A 3D model of a hollow cathode of a thermal plasma torch was developed to study the motion of the electric arc in the upstream part as well as its influence on the characteristics of the thermal plasma generated at the entrance of the downstream part (anode).The translational motion along the axis and the rotational velocity of the cathodic arc root are studied.The results of the model are presented and compared with those of the literature and also with experimental results.Good agreements on the prediction of the axial arc position and of the rotational speed of the arc root are found with the literature.A correlation is also shown between the theoretical positions of the arc root and the experimental traces of erosion observed on the cathode.
W–Ag thin films are produced by magnetron co-sputtering technique using glancing angle co-deposition configuration. Different samples are prepared with similar conditions (same pressure, thickness and tungsten target current) but with a variable Ag target current changing from 0 to 80 mA. The effect of the Ag target current on the film structure and electrical properties is investigated using scanning and transmission electron microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction and van der Pauw technique. Thin films with inclined columns are obtained and the columns section becomes more anisotropic for the films prepared with the lowest Ag target currents. The elemental composition of the films also changes as a function of the Ag target current, varying from tungsten-rich (at low current) to homogeneous (at high current). W–Ag thin films exhibit different crystallographic structures. If the fcc Ag phase is always present, the metastable A15 β -W is pointed out only at low Ag target current while at high current, only the bcc α -W phase is present. The microstructural analysis shows that the core of the columns is formed by W while Ag covers the columns as grains. Room temperature electrical resistivity decreases with Ag target current, whereas its anisotropy decreases. This behaviour correlates with the change in the columnar cross-section morphology.
We conducted a thorough experimental and numerical study of the micromagnetic properties of Permalloy (Ni 80 Fe 20 ) microdisks exhibiting target domain structures at remanence. Vortex configurations are quite common in such microdisks and correspond to an in-plane (IP) flux closure configuration of cylindrical symmetry with an out-of-plane (OOP) magnetized core. In contrast, target domain configuration are observed in thicker microdisks and are characterized by a vortex configuration of the IP component of the magnetization superposed to an OOP component of magnetization which oscillates as a function of the distance to the microdisk center resulting in the formation of concentric domains. The ratio of the OOP oscillatory component of the magnetization to the IP vortex one increases with the thickness of the microdisk. Hysteresis loops were measured under IP and OOP field. The results at remanence and under magnetic field could be interpreted by micromagnetic simulations in which the microdisks were described as an assembly of partially coupled columns representing the granular nanostructure of the films from which the microdisks were patterned. Quite original magnetization processes take place in these microdisks exhibiting target domain remanent configuration. These include in particular entire flipping of the domain configuration and annihilation/creation of ring domains.
Here, we introduce a tailorable coupled resonator surface acoustic waveguide (CRSAW), based on a linear defect of elliptical cylinders inside a phononic crystal of ZnO pillars on a Si substrate. The designed elliptical resonators allow the emergence of a minimally dispersive, monomode shear-guiding band inside the local resonance bandgap, owing to their partially broken structural symmetry in comparison with their previously reported counterparts such as pillars and hollow cylinders. Moreover, by introducing reconfigurable waveguide behavior, we benefit from the acoustoelectric-induced elasticity modulation of ZnO, which is a semiconducting piezoelectric material. Switching the conductivity of ZnO structures between two limiting low and high values (0.01 S m −1 and 100 S m −1 ), a considerable waveguide modulation at full width at half maximum (FWHM) (ΔFWHM = −21%) and guiding frequency (Δ f d = −2.81%) are achieved for the designed optimized elliptical cylinder CRSAW while maintaining an acceptable loss value. Benefiting from the proposed ZnO-based elliptical CRSAW, we have achieved simultaneous monomode and low-bandwidth surface acoustic waveguide behaviors, without involving significant fabrication complications. The designed structures open up new horizons toward the realization of promising building blocks for designing reconfigurable and miniaturized SAW RF-filters, demultiplexers, and Mach–Zehnder devices for wireless communications applications.
We have investigated the behavior of the optical transduced signal of a photonic integrated polymer micro resonator as an evaporating water droplet is positioned upon it. The photonic chip is fabricated by means of deep-UV photolithography, and the circuits are made of polymer UV210. The device is then arranged in an optical bench so as to perform relevant measurements thanks to a broadband laser for the excitation of the resonators and an optical spectrum analyzer remotely controlled by a Matlab software for the acquisition and treatment of data. By dynamically tracking the free spectral range (FSR) of the optical mode, we come up with a signature of the thermodynamic evaporation process. In order to correlate this signature to the evaporation speed of the water droplet, a lateral camera is disposed to measure the evolution of the geometrical characteristics of the droplet, while weight measurements are performed thanks to a precision balance. These measurements provide a numerical link between the temporal variation of the FSR and the variation of the distance between the apex of the droplet and the substrate, correlating clearly the variation of the FSR with the mass change of the droplet. The measurements have been performed with 20 mu l droplets for three different substrate temperatures: 21 degrees C, 24 degrees C and 27 degrees C. Then, theoretical investigations have been also performed in order to interpret the dynamics of the FSR in terms of guiding theory.
