Pure phase perovskite relaxor-based (1 – x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–PT, x = 0.2–0.4) ferroelectric ceramics were prepared by the reaction-sintering method sintered at 1240–1250 °C. The synthesized ceramics exhibit rather homogeneous microstructure morphology and relatively high density. The content of PbTiO3 (PT) exerts successive influences on sintering capability, phase structure and electrical properties of the PMN-PT ceramics. With the increase of the PT content, the crystal structure of the PMN–PT ceramics changes gradually from the rhombohedral phase, across the coexistence of rhombohedral phase and tetragonal phase, and to the tetragonal phase, accompanied by the change of the dielectric response character from typical relaxor ferroelectrics to normal ferroelectrics. The morphotropic phase boundary (MPB) of the PMN–PT system is determined locating at x = 0.3–0.34 based on the structure analysis and the electrical properties measurements, in which the PMN–PT ceramics with the MPB composition exhibit enhanced microstructure and excellent electrical properties, especially superior piezoelectric properties.

We report on metal-oxide-semiconductor (MOS) AlGaN/GaN heterostructure field effect transistors (HFETs) based on InGaN/GaN multiple quantum well (MQW) structure using Ta2O5 dielectric deposited by electron beam evaporation (EBE) simultaneously for surface passivation and as a gate insulator. The device features a 5-pair MQW layer inserted into the AlGaN/GaN two-channel HFET structure. It results in a raised potential barrier, which leads to better carrier confinement and effective access to the InGaN layer. However, it revealed a pronounced leakage current which may be generated from the bottom Si-doped GaN and/or the sidewall leakage paths due to the exposure of channels after mesa etching. Both passivated MQW-HFET and MOS MQW-HFET present enhanced dc- and pulsed-mode performance compared to unpassivated one. In terms of transfer characteristics, MOS MQW-HFET exhibits the larger and broader main peak yet smaller satellite peak relative to passivated MQW-HFET. The reduced gate and mesa-to-mesa leakage current indicates the successful passivation effect from EBE-Ta2O5 dielectric.

The influence of pressure on the MOCVD grown InAlN/AlN/GaN heterostructure has been investigated by high-resolution X-ray diffraction, Hall measurement and atomic force microscopy. High pressure is beneficial to increase indium incorporation efficiency. The electrical properties of InAlN/AlN/GaN heterostructure become better with the pressure decreasing from 100 Torr to 50 Torr. Indium droplets tend to form on the InAlN surface at high pressure. The edge of the indium droplet is the Al-rich region while the interior is the In-rich region, demonstrated by the phase-contrast mode. Phase contrast across the V-defect is strong on the surface of InAlN grown at low pressure (50 Torr) whereas it is not evident at high pressure (100 Torr), indicating that large stress in the InAlN film will enhance the compositional variation.

Thermal evaporation technique was used to prepare thin films of 5,10,15,20-tetraphenyl-21H,23H-porphine nickel (II), NiTPP, onto glass and quartz substrates. The crystal structures and morphologies of all prepared NiTTP thin films were investigated at 298, 423 and 573 K by using X-ray diffraction, XRD, and scan electron microscopy, SEM, respectively. The lattice of all prepared NiTPP films was investigated as a monoclinic with space group P2/M. The surface topography of the prepared films showed granular particles of sizes 49.7, 64.7 and 107 nm. The annealed NiTPP films at 423 K have a spatial configuration of well-defined grains boundary with nanoporous nature and all annealed films at 573 K have higher aggregates and the porosity of the films was increased. Optical constants namely refractive index, n, and the absorption index, k, of NiTPP films have been estimated by using spectrophotometric measurements of transmittance and reflectance in the spectral range from 200 to 2500 nm. The absorption spectra in the UV-vis spectrum were analyzed in terms of both molecular orbital and band theories. The obtained data of n and k were used to estimate the type of transitions and were found to be indirect transition for all films. The optical and fundamental gaps were decreased as the annealing temperature was increased. Some optical parameters namely molar extinction coefficient, εmolar, oscillator strength, f, and electric dipole strength, q2, have been evaluated. According to the single oscillator model and Drude model, some related parameters such as oscillation energy, Eo, the dispersion energy, Ed, the optical dielectric constant, ε∞, the lattice dielectric constant, εL, and the ratio of free carrier concentration to its effective mass, N/m∗, the third-order nonlinear susceptibility, χ(3), and molar polarizability, αp, were estimated before and after annealing.

Magnetic properties of LaCoO3 nanoparticles prepared by a sol-gel method with average particle size (D) ranging from 20 to 500 nm are investigated. All samples exhibit obvious ferromagnetic transition. With decreasing particle size from 500 to 120 nm, the transition temperature Tc decreases slightly from 85 K, however Tc decreases dramatically when D ≤ 85 nm. Low-field magnetic moment at 10 K decreases with reduction of particle size, while the high-field magnetization exhibits a converse behavior, which is different with previous reports. The coercivity Hc decreases as the particle size is reduced. It is different with other nanosystems that no exchange bias effect is observed in nanosized LaCoO3 particles. These interesting results arise from the surface effect induced by sized effect and the structure change in LaCoO3 nanoparticles.

The stabilized fibers with different relative cyclization index were prepared by stabilization of electrospun polyacrylonitrile (PAN) fibers at temperatures of 275, 290 and 300 ºC. Then electrospun PAN-based carbon fibers were prepared by carbonization of the stabilized fibers at 700 ºC in a nitrogen atmosphere. The thermal property of as-spun fibers during the stabilization process was investigated by differential scanning calorimetry. The evolution of chemical structure and morphology of the PAN-based stabilized fibers was studied by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Microwave electromagnetic properties of these carbonized fibers were investigated in the range of 1.5–18.0 GHz by the vector network analyzer. The reflection loss was calculated by the measured electromagnetic parameter. The results indicate that the stabilization has a significant effect on the electromagnetic and microwave absorbing properties of the carbon fibers.

Based on the method of stationary-phase and the mathematic techniques, analytical expressions for the TE and TM terms of an apertured circular flattened Gaussian beam (CFGB) in the far-field have been derived without any approximation, which allows one to calculate the energy flux distributions of the TE term, the TM term, and the apertured CFGB. The analytical formulae of the power of the TE term, the TM term, and the apertured CFGB are also presented. The vectorial structural properties of the far-field of an apertured CFGB are demonstrated. The influences of the f-parameter, the truncation parameter, and the parameter N on the energy flux distributions of the TE term, the TM term, and the apertured CFGB are examined. Also, the effects of the f-parameter, the truncation parameter, and the parameter N on the ratios of the power of the TE and TM terms to the power of the apertured CFGB are investigated.

A diamond-containing material (DCM) produced by detonation was mechanically milled using KM-1 and AGO-2S mills. Experimental spectra for infrared (IR) absorption, Raman scattering and X-ray diffraction patterns (XRD) were obtained for the treated DCM samples. We compared the Raman and IR spectra for the KM-1 milled samples and concluded that the surface of the DCM particles was not uniform. The mechanical force that resulted from milling with the AGO-2S destroyed the non-diamond part of the particles and initiated irreversible physical and chemical changes in them. The destruction of the diamond grains was the consequence of these irreversible changes. It follows from the experiments that the dipole momentum of the DCM particle was caused by the presence of polar fragments of molecules. The constant dipole momentum of the particles facilitated the aggregation. Based on this, we proposed a model of a structurally inhomogeneous DCM particle.

To exploit the potential application of the conductive polymers in incorporating with carbon-based materials, polypyrrole (PPY) nanotube and polyaniline (PANI) nanofiber were synthesized and the electrochemical properties were compared. The morphology, texture and chemical structure of PPY and PANI were tested employing SEM, TEM, FTIR and XPS. The results of electrochemical tests demonstrate that the specific capacitance of PPY nanotube is as high as 463 F/g at a current density of 0.3 A/g, much higher than that of PANI nanofiber (243 F/g). Furthermore, at a current density of 0.8 A/g, the capacitance of PPY nanotube is 172 F/g, higher than that of PANI nanofiber (104 F/g). Additionally, after the long-term charge-discharge test at a current density of 1.5 A/g, the preserved capacitance of PPY nanotube is still higher than that of PANI nanofiber (106.5 F/g vs. 75 F/g). The EIS measurement illustrates that the PPY nanotube shows lower contact interface resistance and shorter ion diffusion path than the PANI nanofiber. It suggests that the PPY nanotube is a promising material to be applied in supercapacitor rather than the PANI nanofiber, because of its extended internal cavity surface area and pore volume.

Dielectric barrier discharges (DBDs) are commonly used for gas effluent cleanup and ozone generation. For these applications, the energy efficiency of the discharge is a major concern. This paper reports on investigations carried out on the voltage shape applied to DBD reactor electrodes, aiming to evaluate a possible energy efficiency improvement for ozone production. Two DBD reactor geometries were used: pin-to-pin and cylinder-to-cylinder, both driven either by a bi-directional power supply (voltage rise rate 1 kV/μs) or by a pulsed power supply (voltage rise rate 1 kV/ns). Ozone formed in dry air was measured at the reactor outlet. Special attention was paid to discharge input power evaluation using different methods including instantaneous current-voltage product and transferred charge-applied voltage figures. The charge transferred by the discharges was also correlated to the ozone production. It is shown that, in the case of the DBD reactors under investigation, the applied voltage shape has no influence on the ozone production efficiency. For the considered voltage rise rate, the charge deposit on the dielectric inserted inside the discharge gap is the important factor (as opposed to the voltage shape) governing the efficiency of the discharge – it does this by tailoring the duration of the current peak into the tens of nanosecond range.

This paper deals with the calculation of eddy current in a copper cylinder. This cylinder rotates in an applied static magnetic field. The electromagnetic problem is solved in two-dimension by considering transient motion. Two methods for eddy current computation are compared: stochastic method and classical finite element method. The main goal of this paper is to compare these methods.

The aim of this work is to propose a simple multi-physics model in order to predict the evolution of the thermodynamic variables during the combustion of kerosene vapors in each compartment of a closed vessel. A special attention is paid to the mechanical effects of combustion, e.g., the pressure evolution. The basic characteristics of the model have been developed as part of a Computational Fluid Dynamics (CFD) approach, in order to represent both the ignition stage and the flame propagation in the reactive mixture. The proposed development is validated in a single compartment vessel by investigations about the equivalence ratio and the reaction dynamics (final pressure, combustion duration, etc.). Moreover, the expected phenomenology is correctly reproduced for tanks composed of several compartments, such as, for instance, a faster combustion process in the presence of internal orifices. The impact of the ignition on the subsequent evolution of the explosion is also investigated, highlighting a strong influence of the ignition location. The model illustrates that the pressure evolution is the result of complex geometry effects: particularly, for a tank made of identical compartments, the total volume is not sufficient to describe the main trends concerning the mechanical effects of the explosion. The calculations are in agreement with classical results available in the literature for a special kind of kerosene (F.34) studied by the laboratory. Despite the proposed model relying on simple assumptions, it represents a useful tool for further vulnerability or risk assessment studies applied to aircraft kerosene tanks.

The rapid development of low-power consumption electronics and the possibility of harvesting energy from environmental sources can make totally autonomous wireless devices. Using piezoelectric materials to convert the mechanical energy into electrical energy for batteries of wireless devices in order to extend the lifetime is the focus in many researches in the recent years. It is important and efficient to improve the energy harvesting by designing an optimal interface between piezoelectric device and the load. In this paper, a self-powered piezoelectric energy harvesting device is proposed based on the velocity control synchronized switching harvesting on inductor technique (V–SSHI). Comparing to the standard full bridge rectifier technique, the synchronized switching harvesting on inductor (SSHI) technique can highly improve harvesting efficiency. However, in real applications when the energy harvesting device is associated with wireless sensor network (WSN), the SSHI technique needs to be implemented and requires being self-powered. The conventional technique to implement self-powered SSHI is to use bipolar transistors as voltage peak detector. In this paper, a new self-powered device is proposed, using velocity control to switch the MOSFET more accurately than in the conventional technique. The concept of design and the theoretical analysis are presented in detail. Experimental results are examined.

In this paper, the tape-helix model is firstly introduced in the field of intense electron beam accelerator to analyze the dispersion effects on the electromagnetic parameters of helical Blumlein pulse forming line (PFL). Work band and dispersion relation of the PFL are analyzed, and the normalized coefficients of spatial harmonics are calculated. Dispersion effects on the important electromagnetic parameters of PFL, such as phase velocity, slow-wave coefficient, electric length and pulse duration, are analyzed as the central topic. In the PFL, electromagnetic waves with different frequencies in the work band of PFL have almost the same phase velocity. When de-ionized water, transformer oil and air are used as the PFL filling dielectric, respectively, the pulse duration of the helical Blumlein PFL is calculated as 479.6 ns, 81.1 ns and 53.1 ns in order. Electromagnetic wave simulation and experiments are carried out to demonstrate the theoretical calculations of the electric length and pulse duration which directly describe the phase velocity and dispersion of the PFL. Simulation results prove the theoretical analysis and calculation on pulse duration. Experiment is carried out based on the tape-helix Blumlein PFL and magnetic switch system. Experimental results show that the pulse durations are tested as 460 ns, 79 ns and 49 ns in order when de-ionized water, transformer oil and air are used respectively. Experimental results basically demonstrate the theoretical calculations and the analyses of dispersion.

This study investigated the stability of shock-waves in brittle granular materials and thus determined whether materials, such as sand, could be represented by a Hugoniot equation to describe their shock response. A series of plate impact experiments on quasi-mono-disperse soda-lime glass microspheres was conducted with the aim of measuring the shock-wave profile to determine if there was any change over time/run distance. Granular bed thickness and input stress were varied to study the effects of dispersion on shock-wave velocity (Csh). It has been shown that it is possible to sustain steady shock-waves in brittle granular materials due to no measurable wave dispersion occurring in the samples tested. This study also highlighted an unsteady precursor wave that is present in the wave profiles at low stresses.

A relevant modeling-method of distributed interconnect line for the high-speed signal integrity (SI) application is introduced in this paper. By using the microwave and transmission line (TL) theory, the interconnect lines are assumed as its distributed RLC-model. Then, based on the transfer matrix analysis, the second-order global transfer function of the interconnect network comprised of the TL driven by voltage source including its internal resistance and the impedance load is expressed. Thus, mathematical analysis enabling the physical SI-parameters’ extraction was established by using the transient response of the loaded line. To verify the relevance of the developed model, RC- and RLC-lines excited by square-wavepulse with 10-Gbits/s-rate were investigated. So, comparisons with SPICE-computations were performed. As results, transient responses perfectly well correlated to the reference SPICE-models were evidenced. As application of the introduced model, evaluations of rise-/fall-times, propagation delays, signal attenuations and even the settling times were realized for different values of TL-parameters. Compared to other methods, the computation execution time and data memory consumed by the program implementing the proposed delay modeling-method algorithm are much better.

The venous circulation in the lower limb is mainly controlled by the muscular action of the calf. To study the mechanisms governing the venous draining and filling process in such a situation, an experimental setup, composed by a collapsible tube under external pressure, has been built. A valve preventing back flows is inserted at the bottom of the tube and allows to model two different configurations: physiological when the fluid flow is uni-directional and pathological when the fluid flows in both directions. Pressure and flow rate measurements are carried out at the inlet and outlet of the tube and an original optical device with three cameras is proposed to measure the instantaneous cross-sectional area. The experimental results (draining and filling with physiological or pathological valves) are confronted to a simple one-dimensional numerical model which completes the physical interpretation. One major observation is that the muscular contraction induces a fast emptying phase followed by a slow one controlled by viscous effects, and that a defect of the valve decreases, as expected, the ejected volume.

We study the problem of scattering by a thin and conducting screen perforated periodically with square apertures, when the screen is illuminated by an electromagnetic wave in subwavelength regime. Our formulation extends the monomodal approximation technique up to the second-order Floquet modes, which enable us to investigate not only propagation mode, but also nonpropagation mode in the low-frequency regime. We also study dispersion relation of the principal Floquet modes and show the behavior of electromagnetic fields in the periodic system at the extremely low frequency, the resonance frequency and Wood’s anomaly frequency. The interesting characteristics of the fields can be found in these specific frequencies.