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See detailMagnetic properties through the Archean/Paleoproterozoic transition from the Pilbara Craton, Western Australia: bio-environmental implications.
Isambert, Aude; Carlut, Julie; Bouquerel, Hélène et al

Conference (2015)

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See detailMagnetic Reconnection During Major Magnetospheric Storms
Hubert, Benoît ULg; Milan, S.E.; Cowley, S.W.H.

Poster (2014, December)

We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of ... [more ▼]

We combine imaging of the proton aurora from the SI12-IMAGE instrument with ionospheric convection measurement from the SuperDARN radar network to analyze the cycle of magnetic flux opening and closure of the Earth magnetosphere. Interaction between the solar wind and the Earth geomagnetic environment causes a reconfiguration of the magnetic field that connects the interplanetary magnetic field (IMF) to the geomagnetic field. This reconnection process produces open magnetic field lines (i.e. field lines of the magnetosphere that close through the interplanetary medium) that are dragged to the magnetotail by the solar wind flow, where they eventually reconnect again, back to a closed topology. The SI12 imaging of the Doppler-shifted Lyman-α emission of the proton aurora is used to estimate the location of the boundary separating open and closed field lines at ionospheric altitude. We then estimate the open magnetic flux of the Earth magnetosphere, encircled by this boundary. The rate of reconnection causing a variation of the open magnetic flux can be expressed as a voltage in application of Faraday’s law. This voltage is measured along the open/closed field line boundary determined from the imaging data. The electric field associated with the voltage has two origins: motion of the boundary and the ionospheric field. We use the ionospheric electric field deduced from ionospheric convection measurement from the SuperDARN to estimate the reconnection voltage at the magnetopause (flux opening) and in the magnetotail (flux closure) accounting for the motion of the open/closed field line boundary determined from the SI12 images. The method is applied during several (strong) geomagnetic storms. These intervals are characterized by large values of open flux and reconnection rates, as a result of coupling between the solar wind and the geomagnetic environment. We present these results in terms of a magnetospheric mode that develops under strong coupling with the solar wind, a condition known to be prone to the development of sawtooth events, characterized by overloading of the magnetosphere with open magnetic flux. [less ▲]

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See detailMagnetic reconnection during steady magnetospheric convection and other magnetospheric modes
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Milan, Steve E. et al

in Annales Geophysicae (2017), 35

We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar ... [more ▼]

We use remote sensing of the proton aurora with the IMAGE-FUV SI12 (Imager for Magnetopause to Aurora Global Exploration-Far Ultraviolet-Spectrographic Imaging at 121.8 nm) instrument and radar measurements of the ionospheric convection from the SuperDARN (Super Dual Aurora Radar Network) facility to estimate the open magnetic flux in the Earth's magnetosphere and the reconnection rates at the dayside magnetopause and in the magnetotail during intervals of steady magnetospheric convection (SMC). We find that SMC intervals occur with relatively high open magnetic flux (average ˜ 0.745 GWb, standard deviation ˜ 0.16 GWb), which is often found to be nearly steady, when the magnetic flux opening and closure rates approximately balance around 55 kV on average, with a standard deviation of 21 kV. We find that the residence timescale of open magnetic flux, defined as the ratio between the open magnetospheric flux and the flux closure rate, is roughly 4 h during SMCs. Interestingly, this number is approximately what can be deduced from the discussion of the length of the tail published by Dungey (1965), assuming a solar wind speed of ˜ 450 km s[SUP]-1[/SUP]. We also infer an enhanced convection velocity in the tail, driving open magnetic flux to the nightside reconnection site. We compare our results with previously published studies in order to identify different magnetospheric modes. These are ordered by increasing open magnetic flux and reconnection rate as quiet conditions, SMCs, substorms (with an important overlap between these last two) and sawtooth intervals. [less ▲]

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See detailMagnetic resonance arthrography of cubital joint in dogs affected with fragmented medial coronoid process
Snaps, Frédéric ULg; Park, R. D.; Saunders, J. et al

in American Journal of Veterinary Research (1999), 20

Objective-To evaluate efficacy of intra-articular injection of gadolinium tetra- azacyclododecane tetraacetic acid (gadolinium-DOTA) for delineating fragmented medial coronoid processes (FMCP) and lesions ... [more ▼]

Objective-To evaluate efficacy of intra-articular injection of gadolinium tetra- azacyclododecane tetraacetic acid (gadolinium-DOTA) for delineating fragmented medial coronoid processes (FMCP) and lesions on the medial aspect of the humeral condyle (MAHC). Sample Population-14 cubital joints in 9 dogs. Procedure-Magnetic resonance imaging (MRI) was performed with and without intra-articular injection of a solution of 2 mmol of gadolinium-DOTA/L. Arthrographic images obtained after injection of contrast medium were compared with those obtained without contrast medium. Evidence of contrast medium around or in the medial coronoid process and infiltration of contrast medium in subchondral bone lesions was recorded, Twenty-four hours after imaging, arthroscopy was performed, and lesions detected were correlated with results of MRI. Results-An abnormal coronoid process was diagnosed in 13 of 14 joints. A fragmented process (free) was seen in 7 of 14 joints; nondisplaced mineralized medial tin situ) coronoid processes were evident in 4 joints; and nondisplaced unmineralized medial coronoid processes were evident in 2 joints. Lesions on the MAHC were diagnosed in 4 of 12 joints. In 5 joints, a hyperintense signal resulted from contrast medium that infiltrated between the fragmented process and ulna. In 2 joints, contrast medium did not infiltrate completely around the process and was stopped by an isointense structure tie, abnormal cartilage). Subchondral bone lesions were enhanced by use of contrast medium. Conclusion and Clinical Relevance-Use of arthrography enabled us to identify FMCP easily, but did not provide important additional information about changes on the medial coronoid process, compared with MRI performed without contrast medium. [less ▲]

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See detailMagnetic Resonance Imaging and biochemical markers of osteoarthritis of the knee
Kothari, Manish; Bruyère, Olivier ULg; COLLETTE, Julien ULg et al

in Arthritis and Rheumatism (2005, September), 52(number 9 (suppl.)), 71

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See detailA magnetic resonance imaging approach for the diagnosis of a triplet cornual pregnancy.
Bassil, Salim; Gordts, Stéphane; NISOLLE, Michelle ULg et al

in Fertility and Sterility (1995), 64(5), 1029-31

Objectives: To describe a rare case of triplet cornual pregnancy after IVF-ET and to assess the role of magnetic resonance imaging (MRI) for early diagnosis. DESIGN: Case report. SETTING: Infertility and ... [more ▼]

Objectives: To describe a rare case of triplet cornual pregnancy after IVF-ET and to assess the role of magnetic resonance imaging (MRI) for early diagnosis. DESIGN: Case report. SETTING: Infertility and IVF Unit, in an university medical center. PATIENT: A 31-year-old healthy patient with a 3-year history of primary male infertility. INTERVENTION: Standard IVF-ET treatment cycle, using a GnRH-agonist (long protocol) and hMG for ovarian stimulation. RESULTS: A cornual triplet pregnancy is described with the approach for the diagnosis. Magnetic resonance imaging was complementary to endovaginal sonography for early diagnosis and permitted a timed conservative management. CONCLUSIONS: When transvaginal ultrasound findings did not provide an accurate location of the pregnancy, MRI was indicated to confirm the diagnosis. [less ▲]

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See detailMagnetic resonance imaging arteriography of canine normal brain: an anatomic study
Jacqmot, Olivier ULg; Hoffmann, A. C.; Bustin, P. H. et al

Poster (2008)

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See detailMagnetic resonance imaging findings in the equine deep digital flexor tendon and distal sesamoid bone in advanced navicular disease--an ex vivo study.
Busoni, Valeria ULg; Heimann, Marianne; Trenteseaux, Jacques ULg et al

in Veterinary Radiology & Ultrasound (2005), 46(4), 279-86

We describe the abnormal magnetic resonance (MR) imaging findings in the deep digital flexor tendon (DDFT) and distal sesamoid bone in horses with radiographic changes compatible with navicular syndrome ... [more ▼]

We describe the abnormal magnetic resonance (MR) imaging findings in the deep digital flexor tendon (DDFT) and distal sesamoid bone in horses with radiographic changes compatible with navicular syndrome. Thirteen postmortem specimens were examined using a 1.5-T magnetic field, with spin echo (SE) T1-weighted, turbo SE (TSE) proton density-weighted (with and without fat saturation), and fat saturation TSE T2-weighted sequences. The limbs were then dissected to compare the MR findings with the gross assessment and histologic examination of the DDFT and distal sesamoid bones. Tendonous abnormalities were detected by MR imaging in 12 DDFTs and confirmed at necropsy. Most tendon lesions were located at the level of the distal sesamoid bone and the proximal recess of the podotrochlear bursa. Tendon lesions were classified based on their MR imaging features as core lesions, dorsal lesions, dorsal abrasions, and parasagittal splits. Areas of increased MR signal in the DDFTs were characterized by tendon fiber disturbance and lack of continuity of the collagen fibers, foci of edema, hemorrhages, and formation of lakes containing eosinophilic plasma-like material or amphophilic material of low density. Bone marrow signal alterations in the distal sesamoid bone were seen in all digits. Two main phenomena were responsible for the abnormal signal, respectively, in T1-weighted (decreased signal) and in T2-weighted fat-suppressed images (increased signal): a decrease in the fat marrow content in the trabecular spaces and an increase in the fluid content. Histologic examination revealed foci of bone marrow edema, hemorrhage, necrosis, and fibrosis. Cyst formation and trabecular abnormalities (disorganization, thinning, remodelling) were also observed in areas of abnormal signal intensity. Increased bone density because of trabecular thickening induced a decrease in signal in all sequences. [less ▲]

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See detailMagnetic resonance imaging of canine elbow joint
Saunders; Snaps, Frédéric ULg

Conference (2006)

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See detailMagnetic resonance imaging of intranasal tumors in 5 dogs
Snaps, Frédéric ULg; Clercx, Cécile ULg; D'Harcour, J. B. et al

in 15th Veterinary Respiratory Symposium - Liège - Belgique - Octobre 1997 (1997, October)

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See detailMagnetic resonance imaging of the palmar aspect of the equine podotrochlear apparatus: Normal appearance
Busoni, Valeria ULg; Snaps, Frédéric ULg; Trenteseaux, Jacques ULg et al

in Veterinary Radiology & Ultrasound (2004), 45(3), 198-204

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of ... [more ▼]

The purpose of this study was to describe the normal magnetic resonance (MR) imaging characteristics of the palmar structures of the equine podotrochlear apparatus by means of retrospective evaluation of MR imaging studies of 16 cadaver limbs. The articular aspect of the distal sesamoid bone was not evaluated in this study. Equine digits were imaged with a human knee radiofrequency coil in a 1.5 T magnetic field, using spin echo (SE) T1-weighted, turbo spin echo proton density (TSE PD)-weighted with and without fat saturation (FS), and FS TSE T2-weighted sequences. The limbs were dissected after imaging to validate the absence of gross abnormalities of the flexor aspect of the distal sesamoid bone, of the deep digital flexor tendon, and the distal impar sesamoidean ligament. Seven deep digital flexor tendons were subjected to histologic examination to exclude any microscopic tendon pathology. The anatomic structures of the podotrochlear apparatus were easily identified on MR images. Compact bone of the flexor cortex of the distal sesamoid bone had low intensity signal on all sequences. In 11 digits an increased signal was seen within the thickness of the sagittal eminence of the flexor cortex in SE T1-weighted images and in TSE PD-weighted images without FS. Trabecular bone had a granular appearance and high signal in SE T1-weighted sequences and TSE images without FS. The deep digital flexor tendon had low signal on FS T2-weighted images, while on short echo time sequences (T1- and PD-weighted sequences), the tendon signal varied depending on the relative orientation between its fibers and the static magnetic field. Seven tendons had stippled appearance due to small intratendonous foci of slightly increased signal on transverse T1-weighted images. MR imaging provides a thorough evaluation of the anatomical structure of the podotrochlear apparatus: A good knowledge of the MR imaging appearance and anatomy and an awareness of potential pitfalls will improve diagnostic specificity for the detection of pathologic changes. [less ▲]

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See detailMagnetic resonance signal changes during time in equine limbs refrigerated at 4 degrees C.
Bolen, Géraldine ULg; Haye, Dimitri; Dondelinger, Robert ULg et al

in Veterinary Radiology & Ultrasound (2010), 51(1), 19-24

When ex vivo magnetic resonance (MR) imaging studies are undertaken, specimen conservation should be taken into account when interpreting MR imaging results. The purpose of this study was to assess MR ... [more ▼]

When ex vivo magnetic resonance (MR) imaging studies are undertaken, specimen conservation should be taken into account when interpreting MR imaging results. The purpose of this study was to assess MR changes during time in the anatomic structures of the equine digit on eight cadaver limbs stored at 4 degrees C. The digits were imaged within 12 h after death and then after 1, 2, 7, and 14 days of refrigeration. After the last examination, four feet were warmed at room temperature for 24 h and reimaged. Sequences used were turbo spin echo (TSE) T1, TSE T2, short tau inversion recovery (STIR), and double-echo steady state (DESS). Images obtained were compared subjectively side by side for image quality and signal changes. Signal-to-noise ratio (SNR) was measured and compared between examinations. There were no subjective changes in image quality. A mild size reduction of the synovial recesses was detected subjectively. No signal change was seen subjectively except for bone marrow that appeared slightly hyperintense in STIR and slightly hypointense in TSE T2 sequence after refrigeration compared with day 0. Using quantitative analysis, significant SNR changes in bone marrow of refrigerated limbs compared with day 0 were detected in STIR and TSE T2 sequences. Warming at room temperature for 24 h produced a reverse effect on SNR compared with refrigeration with a significant increase in SNR in TSE T2 images. After 14 days of refrigeration a statistically significant decrease of SNR was found in bone marrow in TSE T2 and DESS sequences. The SNR in the deep digital flexor tendon was not characterized by significant change in SNR. [less ▲]

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See detailMagnetic resonance spectroscopy and diffusion tensor imaging in coma survivors: promises and pitfalls.
TSHIBANDA, Luaba ULg; Vanhaudenhuyse, Audrey ULg; Galanaud, Damien et al

in Progress in Brain Research (2009), 177

The status of comatose patient is currently established on the basis of the patient-exhibited behaviors. Clinical assessment is subjective and, in 40% of patients, fails to distinguish vegetative state ... [more ▼]

The status of comatose patient is currently established on the basis of the patient-exhibited behaviors. Clinical assessment is subjective and, in 40% of patients, fails to distinguish vegetative state (VS) from minimally conscious states (MCS). The technologic advances of magnetic resonance imaging (MRI) have dramatically improved our understanding of these altered states of consciousness. The role of neuroimaging in coma survivors has increased beyond the simple evaluation of morphological abnormalities. The development of 1H-MR spectroscopy (MRS) and diffusion tensor imaging (DTI) provide opportunity to evaluate processes that cannot be approached by current morphologic MRI sequences. They offer potentially unique insights into the histopathology of VS and MCS. The MRS is a powerful noninvasive imaging technique that enables the in vivo quantification of certain chemical compound or metabolites as N-acetylaspartate (NAA), Choline (Cho), and Creatine (Cr). These biomarkers explore neuronal integrity (NAA), cell membrane turnover (Cho), and cell energetic function (Cr). DTI is an effective and proved quantitative method for evaluating tissue integrity at microscopic level. It provides information about the microstructure and the architecture of tissues, especially the white matter. Various physical parameters can be extracted from this sequence: the fractional anisotropy (FA), a marker of white matter integrity; mean diffusivity (MD); and the apparent diffusion coefficient (ADC) which can differentiate cytotoxic and vasogenic edema. The most prominent findings with MRS and DTI performed in traumatic brain-injured (TBI) patients in subacute phase are the reduction of the NAA/Cr ratio in posterior pons and the decrease of mean infratentorial and supratentorial FA except in posterior pons that enables to predict unfavorable outcome at 1 year from TBI with up to 86% sensitivity and 97% specificity. This review will focus on the interest of comatose patients MRI multimodal assessment with MRS and DTI. It will emphasize the advantages and pitfalls of these techniques in particular in predicting the coma survivors' outcome. [less ▲]

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See detailMagnetic screening with bulk high-temperature superconducting hollow tubes in the “emission” configuration
Vanderbemden, Philippe ULg; Hogan, Kevin ULg; Wera, Laurent ULg et al

Conference (2014, April 28)

Due to their unique ability to trap magnetic fields exceeding the saturation limit of conventional ferromagnetic materials, bulk superconductors can be used successfully in motors and generators. In ... [more ▼]

Due to their unique ability to trap magnetic fields exceeding the saturation limit of conventional ferromagnetic materials, bulk superconductors can be used successfully in motors and generators. In several topologies however, the stray magnetic field produced by the superconducting magnet or coils needs to be strongly reduced outside the device. The screening can be performed using either active or passive magnetic screens. In this respect, a hollow tube made of bulk high temperature superconducting (HTS) material provides a strong attenuation of external low frequency magnetic fields and acts as a very efficient passive screen. The situation where the stray magnetic field generated by an electromagnetic device (e.g. a motor or a generator) needs to be attenuated corresponds to an “emission” problem. In the present work, we report the magnetic behaviour of a bulk HTS hollow cylinder in the “emission” configuration, i.e. a coil is placed inside the cylinder and the magnetic field is recorded outside the cylinder. We study the configuration where the coil is placed in the central part of the superconducting cylinder, either along its axis (axial configuration) or perpendicular to it (transverse configuration). The distribution of magnetic field at several distances of the generating coil is measured by miniature Hall probe mapping. Results show the significant attenuation of the magnetic field provided by the superconductor as well as the dependence with respect to the sweep rate. The experimental data are analyzed by comparing the behaviour of the superconductor in the inhomogeneous and homogeneous magnetic field configurations. It is shown that a simple analytical model is able to reproduce the behaviour of the superconductor in the axial configuration [less ▲]

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See detailMagnetic Shielding Above 1 T at 20 K With Bulk, Large Grain YBCO Tubes Made by Buffer-aided Top Seeded Melt Growth
Wera, Laurent ULg; Fagnard, Jean-François ULg; Kumar, Numbury Devendra et al

in IEEE Transactions on Applied Superconductivity (2017), 27(4),

YBCO tubes of ~ 10 mm diameter closed at one extremity were engineered by a Buffer-Aided Top Seeded Melt Growth fabrication process (BA-TSMG). These tubes can act as efficient “dc” magnetic shields and ... [more ▼]

YBCO tubes of ~ 10 mm diameter closed at one extremity were engineered by a Buffer-Aided Top Seeded Melt Growth fabrication process (BA-TSMG). These tubes can act as efficient “dc” magnetic shields and are observed to reduce axial flux densities of 1.5 T by a factor of 100 at 20 K. Such performances are comparable in magnitude to the record threshold inductions reported for bulk MgB2 and Bi-2212 materials at lower temperatures. Magnetic shielding measurements for open and closed tubes at 77 K also show that the presence of the cap improves substantially the shielding performance at the closed extremity since it reduces the penetration through the open end. This fabrication technique is extremely promising for shielding “dc” stray fields generated by HTS magnets operated in a temperature range obtained by cryocoolers, liquid hydrogen (20 K) or liquid neon (27 K). [less ▲]

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See detailMagnetic shielding above 1 T at 20 K with bulk, large grain YBCO tubes made by Buffer-aided Top Seeded Melt Growth.
Wera, Laurent ULg; Fagnard, Jean-François ULg; Kumar, Nambury Devendra et al

Poster (2016, September 07)

A superconducting tube can be used as an efficient magnetic shield. The best shielding performance levels are usually achieved when the tube is closed at one or both extremities. The purpose of the ... [more ▼]

A superconducting tube can be used as an efficient magnetic shield. The best shielding performance levels are usually achieved when the tube is closed at one or both extremities. The purpose of the present work is to study experimentally the shielding performance of YBCO tubes obtained by Buffer-aided Top Seeded Melt Growth fabrication process (BA-TSMG). This fabrication process enables the tube to be closed at one extremity by a cap containing the seed and there is no air gap between the cap and the tube. The shielding effectiveness is characterized by two parameters: (i) the shielding factor, defined as the ratio between the applied magnetic induction and the local magnetic induction measured inside the shield, and (ii) the threshold induction, i.e. the applied magnetic induction above which a given value of the shielding factor cannot be achieved. The magnetic shielding performances of tubes with different geometry are characterized at 77 K in liquid nitrogen. Further magnetic shielding measurements are carried out on one tube at various temperatures ranging from 20 K to 77 K using a Physical Property Measurement System (PPMS). The tubes are subjected to a quasi-static (“DC”) uniform magnetic field. A Hall probe measures the axial component of the local magnetic induction along the axis of the tube as a function of the applied magnetic induction. In order to investigate how the cap prevents the magnetic flux from penetrating inside the tube, we also characterize open tubes where the cap is removed and compare their properties to those of closed tubes. Magnetic shielding measurements show that the threshold induction increases by a factor of 9 as temperature decreases from 77 K to 20 K. Measurements also show that the presence of the cap improves the shielding performance at the closed extremity of the order of 1000 as it reduces the penetration through the open end. Near the closed extremity, a threshold induction of 1.5 T was reached at 20 K. To our knowledge this threshold induction is the best value reported so far at 20 K, and is comparable in magnitude to the record threshold inductions reported for bulk MgB2 and Bi-2212 materials at lower temperatures. These results give evidence that efficient magnetic shields can be obtained with this fabrication technique. [less ▲]

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See detailMagnetic shielding of an inhomogenous magnetic field source by a bulk superconducting tube
Hogan, Kevin ULg; Fagnard, Jean-François ULg; Wera, Laurent ULg et al

in Superconductor Science and Technology (2015), 28(3), 035011

Bulk type-II irreversible superconductors can act as excellent passive magnetic shields, with a strong attenuation of low frequency magnetic fields. Up to now, the performances of superconducting magnetic ... [more ▼]

Bulk type-II irreversible superconductors can act as excellent passive magnetic shields, with a strong attenuation of low frequency magnetic fields. Up to now, the performances of superconducting magnetic shields have mainly been studied in a homogenous magnetic field, considering only immunity problems, i.e. when the field is applied outside the tube and the inner field should ideally be zero. In this paper, we aim to investigate experimentally and numerically the magnetic response of a high-Tc bulk superconducting hollow cylinder at 77 K in an emission problem, i.e. when subjected to the non-uniform magnetic field generated by a source coil placed inside the tube. A bespoke 3-D mapping system coupled with a 3-axis Hall probe is used to measure the magnetic flux density distribution outside the superconducting magnetic shield. A finite element model is developed to understand how the magnetic field penetrates into the superconductor and how the induced superconducting shielding currents flow inside the shield in the case where the emitting coil is placed coaxially inside the tube. The finite element modelling is found to be in excellent agreement with the experimental data. Results show that a concentration of the magnetic flux lines occurs between the emitting coil and the superconducting screen. This effect is observed both with the modelling and the experiment. In the case of a long tube, we show that the main features of the field penetration in the superconducting walls can be reproduced with a simple analytical 1D model. This model is used to estimate the maximum flux density of the emitting coil that can be shielded by the superconductor. [less ▲]

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See detailMagnetic shielding performances of YBa2Cu3O7−δ -coated silver tubes obtained by electrophoretic deposition
Devendra Kumar, N; Closset, Raphaël ULg; Wera, Laurent ULg et al

in Superconductor Science and Technology (2015), 28

We report a complete procedure to achieve multilayer YBCO thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to optimize the magnetic ... [more ▼]

We report a complete procedure to achieve multilayer YBCO thick films by electrophoretic deposition on silver tubes using a suspension of YBCO powder in butanol. With the aim to optimize the magnetic shielding performances of the coatings, we have carried out an extensive investigation of the influence of the deposition parameters, the multilayer deposition sequence and the intermediate/final heat treatments on the coating microstructure. Using the optimized conditions, a 24-layer YBCO coating has been successfully prepared on an 80 mm long Ag tube: the melt growth processed multilayered YBCO thick film thus obtained can shield an applied magnetic field of 1.9 mT at 77 K, the highest value per thickness unit reported so far in the literature for these materials. [less ▲]

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See detailMagnetic shielding properties of a bulk Bi-2223 superconducting hollow cylinder subjected to an inhomogeneous magnetic field
Hogan, Kevin ULg; Wera, Laurent ULg; Fagnard, Jean-François ULg et al

Poster (2014, August 12)

Bulk superconducting materials are well suited for magnetic shielding applications. At low frequencies, the performances of superconductors are higher than those of conventional ferromagnetic materials ... [more ▼]

Bulk superconducting materials are well suited for magnetic shielding applications. At low frequencies, the performances of superconductors are higher than those of conventional ferromagnetic materials. In shielding applications, two situations may be encountered. The first one corresponds to the case where the screen has to shield a volume from the magnetic field in its environment; this corresponds to an “immunity” problem. In the second situation, the screen has to prevent the magnetic field generated by an electronic device from perturbing its environment; this is an “emission” problem. So far, superconducting screens have been extensively studied in “immunity” and were subjected to uniform magnetic fields. In “emission”, the magnetic field is no longer uniform because a local magnetic source has to be placed inside the screen. In this work, we have studied experimentally at 77K the magnetic flux penetration in a Bi-2223 superconducting hollow cylinder subjected to a non-uniform quasi-static magnetic field generated by a small coil placed inside the sample. Two configurations were investigated: axial and transverse; corresponding respectively to the situation where the axis of the coil is coaxial or perpendicular to the axis of tube. We also investigate the influence of the sweep rate of the magnetic field on the magnetic shielding performances. Planar and circular (i.e. at constant distance of the tube) mappings of the magnetic field at proximity of the external surface of the tube were obtained thanks to a bespoke experimental setup using a three axes miniature Hall probe. It was observed that the three components of the magnetic field measured outside are affected differently by the superconducting screen. A simple one-dimensional model based on the conservation of magnetic flux and the Bean model was developed for the axial configuration. It was found to be in accordance with experimental data. It allows one to predict the maximal magnetic flux that can be generated inside the coil before the tube is fully penetrated and a magnetic field is measured outside the tube. Finally, it was observed that the inner surface of the tube is subjected to a magnetic field higher than the one at the same place without the tube. This concentration phenomenon arises because of the diamagnetic behaviour of the superconductor. [less ▲]

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