Abstract:
An apparatus for distributing electromagnetic waves comprising a first plurality of plates coupled to a first rod. A second plurality of plates coupled to a second rod, wherein at least one of either the first or the second plurality of plates is capable of reflecting an electromagnetic wave. A portion of the second rod is situated inside the first rod. A first motor mechanically connected to the first rod, such that the first motor is capable of rotating the first rod. A second motor mechanically connected to the second rod, such that the second motor is capable of rotating the second rod, wherein rotational direction and speed of the second rod, when rotated by the second motor is independent of rotational direction and speed of the first rod, when rotated by the first motor.

Description:
FIELD OF THE INVENTION 
       [0001]    This disclosure relates generally to reducing electromagnetic interference (EMI) in an electronic device, and in particular, to enclosures containing resonant electromagnetic fields. 
       BACKGROUND OF THE INVENTION 
       [0002]    For purposes of this disclosure, the term electromagnetic interference (EMI) is understood to refer to electromagnetic emission and radiation that includes both electromagnetic interference and radio-frequency interference (RFI). Both of these types of interference generate electromagnetic fields that can interfere with the operation of adjacent electrical equipment. It is desirable to protect electronic devices from external EMI, and also to prevent internal EMI from escaping and possibly interfering with other electronic devices in the vicinity. To accomplish this, EMI shields comprised of EMI absorbing material are often used in enclosures containing electronic equipment, components, and/or circuitry (e.g., computers and test equipment). 
         [0003]    EMI absorbing material provides highly efficient EMI attenuation. However, when dealing with electronic devices generating high levels of EMI within an enclosure, EMI absorbing material is only partially effective in EMI attenuation. Enclosures of electronic devices typically allow for an amplified effect due to EMI. This is due in part to resonance of the EMI waves within the enclosure. Resonance can amplify the EMI occurring in the form of standing waves in the enclosure thus having a greater affect on the electronic devices in the path of these waves. The formation of electromagnetic standing waves produces spikes in amplitude of this interference in areas within the enclosure. 
         [0004]    Mode stirrers typically used in reverberation chambers have the ability to distribute these EMI waves in an enclosure in a homogeneous manner. Mode stirrers distribute these EMI waves to eliminate standing waves through resonance by reflecting these waves throughout the enclosure and establishing a uniform statistical distribution of fields throughout the volume. This lowers the net field strength in an area where seams and apertures are located, thus lowering the radiation outside the enclosure from these seams and apertures. 
       SUMMARY 
       [0005]    One aspect of an embodiment of the present invention discloses an apparatus for distributing electromagnetic waves comprising, a first plurality of plates coupled to a first rod. A second plurality of plates coupled to a second rod, wherein at least one of either the first or the second plurality of plates is capable of reflecting an electromagnetic wave. A portion of the second rod is situated inside the first rod. A first motor mechanically connected to the first rod, such that the first motor is capable of rotating the first rod. A second motor mechanically connected to the second rod, such that the second motor is capable of rotating the second rod, wherein rotational direction and speed of the second rod, when rotated by the second motor is independent of rotational direction and speed of the first rod, when rotated by the first motor. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The following detailed description, given by way of example and not intended to limit the disclosure solely thereto, will best be appreciated in conjunction with the accompanying drawings, in which: 
           [0007]      FIG. 1  depicts an electronic device enclosure in accordance with an embodiment of the present invention. 
           [0008]      FIG. 2  depicts an EMI mode stirrer in accordance with one embodiment of the present invention. 
           [0009]      FIG. 3  depicts a preferred alignment of reflective paddles on a rotational rod of the EMI mode stirrer of  FIG. 2 . 
           [0010]      FIG. 4  depicts a preferred alignment of absorber paddles on the rotational rod of the EMI mode stirrer of  FIG. 2 . 
           [0011]      FIG. 5  depicts an inner rotational rod with attached reflective paddles of the EMI mode stirrer of  FIG. 2 . 
           [0012]      FIG. 6  depicts an outer rotational tube with attached absorber paddles of the EMI mode stirrer of  FIG. 2 . 
           [0013]      FIG. 7  depicts a safety enclosure encompassing the EMI mode stirrer of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Detailed embodiments of the present invention are disclosed herein with reference to the accompanying drawings; however, it is to be understood that the disclosed embodiments are merely illustrative of potential embodiments of the invention and may take various forms. In addition, each of the examples given in connection with the various embodiments is also intended to be illustrative, and not restrictive. This description is intended to be interpreted merely as a representative basis for teaching one skilled in the art to variously employ the various aspects of the present disclosure. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments. 
         [0015]      FIG. 1  depicts an electronic device enclosure in accordance with an embodiment of the present invention. In one embodiment, enclosure  100  is a server rack. In another embodiment, enclosure  100  is a computer tower. In other embodiments, enclosure  100  may be any enclosure designed to contain various electronic devices or components that generate heat and/or electromagnetic emissions during operation. Enclosure  100  is preferably composed of a metal or other conducting material and preferably forms a large portion of a Faraday cage to block electric fields and electromagnetic emissions. Enclosure  100  preferably contains a minimal amount of openings. EMI mode stirrer  102  is meant to be horizontally placed within enclosure  100  in a location dependent on what electronic devices are contained within and is preferably composed of a non-metal. Since, every enclosure  100  is able to hold various electronic devices which emit various ranges of EMI frequency, the location of the EMI mode stirrer further depends on the frequencies emitted and the location of electronic circuitry and devices in enclosure  100 . In one embodiment, EMI mode stirrer  102  can be located on the bottom of enclosure  100  and in another embodiment EMI mode stirrer  102  can be located towards the top of enclosure  100 . In another embodiment, multiple EMI mode stirrers can be used in applications of heavy EMI areas containing a greater range of frequencies or in applications with large enclosures  100 . 
         [0016]      FIG. 2  depicts an isometric view of EMI mode stirrer  102  in accordance with one embodiment of the present invention. 
         [0017]    EMI mode stirrer  102  comprises two variable rotational speed motors designated  202 A and  202 B. The respective direction and rotational speed of motor  202 A and motor  202 B is dependent on the speed required to match the resonance frequency, which creates a destructive interference negating resonant EMI waves present in enclosure  100 . In this embodiment, motor  202 A and motor  202 B are each joined to a fan to provide additional cooling in enclosure  100 . 
         [0018]    In one embodiment, motor  202 A rotates rod  208 A and motor  202 B rotates hollow rod  208 B on an axis. The axis of rotation for motor  202 A is the same axis of rotation for rod  208 A. The axis of rotation for motor  202 B is the same axis of rotation for hollow rod  208 B. Rod  208 A and hollow rod  208 B are concentric with rod  208 A rotating inside hollow rod  208 B. In a preferred embodiment, rod  208 A and hollow rod  208 B are preferably composed of an alloy metal. Hollow rod  208 B can have a set of bearings in which rod  208 A can rotate in. 
         [0019]    Reflective plates  204  are joined to rod  208 A in sets of two so that the center axis of rotation of the reflective plates  204  aligns with the center axis of rotation of rod  208 A. A set of reflective plates  204  are joined on one side to form a “V” arrangement and a set of absorbent plates  206  are joined on one side to form a “V” arrangement. Absorbent plates  206  are joined to hollow rod  208 B in sets of two so that the center axis of rotation of the absorbent plates  206  align with the center axis of rotation of hollow rod  208 B. Each reflective plate  204  is fixed to rod  208 A and rotates with the same rotational speed as rod  208 A. Each absorbent plate  206  is fixed to hollow rod  208 B and rotates with the same rotational speed as hollow rod  208 A. Every reflective plate  204  is preferably of an EMI reflective material. EMI reflective material can be but is not limited to: steel, copper, aluminum, carbon-loaded plastic or high dielectric ceramic. Every absorbent plate  206  is preferably of an EMI absorbent material. EMI absorbent material is any type of material comprising some form of magnetic property. In the preferred embodiment, the shape of reflective plate  204  and absorbent plate  206  is a circle but in other embodiments can take on any symmetrical shape. 
         [0020]    Depending on enclosure  100  and the frequencies being emitted by the electronic devices, the number of sets of reflective plates  204  and absorbent plates  206  varies. For example, where enclosure  100  is a large enclosure storing many electronic devices, the range of frequency of the EMI may be greater. The size and the number of the reflective plates  204  and absorbent plates  206  can be altered to compensate for the size of enclosure  100 . 
         [0021]    In one embodiment, reflective plates  204  and absorbent plates  206  alternate on EMI mode stirrer  102  by sets of two. To allow reflective plates  204  to rotate at a speed set by motor  202 A and absorbent plates  206  to rotate at a speed set by motor  202 B, where the speed may be different. Alternating sets of plates are connected in a fashion to allow rotation independent of an intermediate set of plates. Towards that end, in one embodiment, each set of absorbent plates  206  is connected by plate  210 . This allows absorbent plates  206 , connected to hollow rod  208 B to rotate independent of reflective plates  204  connected to rod  208 A. Plate  210  is preferably of an alloy metal so it does not interfere with the rotational balance of EMI mode stirrer  102 . 
         [0022]      FIG. 3  depicts an isometric view of a preferred alignment of two reflective plates  204  on rod  208 A. The two reflective plates  204  are fixed to rod  208 A at a given angle. In a preferred embodiment the two reflective plates  204  are arranged in a clam-shell or “V” arrangement where the two plates contact each other at one end at an angle between 1 degree and 179 degrees. Optimal angles are such as to produce the maximum number of reflections and re-reflections on the inside surfaces. The center of the reflective plates  204  is concentric to the center of rod  208 A. 
         [0023]      FIG. 4  depicts an isometric view of a preferred alignment of two absorbent plates  206  on hollow rod  208 B. The two absorbent plates  206  are joined to hollow rod  208 B at a given angle. In a preferred embodiment the two absorbent plates  206  are arranged in a clam-shell arranged where the given angle between the two absorbent plates  206  ranges between 1 degree and 179 degrees. The center of the absorbent plates  206  is concentric to the center of hollow rod  208 B. 
         [0024]      FIG. 5  depicts an orthographical view of inner rotational rod  208 A with attached reflective paddles  204  of EMI mode stirrer  102 . 
         [0025]      FIG. 6  depicts an orthographical view of outer rotational hollow rod  208 B with attached absorbent paddles  206  of EMI mode stirrer  102 . As previously mentioned in the discussion of  FIG. 2 , plate  210  allows absorbent plates  206  connected to hollow rod  208 B to rotate independent of reflective plates  204  connected to rod  208 A. Plate  210  connects the two sets of absorbent plates  206  so they rotate in synchronization. 
         [0026]      FIG. 7  depicts a full view of safety enclosure  700  encompassing EMI mode stirrer  102 . Safety enclosure  700  is preferably composed of a non-conducting material. In one embodiment, safety enclosure  700  is a rectangular box comprised of an electromagnetic dissipative (i.e., lossy) grid of holes  702  through which the EMI waves may pass through to be effectively absorbed or reflected by EMI mode stirrer  102 . The grid of holes  702  covers each side of the rectangular box. Holes  702  on safety enclosure  700  can be any shape and the holes are preferably of a size through which a person&#39;s finger cannot pass through. In a preferred embodiment, holes  702  would be round with a diameter ranging between 0.75 mm to 1.25 mm. 
         [0027]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting to the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
         [0028]    Having described preferred embodiments of an EMI mode stirrer (which are intended to be illustrative and not limiting), it is noted that modifications and variations may be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments disclosed which are within the scope of the invention as outlined by the appended claims.