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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of effective coupling strength in high-frequency SQUIDs (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6276-6282 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Understanding the coupling mechanism between SQUID (superconducting quantum interference device) loop and resonator in high-frequency SQUIDs is essential for the application of these devices in sensitive magnetometers or controllable microwave devices. We have investigated, therefore, two kinds of planar microstrip tank circuit resonators: (1) S-shaped λ/2-resonators with direct or indirect coupling to the SQUID loop with optional flux-focussing pads and (2) conventional rf-washer-SQUID structures for which we have found resonant modes of the washer providing a coupling to the SQUID loop. A lumped element representation of SQUID loop and resonator is presented in order to describe the effective SQUID-resonator coupling in case of direct or indirect coupling. According to this approach, the square of the effective coupling constant k in both cases is equal to the ratio of the magnetic energy stored in the SQUID loop to that stored in the resonator. For the indirect coupled S-shaped λ/2-resonators, k can be described in terms of a geometry-defined mutual inductance. The predictions of the lumped element description are compared with simulations using a standard full-wave analysis computer program in order to quantify the effect of the different layouts on microwave current distribution and on k. A method for the determination of k by simulation is described, leading to useful design rules for the optimization of high-frequency SQUIDs. The simulation results will also be compared with experimental data. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360508
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  • 2
    Electronic Resource
    Electronic Resource
    Operation of high-temperature rf SQUID magnetometers using dielectric SrTiO3 resonators (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3183-3185 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The operation of YBa2Cu3O7 rf superconducting quantum interference devices (SQUIDs) using a dielectric SrTiO3 resonator as tank circuit was tested. At 77 K, we attained for such resonators unloaded quality factors Q0 up to 7000 at resonant frequencies near 1 GHz, when measuring without electromagnetic shielding. For a washer SQUID with an area of 4×4 mm2 and an inductance of (approximately-equal-to)100 pH, which was properly coupled to the resonator, we measured an approximately 60 μV peak-to-peak SQUID signal and a white flux noise spectral density of SΦ1/2=1×10−5Φ0/(square root of)Hz, corresponding to a field sensitivity of BN=105 fT/(square root of)Hz. With an additional single-layer flux transformer with a diameter of the pickup loop of 22 mm in flip-chip arrangement, the field sensitivity was improved to 30 fT/(square root of)Hz. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115156
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental evaluation of the nonlinear surface resistance of YBa2Cu3O7−x step-edge grain boundary Josephson junctions (1996)
    Springer
    Journal of superconductivity 9 (1996), S. 233-236 
    Details
    ISSN: 1572-9605
    Keywords: Microwave impedance ; microstrip resonator ; Josephson junction ; nonlinear power dissipation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The temperature, microwave current, and dc magnetic field dependencies of the effective surface resistanceR s of YBa2Cu3O7−x grain boundary Josephson junctions have been investigated at 6 GHz. The junctions were prepared on stepped LaAlO3 substrates and incorporated into tapered linear half-wavelength microstrip resonators. The characteristic parameters of the heterogeneous resonator were analyzed theoretically considering the junction as a lumped element of complex impedance. The microwave properties of the junction could then be extracted and related to their characteristic dc transport properties. The critical currentI c of the junction was found to limit the linear power dissipation in the superconducting strip. At microwave currents aboveI c , highly nonlinear microwave losses occurred, which displayed a characteristic magnetic field modulation. At even higher currents,R s saturated at a level corresponding to the normal resistanceR n of the junction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728308
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