D. Lomparski

Forschungszentrum Jülich, Jülich, North Rhine-Westphalia, Germany

Are you D. Lomparski?

Claim your profile

Publications (24)22.18 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We report our recent work to set up a multi-channel high temperature superconducting (HTS) radio-frequency (rf) SQUID gradiometer and to perform adult and fetal magnetocardiography (MCG). We have compared the adult MCG measurement results using a magnetometer and different gradiometers in a standard magnetically shielded room. The special requirements of a system for fMCG measurements will be discussed. We show that our multi-channel HTS rf SQUID gradiometers are capable of recording the cardiac activity of two fetuses (31st and 33rd week of gestation) in real-time.
    International Congress Series 01/2007; 1300:769-772.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the rf-SQUID and its coupling to the tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation on the YBCO rf-SQUID coupling to the conventional LC tank circuits revealed that the coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4mm for LaAlO3 resulting in an increase of SQUID flux-voltage transfer function signal, Vspp, of 1.5 times, and 0.5 mm for SrTiO3 with an increase of Vspp of 1.62 times compared to that of direct face to face couplings. For the rf-coupling with co-planar resonator, CPR, it has been found that the best configuration, in which a resonator is sandwiched between the SQUID substrate and resonator substrate, provides a Vspp about 3.4 times higher than the worse case where the resonator and the SQUID are coupled back to back. It has also been observed that the noise level does not depend considerably on whether a conventional LC tank circuit or a CPR is used. Though the use of resonator leads to a limitation of the achievable spatial resolution due to its flux-focusing characteristics. This resulted in favouring the use of the conventional tank circuits when considering the desired high spatial resolution. Effect of the YBCO flip-chip magnetic shielding of the SQUIDs in the back coupling with the LC-tank circuit configuration has also been investigated, in order to reduce the SQUID effective area to increase the spatial resolution and also to study the effect of the coupling of various types of the transformers to the SQUIDs. It is revealed that there is no considerable change in the flux-voltage transfer function signal level with respect to the effective shield area, while the lowest working temperature of the SQUIDs was slightly shifted higher by a couple of degrees depending on the shield area.
    Journal of Physics Conference Series 07/2006; 43(1):1239.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Foetal magnetocardiography (fMCG) is a promising technique for prenatal cardiac diagnosis. In this paper, we discuss the special requirements of a system for fMCG measurements. A SQUID system incorporating five HTS rf SQUID magnetometers has been developed and constructed. Four magnetometers are arranged at the bottom of the cryostat in a 4 cm × 4 cm square configuration. One reference magnetometer is located 20 cm above the plane to form four first-order axial gradiometers with the four bottom magnetometers. The magnetometer with a 18 mm diameter flux focuser, which reaches a field sensitivity of 20–30 fT Hz−1/2, proved sufficient for recording foetal magnetocardiograms in a magnetically shielded room. The cardiac activities of two foetuses (31st and 33rd weeks of gestation) were recorded in 90 Hz bandwidth. The foetal QRS peak signals ranged from 4 to 7 pT and could easily be identified in the real-time gradiometer outputs with a signal-to-noise ratio of up to five. Furthermore, the averaged fMCG data enabled the determination of de- and repolarization time intervals. Overall, the fMCG signals proved of sufficient quality to perform foetal heart diagnostics.
    Superconductor Science and Technology 03/2006; 19(5):S266. · 2.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: SQUID (superconducting quantum interference device) microscopes are versatile instruments for biosensing applications, in particular for magnetic nanoparticle detection in immunoassay experiments. We are developing a SQUID microscope based on an HTS rf SQUID magnetometer sensor with a substrate resonator. For the cryogenic set-up, a configuration was realized in which the cryostat is continuously refilled and kept at a constant liquid nitrogen level by an isolated tube connection to a large liquid nitrogen reservoir. The SQUID is mounted on top of a sapphire finger, connected to the inner vessel of the stainless steel cryostat. The vacuum gap between cold SQUID and room temperature sample is adjusted by causing precise approach of a 50 µm thin sapphire window using a single fine thread wheel. We investigated possible sensing tip configurations and different sensor integration techniques in order to achieve an optimized design. A new scheme of coupling the rf SQUID from its back to a SrTiO 3 substrate resonator was adopted for the purpose of minimization of the sensor-to-sample spacing. By SQUID substrate thinning and washer size reduction, the optimum coupling conditions for back coupling were determined for different rf SQUID magnetometers prepared on LaAlO 3 and SrTiO 3 substrates. The SQUID microscope system is characterized with respect to its spatial resolution and its magnetic field noise. The SQUID microscope instrument will be used for magnetic nanoparticle marker detection.
    Superconductor Science and Technology 01/2006; 19(5). · 2.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have investigated the rf SQUID (radio-frequency superconducting quantum interference device) and its coupling to tank circuit configurations to achieve an optimal front-end assembly for sensitive and high spatial resolution magnetic imaging systems. The investigation of the YBCO rf SQUID coupling to the conventional LC tank circuits revealed that coupling from the back of the SQUID substrate enhances the SQUID signal while facilitating the front-end assembly configuration. The optimal thickness of the substrate material between the SQUID and the tank circuit is 0.4 mm for LaAlO 3 resulting in an increase of the SQUID flux–voltage transfer function signal, V spp , of 1.5 times, and 0.5 mm for SrTiO 3 with an increase of V spp of 1.62 times compared to that for direct face to face couplings. For rf coupling with a coplanar resonator, it has been found that the best configuration, in which a resonator is sandwiched between the SQUID substrate and the resonator substrate, provides a V spp about 3.4 times higher than that for the worse case where the resonator and the SQUID are coupled back to back. The use of a resonator leads to a limitation of the achievable spatial resolution due to its flux focusing characteristics. This resulted in a favouring of the use of the conventional tank circuits when considering the desired high spatial resolution. The effect of the YBCO flip chip magnetic shielding of the SQUIDs in the back-coupling with the LC tank circuit configuration has also been investigated, with a view to reducing the SQUID effective area to increase the spatial resolution and also for studying the effect of the coupling of various kinds of transformers to the SQUIDs. It is revealed that there is no very considerable change in the flux–voltage transfer function signal level with respect to the effective shield area, while the lowest working temperature of the SQUIDs was slightly shifted higher by a couple of degrees, depending on the shield area.
    Superconductor Science and Technology 01/2006; 19:821-824. · 2.76 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Many products in the pharmaceutical and food industry are packaged in metallized wrappings. With standard high-frequency search coil metal detectors, they can only be tested for metal contaminations before they are wrapped. However, a key requirement of industrial quality control is the inspection of the products at the end of the production line. We have developed an inspection system for detecting the magnetic remanence of the contaminants. The system utilizes two HTS rf SQUID magnetometers with step edge junctions immersed in liquid nitrogen. The SQUIDs are arranged such that they cover the product channel in a rotated planar electronic gradiometer configuration. In order to suppress the low-frequency magnetic disturbances typically found in industrial environment, the product channel and the SQUID system were mounted inside a coaxial three-layer Mumetal shield. In combination with the gradiometric suppression, homogeneous low-frequency disturbance fields were attenuated by a factor of 400,000. The sensitivity of the system for small magnetic particles was determined experimentally, using numerous steel balls and splinters. A stainless steel particle of 3 μg, corresponding to a sphere diameter of 0.09 mm, was detected with and without aluminized wrapping.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on experiments with a multi-channel HTS radio-frequency (rf) SQUID gradiometer for recording fetal and adult magnetocardiograms. Four sensing SQUID magnetometers and two common reference SQUID magnetometers form a 4 channel electronic gradiometer system of either first or second order. The magnetometers consist of HTS step edge SQUIDs and flux concentrators fabricated from YBaCuO thin films, with dielectric substrate resonators serving as tank circuits. With a washer area of 18 mm in diameter, all six magnetometers reached a field sensitivity of 20-30 fT/√Hz. Each gradiometer channel is formed using two or three such magnetometers with individual readouts in electronic difference. The dc and rf crosstalk between any channel pair was measured. In ordinary operation we did not find any noise contribution from neighboring channels, even though the resonant frequencies of the resonators are closely spaced. In a standard magnetically shielded room, using a first-order gradiometer configuration with an ultra-long baseline of about 20 cm, we demonstrated 4 channel real-time heart signal recordings of a fetus in the 33rd week of gestation.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This version is available at the following Publisher URL: http://ieeexplore.ieee.org/Xplore/dynhome.jsp
    IEEE Transactions on Applied Superconductivity 01/2005; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we analyze the influence of the superconducting quantum interference device (SQUID) gradiometer baseline on the recording of magnetocardiographic measurements. The magnetometers consist of high-temperature superconducting radio-frequency SQUIDs fabricated from YBaCuO thin films, and a substrate resonator which serves as tank circuit. The gradiometers are formed using two or three such magnetometers with individual readouts in electronic difference. We have compared the measurement results using a magnetometer and first- and second-order gradiometers with different baselines. In a standard magnetically shielded room, we found not only an increasing signal-to-noise ratio in adult magnetocardiographic measurements, but also a decreasing distortion of the magnetic field map with increasing baseline of the gradiometer. Using a first-order gradiometer with an ultralong baseline of 18 cm, we have successfully measured the heart signal of a fetus in real time.
    IEEE Transactions on Applied Superconductivity 01/2004; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We have demonstrated and verified the basic feasibility of performing magnetocardiographic (MCG) measurements without magnetic shielding when using a first-order electronic gradiometer with our novel dielectric substrate resonator rf SQUIDs. The setup at the operation site involved adjustment of the gradiometer's baseline length and adaptive balancing. Our experimental portable system was tested in three environments differing in the level of electromagnetic interference.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO<sub>3</sub> substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, I<sub>c</sub>, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz<sup>1</sup>2/ down to few Hz at 77 K while measured with conventional tank circuits. The I<sub>c</sub> of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: This version is available at the following Publisher URL: http://ieeexplore.ieee.org/Xplore/dynhome.jsp
    01/2003;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Physica C Superconductivity 01/2002; · 0.72 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: ISI Document Delivery No.: BU96R
    Review of Progress in Quantitative Nondestructive Evaluation, Vols 21a & B, Edited by D. O. Thompson, D. E. Chimenti, 01/2002: pages 520-527; Amer Inst Physics.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An aircraft wheel testing system using a planar HTS SQUID gradiometer with Joule-Thomson machine cooling in conjunction with differential eddy current (EC) excitation has recently been developed. From a routine performance test in the wheel testing facility at the Lufthansa Base, Frankfurt/M. Airport, we learned that quadrupolar flaw signatures complicate signal interpretation considerably. In order to overcome these difficulties, the system was equipped with a HTS rf magnetometer SQUID sensor and an absolute EC excitation coil. The coil was mounted with a lateral displacement with respect to the SQUID. The geometry was chosen similar to the remote EC technique: a given point on the rotating wheel first passes underneath the excitation coil and then underneath the sensor. We analyzed the dependence of the response field of an inside crack on excitation coil displacement, EC frequency and lock-in phase angle and found an optimum rotation velocity for deep lying defects. The depth selectivity of the technique is discussed
    IEEE Transactions on Applied Superconductivity 04/2001; · 1.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: For eddy current detection of deep-lying flaws in large aircraft wheels, an automated airplane wheel inspection system using a HTS SQUID gradiometer sensor is being developed. Wheel drums made of aluminum alloys have to be tested frequently since they are subject to enormous dynamic loads and very high braking temperatures at landing. For economic reasons, testing should be performed from the outside without removing the inner ferromagnetic keys which fit the brake system. In order to operate the sensor in hostile environments such as airport maintenance hangars, a planar rf double hole SQUID gradiometer was used. SQUID cooling is performed by a closed cycle Joule-Thomson cryocooler, equipped with flexible plastic gas lines. The wheel testing is being performed on an automated test stand with the wheel slowly rotating and a robot with the SQUID enclosure scanning stepwise along the wheel axis. Additional signals due to inner cracks of 10 mm length, penetrating 25 percent of the 10 mm thick wall, are easily identifiable in the periodic signal background due to the presence of ferromagnetic keys. In comparative measurements, the prototype SQUID system clearly exhibited advantages over conventional techniques, with optimization reserve still at hand
    IEEE Transactions on Applied Superconductivity 07/1999; · 1.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have designed an HTS single-layer planar rf double-hole gradiometer with long and well defined baseline up to 5 mm and small washer areas. We measured a gradient field resolution of about 1 pT/(cm·√Hz) above 10 Hz in an unshielded environment. The gradiometer could be operated placed on a swinging pendulum in the geomagnetic field. This permitted a simple demonstration of a movable SQUID system. We placed a SQUID system on a scanning table and performed two-dimensional eddy-current nondestructive evaluation measurements on realistic samples
    IEEE Transactions on Applied Superconductivity 07/1997; · 1.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Nonaqueous Br-ethanol chemical etching was successfully used for the preparation of the Josephson junctions, vias and crossovers in magnetometers including flux transformers. PrBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> thin films were used for the barrier layer in the Josephson junctions of the SQUIDs and as an insulation in the junctions and in the flux transformers. Dc-SQUID magnetometers with small inductances and even without flux antennas were used for NDE applications which mainly require a high dynamic range. Highly sensitive devices were prepared with flip-chip flux antennas. An ac-bias SQUID electronics significantly improves the sensitivity of the magnetometers at low frequencies
    IEEE Transactions on Applied Superconductivity 07/1997; · 1.20 Impact Factor
  • Applied Superconductivity 1997, Vols 1 and 2 - Vol 1: Small Scale and Electronic Applications; Vol 2: Large Scale and Power Applications. 01/1997;
  • [Show abstract] [Hide abstract]
    ABSTRACT: This version is available at the following Publisher URL: http://ieeexplore.ieee.org/Xplore/dynhome.jsp

Publication Stats

88 Citations
22.18 Total Impact Points

Institutions

  • 2006
    • Forschungszentrum Jülich
      • Zentralabteilung für Chemische Analysen (ZCH)
      Jülich, North Rhine-Westphalia, Germany
  • 2003–2006
    • Bilkent University
      • Department of Electrical & Electronic Engineering
      Engüri, Ankara, Turkey