Abstract:
An instrumentation structure includes a sensor array and a support structure. The sensor array is rotatable around multiple axes. Radar absorbent material (RAM) is adapted to conform to non-planar exterior surfaces of the instrumentation structure.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the United States Government for any governmental purpose without payment of any royalties thereon. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to instrumentation structures with reduced electromagnetic radiation interference and interference characteristics. 
     Instrumentation structures may house sensors, such as optical devices. The optical devices may include, for example, infrared cameras, visible light cameras, laser range finders, etc. A instrumentation structure in accordance with the invention may used in a variety of settings including, for example, security systems, aircraft, watercraft, land vehicles, and stationary structures. The user may be, for example, a commercial, governmental, or private entity. The user may desire that the instrumentation structure be compatible with airborne or ground based radar or other electromagnetic radiation transmitters or receivers. Significant advantages are associated with enabling use of instrument systems which mitigate signal returns from the instrumentation structure or interference with radio frequency systems or system operators which receive undesirable radar returns off the instrumentation structure. For example, an instrumentation structure in accordance with the invention can reduce clutter or interference on an air traffic control system which could distract an air traffic controller in controlling aircraft viewed on a radar screen. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention is an instrumentation structure having radar absorbent material (RAM) fixed thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIGS. 1A ,  1 B, and  1 C are elevations views of one embodiment of an instrumentation structure in accordance with the invention. 
         FIGS. 2A and 2B  are front and side elevation views, respectively, of a first piece of RAM. 
         FIGS. 3A and 3B  are front and side elevation views, respectively, of a second piece of RAM. 
         FIGS. 4A and 4B  are front and side elevation views, respectively, of a third piece of RAM. 
         FIGS. 5A and 5B  are front and side elevation views, respectively, of a fourth piece of RAM. 
         FIGS. 6A and 6B  are front and side elevation views, respectively, of a fifth piece of RAM. 
         FIG. 7  is a sectional view of an exemplary RAM installation. 
         FIG. 8  is a schematic drawing of a water jet cutter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1A ,  1 B, and  1 C are elevations views of one embodiment of an instrumentation structure  10  in accordance with the invention. Instrumentation structure  10  may include a rotatable sensor array and a supporting structure. It should be noted that a variety of devices may be installed in ball  14  such as laser systems or other non-sensor systems. In  FIGS. 1A-C , the rotatable sensor array may comprise a generally spherical ball  14  having one or more lenses  16 . Ball  14  may be rotatable  360  degrees around the axis X ( FIG. 1C ) as shown by arrow A. Ball  14  may also be 360 degrees rotatable around axis Y ( FIG. 1C ). Axis Y may be perpendicular to axis X. 
     Supporting structure for instrumentation structure  10  may include a base  12  and a tilt support structure. The tilt support structure may be stationary with respect to rotation of the ball  14  around the X-axis and may rotate with the ball  14  with respect to rotation around the Y-axis. The tilt support structure may include a throat  24  ( FIGS. 1A and 1C ), a neck  18  ( FIG. 1B ), and a pair of opposing ears  20 ,  22  ( FIG. 1B ) connecting the throat  24  and neck  18 . In other words, the throat  24 , neck  18  and ears  20 ,  22  comprise front, back and side sections of the tilt support structure which mount the ball  14 . It should be noted that the term “ears” refers to side mounts for the ball  14  structure. Exterior surfaces of the ears  20 ,  22  may be non-planar. In particular, portions of the exterior surfaces of the ears  20 ,  22  may be convex. 
     RAM may be fixed to exterior surfaces of the instrumentation structure  10 . RAM  36  ( FIG. 2A ) and RAM  50  ( FIG. 3A ) may be fixed to exterior surfaces of the ears  20 ,  22 , respectively. The RAM  36  ( FIGS. 2A and 2B ) may include a generally rectangular portion  46  and a generally semi-circular portion  48 . Semi-circular portion  48  may include one or more slots  38  formed therein such that the RAM  36  substantially conforms to the non-planar exterior surfaces of the ear  20 . Slots  38  may extend from a peripheral edge  60  of the RAM  36  inwardly along a radius R of semi-circular portion  48 . Edges of the RAM  36  within the slots  38  may be caulked. RAM  36  may include notches  40  formed therein to allow access to, for example, fasteners  26  ( FIGS. 1A-1C ). RAM  36  may include one or more openings  42  for access to, for example, a desiccant cartridge cover  28  and an air access  30  ( FIG. 1A ). 
     The RAM  50  ( FIGS. 3A and 3B ) may include a generally rectangular portion  62  and a generally semi-circular portion  64 . Semi-circular portion  64  may include one or more slots  52  formed therein such that the RAM  50  substantially conforms to the non-planar exterior surfaces of the ear  22 . Slots  52  may extend from a peripheral edge  66  of the RAM  50  inwardly along a radius R of semi-circular portion  64 . Edges of the RAM  50  within the slots  52  may be caulked. RAM  50  may include notches  54  formed therein to allow access to, for example, fasteners  26  ( FIGS. 1A-1C ). RAM  50  may include one or more openings  56 ,  58  for access to, for example, a nitrogen input  32  and nitrogen exhaust  34  ( FIG. 1C ). 
     RAM  70  ( FIG. 4A ) may be fixed to the neck  18  ( FIG. 1B ) of instrumentation structure  10 . RAM  70  may be substantially rectangular. RAM  70  may include one or more substantially rectangular notches  72 , or substantially circular notches  74 , for access to fasteners or internal components of the instrumentation structure  10 . 
     RAM  80  ( FIG. 5A ) and RAM  88  ( FIG. 6A ) may be fixed to the base  12  ( FIGS. 1A-1C ) of instrumentation structure  10 . RAM  80  and RAM  88  may comprise substantially rectangular shapes. 
     Generally, the base  12  of instrumentation structure  10  is fixed to a mounting structure and the ball  14  and ears  20 ,  22  depend downwardly from the base  12 . In this orientation, the base  12  may have a lesser radar cross-section than the remainder of the instrumentation structure  10 . Thus, a thickness of the RAM  80 ,  88  fixed to base  12  may be less than a thickness of the RAM  36 ,  50 ,  70  fixed to ears  20 ,  22  and neck  18 . In one embodiment, a thickness of the RAM  80 ,  88  is about 0.06 inches and a thickness of the RAM  36 ,  50 ,  70  is about 0.25 inches. 
       FIG. 7  is a sectional view of an exemplary RAM  100  installed on a surface  102  of the instrumentation structure  10 . The RAM  100  may comprise a closed cell synthetic rubber, such as neoprene. The RAM  100  may include an adhesive backing  44 . Edges  104  of the RAM  100  may be substantially perpendicular to the surface  102  of the RAM  100 . Caulk  108  may be applied along the edges  104  of the RAM  100 . 
     RAM may be supplied in generally rectangular sheets. The processes of shaping the RAM, forming slots in the RAM, forming notches in the RAM, forming openings in the RAM, etc., may be performed using a water jet cutter  120  ( FIG. 8 ). Ideally, when applying the RAM, one should use the thickest RAM possible. The amount of potential radar absorption is directly proportional to the thickness of the material. The natural state of the RAM is flat. When applied to curved surfaces, the RAM tends to crease. Thinner RAM is easier to fit over a more extremely curved surface. 
     Alternative embodiments may employ a radar absorbing coating for the ball  14  or other portions of the instrumentation structure which RAM layers are not applied to. Radar absorbing coatings can be composed of vinyl latex paint and carbon nanotube filaments. Finely ground Mylar and neoprene can be added during mixing of the coating. Adding ground carbon to the paint mixture can provide good coverage and results. Some types of electromagnetic energy can be influenced by increasing or reducing the thickness of the coating. Surface preparation is important to prevent delamination or peeling. 
     RAM sealant or caulking material may have the same carbon nanotube filaments in a vinyl latex caulk base. This thickened substance can contain a finely ground carbon, Mylar and neoprene mix added as a last step before application. Surface preparation again is very important to prevent delamination, pealing or flaking A two part applicator can be used to apply a multi-layered sealant or caulking material but care must be taken to apply the carbon, Mylar and neoprene mix side of the applicator to the metal surface. 
     References to caulk, caulking material or sealant should be understood to be examples of different methods, design features or structures for use in creating seal or edge terminations or transitions for the RAM materials to the surface which a RAM material is applied to. References to caulk, caulking materials or sealants should be understood to also include a termination or transition structure which is designed as a part of the RAM material edge areas. Thus, caulk, caulking material or structure references should be understood to be a reference to a transition or seam design feature of the RAM or structures which are formed into the RAM seams or edges or access holes or areas through the RAM itself. 
     While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations, and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.