Dielectric loaded resonators, by virtue of their high sensitivity, are a de facto standard for the measurement of the microwave surface impedance Z of good conductors, including superconductors. However, new perspective applications of superconductors request measurements in increasingly extreme conditions: cryogenic and magnetic environments, often combined together. Careful evaluations of the dielectric resonator (DR) design are necessary to operate in these conditions. Moreover, the evaluation of the uncertainties and the issues related to an appropriate calibration become problematic. We present here a performance analysis of DRs designed for cryogenic temperature and high magnetic field operation and some sample experimental results on Z measurements on the most technologically interesting superconductors.

We present here a microwave (16 GHz) investigation of the complex surface impedance in a dc magnetic field (up to 1 T) of Fe(Se,Te) thin ( 300 nm) films. We derive the vortex parameters: the flux-flow resistivity yields information on the dynamics of the quasiparticles, the Labusch parameter yields a measure of the steepness of the pinning potential wells, and the depinning frequency assesses the frequency range where the material is suitable for high-frequency applications in a dc magnetic field. We compare the results to the data obtained in YBCO, Nb and Nb3Sn.

The high frequency vortex motion in Nb3Sn was analyzed in this work up to 12 T. We used a dielectric loaded resonator tuned at 15 GHz to evaluate the surface impedance Z of a Nb3Sn bulk sample (24.8 at.%Sn). From the field induced variation of Z, the high frequency vortex parameters (the pinning constant k p , the depinning frequency ν p and the flux flow resistivity ρ ff ) were obtained over a large temperature and field range; their field and temperature dependencies were analyzed. Comparison with other superconducting materials shows that high frequency applications in strong magnetic fields are also feasible with Nb3Sn. In the present work, we report the first measurements about the microwave response in Nb3Sn in strong magnetic fields.

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<p class="Abstract">3D-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 <em>Q</em> of the DR with a disk-shaped sample placed on a DR base, with <em>Q</em> obtained when the sample is substituted with an air gap, allows a reliable determination of the loss tangent.</p>