Reversible Domains Research Articles

Decoupling Control for Dual-Winding Bearingless Switched Reluctance Motor Based on Improved Inverse System Method

Dual-winding bearingless switched reluctance motor (BSRM) is a multivariable high-nonlinear system characterized by strong coupling, and it is not completely reversible. In this paper, a new decoupling control strategy based on improved inverse system method is proposed. Robust servo regulator is adopted for the decoupled plants to guarantee control performances and robustness. A phase dynamic compensation filter is also designed to improve system stability at high-speed. In order to explain the advantages of the proposed method, traditional methods are compared. The tracking and decoupling characteristics as well as disturbance rejection and robustness are deeply analyzed. Simulation and experiments results show that the decoupling control of dual-winding BSRM in both reversible and irreversible domains can be successfully resolved with the improved inverse system method. The stability and robustness problems induced by inverse controller can be effectively solved by introducing robust servo regulator and dynamic compensation filter.

Pattern Transfer of Sub-10 nm Features via Tin-Containing Block Copolymers.

Tin-containing block copolymers were investigated as materials for nanolithographic applications. Poly(4-trimethylstannylstyrene-block-styrene) (PSnS-PS) and poly(4-trimethylstannylstyrene-block-4-methoxystyrene) (PSnS-PMOST) synthesized by reversible addition-fragmentation chain transfer polymerization form lamellar domains with periodicities ranging from 18 to 34 nm. Thin film orientation control was achieved by thermal annealing between a neutral surface treatment and a top coat. Incorporation of tin into one block facilitates pattern transfer into SiO2 via a two-step etch process utilizing oxidative and fluorine-based etch chemistries.

Highly reliable bipolar resistive switching in sol-gel derived lanthanum-doped PbTiO3 thin film: Coupling with ferroelectricity?

Nanoscale PbxLa1−xTi1−x/4O3 (PLT) thin film has been fabricated on Pt\Ti\SiO2\Si substrates by chemi- cal solution deposition (CSD) method. Ferroelectricity of the fresh-made PLT thin film has been clearly detected through piezoelectric force microscopy (PFM) by writing reversible ferroelectric domains. However, PLT thin film also shows off-standard ferroelectric hysteresis loops highly dependent on frequency, indicating large amount of mo- bile space charges in the film. Subsequent current-voltage (C-V) studies show that sandwich-like Pt\PLT\Pt structure exhibits notable bipolar resistive switching (BRS) character- istics with high stability (> 10 3 switching cycles). It is found that the C-V curves of both high- and low-resistance states have the feature of space-charge-limited current (SCLC) conduction, indicating important roles of defects in the con-

Ferroelectric behavior in the high temperature paraelectric phase in a poly(vinylidene fluoride-co-trifluoroethylene) random copolymer

In this report, ferroelectric behaviors were investigated as a function of temperature and poling frequency for a uniaxially stretched poly(vinylidene fluoride-co-trifluoroethylene) 50/50 (mol./mol.) film. A variety of ferroelectric behaviors, including normal ferroelectric, antiferroelectric-like, and paraelectric behaviors, were observed by varying temperature, poling frequency, and poling electric field. Especially, the ferroelectric (FE) to paraelectric (PE) transition and ferroelectric behaviors of the high temperature PE phase were studied in detail by electric displacement-electric field loop measurements. At a high poling frequency (e.g., 1000 Hz) and 100 °C (above the Curie temperature at 64 °C), a paraelectric behavior was obtained due to the nucleation of electric field-induced FE nanodomains inside the PE phase matrix. These FE nanodomains were highly reversible and they quickly depolarized upon removal of the poling field. At an intermediate poling frequency (e.g., 10 Hz) and 100 °C, an antiferroelectric-like behavior was observed, which could be attributed to the competition between depolarization and polarization fields upon reverse poling. Finally, at a low poling frequency (e.g., 1 Hz) and 100 °C, a normal ferroelectric behavior with rectangular hysteresis loops was seen because the small, reversible FE domains had enough time to grow into large irreversible ones. The presence of electric field-induced FE domains in the PE matrix was proved by field dependent Fourier transform infrared study. On the basis of this study, understanding of the paraelectric behavior in polar crystalline polymers will help us design new materials to meet the requirements for high energy density and low loss dielectric applications.

Dielectric Degradation and Reversible Domain Motion in Ferroelectric Thin Films Evidenced by Double-Butterfly Capacitance–Voltage Loops with Sweeping Times from 500 ns to 1 s

Generally, the ferroelectric capacitance under a d.c. voltage drops continuously with time, and the shape of capacitance–voltage (C–V) loops within a sweeping time more than 1 s resemble a butterfly, in comparison to the double-butterfly shape of an antiferroelectric. In this work, we developed a measuring technique for shortening sweeping time down to 500 ns for the rapid study of dielectric relaxation in ferroelectric Pb(Zr,Ti)O3 thin films. It is interestingly found that the traditional butterfly loops of a ferroelectric degenerate into double butterfly loops of an antiferroelectric when the sweeping time is sufficiently short, providing evidence of the nonlinear dielectric contribution of reversible domain motion. Reversible domains can align along a field under a voltage, but reverses back immediately into their previous directions under a reduced field strength to release their polarization charges, similarly to antiferroelectric domains. When the voltage stressing time is sufficiently long, the internal field for driving reversible domain motion is temporally screened by the injected charges accumulated in regions with different polarizations, dielectric permittivities, and conductivities (domain pinning), which results in time-dependent dielectric degradation. This charge injection is different from the traditional model of defect motion with a low mobility. Finally, we showed evidence of the charge injection from the imprint profile and reversible domain freezing into irrecoverable domains upon cooling.

Metal ions and complexes as modulators of protein-interfacial electron transport at graphite electrodes

An extensive investigation of the direct (unmediated) electrochemical activity of various redox proteins at pyrolytic graphite electrodes has been undertaken. With the exception of the “blue” copper protein azurin, a profound preference for the hydrophilic “edge” over the hydrophobic “basal” plane orientation of the graphite surface is observed. This may be identified with the presence of various oxidised (CO) functionalities at the polished “edge” surface which, most probably in a random manner, constitute reversible and productive binding domains for the proteins. Conditions under which the rates and reversibility of heterogenous electron transport may be optimised depend upon the protein under examination. Well-behaved electrochemistry, indicate of diffusion-dominated heterogeneous electron transport, is modulated by electrode surface protonation (p K = 5.6) and levels of redox-inert multivalent cations, including Mg 2+ and Cr(NH 3) 3+ 6. The electrochemistry of several proteins which have negatively charged interaction domains, including plastocyanin, and chloroplast and bacterial ferrodoxins, is promoted and stabilised by electrode surface protonation, and interfacial binding of multivalent cations which is attenuated at high ionic strength. Coversely, the electrochemistry of horse-heart cytochrome c, for which the region around the exposed heme edge carries a net positive charge, is inhibited by electrode surface protonation and destablished by the presence of multivalent cations. These patterns of behaviour may be rationalised in terms of a heterogeneous electrode surface which comprises regions of hydrophilic polar groups at which proteins may associate reversibly if resultant coulombic interactions are favourable, and regions of extensive hydrophobicity at which less reversible and (probably) degradative adsorption occurs. Within this basic model, there is considerable scope for domain selectivity which may arise from variations in medium and short range order and distribution of CO functionalities. Implications for the control of in vivo electron-transport processes are discussed.

Lateral structure of domains in ferroelectric TGS

Laser probe technique1,2 has been used to study the lateral structure of domains in ferroelectric triglycine sulfate. No regular pattern of domains exists along the polar axis. Regions of high pyroelectricsignal are observed and attributed to microscopic reversible domains.

Low birefringent orthoferrites for optical devices

Nonmagnetic optical birefringence for light propagated along the direction of magnetization can be reduced to low levels in orthoferrite compositions such as Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Pr <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> FeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> . This results in a significant improvement in Faraday rotation detection of magnetic domains in thin single crystal orthoferrite platelets. For a simple two polarizer detection scheme, one can obtain light transmitted in the ON state of 10-20 percent of the incident light for contrasts between the ON and OFF states of greater than 20/1, for He-Ne laser light at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda = 0.633 \mu</tex> m and for platelet thicknesses of 0.001- 0.003 in. The low birefringent orthoferrites can be used in optical memory and display devices employing mobile magnetic bubble domains or reversible localized domains which act as binary optical shutters.

Measurements of Magnetic Viscosity in Iron

Magnetic viscosity---the change of induction occurring after the magnetizing field has ceased to vary---has been measured in a bar of commercial iron, with a measuring circuit designed to eliminate spurious effects arising from sparking at switches. Magnetic viscosity is found to depend on previous magnetic states, in agreement with observations of Mitkevitch and contrary to Preisach's results. It appears, therefore, as if reversible domains could retain their lagging propensity while the magnetic force is varying over a considerable range. The viscous effect is found to depend on the magnitude of the previous change of induction if the latter is small, but is independent of this change if it is greater than 60 gauss. In small, subsidiary hysteresis loops, such as are used in determining reversible permeability, it is found that the Barkhausen effect is not present although there is hysteresis and magnetic viscosity. It is therefore concluded that the movement of the boundaries of saturated domains in the material is subject to time-lag.