Direct Current Bias Voltage Research Articles

A Reconfigurable Local Oscillator Harmonic Mixer with Simultaneous Phase Shifting and Image Rejection

A Reconfigurable Local Oscillator Harmonic Mixer with Simultaneous Phase Shifting and Image Rejection

Tunable negative permittivity performance of carbon/silicon dioxide ceramic metacomposites under external DC bias voltage

Metacomposites with negative permittivity have gained increasing momentum in recent years due to their unique electromagnetic characteristics and considerable potential application. However, how to adjust negative permittivity is still a big technical challenge to overcome. In this paper, silicon dioxide (SiO2) ceramic metacomposites consisting of carbon fibers (CFs) were fabricated by vacuum hot press sintering, and their negative permittivity might be modified by adjusting the filler content and applying external direct current (DC) bias voltages. As the CF content increased, the electrical conductivity of composites increased markedly, and the conduction mechanism transformed to a metal-like conductivity from hopping conductivity. The permittivity values of composites with high CF contents were negative at the test frequency range owing to the appearance of a low plasmonic state of unbound electrons in the percolating carbon networks. The conductivity of the composites increased when DC bias voltage was applied, because some of the accumulated local electrons at the CF-SiO2 interface could absorb energy and become free electrons. Larger bias voltages led to increased concentration of free electrons, so the absolute values of the negative permittivity raised according to the Drude model and the frequency band of negative permittivity became wider. This work presents an effective approach for adjusting the negative permittivity value and frequency band, which is advantageous in clarifying the realization and regulation mechanisms of negative permittivity.

Simultaneous cooling and synchronization of the mechanical and the radio-frequency resonators via voltage modulation

We explore the ground state cooling and quantum synchronization of the mechanical and low-frequency inductor-capacitor (LC) resonators in a hybrid three-mode optoelectromechanical system, in which the mechanical resonator is optically and capacitively coupled to the optical cavity and the LC circuit, respectively. We find that when the bias voltage modulation switch is incorporated into the direct current (DC) bias voltage, ground state cooling and quantum synchronization can be simultaneously achieved regardless of whether the mechanical resonator and the low-frequency LC resonator have the identical frequency. Furthermore, we elucidate the relationship between quantum synchronization and ground state cooling of the two resonators, that is, the simultaneous ground state cooling of the resonators must be accompanied by quantum synchronization. Our work may open up an alternative approach to the simultaneous ground state cooling and quantum synchronization of multiple resonators, which has fewer parametric limitations.

Symmetry-Tunable Full-Duty Triangular-Shaped Waveform Generation Using a Simple Single-Drive Mach-Zehnder Modulator

A novel and simple photonic approach for generating symmetry-tunable full-duty triangular-shaped microwave waveforms is proposed and experimentally demonstrated. In this approach, a simple commercial single-drive Mach-Zehnder modulator (MZM) is adopted and driven by the radio frequency (RF) input. By properly presetting the RF modulation index and simply adjusting the direct current (DC) bias voltage of MZM, the full-duty triangular-shaped microwave waveforms with self-defined symmetrical coefficients can be obtained. A complete theoretical analysis on operation principle is presented and a proof-of-concept experiment is carried out. The full-duty triangular-shaped waveforms with tunable symmetrical coefficients at the repetition rate of 5 GHz are successfully generated. This approach features simple architecture, less variables, excellent reconfigurability and integrable capability, which are highly desired for the high-performance triangular-shaped waveform generator.

A New Scheme to Implement the Reconfigurable Optical Logic Gate in Millimeter Wave Over Fiber System

In this work, we employ two Mach-Zehnder modulators (MZM) to achieve a novel six kinds of reconfigurable optical logic gate in millimeter wave over fiber, in which one MZM is used to generate millimeter wave (mm-wave) signal and the other is used to attain optical logic gate. By adjusting the direct current (DC) bias voltage of the first MZM, a frequency doubling mm-wave signal can be obtained and no filter is needed. By controlling the radio frequency (RF) drive voltage and DC bias voltage of the second MZM, the phase of between upper and lower arms can be converted. By adjusting the phase of the first channel RF signal to (π / 2,0), setting the phase of the second channel RF signal to (0,π / 2) and controlling the bias voltage to let the phase of the upper and lower to be π/2 and π/4, respectively, OR logic gate can be obtained. To obtain AND, NOR, NAND, XOR and NXOR logic gate, we just need to get proper phase by adjusting the RF drive voltage and DC bias voltage of the second MZM. According to the simulation, the millimeter wave signal with a frequency of 50 GHz can be obtained, which has completed the logic operation.

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.

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.

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.

A high voltage capacitance measurement method based on alternating coupled signal injection.

As high voltage pulse power capacitors, ceramic capacitors are widely used in high voltage pulse generators, trigger circuits, laser generators, and other fields. The capacitance of ceramic capacitors is closely related to the direct current (DC) bias voltage. However, the current capacitance measurement methods can only achieve a DC bias of 1 kV, which cannot meet the measurement requirements in high voltage environments. This paper proposes a capacitance measurement method that can accurately measure the capacitance under a DC bias of 3 kV. This method decouples the high DC bias voltage and high frequency alternating small signals and realizes low voltage calibration and high voltage isolation. The experimental results show that the proposed method measures the capacitance under a DC bias of 3 kV with a relative error within ±1%, which makes it possible to accurately quantify the capacitance hysteresis deviation in the process of increasing and decreasing back the voltage.

Peak-tracking scanning capacitance force microscopy with multibias modulation technique

Scanning capacitance force microscopy (SCFM) is a good method for capacitance measurements using electrostatic force detection. However, to obtain an entire capacitance–voltage (C–V) curve by SCFM, a sweep of a direct current (DC) bias voltage is required at a certain fixed point on a sample surface during scan suspension, and thus the measurements become very time-consuming when we want to observe some types of image related with C–V characteristics. In this paper, we propose peak-tracking scanning capacitance force microscopy (PTSCFM) for the purpose of extracting the main feature of the C–V curve without DC voltage sweep. In PT-SCFM, alternating current voltages at three different angular frequencies, ω 1, ω 2, and , are applied together with DC voltage, , to generate an electrostatic force, and high-order components at the angular frequencies of and , which represent a voltage derivative of a capacitance () and a second-order derivative of the capacitance (), respectively, are extracted from the electrostatic force. Then, a DC voltage, , giving the peak of is determined from to be adjusted to nullify the component using a feedback controller. From the obtained values of and at , the C–V curve can be outlined. In PT-SCFM, the distributions of those values are simultaneously imaged together with a topography without sweep, and when we operate PT-SCFM under various modulation frequency conditions, analyses similar to those based on the frequency dependence of the C–V property are realized. We have applied the PT-SCFM to a microcrystalline material to discuss the effects of surface depletion and deep-level states, from which the validity of PT-SCFM has been examined.

Fabrication and characterization of In doped Li13.9Sr0.1Zn(GeO4+δ)4 electrolytes for proton-conducting solid oxide fuel cells

Li13.9Sr0.1Zn(GeO4+δ)4 (LSZG) materials can exhibit proton conduction by Li+/H+ ion exchange in hydrogen atmosphere. It can be used in solid oxide fuel cells (SOFCs) as an electrolyte. In this study, In3+ doped LSZG powders are synthesized by sol-gel method. X-ray diffraction, scanning electron microscopy, thermal gravimetric analyzer, and electrochemical impedance spectroscopy are used to investigate the effects of In doping on LSZG. All Li13.9-xInxSr0.1Zn(GeO4+δ)4 (LISZG, 0 ≤ x ≤ 0.3) ceramics exhibit the same phase with LSZG. The dopant of In promotes the sintering activity and Li+/H+ ion exchange rate of LSZG. The optimum doping of In is x = 0.2. At 600 °C, Li13.7In0.2Sr0.1Zn(GeO4+δ)4 (0.2LISZG) shows a proton conductivity of 0.094 S/cm under 0.9 V direct current bias voltage. In addition, the single cell based on 0.2LISZG electrolyte is prepared, and it has been demonstrated that the practical utilization of 0.2LISZG in IT-SOFCs is feasible.

A Microwave Imager Implemented With a Space-Fed Randomized Aperture

Recently, microwave imaging based on randomized illuminations has demonstrated promising potentials. The key to realize such imaging is to implement an imager with a reconfigurable, randomized aperture. In this work, we discuss the theory and the guidelines for implementing such an imager and demonstrate an experimental prototype working in the 24-GHz ISM band. It is realized with a board-integrated, space-fed, 400-element phased array capable of realizing independent 1-bit phase modulations for each element. The fields transmitting through this aperture can be deterministically randomized by simply controlling direct current bias voltages. Assisted by optimized system calibration and standard <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\ell _{1}$ </tex-math></inline-formula> -norm regularization, experimental imaging with a notably improved quality can be obtained. The proposed solution can be used in wide applications, especially suitable for the massive personal security screenings in common public, government, and military areas.

A Frequency Reconfigurable Antenna based on Few Layer Graphene

In this paper, a frequency reconfigurable antenna was presented. This antenna is made up of a square loop and a microstrip line with a gap, in which the few layer graphene (FLG) sheet is located to achieve frequency reconfigurable. FLG is likes a lumped resistor with resistance. And the surface impedance can be adjusted by applying a direct current bias voltage, which obtains two work modes that imitate switch. Additionally, the experimental evidence show the proposed frequency reconfigurable antenna can provide a tunable bandwidth.

Tribological properties and microstructure of monolayer and multilayer Ta coatings prepared by magnetron sputtering

To improve the wear resistance of medical titanium alloy, Ta coatings were prepared by magnetron sputtering method on Ti6Al4V substrates. Phase structure and surface morphology of Ta coatings were characterized by X-ray diffraction and atomic force microscope, respectively. The properties of Ta coatings, including adhesion, nano-hardness, and wear resistance, were tested using nano-scratch, nano-indentation and tribometer, respectively. The results show that both stable body-centered cubic (α-Ta) phase and metastable tetragonal phase (β-Ta) coexist in a multi-layer structure, and it shows a non-columnar feature. Interestingly, only a pure phase with columnar crystals is found in monolayer Ta coating. A body-centered cubic (α-Ta) phase is found in a monolayer prepared under the pulse power bias voltage with low deposition temperature. A pure metastable tetragonal phase (β-Ta) is prepared under the direct current bias voltage, which has the best adhesion and wear resistance compared with other Ta coatings.

Electrochemical migration behavior of low-temperature-sintered Ag nanoparticle paste using water-drop method

The electrochemical migration (ECM) behavior of low-temperature-sintered Ag nanoparticle paste electrode was investigated using water-drop method. The effects of applied direct current bias voltage and NaCl concentration on ECM behavior were discussed. Results show that: at low NaCl concentration levels, mean time to failure caused by ECM decreased with increasing NaCl concentration due to the increase of solution conductivity; at medium NaCl concentration levels, dendrite growth was retarded due to the formation of AgOH or other insoluble products, while at high NaCl concentration levels, due to the turbulent hydrogen evolution, the second spreading of water drop resulted in the circuit broken and thus inhibited ECM behavior. Moreover, mean time to failure decreased with the rising applied bias voltage. More importantly, hexadecyltrimethylammonium chloride (CTAC) was proved to act as an effective inhibitor to migrate dendrite growth by selected adsorption. And the ECM inhibition efficiency increased with the concentration of CTAC. Relevant mechanisms of ECM behavior and ECM inhibition effect of CTAC for low-temperature-sintered Ag nanoparticle paste were proposed.

Instrumentation for tracking electrochemical reactions by x-ray photoelectron spectroscopy under conventional vacuum conditions

A bias application system for tracking electrochemical reactions by x-ray photoelectron spectroscopy (XPS) is constructed using a laboratory-based apparatus. A specialized sample holder and stage with three electrical terminals provide contacts to a potentio-galvanostat on the outside, allowing bias application to an electrochemical device in the analysis chamber under vacuum conditions. The application of a direct current bias voltage to the sample holder is confirmed using metal Au samples. The Au 4f peaks from the Au grounded to the analyzer are identical, while those from the Au insulated from the analyzer shift due to the applied bias voltage. Furthermore, galvanostatic lithiation/delithiation processes and in situ XPS measurements are performed on a Si thin-film electrode after transferring the sample into the XPS apparatus without exposure to open air using a newly developed transfer vessel. After the initial lithiation process, a Li 1s peak containing a lithium-silicide component appears, and the Si 2p peaks shift to a lower binding energy due to the lithiation of the Si electrode. After the subsequent delithiation process, the Si 2p peak from the lithium silicide partially shifts back to a higher binding energy. As a result, in situ XPS measurements of the lithiation/delithiation reactions are successfully performed using the developed system.

High performance infrared detectors compatible with CMOS-circuit process* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11933006, 61805060, and 61290304).

A type of Si-based blocked impurity band photoelectric detector with a planar architecture is designed and demonstrated by a modified silicon semiconductor processing technique. In this route, multiple ion implantation is utilized to ensure the uniform distribution of the P elements in silicon, and rapid thermal annealing treatment is used to activate the P atoms and reduce damages caused by ion-implantation. The fabricated prototype device exhibits an excellent photoelectric response performance. With a direct current (DC) bias voltage of –2.3 V, the device detectivity to blackbody irradiation is as high as 5 × 1013cm⋅Hz1/2/W, which corresponds to a device responsivity of nearly 4.6 A/W, showing their potential applications in infrared detection, infrared astrophysics, and extraterrestrial life science. In particular, the developed device preparation process is compatible with that for the CMOS-circuit, which greatly reduces the manufacturing cost.

Controllability of ferrofluids’ dielectric spectrum by means of external electric forces

A broadband dielectric response of ferrofluids can be effectively controlled by application of an external magnetic field. The interaction of magnetic nanoparticles with magnetic forces and the resulting structural changes in the ferrofluids may tune their dielectric spectra. In this paper, we present an experimental study on the controllability of a dielectric spectrum of Mn-Zn ferrite transformer oil-based ferrofluid by means of a static electric field generated by a direct current (DC) bias voltage. Two experimental configurations of the DC bias voltage are applied. The spectrum of a complex permittivity measured in the frequency range from 1 mHz up to 200 kHz is firstly studied under an internal DC bias voltage applied on the electrodes of a measuring capacitor. Then, the sensitivity of the dielectric spectrum to the external DC bias voltage applied on an external pair of electrodes outside the measuring capacitor is investigated. It is found that the increasing internal DC bias voltage significantly shifts the whole dielectric spectrum to lower frequencies and gives rise to higher permittivity values. The external DC bias voltage is remarkably less capable of such tuning. The obtained dielectric spectra are described by a fitting function composed of Havriliak–Negami and conductivity terms. The fitting parameters are compared in the analysis of the two DC bias voltage effects. An interfacial polarization on the nanoparticles is considered to dominate the dielectric spectrum. The aggregation of nanoparticles due to the induced electric polarization and the acting electric forces is discussed as a primary reason of the changes in the dielectric spectra. The DC bias voltage-tunable dielectric spectrum thus complements the controllability of ferrofluids by external forces and may open a new avenue of research and applications in electrical engineering.

A Modeling and Feasibility Study of a Micro-Machined Microphone Based on a Field-Effect Transistor and an Electret for a Low-Frequency Microphone.

Miniaturized capacitive microphones often show sensitivity degradation in the low-frequency region due to electrical and acoustical time constants. For low-frequency sound detection, conventional systems use a microphone with a large diaphragm and a large back chamber to increase the time constant. In order to overcome this limitation, an electret gate on a field-effect transistor (ElGoFET) structure was proposed, which is the field-effect transistor (FET) mounted diaphragm faced on electret. The use of the sensing mechanism consisting of the integrated FET and electret enables the direct detection of diaphragm displacement, which leads its acoustic senor application (ElGoFET microphone) and has a strong ability to detect low-frequency sound. We studied a theoretical model and design for low-frequency operation of the ElGoFET microphone prototype. Experimental investigations pertaining to the design, fabrication, and acoustic measurement of the microphone were performed and the results were compared to our analytical predictions. The feasibility of the microphone as a low-frequency micro-electromechanical system (MEMS) microphone, without the need for a direct current bias voltage (which is of particular interest for applications requiring miniaturized components), was demonstrated by the flat-band frequency response in the low-frequency region.