two-dimensional clamping of the layers on the substrate which induces tensile stress (from thermal expansion), competing with the decreasing tetragonality of a-domains (shortening of the polar c-axis lattice parameter). Temperature-dependent XRD measurements have revealed an increased fraction of a-domains with temperature, attesting the occurrence of a partial two-dimensional clamping. These observed properties are of critical importance for integrated pyroelectric devices.

Fabrication of solid-state secondary battery using semiconductors and evaluation of its charge/discharge characteristics

Li-ion batteries have attracted interest for use as storage batteries. However, the risk of fire has not yet been resolved. Although solid Li-ion batteries are possible alternatives, their performance characteristics are unsatisfactory. Recently, research on utilizing the accumulation of carriers at the trap levels of semiconductors has been performed. However, the detailed charge/discharge characteristics and principles have not been reported. In this report, we attempted to form new n-type oxide semiconductor/insulator/p-type oxide semiconductor structures. The battery characteristics of these structures were evaluated by charge/discharge measurements. The obtained results clearly indicated the characteristics of rechargeable batteries. Furthermore, the fabricated structure accumulated an approximately 5000 times larger number of carriers than a parallel plate capacitor. Additionally, by constructing circuit models based on the experimental results, the charge/discharge mechanisms were considered. This is the first detailed experimental report on a rechargeable battery that operates without the double injection of ions and electrons.

Extreme dielectric non-linearities at the convergence point in Ba1-xCaxTi1-xZrxO3 thin films

The dielectric properties of Ba1-xCaxTi1-xZrxO3 (BCTZ) thin films are explored by varying x from 0 to 0.18 through an RF magnetron co-sputtering process. Thin films are analyzed by Rutherford Backscattering Spectroscopy, X-Ray Diffraction and dielectric measurements on parallel plate capacitors as a function of temperature (from 100 to 420 K), frequency (from 100 Hz to 1 MHz) and static electric field (from 0 to 250 kV cm−1). The evolutions of their dielectric properties with composition are systematically compared to bulk ceramic counterparts. In both cases, a continuous crossover from classical-to-relaxor ferroelectric behavior along with a decrease of the temperature of the permittivity maximum are observed as x increases. Besides, a phase convergence region (PCR) between cubic, tetragonal, orthorhombic and rhombohedral symmetries is evidenced for compositions close to x = 0.12. This is the first time that such a PCR is observed in thin films. At this point in the phase diagram, all of the dielectric parameters undergo specific variations. In particular, the enhanced permittivity dependence to external electric field for these Ca and Zr contents is attributed to an emerging relaxor behavior together with its vicinity of the PCR. These results make BCTZ thin films potential candidates to achieve electrically tunable devices.

Implementing a dual-touch 4-wire analog resistive touchscreen via regression analysis

As touch mania sweeps across many applications, a large number of venders seek to upgrade to dual-touch if not to multi-touch features, but cannot justify the price of capacitive touchscreens. To get around this, other methods - both legacy and cutting edge – are available. The idea is to create inexpensive alternatives to capacitive touchscreens or retrofit dual-touch/multi-touch gestures to existing resistive-touchscreen designs, for example. This paper introduces a new scheme to detect any dual-touch on an analog resistive touchscreen. A 4-wire version was chosen due to the simplicity of its structure. Both linear and polynomial regression, was used to support the ability of detecting any position. Four screen sizes, 4.3-inch, 5.7-inch, 7-inch, and 10.2-inch, were explored. The findings revealed that resistance changes during touch can be utilized for detecting the coordinates of finger(s), for a single-touch and any dual-touch. The maximum error across all screen sizes, evaluated by RMSE, is under 3mm from the exact position on both the X and Y-axes.

Lower mode excitation in vertex-fed slotted hexagonal S-band antenna

Direct-fed hexagonal patch antenna are limited to |S11| ≥ −10 dB at lower modes, especially when fed at the vertex of the hexagon. This paper demonstrates a technique to compensate impedance mismatch at a lower mode in a vertex-fed slotted hexagonal antenna. A circular parallel-plate capacitor (PPC) is introduced to the antenna structure that improves impedance matching to excite a lower mode for a probe-fed hexagonal patch antenna. With an overall size of 50 × 50 mm2, the proposed antenna is compact and can operate at 2.4 GHz in presence of PPC with a gain of 2.11 dB and is suitable for various S-band applications.

The Effect of Load Modeling on Load Flow Results in Distribution Systems

Effective utilization of power distribution networks requires extensive studies in such areas as using of capacitors, voltage regulators, network reconfiguration, and so on. Indeed, achieving to accurate answers, and managing appropriate solutions for network problems requires a detailed modeling of the network in the process of the above studies. Among the elements that are important for modeling in network research is network loads. Loads are generally being modeled such as constant power. While load nature is often widespread and different. Failure to have a detailed modeling can lead to non-optimal and even wrong answers, and will result in waste of costs and investments. Since the load flow is the basis of any research in distribution networks, in this paper the effect of load modeling on load flow results which can clarify the importance of the load modeling for other network studies are investigated. What can be inferred from this study is that any study in distribution networks can only lead to optimal results if the load model is accurate. Therefore, attempting to measure necessary load parameters and using their exact modeling methods in distribution networks should be done in order to obtain more accurate results and more savings.

Impedance Spectroscopy Study of the Electrical Properties of Cation-Substituted Barium Hexaaluminate Ceramics

We report on the behavior of frequency and temperature dependences of the impedance of a measuring cell in the form of a parallel-plate capacitor filled with barium hexaaluminate ceramics with four aluminum cations replaced by iron (BaO · 2Fe2O3 · 4Al2O3). The measurements have been performed in the frequency range of 0.5–108 Hz at temperatures of 20-375°C. A technique for determining the electrical properties of the investigated ceramics is proposed, which is based on an equivalent electric circuit allowing the recorded impedance spectra to be approximated with sufficiently high accuracy. The established spectral features are indicative of the presence of two electric relaxation times different from each other by three orders of magnitude. This fact is explained by the difference between the charge transport processes in the bulk of crystallites and thin intercrystallite spacers, for which the charge activation energies have been determined.

THERMAL AGING STUDY OF BIODEGRADABLE POLYMER MATERIALS BY DIELECTRIC THERMAL ANALYSIS

Two different studies of the thermal aging of polyesters based on lactic and glycolic acidswere compared. Thermal degradation of poly(L-lactic acid) (PLLA), poly(L-lactic acid-co-glycolicacid) (PLLGA) and poly(DL-lactic acid-co-glycolic acid) (PDLGA) was studied by the dielectricthermal analysis (DETA). The aging was performed at 37C in vacuum oven. The dielectric featuresi.e., dielectric permittivity,, dielectric losses,, and phase lag, tg , were determined by PL-DETAcontaining a parallel plate capacitance cell, from the room temperature to 80, 150, and 180  C,at the heating rates of 2 and 3 Cmin-1. Dielectric scans were obtained at a frequency of 1 kHz anda.c. signal of 200 mV. Different behavior of PLLA, PLLGA, and PDLGA during degradation wasobserved. As the aging of PDLGA proceeds, dielectric losses shift to the lower temperatures,indicating existence of lower molecular weights.  - T, and tg  - T dependences of PLLGA, as wellas those for PLLA show two simultaneous processes occurring, crystallization and degradation.

Fabrications and Performance of Wireless LC Pressure Sensors through LTCC Technology.

This paper presents a kind of passive wireless pressure sensor comprised of a planar spiral inductor and a cavity parallel plate capacitor fabricated through low-temperature co-fired ceramic (LTCC) technology. The LTCC material with a low Young’s modulus of ~65 GPa prepared by our laboratory was used to obtain high sensitivity. A three-step lamination process was applied to construct a high quality cavity structure without using any sacrificial materials. The effects of the thickness of the sensing membranes on the sensitivity and detection range of the pressure sensors were investigated. The sensor with a 148 μm sensing membrane showed the highest sensitivity of 3.76 kHz/kPa, and the sensor with a 432 μm sensing membrane presented a high detection limit of 2660 kPa. The tunable sensitivity and detection limit of the wireless pressure sensors can meet the requirements of different scenes.

Effect of finger geometries on strain response of interdigitated capacitor based soft strain sensors

The finger geometry of embedded elastomeric comb capacitors significantly affects the electromechanical response of interdigitated capacitor (IDC) based soft sensors. When strain is applied to these IDC based soft sensors, the embedded soft combs are deformed, changing the sensor's capacitance to detect a variety of different mechanical loads. To better understand the effect of design parameters on sensor sensitivity, a comprehensive closed-form analytical model using geometric stretch and a parallel plate capacitance model in combination with a coplanar waveguide model to predict the strain response as a function of finger geometry and load orientation were developed. To validate this model, we compare the predicted response with computational and experimental methods using sensors with a combination of two different finger thicknesses and widths in a 4 mm2 area. Strong agreement was shown in all three results from the analytical model, the finite element analysis simulations, and the experiments validating that the sensitivity of IDC soft strain sensors can be tuned by finger geometry.

Efficient electron open boundaries for simulating electrochemical cells

Non-equilibrium electrochemistry raises new challenges for atomistic simulation: we need to perform molecular dynamics for the nuclear degrees of freedom with an explicit description of the electrons, which in turn must be free to enter and leave the computational cell. Here we present a limiting form for electron open boundaries that applies when the magnitude of the electric current is determined by the drift and diffusion of ions in solution, and which is sufficiently computationally efficient to be used with molecular dynamics. We demonstrate its capabilities by way of tight binding simulations of a parallel plate capacitor with and without a dimer situated in the space between the plates.