1,721,035 research outputs found
Ring quasioptical sapphire resonator for studing impedance properties of superconductors
No full textMicrowave measurements to assess the properties of superconducting materials for applications.
No full textA rectangular dielectric resonator for measurements of the anisotropic microwave properties in planar conductors
No full textWe designed, realized and tested a TE011-mode rectangular, high-permittivity, dielectric resonator, in order to obtain a measuring device capable of applying straight microwave currents to conductive samples. We characterized the prototype by means of extensive simulations that we compared to experimental results. Finally, we tested the device on a strongly anisotropic graphite sample. We found that the rotation of the sample produced significant changes in the response of the device. We conclude that the proposed rectangular dielectric resonator can be used as a device to detect the anisotropy of conductive samples
Design and test of a microwave resonator for the measurement of resistivity anisotropy
No full textThe measurement of the microwave surface impedance is a fundamental characterization tool for a wide class of conducting, semiconducting and superconducting materials. In many cases, material anisotropy can show up as an intrinsic or tailored property, and its measure is often desirable. Microwave resonators can be designed to give at the same time non-destructive and highly sensitive measurements, in particular with the surface pertur- bation method for planar samples. Rectangular resonators can be designed to preserve sen- sitivity to the anisotropy of the samples under study, since they can induce straight currents on the sample. We designed a two-mode rectangular dielectric resonator with straight currents on the sample under testing, where the second mode can be used for val- idation of the results. We realized the rectangular dielectric resonator using a moderate-j dielectric (LaAlO3) crystal, which showed the two designed microwave modes. Using the lowest mode, we tested the sensitivity of the device to the anisotropy using a graphite sam- ple. The device was able to track the angular dependence of the microwave response, showing the effect of the anisotropy. The second mode confirmed the results. Thus, despite its low Q factor, the present device is able to track the anisotropy of highly lossy conductors
Superfluid Density and Vortex Dynamics in S/F/S Heterostructures
No full textWe present electrical transport measurements in the microwave range in Superconductor/Ferromagnet/ Superconductor Nb/Pd0.84 Ni0.16 /Nb heterostructures, with different thickness of the ferromagnetic layer. We employ a wideband (1–20 GHz) Corbino disk technique to obtain the real part of the microwave resistivity in the vortex state. We focus on the fundamental properties that can be derived from measurements of the pinning property of the vortices. In particular, we estimate the superfluid density at the same reduced temperature. We describe the method to derive from the measurements the pinning constant kp, and to estimate the the superfluid density. We find a strong reduction of the superfluid density with the ferromagnetic layer thick- ness. Finally, we compare our results to zero-temperature superfluid density estimated in bilayers
Characterisation of dielectric 3D-printing materials at microwave frequencies
No full text3D-printer materials are becoming increasingly appealing, especially for high frequency applications. As such, the electromagnetic characterisation of these materials is an important step in evaluating their applicability for new technological devices. We present a measurement method for complex permittivity evaluation based on a dielectric loaded resonator (DR). Comparing the quality factor Q of the DR with a disk-shaped sample placed on a DR base, with Q obtained when the sample is substituted with an air gap, allows a reliable determination of the loss tangent
The intrinsic surface impedance of coated conductors
No full textCoated conductors, i.e. superconducting thin films grown on tapes consisting in metallic substrates, is an enabling technology for the use of the high-T c YBa2Cu3O7-δ superconductor in applications requiring long superconducting cables, such as high field magnets and electric power distribution grids. The largely used d.c. measurements of the material current carrying capabilities would benefit from being integrated and complemented by local measurements of the material complex a.c. resistivity. Despite the potential of this approach, high frequencies measurements are hindered by the highly conducting substrate, which obscures the superconductor response. In this manuscript we address the problem of extracting the superconductor impedance by properly taking into account the substrate contribution
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