Nmr antenna with slotted metal cover

Details Nmr antenna with slotted metal cover Nmr antenna with slotted metal cover

G - Physics

01

R

G01R 33/44 (2006.01) G01R 33/34 (2006.01) G01V 3/32 (2006.01)

Patent

CA 2482329

A slotted NMR antenna cover (200) for improved mechanical ruggedness during transmission and reception of NMR signals in a down hole environment during either MWD or wire line operations. A NMR slotted antenna cover (200) is provided comprising an elongated tubular structure with longitudinal gaps or slots (205) filled with a RF transmissive or non-conductive material. The slots can befilled at the slots ends with soft magnetic material (210) to improve efficiency of the antenna. The slots are radial concave to reduce eddy currents induced by alternating magnetic flux entering and leaving the slots surrounding the antenna. In another embodiment, the antenna cover is RF transmissive on only a portion of the antenna, via slots or transmissive material, so that the antenna cover can be used to allow RF transmission from the antenna in a side looking or beam pattern restricted mode only.

L'invention concerne un couvercle rainur~ (200) d'antenne NMR, permettant d'obtenir une robustesse m~canique am~lior~e lors de la transmission et de la r~ception de signaux NMR dans un environnement de fond au cours d'op~rations MWD ou par c~bles de forage. Le couvercle rainur~ (200) d'antenne NMR comprend une structure tubulaire allong~e pourvue d'espaces longitudinaux ou de fentes longitudinales (205) remplis d'un mat~riau transmissif RF ou non conducteur. Les fentes peuvent Útre remplies ~ leurs extr~mit~s d'un mat~riau magn~tique doux (210) afin d'am~liorer l'efficacit~ de l'antenne. Les fentes sont radialement concaves pour r~duire les courants de Foucault induits par alternance du flux magn~tique entrant et sortant des fentes entourant l'antenne. Dans un autre mode de r~alisation, le couvercle d'antenne est transmissif RF sur une seul partie de l'antenne, par l'interm~diaire de fentes ou d'un mat~riau transmissif, de mani­re que le couvercle d'antenne puisse Útre utilis~ pour permettre une transmission RF de l'antenne uniquement selon un mode restreint de visualisation lat~rale ou de motif de faisceau.

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