Increasing Dc Bias Research Articles

Tuning quantum pathway interference in two-color laser photoemission using DC bias

Coherent control of quantum systems depends on the manipulation of quantum interference through external fields. In this work, we investigate the effects of DC bias field on coherent control of quantum pathways in two-color laser photoemission using exact analytical solutions of the one-dimensional time dependent Schrödinger equation. Increasing DC bias lowers and narrows the surface potential barrier, shifting the dominant emission to lower order multiphoton photoemission, photo-assisted tunneling and then direct tunneling. Those lower order photon absorption processes result in fewer possible pathways, and therefore modulation of photoemission current can be suppressed as DC field increases. It is shown that a maximum modulation depth of 99.4% can be achieved for a gold emitter at local DC bias F 0 = 0.5 V nm−1, fundamental (800 nm) laser field F 1 = 2.6 V nm−1 and second harmonic laser field F 2 = 0.25 V nm−1 . For a given set of input parameters, the total photoemission consists of different k-photon processes, each of which has their own different multiple possible pathways and interference effects. However, the quantum pathways and their interference for the dominant k-photon process and for the total photoemission probability show the same trends. This study demonstrates strong flexibility in tuning two-color lasers induced photoemission using a DC bias and provides insights into coherent control schemes of general quantum systems.

Losses in the Saturated Iron-Core Superconducting Fault Current Limiter For VSC-HVDC System

This paper presents the loss analysis on the saturated iron-core superconducting fault current limiter (SISFCL) for a VSC-HVDC transmission system. The numerical model of SISFCL as well as its loss calculation on superconducting parts were carried out by the finite-element method (FEM) using the H-formulation merged into the commercial package COMSOL. The SISFCL model was established for a practical ±10 kV VSC-HVDC system, and the fault current situation was simulated using the PSCAD with a SISFCL. The capability of fault current limiting was verified using the analysis of electromagnetic characteristics, and the corresponding patterns of magnetic field in the iron-core were studied. During the process of fault current limiting, the instantaneous power losses in the superconducting components were studied with the increasing DC bias current. Even in a DC grid system, results proved there were considerable amounts of losses occurred in the superconducting parts, when the SISFCL encountered the fault currents.

The Effect of DC Bias Current on Domain Wall Resonance Property of Thin-Film Magnetoimpedance Element

We investigated the influence of the dc bias current on the domain wall resonance of thin-film magnetoimpedance (MI) elements. When the intensity of dc bias current is relatively low (0-0.5 mA), the impedance profile shows a domain wall resonance behavior, which shows another peak and rapid drop of inductance in the low-frequency region. The peak height and resonance frequency do not depend on the dc bias current in this range. On the other hand, though the impedance profiles still show domain wall resonance, the behavior strongly depends on the dc bias current; the impedance peak height and amount of inductance drop decrease as well as the resonance frequency shifts to lower frequency with increasing dc bias current. The domain wall resonance completely disappears at 2 mA in this study. On the static field dependence of impedance with dc bias current, the profile shows asymmetric with respect to the Z-axis, which is the same as the property observed in higher frequency. The slight increment of impedance and inductance changes was admitted around the resonance frequency.

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.

Investigation on Power Dissipation in the Saturated Iron-Core Superconducting Fault Current Limiter

This paper presents the power dissipation analysis on saturated iron-core superconducting fault current limiter (SISFCL). The modeling of SISFCL together with its power dissipation computation on a high-temperature superconducting (HTS) coil was executed by the H-formulation model implemented into the finite element method (FEM) software package COMSOL. The model was based on the practical three-phase 35-kV/90-MVA SISFCL. The ac magnetic field in the crucial parts of SISFCL was studied to discover the origin of power loss on the HTS coil. The instantaneous power dissipations in the HTS coil with increasing dc bias current were computed and compared. Analysis proved that power dissipation in the HTS coil of SISFCL should be taken into account for the real operation.

Preliminary Investigation of a 64-element Capacitive Micromachined Ultrasound Transducer (CMUT) Annular Array Designed for High Intensity Focused Ultrasound (HIFU)

BackgroundTreatment of prostate cancer using endocavitary High Intensity Focused Ultrasound (HIFU) has become more commonplace since the first treatments in the 1990s. The gold standard HIFU strategy to treat prostate cancer is the complete thermal ablation of the entire prostate gland under real-time ultrasound (US) image guidance. A more desirable treatment and the current trend, however, is towards a focal treatment but more accurate and finely tunable thermal lesions are needed along with improved US imaging guidance. In this study, Capacitive Micromachined Ultrasound Transducer (CMUT) technology is being investigated, as they have shown recent promise for US imaging and potential to be used for HIFU therapy. They offer potential advantages over current piezoelectric designs in the context of ultrasound-guided HIFU (USgHIFU) focal therapies. ObjectiveThe presented study evaluates the ability of a planar annular array CMUT design to achieve HIFU dynamic focusing and feasibility of generating thermal lesions in biological tissues. MethodThe proposed CMUT design consists of a 64-element annular array for HIFU delivery with a space in the center that accommodates a high-resolution 256-element linear imaging array. The pressure field simulations of the HIFU portion of the array were performed using the Rayleigh integral method. The bioheat transfer equation was then used to predict lesion formation. The HIFU performances of the proposed CMUT phased-array design were compared to those of the device currently used in the clinic. Partial CMUT prototypes, including the therapeutic part only, were fabricated and experimentally characterized (electromechanical CMUT behavior, ultrasound pressure field distribution and acoustic intensity). ResultsThe planar 64-element annular CMUT design is capable of dynamically focusing a 3 MHz ultrasound beam at distances ranging from 32 to 72 mm, comparable in size and shape to the ones obtained with the clinical device. The simulated ultrasound fields correlated well to experimental measurements. Visual observation and impedance measurements of the CMUT cells allowed direct estimation of the collapse and snapback voltages of the ring-elements. The surface acoustic intensity of the CMUT ring-elements with both AC driving and DC bias voltages can achieve over 6 W/cm2, shown in simulation to be compatible with the generation of thermal lesions. The electro-acoustic efficiency of the CMUT elements increased with increasing DC bias voltages to reach 31%, and remained stable with increasing AC driving voltages. The ultrasound energy could be dynamically focused from this planar CMUT array during several dozen of minutes. ConclusionThis work demonstrates the feasibility of utilizing a planar CMUT probe for generating dynamic HIFU focusing and lesioning compatible with the ablation of prostate tissues under endocavitary treatment approach. Future investigations will consist of validating the lesioning capability experimentally both in vitro and in vivo.

Temperature and DC Bias Dependences of Dielectric Behavior of Different Oriented 0.23PIN-0.52PMN-0.25PT Single Crystals

The dielectric behavior under temperature (− 100°C to 250°C) and DC bias (0–4.0 kV cm−1) of [011]- and [001]-oriented PIN-PMN-0.25PT single crystals are systematically investigated. The micro–macro domain transition at Tf is found for [011]- and [001]-oriented samples under DC bias. The dielectric peak induced by DC bias field is found at about 110°C (named peak II), which is nearly independent of DC bias. The appearance of these dielectric peaks may be caused by “2R” and “4R” multidomain states in [011]- and [001]-oriented crystals. With increasing DC bias, the phase transition temperature of R-to-C increases, and the corresponding dielectric permittivity peak value decreases and the dielectric peak becomes wider. The frequency dispersion of the dielectric peak is strongly affected by DC bias. The dielectric behaviors of [011]- and [001]-oriented crystals induced by temperature and DC bias are also compared with that of a [111]-oriented sample.

Possible origin of nonlinear conductivity and large dielectric constant in the commensurate charge-density-wave phase of 1T−TaS2

The electric field dependence of the dielectric properties and the nonlinear conductance of $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$ below 50 K has been investigated. A large dielectric constant of about ${10}^{4}$ is obtained up to ${10}^{7}$ Hz, which cannot be attributed to hopping of the localized carriers alone, the collective excitations of the commensurate charge-density-wave must be another contributor. The dielectric spectra disperse slightly in our measured temperature and frequency range. At a moderate dc bias field, the real part of the dielectric constant ${\ensuremath{\epsilon}}_{1}(\ensuremath{\omega})$ decreases. We propose that the separation of bound soliton-antisoliton pairs may be a contributor to the reduction of ${\ensuremath{\epsilon}}_{1}(\ensuremath{\omega})$ and the accompanying nonlinear conductivity with increasing dc bias.

Design and Realization of Microwave Frequency Multiplier Based on Field Emission From Carbon Nanotubes Cold-Cathode

This paper reports for the first time the theoretical analysis, design, and realization of a microwave (MW) frequency multiplier based on a field emission from carbon nanotube (CNT) cold-cathode. The nonlinear characteristic of field emission from CNT cold-cathode is utilized for generating field emission current with the harmonics of input signal and achieving frequency multiplication. We demonstrated both theoretically and experimentally that an MW electric field is capable of inducting current with harmonics from CNT cold-cathode and that a direct-current (dc) electric field can effectively increase the amplitudes of the harmonics. A reentrant resonant cavity structure was designed and fabricated to deliver the desired combined MW and dc electric fields onto CNT cold-cathode and realize the MW frequency multiplier. The device has the target second harmonic at a frequency of 1.868 GHz and a third harmonic at 2.802 GHz with a driving signal at frequency of 0.934 GHz. By simply increasing dc bias, a 12.43-dB increase of the amplitude of target second harmonic is successfully obtained. With such a device, directly modulated electron beam with MW frequency harmonics is obtained. Both the principle and the design can find applications in frequency tunable vacuum electron devices.

High-speed and high-performance polarization-based quantum key distribution system without side channel effects caused by multiple lasers

Side channel effects such as temporal disparity and intensity fluctuation of photon pulses caused by random bit generation with multiple laser diodes in high-speed polarization-based BB84 quantum key distribution (QKD) systems can be eliminated by increasing DC bias current condition. However, background photons caused by the spontaneous emission process under high DC bias current degrade the performance of the QKD systems. In this study, we investigated, for the first time, the effects of spontaneously emitted photons on the system performance in a high-speed QKD system at a clock rate of 400 MHz. Also, we further show improvements of system performance without side channel effects by utilizing temporal filtering technique with real-time FPGA signal processing.

Electrical Impedance Properties of Y2NiMnO6 Ceramics for DC Bias at Atmosphere

The electrical impedance of Y2NiMnO6 ceramics sintered at 1400 °C for 6 to 24 hours were investigated. The electrical properties of Y2NiMnO6 ceramics were examined in dc bias from 0 volt to 1.5 volt at room temperature. At frequencies below 105 Hz the high electric impedance decreased significantly with longer sintering time, indicating that the grain and grain boundary effects. Increasing dc bias also reduced impedance at the lower frequencies, with polarisation affect at higher frequencies. This behaviour suggests a decrease in the relaxation time of the mobile charge carriers with increasing dc bias and describes a thermally activated relaxation phenomena in the Y2NiMnO6 ceramics.

Studies of Dielectric Permittivity of Y<sub>2</sub>NiMnO<sub>6</sub> Ceramics for DC Bias at Various Temperatures

The dielectric permittivity (ε) of Y2NiMnO6 ceramics prepared by sintering at 1400 °C over 6 to 24 hours was investigated. The response of the ceramics was measured from 1 kHz to 3 MHz, with the influence of a fixed dc bias from 0 to 1.5 V and temperature from 40 °C to -60 oC. Increasing dc bias was found to reduce ε' at low frequencies, while at higher frequencies the dc bias had less influence on ε'. At 40 °C a sharp transition from high to low ε' occurred starting at ~100 kHz, as the temperature of the ceramic was lowered, the transition shifted to lower frequencies. This behaviour is attributed to the charge ordering of Ni2+ and Mn4+ ions and the thermal effect on the ions energy.

EFFECT OF DC BIAS ON DIELECTRIC RESPONSE IN RELAXOR FERROELECTRIC TERPOLYMER FILMS

The permittivity as a function of temperature and dc bias in the poly(vinylindene fluoride-trifluorethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer was measured and analyzed using both the Vogel–Fulcher and universal Curie–Weiss law. The decreased permittivity with increasing dc bias has been observed. The lower permittivity in dc bias is due to the suppressed diffusion of phase transition rather than the nonlinear dielectric contribution. Furthermore, the suppression of phase diffusion can be explained by the molecular conformation conversion in dc bias.

Effects of DC bias on dielectric and electrical responses in (Y + Zn) co-doped CaCu3Ti4O12 perovskite oxides

The dielectric and electrical properties of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics were investigated under an applied DC bias. Crystalline structure, ceramic microstructure, electrical responses and dielectric properties were systematically investigated. The lattice parameter of Zn-doped Ca0.925Y0.05Cu3Ti4O12 ceramics increased with increasing Zn2+ dopant concentration. The microstructure had grain sizes of 2–4 μm and was slightly changed with Zn2+ concentration. High dielectric permittivities (e′ ~ 4400–5000) and very-low loss tangents (tanδ ~ 0.03–0.06) were successfully achieved. At 1 kHz, e′ slightly increased with increasing Zn2+ concentration, while tanδ was significantly reduced. Variations in a low-frequency tanδ values in a low-frequency range were consistent with changes in the grain boundary resistance. Using impedance spectroscopy, it was found that the grain boundary resistance was significantly reduced by applying a DC bias, while the grain resistance remained unchanged. The conduction activation energy at the grain boundaries tended to decrease with increasing DC bias voltage (0–36 V), which was due to the reduction in the potential barrier height at the grain boundaries. The dielectric and electrical properties were described by the internal barrier layer capacitor model of Schottky barriers at the grain boundaries.

Varistor and dielectric properties of SiO2 doped SnO2-Zn2SnO4 ceramic composites

In this work, SiO2 doped SnO2-Zn2SnO4 ceramic composites with excellent varistor and dielectric properties were prepared through traditional ceramic processing. The obtained nonlinear coefficient α was as high as 9.6, and the breakdown electrical field EB and leakage current density JL was as low as 5.9V/mm and 62μA/cm2, respectively. At a low frequency of 40Hz, the relative permittivity εr measured at room temperature was higher than 2.5×104. The nonlinear decrease of the semicircle diameter in the complex impedance spectra with increasing DC bias voltage indicates that the grain boundary effect is an important origin of the varistor and giant permittivity properties. With an increase of temperature, the relaxor peak of the imaginary part M″ of the complex electric modulus shifted to high frequency and the activation energy Ea obtained from the M″ spectrum was about 0.31eV, much lower than the grain boundary barrier height ϕb. The results suggest that other mechanisms may also be responsible for the giant permittivity property besides grain boundary barriers.

Characteristics of W Doped Nanocrystalline Carbon Films Prepared by Unbalanced Magnetron Sputtering.

Nanocrystalline tungsten doped carbon (WC) films were prepared by unbalanced magnetron sputtering. Tungsten was used as the doping material in carbon thin films with the aim of application as a contact strip in an electric railway. The structural, physical, and electrical properties of the fabricated WC films with various DC bias voltages were investigated. The films had a uniform and smooth surface. Hardness and frication characteristics of the films were improved, and the resistivity and sheet resistance decreased with increasing negative DC bias voltage. These results are associated with the nanocrystalline WC phase and sp(2) clusters in carbon networks increased by ion bombardment enhanced with increasing DC bias voltage. Consequently, the increase of sp(2) clusters containing WC nanocrystalline in the carbon films is attributed to the improvement in the physical and electrical properties.

Dielectric and magnetic properties of Zn-substituted Co2Y barium hexaferrite prepared by sol–gel auto combustion method

This work describes the synthesis, structural, dielectric, and magnetic properties of Y-type Ba2Co2-xZnxFe12O22 hexaferrites prepared by the sol–gel n method. X-ray diffraction (XRD) results revealed a structure of the Zn-substituted samples consistent with the standard patterns for Y-type hexaferrites. The saturation magnetization at room temperature increased with Zn-substitution. Further, the coercive field for the sample with x=2.0 was found to have the lowest value.The results of the dielectric measurements indicated that all samples are insulators, and that the ac conductivity decreased with increasing zinc content. However, the ac conductivity increased with increasing dc bias. The effect of the dc bias was more pronounced on samples with low zinc content. The real part of the dielectric constant decreased markedly with increasing frequency at constant applied bias voltage. Further, the activation energy for the prepared samples depends strongly on the Zn concentration.

Ce0.6Mn0.3Fe0.1O2-δ as an Alternative Cathode Material for High Temperature Steam Electrolysis Using LaGaO3-based Oxide Electrolyte

Ce0.6Mn0.3Fe0.1O2-δ (CMF) has been used as a new oxide cathode of solid oxide electrolysis cell (SOEC) using LaGaO3-based electrolyte for H2 production under a feeding gas composition of 20%steam/1%H2/79%Ar. CMF cathode exhibits good electrolysis performance and well-performed hydrogen production rate with the Faraday’s law at 1173-973K. Through impedance measurement under a DC polarized condition, the studies show that polarization resistance and ohmic resistance decreased with increasing DC bias potential. Furthermore, CMF showed good stability, and no significant aggregation and delamination were noticed during the electrolysis measurement. These results suggest that CMF can be a promising oxide cathode candidate for intermediate temperature SOEC.

DC bias immune nanocrystalline magnetic cores made of Fe73Nb3Cu1B7Si16 ribbon with induced transverse magnetic anisotropy.

The comparative analysis of magnetic properties of cut cores made of nanocrystalline Fe73Nb3Cu1B7Si16 alloy ribbon and cores made of the same ribbon with preliminary tension-induced transverse magnetic anisotropy was carried out. The possibility of improving magnetic properties of cut cores, decreasing loss, and increasing DC bias immunity of reversible magnetic permeability is presented. The influence of induced magnetic anisotropy on DC bias immunity of reversible magnetic permeability was investigated. The advantages and disadvantages of new cores (made of ribbon heated under tensile stress) over cut ones were determined.

The DC Bias Voltage Effect and Non-Linear Dielectric Properties of Titanate Nanotubes.

This work reports the nonlinear current-voltage behavior and the effects of dc bias voltage on the dielectric and electrical properties of titanate nanotubes (TNTs) prepared by hydrothermal method at 130 degrees C for 24 h. The TNTs sample exhibited high dielectric constant of > 10(4) at 100 Hz at room temperature with slight dependence on frequency in the range of 10(2)-10(4) Hz. The external resistance forms at the interface between electrode and surface sample. It was found that the dielectric constant of the sample decreased with increasing dc bias voltage due to the decrease in the electrode capacitance. For the study of the non-linear dielectric properties, the breakdown electric field (E(b)) value of the prepared TNTs sample obtained with J = 1 mA cm(-1) was found to be 149 V cm(-1). The E(b) value of the sample was significantly decreased with increasing temperature. The non-ohmic behavior tends to become linear ohmic in characteristic as the temperature increased.