Abstract:
A reflector employs materials and design features that can transfer both light and sound emission simultaneously, from sources to planes or volumes, in an efficient and controlled manner. Compound orthogonal parabolic reflectors employ an extension onto conventional orthogonal parabolic reflectors to efficiently deliver light and/or sound to a focal volume or surface. The extension shapes the output, and can provide inflow and outflow to the focal region, along with a brush. Pulsed sources may be employed, which may emit light, sound or both light and sound, may erode and may be wire initiated with the wire replaced after each pulse by a wire feed.

Description:
GOVERNMENT SUPPORT 
     The invention was supported in part in an Advanced Technology Program under National Institute of Standards and Technology (NIST) Cooperative Agreement No. 70NANB1H3053, and Housing and Urban Development (HUD) Instrument No. MALTS0090-02. The Government has certain rights in the invention. 
    
    
     BACKGROUND 
     A variety of emission reflectors and reflector/sources are known in the art. For example, fluorescent bulbs have reflectors for illumination that are common in the home. Headlamps of automobiles have parabolic and other shaped reflectors for directing light. Elliptical troughs are used to reimage flashlamps to produce high intensity light for treating surfaces. Parabolic reflectors are used underwater to direct sound from sparker sources into pipes to control zebra mussels. Reflectors known in the art operate efficiently with either light or sound sources. For some applications it would be beneficial for reflectors to operate efficiently with light and sound sources, or sources that emit both light and sound. 
     Many commercial lamp systems use standard reflectors to deliver light. For example, to treat surfaces, a flashlamp is placed at one focus of an elliptical trough and the surface at the other focus. Because of practical limitations on implementing such reflectors, light source reflector combinations are unable to treat some surface areas, such as into corners, where adjacent walls meet with each other, the ceiling or floors, moldings, stairs, surfaces near any protrusions from the surface or other surface areas difficult to access. This is a disadvantage for paint stripping, for instance, because not all surfaces can be stripped of paint, so that a second technique is needed to complete removal. Most known practical implementations result in a light footprint on the work surface that is well inside the projected footprint of the reflector onto the work surface. In typical applications, light from the reflector cannot strip paint from about 10% of the surface area. In such applications it would be beneficial to have a reflector that allows all surfaces to be stripped of paint or otherwise irradiated by light or sound. 
     Impulsive and many other acoustic sources are omni-directional. However, in some uses sound output is used only in specific directions. A reflector that can reach surfaces outside the projected footprint of the reflector and that can direct light or sound source output in specific directions is disclosed in U.S. Pat. No. 6,672,729, incorporated herein by reference in its entirety. 
     Orthogonal parabolic reflectors (OPRs) allow light or sound from a linear or cylindrical source to be focused into a small volume. Many orthogonal reflectors known in the art specify that such reflectors focus the light into a small volume approximating a point. However, for incoherent sources the output is spread over a large volume, with a large fraction lost and not reaching a small volume near the focal point. In some cases in which reflectors known-in-the-art are used with light or sound sources that employ electrodes, erosion during operation causes the source that is initially at a focus of a reflector, to erode away from the focus, and thereby diminish its effectiveness. In those cases it would be advantageous to have a reflector that maintained effectiveness even as the source erodes. 
     SUMMARY 
     The present invention relates to reflectors and reflector/source combinations to direct and/or project light and sound emission. 
     There is a need for an additional reflector capability to capture output that would otherwise be lost, and redirect it to a small volume near focus. There is also a need for a capability to shape the output in the vicinity of the focus to adapt to various applications such as irradiating surfaces with specific shapes. There is also a need for reflectors that can maintain the effectiveness of sound and/or light sources even as electrodes erode. 
     The efficacy of light or sound sources, as well as combined light and sound sources, depends in part on how the emission from the source is transferred for the intended use. In many applications a reflector is used to direct emitted light and/or sound onto surfaces or into volumes for processing. Embodiments of the present inventive reflectors can be used to improve the useful output or the efficiency of utilizing a source emission. The inventive improvement increases the capability of the source and/or reduces the requirements on the emissive source to accomplish an intended objective. 
     One aspect of the present invention provides a reflector that efficiently delivers both light and sound. Another aspect of the present invention is directed to a compound orthogonal parabolic reflector (COPR) that is configured to deliver light and/or sound to small focal volumes or surfaces. Other aspects of the present invention may incorporate eroding sources, pulsed power sources and wire initiated sources, implemented into reflectors in such a way as to maintain the position of the focal volume. 
     Accordingly, a reflector system comprises a source of light and sound emissions and a shaped reflector element for directing and projecting the light and sound emissions to a work surface or into a volume. The reflector element has a material composition and thickness selected for high acoustic reflectivity for wavelengths below a specified maximum. The reflector element includes a shaped reflective surface with a coating having high optical reflectivity. 
     According to another aspect, a reflector system comprises a source of emissions and a reflector for directing and projecting the emissions toward a work surface or to a focal volume. The reflector comprises an orthogonal parabolic reflector (OPR) element having a focus, the extent of the OPR element terminated at one end before the focus, with the source located along an axis defined such that emissions perpendicular to the axis are transferred to the focus, and a shaped reflector extension in a region between the end of the OPR element and the focus. 
     In an aspect of the present invention, features of the reflector are such as to efficiently and compactly deliver both light and sound for specific applications. The reflector may be constructed from selected materials with one or more selected coatings applied to the surface, and featuring appropriate thickness and/or dimensions and/or layers so that both light and sound may be effectively utilized for specific applications. 
     In another aspect of the present invention, a compound orthogonal parabolic reflector (COPR) provides additional reflector elements in conjunction with an orthogonal parabolic reflector element. These additional reflector elements are defined to provide improved delivery of light and/or sound to a focal volume or surface. In OPRs known in the art that employ incoherent sources, a significant portion of the source emission is lost through an opening or otherwise not delivered to the focal region. In some embodiments of the present invention, an additional reflector element may serve to enclose emission that would otherwise be lost and to increase the emission that is delivered to small volumes near the focus and/or surfaces located at or in the vicinity of the focus. Furthermore, for some implementations it may be desirable to shape the emission, for instance, to irradiate a shaped surface. An additional feature or type of element serves to define the shape of the emission from the COPR delivered to small volumes near the focus and/or surfaces located at or in the vicinity of the focus. 
     In some embodiments the COPR may include a brush element or other device, rotating or otherwise, that can be moved across surfaces after being irradiated in the small volumes near the focus and/or surfaces located at or in the vicinity of the focus. 
     Additionally, it may be advantageous to add and/or remove materials associated with processes ongoing in the small volumes near the focus and/or surfaces located at or in the vicinity of the focus. Another feature of the COPR may provide means for defining a passage for the removal of vapors or other materials removed from the surface. Another feature of the COPR may provide means to deliver a flow of air or other gas, or of a liquid, into the volume in the vicinity of the focus or onto surfaces in the vicinity of the focus. 
     A further embodiment of the COPR orients sources whose emission location changes over time, such as from erosion of electrodes, so that the emission continues to be transmitted efficiently to small volumes near the focus and/or surfaces located at or in the vicinity of the focus. 
     It is advantageous to have the source positioned in the reflector and supported so that it maintains its position during practical use. Another feature of the COPR may provide means for inserting and attaching the source into the reflector system, while stabilizing the source at the location to prevent damage to the source. 
     Embodiments of the present invention may also incorporate the use of pulsed lamps, pulsed electrical discharges in the medium within the reflector, and sparkers as light and sound sources with the aforementioned inventive reflectors. 
     A type of source known in the art employs pulsed power to vaporize a wire to initiate an electrical discharge in the medium surrounding the wire. Wire initiated sources known in the art do not have reflectors, and the wire length, diameter and material are not correlated with efficient output from the source. To address this problem, some embodiments of the present invention may include wire initiated sources within the aforementioned inventive reflectors, with the wire diameter, length and material chosen for optimal light and/or sound emission from the source. 
     Accordingly, aspects of the present invention provide for efficient control of the utilization of light and sound source emission, simultaneously or separately, including COPRs and the use of incoherent sources, including lamps of all types, sparker sources and wire initiated sources. 
     Embodiments of the present invention are amenable for use in a wide variety of industrial, commercial, military, academic, and environmental applications such as surface treatment (e.g. paint stripping and UV curing), protection against unfriendly divers, crowd control and other less than lethal applications, sterilization, geophysical exploration, antibiofouling, lithotripsy, underwater surveillance, sonobuoys, shallow water characterization, ballast water control, meat tenderization, mine sweeping, submarine countermeasures, disinfection, destruction of organic compounds, for instance, in industrial waste, groundwater and water supplies, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIGS. 1A ,  1 B are schematic diagrams of first and second embodiments, respectively, of reflector source systems for use with light, sound or light and sound sources. 
         FIG. 2A  illustrates a plot of reflection coefficient as a function of frequency for different thicknesses of steel. 
         FIG. 2B  illustrates a plot of reflection coefficient as a function of frequency for steel versus aluminum. 
         FIGS. 3A ,  3 B illustrate a parabolic reflector (PR) and an orthogonal parabolic reflector (OPR), respectively. 
         FIG. 3C  illustrates a compound orthogonal parabolic reflector (COPR). 
         FIG. 4  is a schematic diagram of a COPR with additional features for practical implementation. 
         FIG. 5A  is a schematic diagram showing an embodiment of a COPR with added tip and effluent capture.  FIG. 5B  illustrates a side view of the embodiment of  FIG. 5A . 
         FIG. 6A  is a schematic diagram showing an embodiment of a COPR with added tip and brush.  FIG. 6B  illustrates a side view of the embodiment of  FIG. 6A . 
         FIG. 7A  is a schematic diagram showing an embodiment of a COPR with added effluent capture and nozzle.  FIG. 7B  illustrates a side view of the embodiment of  FIG. 7A . 
         FIG. 8A  is a schematic diagram showing an embodiment of a COPR with support to maintain the position of a source and a current return to complete an electrical circuit that powers the source.  FIG. 8B  illustrates a side view of the embodiment of  FIG. 8A . 
         FIG. 9A  is a schematic diagram of an embodiment of a COPR featuring a wire initiated source within the COPR, with a feed mechanism.  FIG. 9B  illustrates a side view of the embodiment of  FIG. 9A . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Shown in  FIGS. 1A ,  1 B are embodiments of respective reflector systems  1 A,  1 B that can be used either with sources  2  that emit both light and sound together, or light or sound separately, and are surrounded by an interior medium  3  on the reflective side and exterior medium  4  on the non-reflective side. The reflector shape can be any of the standard shapes known in the art, or other inventive shapes such as shown in  FIG. 2C . The inventive reflector  1 A,  1 B efficiently reflects and delivers both light and sound emissions from source  2 . 
     So that the reflector  1 A,  1 B efficiently reflects light, it has any of the standard sets of coatings  5  known in the art, such as an aluminum coating with an overcoating of SiO 2 , MgF 2 , or multiple layers of such or other dielectrics, which may be chosen to optimize the reflectivity of a desirable optical spectral region. 
     So that the reflector  1 A ( FIG. 1A ) also efficiently reflects the desired sound spectrum while in media  3  and  4 , the material  6 , width  7  and thickness  8  are chosen appropriately. For example, if media  3  and  4  are the same or similar in terms of their acoustic impedance properties, the material  6  is chosen to have a high impedance mismatch with the media. As a further example, many metal materials such as steel have a high impedance mismatch with air or other gaseous media. 
     For sound frequencies with a corresponding half-wavelength on the order of or larger than the width  7 , the sound will diffract and not be well reflected by the reflector. Consequently, the width  7  is chosen to be a large enough size to reflect the longest wavelength desired to have efficient reflection for the particular use. 
     Furthermore, thickness  8  also is such to produce high reflectivity for the largest desired acoustic wavelength. If the thickness  8  is too small, then for long enough wave-lengths, the reflectivity will be low even with sufficient width  7 . To demonstrate the principle of choosing the material  6 , width  7  and thickness  8 , consider the example of a symmetrical reflector  1 A with a surrounding water medium ( 3  and  4 ), the reflector of which has high acoustic reflectivity for wavelengths shorter than about sixty inches. This reflector  1 A will have a width  7  of about 30 inches. Then, based on knowledge known in the art, a steel material  6  with a thickness of 2 inches has high reflectivity of sixty inch wavelength sound, whereas an aluminum material with a thickness of 2 inches would have low reflectivity. Furthermore, steel with a thickness of 0.5 inches would also have very low reflectivity of sixty inch wavelength sound. Similarly for other combinations of media ( 3  and  4 ) and a desired upper limit on acoustic wavelength with high reflectivity, the material  6 , width  7  and thickness  8  are chosen using relationships known in the art. 
     So that the reflector  1 B ( FIG. 1B ) efficiently reflects sound, the center  9  material has a high impedance mismatch with the medium  3 , whereas the material  6  can be any thin material. For instance, if the reflector is in water, then the center  9  could be air or other gaseous medium, and the material  6  could be a plastic or other such material with an approximate match in impedance to the medium  3 . Similarly, for combinations of media ( 3  and  4 ) and a desired upper limit on acoustic wavelength with high reflectivity, the materials  6  and  9 , width  7  and thickness  8  are chosen using relationships known in the art. 
     The theory behind the material and thickness selection is now described. Sound is reflected from an object when its acoustic impedance is not well matched to that of the propagating medium (e.g., air or water). In addition, the frequency of the wave and the thickness of the object also determine the magnitude of the sound reflection, since long wavelengths transmit easily through thin walls. A source such as a sparker is an impulsive source that can generate a broadband spectrum. Acoustic properties differ among different materials and not all materials are suitable for reflectors. 
     An example may be understood by selecting hot rolled steel as the material. For a flat plate with wave impinging at normal incidence, and neglecting dissipation, the power reflection coefficient R is given by: 
     
       
         
           
             R 
             = 
             
               1 
               - 
               
                 1 
                 
                   
                     
                       cos 
                       2 
                     
                     ⁢ 
                     kl 
                   
                   + 
                   
                     
                       1 
                       4 
                     
                     ⁢ 
                     
                       
                         ( 
                         
                           
                             
                               Z 
                               2 
                             
                             
                               Z 
                               1 
                             
                           
                           + 
                           
                             
                               Z 
                               1 
                             
                             
                               Z 
                               2 
                             
                           
                         
                         ) 
                       
                       2 
                     
                     ⁢ 
                     
                       sin 
                       2 
                     
                     ⁢ 
                     kl 
                   
                 
               
             
           
         
       
     
     where 1 is the thickness of the plate, k is the wavenumber, Z 1  is the impedance of the medium and Z 2  is the impedance of the plate material. Here it can be seen that the reflection coefficient is low at low frequency (k 1  is small) as well as at each half wavelength (k 1 =nπ). Increasing the thickness is the easiest way to improve reflection, especially at low frequency as seen in  FIG. 2A  which plots the reflection coefficient as a function of frequency for a steel plate thickness series from 0.5 to 2 inches. The impedance also affects the width of the resonance as seen by comparing aluminum to steel as shown in  FIG. 2B . For the best reflection across the widest frequency range, the thickness and acoustic impedance should be as large as possible. 
     The reflectors  1 A,  1 B ( FIGS. 1A ,  1 B) also have a feed penetration  10  that may support a source  2 , and provide the means to power and control the source. The source  2  may be located at a focus of the reflector  1 A,  1 B or other position that results in light and/or sound being directed to a useful location. Furthermore, the source  2  may be of a type that emits both light and sound, either simultaneously or sequentially. The source  2  could be a pulsed electric discharge in air or water or other medium  3 , which generates both sound and light. The source also could be a pulsed electrical discharge initiated with a wire. 
     Shown in  FIGS. 3A ,  3 B are diagrams illustrating a parabolic reflector (PR)  11  and an orthogonal parabolic reflector (OPR)  12 . The PR  11 , a concept known-in-the-art, can collect incoming parallel rays and concentrate them at the focus  14  or, conversely, light rays emitted from the focus  14  are collected and transmitted as outgoing parallel rays. The OPR  12 , another concept known-in-the-art, utilizes the principle of the PR. The OPR has a line source  15 , placed along the axis of rotation  15   a . Rotating a section of the parabola  16  around the source  15  generates a reflector surface that directs light and/or sound emitted from the source  15  to the focus  14  of the parabola  16 . The OPR  12  projects output that is perpendicular to the line source  15 , to a single focal spot  14 . However, many sources  15  have output that is incoherent or in some way is emitted over many directions, so that much of the output is directed away from the focus  14 . 
       FIG. 3C  illustrates a compound orthogonal parabolic reflector (COPR)  13 . The COPR  13  includes an OPR element  13 A and a reflective extension  17 . The addition of the extension  17  increases the efficiency of transferring emission to a focal volume  18 , a region of high intensity in the vicinity of the focus  14 . The extension  17  is shown to be conical, but may be any shape that increases the delivery of output from the source  15  to the focal volume  18 . 
     Illustrated in  FIG. 4  are several additional features afforded by the COPR. For an appropriately shaped extension  17  the focal volume is outside the open end. This enables the focal volume to, for instance, encompass the surface of a corner  19 . If the source  15  is a pulsed lamp of a high enough intensity, then this inventive system could be used to prepare, clean, strip paint from, or otherwise affect a surface. Although the embodiment in  FIG. 4  shows a corner surface  19 , any shaped surface is contemplated by the principles of the present invention. Further, the embodiment in  FIG. 4  has an opening  20  for implementing, powering and controlling the source  15 . Further, an effluent capture  21  may be attached or otherwise connected to the extension  17  for removing materials, gases, vapors and otherwise associated with delivering output to the focal volume  18  from the source  15 . 
     A nozzle  22  or other means may be attached or otherwise affixed to the extension  17  for delivering a gaseous or liquid material incident on the surface  19  for the purpose of acting synergistically with the output from the source  15  to affect processes at the surface  19 . In addition, the nozzle  22  may include a shaped tip  23  to shape the output delivered to the focal volume  18 . Further, a brush  24  may be attached to or otherwise affixed to the extension  17  that may come in contact with the surface before and/or after the source  15  output impinges on it, to further participate in affecting the surface or materials removed or added to the surface. 
     Illustrated in  FIGS. 5A ,  5 B,  6 A,  6 B,  7 A,  7 B are further detailed embodiments of practical features of the inventive COPR, including those embodied in  FIG. 4 . With reference to  FIGS. 5A ,  5 B, a tip  23  is attached to the open end of the extension  17 , with a channel  25  defined as part of an effluent capture  21 . Although the tip  23  defines a circular shaped opening  26  adjacent to the surface  19 , it is understood that all feasible shapes for delivering output to different specific shaped surfaces are contemplated in accordance with principles of the present invention. The effluent capture  21  shown is a simple channel  25  in the embodiment in  FIG. 5B , but any means for transferring materials from regions at or near the surface  19  are understood to be included in the invention. Furthermore, the effluent capture  21  may have a pump or other means to provide suction for removing the materials, and may include filters or other means for removing processed materials from the air or other medium that contains any materials associated with the process at the surface. 
       FIGS. 6A ,  6 B show an additional embodiment of the extension  17  with a tip  23  and brush  24 , where the brush  24  is mounted in a way to allow rotation. This provides a way, for instance, to clean the surface  19  before and/or after output from the source  15  is incident on the surface  19 . It is understood that other shapes of brushes  24 , powered or un-powered are included in the invention. 
       FIGS. 7A ,  7 B show an additional embodiment of the extension  17  with an effluent capture  21  and a nozzle  22  oriented to provide inflow toward and along the surface  19  in such a way that the inflow proceeds to the channel  25 . Further, the embodiment shows an electrical driver  26  mounted on, or in the vicinity of, the outside of the OPR  12 , with means for electrical connection  27  to the source  15 . The proximity of the electrical driver  26  to the source  15  provides a low inductance arrangement advantageous for fast risetime and short pulse sources. 
     Referring now to  FIGS. 8A ,  8 B, another embodiment utilizes a linear eroding source  28  oriented as the source  15 , which in this case consists of two electrodes  35  but which in general could consist of any eroding source  28 . This configuration provides the means for the output from the source  28  to be transferred to the focal volume  18  even as the emission region changes due to erosion or other source movements along the axis of rotation  15   a . This embodiment also provides for a support  29  to fix the source,  15  or  28 , in place along the axis  15   a . The embodiment shows the support  29  consisting of three linear supports, but may consist of any other number or shapes of supports that may effectively maintain the location of the source,  15  or  28 . Further, this embodiment includes conducting elements  30  to provide the means for electrical current to flow back to the electrical driver  26  to complete the circuit. 
     Referring to  FIGS. 9A ,  9 B, a further embodiment employs a linear source  15  that is initiated by a wire  31 . An electrical driver  26  supplies energy to the wire  31  so as to vaporize or explode it, thereby producing a plasma which emits both sound and light. The wire  31  is of a diameter  32  and length  33  to optimize the sound and/or light in the medium  3 . Other embodiments of the invention in addition may have a wire feed  34  to supply additional wires  31  for repetitive pulse operation. 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.