Ronny Stolz

LTS SQUID sensor with a new configuration

We have developed highly sensitive SQUID-based magnetometers and gradiometers, fabricated in a standard Nb/AlOX/Nb technology. The SQUID itself is designed as a current sensor having an input coil and a feedback coil. The number of turns of the input coil can be adjusted to ensure optimal coupling to the pickup loops with an inductance in the range from 5 nH to 300 nH. Several types of planar pickup loop configurations have been realized. The magnetometer has a pickup loop with a size of 1 cm × 1 cm. With a typical white noise level better than 4 µ0 Hz-1/2 and an effective area of 2.6 mm2 a field resolution of 3.2 fT Hz-1/2 results for the magnetometer. Two loops connected in series with an area of 2 cm × 2 cm each and a baseline of 4 cm were used in the gradiometer. We measured a 7.5 mm2 effective area for each loop and a field gradient resolution of 36 fT m-1 Hz-1/2 corresponding to a field resolution in the loop of 1.6 fT Hz-1/2.

Magnetic full-tensor SQUID gradiometer system for geophysical applications

In 1997, the Institute for Physical High-Technology (IPHT) in Jena, Germany, started a program with the aim of developing an airborne full-tensor magnetic gradiometer superconducting quantum interference device (SQUID) using liquid-helium-based thin-film technology. Since that time, the sensor, system electronics, data acquisition system, and cryogenics have been developed and extensively tested. This article reports on successful tests of the intrinsic planar LTS (low-temperature superconductor) SQUID gradiometers which were conducted by towing the system from a helicopter as well as for a stinger-mounted configuration in a Cessna 208 aircraft.

Sub-micrometer-sized, cross-type Nb―AlOx―Nb tunnel junctions with low parasitic capacitance

We report on a technology for the fabrication of sub-micrometer sized cross-type Josephson tunnel junctions in niobium technology. We present the fabrication scheme and properties of cross-type junctions with linear dimensions from 10 down to 0.6??m. Sidewall passivation of the junctions is achieved by anodization as well as by planarizing the junctions with SiO in a self-aligned deposition step. The measured ratio of the sub-gap resistance to the normal resistance is about 35. Because of their low sub-gap current and low parasitic capacitance such junctions are well suited for applications like high resolution SQUIDs.

Orthogonal sequencing multiplexer for superconducting nanowire single-photon detectors with RSFQ electronics readout circuit

We propose an efficient multiplexing technique for superconducting nanowire single-photon detectors based on an orthogonal detector bias switching method enabling the extraction of the average count rate of a set of detectors by one readout line. We implemented a system prototype where the SNSPDs are connected to an integrated cryogenic readout and a pulse merger system based on rapid single flux quantum (RSFQ) electronics. We discuss the general scalability of this concept, analyze the environmental requirements which define the resolvability and the accuracy and demonstrate the feasibility of this approach with experimental results for a SNSPD array with four pixels.

Low temperature SQUID magnetometer systems for geophysical exploration with transient electromagnetics

Geophysical exploration is getting more and more difficult—many of the easily explorable ore-bodies have been discovered and are already being exploited. Finding new mines requires new technologies and tools. Transient electromagnetics (TEM) is widely used in mineral exploration, but conventional sensors (especially induction coils) cannot fulfil the needs anymore: deep targets, very conductive targets or targets under conductive overburden are more easily (or sometimes only) detected using SQUIDs. In this paper we will focus on low temperature SQUID magnetometers. As the systems are applied worldwide it is necessary to strengthen them for all conceivable application scenarios. Here, we report on the latest development of these systems which are now routinely used in South Africa, Australia, Finland and Canada. This paper highlights the main features of the system and describes one example from mineral exploration.

Instrumentation for simultaneous detection of low field NMR and biomagnetic signals

We have built and demonstrated a simple system with open geometry that measures biomagnetic signals such as magnetoencephalogram (MEG), magnetocardiogram (MCG) and magnetomyogram (MMG) simultaneously with low field nuclear magnetic resonance (NMR) free induction decay signals (FID). The system employs LT/sub C/ SQUID gradiometers and can operate with proton Larmor frequency in the 80 Hz-10 kHz range. A pre-polarizing field of up to 60 mT is generated by resistive coils. Two different types of SQUID gradiometers were used: a tangential thin-film planar first-order gradiometer and an axial second-order gradiometer. The gradiometers were placed inside a fiberglass dewar at about 1 cm distance from a subject. All measurements were performed inside a single-layer magnetic shielded room. This system is the prototype for a system that will ultimately be capable of measuring biomagnetic signals together with magnetic resonance images (MRI).

Investigation of all niobium nano-SQUIDs based on sub-micrometer cross-type Josephson junctions

We report on the development of highly sensitive SQUIDs featuring sub-micrometer loop dimensions. The integration of high quality and low capacitance SIS Nb/AlOx/Nb cross-type Josephson tunnel junctions results in white flux noise levels as low as 66 n

Noise characterization of highly sensitive SQUID magnetometer systems in unshielded environments

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A LTS-SQUID System for Archaeological Prospection and Its Practical Test in Peru

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Archaeometric prospection with high-T/sub c/ SQUID gradiometers

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