Abstract:
An assembly for shielding an aircraft from electromagnetic energy may include a window mounting configured to be conductively coupled to an aperture in a fuselage of an aircraft. The window mounting may include a window pane having an electromagnetically-reflective coating for reflecting electromagnetic energy. The window pane may remain electrically isolated from the fuselage prior to the electromagnetic energy exceeding a frequency of approximately 1 GHz. The window mounting may further include a capacitive gasket capacitively coupling the window pane to the fuselage after the frequency of the electromagnetic energy reflected by the window pane exceeds approximately 1 GHz.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional application of and claims priority to pending U.S. application Ser. No. 11/812,300 filed on Jun. 18, 2007, and entitled RADIO FREQUENCY SHIELDING APPARATUS SYSTEM AND METHOD, the entire contents of which is expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     The present disclosure generally relates to radio frequency shielding for a commercial aircraft. More particularly, the disclosure pertains to a method and system that assists in attenuating electromagnetic propagation through commercial aircraft passenger windows, aircraft doors or the like. 
     BACKGROUND 
     Generally, the fuselage of commercial aircraft are extremely efficient at attenuating electromagnetic radiation or energy such as radio frequency (RF) energy. Conventional aircraft typically include an outer skin of aluminum or include a conductive mesh or coating to dissipate lightning strikes. This conductive skin reflects and attenuates RF energy to a high degree. However, commercial aircraft generally also include a number of electromagnetic apertures. Aircraft windows and doors are two of the most common electromagnetic apertures inherent to most commercial aircraft designs. During operation of commercial aircraft, these apertures allow RF energy to enter and exit the aircraft. 
     This property of aircraft windows and doors is undesirable for several reasons. For example, externally generated RF transmissions may interfere with on-board systems. In another example, internally generated RF transmissions may interfere with on-board systems and/or may violate the rules of the United States Federal Communications Commission (FCC) and other such regulatory institutions. 
     Accordingly, it is desirable to provide a cost effective method and apparatus for attenuating electromagnetic propagation through aircraft passenger windows or the like at least to some extent. 
     SUMMARY 
     The foregoing needs are met, at least to some extent, by the present disclosure, wherein in one respect a system, assembly, and method is provided that in some embodiments attenuates electromagnetic propagation through an aperture in an aircraft. 
     An embodiment relates to a system for shielding an aircraft from electromagnetic energy. The system includes a fuselage, aperture, window mounting, and window plug. The fuselage provides an electrically conductive envelope. The aperture is disposed in the fuselage. The window mounting spans the aperture. The window plug spans the aperture. The window mounting and the window plug are electrically coupled to the fuselage and provide an electrical path spanning the aperture. 
     Another embodiment pertains to an assembly for shielding an aperture in a fuselage of an aircraft from electromagnetic energy. The assembly includes a window mounting and a window plug. The window mounting spans the aperture. The window plug spans the aperture. The window mounting and the window plug are electrically coupled to the fuselage and provide an electrical path spanning the aperture. 
     Yet another embodiment relates to a method of shielding an aperture in a fuselage of an aircraft from electromagnetic energy. In this method, a window mounting is conductively connected to the fuselage and a window plug is conductively connected to the window mounting. 
     There has thus been outlined, rather broadly, certain embodiments that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments that will be described below and which will form the subject matter of the claims appended hereto. 
     In this respect, before explaining at least one embodiment in detail, it is to be understood that embodiments are not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. In addition to the embodiments described, the various embodiments are capable of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
     As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the disclosure. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the various embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view of a system for shielding an aperture according to an embodiment. 
         FIG. 2  is a cross-sectional perspective view of a window mounting suitable for use with the system according to  FIG. 1 . 
         FIG. 3  is a cross-sectional view of a capacitive gasket suitable for use with the window mounting according to  FIG. 2 . 
         FIG. 4  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of coated windows suitable for use with the system according to  FIG. 1 . 
         FIG. 5  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of coated windows and electronically dimmable windows suitable for use with the system according to  FIG. 1 . 
         FIG. 6  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of coated windows and grounded electronically dimmable windows suitable for use with the system according to  FIG. 1 . 
         FIG. 7  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of coated windows and circumferentially bonded electronically dimmable windows suitable for use with the system according to  FIG. 1 . 
         FIG. 8  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of a coated bellows suitable for use with the system according to  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment in accordance with the present disclosure provides a method and system that assists in attenuating electromagnetic propagation, for example RF energy, through commercial aircraft apertures such as passenger windows, aircraft doors or the like. More particularly, an embodiment provides an aircraft aperture assembly or system having a plurality of components that, when assembled in an aircraft frame or fuselage, assists in the attenuation of the transmission of RF energy therethrough. 
     Referring now to  FIG. 1 , a window system  10  includes a window mounting  14  and window plug  16 . The window mounting  14  is configured to be mounted in or mated with a window opening  18  in an outer skin  20  of an aircraft (not shown). The window plug  16  is configured to be mounted in or mated with a plug opening  22  in an inner skin  24  of the aircraft. The window mounting  14  includes a capacitive gasket  28 , outer window  30 , inner window  32 , and window forging  34 . The window mounting  14  is further described in  FIGS. 2 and 3 . The window plug  16  includes a bellows seal  40 , outer reveal  42 , electronically dimmable window (EDW)  44 , inner reveal  46 , dust cover  48 , and window plug molding  50 . 
     In general, some or all of the various components of the window system  10  are configured to conduct electricity sufficiently well enough to reflect and/or attenuate electromagnetic energy such as RF energy. More particularly, when installed in an electrically conductive envelope such as a fuselage of an aircraft, the assembled components of the window system  10  provide a conductive path spanning the window opening  18  in the outer skin  20  of the fuselage. In this manner, electromagnetic energy such as RF energy generated within the fuselage may be attenuated or essentially prevented, to a large extent, from entering or exiting the fuselage. It is an advantage of various embodiments that RF energy may be attenuated to such an extent that signals emanating from within the fuselage can not reasonably be detected outside the fuselage. It is another advantage of various embodiments that, for the purposes of the United States Federal Communications Commission (FCC) and other such regulatory institutions, the interior of an aircraft outfitted with the window system  10  may be classified an indoor environment due to the attenuation of RF energy provided by the window system  10 . 
     In  FIG. 2 , a particular embodiment of the commercial aircraft window mounting, generally designated  14 , is illustrated. The commercial aircraft window mounting  14  includes the capacitive gasket  28  positioned between and/or partially surrounding the outer window  30  and the inner window  32 . The commercial aircraft mounting  14  additionally includes the window forging  34  that is configured to mate with the airframe or outer skin  20  of the aircraft. The window forging  34  includes a radial flange  56  and an axial flange  58 . The window forging  18  also includes a base portion  60  that extends in opposing relationship to the radial flange  56 . That is, the base portion  60  extends generally inwardly or opposite the radial flange  56  as previously discussed, and provides an inwardly and downwardly sloping surface  62 . 
     As illustrated in  FIG. 2 , the commercial aircraft window mounting  14  further includes a series of spring clips  64  positioned about the periphery of the window forging  34 . The commercial aircraft window mounting  14  also has a series of mounting flanges  66  and a series of bolts  68 , or other such mechanical attachments or fasteners, also positioned about the periphery of the forging  34 . The mounting flanges  66  are connected to, and extend from, the axial flange  58  of the window forging  34 . The mounting flanges  66  are positioned about the periphery of the window forging  34  as illustrated in  FIG. 1 , and combine with the spring clips  64  and the bolts  34  to mount the gasket  28  and outer and inner windows  30 ,  32  to the window forging  34 . 
     Referring now to  FIGS. 2 and 3 , a cross-sectional view of the gasket  28  is illustrated. As depicted in  FIGS. 2 and 3 , the gasket  28  encircles the outer window  30  and inner window  32  and provides a circumferential bond between the outer and inner windows  30 ,  32  and the window forging  34 . The gasket  28  is a capacitive gasket that provides a capacitive bond between the windows  30 ,  32  and the window forging  34 . The gasket  28  includes a lower portion or section  70 , a mid-section or portion  72  and an upper portion or section  74 . 
     As illustrated in  FIGS. 2 and 3 , the lower section  70  of the gasket  28  extends from the mid-section  72  of the gasket  28  at an angle in a downwardly direction, away for the window forging  34 . The aforementioned geometry of the lower section  70  of the gasket  28  generally mirrors or compliments the downwardly sloping surface  62  of the base portion  60 . The lower section  70  includes a series of ridges, generally designated  78 , that extend outwardly from the lower section  70 . As depicted in  FIGS. 2 and 3 , the mid-section  72 , as the name suggests, occupies the middle portion of the gasket  28  and functions as a spacer between the outer window  30  and inner window  32 . The upper portion  74  extends upwardly from the mid-section  72 , generally parallel to the axial flange  58  of the window forging  34 . 
     In various embodiments, the gasket  28  includes a conductive media that is bound by an elastomeric matrix. The conductive media includes any suitable strongly, weakly, and/or semi-conductive materials. Specific examples of conductive materials include conductive carbon black, aluminum, silver, and the like. The elastomeric matrix includes ethylene propylene diene monomer (EPDM) and the like. In one embodiment, the capacitive gasket  28  includes a carbon black media in an EPDM or other such elastomeric matrix. Alternatively, the gasket  28  may include silver and/or aluminum flakes in an EPDM or other such elastomeric matrix. The carbon black media provides greater than 20 dB to about 45 dB of RF energy shielding in the range of from about 80 MHz to approximately 18 GHz of the electromagnetic spectrum. The silver and/or aluminum flake media provides approximately 10 dB to about 47 dB of RF energy shielding in the range of from about 80 MHz to approximately 18 GHz of the electromagnetic spectrum. 
     As previously discussed, during operation of commercial aircraft for example, the aircraft encounters electromagnetic energy in the form of RF radiation from external sources. This RF radiation can interfere with the operation of the commercial aircraft systems such as the communication system and the navigation system. Accordingly, in order to attenuate the propagation of RF radiation through the commercial aircraft passenger windows, techniques such as shielding are implemented to reduce electromagnetic propagation. During the shielding process and, prior to assembly of the window system  10  the windows are treated with a film or material that reflects electromagnetic energy. As illustrated in  FIG. 1 , the inner window  32  has been shielded or treated, as generally designated by reference numeral  76 , with a film or other material that reduces or attenuates the propagation of electromagnetic radiation. The shielding  76  includes any suitable film, layer, and/or treatment operable to reflect, attenuate, or otherwise reduce the propagation of electromagnetic energy. Suitable examples of the shielding  76  include conductive films, meshes, and the like. 
     The shielded inner window  32  combines with the gasket  28  to reduce electromagnetic propagation through the passenger windows of a commercial aircraft. As previously discussed, the shielded window  32  reflects electromagnetic radiation, however as the frequency of electromagnetic energy increases, for example, to approximately 1 GHz to approximately 2 GHz, the window may begin to lose its attenuation characteristics and begin to resonate and retransmit the electromagnetic energy. To avoid such instances, the gasket  28  provides a capacitive coupling between the inner window  32  and the commercial aircraft frame, dissipating the electromagnetic energy onto the aircraft frame or outer skin  20 . In this regard, the gasket  28  includes a material having a dielectric constant, permittivity, and/or resistance such that the gasket  28  is configured to discharge electromagnetic energy from the window  32  to the window forging  34  prior to resonance of the window  32 . That is, the window  32  is configured to reflect electromagnetic energy until the energy exceeds a predetermined maximum amount of energy. If the window  32  were to remain electrically isolated past this predetermined maximum amount of energy, the window  32  may transmit RF energy. The gasket  28  is configured to conduct electromagnetic energy or electricity from the window  32  to the window forging  34  prior to the amount of energy in the window  32  exceeding the predetermined maximum. The gasket  28  further assists the attenuation electromagnetic radiation by absorbing some of the electromagnetic energy as heat. 
       FIGS. 4-7  are examples of graphs showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of components suitable for use with the system according to  FIG. 1 . As shown in  FIG. 4 , the window  30  and/or  32 , when coated with a thin, essentially transparent, coating of gold, attenuates approximately 20 decibels (dB) of electromagnetic (EM) energy within a frequency range of about 300 megahertz (MHz) to about 11,000 MHz. As shown in  FIG. 5 , when the coated window  30  and/or  32  is combined with the EDW  44 , approximately 25 dB of EM energy is attenuated within a frequency range of about 300 MHz to about 11,000 MHz. That is, assembling these two components increases the attenuation. Similarly, as shown in  FIG. 6 , by grounding the EDW  44 , approximately 35 dB of EM energy is attenuated within a frequency range of about 300 MHz to about 11,000 MHz. The attenuation is further again increased by circumferentially bonding the EDW  44  within the window system  10 . In a particular embodiment, the EDW  44  is circumferentially bonded to the window system  10  via the bellows seal  40 . For example the bellows seal  40  is conductively coated or otherwise configured to conduct EM energy. In a particular example, the bellows seal  40  is coated with an electrically conductive silicone-based ink. This ink may include any suitable conductive material such as, for example, aluminum, silver, gold, carbon, and the like. While in general, any suitable coating material that exhibits good adhesion to the bellows seal  40 , flexibility, and conductivity may be utilized in various embodiments, specific examples of coating materials may be manufactured by Creative Materials, Inc. of Tyngsboro, Mass. 01879, U.S.A. In particular, product number 115-08, electrically conductive silicone ink with 87% silver (cured) is suitable for use with various embodiments. It is to be understood that the graphs illustrated in  FIGS. 4-7  are for illustrative purposes only, and thus, the respective curvatures, slopes and y-intercepts may be the same or different depending on the response of the various EM energy attenuators. 
       FIG. 8  is an example of a graph showing frequency in MHz (abscissa) as it affects the shielding effectiveness in dB (ordinate) of a coated bellows suitable for use with the system according to  FIG. 1 . As shown in  FIG. 8 , when coated with electrically conductive silicone ink with 87% silver (cured), the bellows seal  40  attenuates approximately 20 dB. It is to be understood that the graph illustrated in  FIG. 8  is for illustrative purposes only, and thus, the respective curvatures, slopes and y-intercepts may be the same or different depending on the response of the various EM energy attenuators. 
     The many features and advantages of the various embodiments are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages that fall within the true spirit and scope of the embodiments. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the embodiments to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the various embodiments.