AC Mode Research Articles

Wearable broadband MoS2 photodetector for dual heart rate and UV detection powered by PDMS-MXene TENG

Wearable electronic devices capable of monitoring health parameters and environmental factors are tremendously desirable. Environmental energy harvesting as a power source is crucial to replace traditional batteries. This study aims to contribute to the development of sustainable and efficient wearable devices for health monitoring and environmental sensing. In this study, a self-powered wearable MoS2-based photodetector, integrated with a PDMS-MXene-based triboelectric nanogenerator (TENG) is presented. The TENG generates isometric AC voltage using a diode, and it is used to charge a capacitor for DC voltage output. The photodetector, with a responsivity of 1.25 × 105A/W, specific detectivity of 2×1013 Jones, millisecond response time, enhanced responsivity of 1.1×1010 V/W and specific detectivity of 9.5×1016 Jones while coupled with TENG, successfully measured heart rate using a 660 nm LED and compared well with a commercial pulse meter. Additionally, UV illumination was detected using a 395 nm LED in the AC mode of the TENG. The study’s results support the advancement of flexible, integrated, and sustainable wearable devices, offering solutions to challenges posed by current battery-powered devices.

Comparative Evaluation of Dual-Purpose Converters Suitable for Application in DC and AC Grids

This paper presents a comparative evaluation of several topological solutions to the universal power electronics interface for the dc or single-phase ac grids using the same terminals. The idea of a dual-purpose approach lies in the utilization of the same semiconductors in the dc-dc and in the dc-ac configuration, resulting in minimal redundancy. Particular focus is on the power density improvement and control. Out of the three solutions under investigation, the first is the buck-boost cell with unfolding circuit presented earlier. The second solution is a conventional voltage source inverter with an intermediate boost cell considered as one of obvious competitors. The third design is based on a phase-modular solution with buck-boost cells. The design example and experimental prototypes of the universal power electronics interface converter rated for 3.6 kVA power in the ac mode and more than 5 kW in the dc mode are presented. Our experimental results demonstrate the ability of operation in the ac or dc grids with main corresponding modes. Possible applications along with main benefits are addressed in the conclusions.

Feasibility Study of Three-Phase Modular Converter for Dual-Purpose Application in DC and AC Microgrids

The modern concept of a universal converter is intended as a power converter suitable for application in both dc or ac grids using the same external connectors. This novel family was recently proposed to allow an easier integration of renewable energy sources and energy storage systems, interfacing with dc/ac grids and/or loads with a minimum redundancy of power switches and passive elements. This kind of solution and applications are expected to be a reality in the nearest decade, as ac and dc low voltage distribution networks will coexist. Nevertheless, the initial solutions proposed as universal converter were focused on ac single-phase power conversion systems. In this sense, this article proposes and describes a new member of the universal converter family suitable for dc to dc and dc to ac power conversion (both in three-phase three-wire and in three-phase four-wire). The proposed power topology is derived as a modular extension from the single buck-boost bidirectional cell. Its main operation modes (buck and boost) are discussed, and a pulse-width-modulation technique is developed to generate the corresponding switching patterns. The proposed solution is successfully validated in open-loop mode both in simulation and experimentally with a laboratory prototype. The measured efficiency of the power converter was above 97% in the dc to ac mode and around 99% in the dc to dc mode.

Trisodium citrate as a potential and eco-friendly corrosion inhibitor of copper in potable water

In this work, the mixture of trisodium cittrate and Zn2+ was used as binary (hetero type) inhibitor for corrosion inhibition of copper metal in potable water. The binary inhibitor system (Zn2+ and trisodium citrate) was used to form hydrophobic surfaces on copper submerged in potable water. Water contact angle (WCA) was found to be 155°4° when the inhibitor was present, whereas it was 84°2° when there was no inhibitor. These observations suggested the development of superhydrophobic layer on the surface of copper in drinkable water. Electrochemical impedance spectroscopy (EIS – AC mode), and potentiodynamic polarization (DC mode) experiments conveyed that the copper surface could be protected by utilizing the mixture of trisodium citrate and Zn2+ in potable water. The morphological studies including SEM (coupled with EDX), AFM, and WCA were evidenced the formulation of a hetero-type inhibitor for the corrosion inhibition of copper in potable water. In this study, the decline in the double-layer capacitance and the rise in the charge transfer resistance were due to the adsorption of inhibitor confirming the development of protective layer, which EIS, SEM, EDX, AFM, and WCA studies also supported. Thus, there was a synergism observed between TSC and Zn2+, and the formulation consisting of TSC and Zn2+ provided 83% of inhibition efficiency (IEp). So, it was suggested that the approach reported in this study could be a simple method for obtaining the superhydrophobic copper surface.

The study of hydroxyapatite growth kinetics on CP – Ti and Ti65Zr treated by Plasma electrolytic oxidation process

The kinetics of hydroxyapatite growth on titanium alloys (CP–Ti and Ti65Zr) was studied. Specimens were treated by Plasma Electrolytic Oxidation (PEO) and immersed into the Hanks' solution. The PEO method was performed at AC mode with the current density of 4 A/dm2 in an electrolyte containing calcium acetate and calcium glycerophosphate, allowing the inclusion of calcium and phosphorus in the obtained oxide layer, which promotes the osseointegration when applied to bone tissue. The treated specimens were immersed in the Hanks’ solution with different exposure times, followed by studying changes in morphology, chemical, and phase composition. In addition, the surface wettability was tested, and the corrosion behavior of the treated samples was investigated. Tiny HA crystals can be seen on the surface of CP-Ti samples treated by PEO for 5 and 30 min. The morphology with a distinct layer of HA was obtained for the Ti65Zr sample after 5 min of PEO treatment. As for the immersion times, the highest crystal growth velocity was observed for the Ti65Zr of 5 min of PEO and 14 days of immersion. The change in morphology and EIS analysis confirms the observed behavior. Finally, based on the XRD analysis for the Ti65Zr of 5 min PEO treatment samples, the Srilankite phase in an amount of 60% is responsible for the crystal growth, resulting in the best crystal growth velocity and good corrosion properties (Rp = 0.732 MΩ cm2).

Comparative Evaluation of Common-Ground Converters for Dual-Purpose Application

The focus of this paper is to provide a comparative analysis of various common-ground converters that serve as dual-purpose power electronic interfaces. These interfaces are designed to be used in both DC and single-phase AC grids, utilizing the same terminals for both modes of operation. The idea lies in the utilization of the same semiconductors in the DC-DC and DC-AC configurations, resulting in minimal redundancy. Particular attention is focused on the comparative evaluation approach. A novel Flying Inductor (FI)-based converter was selected for experimental verification. The design example and experimental prototype of a dual-purpose DC-DC/AC power electronic converter is capable of providing 2 kVA of power in AC mode and 4 kW in DC mode. The experimental results indicate that the converter can operate in both AC and DC grids according to their respective modes. The conclusion of the study highlights the potential applications and main benefits of this technology.

Visualization and Characterization of Liposomes by Atomic Force Microscopy.

Atomic force microscopy is a high-resolution and nonoptical technique used to visualize and characterize biological samples and surfaces. In pharmaceutical research and development (R&D) andquality control (QC), drug delivery systems, like liposomes with sizes in a nanometer range, are preferred samples to be studied through atomic force microscopy. The instrument can determine the sample's topography (e.g., height), morphology, and material properties (e.g., hardness, adhesiveness). Various measuring modes, e.g., intermittent contact (AC mode), can generate height (measured), lock-in amplitude, and lock-in phase data, revealing interesting details about the drug delivery system.In this study, empty and drug-loaded liposomes with various lipid compositions and sizes (50-800nm) were visualized and characterized with state-of-the-art atomic force microscope(AFM). The main focus here was the preparation methods of the samples, instrumental settings, and pitfalls that can occur during the whole imaging process. Moreover, troubleshooting and postdata processing are essential for a high-quality outcome.

A novel TiO2-SnO2 film pH sensor prepared by micro-arc oxidation

In this work, we have used a micro-arc oxidation technique operating in the AC mode to prepare a TiO2-SnO2 film sensitive to pH on a Ti substrate. The microstructure and elemental and material composition of the film was studied. The results show that a porous structure formed on the film surface. XRD indicated that the film contained hydrophilic amorphous TiO2, and XPS showed the formation of oxide SnO2 in the film. TiO2-SnO2/0.5 films doped with 0.5 g/L Na2SnO3 had excellent pH-sensing properties. Performance tests showed that for pH in the range 2–12, the TiO2-SnO2/0.5 films had a sensitivity of 64.60 mV/pH, as well as fast response times, low hysteresis, good stability, and resistance to temperature and interference by ionic impurities. The prepared TiO2-SnO2/0.5 films were used with a commercial pH meter to detect several common fluids with an accuracy of ± 0.09 pH.

Stretchable ionics: How to measure the electrical resistance/impedance

Stretchable ionic conductors have attracted increasing interest in the field of sensors, actuators, bioelectronics, and flexible energy devices due to their high elasticity and biocompatibility. Ionic conductors conduct electrical charges via the migration of mobile ions and the “ion-electron” conversion on the electrode interfaces. Therefore, the measurement of electrical resistance or impedance of ionic conductors is normally carried out under AC mode. However, it seems that recently studied ionic devices, especially those “resistive mode” ionic strain sensors, often use DC mode for the characterization. This Matter of Opinion revisits the conduction mechanism of emerging stretchable ionics and discusses the methods to measure ionic resistance/impedance, aiming to attract more research attention to study the conduction mechanism and characterization protocols for stretchable ionic devices. Stretchable ionic conductors have attracted increasing interest in the field of sensors, actuators, bioelectronics, and flexible energy devices due to their high elasticity and biocompatibility. Ionic conductors conduct electrical charges via the migration of mobile ions and the “ion-electron” conversion on the electrode interfaces. Therefore, the measurement of electrical resistance or impedance of ionic conductors is normally carried out under AC mode. However, it seems that recently studied ionic devices, especially those “resistive mode” ionic strain sensors, often use DC mode for the characterization. This Matter of Opinion revisits the conduction mechanism of emerging stretchable ionics and discusses the methods to measure ionic resistance/impedance, aiming to attract more research attention to study the conduction mechanism and characterization protocols for stretchable ionic devices.

Observation of the depassivation effect of attrition on magnesium silicates' direct aqueous carbonation products

The main obstacle to the aqueous carbonation of non-serpentinised magnesium silicates is the formation of surface passivation layers, which severely limits the reaction rate and thus the overall efficiency of the process. A technological solution to overcome this problem is to perform the carbonation process inside a stirred bead mill, which aims to continuously remove the surface by-product layers by attrition. In this work, the aqueous carbonation of ferronickel slag, a mineralogically complex mining waste composed of a Mg/Si rich amorphous phase and a crystalline ferrous forsterite, was studied at 150°C and under 10 bar of CO2 with different operating configurations: carbonation alone (C mode), attrition followed by carbonation (A-C mode) and concomitant attrition and carbonation (AC mode). By careful observation of the mineralogy and the surface of the secondary phases formed using complementary analytical techniques, the article allows a better understanding of the passivation phenomenon inherent to the carbonation of magnesium silicates, and confirms the effectiveness of continuous surface mechanical depassivation for reaching high carbonation rates with this type of material. Comparative analysis of the products obtained with the three operating modes shows that a true synergy takes place between attrition and carbonation due to the combined effect of continuous exfoliation and mechanical activation of particle surface, which goes far beyond the simple increase in surface area due to particle size reduction. While mechanical depassivation is here substantiated by several evidence, the additional mechanochemical activation effect cannot be delineated from experiment; however its beneficial contribution to carbonation is inferred from its observation in A-C mode. The work finds that the synergy between attrition and carbonation also yields very characteristic products. They consist in micrometric agglomerates formed by bound spherical particles a few tens of nanometers in size. These particles themselves contain an entanglement of nanometric grains of carbonates and amorphous silica dispersed inside a magnesium-depleted alumino-siliceous matrix. These results confirm that concomitant attrition and carbonation offers one of the most promising pathways for developing direct aqueous carbonation processes with non-thermally activatable magnesium silicates.

POROUS SILICON NANOSYSTEMS FOR ETHANOL SENSOR

Sensory elements based on hybrid films containing porous silicon and reduced graphene oxide nanostructures have been created. A decrease in electrical resistance and an increase in the capacitance of sensor elements in the AC mode due to the adsorption of ethanol molecules have been registered. To assess the sensory properties of hybrid films, the concentration dependences of the adsorption ability in the 0–4.5% range were determined and the dynamic characteristics of ethanol sensors based on them were studied. It was found that sensor films with different ratios of porous silicon and reduced graphene oxide nanoparticles have the maximum sensitivity to ethanol in different concentration ranges. The functional properties of hybrid films can be controlled by changing the proportions of their components. The reaction time of sensory elements to changes in the concentration of ethanol molecules is 40–50 s. The obtained results expand the perspective of the application of nanosystems based on porous silicon in sensor devices.

Arc characteristics and weld formation of aluminum alloy by AC/DC mixed GTAW

ABSTRACT The purpose of the method of AC/DC mixed gas tungsten arc welding (GTAW) is to improve the welding efficiency of aluminum alloy AC-GTAW. It is expected to make a great change in the aluminum alloy manufacturing industries. The feature of AC/DC mixed GTAW includes two parts, AC mode and DC mode, during the welding process. A comparison study between the AC/DC mixed GTAW and AC-GTAW is carried out by analyzing the arc characteristics and weld formation. The results showed that the uniformly distributed AC and DC signals were obtained in the AC/DC mixed GTAW. The front width and back reinforcement of the weld bead in the AC GTAW and the AC/DC mixed GTAW increased first and then decreased with increasing frequency. The geometrical parameters of the weld cross-section in the AC/DC mixed GTAW was increased, when the same frequency was used. For example, the frequency of 30 Hz was employed, the front width of the weld bead in the AC/DC mixed GTAW was increased to 0.3 mm compared with that of the AC-GTAW. The AC/DC mixed GTAW has a greater effective heat input compared with the AC GTAW due to introduction of the DC mode.

Ultrastructural characterisation of young and aged dental enamel by atomic force microscopy.

Recent advances in atomic force microscopy (AFM) have allowed the characterisation of dental-associated biomaterials and biological surfaces with high resolution. In this context, the topography of dental enamel - the hardest mineralised tissue in the body - has been explored with AFM-based approaches at the microscale. With age, teeth are known to suffer changes that can impact their structural stability and function; however, changes in enamel structure because of ageing have not yet been explored with nanoscale resolution. Therefore, the aim of this exploratory work was to optimise an approach to characterise the ultrastructure of dental enamel and determine potential differences in topography, hydroxyapatite (HA) crystal size, and surface roughness at the nanoscale associated to ageing. For this, a total of six teeth were collected from human donors from which enamel specimens were prepared. By employing intermittent contact (AC mode) imaging, HA crystals were characterised in both transversal and longitudinal orientation (respect to surface plane) with high resolution in environmental conditions. The external enamel surface displayed the presence of a pellicle-like coating on its surface that was not observable on cleaned specimens. Acid-etching exposed crystals that were imaged and morphologically characterised in high resolution at the nanoscale in both the external and internal regions of enamel in older and younger specimens. Our results demonstrated important individual variations in HA crystal width and roughness parameters across the analysed specimens; however, an increase in surface roughness and decrease in HA width was observed for the pooled older external enamel group compared to younger specimens. Overall, high-resolution AFM was an effective approach for the qualitative and quantitative characterisation of human dental enamel ultrastructure. Future work should focus on exploring the ageing of dental enamel with increased sample sizes to compensate for individual differences as well as other potential confounding factors such as behavioural habits and mechanical forces.

Novel Concept of Solar Converter With Universal Applicability for DC and AC Microgrids

This article presents a novel concept of a universal solar converter suitable for application in both in the dc or single-phase ac grids using the same terminals. The idea lies in the utilization of the same semiconductors in the dc–dc and in the dc–ac configuration, resulting in minimal redundancy. Possible semiconductor stages are considered. The particular attention is focused on the output filter design along with proper protection circuit selection for dc and ac grids. The design example and comparative analysis between dc–dc, dc–ac, and universal solutions are given. The experimental prototype of the universal solar converter that is rated for 3.6 kVA power in the ac mode and 5 kW in the dc mode is presented. The experimental results demonstrate the ability of operation in ac or dc grids with main correspondent modes. Possible fields of application along with main benefits are addressed in conclusions.

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.

Diode and Active Negative Resistance Behaviors of Helminth Eggs as a Novel Identification/Differentiation Probe.

Helminths have always been studied as one of the critically annoying pathogens of parasite classes due to their adverse effects on the ecosystem of human life. They have the potency to negatively affect their hosts as points of disease, infection, cancer, and death, but in this study, we found interesting electronic properties in Fasciola hepatica, Parascaris equorum (with and without larvae), Dicrocoelium dendriticum, Taenia multiceps, and Moniezia expansa eggs. This claim is attributed to some surprising characteristics such as significant diode behavior [forward bias, 5.36–11.17 (±0.01) V, versus the ground, GND] and backward bias (−45.0 to −125.0 (±7.0) V, versus the GND) and highly active negative resistance (−2.59 to −7.11) × 1015 (±1.5) Ω in the AC mode. These traits were measured by the “blind patch-clamp, single-unit recording” methodology using a three-microelectrode system, implanted onto each tested egg under giga ohm sealed conditions (6.28 ± 0.02 GΩ cm–1 and n = 4). All the characteristic parameters were simultaneously attributed to the helminth egg structure by acceptable reproducibility (percentage of relative standard deviation: > 5%) and high enough rectitude with enough differentiation in their magnitudes, relatively. The reliability of these results was further confirmed using multiple calibrated techniques such as alternative/direct current voltammetry. Also, the significant role of water molecules as the key medium in creating these properties is evaluated qualitatively. In addition, the study aims at introducing these interesting parameters as a new approach to the fabrication of bio-based electronic elements, which are considered as a novel class of helminth egg-detection and -identification probes.

An Optimal Control Algorithm with Reduced DC-Bus Current Fluctuation for Multiple Charging Modes of Electric Vehicle Charging Station

This paper presents a systematic structure and a control strategy for the electric vehicle charging station. The system uses a three-phase three-level neutral point clamped (NPC) rectifier to drive multiple three-phase three-level NPC converters to provide electric energy for electric vehicles. This topology can realize the single-phase AC mode, three-phase AC mode, and DC mode by adding some switches to meet different charging requirements. In the case of multiple electric vehicles charging simultaneously, a system optimization control algorithm is adopted to minimize DC-bus current fluctuation by analyzing and reconstructing the DC-bus current in various charging modes. This algorithm uses the genetic algorithm (ga) as the core of computing and reduces the number of change parameter variables within a limited range. The DC-bus current fluctuation is still minimal. The charging station system structure and the proposed system-level optimization control algorithm can improve the DC-side current stability through model calculation and simulation verification.

Research of Emergency Modes of Wind Power Plants Using Computer Simulation

The aim of this study is to investigate changes in the wind power plant energy production parameters under the conditions of sudden wind changes and voltage drop. To achieve these goals, a simulation of operation of wind power plants was performed. Twelve wind turbines with variable rotational speed equipped with a Fuhrländer FL 2500/104 asynchronous double-fed induction generator (DFIG) were used, each with an installed capacity of 2.5 MW. A general scheme of a wind power plant has been developed using a modular-trunk power distribution scheme. The system consists of wind power modules and a central substation, which allows total power to be supplied to the power system at a voltage of 35 kV. The central substation uses two high voltage switchgears. Four modules were used, each of them consisting of three wind turbines, with a power of 7.5 MW. The simulation of the wind turbines was performed in the MATLAB® Simulink® software environment. The mode of response of the turbines to a change in wind speed, a voltage drop in the 35 kV voltage system, and a one-phase short circuit to the ground in the system of 10.5 kV voltage was explored. The results show that a sudden voltage drop and the appearance of short circuits influence the wind power plant (WPP) operation in a different way independent of regulation mode. The power generation from WPP will be limited when voltage drop occurred for both AC and Voltage regulation mode and during short circuits while WPP is set on AC regulation mode.

Comfort temperature prediction according to an adaptive approach for educational buildings in tropical climate using artificial neural networks

Following the adaptive thermal comfort approach, we show a thermal comfort modeling by artificial neural networks to predict the preferred comfort temperature Tcomf for educational buildings occupants in a tropical climate. The field data collected in 27 educational buildings, climatized with air conditioning systems AC, and natural ventilation NV, in Tuxtla Gutiérrez-México, allow developing the Tcomf modeling by artificial neural network-based models ANN-BM. The predictor variables were the outdoor running mean temperature, relative humidity, air velocity, weight, clothing insulation, and activity level. For AC, the R2 and the mean absolute error were 0.985 and 0.319°C; for NV, 0.981 and 0.286°C. Concerning local models and current standard models, the accuracy improvement to determine Tcomf was significant, following R2; for AC mode, the ANN-BM was 50 times better; for NV was 41.5 times better. The mean Tcomf by ANN-BM was 2.4°C above obtained with the CIBSE guide and 1.3°C concerning a Local model. For NV, the mean Tcomf was 0.5°C above following CEN standard EN15251, 2.0°C above ASHRAE standard 55, and 1.1°C above the Local model. Thus, allowing the air conditioning to run at a higher Tcomf than calculated with current standard models, making it possible to reduce thermal cooling loads while thermal satisfaction also increases.

Influence of Matrix and Surfactant on Piezoelectric and Dielectric Properties of Screen-Printed BaTiO3/PVDF Composites.

The aim of this paper was to provide insight into the impact of matrix and surfactants on the rheology, morphology, and dielectric and piezoelectric properties of screen-printed BaTiO3/PVDF composites. Two matrices were compared (PVDF–HFP and PVDF–TrFE), and lead-free BaTiO3 microparticles were added in volume fractions of 30% and 60%. Here, we demonstrated that the presence of surfactants, helping to prevent phase separation, was crucial for achieving a decent screen-printing process. Fourier-transform infrared (FTIR) spectroscopy together with scanning electron microscopy (SEM) showed that the two “fluoro-benzoic acid” surfactants established stable bonds with BaTiO3 and improved the dispersion homogeneity, while the “fluoro-silane” proved to be ineffective due to it evaporating during the functionalization process. PVDF–TrFE composites featured a more homogeneous composite layer, with fewer flaws and lower roughness, as compared with PVDF–HFP composites, and their inks were characterized by a higher viscosity. The samples were polarized in either AC or DC mode, at two different temperatures (25 °C and 80 °C). The 30% BaTiO3 PVDF–TrFE composites with two fluorinated surfactants featured a higher value of permittivity. The choice of the surfactant did not affect the permittivity of the PVDF–HFP composites. Concerning the d33 piezoelectric coefficient, experimental results pointed out that PVDF–TrFE matrices made it possible to obtain higher values, and that the best results were achieved in the absence of surfactants (or by employing the fluoro-silane). For instance, in the composites with 60% BaTiO3 and polarized at 80 °C, a d33 of 7–8 pC/N was measured, which is higher than the values reported in the literature.