Voltage Coefficient Research Articles

A new modulation strategy and power balance method of unsymmetrical CHB inverter

There exist the problems of the low utilization rate of DC voltage, power imbalance and current backflow in the modulation process of traditional unsymmetrical cascaded units. In view of these, a pulse width modulation strategy with an improved trapezoidal wave as the modulation wave and its corresponding power balance method are proposed. First, through double Fourier analysis of the output line voltage, an appropriate sine coefficient δ is obtained. Second, the waveform of the modulation wave is determined according to δ. Third, through the simple logic operation of the initial driving signals of the switch transistors, the required switch driving signals are obtained, and the power balance of each unit with the same voltage level is realized. In order to verify the effectiveness of the strategy and the method, a simulation and experiment platform are built, and a large number of simulations and experiments are carried out. The results show that compared with the traditional sinusoidal modulation method, the utilization rate of DC voltage obtained by the method can be improved by 22.28% and compared with the trapezoidal wave modulation method, the waveform distortion coefficient of the output voltage can be significantly reduced, and the utilization rate of DC voltage can be further improved. Meanwhile, the power balance can be achieved within one voltage cycle and the phenomenon of current backflow is eliminated.

Electrical, optical characterization and degradation of Cu(InGa)Se2 devices with fluorine-doped tin oxide back contact

In this letter, we present a complete electrical and optical study of the characteristics and degradation of Cu(InGa)Se2 (CIGS) solar cells with Florine-doped Tin Oxide (FTO). This is an alternative structure of CIGS solar cell, that is fundamental for the development of bifacial or tandem devices. In the first part of this paper, we report on the electro-optical properties of the devices, based on the results obtained by a set of characterization techniques, including external and internal quantum efficiency (EQE/IQE) and current-voltage (I-V). In addition, the temperature coefficient of the cells is evaluated based on the method proposed in the standard EN 60891: results indicate a very good stability of the short circuit current with temperature, and a temperature coefficient of the open circuit voltage of −1.8 × 10−3 V/°C, which is slightly lower than what detected in silicon cells. In the last part of the paper, we present the results of a forward current stress experiment, to demonstrate the existence of metastable conductive defects in the crystalline structure of the material, through the analysis of spatial-resolved electroluminescence data.

Experimental investigation on statistical characteristics of cell voltage distribution for a PEMFC stack under dynamic driving cycle

The proton exchange membrane fuel cell (PEMFC) stack consists of individual cells in series. Its operating life is subjected to performance of the weakest cell because of the short-board effect, thus voltage uniformity during dynamic long-running process is significant to its durability. In this work, based on a 1044 h aging experiment on a 6.55 kW PEMFC stack under dynamic driving cycle, voltage uniformity is analyzed. In a single cycle, voltage uniformity becomes worse with the increase of loading current and there are some local maxima of voltage coefficient variation (Cv) at the moment of loading or unloading step. Cv value at higher current is greater and increases faster with cycles. At the end of experiment, Cv at 135 A is more than 6%. Besides, skewness (Sk) is used to evaluate the skew direction and degree of cell voltage data in a cycle. In most cycles, Sk values at 34.22 A are above 0 and Sk values at 59.70 A and 135 A are below 0. After the Box-Cox transformation, which is used to improve symmetry of data and reduce Sk, the cell voltage data have passed the verifications of normal fitting, probability-probability plot and quantile-quantile plot. Therefore, it is found that cell voltage data tend to obey skewed normal distribution, which is of positive significance for improving voltage uniformity and durability of PEMFC stack.

Component fraction effect on microstructure and properties of CoFe2O4−K0.5Na0.5NbO3 composites

AbstractCoFe2O4−K0.5Na0.5NbO3 (CFO−KNN) composites were sintered in air at 1100°C for 2 h. The relative density of sintered CFO−KNN varied with the KNN/CFO ratio and when the volume fraction of KNN reached 50% or more, the sintered composites had a relative density higher than both of the components (i.e., individually sintered KNN and CFO). The highest relative density (94%) was obtained with the composites of 80 vol% KNN. Transmission electron microscopy did not observe any secondary phase at the interface between CFO and KNN grains. However, elemental analyses showed traces of interdiffusion of Na, K, Co, and Fe ions, which were within the solubility limit of both lattices so that no segregation of other phase occurred. Nevertheless, the interdiffusion altered grain growth kinetics for both phases, resulting in the changes in grain sizes for both KNN and CFO in the composites. The composites of higher CFO content showed lower piezoelectric d33 due to a higher DC conductivity that resulted in an incomplete poling of samples. The attainable magnetoelectric voltage coefficient was 3.6 mV cm−1 Oe−1, which was measured with the composites of 50 vol% KNN.

Magnetoelectric Response of Laminated Cantilevers Comprising a Magnetoactive Elastomer and a Piezoelectric Polymer, in Pulsed Uniform Magnetic Fields.

The voltage response to pulsed uniform magnetic fields and the accompanying bending deformations of laminated cantilever structures are investigated experimentally in detail. The structures comprise a magnetoactive elastomer (MAE) slab and a commercially available piezoelectric polymer multilayer. The magnetic field is applied vertically and the laminated structures are customarily fixed in the horizontal plane or, alternatively, slightly tilted upwards or downwards. Six different MAE compositions incorporating three concentrations of carbonyl iron particles (70 wt%, 75 wt% and 80 wt%) and two elastomer matrices of different stiffness are used. The dependences of the generated voltage and the cantilever’s deflection on the composition of the MAE layer and its thickness are obtained. The appearance of the voltage between the electrodes of a piezoelectric material upon application of a magnetic field is considered as a manifestation of the direct magnetoelectric (ME) effect in a composite laminated structure. The ME voltage response increases with the increasing total quantity of the soft-magnetic filler in the MAE layer. The relationship between the generated voltage and the cantilever’s deflection is established. The highest observed peak voltage around 5.5 V is about 8.5-fold higher than previously reported values. The quasi-static ME voltage coefficient for this type of ME heterostructures is about 50 V/A in the magnetic field of ≈100 kA/m, obtained for the first time. The results could be useful for the development of magnetic field sensors and energy harvesting devices relying on these novel polymer composites.

Fabrication and properties of 3-3 type PZT-ordinary Portland cement composites

In this study, porous lead zirconate titanate (PZT) ceramics with porosity ranging from 46.4% to 82.3% were produced by the gel casting technology of particle-stabilized ceramic foams with the solid loading of 5–25 vol%, then the Portland cement paste was cast in porous PZT ceramics with continuous vibration to fabricate 3-3 type cement-based piezoelectric composites. The microstructure, dielectric, piezoelectric, and electromechanical coupling properties of the composites were characterized. With the increase in initial solid loading of PZT slurry, both the porosity, open porosity and pore size of porous PZT ceramics decreased correspondingly, which have prevented the filling of cement paste into the porous ceramics and led to the increment of PZT content in the composites. Increase in the PZT content contributed to the relative permittivity (εr) and longitudinal piezoelectric strain coefficient (d33), and a resultant reduction in piezoelectric voltage coefficient (g33). The prepared composites possessed a maximal thickness electromechanical coupling coefficient (Kt) value of 41.22%, higher than that of planar electromechanical coupling coefficient (Kp), indicating enhanced thickness mode oscillations of the composite. With the increase in PZT volume fraction, the PZT-cement composites turned from typical 3-3 structure to appoximate sandwich structure gradually, leading to more energy loss during electromechanical process and obvious decrease of the mechanical quality factor (Qm). The acoustic impedance (Z) of specimens ranged from 6.69 to 8.27 MRayls, close to that of cement materials (∼10 MRayls), making them promising candidate for application in civil engineering.

The Interfacial Effect on the Open Circuit Voltage of Ionic Thermoelectric Devices with Conducting Polymer Electrodes

AbstractOrganic‐based energy harvesting devices can contribute to a sustainable solution for the transition to renewable energy sources. The concept of ionic thermoelectrics (iTE) has been recently proposed and motivated by the high values of thermo‐voltage in electrolytes. So far, most research has focused on developing new electrolytes with high Seebeck coefficient. Despite the major role of the electrode materials in supercapacitors and batteries, the effect of various electrodes on energy harvesting in iTE devices has not been widely studied. In this work, the conducting polymer poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is investigated as the functional electrodes in iTE supercapacitors. Through investigating the thermo‐voltage of iTEs of the same electrolyte with varying composition of PEDOT electrodes, it is identified that the different PSS content greatly affects the overall thermo‐induced voltage coefficient, Seff (i.e., effective thermopower). The permselective polyanion in the electrode causes cation concentration differences at the electrode/electrolyte interface and contributes to an interfacial potential drop that is temperature dependent. As a result, the overall thermo‐voltage of the device possesses both an interfacial and a bulk contribution. The findings extend the fundamental understanding of iTE effect with functional electrodes, which could lead a new direction to enhance the heat‐to‐electricity conversion.

Demonstration and characterization of 500 V MIM capacitor with Al2O3 dielectric layer for power integrated circuits

In this work, the metal–insulator–metal (MIM) capacitor with Al2O3 dielectric layer above 1 μm and TiN electrodes has been fabricated by magnetron sputtering for power integrated circuits application. The characteristics of the TiN and Al2O3 films were inspected by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) technologies. According to the experimental results, the fabricated MIM capacitor exhibits a very low leakage current density of 4.2×10-5 A/cm2 at 500 V, although the capacitance density is relatively small (0.08 fF/μm2at 100 kHz) due to its high voltage withstanding capability. In addition, the quadratic and linear voltage coefficients of the capacitor are 0.08 ppm/V2and −2.39 ppm/V, respectively (at 100 kHz), indicating its excellent voltage linearity. Leakage mechanisms of the capacitor have been investigated as well. As a result, the fabricated Al2O3 MIM capacitor is a very promising candidate for power integrated circuits application.

Tailored magnetoelectric coupling in magnetically oriented polymer-based iron fiber composite

Artificial multiferroics magnetoelectric (ME) polymer composite films exhibiting collective ferroelectric and magnetic orderings are gaining attractive for the use of flexible ME devices. Herein an anisotropic polymer-based ME composites films is developed, composed of magnetically oriented polycrystalline iron fiber (Fef) and poly(vinylidene fluoride-co-trifluoroethylene) P(VDF–TrFE). The structure, ferroelectric, piezoelectric, magnetic, and ME properties was systematically investigated. Both Fef fillers content and magnetic field direction determined the ME voltage coefficient, magnetical polarization and dielectric response in anisotropic P(VDF-TrFE)–Fef composites. Specifically, the composite with 16% filler loading delivers a peak ME value of 44.5 mV·cm−1·Oe−1 with magnetic field exerted along the fiber axial alignment direction. Such extracted results may encourage a way to optimize flexible composite in anisotropic contactless sensing and detecting applications.

Prediction of magnetoelectric properties of defect BiFeO3 thin films using Monte Carlo simulations

Magnetoelectric materials have received astonishing attention due to their great potential for nanotechnology and magnetoelectric applications. Herein, the ferroelectric, magnetic and magnetoelectric properties of multiferroic BiFeO3 (BFO) thin films have been carried out using Monte Carlo simulation investigations in the framework of the Heisenberg model. Exchange coupling interactions in magnetic and ferroelectric sublattices that correspond to the experimental critical temperature were estimated. Temperature dependence of the internal energy, specific heat, magnetization, electric polarization and their susceptibilities in BFO thin films have been systematically analyzed. Moreover, the effect of magnetoelectric coupling interaction Jme on M−H and P-H hysteresis loopsand magnetoelectric voltage coefficient were studied. A large magnetoelectric voltage coefficient of 104 mV/(cm.Oe) was predicted in BFO thin films with 25% defects. Furthermore, the defect mechanism can be used to control the polarization switching by the magnetic field in BFO system. The obtained results highlight the large magnetoelectric effect in BFO multiferroic thin films for multifunctional magnetoelectric devices.

Impact of ionizing radiation on structural, dielectric, and piezoelectric properties of Sr modified PZT

Ion irradiation effects on piezoceramic (Pb0.94 Sr0.04) (Zr0.52 Ti0.48)O3 (PSZT) are investigated by using 4 MeV carbon (C), 9 MeV copper (Cu), and 20 MeV gold (Au) ions. The energies of incident ions are selected in order to target the same range of all incident ions in the material, while producing different amounts of vacancies. The ion irradiation is performed with fluences of 1×1013, 1×1014, and 1×1015 ions/cm2 using Tandem Pelletron accelerator (5UDH-2). Post irradiation changes in PSZT are investigated via various structural, dielectric, and piezoelectric measurement techniques. Results divulge that the irradiation process disturbs the crystallinity along with reduction in X-ray diffraction (XRD) peak intensities owing to strain induced structural defects. A small decrease in dielectric constant is observed due to trapped charges, which screen the depolarization after irradiation. However, a significant decrease is detected in piezoelectric charge coefficients (d33) and piezoelectric voltage coefficients (g33) due to switching of micro domains of PSZT as a result of energy observed during irradiation process. These results indicate that ion irradiation has damaging effects on the properties of PSZT. The discussed information may be utilized to assess performance of PSZT based devices under radiation rich environments such as space.

Lead-free laminated structures for eco-friendly energy harvesters and magnetoelectric sensors

The ferromagnetic and ferroelectric laminated structure has been utilized to study the magnetoelectric (ME) effect, which holds great potential to fabricate micro-electro-mechanical devices with a high figure of merit. Designed a laminated heterostructure using ribbons of Metglas (Fe–Co–Si–B alloy) having high magnetic permeability and lead-free piezoelectric composites of 0.92(Na0.5Bi0.5)TiO3-0.08BaTiO3 (NBT-BT) to generate the significant magnitude of direct ME voltage. The displacement-voltage measurements of NBT-BT yield a high response showing the nature of the piezoelectricity effect. The strength of ME coupling is determined from the ME voltage coefficient (αME), ME measurements have been carried out in the range of 0–6 kHz frequencies. The magnitude of the direct ME effect was found about 45–50 mV/Oe.cm over a low magnetic field of less than ±8 kOe. The real-time ME effect produced nearly 274.5 and 280.2 mV of ME voltages for the applied field of 200 and 300 Oe, respectively. It shows that the trilayer composite structure may be used as weak magnetic field sensors and energy harvesters.

Effects of post-annealing temperature and micropillar shape on physical properties of micropillar-type multiferroic composite thin films

Microplate (MP) and microrod (MR)-type CoFe2O4/(Bi3.25Nd0.65Eu0.10)Ti3O12 composite thin films were fabricated by a combination of reactive ion etching and metalorganic chemical vapor deposition. The effects of post-annealing temperature on the structural, magnetic, electrical, and magnetoelectric (ME) properties of the films were investigated. Based on the results, the optimal ferroelectric pillar structure to obtain a large ME voltage coefficient (α ME ) was determined. The electrical insulation properties for the films improved with increasing post-annealing temperature. On the other hand, magnetic and ferroelectric properties were degraded at high-temperature. Judging from the structural, magnetic, electric, and ME properties, the optimum post-annealing temperature was 700 °C. The shape of the ferroelectric layer had a significant influence on the ferroelectric properties and consequently on α ME . The MR shape exhibited a smaller clamping effect than the MP shape, producing a greater ME effect. The α ME for the MR-type film post-annealed at 700 °C was 5.5 mV cm−1 Oe−1.

AC/DC Magnetic Field Sensing Utilizing Mechanically Mediated Product Effect of Ampere Force Caused by Eddy Currents and Piezoelectricity in a Magnetoelectric Disk

The last two decades have witnessed an ever‐increasing research effort devoted to the development and application of magnetoelectric (ME) sensing composites. Herein, the ME effect in a metallic/polymeric composite fabricated by adhering silver electrodes to two surfaces of one poly(vinylidine fluoride) (PVDF) disk is explored. To obtain obvious ME response, the resonance frequency of the experimental setup is measured. Furthermore, it is proved that the ME coupling in the composite (silver/PVDF/silver) originates from the product effect of the piezoelectric effect and ampere force produced by eddy currents under DC bias magnetic fields. By observing measurement results, the ME voltage is approximately considered to be proportional to both AC and DC magnetic fields. Consequently, the average ME voltage coefficient is obtained as 384.73 mV cm−1 Oe at a DC magnetic field value of 1000 Oe. Considering the magnetic fields and eddy current, a theoretical model of ME coupling is developed by combining the ampere force expression and piezoelectric equations, which matches well with measurement results. Without the need of magnetic phase and an external power supply, the proposed disk with excellent linear responses and a considerable ME voltage coefficient has the potential for application in real‐time monitoring sensors.

Ferroelectric domain formation and photocatalytic activity on porous alkali niobate piezoelectric ceramics

Present study showed synthesis of novel type of porous alkali niobate piezoelectric ceramics, and the formation of domains and photocatalytic activity for the porous piezoelectric ceramics were investigated while comparing with dense ceramics to confirm enhancement of domain orientation and photocatalytic activity around pores. Porous Li0.06Na0.47K0.47NbO3 piezoelectric ceramics were synthesized by a template method using polymethylmethacrylate as a pore former agent. Uniform pores with 6 µm in diameter were dispersed in the porous ceramics. Porous ceramics synthesized with 10 vol % of the pore former agent showed piezoelectric voltage coefficient, 29 mVm/N, which is same as that of the dense ceramics. Smaller striped domains formed at an edge of pores on the porous ceramics, indicating that orientation of domains was promoted by electric field concentration around the pores. Through photoreduction reaction of Ag+ ion, local precipitation of Ag was shown around the pores on the poled porous ceramics, whereas Ag was located over an entire surface of unpoled porous ceramics. Highest photocatalytic activity was shown for the poled porous ceramics in photodecomposition test of methylene blue. These results clearly indicated photocatalytic activity was enhanced on ferroelectric domains around pores of porous piezoelectric ceramics.

Enhanced dielectric and piezoelectric properties in potassium sodium niobate/polyvinylidene fluoride composites using nano-silicon carbide as an additive

Piezoelectric materials are an indispensable part of modern life. Yet the existing environmental issues with conventional lead-based piezoelectrics has motivated scientist to develop novel substitutes including lead-free piezoelectric polymer composites. Following this path, the present research has focused on the fabrication of ternary composites of Polyvinylidene fluoride (PVDF)/Potassium Sodium Niobate (KNN)/nano-Silicon carbide (SiC) via hot compression molding and studying the effect of additives on the PVDF structure and the electrical properties of the composite. The obtained scanning electron micrographs and density measurements showed that the fabrication method provided dense samples. The activated polarization phenomena in the prepared samples enhanced dielectric permittivity and dielectric loss at a constant frequency with increasing KNN and SiC contents. Besides the expected dipole polarization, the presence of interfaces in the composites gave rise to the Maxwell–Wagner–Sillars effect and its corresponding polarization phenomenon. The semiconductive nature of SiC also promoted space charge polarization. However, these properties were frequency-dependent because the first two polarization mechanisms are deactivated at high frequencies. XRD patterns showed that SiC addition can alter the primary crystalline structure of PVDF and promote β-phase formation in the poled samples. Piezoelectric measurements confirmed the significant role of SiC addition to PVDF-KNN composites. The most significant increase in the piezoelectric properties was observed in PVDF-60KNN-1SiC, with a 183% increase in d33 value. The PVDF-80KNN-1SiC had the highest d33 value of 30.5 pC/N. It also had the best piezoelectric voltage coefficient and hence the highest figure of merit. Higher SiC contents restrict the efficiency of poling by forming a conductive path across the sample which would deteriorate the piezoelectric performance of the material. The present findings show that PVDF-KNN-SiC composites can be considered as a potential flexible piezoelectric material for future applications.

Temperature dependence correction method of LED filament lamp for total luminous flux calibration based on voltage measurement

Light-emitting diode (LED) standard lamps are interesting since the traditional incandescent standard lamps for photometry are difficult to obtain. Many of the National Metrology Institutes have started projects to study the use of LED standards for photometric comparison. The National Institute of Metrology, China, has developed a type of LED filament lamp for total luminous flux. The lamp mimics the 4π incandescent standard lamp and has no space for an active temperature control component. A temperature dependence correction method is reported using the coefficient of the lamp voltage to the output luminous flux. The luminous flux correction is derived from the lamp voltage value. By applying correction, the stability test of the LED filament lamp shows that the ageing effect was estimated to be less than 0.1%/210 days. The temperature dependence was suppressed to less than 0.1% for a range of 21 °C ± 2 °C, which could be due to possible temperature fluctuations of the lamp ambient temperature during measurement by the goniophotometer or integrating sphere.

A Systematic Review of Piezoelectric Materials and Energy Harvesters for Industrial Applications.

In the last three decades, smart materials have become popular. The piezoelectric materials have shown key characteristics for engineering applications, such as in sensors and actuators for industrial use. Because of their excellent mechanical-to-electrical and vice versa energy conversion properties, piezoelectric materials with high piezoelectric charge and voltage coefficient have been tested in renewable energy applications. The fundamental component of the energy harvester is the piezoelectric material, which, when subjected to mechanical vibrations or applied stress, induces the displaced ions in the material and results in a net electric charge due to the dipole moment of the unit cell. This phenomenon builds an electric potential across the material. In this review article, a detailed study focused on the piezoelectric energy harvesters (PEH’s) is reported. In addition, the fundamental idea about piezoelectric materials, along with their modeling for various applications, are detailed systematically. Then a summary of previous studies based on PEH’s other applications is listed, considering the technical aspects and methodologies. A discussion has been provided as a critical review of current challenges in this field. As a result, this review can provide a guideline for the scholars who want to use PEH’s for their research.

The Electrical Performances and Leakage Current Conduction Mechanism of Al2O3/ZrO2/SiO2/ZrO2/Al2O3 MIM Capacitors

In this paper, we prepared the Al2O3/ZrO2/SiO2/ZrO2/Al2O3 (AZSZA) metal-insulator-metal (MIM) capacitors by atomic-layer-deposition technique. By increasing the thickness of SiO2 from 0 nm to 3 nm, the quadratic capacitance voltage coefficients improved significantly from 2130 ppm/V2 to −121 ppm/V2 because of the offsetting effects of ZrO2 and SiO2 dielectric. Meanwhile, for our interested SiO2=3nm sample, the capacitance density is 7.40 fF/µm2 and the leakage current density is 3.08 × 10−8 A/cm2 at 5 V. We also studied the leakage current conduction mechanism of AZSZA dielectric MIM capacitors and found that at high field the conduction mechanism was dominated by Poole Frenkel emission.

A phenomenological approach to study the magnetoelectric (ME) response of lead free magnetostrictive NiFe2O4–Piezoelectric BaZr0.2Ti0.8O3 particulate composites

Lead-free magnetoelectric (ME) composites comprises NiFe2O4 (NFO) and BaZr0.2Ti0.8O3 (BZT) were synthesized by using conventional double sintering solid-state reaction technique and it's structural, electric, dielectric, magnetic and ME properties were studied. The spectra of X-ray diffraction displayed the formation of parent phase and presence of two phases within the composites (ferrite-ferroelectric). DC resistivity as a function of temperature has been studied, it indicates the semiconducting behavior. Frequency dependent dielectric spectra of the composites indicates small polaron hopping model of conduction mechanism. Magnetic measurements at room temperature shows the composites are soft magnetic and such materials reveals M-H hysteresis type behavior. The composite with x = 0.3 showed the highest value of ME voltage coefficient ~3.82 mV/cmOe. Such ME composite materials furnish fabulous chances as prospective lead-free systems for multifunctional device applications.