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Magnétomètres - Gradiomètres à capteurs supraconducteurs à haute température critique; Mise en oeuvre dans un cryogénérateur portable à tube pulsé

Sébastien Saez 1
1 Equipe Electronique - Laboratoire GREYC - UMR6072
GREYC - Groupe de Recherche en Informatique, Image, Automatique et Instrumentation de Caen
Abstract : High Tc SQUIDs (Superconducting Quantum Interference Device) are high sensitivity directional magnetometers operating from dc to a few hundred kHz. Their sensitivity is high enough to perform fine bio-magnetism characterization in shielded rooms. The objective of the thesis was the fabrication of a hand portable magnetometer able to measure cardiac signal in unshielded environments. (\footnotesize The magnetic field of the heart was modellised by a variable magnetic dipole. We then demonstrated that the optimal magnetic field measurement is obtained when the magnetometer direction is perpendicular to the study plane. A sensitivity of $100\,\mathrm(fT)/\sqrt(\mathrm(Hz))$ in 100 Hz bandwidth is required for bio-magnetic characterization. However, this value cannot be achieved directly because of many magnetic disturbances. Distinguished by their various spatial evolution, these perturbations can be partly cancelled using a gradiometer, which acts as spatial filter. Such a system was worked out using 2 high sensitivity flux-gates, and associated with a Digital Signal Processor (DSP), it enabled the measurement of peak of the heart magnetic signal. It shows that reel time signal processing is very concvenient and useful way in our application and open environment. Experiments were carried out using a Pulse-Tube Cryocooler to cool a SQUID dc magnetometer. It appeared that this cryocooler produced excess noise in the useful bandwidth and is not well suited to magneto-cardiography. Liquid nitrogen cooled SQUID gradiometers were then used to measure the heart magnetic field in unshielded environments. In order to improve the magneto-cardiogram signal to noise ratio, the low frequency noise cancellation techniques have to be further introduced.
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https://tel.archives-ouvertes.fr/tel-00011006
Contributor : Sébastien Saez <>
Submitted on : Wednesday, November 16, 2005 - 5:17:34 PM
Last modification on : Tuesday, April 28, 2020 - 4:00:41 PM
Long-term archiving on: : Friday, April 2, 2010 - 11:02:54 PM

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  • HAL Id : tel-00011006, version 1

Citation

Sébastien Saez. Magnétomètres - Gradiomètres à capteurs supraconducteurs à haute température critique; Mise en oeuvre dans un cryogénérateur portable à tube pulsé. Micro et nanotechnologies/Microélectronique. Université de Caen, 2000. Français. ⟨tel-00011006⟩

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