The invention is generally related to an improved steel sheeting for use in room size radio frequency shielded enclosures and a method for making improved steel sheeting. In particular, the invention uses tin plated steel sheet of varying thicknesses which are continuously soldered together at the seams to provide the means to construct a Radio Frequency (“RF”) Shielded enclosure.
There exists a current need for RF shielding in connection with various needs, including medical and government applications. Specifically, where magnetic resonance imaging (“MRI”) is used in medical applications, it is important to screen and shield external radio frequencies from the room in which MRI procedures are conducted. In addition, in some applications, it is also important to shield the room from external magnetic fields as well. Similar concerns arise in government and military applications where it is also desired to shield against radio frequencies and magnetic fields.
Electromagnetic shielding is the process of limiting the flow of electromagnetic fields between two locations, by separating them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the ‘outside world’. Electromagnetic shielding used to block radiofrequency electromagnetic radiation is also known as RF shielding.
RF shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields, though not static or low-frequency magnetic fields. (A conductive enclosure used to block electrostatic fields is also known as a Faraday cage.) The amount of reduction depends very much upon the material used, its thickness, and the frequency of the fields of interest. Typical materials used for electromagnetic shielding include sheet metal, metal mesh, ionized gas, and plasma. Any holes in the shield or mesh must be significantly smaller than the wavelength of the radiation that is being kept out, or the enclosure will not effectively approximate an unbroken conducting surface.
Electromagnetic radiation consists of coupled electric and magnetic fields. The electric field produces forces on the charge carriers (i.e., electrons) within the conductor. As soon as an electric field is applied to the surface of an ideal conductor, it generates a current that causes displacement of charge inside the conductor that cancels the applied field inside, at which point the current stops.
Similarly, varying magnetic fields generate current vortices that act to cancel the applied magnetic field. (The conductor does not respond to static magnetic fields, so static magnetic fields can penetrate the conductor freely.) The result is that electromagnetic radiation is reflected from the surface of the conductor: internal fields stay inside, and external fields stay outside.
Several factors serve to limit the shielding capability of real RF shields. One is that, due to the electrical resistance of the conductor, the excited field does not completely cancel the incident field. Also, most conductors exhibit a ferromagnetic response to low-frequency magnetic fields, so that such fields are not fully attenuated by the conductor. Any holes in the shield force current to flow around them, so that fields passing through the holes do not excite opposing electromagnetic fields. These effects reduce the field-reflecting capability of the shield.
Currently, RF shielded enclosures are constructed using the following methods:
These existing methods for providing RF shielding each have disadvantages as described below:
However, since copper is non-ferrous, a method five type of enclosure has little shielding to magnetically generated fields. In addition, this the costs associated with this method rise and fall with the costs of copper.
Accordingly, a need exists for an improved method of RF shielding that has a low cost and is also suitable for shielding of magnetically generated fields.
An object of the present invention is to provide an improved method of RF shielding that has a low cost and is also suitable for shielding of magnetically generated fields. Specifically, the present invention uses tin-plated sheets of various thicknesses that are applied to an existing structure of wood or steel studs on the floor, walls and ceiling. The tin-plated steel sheet are continuously soldered together at the seams to provide the means to construct a Radio Frequency (“RF”) Shielded enclosure that also provides shielding against magnetically generated fields.
The invention will now be described in detail in relation to a preferred embodiment and implementation thereof which is exemplary in nature and descriptively specific as disclosed. As is customary, it will be understood that no limitation of the scope of the invention is thereby intended. The invention encompasses such alterations and further modifications in the illustrated apparatus, and such further applications of the principles of the invention illustrated herein, as would normally occur to persons skilled in the art to which the invention relates.
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Each tin-plated steel sheet 10a and 10b is preferably positioned on a backer material 13 that can be of varying thicknesses and fire ratings and is typically constructed from wood, although other materials can also be used. Alternatively, no backer material may be used. The backer material 13 provides support for the tin-plated steel sheets 10a and 10b. Backer 13 is preferably attached to the tin-plated steel sheets 10a and 10b by an adhesive or glue, including, without limitation, contact cement or neoprene.
The tin-steel steel sheets 10a and 10b are aligned and overlapped at the point of soldering 14. At the point of overlap 14, no backer material is used so that one tin-plated steel sheet 10a can be directly soldered to a second tin-plated steel sheet 10b. This process can continue to allow for joinder of several sheets. The width of the overlap area 14 that is soldered can vary, but is preferably in a range of about ½ inch to 1 inch. Any alloy-based solder can be used, including, without limitation, lead-based or tin-based solder. This process is repeated, as necessary, using sheets of needed sizes and shapes to create a shielded enclosure.
The present invention differs from and improves upon the prior methods in the present invention's use of tin-plated steel sheet of various thicknesses. In particular, tin-plated sheet and the related method of creating shielded enclosures using tin-plated metal sheeting provides all of the benefits of method five, described above, including flexibility, resistance to physical damage, and lifetime performance, but with lower costs and enhanced magnetic fields. This present invention allows provides the enhanced attenuation to magnetic fields provided by methods one and four, but again with lower costs as compared to method four and more resistance to physical damage as compared to method one.
Currently, where enhanced magnetic shielding is needed in existing methods (where possible), either a layer or layers of steel sheet is installed behind the copper sheet in methods three or five, or thicker layers of galvanized sheet metal are used in method 1 to enhance magnetic shielding performance in these methods. However, none of the existing methods offer the combination of lifetime performance, enhanced magnetic shielding performance and cost performance as with the present invention. Indeed, despite a long felt need for an RF shielding combining these desired properties, no such shielding method existed prior to the present invention.
This application hereby claims priority to provisional patent application Ser. No. 60/896,153, filed on Mar. 21, 2007.
Number | Date | Country | |
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60896153 | Mar 2007 | US |