Superconducting Quantum Interference Device Array Research Articles

Olli V. Lounasmaa

Olli V. Lounasmaa

Superconducting SET with tunable electromagnetic environment

We have studied the environmental effect on superconducting single-electron transistors (S-SETs) by biasing S-SETs with arrays of small-capacitance DC superconducting quantum interference devices (SQUIDs), whose effective impedance can be varied in situ. As the zero-bias resistance of the arrays is increased, Coulomb blockade in the S-SET becomes sharper, and the gate-voltage dependence changes from e-periodic to 2 e-periodic. The SQUID arrays could be used as on-chip noise filters.

High-current resolution broad-band SQUID amplifier suitable for TES calorimeter

A superconducting quantum interference device (SQUID) amplifier has been developed as a current detector with both high-current resolution and broad bandwidth for a transition edge sensor calorimeter. The amplifier is a two stage SQUID (TSS) that consists of an input-SQUID with a 38-turn input coil and a 100-serial SQUID array (100-SSA) output, and has been integrated on a 3 /spl times/ 3 mm Si chip using Nb thin film fabrication technology. It is designed to increase the amplifier gain and maintain matching with the parameters of the calorimeter. To avoid flux trapping in the SSA, the washer coil of the dc-SQUIDs in the SSA was made with a narrow line width of 17.5 /spl mu/m. We experimentally confirmed that the designed output voltage was achieved using a one-layer p-metal magnetic shield tube in the earth's magnetic field. The performance of the shielded TSS amplifier was evaluated in liquid helium. The TSS amplifier had a gain of 10 kV/A and an impedance of 0.07 /spl Omega/ at 100 kHz. When a flux locked loop circuit was used to drive the amplifier, a current resolution of 1 pA//spl radic/Hz and a rise time of 1 /spl mu/s were achieved.

Non-destructive evaluation of aircraft structures with a multiplexed HTS rf SQUID magnetometer array

Eddy current (EC) testing of aircraft components for material flaws hidden deeply in the tested structure is facilitated by using an array of HTS rf superconducting quantum interference device (SQUID) sensors. Recently, the multiplexed operation of three planar HTS rf gradiometers with one electronics and one cable was shown [IEEE Trans. Appl. Supercond. 11 (2001) 1168]. In this paper, a multiplexing setup with three magnetometers is presented. SQUID magnetometers have proven advantageous over short-baseline gradiometers for EC measurements of deep flaws. Using three standard HTS rf washer SQUID magnetometers with step-edge junctions, we implemented a multiplexed SQUID array. In conjunction with EC excitation and lock-in readout, measurements of aluminium aircraft samples were carried out in an unshielded laboratory environment. Newly developed software controls the continuous switching of the SQUIDs during the scan of the samples. The quasi-simultaneously obtained traces of the magnetometers are lock-in demodulated to yield in-phase and quadrature components, respectively. For EC excitation, a double-D excitation coil was selected. We performed measurements to localize an artificial crack of 20 mm length in an aluminium sheet with 0.6 mm thickness uncovered and covered by unflawed aluminium plates. In addition, the angle between crack and scanning direction was varied. Recorded signals of the SQUID array are presented and compared to signals received by scanning with just one and two magnetometers.

A study on direction‐of‐arrival estimation methods using cosθ amplitude response antenna

AbstractAt present, when the direction of arrival of a low‐frequency electromagnetic wave such as one in the HF band is measured, loop antennas are used. However, in low‐frequency measurement such as is used in underwater communications, subsurface resource detection, volcanic activity observation, and natural electromagnetic wave observation, the receiving power sensitivity decreases as the frequency is decreased. The purpose of this paper is to use a SQUID (Superconducting QUantum Interference Device), known as an ultrasensitive magnetic sensor, for construction of a small magnetic antenna for estimating the direction of arrival of low‐frequency electromagnetic waves. As a first step, the antenna configuration and direction of arrival estimation method shown below are proposed. As a low‐frequency broadband antenna with an amplitude response type, we consider a SQUID array, which has a cosθ mode vector consisting of SQUID elements on a circle with a small radius, which is negligible in comparison with the wavelength of the incident wave. For an antenna with a real‐valued cosθ mode vector, we consider a direction‐of‐arrival estimation method within the framework of the estimation principle of ESPRIT and MUSIC, known as high‐resolution direction‐of‐arrival estimation methods, and derive an estimation method. The obtained estimation method is shown to be ultimately reducible to a simple estimation equation for deriving the phase difference between the −1st and 1st fundamental waves after beam subspace transformation of the correlation function without eigenfunction expansion. By computer simulation, it is shown that an estimation accuracy of 0.2 to 2° is obtained by this estimation equation for the finitely many elements and snapshots that are actually anticipated. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 85(10): 8–22, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10009

Coded SQUID arrays

We report on a superconducting quantum interference device (SQUID) system to read out large arrays of cryogenic detectors. In order to reduce the number of SQUIDs required for an array of these detectors, we used code-division multiplexing. This simplifies the electronics because of a significantly reduced number of wires from the cryogenic detectors to the SQUIDs and the room temperature electronics. Several prototype chips based on SQUIDs with multiple inputs coils have been developed and direct and indirect crosstalk properties are discussed.

Designing, Building and Operating a Microcalorimeter Eds Outside a Cryogenic Research Facility

In 1999 Thermo NORAN completed licensing agreements with NIST for the microcalorimeter x-ray spectrometer technology developed by Martinis, Irwin, Hilton and Wollman.Steady progress has been made to commercialize this technology.Briefly, the NIST microcalorimeter consists of a Transition Edge Sensor (TES) which measures the temperature rise in an absorber due to an incident photon. The sensor must be operated at temperatures below 100 milliKelvin, which is provided by an Adiabatic Demagnetization Refrigerator (ADR), coupled with a traditional liquid helium cryostat. Additional enabling technology includes a Superconducting Quantum Interference Device (SQUID) and a SQUID Array for device readout and low temperature signal amplification. All of this technology has been widely used in cryogenic research facilities for many years, but is not readily available for commercial purchase and use.Initial work focused on adapting the NIST design to a modern FESEM. The available ports in an FESEM required scaling the heat shields, and cold extension diameters by 68%.

Direct detection of the magnetic flux noise from moving vortices in wide YBa2Cu3O7−δ grain boundary junctions

We measured the flux of a wide bicrystal grain boundary of YBa2Cu3O7−δ film, cooled to 77 K in a field of 10 μT, using a superconducting thin-film coil and Nb-based superconducting quantum interference device (SQUID). When the applied field was changed to, and above, a small threshold value, the sample showed random switching noises with a sharp increase in low-frequency noise power. The results suggested that there was long-distance movement of vortices over 20–500 μm within the grain boundary, driven by the shielding current. The vortex movement was suppressed to lengths of less than 1 μm in a slotted grain boundary by making an array of SQUIDs that can hold vortices stably.

Performance of multiplexed SQUID readout for Cryogenic Sensor Arrays

We report on the implementation of a multiplexer that uses superconducting quantum interference devices (SQUIDs) to read out low-impedance cryogenic detectors. Using prototype chips, a circuit was built which interfaces eight input SQUID channels with a close-packed array of eight transition-edge sensor (TES) infrared bolometers. Circuit elements were measured and crosstalk specifications are reported. Digital feedback is employed to flux-lock a single element in the array of SQUIDs.

Ultralow temperature NMR detection using dc SQUIDs

Nuclear magnetic resonance (NMR) experiments at ultralow temperatures place high demands on superconducting quantum interference device (SQUID) amplifiers. We have developed a suitable direct-coupled readout SQUID electronics system, which utilizes additional positive feedback (APF), and have achieved a system bandwidth of 5 MHz, maximum slew rate of 1.3×10 7 Φ 0 /s at 14 kHz and a white noise level of 3.4 μ Φ 0 / Hz . We have also investigated improving the signal-to-noise ratio by using a low noise series array of dc SQUIDs and by placing the SQUID amplifier closer to the ultralow temperature experiment. We will discuss how we have configured our SQUID amplifiers for operation at T ≪1 K.

Dynamic cortical activity in the human brain reveals motor equivalence.

That animals and humans can accomplish the same goal using different effectors and different goals using the same effectors attests to the remarkable flexibility of the central nervous system. This phenomenon has been termed 'motor equivalence', an example being the writing of a name with a pencil held between the toes or teeth. The idea of motor equivalence has reappeared because single-cell studies in monkeys have shown that parameters of voluntary movement (such as direction) may be specified in the brain, relegating muscle activation to spinal interneuronal systems. Using a novel experimental paradigms and a full-head SQUID (for superconducting quantum interference device) array to record magnetic fields corresponding to ongoing brain activity, we demonstrate: (1), a robust relationship between time-dependent activity in sensorimotor cortex and movement velocity, independent of explicit task requirements; and (2) neural activations that are specific to task demands alone. It appears, therefore, that signatures of motor equivalence in humans may be found in dynamic patterns of cortical activity.

A low-noise, two-stage DC SQUID amplifier with high bandwidth and dynamic range

We describe a low-noise, two-stage dc Superconducting QUantum Interference Device (SQUID) amplifier that is designed for applications requiring high bandwidth and dynamic range. The output signal of a low-noise SQUID in the input stage coherently modulates a series array of identical SQUIDs in the output stage via a common modulation line. The input stage is designed so its output signal does not produce multiple modulation periods in the output stage. The output stage is designed to have sufficient gain so the output noise is dominated by the amplified noise of the input SQUID and exceeds the noise of a preamplifier in the room temperature readout electronics. The SQUID amplifier may therefore be operated without flux modulation or any impedance matching network, resulting in a large dynamic range and high bandwidth.

A 35-Series Superconducting Quantum Interference Device Array for High-Dynamic-Range Magnetic Measurements

A 35-Series Superconducting Quantum Interference Device Array has been developed for a magnetometer with a high dynamic range. The coherence of each SQUID was observed in a double-shielded tube made of cryoperm and lead; a maximum voltage swing of 2 mV and flux noise of 0.6 µΦ0/√ Hz were obtained. The nonuniform inductance of the SQUIDs in the array, which causes Φ–V curve modulation, is decreased by using dummy SQUIDs at each end of the array. A gradiometer for biomagnetic measurement was constructed using a 35-SQUID array and a 10×10-mm planar pick-up coil. A magnetic-field sensitivity of 5.4 fT/√ Hz, a maximum slew rate of 1.9 mT/s, and a maximum feedback amplitude of ±2.23 µ T were achieved by using a direct-coupled flux-locked-loop circuit. The dynamic range of the magnetometer input field was ±4.13×108 √ Hz.

Self-organizing dynamics of the human brain: Critical instabilities and Sil'nikov chaos.

Using a sensorimotor coordination task in conjunction with an array of SQUIDs (Superconducting QUantum Interference Devices) we demonstrate critical instabilities in human brain activity patterns. Analysis of the dominant spatial pattern of the brain and its time-varying amplitude displays a task-dependent geometry characteristic of Sil'nikov-like chaos, which changes qualitatively at the transition. (c) 1995 American Institute of Physics.

A theoretical model of phase transitions in the human brain.

An experiment using a multisensor SQUID (superconducting quantum interference device) array was performed by Kelso and colleagues (1992) which combined information from three different sources: perception, motor response, and brain signals. When an acoustic stimulus frequency is changed systematically, a spontaneous transition in coordination occurs at a critical frequency in both motor behavior and brain signals. Qualitatively analogous transitions are known for physical and biological systems such as changes in the coordination of human hand movements (Kelso 1981, 1984). In this paper we develop a theoretical model based on methods from the interdisciplinary field of synergetics (Haken 1983, 1987) and nonlinear oscillator theory that reproduces the main experimental features very well and suggests a formulation of a fundamental biophysical coupling.

Two-stage integrated SQUID amplifier with series array output

A two-stage integrated DC superconducting quantum interference device (SQUID) amplifier has been fabricated which uses a compact series array of 100 DC SQUIDs as the readout device for a low-noise single SQUID. The output noise is dominated by the amplified noise of the input SQUID and substantially exceeds the input noise of a good room-temperature preamp. The input stage is a low-inductance double-loop SQUID with energy sensitivity of approximately 30-h (equivalent flux noise phi /sub n/ approximately=0.3 mu phi /sub 0// square root Hz), with an input transformer having input inductance L/sub in/ approximately=0.25 mu H and net coupling to the SQUID of k/sup 2/ approximately=0.1. The bandwidth extends from DC to about 390 kHz. The series array has an output voltage swing of 3-4 mV, providing a dynamic range of over 50 dB at full bandwidth. The results suggest the general utility of series SQUID arrays as readout devices for SQUIDs. >

Radiation detection from phase-locked serial dc SQUID arrays

We report on synchronous operation of series arrays of inductively coupled superconducting quantum interference devices (SQUIDs). Each array consisted of N=3 or 11 dc SQUIDs with common inductances providing a strong interaction between neighboring cells. Externally shunted (βc≊1) trilayer Nb—AlOx—Nb Josephson junctions were used. Coherent radiation was detected in the frequency range f=67–73 GHz while the array voltage was VN=NfΦ0 (Φ0=2.07×10−15 V s). The stability of the coherent state was influenced by the external dc magnetic field. The linewidth depended on the external loading. For small loading it was N times smaller than expected for a single cell. The influence of the inductive coupling mechanism on the operation of discrete Josephson junction circuits and the similarity to the coupling in layered structures of long Josephson junctions is discussed.