Direct Current Bias Research Articles

The Fe79Si8B13 and Fe75Si8B13Nb3Cu1 powder prepared by gas-water two-phase coupled rapid-setting sedimentation atomization (WGC)

To satisfy the reliability and magnetic property requirements of surface mounted devices (SMD), the high-performance Fe79Si8B13 and Fe75S8iB13Nb3Cu1 powders were prepared by gas-water two-phase coupled rapid-setting sedimentation atomisation technology (WGC). They were compared with the Fe79Si8B13 and Fe75S8iB13Nb3Cu1 powders prepared by the traditional water-gas combined atomisation technology (W-G). The result shows that the morphology of the Fe79Si8B13 and Fe75S8iB13Nb3Cu1 powders prepared by the WGC device is better. The defects, such as burrs and protrusions on the surface of powder particles, were removed, and the formed powders were almost entirely spherical. Through x-ray diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and vibrating sample magnetometer (VSM) analyses, we concluded that the Fe79Si8B13 and Fe75S8iB13Nb3Cu1 raw powder developed by the WGC device exhibited higher amorphousness and magnetic properties. Therefore, the novel WGC device exhibits a higher cooling capacity while preparing amorphous and nanocrystalline powders. It is also more suitable for the commercial production of amorphous and nanocrystalline powders. The magnetic properties of the powder were further evaluated by preparing them into a powder core. The powder developed by the WGC device with higher permeability can achieve similar direct current (DC) bias characteristics under higher permeability and lower core losses. These advantages of magnetic properties were pursued via SMD.

Research and analysis on suppression and influence of transformer direct current bias

DC bias generates a large DC component in the windings of the transformer in operation, thereby generating harmonics, causing vibration, noise, and overheating. In severe cases, it can cause damage to the transformer, which will affect the safe and stable operation of the AC system. This article takes the DC bias of the main transformer of a 220kV substation as an example, and uses the capacitance isolation method to suppress the DC bias. Due to the addition of capacitor equipment at the neutral point, the zero-sequence impedance of the main transformer and the change of the zero-sequence impedance of the power grid are changed, which has an impact on the zero-sequence (directional) current protection and ground distance protection. Through theoretical analysis and simulation research verification, for general 220kV substations, the capacitor DC isolation method (1.2Ω) can be used to suppress DC bias, which has a small impact on the relay protection and does not need to adjust the related protection settings.

Spray-Coated Superhydrophobic Overlayer with Photothermal and Electrothermal Functionalities for All-Weather De/anti-icing Applications.

High-performance de/anti-icing overlayers which can be deposited on diverse surfaces offer great potential in many industrial settings and daily life, yet a versatile overlayer applicable to all-weather conditions (high humidity, low temperature, raining, snowing, etc.) is in high demand for practical applications. This study presents the fabrication and application of a superhydrophobic overlayer with a bioinspired hierarchical surface which additionally possesses photothermal and electrothermal functionalities, so it can operate as a de/anti-icing layer in extreme environments. The overlayer, with a papilla-like microstructure similar to that of a lotus leaf, features polydopamine-decorated layered basic zinc acetate microparticles distributed in the framework of multiwalled carbon nanotubes. Specifically, the overlayer is superhydrophobic, and its capability of suppressing the condensation of water droplets and growth of ice crystals is verified by both in situ environmental scanning electron microscopy observations and freezing experiments. Moreover, the overlayer can be warmed up to 74 and 105 °C under the excitation of sunlight and direct current bias, respectively, which is sufficiently high for deicing in severe weather. It is worth mentioning that the overlayer is produced by a spray-coating technique; therefore, it is suitable for large-scale deployment on arbitrary substrate materials. The findings provide insights into a new strategy for engineering multifunctional overlayers and can lead to expanding applications of composite coatings.

Microstructure evolution and soft magnetic property optimization of core-shell FeSiBCCr@SiO2&ZrO2 amorphous magnetic powder cores

In this study, core-shell structured FeSiBCCr@SiO2&ZrO2 amorphous magnetic powder cores (AMPCs) were successfully prepared by the sol-gel method using tetraethyl orthosilicate (TEOS) and zirconium oxychloride hydrate (ZrOCl2·8H2O) as raw materials. The growth mechanism and potential chemical reactions of the SiO2&ZrO2 mixed insulation layer were analyzed by XRD, XPS and SEM‒EDS. In addition, the effect of the insulation layer content on the soft magnetic properties of FeSiBCCr@SiO2&ZrO2 AMPCs was systematically investigated. The SiO2&ZrO2 insulation layer can significantly increase the resistivity, effectively improve the DC bias performance and reduce the core loss of AMPCs. S2* (1.2 mL TEOS and 1.4 g ZrOCl2·8H2O) had a minimum core loss of 2290 mW/cm3 at high frequency (50 mT, 1 MHz). It had a high effective permeability of 48.2 and a superior direct current (DC) bias performance of 77.9% at 8 kA/m. This study provides a valid method to practically produce SMPCs with high resistivity, low core loss at high frequency and excellent DC bias performance through a novel insulation coating process.

Single-modulator Based Multi-Format Switchable Signal Generator Without Background Noise

A photonic multi-format background-free binarily modulated microwave signal generator using a single dual-polarization dual-parallel Mach–Zehnder modulator is proposed and demonstrated. The proposed generator features good reconfiguration and switchability. By simply adjusting the direct current biases of the modulator, amplitude shift keying (ASK), phase shift keying (PSK) and frequency-shift keying (FSK) microwave signals can be generated. Benefiting from the complementary intensity modulation, there is no residual baseband modulated signal in the generated binarily modulated signals. The system does not involve any optical or electrical filters, which ensures good tunability of the generator. By changing the frequency of the driven microwave carrier and bit rate of the electrical coded signal, the frequency and rate of the generated multi-format signals can be adjusted accordingly. The multi-format switchable signal generator has great potential in multi-functional communication and radar systems.

Millimeter‐wave frequency reconfigurable antenna using simple VO 2 ‐based paired metasurface

In this article, a millimeter-wave frequency-reconfigurable metasurface antenna by electrically controlling vanadium dioxide (VO2) is proposed and studied. As a phase change material, VO2 is an insulator at room temperature but can turn into high conductivity metallic state when activated by continuous direct current (DC) voltage. By integrating the VO2 film between two simple rectangle metasurface cells, a frequency-reconfigurable paired metasurface structure (FRPMS) is achieved. The FRPMS can be considered as one unit when VO2 film is activated to metallic state while as two independent cells when VO2 film is in insulating state. In this way, the FRPMS can operate, respectively at 28 and 38 GHz with independent tunability. Moreover, a coplanar and staggered DC bias circuit with little effect on radiation is designed to switch the operating modes of VO2 easily. The antenna is fed by a stepped waveguide with ridges through a loop slot, which is suitable for dual-band feeding with large frequency ratio. One prototype is fabricated and measured for demonstration. When the VO2 film is in metallic state, the measured working band covers from 28.5 to 29.6 GHz with the maximum gain of about 7.1 dBi. When cooled down to insulating state, the antenna can work in a higher band from 36.7 to 38.3 GHz with the maximum gain of about 7.9 dBi. Due to the advantages of simple structure, high gain and easy tuning, the antenna can be expected to use in mmW wireless communication.

Acoustic wave amplification with thin film silicon bonded on lithium niobate

Signal processing with the use of acoustic waves is an important technology for various functions in radio frequency (RF) systems, including matched filtering in congested parts of the frequency spectrum. In order to generate long time delays on chip required for these applications, the acoustoelectric effect offers the ability to counter acoustic propagation losses while also generating inherent non-reciprocity. In this work, we demonstrate an approach to directly bond thin film silicon from 200 mm commercial silicon on insulator wafers on X-cut lithium niobate substrates with the use of plasma surface activation. The resulting delay line devices at 410 MHz demonstrate amplification of Rayleigh waves, with a peak non-reciprocal contrast between forward and reverse traveling waves of over 25 dB mm−1 under continuous direct current bias conditions. The demonstrated process can extend the functionality of traditionally passive piezoelectric RF microsystems.

Enhancement of electrohydrodynamic force with AC bias voltage in three-electrode dielectric barrier discharge plasma actuators

A novel dielectric barrier discharge (DBD) plasma-actuator module with an exposed electrode and two covered electrodes was developed to enhance electrohydrodynamic force generation based on the concept that it separates the ionization and acceleration processes. The conventional three-electrode configuration of the DBD plasma actuator suffers from unexpected spark discharge between the exposed electrodes, thereby failing to strengthen the electric field intensity for accelerating charged particles or generating a stable ionic wind. In this study, a third electrode was embedded in the dielectric layer to prevent spark discharge. Furthermore, an alternating current (AC) waveform was employed as the bias voltage, which was applied to the third electrode, instead of the direct current (DC) voltage used in a conventional DBD plasma actuator. Induced flow visualization using particle image velocimetry technique revealed that the DC bias voltage forms a weak ionic wind in the proposed DBD plasma actuator owing to the electric field screening effect, and the ionic wind periodically appears when the polarity of the voltage is reversed by applying an AC-bias voltage. The velocity of the ionic wind increases with increasing frequency and the AC bias voltage amplitude. Also, decreasing the distance between the second and third electrodes results in ionic wind enhancement. The results obtained in this study provide insights into the drastic improvement in the performance of DBD plasma actuators with the enhancement of the electric field intensity for charged particle acceleration.

Particle size selection principle of Fe-Si-Al SMCs for high-frequency and high-power applications

Fe-Si-Al soft magnetic composites (SMCs) with different particle sizes were prepared. Good insulation quality was achieved for all samples. The influences of the particle size on permeability, direct-current bias (DC-bias) performance, and core loss for SMCs with the same insulation content and with the same permeability were investigated in detail. SMCs made of small particles were found to possess low core loss at high frequency and high maximum magnetic induction (Bm) and enhanced DC-bias performance. However, the variation of particle size has little effect on the anti-saturation ability and the core loss at low frequency and low Bm for SMCs with fixed permeability. Based on the analysis of SMCs’ density, volume resistivity, core loss, effective demagnetizing field and eddy current, particle size dependence of these magnetic parameters were reasonably explained. This study suggests that particle miniaturization is the development direction of SMCs for high-frequency and high-power applications.

Design and Fabrication of Millimeter-Wave Frequency-Tunable Metamaterial Absorber Using MEMS Cantilever Actuators.

In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were −5.68 dB and −33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively.

Plasma-enhanced electrostatic precipitation of diesel exhaust particulates using nanosecond high voltage pulse discharge for mobile source emission control

This study reports enhancement in the electrostatic precipitation (ESP) of diesel engine exhaust particulates using high voltage nanosecond pulse discharge in conjunction with a negative direct current (DC) bias voltage. The high voltage (20 kV) nanosecond pulses produce ion densities that are several orders of magnitude higher than those in the corona produced by a standard DC-only ESP. This plasma-enhanced electrostatic precipitator (PE-ESP) demonstrated 95 % remediation of PM and consumes less than 1 % of the engine power (i.e., 37 kW diesel engine at 75 % load). While the DC-only ESP remediation increases linearly with applied voltage, the plasma-enhanced ESP remains approximately constant over the applied range of negative DC biases. Numerical simulations of the PE-ESP process agree with the DC-only experimental results and enable us to verify the charge-based mechanism of enhancement provided by the nanosecond high voltage pulse plasma. Two different reactor configurations with different flow rates yielded the same remediation values despite one having half the flow rate of the other. This indicates that the reactor can be made even smaller without sacrificing performance. Here, this study finds that the plasma enhancement enables high remediation values at low DC voltages and smaller ESP reactors to be made with high remediation.

Fabrication of airbridges with gradient exposure

In superconducting quantum circuits, airbridges are critical for eliminating parasitic slotline modes of coplanar waveguide circuits and reducing crosstalks between direct current magnetic flux biases. Here, we present a technique for fabricating superconducting airbridges. With this technique, a single layer of photoresist is employed, and the gradient exposure process is used to define the profile of airbridges. In order to properly obtain the bridge profile, we design exposure dosage based on residual photoresist thickness and laser power calibrations. Compared with other airbridge fabrication techniques, the gradient exposure fabrication technique provides the ability to produce lossless superconducting airbridges with flexible size and, thus, is more suitable for large-scale superconducting quantum circuits. Furthermore, this method reduces the complexity of the fabrication process and provides a high fabrication yield.

Tunable dual-frequency coherent Doppler lidar using bi-directional electro-optic modulation in a Sagnac loop

A novel tunable dual-frequency coherent Doppler lidar (DF-CDL) for velocity detection is proposed and experimentally demonstrated. In the laser source, although dual-frequency laser light can be generated by an electro-optic intensity modulator biased in the double-sideband suppressed-carrier mode, a slight drift in the direct-current (DC) bias voltage leads to a non-ideal carrier suppression. To address this problem, bi-directional electro-optic phase modulation in a Sagnac loop is employed. Due to the use of electro-optic phase modulators, no bias voltage is needed, resulting in no bias drifts. In the signal processing module, since the envelope of the Doppler signal is a cosine function of the differential Doppler shift, envelope-demodulation is employed to directly derive the differential Doppler shift from the analog Doppler signal. Due to the low-frequency characteristic of the differential Doppler shift, the sampling rate request of the ADC is reduced. In the experiments, the performance of the DF-CDL is validated under the conditions of different dual-frequency spacings and different target speeds. A speed measurement of 10.01 mm/s with a relative error of 0.10% is achieved when the dual-frequency spacing is 40 GHz and the target speed is 10 mm/s.

Does concurrent self-administered transcranial direct current stimulation and attention bias modification training improve symptoms of binge eating disorder? Protocol for the TANDEM feasibility randomized controlled trial.

BackgroundBinge eating disorder (BED) is a common and disabling problem associated with impaired cognitive control. Preliminary studies show that brain-directed treatments, including transcranial direct current stimulation (tDCS) and attention bias modification training (ABMT), improve cognitive control and alleviate symptoms of BED. When combined, tDCS may enhance the effects of ABMT, and vice versa, thereby improving treatment outcomes.MethodsThis protocol describes a feasibility single-blind randomized sham-controlled trial of concurrent self-administered tDCS and ABMT in adults with BED (The TANDEM Trial). Eighty adults with BED will be randomly assigned to one of four groups: ABMT with real or sham self-administered tDCS, ABMT only, or waiting list control. In the treatment arms, participants will complete 10-sessions of their allocated intervention over 2–3 weeks. Outcomes will be assessed at baseline (T0), immediately post treatment (T1), and 6 weeks after end of treatment (T2), and at comparable timepoints for participants in the waitlist control group. Feasibility will be evaluated by assessing recruitment/retention rates and blinding success. Acceptability will be assessed quantitatively via participant ratings and qualitatively via semi-structured interviews. Episodes of binge eating at follow-up will be the primary clinical outcome and rate ratios from Poisson regression will be reported. Secondary outcomes will assess changes in ED and general psychopathology, attention bias toward high calorie foods, and executive function.DiscussionIt is hoped that data from the trial will contribute to the development of neurobiologically informed treatments for BED, provide insights into the potential use of at-home variants of tDCS, and inform the design of future large scale trials.

Effect of argon flow rate and direct current bias on the growth of boron nitride coating in low-temperature plasma

A microwave plasma chemical vapor deposition system was used to synthesize cubic boron nitride (cBN) coatings on diamond seeded silicon substrates using direct current (DC) bias. Effects of the argon (Ar) flow rate and bias voltage on the growth of the cBN coatings were investigated. Hydrogen (H2), argon (Ar), a mixture of diborane in H2 (95% H2, 5% B2H6), and N2 were used in the feed gas. A DC bias system was used for external biasing of the sample, which facilitates the goal of achieving sp3 bonded cBN. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) revealed the existence of sp3-bonded BN in the produced samples. With increasing Ar flow, the cBN content in the coating increases and reaches a maximum at the maximum Ar flow of 400 SCCM used in this study. High-resolution XPS scans for B1s and N1s indicate that the deposited coating contains more than 70% cBN. This study demonstrates that energetic argon ions generated in a microwave-induced plasma significantly increase cBN content in the coating.

A Bridge-Shaped Vibration Energy Harvester with Resonance Frequency Tunability under DC Bias Electric Field.

A vibration piezoelectric energy harvester (PEH) is usually designed with a resonance frequency at the external excitation frequency for higher energy conversion efficiency. Here, we proposed a bridge-shaped PEH capable of tuning its resonance frequency by applying a direct current (DC) electric field on piezoelectric elements. A theoretical model of the relationship between the resonance frequency and DC electric field was first established. Then, a verification experiment was carried out and the results revealed that the resonance frequency of the PEH can be tuned by applying a DC electric field to it. In the absence of an axial preload, the resonance frequency of the PEH can be changed by about 18.7 Hz under the DC electric field range from −0.25 kV/mm to 0.25 kV/mm. With an axial preload of 5 N and 10 N, the resonance frequency bandwidth of the PEH can be tuned to about 13.4 Hz and 11.2 Hz, respectively. Further experimental results indicate that the output power and charging response of the PEH can also be significantly enhanced under a DC electric field when the excitation frequency deviates from the resonance frequency.

Effects of Electric Bias on Different Sc-Doped AlN-Based Film Bulk Acoustic Resonators

Film bulk acoustic resonators (FBARs) based on aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN) exhibit tremendous application aspects in the radio frequency front-end due to achievable high-frequency characteristics, superior thermal performances and compatibility with harsh environments. Delicately controlling the resonant frequency (fs) of FBAR is essential for integrating filters or modules. In this work, we provide a practical feasibility in adjusting fs of AlN and AlScN FBAR using external direct current electric bias (EDC). When applying a negative EDC (the direction along the reversed c-axis), fs shifts to a lower frequency, whereas a positive EDC brings a higher fs. In order to extract the equivalent values of the stiffness coefficient (c33), piezoelectric coefficient (e33) and dielectric constant (εzz) of AlN and AlScN piezoelectric materials, we adopted the electromechanical equivalent Mason model. The results show that the equivalent values of c33 increase with the change of EDC from negative to positive, and, on the other hand, those of e33 and εzz decrease. Our work provides a systematic investigation on the electric field-influenced stiffening effect of AlN and AlScN piezoelectric films and opens a feasibility for frequency-tunable resonators.

Utilizing deep neural networks to extract non-linearity as entities in PAM visible light communication with noise.

Herein, we propose a novel entity extraction neural network (EXNN) with a newly designed sampling convolution kernel approach and a deep learning-based structure to differentiate noise in visible light communication (VLC) systems. In particular, EXNN is used to extract linear and nonlinear distortion in a received signal as an entity and compensate for the signal by removing it. First, we designed a deep learning structure tailored for VLC systems, used experimentation to validate our algorithm's usability, and determined an appropriate range for the hyper-parameters that govern the PAM-8 system. Second, we compared our approach with existing finite impulse response (FIR) linear and Volterra nonlinear compensation algorithms via experiments. Below the hard-decision forward error correction (HD-FEC) threshold limit of 3.8×10-3, experimental results show that the use of the EXNN increased the operating range of the direct current (DC) bias and the voltage by ∼33.3% and by ∼50% under optimal conditions, respectively. Furthermore, under corresponding optimal power conditions, the proposed approach improved the Q factor of the VLC system by 0.36 and 1.57 dB compared with the aforementioned linear and nonlinear equalizers, respectively. To the best of our knowledge, this is the first time that a deep learning operator has been custom-designed for the VLC system and we have named the completely redesigned network with this sampling convolution kernel operator as EXNN.

A miniaturized low frequency direct-current magnetic-bias-integrated magnetoelectric wireless power transfer system with enhanced energy conversion efficiency

Wireless power transfer (WPT), which transfers energy without a physical link, has recently received significant research interest. Due to the advantages of small dimension, low operation frequency, and low transmission loss, magnetoelectric WPT (ME-WPT) has been shown to be a promising technology for internet of things (IoT) and implantable medical device (IMD) applications. However, ME-WPT requires a direct-current (DC) magnetic bias for optimal performance and prior arts have implemented large electromagnets, Helmholtz coils, or externally positioned magnet bias systems, which increase the system dimension. Furthermore, the highest energy conversion efficiency (ECE) reported by prior ME-WPT studies is 0.62%, which needs to be improved. In this paper, we present an ME-WPT system with a novel miniaturized ME-WPT receiver and a spiral coil based transmitter. Four DC magnets are integrated onto the ME-WPT receiver to significantly reduce its dimension while providing a DC magnetic bias of 190 Oe for optimal performance. Electrochemical polarization characterizations are introduced to analyze the performance of the WPT receiver, which reveal that a maximum output power of 4.096 mW is obtained. A record ECE of 2.64% is reported, the highest among all ME-WPTs to date. The output power is improved by at least 49.3 times compared with the ME-WPT without integrated DC magnets. The influence of the input voltage and the distance between transmitter/receiver on the performance of the ME-WPT system is studied, which shows that the output power increases as the distance decreases and the input voltage increases. The proposed ME-WPT system with integrated DC magnets has potential applications in IoT and IMDs.

Electrothermally controllable terahertz metamaterial for sensing application

A design of electrothermally controllable terahertz (THz) metamaterial (ECTM) is presented, which is composed of split-ring resonator (SRR) on Si substrate. All SRR unit cells are connected to form ECTM with a current loop. By driving a direct-current (DC) bias voltage on ECTM, the heating energy is generated and then changed the surrounding refraction index. Therefore, it results in a resonant shift. While the DC bias voltage is applied from 0 volt to 0.95 volts in transverse electric (TE) mode, ECTM shows a tunable triple-resonance with the tuning ranges of 24 GHz, 40 GHz, and 32 GHz, respectively. The maximum sensitivity is 42 GHz/volt. Meanwhile, the maximum Q-factor is 24.5. These results pave a way for ECTM to be applied in polarization-dependent filters and sensors for further tunable and controllable optoelectronics applications.