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Applied Superconductivity, IEEE Transactions on

Issue 2  Part 3 • Date June 1999

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Displaying Results 1 - 25 of 423
  • The 1998 Applied Superconductivity Conference

    Page(s): 0_1 - 0_30
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    Freely Available from IEEE
  • Superconducting electronics coming to market

    Page(s): 2825 - 2836
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    Superconducting electronic (SCE) products have been commercially available for over 25 years. However, the market remained extremely small. A conservative estimate of the total 1997 volume gives, approximately, US$ 30 million. Until 1997, LTS SQUID systems, mostly for biomagnetic research, represented the dominant share. High-temperature superconductivity (HTS) hadn't yet had any real impact on the market. However, in 1998 HTS filter subsystems for wireless telecommunication receiver front end represent a small, but rapidly growing segment of the market. This paper gives highlights of technical achievements and progress in SQUIDs, and in SCE for wireless, while emphasizing obstacles to and opportunities for much larger markets. A summary of an industry survey conducted prior to writing the paper is also included. Most other SCE products and the identified potential new products, LTS and HTS, represent very small niches having little chance for major growth. These are not discussed. A notable exception is single flux quantum digital electronics. It does not command any market share today, but still has the largest long-term potential for a very large market in telecommunications and in massive data processing. View full abstract»

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  • Recommended directions of research and development in superconducting electronics

    Page(s): 2837 - 2848
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    For some time, work has been continuing within the U.S.A. on a "Technology Roadmap for the Superconducting Electronics Industry". A similar roadmap exercise is underway in Europe, and in Japan, recently announced research projects in superconductivity involved a detailed planning process. However, the U.S. Roadmap is not complete, and a consensus of industry opinion has not yet been reached on its recommendations. This manuscript should be regarded as a distillation of inputs from many sources, heavily weighted with the author's own prejudices. He suggests that a system level view of superconducting electronics technology should lead to revisions of today's research priorities. In particular, the importance of the cryocooler and cryopackage in each system has broad implications, even affecting the directions of materials and device research. View full abstract»

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  • Application of TBCCO based HTS devices to digital cellular communications

    Page(s): 2849 - 2852
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    Linear microstrip resonators suffer from high peak current density inside the resonators which limit the power handling characteristics and hence their use in cellular transmitter applications. To realise higher power filter and combiner networks for cellular applications it is possible to use two dimensional microstrip resonators (such as disks) to equalise the internal current distribution. We have designed and tested such microstrip resonators, fabricated from TBCCO 2212 thin films deposited by RF sputtering onto 50 mm diameter LaAlO/sub 3/ substrates. The R/sub s/ of such films has been measured at 5.5 GHz using a sapphire dielectric resonator and shown to be less than 1 m/spl Omega/ scaled to 10 GHz and at 80 K. The power handling of disk resonators designed for operation in the PCS and DCS1800 cellular bands has been shown to be superior to that of linear resonators fabricated from similar material. The operation of such devices using high power levels and realistic signals encountered in 2/sup nd/ generation digital cellular systems (e.g., DQPSK and GMSK) will be presented. The application of these devices to 3/sup rd/ generation wide band CDMA systems will also be discussed. View full abstract»

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  • Performance of superconducting dual mode resonators with different input/output feedline angles

    Page(s): 2853 - 2856
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    High-temperature superconducting (HTS) dual mode ring resonators have been fabricated using YBa/sub 2/Cu/sub 3/O/sub 7-x/ films on MgO substrates. Epitaxial YBCO superconducting thin films were deposited on MgO substrates by pulsed laser deposition (PLD). The transition temperature of YBCO thin films were 85-88 K. Dual mode ring resonators are patterned using YBCO superconducting films by conventional photolithography and wet-etching process. The opposite side of the substrate has been made up the ground plane with two layer metal films (Ti/Ag) deposited by e-beam and thermal evaporation. Two types of dual mode ring resonators were fabricated with different input and output feedline angles of 60/spl deg/ and 100/spl deg/. The frequency response shows the resonant center frequency of about 8.5 GHz and stringent narrow bandwidths. These types of dual mode ring resonators could be utilized for dual mode resonator based filters for satellite communications. View full abstract»

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  • HTS power filters for output multiplexers in satellite communications

    Page(s): 2857 - 2861
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    The paper reports on advances in the development of high temperature superconducting 40 MHz bandwidth four-pole bandpass filters with elliptic frequency response for 3.4-4.2 GHz (extended C-band) output multiplexers of communication satellites. By employing the concept of "edge-current-free" disk and ring resonators the filters possess a small size but can handle 60 W transmitted power with sufficiently low insertion loss and intermodulation. Measurements of the unloaded Q-factor and power handling as function of the temperature, performed at single disk resonators made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// on LaAlO/sub 3/ and sapphire substrates indicate the conditions under which the required Q-factor of about 1.5/spl middot/10/sup 5/ and sufficiently low nonlinear response up to an oscillating power of 15 kW can be obtained. Approaches for shifting the resonant frequencies of unwanted modes relative to the resonant frequency of the employed TM/sub 010/-mode are outlined and shown to be necessary for the envisaged multiplexer applications. View full abstract»

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  • Effects of the finite HTS film thickness on the resonant frequency of the axially symmetric TE/sub 01/spl delta// mode of a parallel plate dielectric resonator

    Page(s): 2862 - 2865
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    An axially symmetric TE/sub 01/spl delta// mode of a parallel plate dielectric resonator is studied for investigating effects of the film thickness (t) of high-temperature superconductor (HTS) films on the mode resonant frequency (f/sub 0/). A sapphire-loaded cylindrical cavity resonator with YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) endplates and mode f/sub 0/ of about 19 GHz has been prepared and its unloaded Q (Q/sub 0/) and f/sub 0/ are investigated at temperatures below the critical temperature of YBCO. From theoretical analysis, it appears that f/sub 0/ changes by less than 0.4% for different t's when the ratio of t to the London penetration depth (/spl lambda/) is more than 10/sup -2/. Meanwhile, from experiments, significant dependence of f/sub 0/ on the gap distance (s) between the sapphire rod and the top endplate is observed with f/sub 0/ changing by about 1 GHz (/spl sim/5%) from 19.578 GHz to 18.648 GHz, as s increases from 0 to 1 mm at 77 K. The experimental values of f/sub 0/ are observed to agree well to the calculated f/sub 0/. Applicability for tunable high-Q resonators is described. View full abstract»

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  • Design and fabrication of coplanar YBCO structures on lithium niobate substrates

    Page(s): 2866 - 2869
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    YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) with low RF losses has been successfully deposited onto lithium niobate (LNO) to improve the performance of electrooptic Mach-Zender modulators. Epitaxial, c-axis oriented superconducting YBCO thin films have been grown on X-cut LNO single crystals with a yttria-stabilized zirconia (YSZ) buffer layer by RF magnetron sputtering. This buffer layer is needed to obtain good superconducting properties of the YBCO grown. Numerical tools have been developed to analyze CPW structures based on YBCO/YSZ/LNO trilayers, and they indicate that YSZ thickness has to be kept to the minimum necessary for good YBCO growth. With this restriction, the RF losses of YBCO/YSZ/LNO samples have been measured. The results from these measurements are used to quantify the performance enhancement in a Mach-Zender modulator using YBCO electrodes. View full abstract»

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  • Fine tuning of high Q HTS shielded resonators using HTS coated SrTiO/sub 3/ pucks

    Page(s): 2870 - 2873
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    The combination of very low loss dielectric single crystal materials (such as sapphire) with a HTS shielding enclosure has led to the achievement of high Q resonators operated in the temperature range 40 K-70 K which show great promise for frequency standard applications. A number of problems remain to be solved. We have already reported how high frequency stability with minimum temperature control may be achieved by means of composite dielectric pucks, the components having opposite signs for their temperature coefficients of permittivity. A second requirement for a frequency standard is that it should possess a specified frequency. Here we report implementation of electronic tuning of a sapphire dielectric puck resonator by using a SrTiO/sub 3/ (STO) tuning element situated in the evanescent field region outside the sapphire puck. In addition the same structure may be used when the sapphire and STO elements act as weakly coupled resonators so that the resonant frequency becomes a very sensitive function of temperature, allowing the possibility of very high resolution thermometry. View full abstract»

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  • Properties of SNS Josephson junctions fabricated by 200 keV oxygen implantation into YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

    Page(s): 2874 - 2877
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    The properties of SNS Josephson junctions in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films have been investigated, which were fabricated by oxygen irradiation at 200 keV through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500/spl deg/C in an oxygen atmosphere, the implanted region has a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of <15 K. Close to the coupling temperature the critical current shows a nearly complete modulation in an applied magnetic field. This indicates a homogeneous current distribution in the junctions and therefore a homogeneous defect distribution throughout the implanted and subsequently annealed region of the superconducting microbridges. Over the entire temperature range of Josephson coupling, the junctions exhibit resistively shunted junction like I-V characteristics with additional excess current. Furthermore, the exponential dependence of the critical current on temperature is in good agreement with conventional superconductor-normal-superconductor proximity effect theory. View full abstract»

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  • High-Tc Josephson junctions on micro V-shape groove prepared by focused ion beam

    Page(s): 2878 - 2881
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    For Josephson junctions using a narrow groove on a substrate etched by a focused ion beam (FIB), there is a strong relation between junction properties and groove shapes. We have developed the FIB milling method which has flexibility to produce a variety of different groove shapes. V-shape grooves with different sizes (width=215-594 nm, depth=27-92 nm) have been formed with the same slope angle on the MgO [100] substrate. The top surface profile of the 300 nm thick YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) film had the same V-shape as the grooves on the substrate, but the YBCO groove widths were 110 nm narrower than the FIB groove widths. The 3 /spl mu/m width junctions fabricated on these grooves showed RSJ type I-V curves without exception and had the average of critical current (Ic) values of 0.520 mA at 4.2 K. View full abstract»

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  • Asymmetrical FIB junctions as components for HTS SFQ circuits

    Page(s): 2882 - 2885
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    High-temperature superconductor (HTS) Josephson junctions have been formed on asymmetrical V-shape grooves etched by a Ga focused-ion beam (FIB). The asymmetrical groove is made by tilting the substrate during FIB etching. Transmission electron microscopy (TEM) shows a tilted V-shape groove and two clear grain boundaries in the NBCO film. The I-V characteristics of the junctions are controlled by the dose amount of Ga ions and the NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (NBCO) film thickness. The inductance of the lines was estimated to be 0.5 pH//spl mu/m for the film thickness of 200 nm for the characteristics of a SQUID fabricated with the asymmetrical FIB junctions. View full abstract»

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  • Electrical properties of electron and ion beam irradiated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//

    Page(s): 2886 - 2889
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    An electron beam with sufficient energy can be used to create a high quality Josephson junction in a single layer of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//. The number of junctions thus produced is severely limited by the serial nature of the technique. An alternative method to create similar high quality Josephson junctions without such a serious throughput limitation is possibly the combination of high resolution masking and ion irradiation. For this reason we have studied the electrical properties of both electron and proton irradiated YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// in some detail. It was found that the resistivity of electron beam irradiated barriers of intermediate length (200 nm) are strongly influenced by a proximity effect when the irradiated material has a finite T/sub c/. At higher electron doses the superconducting properties are fully suppressed and the electrical behaviour is dominated by a Variable Range Hopping mechanism. View full abstract»

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  • Fabrication of YBaCuO junctions by the irradiation of focused ion beam

    Page(s): 2890 - 2893
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    We have fabricated Josephson junctions in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBaCuO) thin films by the irradiation of focused ion beam (FIB). We used Be/sup 2+/ ions with the energy of 200 keV. When the fluence of Be/sup 2+/ ions was 1.2/spl times/10/sup 16/ ions/cm/sup 2/, the I-V characteristics of the junctions at 4.2 K showed RSJ-like characteristics with the excess current. The I/sub c/R/sub n/ product of the junctions was 1.1 mV at 6.3 K. Shapiro steps up to 20th step could be observed by the irradiation of 8.47 GHz microwave at 6.3 K. The magnetic modulation curve of the junction at 4.2 K was similar to the Fraunhofer pattern. These characteristics remained unaltered after preservation in a desiccator for 6 months. View full abstract»

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  • Fabrication of HTS Josephson junctions on substrates prepared by focused ion beam system

    Page(s): 2894 - 2897
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    YBCO Josephson junctions were fabricated by using a Focused Ion Beam (FIB) of 20-nm diameter gallium ion beam. We first made trenches of 100-nm width and 300-nm depth on LaAlO/sub 3/ (LAO) substrates that were covered by 100-nm chromium (Cr) conducting layer. After removing the conducting layer by chemical etching, YBCO followed by a gold layer was pulsed laser deposited in-situ. The deposited YBCO was disconnected over the trenches and the gold layer filled the trenches and made connections between the separated YBCO so that it formed SNS junctions. We observed proximity coupling up to 86 K. View full abstract»

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  • Simultaneous quasiparticle and Josephson tunneling in BSCCO-2212 break junctions

    Page(s): 2898 - 2901
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    Tunneling measurements are reported for superconductor-insulator-superconductor (SIS) break junctions on underdoped, optimally-doped, and overdoped single crystals of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+/spl delta// (Bi-2212). The junction I-V characteristics exhibit well-defined quasiparticle current jumps at eV=2/spl Delta/ as well as hysteretic Josephson currents. The quasiparticle branch has been analyzed in the framework of d(x/sup 2/-y/sup 2/) (d-wave) superconductivity and indicates that there is preferential tunneling along the lobe directions of the d-wave gap. For overdoped Bi-2212 with T/sub c/=62 K, the Josephson current is measured as a function of junction resistance, R/sub n/, which varied by two orders of magnitude (1 k/spl Omega/ to 100 k/spl Omega/). I/sub c/R/sub n/ product is proportional to the 0.47 power of I/sub c/ and displays a maximum of 7.0 mV. When the hole doping is decreased from overdoped (T/sub c/=62 K) to the underdoped regime (T/sub c/=70 K), the average I/sub c/R/sub n/ product increases as does the quasiparticle gap. The maximum I/sub c/R/sub n/ is /spl sim/40% of the /spl Delta//e at each doping level, with a value as high as 25 mV in underdoped Bi-2212. View full abstract»

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  • Two-stage S-band DC SQUID amplifier

    Page(s): 2902 - 2905
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    A 6 mm/spl times/6 mm chip comprising two identical DC SQUID based amplifiers (SQAs) has been designed, fabricated and tested as a two-stage RF amplifier in a frequency range 3.5-4.0 GHz. Each SQA consists of a double washer type DC SQUID with novel integrated input resonant circuit. The reflection coefficient of both input and output of the SQA has been measured in the two stage configuration. To avoid SQA saturation at the wide band noise tests a tunable 40 MHz bandpass YIG-filter has been used. The following parameters of the two-stage SQA have been measured at the 3.65 GHz: gain of (17.5/spl plusmn/1) dB, 3 dB bandwidth of about 250 MHz, and noise temperature (4.0/spl plusmn/0.5)K what corresponds to intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.6 /spl mu//spl Phi//sub 0/Hz/sup -1/2/ and energy sensitivity /spl epsiv//sub i//spl ap/75 /spl planck/ (7.8/spl middot/10/sup -33/ J/Hz). If the measured RF mismatch between the input/output of SQA and source signal/post-amplifier is taken into account a gain of (20.5/spl plusmn/1.5) dB and noise temperature as low as (2.5/spl plusmn/1.0) K (intrinsic flux noise S/spl phi//sup 1/2//spl ap/0.4 /spl mu//spl Phi//sub 0/Hz/sup -1/2/, energy sensitivity /spl epsiv//sub i//spl ap/47 /spl planck/) can be estimated. View full abstract»

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  • Advanced version of two-stage dc SQUID-based amplifier

    Page(s): 2906 - 2908
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    An advanced version of a two stage dc SQUID-based low frequency amplifier and its measured signal and noise parameters are presented in this report. An effective input inductance of about 2.9 /spl mu/H, a SQUID's inductance of about 11 pH, an effective coupling k/sup 2/ of about 0.24 and a white noise level of about 0.87 /spl mu//spl Phi//sub 0//Hz/sup 1/2/ at 4.2 K were achieved. The gradiometric scheme, a modified distributed damping filter and a modified geometry of coupling transformers have been used to suppress the influences of the external noise and resonances in the SQUID microstructure. View full abstract»

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  • A ring-weak link superconducting quantum electron interferometer

    Page(s): 2909 - 2910
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    Properties of a new superconducting quantum election interferometer are investigated. This new interferometer has only one tunnel junction as compared to a classical SQUID which has two junctions. Our measurements have shown that the amplitude of resistance oscillations versus the magnetic field increases as the temperature is lowered. View full abstract»

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  • Noise analysis of the double-loop SQUID with unshunted junctions

    Page(s): 2911 - 2914
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    The unshunted (un) SQUID is a two-junction device whose Josephson junctions are damped at high frequencies only. Single-valued rather than hysteretic behaviour on the negative resistance region is obtained by using a voltage bias rather than a current bias. We have studied numerically the noise properties of the un SQUID with a double-loop (dl) washer configuration, in which the SQUID inductance is capacitively split into two loops. Our simulations with /spl beta//sub c/=0.7 and /spl beta//sub l/=0.5-3 suggest that noise level in the un dl SQUID depends more weakly on the device parameters than in the un SQUID. The best energy resolution obtained in the smooth area of the IV curves is /spl epsiv//spl ap/5k/sub B/T/spl radic/(LC) but in narrow pockets in the non-smooth region /spl epsiv//spl ap/3k/sub B/T/spl radic/(LC) is approached. View full abstract»

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  • A 1-MHz low noise preamplifier based on double relaxation oscillation SQUIDs

    Page(s): 2915 - 2918
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    A low noise and wideband preamplifier based on Double Relaxation Oscillation Superconducting Quantum Interference Devices (DROSs) has been realized. A major advantage of a DROS is that it can be operated in a simple flux modulation. So far, biomagnetic measurements performed in our group required only a limited bandwidth smaller than 100 kHz. Other applications, like for instance readout of radiation and particle detectors, demand a larger bandwidth. In this paper, we will discuss our efforts aimed at increasing the operational bandwidth of a DROS in flux locked loop. Presently, a flux locked loop scheme with a -3 dB bandwidth of 1.45 MHz has been built. With this system a white flux noise of 8 /spl mu//spl Phi//sub 0///spl radic/Hz was measured with a 1/f-corner frequency of 10 Hz. The slew rate was 2.5/spl middot/10/sup 5/ /spl Phi//sub 0//s. With the mutual input inductance of 6.7 nH, an input current noise of the preamplifier of 2.5 pA//spl radic/Hz was found and a current slew rate of 80 mA/s. We will discuss the suitability of our DROS-based preamplifier for readout of cryogenic particle detectors based on superconducting tunnel junctions. View full abstract»

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  • Smart SQUIDs based on relaxation oscillation SQUIDs

    Page(s): 2919 - 2922
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    Smart SQUIDs based on double Relaxation Oscillation SQUIDs (DROS) and a superconducting up-down counter have been developed. DROS and counter form a flux locked loop on one single chip. The DROS output consists of a series of pulses that controls the two up and down write gates of the counter. The pulsed output structure of the DROS constitutes the internal clock for this single-chip device. Several prototypes were built with a clock frequency of 100 MHz, a linear operation flux range of about 2.5 /spl Phi//sub 0/, and a white noise level of 6.5 /spl mu//spl Phi//sub 0///spl radic/Hz. The smart SQUID is in principle a promising device for application in multichannel SQUID systems. View full abstract»

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  • Design of series SQUID array suppressing Josephson oscillation interference between element-SQUIDs

    Page(s): 2923 - 2926
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    We have designed and fabricated single-stage series SQUID arrays usable for current amplifiers with filtering resistors in its input coil. From experimental results, it was revealed that filtering in each SQUID in the array successfully suppressed the interference between element-SQUIDs. An array with 1000 SQUIDs showed relatively smooth flux-voltage curves, large voltage swing (/spl sim/50 mV) and current-voltage conversion coefficient (/spl sim/1000 V/A). View full abstract»

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  • First results for a novel superconducting imaging-surface sensor array

    Page(s): 2927 - 2930
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    A superconducting imaging-surface system was constructed using 12 coplanar thin-film SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter lead imaging-plane. Some measurements included two additional sensors on the "back" side of the superconducting imaging-plane to study the field symmetry for our system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been used to: (a) understand the noise characteristics of the dewar-SQUID imaging plate arrangement, (b) to verify the imaging principle, (c) measure the background rejection factor of the imaging plane, and (d) compare superconducting materials for the imaging plane. A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shape and absolute values of the measured and predicted curves agree very well indicating the system Is behaving as a gradiometer in accordance with theory. The output from SQUIDs located behind the imaging surface that sense background fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded form the background sensors by more than a factor of 1000. Measurement of the symmetry of sensor sensitivity to uniform fields exactly followed theoretical predictions. View full abstract»

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  • Continuous feedback operation of a two-stage dc SQUID system

    Page(s): 2931 - 2934
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    We report on the continuous feedback operation of a two-stage dc Superconducting Quantum Interference Device (SQUID) system in which one SQUID works as a low-noise preamplifier to read out a second low-noise sensor SQUID. We first flux-locked the readout SQUID and measured the characteristics of the sensor SQUID, including its current-voltage characteristics, current-flux characteristics, and noise spectrum. We then investigated how the two SQUIDs could work together by simultaneously flux-locking both the sensor and the readout SQUIDs. With this two-SQUID flux-locking scheme, we recovered the noise spectrum of the sensor SQUID to within 4%. We discuss how to understand and optimize the two-stage SQUID feedback system. View full abstract»

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IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde