HTS-SQUID Magnetometer with Digital Feedback Control for NDE Applications

Zimmermann, Egon; Brandenburg, G.; Clemens, U.; Rongen, Heinz; Halling, H.; Krause, H.; Hohmann, R.; Soltner, H.; Lomparski, D.; Grüneklee, M.; Husemann, K.‐D.; Bousack, Herbert; Braginski, A. I.

doi:10.1007/978-1-4615-5947-4_278

Cited by 7 publications

(5 citation statements)

References 5 publications

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“…Experimentally, dynamic ranges of up to of 8 × 10 4 0 were demonstrated [86]. A short integrator reset time is essential to allow a high system slew rate [6].…”

Section: Dynamic Rangementioning

confidence: 99%

“…Flux-quanta counting can be conveniently implemented in a digital feedback electronics. Here, the analogue output of the preamplifier is digitized, integrated digitally and fed back into the SQUID via a digital-to-analogue (D/A) converter [85,86]. The digital integrator can easily be reset and yields the digitized feedback signal with an accuracy given by the D/A converter.…”

Section: Dynamic Rangementioning

confidence: 99%

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High-T_cand low-T_cdc SQUID electronics

Drung

2003

Supercond. Sci. Technol.

129

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Superconducting quantum interference devices (SQUIDs) are commonly operated in a flux-locked loop (FLL). The SQUID electronics amplifies the small SQUID signal to an acceptable level without adding noise, and it linearizes the transfer function of the SQUID in order to provide sufficient dynamic range. In this paper, the fundamentals of SQUID readout are reviewed including a discussion of preamplifier noise. The basic FLL concepts, direct readout and flux modulation readout, are discussed both with dc bias and bias reversal. Alternative readout concepts such as additional positive feedback (APF), two-stage SQUIDs, SQUID series arrays, relaxation oscillation SQUIDs and digital SQUIDs are briefly described. The FLL dynamics are discussed on the basis of a simple model with finite loop delay. It is shown that with optimized SQUID electronics a system bandwidth of ≈18 MHz and a corresponding slew rate of ≈8 Φ0 µs−1 are possible. A novel FLL scheme involving a Smith predictor is presented which allows one to increase the FLL bandwidth to about 100 MHz. The theoretical predictions are experimentally checked using a high-speed SQUID electronics prototype with a small-signal bandwidth of 300 MHz. Methods for increasing the dynamic range of SQUID systems are described: flux-quanta counting and dynamic field compensation (DFC). With DFC, the residual magnetic field at the SQUID can be kept close to zero even if the device is moved in the Earth's field. Therefore, the noise level of a high-Tc magnetometer measured inside a magnetically shielded room (60 fT Hz−1/2 with a 1/f corner at 2 Hz) remained unchanged after moving the device in the magnetic field outside the room (60 µT dc plus 0.8 µT peak-to-peak power line interference).

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“…Experimentally, dynamic ranges of up to of 8 × 10 4 0 were demonstrated [86]. A short integrator reset time is essential to allow a high system slew rate [6].…”

Section: Dynamic Rangementioning

confidence: 99%

Section: Dynamic Rangementioning

confidence: 99%

High-T_cand low-T_cdc SQUID electronics

Drung

2003

Supercond. Sci. Technol.

129

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“…• Flux counting electronics [51][52][53] • Hybrid SQUIDs exploit the deformed voltage-fluxcharacteristics of a dc SQUID with additional positive feedback [56][57][58] to gain a steep slope for flux quanta counting and a flat slope for the fractions of one flux quantum; both numbers will be merged to provide a hybrid readout of the magnetic field amplitude (Leibniz IPHT, unpublished), • Digital SQUIDs [59][60][61][62][63][64][65] with digitization at the cryostage(s); however, most implementations of digital superconductor electronics are so far not operational in Earth field and require at least a moderate shielding e.g. [64,66], • Flux ramp modulation readout which read out the phase of a dc SQUID voltage-flux-characteristics driven by a fast sinusoidal signal [67] (significantly faster than the signals to be measured).…”

Section: High Dynamic Range Magnetometersmentioning

confidence: 99%

Superconducting sensors and methods in geophysical applications

Stolz

Schmelz

Zakosarenko³

et al. 2021

Supercond. Sci. Technol.

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More than 50 years ago superconducting quantum interference devices (SQUIDs) were invented. Since then many applications opened up. Already in a 1980 workshop (Weinstock and Overton 1981 SQUID Applications to Geophysics (Society of Exploration Geophysicists)) the application of SQUIDs in geosciences was reviewed. The fabrication and cooling technologies, electronics and other SQUID system components underwent significant improvement within the past years. Thus, SQUIDs are today better suited, more sensitive and effective as well as robust and reliable in operation for geophysical measurements. Many successful application examples, demonstrations and discoveries of mineral resources have been made using them in laboratory devices for investigation of magnetic properties, magnetic exploration, transient electromagnetics and for superconducting gravimeters as well as gravity gradiometers. Therefore, this article intends to review the past, present, and some future aspects of SQUIDs in geo-scientific applications such as e.g. mineral exploration. Since this field is still very active and quite a number of developments are ongoing, this review cannot be comprehensive.

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“…The resolution data refer to the white noise region measured in magnetically shielded environment. The rf magnetometers were operated with a digital signal processor controlled flux-locked loop electronics [10,11], the dc gradiometers with a commercial electronics.…”

Section: Squ/ds and Electronicsmentioning

confidence: 99%