Nonperiodic flux to voltage conversion of series arrays of dc superconducting quantum interference devices

Abstract

A theoretical study on the voltage response function V of a series array of dc SQUIDs is presented in which the elementary dc SQUID loops vary in size and, possibly, in orientation. Such series arrays of two-junction SQUIDs possess voltage response functions vs. external magnetic field B that differ substantially from those of corresponding regular series arrays with identical loop-areas, while maintaining a large voltage swing as well as a low noise level. Applications include the design of current amplifiers and quantum interference filters.Recently series arrays of dc SQUIDs have been successfully exploited as current amplifiers with wide bandwidth, large dynamic range and low noise level 1 . Using thin-film Nb-technology, amplifiers consisting out of up to 10 3 identical dc SQUID loops have been fabricated. Such serial devices are characterized by large voltage swings of several mV and current-to-voltage transfer functions of some V /mA so that a direct connection to a room temperature preamplifier is feasible.At present only series arrays consisting out of identical dc SQUID loops have been described in the literature 1 . The dc voltage response function V of such regular series arrays displays a Φ 0 -periodicity just as a single dc SQUID where Φ 0 = h 2e is the elementary flux quantum 2 . However, this periodicity may represent a serious limitation for the modes of operation of such devices. To get a linear flux-to-voltage conversion a feedback circuit is used in most applications in which the dc SQUID acts as a null-flux detector. Furthermore special electronic devices and efficient background shielding is often required 2 . Here theoretical studies on the voltage response of arithmetic and irregular series arrays of dc SQUID loops are presented, in which the individual loopareas are not all equal. For such devices the advantages of dc SQUID series arrays are preserved but limitations due to the periodicity of the voltage response can be circumvented.The arrays under consideration consist of N two junction SQUID loops connected in series. The bias current I b is fed into the array as indicated in Fig.(1). In general the areas of the N loops in a generic array differ in size and, possibly, in orientation. Let a n be the orientated area element of the n th dc SQUID loop. The magnetic flux threading a n is then Φ n = B, a n , where B is the total magnetic field. Taking into account all inductive effects in the dc SQUID array the total magnetic field B = B (p) + B (s) + B (c) is a superposition of the primary magnetic field B (p) one wants to measure, the secondary magnetic field B (s) induced by currents that flow in the dc SQUID array and, possibly, the magnetic compensation field B (c) induced by compensation current(s) I comp flowing through a set of suitable orientated compensation coils or wires.As a special case a generic planar dc SQUID array is shown in Fig.(1). The primary magnetic flux is coupled into the individual dc SQUID loops by the signal or input current I inp which flows through a common in...

Superconducting Quantum Interference Filters as Absolute Magnetic Field Sensors

“…Recently, Superconducting Quantum Interference Filters (SQIFs) have been proposed as high resolution magnetometers [8], [9]. SQIFs are arrays of Josephson junctions (JJs) with a specially selected distribution of the loop areas, such that the magnetic field dependent voltage response is a delta-like dip in the vicinity of zero magnetic field.…”

Multistability and self-organization in disordered SQUID metamaterials

“…Recent advances that led to nano-SQUIDs makes possible the fabrication of SQUID metamaterials at the nanoscale 27 . The use of SQUID arrays in dc current sensors 28 , filters 29,30 , magnetometers 31 , amplifiers [32][33][34] , radiation detectors 35 , flux-to-voltage converters 36 , as well as in rapid single flux quantum (RFSQ) electronics 37 , has been suggested and realized in the past. However, in most of these works the SQUIDs in the arrays were actually directly coupled through conducting paths.…”

Novel Coupling Scheme for the Dynamics of Non-Uniform Coupled SQUID

“…5 demonstrates that the maximum voltage response ( ) can increase due to the coupling parameter . Previous work has shown that the dynamic range can increase due to the number of loops in a series [1], [2]. The work in this paper demonstrates that by increasing the inductive coupling between the neighboring loops we can also achieve an increase in dynamic range.…”

“…4. The dynamic range of a typical SQUID array device with 50 loops is times (or 17 dB) larger than for a conventional single loop SQUID [1], [2]. Hence, increasing the number of element in an the array of SQUIDs increasing the dynamic range.…”

“…Interesting, when loop sizes of each individual element in the SQUID array are chosen to be different we can find a voltage response such that there exists a unique anti-peak around the zero magnetic field [1], [2]. This paper explorers variations in system parameters including: inductive coupling between neighboring elements, unconventional grating, and varying the number of element in super conducting SQUID arrays for achieving a new generation of low-noise amplifiers (LNA).…”