Effect Of DC Bias Research Articles

Scalable Parallel Manipulation of Single Cells Using Micronozzle Array Integrated with Bidirectional Electrokinetic Pumps.

High throughput reconstruction of in vivo cellular environments allows for efficient investigation of cellular functions. If one-side-open multi-channel microdevices are integrated with micropumps, the devices will achieve higher throughput in the manipulation of single cells while maintaining flexibility and open accessibility. This paper reports on the integration of a polydimethylsiloxane (PDMS) micronozzle array and bidirectional electrokinetic pumps driven by DC-biased AC voltages. Pt/Ti and indium tin oxide (ITO) electrodes were used to study the effect of DC bias and peak-to-peak voltage and electrodes in a low conductivity isotonic solution. The flow was bidirectionally controlled by changing the DC bias. A pump integrated with a micronozzle array was used to transport single HeLa cells into nozzle holes. The application of DC-biased AC voltage (100 kHz, 10 Vpp, and VDC: −4 V) provided a sufficient electroosmotic flow outside the nozzle array. This integration method of nozzle and pumps is anticipated to be a standard integration method. The operating conditions of DC-biased AC electrokinetic pumps in a biological buffer was clarified and found useful for cell manipulation.

Analysis of the DC Bias Effects on the UHV Autotransformer with Rated Load Based on a Reduced-Scale Model Experiment

The DC bias of transformers as a result of geomagnetically induced currents (GIC), monopole operation of high voltage direct current (HVDC) transmission and the increasing power electronic devices in the power grid, creates a high magnitude of fundamental and harmonic components in winding currents, reactive power, and vibro-acoustic noise. For transformers with large capacity, it is very expensive and difficult to carry out an in-depth DC bias effects investigation on a practical equipment, especially for the ultra-high voltage (UHV) transformer. In this paper, a reduced-scale model (RSM) based on the principle of identical saturation degree is proposed, and the equivalent relationship of DC bias current is obtained. Furthermore, the DC bias platform with the RSM is established, experiments have been conducted to analyze the characteristics of the transformer under DC bias. It turns out from the experiments that the current of high voltage side and excitation are less tolerated to the DC bias current, the distortion occurs during the first half of the cycle and peaking at the quarter. Besides, the no-load loss and total harmonic distortion (THD) increase significantly with an increasing DC bias. The results of the characteristics of RSM with load under DC bias may provide great services in protecting and reducing the DC bias effects on the UHV transformer in actual operation.

Dielectric properties and impedance versus dc bias and I–V characteristics of La2/3Cu3Ti4O12 ceramics

The La2/3Cu3Ti4O12 (LCTO) ceramic samples with a higher permittivity were prepared by the sol-gel technique. The study indicated that the effects of dc bias on grain boundaries electrical properties were very evident, but the grain electrical properties were independent of dc bias. The dielectric constant decreased whereas the dielectric loss increased with increasing of dc bias, and the resistances and the activation energies of grain boundaries decreased. According to the analysis of impedance and the I–V curve, there was a potential barrier existed at the grain boundaries of LCTO ceramic samples, which be considered as the Schottky potential barriers.

Analysis of two-color laser-induced electron emission from a biased metal surface using an exact quantum mechanical solution

Photoelectron emission from nanotips via strong-field lasers is a powerful technique for coherent control of ultrafast electron dynamics, and so is important in many areas, including time-resolved electron microscopy and free-electron lasers. The effects of dc bias are typically ignored, though. Exact solution of the time-dependent Schr\odinger equation reveals that, under large dc bias, strong modulation persists in the emission current, the magnitude of which increases significantly. In the authors' model, the dynamics of the multiphoton excited states depend strongly on the applied dc field. This work suggests a practical approach to strong control of high-current photoemission.

Calculation Method of Magnetic Material Losses Under DC Bias Using Statistical Loss Theory and Energetic Hysteresis Model

The loss prediction of magnetic materials under dc bias is of great significance for the optimization of magnetic components, because the efficiency evaluation of magnetic components involves core loss computation under dc bias. Aiming to develop a calculation method for magnetic material losses under dc bias, a novel dynamic energetic hysteresis model combining the statistical theory of losses (STL) with a static energetic hysteresis model is proposed. Firstly, the effects of dc bias on the hysteresis, classical, and excess loss components are analyzed, respectively, using STL. Then, based on the equivalent field separation technique, the magnetic fields corresponding to classical and excess losses are derived using the analytical equations proposed by STL. Finally, a new dynamic energetic hysteresis model, which can take all the hysteresis, classical, and excess losses of magnetic materials under dc bias into account, is devised with the superposition principle. The simulation and experimental results confirmed the accuracy and efficiency of the proposed model.

Polarization- and wave-vector direction-sensitive photocurrent in Ag/Pd nanocomposite films: effect of dc bias

Polarization- and wave-vector direction-sensitive photocurrent in Ag/Pd nanocomposite films: effect of dc bias

Impact of DC bias on differential protection of converter transformers

Converter transformers in high-voltage direct current (HVDC) systems are often subjected to DC bias induced by earth return currents (ERCs) from HVDC systems or by geomagnetically induced currents (GICs). DC bias may adversely affect the performance of converter transformers, but its impact on the protection of converter transformers remains uncertain. This paper thoroughly investigates the response of converter transformer differential protection under the effect of DC bias. The network was simulated in PSCAD/EMTDC, and the modeled components included the converter transformers, the current transformers (CTs), and the DC bias signatures. The fault currents generated by the simulator were downloaded into a numerical relay and its operating behavior was observed. The results indicated the pre-existing harmonics, induced by DC bias, do not cause harmonic blocking to incorrectly inhibit the relay for in-zone faults; and any spurious trip, caused by DC bias, can be prevented by appropriate harmonic blocking and the use of a higher slope 2 in the differential current versus bias current characteristic. It was demonstrated the low-frequency characteristic of GIC did not pose any new threats to differential protection. This indicates the low-frequency characteristic of GIC is negligible when investigating the impact of GIC.

The influence of AC and DC voltages on electrical treeing in low density polyethylene

Electrical tree growth is a well-documented process leading to failure of high voltage polymeric insulation under AC stresses. However, tree growth in HVDC insulation failure is not well understood. This work considers electrical tree degradation in polymeric insulation subjected to combined AC and DC voltages. Tests in LDPE samples of needle-plane geometry yield three types of electrical trees, which grow depending on the magnitude of the AC components, irrespective of the DC voltages. In tests with an AC component of 10 kV (peak amplitude), 12 kV and 15 kV trees are distinguished by both the conductivity of tree channels and the tree shape, and are referred to as either conducting trees, non-conducting branch trees or non-conducting bush trees respectively. With 10 kV AC, tree initiation was significantly accelerated by superimposing −20 kV DC. With +20 kV DC, the incepted trees had more bifurcations, but there was no major change to tree initiation time. Space charge measurements on thin LDPE films provide a basis for understanding the difference between tree initiation with +DC and −DC voltages. The subsequent propagation of conducting trees were not influenced by biasing the 10 kV AC. With 12 kV AC and 15 kV AC, the growths of non-conducting branch and bush trees were both accelerated by positive biasing. A retardation was observed in bush tree growth with −15 kV DC. The effects of DC voltage polarity on tree morphology are different for branch and bush trees. Different relationships between PD magnitudes and tree growth were also found between branch and bush trees. The tree length determined PD magnitudes in branch trees and the evolution of PD in bush trees suggest that the additional DC stress has no impact to PD magnitudes. Nevertheless, DC bias effects on the symmetry between positive and negative discharges have been evidenced through PD analysis for bush trees. Moreover, the modifications on the shape of bush trees are believed to be associated with the changes in PD asymmetry. This work has illustrated the importance of AC ripples in the failure mechanisms in HVDC insulation.

Magnetostrictive Properties of the Grain-Oriented Silicon Steel Sheet under DC-Biased and Multisinusoidal Magnetizations

As an intrinsic property, elasticity of soft material is affected significantly by the externally applied alternating magnetic field. Magnetostrictive properties of the grain-oriented (GO) silicon steel under DC-biased and multisinusoidal magnetizations are measured by using a laser-based measuring system. Magnetostriction curves of the GO silicon steel sheet under different magnetizations are obtained and the influence of frequency and DC bias on the magnetostrictive property is observed and analyzed based on the measured data. In addition, the spectrum of magnetostriction under harmonic magnetization is obtained, and the acoustic noise level of the GO silicon steel sheet represented by the A-weighted decibel value caused by magnetostriction is measured under DC-biased and multisinusoidal magnetizations. The measurement results are applied to the simulation of the three-limb laminated core model, and the effects of DC bias and harmonics on magnetic flux density and displacement are analyzed.

ILC-Based Voltage Compensation Method for PMSM Sensorless Control Considering Inverter Nonlinearity and Sampling Current DC Bias

Inverter nonlinearity and sampling current dc bias can cause harmonic distortion of estimated back electromotive forces (EMFs), and therefore results in position estimation error and degrades control performance of model-based sensorless techniques of permanent-magnet synchronous motors, especially in low speed region. In this paper, the effects of inverter nonlinearity and sampling current dc bias on back EMF estimation are analyzed. A voltage feedforward compensation method based on an iterative learning control (ILC) algorithm is proposed and it is used to eliminate the harmonics of estimated back EMFs and position estimation error, so as to improve the performance of sensorless control. Compensated voltages at different rotor positions are calculated online by the ILC algorithm and stored in a lookup table. The method does not depend on current polarity and inverter model. And it is simple and easy to implement. The effectiveness of the proposed compensation method is verified by experiments.

The Role of DC Biased Plasma Treatment of Polystyrene on the Formation of the C≡N Functional Group Controlling Its Hydrophobicity

Nitrogen plasma treatment was carried out to modify the surface of polystyrene film deposited on a quartz crystal microbalance (QCM) sensor. The modification was intended to enhance the wettability of the film by inducing the formation of CN functional group on its surface. This work investigated the effect of DC bias controlling N* in the plasma on the effectiveness of the nitrogen plasma treatment. The polystyrene was deposited by a spin coating method on the surface of a quartz crystal normally used in an electronic resonator. The nitrogen plasma was generated in an aluminium vacuum chamber using a 2 MHz radio frequency (RF) generator. The vacuum pressure and the gas flow rate were kept constant during the experiments. The plasma character in the chamber was controlled by applying a DC bias between the RF electrodes and the sample stage. The DC voltage was varied from 100 to 500 volts at 100 volts’ step, while maintaining the RF voltage constant. During the process, the species in the plasma was characterized using an optical emission spectroscopy (OES). The wettability of the treated samples was tested using a contact angle measurement system. FTIR measurement was utilized to study the polar functional groups on the surface of the polystyrene before and after the treatment. The OES identified the existence of N radical (N*). The reduced intensity of emission line of the N* increased with the increase of the DC voltage. However, a small decrease was also evidence at DC voltage higher than 400 volts. The decrease of the line intensity was directly related to the decrease of the contact angle (CA < 40°). The relation of the N* and the resulted wettability is related to the polar functional group of the C≡N bond found in the treated polystyrene’s surface.

Uncertainty of Geomagnetically Induced Current in Xinjiang 750kV Planned Power Grid Based on Polynomial Chaos Expansion

Geomagnetically inducted current (GIC) can cause DC bias of the transformer. The derivative effect of DC bias may threaten the safety of power equipment and power grid. To study the GIC uncertainty caused by the grid parameters variation is of great significance for the assessment and defense of GIC during magnetic storm. Based on the polynomial chaos expansion (PCE) method, the chaos polynomial expansion of GIC is constructed assuming the line impedance, transformer impedance and grounding impedance in the power grid as input variables. For planned Xinjiang power grid in 2020, the uncertainty analysis for the GIC of substations flowing into the earth is carried out by using the derived polynomial chaos expansions. The 95% confidence interval, mean and variance statistics of the GIC are obtained. Comparison between PCE method and Monte Carlo (MC) method shows the validity and the efficiency of the PCE method.

Study of Magnetostriction Influence of Electrical Sheet Steel Under Different DC Biases

Power transformer iron core is mainly composed of electrical sheet steel, which is easily affected by vibration and noise. Therefore, it is necessary to measure the magnetostriction influence of electrical sheet steel. This paper analyzes the performance of vibration and noise in the power transformer iron core considering the magnetostriction influence of electrical steel sheet under different dc biases. First, the butterfly loops of magnetostrictive and magnetic hysteresis loops of electrical steel sheet measured by using a laser displacement magnetostriction measurement system, and the effect of dc bias on magnetostrictive and hysteresis characteristics was analyzed. Second, modeled to single-valued curves along the rolling direction and transversal direction for the finite-element method. Finally, the simulation results of a single-phase power transformer are verified by the experimental results under the dc bias.

A Novel Sensor to Measure the DC Bias in Distribution Power Transformers

With the advantages of long-distance transmission and correlation of the power system, HVDC project has become increasingly popular of implementation in china. When the HVDC system operated in mono-pole ground return mode, the DC bias occurred by the accumulated DC current at the point of common coupling of transformers and cause series bad influences to transformer itself. In order to reduce the DC bias phenomena in the secondary side of the transformer, it is of prime need to accurate and fast sense the DC bias. Firstly, this paper narrative the effect of DC bias to transformers. Then, a novel DC bias sensor is raised, which achieve the objective by measuring the DC voltage that across the resistance caused by the following of DC current. Last, simulations are taken to assess the accuracy and validity of the proposed DC bias sensor, and simulation results prove that the proposed sensor can accurately and quickly sense the DC bias.

The DC Bias Model and Simulation Analysis of Three-phase Five-limps Transformer Based on EIC Principle

In this paper, the model of transformer DC bias simulation is established based on EIC principle. This model considers the hysteresis loss and eddy current loss of the transformer core through the J-A model and the Bertotti theory. This model simulates the electromagnetic characteristics of the transformer under DC bias more accurately, providing a basis for reliable evaluation of transformer resistance to DC bias and determination of effective and reasonable control measures. Based on this model, the effects of DC bias on the operating characteristics of single-phase transformers are analyzed. Moreover, this paper summarizes the variation of field current and leakage flux as well.

Electrical tree growth and partial discharge in epoxy resin under combined AC and DC voltage waveforms

The effect of DC bias on electrical tree growth and partial discharge (PD) characteristics in epoxy resin (Araldite LY® 5052/Aradur® HY 5052 supplied by Huntsman) is investigated using three waveforms: AC, AC with positive DC bias, and AC with negative DC bias. Needle-plane samples are used. Tree growth is shown to be accelerated by the combined effect of DC and 50 Hz AC, beyond the AC growth rate. Positive and negative DC biased tests result in 62% and 54% reductions in average time to breakdown, respectively. Different tree structures and stages of development are associated with different partial discharge characteristics, with thick dark tree branches associated with high PD magnitudes, whereas fine tree channel growth is linked with PD magnitudes below 1 pC. AC tests showed five distinct stages of tree growth compared to four stages seen in DC biased tests. In particular, trees growing in the ‘reverse direction’ from the planar to the point electrode, which is observed in the latter stages of AC tests, is not seen in the DC biased tests. It is concluded that for composite voltages, the AC component is the essential driver of tree growth but the DC component can accelerate propagation. AC noise may therefore compromise the reliability of insulation in HVDC networks.

Effects of DC Bias on Regional Flux and Magnetostriction of a Single-Phase Transformer Core Modeled by 3-D MACC

Traditionally, flux distributions in transformer cores are modeled as a 2-D problem. However, experimental studies indicate that 3-D models are needed. The main reason is that limbs of circular cross section are combined with roughly semi-circular yokes. At the joints, this yields shifts of overlap regions as a reason of significant (off-plane) normal direction (ND) induction $B_{\mathrm {ND}}$ . This paper reports a first corresponding 3-D modeling of a two-package one-phase core with the consideration of non-linear characteristics of material. For corners, the so-called critical induction $B_{\mathrm {CRIT}}$ of joints—as arising close to 1.4 T—is considered. Two instants of the cycle of global magnetization are addressed, i.e., $B_{\mathrm {GL}} = 1.7$ T for normal operation and 1.9 T as a value that may arise for dc bias. For 1.7 T, the results indicate strong inhomogeneity, in particular in the wide main package of the core. On the other hand, 1.9 T is characterized by distinct homogenization. As 3-D effects, the cycle of magnetization involves distinct changes of flux in ND, with values up to more than 0.2 T. Half-cycle saturation is indicated especially for inner (window-sided) corner regions. The corresponding consequences on local magnetostriction (MS) values are over-proportional due to the complex dependence of strain $\lambda$ and induction. The so-called butterfly curve is dynamically passed beyond the turn point and even into its positive range. In particular, this yields distinct distortion of $\lambda$ , which can be assumed as a source of over-proportional rises of A-weighted noise. Apart from MS, further enhancement is to be expected from inter-laminar forces.

Effects of dc bias on dielectric relaxations in CaCu3Ti4O12 ceramics

Effects of dc bias on dielectric relaxations in CaCu3Ti4O12 ceramics were investigated via an improved dielectric spectroscopy. A new low-frequency dielectric relaxation, which was assigned to space charge polarization, was found shifting towards higher frequency with increasing bias voltage in the improved spectra. It was suggested that the Schottky barrier at grain boundary was lowered under dc bias resulting in higher possibility for carriers to migrate. Therefore, the relaxation time was decreased, which was in accordance with rightward shift of this relaxation under increased dc bias. In addition, dependence of the widely reported high-frequency relaxation (> 105 Hz) and middle-frequency relaxation (103–105 Hz) on bias voltage was also discussed. Permittivity contributed by either high-frequency or middle-frequency relaxation presented inverse dependence on dc bias. Discrepancy on barrier parameters was obtained assuming both of them physically correlated with the barrier at grain boundary.

Electrical and nonlinear current-voltage characteristics of La-doped BiFeO3 ceramics

Multiferroic Bi1-xLaxFeO3(x=0, 0.05, 0.1, 0.2, and 0.3) ceramics with particle sizes of ~67–19nm were prepared by a simple co-precipitation method. The effects of La dopant on the microstructure, giant dielectric response, and electrical properties were investigated. The grain size of Bi1-xLaxFeO3 ceramics significantly decreased with increasing La doping ions. The Bi0.95La0.05FeO3 ceramic exhibited the highest leakage current density value. Interestingly, it strongly decreased as the concentration of La increased. The nonlinear coefficient of La doped BFO slightly decreased with increasing La. This shows a space-charge-limited conduction mechanism, which is involved in low electric field regions for all samples investigated. La substitution significantly enhanced the breakdown field. It was found that the potential barrier height at the grain boundary was slightly reduced from 0.3 to 0.16eV by substitution of La ions. Using impedance spectroscopy analysis, except for the Bi0.7La0.3FeO3 ceramic, the grain boundary resistance at room temperature was affected by dc bias, whereas the grain resistance of all samples was independent of dc bias. This result was well consistent with the variation in low-frequency dielectric constant and loss tangent value due to the effect of dc bias. These results were closely related to the existence of the interfacial polarization at the grain boundary.

Origin(s) of the apparent colossal permittivity in (In1/2Nb1/2)xTi1−xO2: clarification on the strongly induced Maxwell–Wagner polarization relaxation by DC bias

The effects of DC bias on the dielectric and electrical properties of co-doped (In1/2Nb1/2)xTi1−xO2 (IN-T), where x = 0.05 and 0.1, and single-doped Ti0.975Nb0.025O2 ceramics are investigated.