AC Modes Research Articles

Smart electro-magneto-viscoelastomer minimum energy structures with particle-reinforcements: Theoretical equilibrium and nonlinear dynamics of actuated configurations

Soft transduction technology is rapidly adopting soft active elastomer-based minimum energy structures because of their distinctive programmable shape-morphing characteristics. For effective device design, an understanding of the nonlinear dynamic behavior is crucial as they often experience time-dependent motion while operating. Moreover, there has been an increasing scientific interest in enhancing the actuation performance of soft active elastomers by imparting particle reinforcements. This article provides a theoretical framework for investigating the nonlinear dynamics of smart composite elastomer-based minimum energy structures (SCEMES) with the provision of non-aligned electric and magnetic fields, leading to an actively programmable pre-stretch paradigm. Unlike conventional actuators, the proposed SCEMES is made up of a polymer that has electro-magnetic properties and is filled with appropriate fillers with specific volume fractions. An electromagneto-viscoelastic model is developed here to predict actuator behavior and investigate the effects of particle reinforcement on equilibrium and actuated configurations. Besides strengthening the polymer, particle reinforcement is observed to enhance the equilibrium angle achieved by the structure with enhanced functionality. The proposed nonlinear dynamic model is extended to investigate a number of critically influential parameters, including shear modulus ratio of fiber to matrix, frame bending stiffness, membrane pre-stretching, and electro-magnetic loading with time-dependent DC and AC modes of actuation. The results reveal that the combined electro-magnetic actuation enhances the actuation range significantly. The attained tip angle of the actuator increases appreciably when the magnetic and electric fields are applied mutually perpendicular to each other, indicating that the direction of applied magnetic field governs the attained actuated configuration. Further, particle reinforcement enrichments result in a depletion in oscillation amplitudes and an increase in excitation frequencies under the AC actuation mode. The efficient semi-analytical framework presented here would be crucial in developing new actuators, smart devices and soft robots for a variety of advanced engineering and medical applications.

PHOTOSENSITIVE FIELD-EFFECT TRANSISTOR BASED ON REDUCED GRAPHENE OXIDE FILM

A photosensitive graphene field-effect transistor was created by depositing a reduced graphene oxide (rGO) film on the surface of the SiO2 layer on a silicon substrate, which serves as both a photosensitive medium and the field-effect transistor gate. The electrical and photoelectric properties of the field-effect transistor based on the rGO film were studied in DC and AC modes. Linear sections of the drain current on the gate voltage dependence and significant dependence of the electronic component of the rGO film conductivity on the irradiation with white light were revealed based on the analysis of the switching characteristics of the obtained field-effect transistor. A photoinduced decrease in the internal resistance and an increase in the capacitance of the conducting channel of the graphene field-effect transistor in the range of 102–105 Hz were revealed. It has been established that the photoresponse time of the obtained field-effect transistor to light pulses of IR, visible, and UV radiation is about 1.5 ms. The obtained results can be used to simplify the technology of manufacturing photodetectors based on graphene.

Nanocomposites based on porous silicon and reduced graphene oxide for ionizing radiation sensing

In this study, the field-effect transistor (FET) based on the oxidized porous silicon (PS) – reduced graphene oxide (rGO) sandwich-like composite has been created. The electrical characteristics of the obtained FET were studied in both DC and AC modes. I-V curves and switching characteristics of the PS–rGO-based FET were analyzed. An increase in resistance and a decrease in capacitance of the experimental structures have been found in the 25 Hz − 1 MHz frequency range due to the joint action of α-, β-, and γ-radiation. The parameters of the equivalent circuit model of the PS–rGO-based FET before and after irradiation with 226Ra isotope have been determined using the impedance spectra. The formation of radiation-induced defects and the charge accumulation in the PS layer is considered a possible mechanism of the ionizing radiation influence on the graphene FET conductivity. The FET based on the PS–rGO structures has a high potential for application in ionizing radiation sensors due to the linear dependencies of resistance and capacitance on the irradiation duration.

A New Flying Capacitor-Based Buck–Boost Converter for Dual-Purpose Applications

A novel dual-purpose common ground dc–dc/dc–ac power converter is proposed in this article. It is based on the flying capacitor circuit along with a boost circuit, which in turn provides a wide range of input voltage regulation with the capability of stepping up or down the output voltage. The same components are used under both dc–dc and dc–ac modes, which reduces the redundancy of the used devices. Particular attention is dedicated to the working modes of the proposed solution. The special control system is implemented to provide acceptable current and voltage quality in off-grid and grid-connected modes. To underline the pros and cons of the proposed solution, a comprehensive comparison is performed. Finally, the performance of the proposed dual-purpose power converter is investigated through an experimental 3.5-kW/5-kW setup, for dc–ac and dc–dc operating modes, respectively. Main oscillograms along with efficiency analysis are presented and discussed in conclusions.

Impact of electric mobility on the design of renewable energy collective self-consumers

European countries aim to reach important targets in the energy field through the increase of energy efficiency in final uses, the exploitation of renewable energy sources, and the implementation of energy communities. In the aforesaid framework, renewable energy self-consumers represent a smart solution to foster the adoption of renewable energy power plants and storage systems in the residential and tertiary sectors. The goal of the paper is to propose an optimisation-based methodology to evaluate the impact of electric mobility on the optimal design of renewable energy collective self-consumers. The integration of renewable sources and storage systems with charging infrastructures for electric vehicles is analyzed and discussed by running a stochastic optimization model, developed in Matlab/Yalmip, to evaluate different scenarios with different electric mobility penetration levels. The paper shows how the presence of electric vehicles increases the optimal installed size of the RES plants significantly, from 15% up to more than 25%. Moreover, it underlines how the optimal charging system, in terms of type, number, and size of charging stations, is affected by the considered number of electric vehicles but also by the model and thus the characteristics of the electric vehicles such as the maximum accepted charging power in AC and DC modes.

Realization of Outstanding Stable 1S1R Behavior Based on Al-Doped NbOx

In this study, we proposed a remarkable one-selector one-resistor (1S1R) device with a single Al-doped NbOx layer, which performed reasonable resistance and switching voltages without degeneration, implying robust stability and outstanding uniformity. The measurements of dc and ac modes were applied to confirm the nonvolatility and effective storage performance. Besides that, a conduction model based on the results of the first principles calculations was proposed to explain the reason for the oxygen vacancies were generated more and tended to the cluster. Meanwhile, they were easier to migrate in Al-doped due to a lower barrier. These contributed to achieving stable conductive filaments as well as the switching process and improve uniformity and stability. Consequently, we developed an excellent 1S1R without an independent rectified cell, which has the potential for 3-D architecture.

Physically Detachable and Operationally Stable Cs2SnI6 Photodetector Arrays Integrated with µ‐LEDs for Broadband Flexible Optical Systems

AbstractWith the surge in perovskite research, practical features for future applications are desired to be secured, but the reliability of the materials and the use of hazardous Pb are longstanding problems. Here, an air‐stable Cs2SnI6 (CSI) is prepared via diluted hydriodic acid solvent‐based precursor optimization during scalable hydrothermal growth. Materials characterization is performed using various elemental peak analyses and crystallographic identification. The resulting CSI exhibits long‐term operating stability over 6 months, i) at elevated temperatures, ii) in ambient air, and iii) under light illumination from UV to near‐infrared. More importantly, to demonstrate an intriguing class of applications up to system level, physically detachable CSI photodetector arrays (PD‐arrays), integrated with micro‐light‐emitting‐diodes (μ‐LEDs) arrays, are successfully fabricated. In addition, 3 × 3 flexible CSI PDs are fully operational, even in air, and their spatial uniformity in pixels is quantitatively evaluated. The charge‐transport mechanisms of the CSI PDs under light and elevated temperature are assessed via temperature‐dependent characterization from 148 to 373 K, implying the involvement of 3D variable‐range hopping. Multicycle evaluation of the CSI PD‐arrays confirms their operational stability in AC and DC modes, demonstrating this platform's potential benefit for wireless optical interconnection in advanced Si technology.

Combined Propulsion and Levitation Control for Maglev/Hyperloop Systems Utilizing Asymmetric Double-Sided Linear Induction Motors

This article presents a new method for combined levitation and propulsion control in maglev/Hyperloop systems by selectively applying AC and DC modes of operation to a group of asymmetric double-sided linear induction motors (ADSLIMs). Although adjusting the AC current magnitude of lower and upper primary windings in ADSLIMs allows simultaneous control of thrust and lift forces, the limitation of this current balancing technique prohibits them from producing a high lift force while operating with low thrust force. To overcome this limitation and to simultaneously control the thrust and lift forces of the ADSLIMs with high efficiency under different operating conditions, a combination of AC and DC modes of operation is proposed. AC mode of operation consists of feeding different AC current amplitudes to the upper and lower ADSLIM primary windings to produce and control the required thrust and lift forces. The DC mode of operation consists of controlling one or several ADSLIMs to operate with DC excitation to realize the desired lift force at lower thrusts which otherwise cannot be achieved by operating in AC mode alone. The concept of the new combined control strategy is studied using two-dimensional finite element (FE) electromagnetic simulations and compared with an Inductrack permanent magnet (PM) based passive magnetic levitation system.

Plasmon modes in N-layer silicene structures

We investigate the plasmon properties in N-layer silicene systems consisting of N, up to 6, parallel single-layer silicene (SLS) under the application of an out-of-plane electric field, taking into account the spin–orbit coupling within the random-phase approximation. Numerical calculations demonstrate that N undamped plasmon modes, including one in-phase optical (Op) and (N − 1) out-of-phase acoustic (Ac) modes, continue mainly outside the single-particle excitation area of the system. As the number of layers increases, the frequencies of plasmonic collective excitations increase and can become much larger than that in SLS, more significant for high-frequency modes. The Op (Ac) plasmon mode(s) noticeably (slightly) decreases with the increase in the bandgap and weakly depends on the number of layers. We observe that the phase transition of the system weakly affects the plasmon properties, and as the bandgap caused by the spin–orbit coupling equal that caused by the external electric field, the plasmonic collective excitations and their broadening function in multilayer silicene behave similarly to those in multilayer gapless graphene structures. Our investigations show that plasmon curves in the system move toward that in SLS as the separation increases, and the impacts of this factor can be raised by a large number of layers in the system. Finally, we find that the imbalanced carrier density between silicene layers significantly decreases plasmon frequencies, depending on the number of layers.

Performance analysis and implementation of a scanning tunneling potentiometry setup: Toward low-noise and high-sensitivity measurements of the electrochemical potential.

Scanning tunneling potentiometry allows for studying charge transport on the nanoscale to relate the local electrochemical potential to morphological features of thin films or two-dimensional materials. To resolve the influence of atomic-scale defects on the charge transport, sub-µV sensitivity for the electrochemical potential is required. Here, we present a complete analysis of the noise in scanning tunneling potentiometry for different modes of operation. We discuss the role of various noise sources in the measurements and technical issues for both dc and ac detection schemes. The influence of the feedback controller in the determination of the local electrochemical potential is taken into account. Furthermore, we present a software-based implementation of the potentiometry technique in both dc and ac modes in a commercial scanning tunneling microscopy setup with only the addition of a voltage-controlled current source. We directly compare the ac and dc modes on a model resistor circuit and on epitaxial graphene and draw conclusions on the advantages and disadvantages of each mode. The effects of sample heating and the occurrence of thermal voltages are discussed.

High Frequency MOSFET Charging Circuit Using Series Parallel DC-DC Resonant Converter for Wireless Power Application

This paper proposes a new circuit topology of high frequency switching DC-DC Series Parallel Loaded Resonant Converter (SPLRC). The circuit is proposed to be used for a wireless power transmission application that required fast-charging operation. Most of the components used here are low-cost and commercially available in the market. Then, the purpose circuit is transformed into a different equivalent circuit that can efficiently analyze AC and DC modes. For each model, the operation for the converter is first described and explained. A full detailed circuit simulation is then carried out to find out the workability of the purpose converter. From the simulation, optimization is carried out. Here the components value is obtained. MATLAB R2018A is used for simulation purposes rather than being tested again using PSIM software to further prove the validity of the model. All the finding is explained and discussed, here, from the simulation result, it is confirmed that a high-frequency switching circuit is operated as expected.

Metal Oxide Nanoheterostructures for Gas Sensing

1. Introduction.Metal oxides such as SnO2, MoO3. TiO2, CuO, are well-known to exhibit significant changes in their electrical resistance upon admission of certain oxidizing or reducing chemical species which constitutes the base for their application as gas sensors. These materials can be synthesized in different forms ranging from bulk ceramics to thin films. Thin-film technology has contributed significantly to the development of reliable chemical sensors as it is easily controllable and results in reproducible parameters of deposited layers [1,2]. Moreover, it is compatible with interdigitated transducer IDT electrodes which facilitates film deposition and subsequent electrical contacts with the resistance measuring units [3]. Emerging nanotechnology has led to a revolution in sensing especially as far as different forms of nanomaterials have demonstrated better response, sensitivity and selectivity to different stimuli. Moreover, the nanostructured sensors can operate much faster due to better kinetics of responses at relatively low temperatures, i.e., close to room temperature. The aim of this contribution is to review the most recent work performed in the field of thin film resistive-type gas sensors with a special emphasis on the n-n and n- p nanostructures.2. ExperimentalThin films of different stoichiometry and crystal structures have been deposited by magnetron sputtering of Ti, Sn, and Cu targets in reactive Ar+O2 atmosphere with controlled composition. Characterization of films has been performed by X-ray diffraction XRD, X-ray reflectivity, XRR, X-ray photoelectron spectroscopy XPS, atomic force microscopy, AFM, scanning electron microscopy, SEM and optical spectrophotometry over uv and visible range of the light spectrum. Gas sensing measurements both in dc and ac modes have been carried out in a custom-made set-up capable of detecting changes in the electrical resistance under stabilized temperature and humidity level. Modular XM-MTS unit from Solartron Analytical has been used to detect the impedance spectra in reference atmosphere (air) and upon gas (NO2, H2) admission.3. ResultsExperimental results concerning thin film characterization will be presented and compared with the most representative data obtained by other authors. Fundamental properties of different n-type (TiO2, SnO2) and p-type (CuO) semiconductors will be discussed.Depending on the material being sputtered and the substrate on which a thin film is deposited one can observe a growth of different nanostructures. Typically, a columnar structure is obtained in the case of TiO2 while the amorphous films of SnO2 result in a smooth top SEM image composed of small, isolated grains. CuO thin films crystallize easily with relatively large, well-developed grains.Gas sensor responses are good and reproducible in the case of n-type semiconductors such as TiO2 and SnO2. CuO being a p-type semiconductor demonstrates much lower response which can be improved by forming TiO2/CuO n-p type hetero-structure.

Renewable sources based DC microgrid using hydrogen energy storage: Modelling and experimental analysis

A microgrid (µG) system can be operated in DC or AC modes using suitable power electronics interface which interconnect power generators, loads and energy storage mediums. It can be interesting to analyze the potential advantages of hydrogen storage-based DC µG system. In this study, a mathematical model is developed for the theoretical prediction of the performance in terms of energy analysis of overall system and charging/discharging characteristics of hydrogen storage unit in the µG. It is found that DC mode of operation of the µG significantly increases the performance and energy efficiency of overall system. A power management system (PMS) is designed which addresses the issues related to the integration of renewable power sources, stability of DC bus voltage, demand–supply balance, and load dynamics involved in the system. The designed PMS working shows that integration of the PV, FC, electrolyzer, and battery is suitable to meet the load demand in the transient operating conditions such as low and high PV power generation; and abrupt increase and decrease in the load demand. After simulation realization, a hardware prototype of PMS is designed and developed which validates its working.

Study of ozone concentration from CO2 decomposition in a water cooled coaxial dielectric barrier discharge

In this paper, study of ozone concentration from dissociation of CO2 at atmospheric pressure by a 6 l/min water-cooled cylindrical dielectric barrier discharge was reported. The discharge was powered by a high voltage generator (20 kV, 300 W, ~20 kHz) at 25% and 50% burst and pure AC modes. All experiments were done in three different CO2 gas flow rates namely 1.5, 2 and 2.5 l/min. Because of cooling rate of ~3 °C/s, dielectric of fused quartz and grounded mesh electrode were kept at room temperature 298±1 K, during micro plasma discharges. Ozone concentration at different flow rates versus electrical power dissipated in the plasma were presented in burst mode and pure AC mode. The highest ozone concentration of 336 ppm was observed for 1.5 l/min of CO2 flow rate at 12.5 kV, 37.2 mA filamentary pure AC mode discharge whilst the lowest ozone production rate of 13.5 ppm was observed for 2.5 l/min of CO2 flow rate at 10.5 kV, 27.2 mA and 25% duty cycle in burst mode discharge. The activated species formed inside the CO2 plasma were identified by optical emission spectroscopy. Effect of water cooling on ozone concentration in a cylindrical micro plasma discharge was studied.

Realization of Synapse Behaviors Based on Memristor and Simulation Study With KMC Method

The memristor, emulating biological synapse, is recognized as one key way to overcome the classic von Neumann bottleneck. In this work, by using active metal Cu as electrode, the device of Cu/GeTeOx/TiN exhibited typical resistive switching characteristic based on the electrochemical metallization mechanism (ECM). Moreover, it realized gradual potentiating and depressing conduction under DC and AC modes, which lead to emulating excitation and inhibition of biological synapses. According to these properties, spike-timing-dependent plasticity (STDP) learning rule was reproduced by applying appropriate pulse sequences. Furthermore, the kinetic Monte Carlo method was utilized to analyze and provide further demonstration for the behaviors of gradual change. These indicated that the device had great potential applied in the neuromorphic computing systems and the properties could be commonly realized by ECM mechanism.

Determining the input impedance of ECG amplifiers using accurate electrode modelling

Objective: The influence of the skin-electrode-amplifier interface and the input impedance of ECG recording amplifiers on transient response performance is investigated using accurate modeling of surface contact electrodes. The paper aims to establish the input impedance requirements of ECG recording amplifiers based on the electrical properties of the electrodes. Approach: The IEC 60601 standard stipulates the performance requirements for electrocardiographs. Analyses and simulation of both dc and ac modes of coupling the electrodes to the input of the amplifier have been undertaken using an accurate double time-constant model of the electrodes in order to establish design constraints for amplifier input impedance to meet this performance specification. These have been backed up with bench tests. Main Results: Investigations carried out indicate that the minimum 10 MΩ resistance at the amplifier input recommended in the specification is insufficient when using some modern adhesive electrodes and increasingly popular un-gelled or dry electrodes. Design constraints are established based on the electrical properties of the electrodes. These constraints suggest that the input impedance of the amplifier should be as high as 10 GΩ and the amplifier ac coupled cut-off frequency should not to be higher than 0.05 Hz for all the electrode models considered. Significance: Signal distortions in the form of false S-wave creation and depression of the S-T segment have been observed when the previously recommended 10 MΩ input impedance is used in the amplifier. This distortion can lead to clinical misdiagnosis but can be avoided if the design constraints established in the paper are adopted.

Dielectric relaxation behaviors and dissipation characteristics of colloidal nanocarbon (graphene and CNTs) complex fluids

The present article reports the dynamic complex dielectric responses of non-polar nanocolloids of graphene (G) and carbon nanotubes (CNTs). The frequency dependent complex relaxation behaviors of G and CNT colloids were determined in the range of 100 Hz to 3 × 105 Hz employing dielectric spectroscopy at a constant temperature. The governing roles of nanostructure concentration, conductivity, frequency, and amplitude variation of the forcing electric field on the dielectric response have been examined. The experimental observations reveal that the presence of G or CNT, as well as their concentrations, significantly governs the overall dielectric responses of the nanocolloids. The dilute and concentrated colloids display grossly distinguishable capacitive and dissipative behaviors, hinting at the major role of concentration regimes on the dielectric behavior of such colloids. In addition, the variation of electric field intensity results in altering the dielectric responses of the colloids, which points at the role of polarization of the nanomaterials on the overall dielectric relaxation. To model the complex dipolar interactions, the classical Havriliak-Negami model is employed and good agreement has been achieved against the experimental observations. It has been observed that increasing nanomaterial concentration and field amplitude has a dominant influence upon the relaxation parameters. Further, the effects of colloidal concentration on the AC and DC conductivity modes have also been analyzed. The conductivity response of the colloids has been explained by appealing to percolation theories. The present article may find strong implications toward the design and development of liquid dielectric based electrical and electronics systems.

Multifunctional materials based on the double-perovskite organic-inorganic hybrid (CH3NH3)2[KCr(CN)6] showing switchable dielectric, magnetic, and semiconducting behaviour.

Herein, we have synthesised and characterised a novel organic-inorganic hybrid crystal, [CH3NH3]2KCr(CN)6 (MACr). Thermal analysis (DSC, TGA-DTA) indicates one structural phase transition (PT) at 450 K. The modified equation of the tolerance factor, t, was used to estimate the theoretical PT temperature for a crystal with Mn(iii). According to the X-ray diffraction experiment, in the low-temperature (LT) phase, the solid-to-solid PT is described by the monoclinic space group C2/c. The creation of the ferroelastic domain structure in phase II was proved on the basis of the observation under a polarising microscope. The crystals of MACr and its isomorphous analogues with Fe(iii) and Co(iii) appeared to be semiconducting materials in the LT phase. The type of PT is order-disorder and occurs between "low" (ordered-frozen) and "high" (orientationally disordered) dielectric states. Dielectric spectroscopy was used to characterise the switching properties of the dipole moments in the vicinity of the PTs. The magnetic properties of the MACr hybrid were investigated in DC and AC modes. The DC data show a sizeable weak exchange interaction between the nearest Cr(iii) centres in the crystal lattice. The AC susceptibility data confirm a slow magnetic relaxation in the applied DC field with two relaxation channels. The low-frequency relaxation time is very long as τLF = 1.4(1) s at T = 2.0 K. The organic-inorganic hybrid, described above, can be considered a rare example of multifunctional materials which exhibit dielectric, magnetic, and conductive activities.

Numerical simulation of melt convection in a dual-electrode arc furnace for MgO production

DC electric arc melting is emerging as a promising technology for production of fused MgO. The dual-electrode DC electric arc furnace (EAF), an alternative design using an anode and cathode electrode instead of a three phase AC arc furnace, is investigated using computational modelling methods. Since the thermal field of the EAF is significantly influenced by the electromagnetic stirring of the molten bath, the melt convection are investigated with different electric currents and bath dimensions. Only a quarter 3D symmetry sector is considered for the analysis. The coupled non-linear conservation equations for mass, momentum, energy and electrical charge are solved with the commercial software ANSYS. The calculated flow field indicates that the melt convection is fully turbulent when the electric current reaches the rated value. The Lorentz force is the dominating driving force for the convection, and the mean velocity is almost a linear function of the Lorentz force. According to the Richardson number, the buoyancy becomes more important when the bath volume grows and the electric current decreases, and the Lorentz force becomes more important when the bath volume shrinks and the electric current increases. In order to make a comparison of magnetic stirring between DC and AC modes, 50 Hz AC power is assumed to supply the dual-electrode EAF. The time-averaged Lorentz force is computed in the time-harmonic analysis for the AC mode. It is found that the Lorentz force distribution is the same if the effective value of the AC current is equal to the DC current.

Corona discharge as affected by the presence of various dielectric materials on the surface of a grounded electrode

This paper is aimed at the characterization of the corona discharge generated from a high-voltage wire electrode facing a grounded plate that carries dielectric layers composed of granules, sheets, and non-woven media. Current-voltage and current-frequency characteristics were measured, respectively in DC and AC modes, for several values of the thickness of the PE granular layer, PET sheets and PP non-woven media considered in the present study. The measurements show that the corona onset voltage and the behavior of the current-voltage characteristics are dependent on both nature and thickness of the dielectric layer. Both the estimated capacitive component and the ionic component in AC mode vary with the amplitude and the frequency of the voltage. The ionic component is particularly affected by material non-uniformity.