Capacitive Reactance Research Articles

Association of Superior Vena Cava Syndrome with Sleep Apnea: Investigation Using an Impulse Oscillometry System

Superior vena cava syndrome (SVCS) patients sometimes show signs of obstructive sleep apnea (OSA). However, the mechanism causing hypoxia during sleep in SVCS patients is still uncertain. The aim of this study was to elucidate 1) the changes in central and peripheral respiratory resistance with SVCS, and 2) interpret the mechanism underlying the development of hypoxia during sleep in patients with SVCS related to OSA. Ten SVCS patients related to a neoplasm were recruited for this study. The degree of apnea hypopnea index (AHI) for OSA was evaluated by portable diagnosing device before and after SVCS treatment. We also analyzed the airway resistance and reactance quantitatively in the supine position by Master Screen impulse oscillometry system (MS-IOS?). After SVCS treatment, mean values of AHI were significantly decreased from 30.9 to 16.9 (/hour) (p = 0.001). Central respiratory resistance (R20) also decreased significantly from 0.40 to 0.33 kPa/L/s (p = 0.025) in the supine position. In contrast, peripheral respiratory resistance (R5-R20) and distal capacitive reactance (X5) did not change significantly. It is thought that the exacerbation of OSA due to SVCS is caused by increasing upper airway resistance related to reversible edema of the upper airway mucous or tissue. In contrast, SVCS may not cause peripheral respiratory tract and lung parenchyma edema.

Effects of Temperature on the Impedance of PEM Fuel Cell

Electrochemical impedance (EI) plays a very important role on the characteristics of proton exchange membrane (PEM) fuel cell. In this paper, the effects of the cell temperature and the humidification temperature on the electrochemical impedance are analyzed by the equivalent circuit. The results show: when the cell temperature is higher than the gas humidification temperature, ohms impedance and Faraday impedance increase markedly, and electric double layer in the PEM fuel cell inclines to the specialty of capacitive reactance; the more than the cell temperature the gas humidification temperatures is, the more the extent of specialty of capacitive reactance the electric double layer shows. These results are very helpful to understand the operating principle of PEM fuel cell and improve its performance.

MATLAB Design and Simulation of Series Controller for Damping of Energy System Oscillations

state power electronic devices or Flexible AC Transmission Systems technologies has brought an scope for electric utilities to operate their bulk power flow network close to their thermal limits while maintaining and/or improving network security or reliability. High-power electronic devices can provide unprecedented control over electricity flow in transmission networks. These devices responds quickly enough to changing network conditions to provide real-time power flow control, which is essential when large numbers of power transactions occur in a fully deregulated electric industry. In this paper a MATLAB / SIMULINK model of Electronic Controller has been developed for quick power flow control between two Areas connected by two transmission lines. This is achieved by increasing /decreasing its capacitive reactance online. The TCSC also helps in limiting and damping the angular/frequency swings caused by the disturbances. The simulations are carried out using MATLAB/SIMULINK.

Estimation of postmortem interval using an electric impedance spectroscopy technique: A preliminary study

The objective of this study was to develop a rapid method for the estimation of postmortem interval (PMI) using electric impedance spectroscopy. Postmortem rat spleens were studied at 10°C, 20°C, and 30°C; The results obtained demonstrated that postmortem interval negatively correlated with the absolute value of Im Z(//) (capacitive reactance component) in electrical impedance. This suggests that electric impedance spectroscopy may be a sensitive tool to determine the postmortem interval.

Influence of ZnWO4 nanorod aspect ratio on the photocatalytic activity

ZnWO4 nanorod photocatalysts with various aspect ratios were synthesized by a hydrothermal method. The aspect ratio of the ZnWO4 nanorods was governed by the hydrothermal temperature and pH value. ZnWO4 nanorod photocatalysts showed highly efficient photocatalytic activity for the degradation of methylene blue under ultraviolet light irradiation. The photocatalytic activity and the effective separation of photogenerated electron–hole pairs were promoted by the increasing aspect ratio of the ZnWO4 nanorods. The amount of electron donors in the ZnWO4 increased with the aspect ratio of ZnWO4, which was in good agreement with photocurrent results. The enhancement of photocurrent density and photocatalytic activity resulted from the reduction of charge-transfer resistance and capacitive reactance, which were deduced by the high aspect ratio of ZnWO4 nanorods.

UHF RFID H-Shaped Tag Antenna using Microstrip Feed Design on Metallic Objects

A novel UHF RFID antenna structure that can stick on metallic surface is presented. A printed H-shaped antenna by using microstrip feed structure on system ground which has the same size as antenna and operated at its halfwavelength (λ/2) mode as the fundamental resonant mode is designed. The printed H-shaped antenna generates about 925 MHz operations. Further, the proposed antenna has a simple planar structure and occupies only a small area of 13 × 66 mm2 on the system circuit board. By using the inductive property of the microstrip line with short end to match the capacitive reactance of tag chip, the performance in free space on metallic surface was measured. The matched impedance bandwidth (VSWR < 2) of the proposed antenna in free space was measured in the frequency range 830–951 MHz. The proposed antenna with good matched impedance, high direction radiation patterns, compact size, low-profile, low cost and measured reading range (5–6 m) in free-space can be suitable for UHF RFID applications.

A NEW ACCURATE MODEL OF HIGH-IMPEDANCE SURFACES CONSISTING OF CIRCULAR PATCHES

In this paper, we consider a dense array of metallic circular patches printed on a electrically thin metal-backed dielectric substrate. Since the sub-wavelength dimensions, the array and the metal-backed substrate can be described in terms of a lumped capacitance and a lumped inductance, respectively. Around the resonant frequency, the structure, known as high-impedance surface, re∞ects totally an incident electromagnetic wave with zero shift in phase. Due to this property, it is widely employed in antenna systems as compact back re∞ector with improved performances with respect to typical metal re∞ector. Starting from the concept of the grid capacitive reactance of a planar array of squared patches and its related formulas, we investigate on the fleld distribution on the array plane and properly modify the formulas for the case of the circular patches. We present two new analytical formulas which can be efiectively used for the fast design of 2D-isotropic circular HISs. In order to validate the models, we compare the resonant frequency of the array obtained through our approaches to the one resulting from full-wave numerical simulations and from other analytical methods available in the open technical literature.

DUAL FREQUENCY RING ANTENNAS WITH COPLANAR CAPACITIVE FEED

In this paper, design of a coplanar capacitive coupled probe fed microstrip ring antenna for dual frequency operation is presented. The proposed antenna is excited by a single probe feed connected to a capacitive feed strip placed along one of the radiating edges of the ring antenna. The coplanar capacitive feed strip is modifled to obtain the best possible match with the antenna input impedance and to tune out the excessive capacitive reactance due to feed strip. It is also demonstrated that the modifled feed strip can be placed either inside or outside the ring and similar radiation characteristics can be obtained at both the resonant frequencies. Ring dimensions decide the resonant frequencies values and their separation. Measured data fairly agree with the simulated characteristics.

Input impedance matching of acoustic transducers operating at off-resonant frequencies

The input impedance matching technique of acoustic transducers at off-resonant frequencies is reported. It uses an inherent impedance property of transducers and thus does not need an external electric matching circuit or extra acoustic matching section. The input electrical equivalent circuit includes a radiation component and a dielectric capacitor. The radiation component consists of a radiation resistance and a radiation reactance. The total reactance is the sum of the radiation reactance and the dielectric capacitive reactance. This reactance becomes zero at two frequencies where the impedance is real. The transducer size can be properly chosen so that the impedance at one of the zero-crossing frequencies is close to 50 Ω, the output impedance of signal generators. At this off-resonant operating frequency, the reflection coefficient of the transducer is minimized without using any matching circuit. Other than the size, the impedance can also be fine tuned by adjusting the thickness of material that bonds the transducer plate to the substrates. The acoustic impedance of the substrate and that of the bonding material can also be used as design elements in the transducer structure to achieve better transducer matching. Lead titanate piezoelectric plates were bonded on Lucite, liquid crystal polymer (LCP), and bismuth (Bi) substrates to produce various transducer structures. Their input impedance was simulated using a transducer model and compared with measured values to illustrate the matching principle.

Effect of Magnesium Content on the Corrosion Behaviors of Grf/Al Composite

Graphite-fiber-reinforced aluminum composites (Grf/Al) with different magnesium content were fabricated with the pressure infiltration method. Their corrosion behaviors were investigated by potentiodynamic polarization measurements, immersion tests, electrochemical impedance spectroscopy (EIS) analysis, and scanning electron microscopy (SEM). Both the corrosion potential (Ecorr) and the pitting potential (Epit) decreased with the increase of magnesium content, whereas the corrosion current density (icorr) decreased sharply at first and then increased slightly. The icorr of Grf/Al-3.2Mg was the lowest among the four composites with different magnesium contents, which indicated that Grf/Al-3.2Mg had the best corrosion resistance. EIS showed that the capacitive reactance of Grf/Al-8.5Mg was 1682 Ω × cm−2, which was the worst, whereas that of Grf/Al-3.2Mg was 3498 Ω × cm−2, which was the best. SEM results revealed that magnesium and silicon formed the Mg2Si phase in Grf/Al-3.2Mg, which hindered the extension of corrosion crack and improved the corrosion resistance.

Study on the Combined Anticorrosion Method of Thermal Spraying and Coating of Carbon Steel in Deposit Water of Storage Tank

Storage tank was protected from corrosion with the combined method of thermal spraying and coating, and corrosion resistance of the coating was studied through on-the-spot static weight loss method, potentiodynamic polarization curve and electrochemical AC impedance test. The result showed that the hanging slices with thermal sprayed aluminum powder, glass flake and epoxy resin coating had least weight loss and best corrosion resistance after 10 months of corrosion with on-the-spot weight loss experiment. In the polarization curve experiment, the anodic polarization curve of the hanging slices with thermal sprayed aluminum powder and glass flake had passivation characteristics, strong polarization area shifted left, weak corrosion current and greater polarization resistance. In the AC impedance spectra, hanging slices with thermal sprayed aluminum powder and glass flake had greater capacitive reactance arc and better corrosion resistance.

Role of Cu additive on the dielectric relaxation of Se75Te25and Se85Te15glassy alloys

The effect of Cu additive on the dielectric relaxation of two binary Se-Te glassy systems, comparing the properties of a-Se 75 Te 25 , a-Se 85 Te 15 and a-Se 75 Te 15 Cu 10 alloys has been reported. The temperature and frequency dependence of dielectric parameters in Glassy Se 75 Te 25 , Se 85 Te 15 and Se 75 Te 15 Cu 10 alloys are studied by measuring capacitance and dissipation factor in the frequency range (1 kHz-5 MHz) and temperature range (300-350 K). A Debye like relaxation of dielectric behavior has been observed. A comprehensive study on the relaxation mechanism revealed that the presence of grains and grain boundaries across the pallet thickness is the basic relaxation process. A detailed analysis shows that the observed dielectric loss is in agreement with the Guintini's theory of dielectric dispersion based on two electron hopping over a potential barrier and is applicable in the present case. Dielectric constant ( e ’), dielectric loss ( e ”), loss tangent ( δ ) and capacitive reactance ( X c ) are found highly frequency and temperature dependent. Dependence of these dielectric parameters over the metallic impurity Cu, has also been found in the present glassy system and has been discussed in terms of electronegativity difference between the elements used in making the aforesaid glassy system.

A Loop Loading Technique for the Miniaturization of Non-Planar and Planar Antennas

A size reduction technique of non-planar and planar antennas using a self-resonant topology is highlighted. The antennas considered are the dipole, the monopole and the slot radiator. The dipole below its resonant frequency is known to possess a capacitive reactance. It is shown that the inductive reactance of a loop can be used to match a below-resonant dipole similar to the inductive load offered by a metamaterial shell. The configuration reduces the resonant frequency of the dipole by 26.01%, causing the dipole to almost reach the electrically small limit. Despite the loaded dipole touching the electrically small limit, the antenna needs no matching networks, offers a high efficiency and exhibits a bandwidth better than the unperturbed dipole. The radiation pattern is also seen to be unaffected by the presence of the loops. The concept is also demonstrated for the size-reduction of a monopole and for a planar slot.

Selection of capacitance for self-excited six-phase induction generator for stand-alone renewable energy generation

Abstract This paper presents a simple method for finding the suitable value of shunt and series capacitance necessary to initiate self excitation and self-regulation (voltage regulation) in a self-excited six-phase induction generator (SPSEIG) for stand-alone renewable energy generation in conjunction with the hydropower. The problem is formulated as multivariable unconstrained nonlinear optimization problem. The admittance of the equivalent circuit of SPSEIG is taken as an objective function. Frequency and magnetic reactance or speed and magnetic reactance or frequency and capacitive reactance are selected as an independent variables depending upon the operational condition of the machine. Fmincon method is used to solve the optimization problem. Computed results were experimentally verified to validate the analytical approach presented in the paper.

A transformer type fault current limiter with spark gap

A novel fault current limiter (FCL) is proposed in this paper. The FCL consists of a capacitor, a transformer and a spark gap. The spark gap is used to control the inductive reactance of the transformer for matching the capacitive reactance of the capacitor. During the short-circuit faults, the FCL resonantly produces a high impedance in the fault circuit after the breakdown of the spark gap, which enables the fault currents to be reduced. A steady-state analysis is made for investigating the current-limiting operation condition of the FCL. Laboratory test and Alternative Transients Program (ATP) are also employed to examine the current-limiting effect of the FCL. The results obtained from measurement and ATP-simulation show that the FCL has the capability of limiting the fault currents to lower levels.

Synchronous Study of Ferroresonance and Inrush Current Phenomena and their Related Reasons in Ground Power Networks

Synchronous Study of Ferroresonance and Inrush Current Phenomena and their Related Reasons in Ground Power NetworksEnergizing the power transformers usually results in flowing very high inrush currents. This harmful current can be minimized using controlled switching and considering the value of residual flux. But nowadays, developing the ground power networks results in high increment of ferroresonance phenomenon occurrence due to the line' capacitance reactance and nonlinear inductive reactance of power transformer's core. In this study, these transient phenomena and their cause have studied synchronously.

Major Improvements of Quartz Crystal Pulling Sensitivity and Linearity Using Series Reactance

This paper presents a new method of substantially improving frequency pullability and linearity using reactance in series with an AT fundamental crystal operated with a series load capacitance in the range of 3 to 50 pF and frequencies in the range of 3.5 to 21 MHz. The research describes high quartz pullability and linearity by varying the load capacitance. The paper also gives impedance circuits for crystal unit (3.5 MHz) together with load capacitance and compensation reactance. The experimental results show that the new approach using compensation method of quartz crystal connected in series reactance increases the frequency pulling range by ×25 to ×100 depending on the type of oscillator and compensation factor “k” in the temperature range of 10 to 40 °C.

Do we need a phase-locked loop?

A phase-locked loop circuit compares the waveforms of input and reference electrical signals in terms of their frequency and phase. This type of circuit uses electronic feedback to adjust the frequency and phase of the input signal to match the properties of the reference signal. The frequency of changes to international radiation protection recommendations is often different from the frequency of their implementation into national legislation. There is also what could be viewed as a phase lag in this system that occurs because of a natural resistance to change. This is much like capacitive reactance in an A-C circuit. Perhaps an analogue of the phase-locked loop circuit can be developed and applied to the implementation of international radiation protection recommendations and regulations. International agencies, commissions and organisations develop and promulgate documents dealing with radiation protection and radiation protection dosimetry. Many countries have representatives taking part in the activities of the various organisations, and some but not necessarily all of those countries incorporate the jointly developed recommendations and standards into their national legislation. The fact that there is a phase shift or time lag between recommendation development and incorporation into national legislation is well known. A change to national legislation will obviously take time, and if the frequency of the recommendation-change-function differs from the frequency of the legislation-change-function there may be interference resulting in amplitude fluctuations. Phase differences between the two functions can lead to destructive interference resulting in a decrease in amplitude. The amplitude in this analogy might be imagined as the efficiency in implementing the recommendations. This is where the phase-locked loop circuit would be useful to harmonise the implementation of radiation protection recommendations into national legislation. Unfortunately, the two change functions are certainly fictitious and do not act as if they were electrical waves.

Microwave-Frequency Effects on Microplasma

Capacitively coupled microplasma generation becomes more efficient at microwave frequencies. Helium and argon microplasmas are characterized using excitation frequencies of 450 MHz, 900 MHz, and 1.8 GHz. These microplasmas are tested at both atmospheric pressure and 0.4 torr. We have experimentally determined the microplasma's electrical impedance, which consists of bulk plasma resistance and capacitive sheath reactance. These two parameters were measured by fitting theoretical power reflection coefficients to experimental forward and reflected microwave power as a function of frequency. Microplasma resistance decreases with increasing frequency, showing that the generation of free electrons depends on the driving frequency. In addition, the reactive sheath impedance and the microwave electrode voltage also decrease with an increase of frequency. A 3-D microplasma simulation shows that a narrower sheath width exists for higher frequency microplasma, and this is responsible for reducing the reactive impedance and the peak-to-peak electrode voltage. At higher microwave frequency, the decreased electrode voltage reduces both the plasma potential and the ion kinetic energy losses, thus increasing the electron density.

A Miniature RFID Tag Antenna Design for Metallic Objects Application

This letter proposes a miniature radio frequency identification (RFID) tag antenna design for metallic objects application. The antenna structure consists of two rectangular patches electrically connected through vias to the ground plane and a nonconnected interconductive layer to form an RFID tag antenna that is suitable for mounting on metallic objects. The miniature design is achieved by inserting a conductive layer into the antenna structure to increase the capacitive reactance of the antenna. This causes the self-resonant frequency of the proposed antenna to approach low frequency; therefore, the high imaginary part of the antenna impedance can be obtained with a small-size RFID tag antenna. The experimental tests show that the maximum read range of RFID tag placed on a metallic object is about 1.5 m, and the overall size is 32 times 18 times 3.2 mm3. Simulation and measurement results of the proposed RFID tag antenna are also presented in this letter.