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In this paper we explore the effects of open and shorted Josephson Junctions (JJs) on the current-voltage (I-V) curve, and the voltage-field (V-B) curve of two-dimensional high temperature superconductor (HTS) Gaussian distributed Superconducting Quantum Interference Device (SQUID) Arrays (SQAs). We examine two cases here. The first case involves having a portion of the parallel rows of junctions containing either a single open or shorted junction. The second case involves an array having large blocks of open JJs. The large blocks represent a large damaged area on an array.

This paper presents an extension to the subspace-based direction-of-arrival (DOA) estimation algorithm dimensionality reduction multiple signal classification (DR-MUSIC). The extension operates with a single six-component vector sensor collecting multiple temporally displaced data sets. The temporal displacements invoke phase-shifts specific to the carrier frequencies of each signal to be located and are arranged into a matrix that is combined via tensor product with the arrival angle function steering matrix used in DR-MUSIC's iterative search. This procedure creates a more robust steering matrix that can resolve the directions of a number of signals greatly exceeding the number of antenna elements while rejecting interfering signals with impressive accuracy. Simulations demonstrate that the method also performs well under sub-zero SNR and SIR conditions.

In this investigation we explore the effects of nonuniform magnetic bias fields on the voltage-flux curve of large two-dimensional arrays of superconducting quantum interference devices (SQUIDs). The SQUID arrays (SQAs) contain 1020 SQUIDs modeled with parallel coupling in the x-direction and series coupling in the y-direction. Each array is composed of individual SQUID elements having non-uniform size loop areas, resulting in a non-uniform inductance parameter $\beta_{L}$ , and a single “anti-peak” feature at zero magnetic field in the voltage-flux transfer function. We examine the changed induced in the profile of the transfer function by gradients in the magnetic field in both the x- and y-directions. The height, slope, and symmetry of the anti-peak feature is compared with that from the same SQA exposed to a uniform field.

The capability of an all-niobium superconducting quantum interference device (SQUID) array to operate as an electrically small antenna capable of detecting radio frequency from distant sources was demonstrated. The measurements were performed in three different arrays, with each array consisting of 2400 identical cells. The intrinsic broadband characteristics of the device were confirmed by the flat frequency response of the ratio of the output and input voltages (the S21 parameter) of the array between 300 kHz and 1 GHz. Setting the device to its optimal operating parameters allowed the detection of signals from local frequency-modulation stations.

High-temperature-superconductor (HTS) superconducting quantum interference devices (SQUIDs) have a much greater variance in the values of the critical currents than their low-temperature-superconductor counterparts. To explore the effects of this increased variance, we add a noise term into the critical current of each junction. We perform numerical simulations of previously derived phase equations from series- and parallel-coupled arrays of SQUIDs, and series-and parallel-coupled arrays of bi-SQUIDs. These results support ongoing work to design an electrically small magnetic field antenna and low-noise amplifier with high bandwidth using HTS SQUIDs.

We explore SQUID array designs that could be beneficial in a robust 3-D structure involving several substrates and find a design for which there may be some advantages in linearity and dynamic range. Traditional substrates are square in shape, for a 3-D structure three squares would need to be attached together to create a structure with three sides of a cube. We explored how we would arrange an array of SQUIDs on this structure if the substrates were cut into triangles. This would result in a three-sided pyramid (or tetrahedron) shape. The arrays have a feed line at the top entering a single SQUID (or small array) and the number of SQUIDs (small arrays) increased in number each row and a decreasing critical current. We simulated the effects of varying the critical currents and SQUID loop sizes on the average response output and determined that for arrays of 21 10 × 10 bi-SQUIDs have a more linear anti-peak and larger voltage swing than a comparable size 35 × 60 array.

In this paper we explore different configurations of loop sizes in two-dimensional high temperature superconductor (HTS) Superconducting Quantum Interference Device (SQUID) Arrays. Fixing the number and loop sizes, we changed the placements of the loop sizes to see the effects on the voltage-flux response. We find an asymmetry in the voltage-flux response of the anti- peak feature when the large and small loop sizes are organized on opposite sides of the array. Additionally, we investigate increasing the number of junctions in parallel to mitigate the effects of the junction critical current spread on the voltage-flux response.

Two-dimensional arrays of YBCO step-edge Josephson junctions with identical number of superconducting quantum interference devices (SQUIDs) and varying inductance parameter were characterized to determine the dependence of the voltage- flux response on the loop size variations. Simulations were also performed, and the results show a pronounced dependence of the anti-peak in the voltage-flux response on the value of the inductance parameter.

Research into the development of advanced RF electronics and devices having high-Temperature Superconducting (HTS) circuitry is being carried out in the Cryogenic Exploitation of RF (CERF) laboratory at SPAWAR Systems Center (SSC) - Pacific. Recently, we have developed a novel annealing process wherein a film of YBa2Cu3Ox is produced having a gradient of oxygen composition along a given direction which we refer to as YBa2Cu3O∇x. Such samples are intended for rapid experimental investigation of the evolution of electronic properties within the compound and in combination with structurally compatible functional oxide materials as integrated sensor devices. We present here an investigation as to the extent to which local oxygen content affects the ion milling process in the formation of Josephson junctions in the HTS compound YBa2Cu3O∇x. We find an abrupt transition in the profile and depth of ion milled trenches at oxygen concentrations at and below the well ordered oxygen level, O6.72. The method described here shows good potential for use in the fabrication of large numbers of uniform Josephson junctions in films of YBa2Cu3Ox, as either a complementary processing tool for grain boundary, step edge, or ion damaged formed JJs, or as a stand alone method for producing nano-bridge JJ’s. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

In this paper we provide numerical simulations for modeling an array of non-locally coupled DC SQUIDs that are coupled through the magnetic field created by the circulating current. The motivation is based on work using an array of non-identical SQUID loops or SQIFs to produce a non-periodic voltage response with a unique anti-peak centered at the zero applied flux. Our approach differs by using an array of identical SQUID loops and varying the spacing between each of these loops. Certain distributions of spacing between SQUIDs demonstrate the anti-peak response as seen in the SQIF.

Coupled dynamical systems that operate near the onset of a bifurcation can lead, under certain conditions, to strong signal amplification effects. Over the past years we have studied this generic feature on a wide range of systems, including: magnetic and electric fields sensors, gyroscopic devices, and arrays of loops of superconducting quantum interference devices, also known as SQUIDs. In this work, we consider an array of SQUID loops connected in series as a case study to derive asymptotic analytical approximations to the exact solutions through perturbation analysis. Two approaches are considered. First, a straightforward expansion in which the non-linear parameter related to the inductance of the DC SQUID is treated as the small perturbation parameter. Second, a more accurate procedure that considers the SQUID phase dynamics as non-uniform motion on a circle. This second procedure is readily extended to the series array and it could serve as a mathematical framework to find approximate solutions to related complex systems with high-dimensionality. To the best of our knowledge, an approximate analytical solutions to an array of SQUIDs has not been reported yet in the literature.

Flux trapping in superconducting devices has shown to be detrimental to the consistent operation of superconducting electronics (SCE). Approaches to improve reliability of SCE components have focused on introduction of flux trap regions and highly elaborate degaussing procedures. Nevertheless, a controlled and reproducible method to assure the elimination of trapped flux on SCE devices remains elusive. A substantial body of work on artificial defects utilizing the so called ratchet effect has demonstrate limited control of the magnetic vortices in niobium films. These early attempts to control the spurious vortices distribution have been limited to small geometrical regions having no practical effect on improving SCE devices operational parameters. In this paper, we report simulations and propose an improved method utilizing the ratchet effect that can be extended to physical sizes compatible to existing fabrication techniques of SCE devices.

We explore the effects of fabrication spreads and noise in a series array of DC bi-SQUIDs. The investigation is performed through numerical simulations of phase equations derived from circuit diagrams. It has been previously determined that the series coupled bi-SQUID arrays dynamic range increases with the number of bi-SQUIDs in the array and that non-uniform bi-SQUID loops sizes produces a zero-field single anti-peak in the voltage response. Results show the effects of industry standard fabrication spreads to the anti-peak feature are minimal, while the effects to the voltage response of arrays of identical bi-SQUIDs can be drastic. The findings presented here will be used to support the design of an electrically small magnetic field antenna and low-noise amplifier with high bandwidth.

We develop a two-dimensional (2D) Superconducting Quantum Interference Filter (SQIF) array based on recently introduced high-linearity tri-junction bi-SQUIDs. Our bi-SQUID SQIF array design is based on a tight integration of individual bi- SQUID cells sharing inductances with adjacent cells. We provide extensive computer simulations, analysis and experimental measurements, in which we explore the phase dynamics and linearity of the array voltage response. The non-uniformity in inductances of the bi-SQUIDs produces a pronounced zero-field single antipeak in the voltage response. The anti-peak linearity and size can be optimized by varying the critical current of the additional junction of each bi-SQUID. The layout implementation of the tight 2D array integration leads to a distinct geometrical diamond shape formed by the merged dual bi-SQUID cells. Different size 2D arrays are fabricated using standard HYPRES niobium 4.5 kA/cm2 fabrication process. The measured linearity, power gain, and noise properties will be analyzed for different array sizes and the results will be compared with circuit simulations. We will discuss a design approach for the electrically small magnetic field antenna and low-noise amplifiers with high bandwidth based on these 2D bi-SQUID SQIF arrays. The results from this work will be used to design chips densely and completely covered in bi-SQUIDs that has optimized parameters such as linearity and power gain., 9 pages, 13 figures, Applied Superconductivity Conference (ASC'12)

Large two-dimensional SQUID arrays were made using the step-edge Josephson junction process. The performance of the arrays is analyzed with respect to determining the conditions under which the optimal performance is achieved. We find that optimization of the field-voltage transfer function V B is reached at a specific temperature and device current bias point, and arrive at an empirical expression describing the dependence of V B on the critical current and dynamic resistance of the SQUID array and as a function of temperature. The empirical expression for V B of the SQUID arrays is similar to that given by well known theoretical models for a single SQUID.

This work investigates through numerical simulations a novel device that improvesdynamic range and linearity. The standard DC SQUID can increase in linearity by adding athird junction, changing to a device known as the bi-SQUID. It is known that the dynamicrange can increase by connecting SQUIDs in series, and it has been shown that nonuniformityin the loops sizes in arrays of SQUIDs can produce a unique 'anti'-peak at thezero magnetic flux (device know as a SQIF). Thus, combining these ideas we can improvethe dynamic range and design a highly linear device with a unique 'anti'-peak. Hence, this device can be referred to as a bi-SQIF or non-uniform bi-SQUID array. Results have shown that the maximum voltage swing increase proportional to N, where N is the number of loops connected in series. The spur free dynamic range also improves as N increases, which is directly related to the linearity of the device. Therefore, we have designed a device which can lead to improvements which can be applicable to low noise amplifier (LNA), and provide a platform for creating "electrically" small antennas.

In this work we numerical model series and parallel non‐uniform superconducting quantum interference device (SQUID) array. Previous work has shown that series SQUID array constructed with a random distribution of loop sizes, (i.e. different areas for each SQUID loop) there exists a unique ‘anti‐peak’ at the zero magnetic field for the voltage versus applied magnetic field (V‐B). Similar results extend to a parallel SQUID array where the difference lies in the arrangement of the Josephson junctions. Other system parameter such as bias current, the number of loops, and mutual inductances are varied to demonstrate the change in dynamic range and linearity of the V‐B response. Application of the SQUID array as a low noise amplifier (LNA) would increase link margins and affect the entire communication system. For unmanned aerial vehicles (UAVs), size, weight and power are limited, the SQUID array would allow use of practical ‘electrically small’ antennas that provide acceptable gain.

SQUID arrays are promising candidates for low profile antennas and low noise amplifier applications. We present the integrated circuit designs and results of DC and RF measurements of the wideband serial arrays based on integration of linear bi-SQUID cells forming a Superconducting Quantum Interference Filter (bi-SQUID SQIF). Various configurations of serial arrays designs are described. The measured linearity, power gain, and noise temperature are analyzed and compared. The experimental results are matched to results of mathematical modeling. A serial bi-SQUID SQIF arrays are mounted into a coplanar waveguide (CPW) and symmetrically grounded to corresponding sides of CPW. The RF output comes out from the central common line, which is also used for DC biasing and forms a symmetrical balanced output. The signal and DC flux biasing line is designed as coplanar lines passed in parallel over each bi-SQUID cell in a bidirectional fashion concentrating magnetic flux inside of each cell. Serial bi-SQUID SQIF arrays are fabricated on 5 mm x 5 mm chips using standard HYPRES niobium 4.5 kA/cm2 fabrication process., Comment: 7 pages, 10 figures, Applied Superconductivity Conference (ASC'12)

Multi-loop arrays of Josephson junctions (JJs) with non-uniform area distributions, which are known as superconducting quantum interference filters (SQIFs), are the most highly sensitive sensors of changes in applied magnetic field as well as the absolute magnitude of magnetic fields. The non-uniformity of the loop sizes allows the array to produce a unique collective voltage response that has a pronounced single peak with a large voltage swing around zero magnetic field. To obtain high linear dynamic range, which is critical for a wide variety of applications, the linearity of the slope of the anti-peak response must be improved. We propose a novel scheme for enhancing linearity—a new configuration combining the SQIF array concept with the recently introduced bi-superconductive quantum interference device (SQUID) configuration, in which each individual SQUID loop is made up of three JJs as opposed to using two JJs per loop in standard dc SQUIDs. We show, computationally, that the additional junction offe...