WO2007144578A2 - Écran protecteur - Google Patents

Écran protecteur Download PDF

Info

Publication number
WO2007144578A2
WO2007144578A2 PCT/GB2007/002120 GB2007002120W WO2007144578A2 WO 2007144578 A2 WO2007144578 A2 WO 2007144578A2 GB 2007002120 W GB2007002120 W GB 2007002120W WO 2007144578 A2 WO2007144578 A2 WO 2007144578A2
Authority
WO
WIPO (PCT)
Prior art keywords
emf
screen
radiation
screen according
electric
Prior art date
Application number
PCT/GB2007/002120
Other languages
English (en)
Other versions
WO2007144578A3 (fr
Inventor
Peter Hobden
Original Assignee
Peter Hobden
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Peter Hobden filed Critical Peter Hobden
Priority to GB0820020A priority Critical patent/GB2452641A/en
Publication of WO2007144578A2 publication Critical patent/WO2007144578A2/fr
Publication of WO2007144578A3 publication Critical patent/WO2007144578A3/fr

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/025—Compensating stray fields
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K9/00—Screening of apparatus or components against electric or magnetic fields
    • H05K9/0001—Rooms or chambers
    • H05K9/0005—Shielded windows

Definitions

  • This invention relates to a protective screen, and more specifically to a protective screen for individuals who may be exposed to varying forms of radiation, in particular time- varying electromagnetic (TV EMF) and radiofrequency (RF) electromagnetic fields - frequencies encountered in magnetic resonance imaging (MRI).
  • TV EMF time- varying electromagnetic
  • RF radiofrequency
  • the invention should not be considered as limited by the type of apparatus emitting such radiation, nor by the application that such apparatus might have, or the function it might perform.
  • the invention could also be used in protection of non-human components, such as electronics, where conventional methods of passive ferromagnetic shielding may not be possible or practicable.
  • NMR Nuclear magnetic resonance
  • ICNIRP International Commission on Non-Ionising Radiation Protection
  • a Faraday cage being a structure commonly used in MRI equipment and consisting essentially of a conductive structure of a fine wire mesh or continuous copper sheet, will function as a simple RF screen.
  • EMF shielding works by interacting and diverting/deflecting the EMF away from the protected area.
  • a crucial criterion when designing a shield is the level of attenuation required at specific frequencies and powers of EMF.
  • a protective screen adapted for restricting and/or reducing the amount of radiation passing therethrough, said radiation including both RF and EMF components, characterised in that the screen is of laminar construction and comprising at least two laminae of differing materials, a first of said materials being chosen so as to attenuate RF radiation passing therethrough, and the second material being capable of having an electric and/or a magnetic field induced therein as a result of the existence of an EMF source, said induced electric and/or magnetic fields giving rise to destructive interference with the original inducing EMF thus reducing the resulting amplitude of EMF on the side of the screen being more remote from the EMF source.
  • the frequency of the EMF is unaffected by the second material, and only the amplitude, and thus the power contained within the radiation (indicative of its potential to harm) is reduced.
  • the first material is of copper or other well known, similar RF attenuator, most preferably solid high-purity copper because of its inherent high conductivity and low resistivity.
  • aluminium or similar metal of low conductivity and resistance may be used for the first material.
  • the second material is preferably a strong dia- or paramagnetic material or alloy thereof.
  • the second material may be a non- ferromagnetic stainless steel.
  • a conductive glass impregnated with suitable substances which on the one hand are capable of RF attenuation, and on the other hand are capable of having electric and/or magnetic fields induced therein.
  • suitable substances which on the one hand are capable of RF attenuation, and on the other hand are capable of having electric and/or magnetic fields induced therein.
  • a further alternative is a copper mesh material
  • the screen shape is complementary to that of an MRI scanner around which it is to be disposed.
  • the screen may also be floor or ceiling mounted. Most preferably, the screen passively interacts with the EMF (which for the purposes of this application is always considered to be the time-varying EMF produced by the magnetic gradient-generating coils, and RF if present).
  • EMF which for the purposes of this application is always considered to be the time-varying EMF produced by the magnetic gradient-generating coils, and RF if present.
  • Fig. 1 shows schematically a laminar structure for a screen
  • Fig. 2 shows schematically the structure of the screen at the level of a window.
  • a laminar structure 2 comprising two laminae 4, 6 of different materials which are ideally used in the manufacture of a screen, or of material from which screens may be manufactured, according to the present invention.
  • the material of the first lamina 4 comprises a material of copper or other well known, similar RF attenuator, such as Aluminium.
  • the material of the second lamina 6 is a strong dia- or paramagnetic material or alloy thereof. Alternatively, the material of the second lamina may be a non-ferromagnetic stainless steel.
  • a window area 8 constituted by a conductive or transmissive glass, impregnated with suitable substances which on the one hand are capable of RF attenuation, and/or on the other hand are capable of having electric and/or magnetic fields induced therein, as shown in Figure 2.
  • the window is made of a fine copper mesh.
  • the material of the first lamina would be a conductive/transmissive glass having been impregnated with a first substance capable of attenuating RF signals, or alternatively a fine copper mesh
  • the material of the second lamina would be a conductive/transmissive glass having been impregnated with a second substance capable of having electric and/or magnetic fields induced therein which destructively interfere with the EMF source that induced them.
  • the present invention at least in terms of attenuating TVEMF signals, relies on the physical principle of skin depth, a measure of the distance over which the current in a conductor falls to 1/e of its original value from the surface of said conductor.
  • the equation for calculating the skin depth (EMF attenuating thickness) of a conductor is well known and depends on the screen conductor's permeability, resistivity and conductivity values. The skin depth will vary with EMF frequency.
  • time varying magnetic gradient EMF frequencies exist] up to the KHz level (TVEMF from the magnetic gradient coils) and up to MHz levels in respect of RF radiation from the transmitting RF coil.
  • Appropriate thicknesses of copper screen have been calculated to attenuate this range (the lower frequency EMFs resulting in thicker skin depth values than the higher frequencies). It is suggested a value of between 2 and 6mm of effective copper thickness would be appropriate for most MRI applications. Thicker screens could be used for lower frequency TV EMF protection.
  • the screen would have to be flexible with fastenings around the waist.

Abstract

La présente invention concerne un écran protecteur conçu pour limiter et/ou réduire la quantité de rayons le traversant, lesdits rayons comprenant à la fois des composants RF et EMF. L'écran protecteur se caractérise en ce qu'il présente une structure laminaire et comprend au moins deux couches de matériaux différents, le premier matériau étant sélectionné afin d'atténuer les rayons RF le traversant et le second matériau pouvant contenir un champ électrique et/ou magnétique induit dans celui-ci par une source EMF. Lesdits champs électriques et/ou magnétiques induits génèrent une interférence destructive avec l'EMF inducteur de départ, réduisant ainsi l'amplitude découlant de l'EMF sur le côté de l'écran se trouvant le plus éloigné de la source EMF. En principe, le premier matériau est en cuivre et le second est un composé ou un élément dia- ou paramagnétique.
PCT/GB2007/002120 2006-06-13 2007-06-08 Écran protecteur WO2007144578A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB0820020A GB2452641A (en) 2006-06-13 2007-06-08 Protective screen

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0611617A GB2439109A (en) 2006-06-13 2006-06-13 Electromagnetic radiation screen
GB0611617.2 2006-06-13

Publications (2)

Publication Number Publication Date
WO2007144578A2 true WO2007144578A2 (fr) 2007-12-21
WO2007144578A3 WO2007144578A3 (fr) 2008-04-10

Family

ID=36745754

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2007/002120 WO2007144578A2 (fr) 2006-06-13 2007-06-08 Écran protecteur

Country Status (2)

Country Link
GB (2) GB2439109A (fr)
WO (1) WO2007144578A2 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102011076717A1 (de) * 2011-05-30 2012-12-06 Siemens Aktiengesellschaft Hochfrequenzantenneneinheit, eine Magnetresonanzvorrichtung mit einer Hochfrequenzantenneneinheit, sowie ein Herstellungsverfahren für eine Hochfrequenzantenneneinheit
RU2646439C1 (ru) * 2017-03-14 2018-03-06 Федеральное государственное бюджетное учреждение науки Институт космических исследований Российской академии наук Многослойный электромагнитный экран

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5012041A (en) * 1989-06-22 1991-04-30 The Curran Company Screened window for shielded enclosure
US6252159B1 (en) * 1999-01-21 2001-06-26 Sony Corporation EMI/RFI and vibration resistant electronics enclosure
US20030107025A1 (en) * 2000-11-21 2003-06-12 Katsumi Okayama Radio-wave absorber
US20040001299A1 (en) * 2001-12-14 2004-01-01 Laird Technologies, Inc. EMI shield including a lossy medium
US20040020674A1 (en) * 2002-06-14 2004-02-05 Laird Technologies, Inc. Composite EMI shield

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE8007075L (sv) * 1979-10-31 1981-05-01 Illinois Tool Works Skermning
US4514586A (en) * 1982-08-30 1985-04-30 Enthone, Inc. Method of using a shielding means to attenuate electromagnetic radiation in the radio frequency range

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5012041A (en) * 1989-06-22 1991-04-30 The Curran Company Screened window for shielded enclosure
US6252159B1 (en) * 1999-01-21 2001-06-26 Sony Corporation EMI/RFI and vibration resistant electronics enclosure
US20030107025A1 (en) * 2000-11-21 2003-06-12 Katsumi Okayama Radio-wave absorber
US20040001299A1 (en) * 2001-12-14 2004-01-01 Laird Technologies, Inc. EMI shield including a lossy medium
US20040020674A1 (en) * 2002-06-14 2004-02-05 Laird Technologies, Inc. Composite EMI shield

Also Published As

Publication number Publication date
GB0611617D0 (en) 2006-07-19
WO2007144578A3 (fr) 2008-04-10
GB0820020D0 (en) 2008-12-10
GB2452641A (en) 2009-03-11
GB2439109A (en) 2007-12-19

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