Abstract:
Camera arrangements that can include electromagnetic protection, such as from EMP/IEMI events, is disclosed. One example camera arrangement includes a camera including a viewfinder having a lens, and an electromagnetically shielded enclosure defining an interior volume containing the camera and configured to include at least one opening aligned with the lens. The camera arrangement includes a waveguide beyond cutoff disposed across the at least one opening, the waveguide beyond cutoff including a plurality of cells sized and oriented to shield the interior volume of the enclosure from electromagnetic signals while exposing an optical path between the lens and objects external to the enclosure.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from U.S. Provisional Patent Application No. 61/410,755 filed on Nov. 5, 2010, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to structures for protection of electronic devices from electromagnetic events. In particular, the present disclosure relates to an electromagnetically shielded video or infrared camera, and a shielded enclosure for image capture devices. 
     BACKGROUND 
     Exposure to electromagnetic fields can cause interference or damage to electrical equipment, causing that equipment to malfunction or rendering it nonoperational. For example, electrical equipment and electronics can be destroyed, or otherwise fail in the event of a strong electromagnetic pulse or intentional electromagnetic interference event (EMP/IEMI). 
     EMP/IEMI events typically take one of two forms. First, high field events correspond to short-duration, high voltage events (e.g., up to and exceeding 100 kilovolts per meter), and typically are of the form of short pulses of narrow-band or distributed signals (e.g., in the frequency range of 14 kHz to 10 GHz). These types of events typically generate high voltage differences in equipment, leading to high induced currents and burnout of electrical components. Second, low field events (e.g., events in the range of 0.01 to 10 volts per meter) are indications of changing electromagnetic environments below the high field damaging environments, but still of interest in certain applications. 
     Existing systems are used to adjust to a narrow range of threats, and thus systems developed to address a certain problem are not useful to address other problems necessitating electromagnetic shielding that are exposed during use of other electronic equipment. One such unaddressed concern is for example equipment related to surveillance, such as video and infrared cameras. Typically, video camera lenses require exposure to an external environment to provide a field of view for that camera to capture. In circumstances where reliable operation through possibly damaging events is desirable, such as in the case of security cameras or sensitive image capture equipment, there is currently no reliable way to ensure such operation in the case of exposure of the camera to possible damage due to EMP/IEMI events. 
     For these and other reasons, improvements are desirable. 
     SUMMARY 
     In accordance with the following disclosure, the above and other issues are addressed by the following: 
     In a first aspect, an electromagnetically protected camera arrangement includes a camera including a viewfinder having a lens. The camera arrangement also includes an electromagnetically shielded enclosure defining an interior volume containing the camera and configured to include at least one opening aligned with the lens. The camera arrangement also includes a waveguide beyond cutoff disposed across the at least one opening, the waveguide beyond cutoff including a plurality of cells sized and oriented to shield the interior volume of the enclosure from electromagnetic signals while exposing an optical path between the lens and objects external to the enclosure. 
     In a second aspect, a camera arrangement includes a video or infrared camera including a viewfinder having a lens, and an electromagnetically shielded enclosure defining an interior volume containing the video camera and configured to include at least one opening aligned with the lens. The camera arrangement also includes an electrical filter positioned along a surface of the electromagnetically shielded enclosure and configured to receive a power signal external to the electromagnetically shielded enclosure and pass a filtered power signal to the video camera. The camera arrangement further includes a waveguide beyond cutoff disposed across the at least one opening and at a distance from the lens less than a focal length of the lens, the waveguide beyond cutoff including a plurality of hexagonal or other shape cells sized and oriented to shield the interior volume of the enclosure from electromagnetic signals while exposing an optical path between the lens and objects external to the enclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a schematic block diagram of an electromagnetically shielded camera, according to a possible embodiment; 
         FIG. 2  is a side cross-sectional schematic block diagram view of the electromagnetically shielded camera of  FIG. 1 ; 
         FIG. 3  is a schematic front layout of a portion of a waveguide beyond cutoff useable to implement aspects of the present disclosure; 
         FIG. 4  is a schematic side layout of a portion of a waveguide beyond cutoff useable to implement aspects of the present disclosure; and 
         FIG. 5  is a schematic perspective view of a portion of a waveguide beyond cutoff useable to implement aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the present invention will be described in detail with reference to the drawings, wherein like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention. 
     In general, the present disclosure relates to an electromagnetically shielded video camera and a shielded enclosure for image capture devices. In some embodiments disclosed herein, the shielded enclosure is configured to shield the camera from Electromagnetic Pulse or Intentional Electromagnetic Interference (EMP/IEMI) events. The electromagnetically shielded camera arrangements disclosed herein mitigate a risk of damage to optical equipment in the event of an electromagnetic event that would otherwise cause such damage. As such, electromagnetically shielded camera arrangements can be used in a variety of secure locations where monitoring is desired, such as in secure facilities (e.g., banks, utility buildings, government buildings, or other locations). 
     Referring now to  FIGS. 1-2 , an electromagnetically shielded camera  100  is shown, according to a possible embodiment of the present disclosure.  FIG. 1  illustrates a front view of a schematic block diagram of the electromagnetically shielded camera  100 , while  FIG. 2  illustrates a side cross-sectional schematic view of that camera along an axis “A” depicted in  FIG. 1 . 
     In the embodiment shown, the electromagnetically shielded camera  100  includes a waveguide beyond cutoff  102  mounted in a wall of an enclosure  104 . 
     Specifically, the arrangement  100  includes a waveguide  102 , usually comprised of small, thin-walled conductive hexagonal or other shape cells  103 , mounted in a wall of an enclosure  104  which encloses and shields a camera  106  and associated lens  108 . 
     The waveguide beyond cutoff  102  can be, in various embodiments, constructed from metal or other materials, and is configured and positioned to allow optical communication between an internal area of the enclosure  104  and an area external to the enclosure, for example providing an optical path, or field of view, to a camera  106  and associated lens  108 . 
     In general, the waveguide beyond cutoff  102  includes a honeycomb-shaped (i.e., hexagonal) or otherwise regularly-shaped geometric cells having a predetermined size and length, such that incident, high frequency signals external to the enclosure  104  are attenuated upon reaching the waveguide beyond cutoff  102 . In certain embodiments, the waveguide  102  is a honeycomb structure and is designed such that it attenuates EMP and IEMI waves to a sufficient level (sometimes the level is 80 db with a frequency range from typically 14 kHz to as high as 10 GHz but other levels and other frequencies are obtainable to meet different levels of protection desired) so as to protect the electronics within the enclosure  104  and within the camera. It is understood that the waveguide  102  may be typically be made of one or more of the cells  103 , such as honeycomb shaped hexagonal cells, round cells, square cells, vanes or other structures with small effective diameter and sufficient length through to provide the proper shielding. Usually, the air or in this case light passage is through the multiple openings in the waveguide  102  that are typically in the order of 1/16″ to ⅛″ in size. For optical use, the vanes defining the cells  103  should have a minimized thickness to minimize interference with optical paths passing through the waveguide beyond cutoff  102 . 
     In the embodiment shown, the waveguide  102  is oriented in line with the light passing to the lens  108 , so that the thin walls of the cells  103  provide minimal distortion, blockage or degradation of the image. The waveguide  102  is similar in principle to commercial waveguides designed to block entry of electromagnetic fields through air ducts used for cooling computers in shielded enclosures. Such waveguides are as described below. It is understood that other features of the enclosure must work in concert with the shielding of this light path to the lens  108  to provide complete, enclosed protection of the camera  106 , including shielding of all necessary penetrations of the enclosure  104  from electromagnetic field penetration, interference or damage. Examples of a waveguide beyond cutoff useable in conjunction with the present disclosure are discussed below in connection with  FIGS. 3-5 . 
     The enclosure  104  is generally configured to be an electromagnetically-shielding enclosure, capable of shielding an interior volume  110  of the enclosure from undesirable electromagnetic signals (e.g., electromagnetic signals exceeding a particular amplitude and frequency). In various embodiments, the enclosure  104  can be constructed from conductive materials, such as a metal (e.g., sheet metal or aluminum) having a thickness generally sufficient to attenuate electromagnetic signals to acceptable levels. Although in the embodiment shown the enclosure  104  is generally rectangular, it is understood that the enclosure  104  could be any of a variety of shapes. 
     In an example embodiment, the enclosure  104  provides about 70 dB or more of attenuation. However, in alternative embodiments, other levels of attenuation could be provided as well. Various features relating to electromagnetically-shielding enclosures, as well as methods for sealing such enclosures, are provided in copending U.S. patent application Ser. No. 13/285,581, filed on Oct. 31, 2011, the disclosure of which is hereby incorporated by reference in its entirety. 
     In the embodiment shown, a frame  105  can be used to mount the waveguide beyond cutoff  102  to the enclosure  104 . In various embodiments, the frame can provide a sealing connection to the enclosure  104 , for example using an electromagnetically-shielded gasket arrangement or other arrangements, as explained in copending U.S. patent application Ser. No. 13/285,581, which was previously incorporated by reference. 
     As illustrated in further detail in  FIG. 2 , the camera  106  can be, in various embodiments, any of a variety of camera types, such as a still camera or video camera or infrared camera, and can be configured for use in various types of systems, such as security systems, closed-circuit monitoring systems, or other integrated systems. Alternatively, the camera  106  can be a stand-alone component, without a data connection external to the camera. In the embodiment shown, the camera  106  is powered by an external power signal line  112  which enters the enclosure  104  at an electrical filter  114 . Various types of electrical filters could be used, such as a low-pass, band pass, or spark gap type filter; generally, the filter is selected to be capable of receiving a power signal (e.g., either a direct current signal having a predetermine voltage and amplitude, or an alternating current signal having an expected frequency and amplitude). The filter can be configured to prevent signals over a predetermined amplitude or frequency (e.g., within the range of typical EMP/IEMI events up to 10 GHz) from entering the enclosure via the power signal line  112 . 
     The lens  108  can be any of a variety of types of automatically focusing or manually focused lenses. Generally, the lens  108  will have a focus length at a distance greater than the distance at which the waveguide beyond cutoff  102  is placed, such that the camera  106  does not focus on the waveguide, but instead focuses “through” the waveguide beyond cutoff on objects external to the enclosure  104 . That is, the camera lens  108  can be selected, specific focal length and f-stop, such that the camera  106  focuses on objects in the far field. Hence the honeycomb waveguide material of the cells  103 , which is in the near field, will be outside the depth of focus of the camera, and obscuration will be minimized. In this way, the imaging quality of the camera image will be retained with minimal distortion. In the embodiment shown, because the camera  106 , lens  108  and waveguide  102  are mounted in alignment, viewing through the honeycomb waveguide cells  103  is nearly unobstructed. 
     In certain embodiments, an additional optical grade lens or window could optionally be located in “front” of the waveguide beyond cutoff  102  (external to the enclosure  104 ) to protect the camera and wave guide from exposure to environmental conditions. 
     Referring to  FIGS. 3-5  example diagrams of the honeycomb waveguide beyond cutoff  102  are illustrated. In various embodiments, cells  103  forming the waveguide beyond cutoff  102  can be constructed of either aluminum or steel, or other types of electromagnetically conductive materials. The honeycomb structure of the waveguide beyond cutoff  102  typically has ⅛″ diameter (i.e., width) hexagonal holes forming an array of cells  103 . To achieve the desired electromagnetic wave attenuation, typically 80 db, the thickness of the material (represented in  FIG. 4  as length “X”) is typically on the order of one inch, but may vary in different embodiments. For a ⅛″ hole diameter this represents an length to diameter ratio of about eight (8). The honeycomb material of the waveguide beyond cutoff  102  can be plated or coated with a coating that is highly absorptive and non-reflective in the wavelengths of interest, to prevent unwanted off-axis light, or infrared, from entering the camera. 
     Referring generally to  FIGS. 1-5 , it can be seen that the shielded enclosure and waveguide beyond cutoff arrangement disclosed herein protect the path or opening for light to enter a shielded enclosure and then to enter the camera lens and image sensors without providing a leakage path for electromagnetic fields potentially harmful to the electrical and electronic systems of the camera to enter the enclosure. 
     The above specification, examples and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.