External DC Research Articles

Binary Memory Implemented by Using Variable Gain Amplifiers With Multipliers

This work describes design process toward fully analogue binary memory where two coupled piecewise-linear (PWL) resistors are implemented using novel network topology with the voltage gain amplifiers (VGA). These versatile active devices allow slopes of individual segments of ampere-voltage (AV) characteristics associated with PWL two-terminals to be electronically adjustable via the external DC voltage. Numerical analysis of designed binary memory cell covers all mandatory parts: phase portraits, calculation of the largest Lyapunov exponent (LLE), basins of attraction for the typical strange attractors, and high-resolution circuit-oriented bifurcation sequences. A transition from the stable states toward chaotic regime through metastability is proved via real measurement. The robustness of the generated chaotic attractors is verified by captured oscilloscope screenshots.

ZSI Based Speed Controller for Three Phase Induction Motor

This paper proposes a z source inverter based speed controller for controlling the speed of three phase induction motor. The induction motor is used in several industries for making the work easier and more reliable. Some times it is necessary to control the speed of induction motor, the speed of motor is controlled manually which takes much time and during speed controlling the power loss also increases. Therefore, this paper publish a less power consuming and reliable controller that control the speed of motor without using external dc to dc converter.

Light amplification in tunable multicolor liquid crystalline system

Multicolor emission exhibited by complex organic systems is interesting and desired phenomenon for many optical applications. Laser devices capable to emit the light in the spectral range of three fundamental colors (red, green and blue) can revolutionize the modern display and lighting technologies. In this paper we demonstrate a multicolor stimulated emission (STE) phenomenon obtained in dye doped, liquid crystalline (LC) material. The polychromatic STE was obtained for LC cell, filled with nematic mesophase doped with three luminescent dyes. The CIE XYZ chromaticity diagram (1931) demonstrates effective color modulation with respect to relative concentration of utilized dyes and applied voltage. The precise color adjustment can be provided by applying the external electric DC fields, with voltages ranging from 0 to 20 V.

Suppression of high-power microwave window breakdown by the sweeping-out-electron effect with an external dc bias electric field

To suppress microwave window breakdown, an external parallel dc bias electric field is applied to sweep out the electrons from the discharge zone. The development of microwave window breakdown under an external dc electric field is investigated using particle-in-cell and Monte Carlo collision simulation. The results show that the number of multipactor electrons decreases with the strength of the external unidirectional dc electric field when the size of the microwave window is finite. In addition, the threshold of breakdown is strongly influenced by the direction of the external bidirectional dc electric field. When the electric field is directed from the center to the edge of the microwave window, breakdown occurs more readily than in the absence of the electric field. However, when the electric field is directed toward the center of the microwave window, the discharge process starts at the edge of the window and develops to the center of the window. This is because a smaller density of electrons at the window edge results in a smaller gas pressure and the low gas pressure above the dielectric surface thus makes formation of the plasma more difficult. As a result, the early stage of breakdown is suppressed and the maximum transmitting power is enhanced.

Experimental investigation of weld pool flow under external DC magnetic field

Experimental investigation of weld pool flow under external DC magnetic field

Electronically-engineered metasurface for directional beaming of electromagnetic waves through a subwavelength aperture.

Controlling diffracted waves has attracted extensive research interests these last years particularly for the potential application of beaming functionality. In this paper, we propose to realize on-axis beaming of diffracted electromagnetic waves by using a phase- gradient metasurface. The structure is optimally designed in order to transform surface waves to propagating waves and to enhance transmission through a subwavelength aperture. Both numerical simulations and near-field measurements are performed at microwave frequencies to validate the proposed concept. Furthermore, the metasurface is frequency-tunable and can be controlled by an external DC bias voltage. Consequently, by adjusting the electromagnetic response of each unit cell through the bias voltage, different phase gradients can be tailored, enabling broadband operation spanning from 9 GHz to 12 GHz.

Design and characterization of a compact magnetic shield for ultracold atomic gas experiments.

We report on the design, construction, and performance of a compact magnetic shield that facilitates a controlled, low-noise environment for experiments with ultracold atomic gases. The shield was designed to passively attenuate external slowly varying magnetic fields while allowing for ample optical access. The geometry, number of layers, and choice of materials were optimized using extensive finite-element numerical simulations. The measured performance of the shield is in good agreement with the simulations. From measurements of the spin coherence of an ultracold atomic ensemble, we demonstrate a residual field noise of 2.6 μG and a suppression of external dc magnetic fields by more than five orders of magnitude.

Low-voltage-driven electrostatic microspeakers with potassium-ion-electrets

Electrostatic microactuators require external DC biasing in order to achieve the widest possible range of displacements for a given AC input. This report proposes a novel microspeaker structure that utilizes a potassium-ion-electret to reduce the need for such DC voltage application. Electrets exhibiting quasi-permanent charges enable large fixed voltages to be integrated directly within the MEMS structure, acting as an ersatz DC bias. Prototype devices were fabricated and characterized to approximate the effects of electret incorporation on the device performance.

A giant magnetoimpedance effect based nonvolatile Boolean logic gate

The biphase magnetic heterostructure (Ni/Fe20Ni45Co25Si2B8/micro-planarcoil/Fe20Ni45Co25Si2B8/micro-planar coil/Fe20Ni45Co25Si2B8/Ni) bonded with a pair of thin magnets shows an improved asymmetric and hysteretic giant magnetoimpedance (GMI) effect with respect to an external dc magnetic field. This is attributed to the modification of the soft amorphous magnetic alloy’s (Fe20Ni45Co25Si2B8) permeability by the hysteretic magnetostrictive stress from the neighboring magnetostrictive Ni layer besides the magnetostatic coupling. More importantly, nonvolatile logic gates, such as NOR and NAND, can be implemented with either a single GMI laminate or arrays. On one hand, after applying two sequential magnetic field pulses as the logic inputs to a single proposed laminate, the nonvolatile output voltages are positive high (logic 1) or positive low (logic 0) depending on the signs and magnitudes of pulses. On the other hand, after applying the magnetic field pulses parallel to the GMI laminates arrays, different logic functions can be programmed and realized at run-time. The integration of memory and logic functions enables the proposed GMI laminate to be a possible candidate for future computing systems beyond von Neumann architecture.

Multilevel nonvolatile memory based on the hysteretic giant magnetoimpedance effect of heterogeneous magnetic laminate

This work investigates the asymmetric and hysteretic GMI effect of two-phase heterogeneous magnetic laminate consisting of Ni/Fe30Ni45Co18Si2B5/micro-planar coil/Fe30Ni45Co18Si2B5/Ni for nonvolatile memory application. Since the magnetostrictive Ni ribbon produces the remanent magnetoelastic and magnetostatic fields to the neighboring soft amorphous magnetic alloy (Fe30Ni45Co18Si2B5) when the external dc magnetic field is removed, the proposed laminate manifests multi-level remanent impedances depending on the previously applied magnetic field. And the maximum nonvolatile GMI ratio of 130% is obtained at 400 kHz frequency. Furthermore the laminate can function as multilevel nonvolatile memory, which consumes zero standby power without losing data.

Ultra wideband THz graphene four‐port circulators

AbstractIn the presence of a DC magnetic field, the conductivity of graphene acquires tensor character with antisymmetric nondiagonal elements. This property can be used for creation of nonreciprocal elements in THz region. In this work, we propose and investigate two 4‐port circulators with a planar structure. They are composed of a graphene layer placed on a dielectric substrate. The orientation of the external DC magnetic field is normal to the graphene layer. The graphene geometry of the first circulator presents four strips with surface plasmon‐polariton waves. The strips are connected symmetrically to the magnetized central region such that the whole structure possesses 4‐fold rotational symmetry. The operating region of the circulator at low frequency end is limited by the cyclotron frequency of magnetized graphene and at high frequencies by the appearance of the higher mode in the graphene waveguidings structures. Using numerical calculus, we give an example of the circulator project with the following scattering parameters: S11 is better than −10 dB, the isolation level is less than −15 dB, insertion loss is better than −3 dB in the (1.6 ÷ 2.65) THz region with the bandwidth of 44%. The second four‐port circulator has a linear geometry with lower symmetry where the number of ports can be easily increased. It has the bandwidth also of about 44%. In both cases, the DC magnetic field is 1.5 T and the Fermi energy of graphene μc = 0.15 eV.

Analysis and Design of a Reconfigurable Rectifier Circuit for Wireless Power Transfer

An efficient and reconfigurable rectifier circuit, with the capability of automatically switching from low-power to high-power operation mode, is presented in this paper. The new topology allows the rectifier to convert RF power to dc power efficiently over an extended input power range. The circuit consists of diodes as rectifying elements and of n-channel field effect transistor in a depletion mode acting as the automated switch. Without using an external dc source, the circuit directly uses the rectified output dc voltage to bias the transistor, allowing high conversion efficiency over a wide input power range. This results in a compact and self-contained circuit. A total of two prototypes optimized for near-field and far-field wireless power transfer systems are fabricated and the measured results show that the performance exceeds that of the conventional rectifier circuit, which can only stay efficient over a limited range of the input power. The proposed design can maintain more than 50% of conversion efficiency over more than 25-dB range of the input power, with peak efficiency of 88% and 80% for near-field and far-field rectifiers, respectively. A system-level validation also confirms the improvement of the proposed rectifier design.

57.3: Improvement of Image Sticking for High Standard Automotive Application

As the rapid growth of LCD market, higher level of image quality is required. Image sticking is a phenomenon that a faint outline of previously displayed image remains visible on the screen as the frame is refreshed and it is an unvarying problem as the birth of LCD display. Furthermore, it has been a critical issue for high standard automotive application. In essence, the image sticking arises from the residual electric field (DC) in liquid crystal which caused by the ordered arrangement of ionic charges or dielectric polarization under the external DC offset voltage. In this paper, we will summarize the mechanism of the the residual DC voltage generation and image sticking. And an optimum Vcom setting method minimizing external DC offset voltage is introduced to improve image sticking.

1.2: Invited Paper: Dynamic threshold voltage compensation IGZO‐GOA circuit for AMOLED display

A dual‐gate amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistor (TFT) has been proposed and designed in this work. Based on this specific structure, a technologically advanced external Vth compensation system, where Vth can be controllable by an external DC signal source, has been developed for gate driver on array (GOA). Subsequently, the working mode of this circuit was introduced. Moreover, detailed simulation has been performed to study the appropriate process window. Finally, the proposed GOA circuit exhibited stable high‐voltage output pulse, meanwhile, the lifetime showed an significant improvement with the utilization of the external Vth compensation system. It should be also mentioned that a wide pulse of 3.6ms has been obtained to sense Vth of driving TFTs in pixel circuits.

Face-to-face intercrossed ZnO nanorod arrays with extensive NR-NR homojunctions for a highly sensitive and self-powered ultraviolet photodetector

A self-powering ultraviolet photodetector (UVPD) that effectively utilizes UV energy in an easy-to-implement way is an attractive alternative for the UV optical sensing and communication. Here we report a novel self-powered UVPD based on a face-to-face hybrid ZnO nanorod arrays (ZNRAs) nanostructure. Large-area free-standing ZNRAs have been grown on indium tin oxide (ITO) conductive glass and Ti substrates through a hydrothermal method. Different geometric dimension of ZNRAs/ITO and ZNRAs/Ti structures were designed to pair hybrid each other for achieving the optimum photoelectric performance. Experimentally, it is found that the optimum UVPD based on face-to-face hybrid ITO/l-ZNRAs/l-ZNRAs/Ti structure exhibits an enhancement of ‘1+1>2’ in photoelectric conversion without applying any external DC voltage when compared with single-face ZNRAs-based UVPDs, and the optimum UVPD demonstrates a responsivity of 2.45 mA W−1 and on/off current ratio of 6.6 × 105 under a UV irradiation of 3.06 μW cm−2 as well as a high durability with a cyclic balance of no less than 93.5% in a 4250-s on/off irradiation. The generation of self-power and the high photoelectric performance of face-to-face hybrid ZNRAs-based UVPDs are associated to the Schottky junctions in ITO/ZnO interface as well as the extensive ZnO nanorod-nanorod homojunction.

Dual Output Sinusoidal Oscillator Using Second Generation Current Controlled Conveyor

Second Generation Current Controlled Conveyor (CCCII) based tunable Dual Output Sinusoidal Oscillator (MSO) is proposed. It consists of three CCCIIs, a resistor and two grounded capacitors. By tuning external DC bias current, the oscillator frequency and commencement of its oscillations are controlled electronically. The proposed circuit is verified using PSPICE simulator and also on laboratory breadboard using commercially available integrated circuits Current Feedback Operational Amplifier (AD844AN) and Operational Transconductance Amplifier (LM13600) at a supply rail voltage of ±6 V. Further its nonlinearities, sensitivities, performance characteristics are also verified. Comparison of the proposed topology with the ongoing methods are also undertaken. PSPICE simulation results are verified with a low supply voltage of ±1 V, temperature analysis, analysis by using Montecarlo method and finally Total Harmonic Distortion (THD) is also demonstrated.

Influence of a Counteranion on the Zero-Field Splitting of Tetrahedral Cobalt(II) Thiourea Complexes.

Four mononuclear cobalt(II) complexes with pseudo tetrahedral geometry were isolated with different counteranions; their structure solution reveals the molecular formula as [Co(L1)4]X2 [where L1 = thiourea (NH2CSNH2) and X = NO3 (1), Br (2), and I (3)] and [Co(L1)4](SiF6) (4). The detailed analysis of direct-current (dc) magnetic data reveals a zero-field splitting (ZFS; D) with mS = ±3/2 as the ground levels (D < 0) for the four complexes. The magnitude of the ZFS parameter is larger, in absolute value, for 1 (D = -61.7 cm-1) than the other three complexes (-5.4, -5.1, and -12.2 cm-1 for 2-4, respectively). The sign of D for 1, 2, and 4 was unambiguously determined by X-band electron paramagnetic resonance (EPR) spectroscopy of the diluted samples (10%) at 5 K. For 3, the sign of D was naturally endorsed from the frequency-dependent out-of-phase signal (χM″) observed in the absence of an external dc magnetic field and confirmed by high-frequency EPR (70-600 GHz) experiments performed on a representative pure polycrystalline 3, which gave a quantitative D value of -5.10(7) cm-1. Further, the drastic changes in the spin Hamiltonian parameters and their related relaxation dynamics phenomena (of 2-4 compared to 1) were rationalized using ab initio complete-active-space self-consistent field/n-electron valence perturbation theory calculations. Calculations disclose that the anion-induced structural distortion observed in 2-4 leads to a nonfavorable overlap between the π orbital of cobalt(II) and the π* orbital of the sulfur atom that reduces the overall |D| value in these complexes compared to 1. The present study demonstrates that not only the first but also the second coordination sphere significantly influences the magnitude of the ZFS parameters. Particularly, a reduction of D of up to ∼90% occurs (in 2-4 compared to 1) upon a simple variation of the counteranions and offers a viable approach to modulate ZFS in transition-metal-containing single-molecule magnets.

Control of terahertz pulse polarization by two crossing DC fields during femtosecond laser filamentation in air

Terahertz (THz) radiation induced by the femtosecond laser filament in air can be strongly enhanced through applying an external DC field. In the present work, this technique has been extended to two-dimensional biasing; namely, two pairs of electrodes, which are placed perpendicular to each other, are applied to provide two crossing DC fields. The experimental results have demonstrated that the amplitudes of two orthogonal components of the polarized THz pulse could be modulated by the electric field parallel to it, in an in situ and real-time manner, while the phase delay between them remains constant. Hence, the polarization of the output THz pulse could be freely controlled by adjusting the voltages of the two crossing DC fields, achieving arbitrary ellipticity. It might be the simplest method to manipulate the THz polarization during femtosecond laser filamentation in air.

Fully Electronically Tunable and Easily Cascadable Square/Triangular Wave Generator with Duty Cycle Adjustment

A novel multiple-output dual-X current conveyor transconductance amplifier with buffer-based square/triangular wave generator is introduced in the paper. The proposed generator provides square wave in current mode and triangular wave in voltage mode. Outputs as square and triangular waves are available from terminals with appropriate impedance levels thereby making the proposed generator circuit easily cascadable in both current and voltage modes. The oscillation frequency and amplitude of output square wave are electronically and independently controllable. One more interesting feature of the proposed generator circuit is the adjustable duty cycle. The proposed circuit of square/triangular wave generator is verified through the HSPICE simulation results carried using 0.18[Formula: see text][Formula: see text]m CMOS technology. The simulation results show linear variation of duty cycle against external DC current over a range of 6.5–96%. The variation of square wave’s amplitude via bias current is found to be linear from 10[Formula: see text][Formula: see text]A to 80[Formula: see text][Formula: see text]A. Moreover, the proposed generator can operate very well up to 23.8[Formula: see text]MHz with nonlinearity less than 5%. The proposed generator circuit is also experimentally verified.

Temperature dependence of ferroelectricity and domain switching behavior in Pb(Zr0·3Ti0.7)O3 ferroelectric thin films

Abstract Owing to their high remanent polarization, fast switching behavior, and controllable preparation process, Pb(Zr0·3Ti0.7)O3 (PZT) thin films are considered to be one of the most promising materials for non-volatile ferroelectric random access memory (FRAM). In this work, high-quality PZT thin films with a preferred (111) orientation and smooth surface are obtained by the sol–gel method. The temperature dependence of the ferroelectricity and domain switching behavior is thoroughly investigated by piezoresponse force microscopy (PFM). The domain structure undergoes distinct 180° switching and reconstruction under an external DC voltage. Polarization hysteresis loop analysis of PZT reveals that the spontaneous polarization (Ps), remanent polarization (Pr), and coercive voltage (Vc) decrease as the temperature increases from 20 to 70 °C, in agreement with the Landau classical theory of phase transition. In addition, the PFM results show that the PZT films consistently exhibit good switching behavior as the temperature increases from 23.7 to 70 °C. An increase in the piezoelectric constant (Dmax) with increasing temperature is ascribed to more rapid domain wall movement and easier domain reorientation, as predicted by thermodynamic theory. This investigation suggests that the temperature strongly affects the ferroelectricity and switching behavior of PZT thin films and offers guidance for the design of FRAM.