Strip Geometry Research Articles

Transmission line high-T/sub c/ dc-SQUIDs

Because of high permittivity of SrTiO/sub 3/ (STO) substrate, YBCO high-Tc SQUIDs have distributed impedance. Based on the simulation by the analytical method to calculate the I-V characteristic, we have designed and fabricated YBCO dc SQUIDs that have a transmission-line-like geometry of thin parallel strips with a wide slit between them. The geometrical parameters were determined to give high modulation voltage. The fabricated SQUIDs had a white noise of (0.5-1.0)/spl times/10 /spl Phi//sub 0//Hz/sup 1/2/. We also designed a direct coupling magnetometer, in which the transmission line SQUID was located within the hole of the pickup coil. On a small substrate area of 5 mm/spl times/10 mm, the fabricated magnetometer had an effective area of 0.22 mm/sup 2/. The field noise of about 100 fT/Hz/sup 1/2/ was obtained in the white noise region.

Nonlocality in mesoscopic Josephson junctions with strip geometry

We study the current in a clean superconductor-normal-metal-superconductor junction of length d and width w in the presence of an applied magnetic field H. We show that both the geometrical pattern of the current density and the critical current as a function of the total flux in the junction, depend on the ratio of the Josephson vortex distance a_0 and the range r of the nonlocal electrodynamics. In particular, the critical current has the periodicity of the superconducting flux quantum only for r<a_0 and acquires, due to boundary effects, the double (pseudo-) periodicity for strong nonlocality, r>a_0. Comparing our results to recent experiments of Heida et al. [Phys. Rev. B 57, R5618 (1998)] we find good agreement.

Magneto-optical study of magnetic-flux penetration into a current-carrying high-temperature-superconductor strip

The magnetic-flux distribution across a high-temperature superconductor strip is measured using magneto-optical imaging at 15 K. Both the current-carrying state and the remanent state after transport current are studied up to currents of ${0.97I}_{c}$ where ${I}_{c}$ is the critical current. To avoid overheating of the sample current pulses with a duration of 50 ms were employed. The results are compared with predictions of the Bean model for the thin strip geometry. In the current-carrying state, reasonable agreement is found. However, there is a systematic deviation---the flux penetration is deeper than theoretically predicted. A much better agreement is achieved by accounting for flux creep as shown by our computer simulations. In the remanent state, the Bean model fails to explain the experimental results. The results for the currents $I&lt;~{0.7I}_{c}$ can be understood within the framework of our flux creep simulations. However, after the currents $I&gt;{0.7I}_{c}$ the total flux trapped in a strip is substantially less than predicted by the simulations. Furthermore, it decreases with increasing current. Excessive dissipation of power in the annihilation zone formed in the remanent state is believed to be the source of this unexpected behavior.

AC transport losses in multifilamentary (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tapes

The results of ac transport losses measurements are presented for multifilamentary HTSC composite Bi-2223/Ag tapes with the number of filaments N=7, 19, 37, 61, 91, 127, 169, and 703. The measurements have been made under the self-field conditions as well as in a constant magnetic field applied to the tapes at different angles. The dependence of AC losses on the amplitude and frequency of the alternating transport current have been obtained. It is found that the dependence of the AC losses on the current amplitudes for all the tapes are in accord with the Norris theoretical predictions for an elliptical or strip geometry of the wire. The external magnetic field increases the magnitude of the AC losses. It is concluded that transport AC losses in multifilamentary HTSC composites are “saturation losses.”

A linear multisensor for temperature and magnetic field based on diode structure

A new type linear silicon multisensor using the functional principle for simultaneous and independent measurement of temperature and magnetic field is suggested and investigated experimentally in wide temperature range 77 K≤ T≤393 K. The structure is a differential microdiode with strip geometry. The temperature output signal is the anode–cathode voltage at a constant supply current, which is linear in the range 77 K≤ T≤393 K, but the magnetosensitive one is a differential current between both base contacts. A strong magnetic field up to 1.5 T at T=300 K does not influence the selected thermometric signal.

Effect of Coiling Operation on Strip Quality of 4.5% Si Steel in Twin-roll Casting Process.

Rapid solidification in the twin-roll casting process allows the production of thin strip with a unique combination of properties, directly from the melt. However, the production of the thin strip without any intermediate technological processing, is accompanied by strong demands on quality of the as-cast strip and requires full understanding of all aspects of twin-roll casting technology. The present study was aimed at an experimental analysis of the influence of continuous coiling in the twin-roll casting process on structure, properties and the shape of as-cast high silicon electrical steel strip. It was found that solidification, cooling and plastic deformation produce high residual stress heterogeneity in the as-cast strip which exists in a non-equilibrium state. When the compressive residual stress, attains a critical value the strip loses its flatness and waviness of a sinusoidal shape appears on the surface in the casting direction. When the tensile residual stress reaches the yield strength of the casting materials, cracks may be appear in the strip. The use of continuous coiling at elevated temperatures and with the as-cast strip under tension, leads to a change in structure, properties, geometry and shape of the as-cast strip. The structure and properties can be effectively controlled by regulating the temperature of the coiled strip and the shape can be controlled by regulation of the strip tension. The use of optimal temperature and strip tension during the continuous coiling operation are effective control strategies for stabilising structure, properties, and shape of the as-cast strip, reducing the residual stresses in the strip and improving its quality.

AC losses in multifilamentary HTS-composite tapes based on BiPbSrCaCuO

Some results of AC loss measurements are presented for 19, 61, 127-filamentary Bi-2223/Ag tapes prepared by the `powder-in-tube' method. All measurements have been made at T=77 K under sinusoidal transport current with frequency in the range of 30–600 Hz and the current amplitude up to 30 A. The measurements have been carried out both in self field conditions and at the external magnetic field applied to the tape at the different angles. The dependencies of the AC losses on current amplitude and frequency have been obtained. It is found that for all tapes the current amplitude dependencies of the AC losses show good agreement with the Norris prediction for an elliptical or strip geometry. The AC loss dependencies on frequency were linear. The measurements of AC losses in external magnetic field show that the change of AC losses is only through the change of the critical current. So the transport AC losses in the tapes are the `saturation losses' that is they are different from classic hysteresis losses.

Transport Properties ofBi2Sr2CaCu2O8Crystals with and without Surface Barriers

${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ crystals with electrical contacts positioned far from the edges are studied by transport measurements, then cut into narrow strip geometry, and remeasured. Instead of showing larger resistance, the strips display a dramatic drop in the resistance, enhanced activation energy, and nonlinear behavior due to strong surface barriers. The surface barriers also dominate the resistive drop at the first-order phase transition. Because the surface barriers are avoided in large crystals, we are able to probe the solid phase and find good agreement with the recent predictions of Bragg glass theory.

Magnetoquenched superconducting valve

A superconducting switch has been developed in a simple bilayer cross strip geometry using the magnetic fringe field of a ferromagnetic film to control the critical current in an underlying superconducting bridge. The magnetization of the ferromagnet is rotated in the plane of the film to vary the magnitude of the fringe field locally applied to the superconductor from negligible to substantial values. In the latter case, the magnetization is oriented such that the magnetic poles are along the edges of the cross strip directly above the superconductor. The large fringe field near the poles suppresses superconductivity over a length of order microns, giving rise to superconducting weak link behavior. A large modulation of the critical current is observed. The effect is demonstrated in the low Tc superconductors Pb (Tc=7.3 K) and Sn (Tc=3.9 K). Fabrication of the device involves minimal processing. Applications as a high speed switch, amplifier, nonvolatile storage cell, and controllable weak link are possible.

Star–triangle approach to boundary behavior in the two-dimensional Ising model

Hilhorst and van Leeuwen showed how to calculate boundary properties of the Ising model on the triangular lattice by iterating a mapping based on the star–triangle transformation. We apply this approach to the Ising model with homogeneous initial couplings in both the semi-infinite and strip geometries. Several exact results for the boundary correlation length and the magnetization are reproduced. The correlation-dimensionality transition for enhanced edge couplings (dual of Abraham’s interface-unbinding transition) is also considered.

Disk-loaded monopoles with parallel strip elements

Design considerations and experimental performance data are presented for disk-loaded folded monopoles in which the vertical elements consist of flat parallel strips separated by a dielectric. The presence of the dielectric and the flat strip geometry permit control of resonance frequency, susceptance slope, and impedance step-up ratio over ranges suitable for the design of electrically small antennas with a broad double-tuned response. Graphs are presented giving the impedance step-up ratio due to folding for various strip dimensions derived from static calculations. Experimental results are shown for antennas with heights in the range of one-eighth to one-tenth wavelength.

Critical-state model for harmonic generation in a superconducting microwave resonator

A critical-state model is developed for the treatment of the nonlinear ac response of a superconducting coaxial-type transmission line. Analytical results are presented for the resistance and reactance as well as the response at overtone frequencies. Center conductors of both elliptical and rectangular thin-film cross section are considered. The dominant response, in the case of the elliptical geometry, is found to be independent of the aspect ratio of the ellipse. Significant differences are found between the elliptical and strip geometries. These differences are due to the difference in structure of the critical state in the two geometries. The model is applied to resonators with the assumption that end effects can be neglected. Qualitative agreement is found with experimental results. @S0163-1829~97!01317-9#

Wedge silicon detectors for the inner trackering system of CMS

One “wedge” Double Sided Silicon Detector prototype for the CMS forward inner tracker has been tested both in laboratory and on a high energy particle beam. The results obtained indicate the most reliable solutions for the strips geometry of the junction side. Three different designs of “wedge” Double Sided detectors with different solutions for the ohmic side strip geometry are presented.

Gallium arsenide for vertex detectors

We give an overview of recent results in the development of GaAs detectors: they now have 100% charge collection efficiency with good reliability; they are bond-compatible with silicon detectors, with both strip and pixel geometry. New results on pixel detectors are reported as well as a short summary on the radiation hardness of SIU-GaAs detectors.

Patterning for planar waveguides

The synthesis of planar strip geometries for planar waveguides by a layered manufacturing technique, called fused deposition modelling (FDM™), is presented. Channels were deposited on silicon wafers by melting a thermoplastic polymer and extruding it through a small orifice. Sol-gel-derived, amorphous fluoride films were dip-coated into these channels and yielded straight, 1 mm strips on subsequent removal of the polymer.

Self-field a.c. losses in mono- and multi-filamentary Bi-2223/Ag tapes at power frequencies

The measured self-field a.c. losses in mono- and multi-filamentary tapes with varying transport current, frequency and voltage tap configurations are compared to theoretical models. The observed losses are found to approach asymptotic values when the loop of the voltage taps is comparable to the width of the tapes. The measured quadrature electric field is found to be nonlinear with applied current. A model is presented to describe this nonlinearity for homogeneous elliptical and strip geometries. The possible significance of the model to the observed losses is also discussed.

Computer simulation of complex dragline operations

ABSTRACT Large walking draglines are capital intensive pieces of equipment. To maximise the return on investment and to improve the performance of a dragline, its operation and influencing parameters must be understood and fully analysed with the view of optimising the process. Finding the normal working ranges for a given dragline and optimising its operation usually requires that various possible mining scenarios and pit configurations be assessed. This task is normally both difficult and time consuming and requires an analytical solution. This is ideally suited to the application of computer simulation methods. An integrated computer simulation model was developed to assist the mine engineer in planning dragline operations. The model uses a 3D geological modelling system to access the geological database. The model can simulate complex multi seam operations and different digging methods using a developed database. A generalised computer package, DSLX, is used to simulate various dragline digging methods. The software is based on a highly flexible simulation language which uses predefined functions to build strip geometry, working benches, blast profiles and spoil piles. The basic features of the simulation model, the algorithms used in developing dragline pit designs. and the results of two case studies are discussed.

Study of spatial resolution and efficiency of silicon strip detectors with charge division readout

The spatial resolution and efficiency of silicon strip detectors with a large readout pitch using charge division readout have been studied. In particular, we aimed for an optimisation of the strip detector layout for a given readout pitch. We have used a method of analytical calculation of strip capacitances for different strip geometries which allowed us to study a series of different configurations. The study has been performed taking into account all important limitations and requirements for a tracking system like the semiconductor tracker of the ATLAS detector. In full simulations a series of effects like the influence of magnetic field on the charge collection in the detectors, ballistic deficit in the electronics, distributed structure of silicon strips, electronic cross talk via the interstrip capacitance, noise injection from adjacent channels, effect of the charge collection time on timing performance of silicon strips has been taken into account. The results show that a significant improvement of spatial resolution and efficiency can be obtained in configurations with more than one intermediate strip.

Direct observation of the current distribution in thin superconducting strips using magneto-optic imaging.

Magneto-optic imaging was used for a detailed study of the flux and current distribution of a long thin strip of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ placed in a perpendicular external magnetic field. The inverse magnetic problem, i.e., that of deriving from a field map the underlying current distribution, is formulated and solved for the strip geometry. Applying the inversion to the magneto-optically found field map we find on a model-independent basis the current distribution across the strip to be in remarkable agreement with the profile predicted by the Bean model. The paper also presents results on the behavior of the Bi-doped YIG film with in-plane anisotropy which we use as field indicator, explaining why previous measurements of flux density profiles have displayed surprisingly large deviations from the expected behavior. \textcopyright{} 1996 The American Physical Society.

Charge collection efficiency in double-sided silicon microstrip detectors

We present measurements of charge collection efficiency in double-sided silicon microstrip sensors using the signal from a pulsed laser. We compare the efficiency as a function of voltage and position for various strip geometries. The sensors studied here were manufactured as prototypes for the SVXII detector, an upgrade of the CDF silicon vertex detector for run II of the Fermilab Tevatron. Large inefficiencies were observed in prototypes with certain n-side strip geometries.