Abstract:
A variable gap switch includes a first electrode having a first gap surface; a second electrode having a second gap surface, the second gap surface formed in an initial fluid state that hardens to substantially conform to the first gap surface, the first electrode being moveable with respect to the second electrode; an alignment guide providing substantially parallel and substantially opposed alignment of the first gap surface and the second gap surface; and a displacement mechanism positioned to provide selective movement of the first electrode with respect to the second electrode so that a gap between the electrodes is selectively adjustable.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of U.S. patent application Ser. No. 13/151,477, filed 2 Jun. 2011, titled “Variable Capacitor Based Mechanical to Electrical Generator”, incorporated by reference herein in its entirety. 
    
    
     FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT 
     This invention is assigned to the United States Government. Licensing inquiries may be directed to Office of Research and Technical Applications, Space and Naval Warfare Systems Center, Pacific, Code 72120, San Diego, Calif., 92152; telephone 619-553-2778; email: T2@spawar.navy.mil. Please reference Navy Case No. 101257. 
    
    
     BACKGROUND 
     This disclosure relates generally to the field of electrical switches and more particularly to the field of thermally isolating electrical switches. 
     A prior art technique for electrical switching is accomplished through transistors. Transistors however use variable resistance to control current and as a consequence generate heat that may ultimately lead to the degradation and destruction of the transistor-based switch. For certain applications, it is desirable to have a switching configuration that exhibits greater heat tolerance than a traditional transistor switching scheme. 
     SUMMARY 
     A variable gap switch includes a first electrode having a first gap surface; a second electrode having a second gap surface, the second gap surface formed in an initial fluid state that hardens to substantially conform to the first gap surface, the first electrode being moveable with respect to the second electrode; an alignment guide providing substantially parallel and substantially opposed alignment of the first gap surface and the second gap surface; and a displacement mechanism positioned to provide selective movement of the first electrode with respect to the second electrode so that a gap between the electrodes is selectively adjustable. The gap of the switch permits thermal isolation of one side of the switch from the other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary variable gap tunnel junction switch according to the description herein. 
         FIG. 2  illustrates an exemplary electrode-to-electrode interface according to the description herein. 
         FIG. 3  illustrates an exemplary thermal isolation configuration according to the description herein. 
     
    
    
     DETAILED DESCRIPTION 
     The inventor&#39;s previous work with a variable capacitor (see co-pending U.S. patent application Ser. No. 13/151,477) revealed that it is possible to form a surface-conformable electrode directly upon a capacitor&#39;s ceramic element. Moving the electrode with respect to the ceramic element varied the capacitance of the capacitance. 
     This concept is taken further within the present disclosure such that a switch is created between a first electrode and a second electrode. The second electrode is formed on the surface of the first electrode. In essence, the second electrode surface closely conforms to surface irregularities in the first electrode. When displaced from each other, the resulting narrow gap between the surfaces permits electron tunneling. The electron tunneling allows an electrical connection to be made while simultaneously thermally isolates one electrode from the other. The thermal isolation makes it possible, in one scenario, to thermally isolate a load from a power supply. Such isolation minimizes the deleterious effects of heat on a thermally-sensitive load or on-the-other-hand allows a hot load (such as a heater) to be thermally isolated from a power source and its sensitive electronics. 
     Referring now to  FIG. 1 , component parts of the variable gap tunnel junction switch (VGTJS)  10  are shown. Switch  10  has a first electrode  12  having a first “gap” surface  14 . By “gap’ surface, what is meant is a surface that ultimately makes up one of the surfaces of the gap that is selectively formed between two electrodes of switch  10 . First gap surface should be a highly polished surface. Generally, highly polished surfaces are obtained by fine mechanical polishing followed by electrolyte polishing. Such a surface will have a surface roughness of about 50 nano-meters or less. It is worth noting that at the nano-meter level, first gap surface  14  will still likely contain a number of surface irregularities that, unless matched corresponding well by an adjacent gap surface, will substantially limit the ability to carry out efficient electron tunneling across gap  16  as shown in the figure. 
     To lessen the effects of surface irregularities and to enhance the ability of successful electron tunneling, a second electrode  18  is provided that has a second gap surface  20  that substantially conforms to first gap surface  14 . The conforming surface of second gap surface  20  is made possible by forming the second gap surface initially in a liquid state and then allowing the surface to harden. An example of a suitable material for such a surface is solder, wherein any of a range of solders can be used including high temperature hard silver solder for example. By melting the second gap surface onto the first gap surface  14 , no substantial air gap will exist between the two gap surfaces when immediately adjacent. The entire second electrode  18  may be made of solder wherein the first electrode may be of any suitable conducting metal such as nickel or copper. The charge (+ or −) designation of these electrodes is arbitrary and may be reversed from those shown, these charges being provided to the electrodes by way of contacts  22 . 
     To move first electrode  12  with respect to second electrode  18 , a displacement mechanism  24  is provided that may be any suitable mechanism. Specific examples of such a mechanism are those of mechanical or electro-mechanical construction. To retain alignment of first electrode  12  and second electrode  18 , there is provided at least one alignment guide  26  that is non-conducting and that may be placed through vias  28  defined in electrode  18 . In this example, guide  26  is fixed to electrode  12 . Of course, other ways may be devised to confine movement of the electrodes, for example by a guide mechanism placed exterior of the electrodes that permits movement of the electrodes only towards or away from each other. When a guide is positioned within an electrode, the guide may take on a cross-section of any of a variety of shapes, such as circular, square, rectangular and the like. 
     In the embodiment shown in  FIG. 1 , first electrode  12  is designed to move. Which electrode moves with respect to the other is arbitrary and may be selected for design convenience. In the example shown, second electrode  18  is “fixed” in position with regard to a fixed foundation  30 . The stabilization of second electrode  18  is accomplished via anchor posts  32  and  34 . It should also be readily apparent that the displacement mechanism used may be directly coupled to either of the electrodes desired to be moved. Such a mechanism is not restricted to being directly attached to first electrode  12  any more than second electrode  18 . 
     During fabrication, such as when second electrode  18  is poured or cast to conform to first electrode  12 , the hardened second electrode can be easily freed from the first electrode by displacement mechanism  24  acting to draw first electrode  24  from second electrode  18 . Where displacement mechanism  24  is a piezo-electric material, such as lead zirconate titanate (PZT), energization of the material can be used to pull electrode  12  from electrode  18 . In many instances however, the solder used as electrode  18  will readily be freed from electrode  12 . 
     Finally, the components of the Variable Gap Tunnel Junction Switch  10  so far discussed are placed into a vacuum container  36  and the contents of the container placed under a vacuum. The vacuum is provided to enhance the separation of the two electrodes. 
     Referring now to  FIG. 2 , a more detailed perspective is shown regarding construction and configuration of the electrodes as used in switch  10 . As previously described, second electrode  18  is formed by melting it to the exposed gap surface of first electrode  12 . This “casting” procedure allows electrode  18  to conform its molecular boundary to match the molecular boundary of electrode  12 . As such, surface roughness or irregularities are accounted for by providing a “matched” boundary  38 . By utilizing molten, liquefied, metal to generate a conforming surface, any air gap that would otherwise exist between the surfaces is substantially removed. 
     The upper close-up shown in  FIG. 2  illustrates how practically no air gap exists at matched boundary  38 . The lower close-up shown in  FIG. 2  shows air gap  16  that is present when electrode  12  is purposely separated from electrode  18 . The conformal surfaces present at gap  16  enhance tunnel currents when the two electrodes are appropriately positioned from each other. Specifically, while gap  16  can be adjusted from zero to any desired gap thickness, at gap widths of 1 to 10 nano-meters (nm), strong tunnel currents can exist if a potential difference is present between the electrodes. The switch is considered to be fully conducting at gap=0, partially conducting at a gap of approximately 1 to 10 nm, and essentially non-conducting for gap of approximately &gt;&gt;10 nm. It should be noted that using technology from atomic force microscope, a PZT displacement mechanism can be used to control adjustment of the gap to less than 0.1 nm precision. 
     Referring now to  FIG. 3 , there is shown an exemplary embodiment of the variable gap tunnel junction switch (VGTJS) utilized in a thermal isolation configuration. In this configuration, a VGTJS (shown as  100   a  and  100   b ) is placed in electrical series between each side of a load  102  and a power supply  104  that can be either alternating current (AC) or direct current (DC). 
     Use of the VGTJS allows heat to be confined to the power supply side. This is contrasted to the use of semiconductor transistor switches that will permit heat to be conducted more widely including back to a utilized power supply. By using the VGTJS, heat is prevented from migrating from the power supply to the load side as thermal electrons cannot readily pass over the vacuum gap of the VGTJ switch. In the VGTJS, there are no semiconductor materials to burn out. For those situations wherein the electrodes of the VGTJS become hot, the heat can be conducted from the electrodes by sufficient heat sinks such as cooling fins. 
     In view of the above, it will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated to explain the nature of the disclosure, may be made by those skilled in the art within the scope of the disclosure as expressed in the appended claims.