Patent Publication Number: US-7915897-B2

Title: Foil-leaf electrometer for static field detection with permanently separating leaves

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the following copending U.S. applications: 
     1. U.S. application Ser. No. 12/340,028 filed Dec. 19, 2008 entitled “Foil Leaf Electrometer for Static Field Detection with Triggered Indicator.” 
     2. U.S. application Ser. No. 12/340,055 filed Dec. 19, 2008 entitled “MEMS Electrometer that Measures Amount of Repulsion of Adjacent Beams from Each Other for Static Field Detection.” 
     BACKGROUND OF THE INVENTION 
     Electronics, such as those found on printed circuit boards (PCBs), can be very sensitive, and are likely to be damaged in the presence of a electrostatic (static) field. Such fields can be encountered during manufacturing, handling, shipping, and use of PCBs. Even the failure of a component as simple as a transistor on a PCB can be enough to ruin a larger device, such as a computer. The Electrostatic Discharge (ESD) Association has even proliferated Specification S20.20, which requires that all charge-generating materials that have electrostatic fields that exceed 2,000 volts (V) should be kept at least twelve inches away from ESD sensitive products at all times. Industrial sheet plastic web packaging and fluid cleaning processes are just a few of the many other applications that are also capable of generating damaging electrostatic fields. 
     A simple method of detecting the presence of an electric field was developed in the late 1700&#39;s. Two thin gold leaves are suspended from a conductive rod, forming a “gold-leaf electrometer.” By contacting the conductive rod with an electrified piece of material, the gold leaves become identically charged through induction and repulse one another. This device is regarded as inaccurate and unstable. 
     Modern electrometers employ more sophisticated and accurate techniques of detecting and measuring the presence of charge. However, these devices can be expensive and are impractical for detecting fields under certain circumstances, such as within small equipment or fluids. 
     BRIEF SUMMARY OF THE INVENTION 
     An apparatus is provided for detecting a static field includes two surfaces of conductive material that are (i) electrically coupled to each other, and adjacent to each other. The two surfaces repel each other in the presence of a static field. The conductive material has a deformation property such that stress caused by repulsion of the two surfaces from each other by at least a predetermined distance causes at least one of the surfaces to permanently deform. 
     An apparatus is also provided for detecting a static field includes two surfaces of conductive material that are (i) electrically coupled to each other, and (ii) adjacent to each other in a rest position. The two surfaces repel each other in the presence of a static field. At least one of the surfaces has a movement path resulting from the repulsion of the two surfaces. At least one stopper is located in the movement path of at least one of the surfaces. The stopper prevents the at least one surface from returning to the rest position after the two surfaces are repulsed from one another by at least a predetermined distance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there is shown in the drawings an embodiment which is presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
         FIG. 1  is an enlarged perspective view of two surfaces for detecting the presence of a static field that may be used in preferred embodiments of the present invention as shown in  FIGS. 4-15 ; 
         FIG. 2  is an enlarged perspective view of two surfaces adjacent to each other in a rest position that may be used in preferred embodiments of the present invention as shown in  FIGS. 4-15 ; 
         FIG. 3  is an enlarged perspective view of one of the surfaces of  FIG. 1  or  2 ; 
         FIG. 4  is an enlarged perspective view of a static detecting apparatus having a rupturable indicator filled with encapsulated material in accordance with a preferred embodiment of the present invention; 
         FIG. 5  is an enlarged perspective view of the static detecting apparatus of  FIG. 4  following a rupturing of the indicator; 
         FIG. 6  is an enlarged perspective view of a static detecting apparatus having a rupturable adhesive indicator in accordance with another preferred embodiment of the present invention; 
         FIG. 7  is an enlarged perspective view of a static detecting apparatus having a rupturable dimple weld indicator in accordance with another preferred embodiment of the present invention; 
         FIG. 8  is a schematic view of a static detecting apparatus having a bistable multivibrator electrical circuit and an indicator in accordance with another preferred embodiment of the present invention; 
         FIG. 9  is a schematic view of a static detecting apparatus having an optical sensor and an indicator in accordance with another preferred embodiment of the present invention; 
         FIG. 10  is an enlarged perspective view of a static detecting apparatus wherein the surfaces exhibit a permanent bending in accordance with another preferred embodiment of the present invention; 
         FIG. 11  is an enlarged perspective view of a static detecting apparatus wherein the surfaces have fractured in accordance with another preferred embodiment of the present invention; 
         FIG. 12  is an enlarged side elevational view of a static detecting apparatus having stoppers in accordance with another preferred embodiment of the present invention; 
         FIG. 13  is an enlarged side elevational view of a static detecting apparatus having a plurality of incrementally spaced apart stoppers in accordance with another preferred embodiment of the present invention; 
         FIG. 14  is a schematic view of a static detecting apparatus having stoppers coupled to an electric circuit and an indicator in accordance with another preferred embodiment of the present invention; 
         FIG. 15  is an enlarged side elevational view of a static detecting apparatus wherein one of the surfaces is fixed in accordance with another preferred embodiment of the present invention; 
         FIG. 16  is a schematic view of a static detecting apparatus having a MEMS device with two cantilevered beams in accordance with another preferred embodiment of the present invention; 
         FIG. 17  is an enlarged perspective view of the static detecting apparatus of  FIG. 16  wherein the cantilevered beams are adjacent and substantially parallel to one another in a rest position; 
         FIG. 18  is a schematic view of the static detecting apparatus of  FIG. 16  wherein the cantilevered beams are fractured; 
         FIG. 19  is an enlarged perspective view of a printed circuit board having a static detecting apparatus mounted thereto in accordance with preferred embodiments of the present invention; 
         FIG. 20  is an enlarged perspective view of a static shield bag having a static detecting apparatus mounted thereto in accordance with preferred embodiments of the present invention; 
         FIG. 21  is an enlarged partial perspective view of an integrated circuit shipping tube having a static detecting apparatus mounted thereto in accordance with preferred embodiments of the present invention; 
         FIG. 22  is a schematic view of a container of liquid having a static detecting apparatus disposed therein in accordance with preferred embodiments of the present invention; and 
         FIG. 23  is a schematic view of an ionizing system having a static detecting apparatus mounted thereto in accordance with preferred embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “right”, “left”, “lower”, and “upper” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the apparatus and designated parts thereof. The terminology includes the above-listed words, derivatives thereof, and words of similar import. Additionally, the words “a” and “an”, as used in the claims and in the corresponding portions of the specification, mean “at least one.” In the drawings, the same reference numerals indicate like elements throughout. 
       FIG. 1  shows two surfaces  10   a ,  10   b  of a conductive material for use in preferred embodiments of the present invention. The conductive material may be copper, silver, aluminum, tin, gold, or another conductive metal, conductive plastic, a doped semiconductive material (e.g., silicon), or combinations thereof. The surfaces  10   a ,  10   b  may be respective surfaces of two beams  12   a ,  12   b , but may also be fastened to, adhered to, or coated onto the beams  12   a ,  12   b . The beams  12   a ,  12   b  may be constructed of a conductive material (either similar to or different from the material of the surfaces  10   a ,  10   b ), an insulative material, or a semiconductive material. The beams  12   a ,  12   b  and the surfaces  10   a ,  10   b  are preferably fastened at a common end  14 . 
     The beams  12   a ,  12   b  and/or the surfaces  10   a ,  10   b  may be formed by a single folded piece of conductive material, but may also be separate and distinct bodies that are fastened together or in close proximity to one another at the common end  14  (see  FIG. 2 ). In preferred embodiments, the surfaces  10   a ,  10   b  face each other. As shown in  FIG. 3 , the surface  10   a  has a length dimension L and a width dimension W. The surface  10   a  also has a thickness dimension T, which is illustrated in  FIG. 3  as being the thickness T of the entire beam  12   a  for instances when the surface  10   a  is a surface of the beam  12   a  of the same conductive material. When the surface  10   a  is fastened or adhered to the beam  12   a , the thickness T includes only a thickness of the surface  10   a.  Surface  10   b  preferably is identically sized with respect to surface  10   a . In preferred embodiments, the ratio of length L to width W to thickness T is 1 unit by 0.25 units by 0.001 units. For example, surfaces  10   a ,  10   b  of tin with dimensions of 1 inch by 0.25 inches by 0.001 inches exhibits a 2 inch separation in a 20 kilo-Volt (kV) static field, illustrated by field lines  16  in  FIG. 1 . 
     The surfaces  10   a ,  10   b  are preferably electrically coupled to each other, which is achieved in  FIG. 1  by direct contact of the two surfaces  10   a ,  10   b  near the common end  14 , although other techniques for electrical coupling may be utilized, such as by connecting the two surfaces  10   a,    10   b  via a conductive material at the common end  14 . As a result, the two surfaces  10   a ,  10   b  will be charged by field induction in the presence of a static field  16 . Prior to being subjected to a static field  16 , the two surfaces  10   a ,  10   b  are preferably adjacent to each other (see, e.g.,  FIG. 2 ), and may be substantially parallel to each other. 
       FIG. 4  illustrates an apparatus  100  for detecting a static field  16  in accordance with certain preferred embodiments of the present invention. The apparatus  100  contains the two surfaces  10   a ,  10   b  and a rupturable indicator  122  that bridges and couples the surfaces  10   a ,  10   b . The indicator  122  ruptures (e.g.,  FIG. 5 ) upon repulsion of the two surfaces  10   a ,  10   b  by at least a predetermined distance. The predetermined distance may, for example, be calculated to correspond to a threshold static field  16  strength that is undesirable for the particular application. The two surfaces  10   a ,  10   b  and the indicator  122  are preferably surrounded by a clear insulative cover  28 , which may be formed from glass, plastic, or the like and can be used for applications requiring complete enclosure, such as during fluid immersions, without affecting the performance of the apparatus  100 . 
     The indicator  122 , shown in  FIG. 4  as a capsule, may include an encapsulated material  124  that is releasable from the indicator  122  upon rupture. The capsule  122  may be made from a thin, fragile plastic or other suitable material. The capsule  122  is preferably coupled to the surfaces  10   a ,  10   b  using a strong adhesive (not shown), or may be welded to the surfaces  10   a,    10   b . The encapsulated material  124  is preferably a dye, but may also be an ink, gel, powder, or the like. The apparatus  100  also preferably includes a surrounding medium  126  that receives the encapsulated material  124  released by the ruptured indicator  122 . The surrounding medium  126  preferably undergoes a visible color change upon receipt of the encapsulated material  124 . For example, the surrounding medium  126  may be a blotting paper or fabric that absorbs the released dye  124 , as shown in  FIG. 5 . The visible color change in  FIG. 5  is most concentrated at the center, but more diffuse at edge regions of the apparatus  100 , although over time the visible color change of the surrounding medium  126  may become more uniform. The surrounding medium  126  may also be a liquid that undergoes a visible color change as the encapsulated material  124  becomes mixed with the liquid. Alternatively, the surrounding medium  126  may be air or another gas that does not visibly change color. In certain embodiments, the encapsulated material  124  may visibly change color upon exposure to the surrounding medium  126 . 
     In an alternate embodiment, shown in  FIG. 6 , the rupturable indicator  222  of the apparatus  200  is a bead of adhesive which may break apart or separate from one or both of the surfaces  10   a ,  10   b  upon repulsion of the surfaces  10   a ,  10   b  by a predetermined distance. The adhesive bead  222  is preferably visually inspected for damage following use, such as under a microscope or by direct observation. In a further alternate embodiment, shown in  FIG. 7 , the rupturable indicator  322  of the apparatus  300  may be a dimple weld including, for example, a concavity  329   a  and a protrusion  329   b . The protrusion  329   b  is initially disposed within the concavity  329   a,  but repulsion of the surfaces  10   a ,  10   b  by a predetermined distance separates the protrusion  329   b  from the concavity  329   a , as shown in  FIG. 7 . The fit between the concavity  329   a  and the protrusion  329   b  is constructed such that the protrusion  329   b  cannot reenter the concavity  329   a  upon a return of the surfaces  10   a ,  10   b  to the initial adjacent position. 
       FIG. 8  illustrates an apparatus  400  for detecting a static field  16  in accordance with certain other preferred embodiments of the present invention. The apparatus  400  includes a sensor  432  that detects repulsion of the two surfaces  10   a ,  10   b  from each other by at least a predetermined distance. The apparatus  400  further includes an indicator  434  coupled to an output of the sensor  432 . The indicator  434  communicates that repulsion of the two surfaces  10   a ,  10   b  has exceeded the predetermined distance. 
     In  FIG. 8 , the sensor  432  is illustrated as a conventional bistable multivibrator electrical circuit and the indicator  434  is a light. Other indicators  434  may also be used, such as, for example, audible alarms, electrical signals, or wireless signals. Preferably, the light  434  is initially off, but may also initially be on. Once the two surfaces  10   a ,  10   b  repulse one another by a predetermined distance, the bistable multivibrator electrical circuit  432  changes states, which thereafter triggers a change in the light  434 . The light  434 , which preferably was initially off, turns on. With the light  434  on, a user is now aware that the apparatus  400  was subjected to at least a threshold level of a static field  16 . 
     The bistable multivibrator electrical circuit  432  preferably includes at least one trigger  436  for actuation by one or more of the surfaces  10   a ,  10   b  or beams  12   a ,  12   b . For example, the apparatus  400  may include two triggers  436  that are contact pads set apart at the predetermined distance. Repulsion of the surfaces  10   a ,  10   b  may then cause the beams  12   a ,  12   b  to touch the contact pads  436  to conduct electricity to the bistable multivibrator electrical circuit  432 . The trigger  436  may also be a mechanical switch, a capacitor, or the like. Preferably, subsequent repulsion of the two surfaces  10   a ,  10   b  by a predetermined distance does not change the state of the sensor  432  or the indicator  434 . 
     Similar to the embodiments shown in  FIGS. 4-7 , the surfaces  10   a ,  10   b , the sensor  432 , and the indicator  434  may all be contained within a clear insulative cover  28 , but it is also envisioned that individual components, particularly the indicator  434 , may be external or separate and apart from at least the surfaces  10   a ,  10   b.    
     In an alternate embodiment, shown in  FIG. 9 , sensor  532  of apparatus  500  is an optical sensor. For example, a light source  538  may be optically coupled with the sensor  532 . The light source  538  may initially be blocked by the surfaces  10   a ,  10   b  and/or beams  12   a ,  12   b , and upon repulsion of the surfaces  10   a ,  10   b  from each other by a predetermined distance, the light source  538  is exposed to the sensor  532 , triggering an indicator  534 , which may be a light. Alternatively, during repulsion by the surfaces  10   a ,  10   b  by a predetermined distance, one of the surfaces  10   a ,  10   b  and/or beams  12   a ,  12   b  may block the light source  538  from the sensor  532 , triggering the indicator  534 . As before, subsequent repulsion of the two surfaces  10   a ,  10   b  by a predetermined distance preferably does not change the state of the sensor  532  or the indicator  534 . 
       FIG. 10  illustrates an apparatus  600  for detecting a static field  16  in accordance with another preferred embodiment of the present invention. The surfaces  10   a ,  10   b  and/or beams  12   a,    12   b  have a deformation property such that stress caused by repulsion of the two surfaces  10   a,    10   b  from each other by at least a predetermined distance causes at least one of the surfaces  10   a,    10   b  and/or beams  12   a ,  12   b  to permanently deform. That is, the surfaces  10   a ,  10   b  do not completely return to be adjacent to one another as the surfaces  10   a ,  10   b  had been prior to exposure to the static field  16 , as shown in  FIG. 2 . For example, the conductive material may have a degree of plasticity such that the stress caused by repulsion of the two surfaces  10 ,  10   b  from each other by at least a predetermined distance causes at least one of the surfaces  10   a ,  10   b  to bend permanently. In  FIG. 10 , ends of the surfaces  10   a ,  10   b  opposite to the common end  14  exhibit outward curl deformations  642   a ,  642   b . The curls  642   a ,  642   b  provide a visual indication that the surfaces  10   a ,  10   b  have experienced at least a threshold level of a static field  16 . At the dimensions of 1 inch by 0.25 inches by 0.001 inches described above, surfaces  10   a ,  10   b  made of aluminum exhibit clearly visible curl deformations  642   a ,  642   b , unlike tin surfaces  10   a ,  10   b  having identical dimensions. 
     In an alternate embodiment, shown in  FIG. 11 , the surfaces  10   a ,  10   b  and/or beams  12   a,    12   b  of apparatus  700  include a conductive material having a fracture point such that the stress caused by repulsion of the two surfaces  10 ,  10   b  from each other by at least a predetermined distance causes at least one of the surfaces  10   a ,  10   b  to fracture. In  FIG. 11 , ends of the surfaces  10   a ,  10   b  opposite to the common end  14  are broken off, leaving fractured ends  744   a ,  744   b,  indicating that the surfaces  10   a ,  10   b  have experienced at least a threshold level of a static field  16 . For example, the beams  12   a ,  12   b  may be constructed from an extremely brittle material, such as thin quartz or glass, having a conductive coating forming the conductive surfaces  10   a,    10   b.    
     Detection of the deformation of the surfaces  10   a ,  10   b  preferably occurs by visual inspection, either directly or using magnification. However, other methods may be used, such as optical sensors or electrical sensors. 
       FIG. 12  illustrates an apparatus  800  for detecting a static field  16  in accordance with another preferred embodiment of the present invention. In previous embodiments, at least one of the surfaces  10   a ,  10   b  has a movement path resulting from the repulsion of the two surfaces  10   a,    10   b  from each other. That is, the surfaces  10   a ,  10   b  tend to move away from the rest position (e.g.,  FIG. 2 ) when in the presence of a static field  16 . The apparatus  800  includes at least one stopper  852   a  in the movement path of at least one of the surfaces  10   a . Preferably, a stopper  852   a ,  852   b  is located in each respective movement path of the two surfaces  10   a ,  10   b . The stoppers  852   a  are “one-way stoppers” and prevent the respective surfaces  10   a ,  10   b  from returning to the rest position after the two surfaces  10   a ,  10   b  are repulsed from each other by at least a predetermined distance. 
     In preferred embodiments, the stoppers  852   a ,  852   b  may be protrusions placed at the predetermined distance. The stoppers  852   a ,  852   b  should therefore be shaped to allow the surfaces  10   a ,  10   b  to traverse the stoppers  852   a ,  852   b  during repulsion, but prevent the surfaces  10   a ,  10   b  from traversing back to the rest position. For example, the surfaces  10   a ,  10   b  and beams  12   a ,  12   b  are shown in phantom in  FIG. 12  when bending to traverse the respective stoppers  852   a,    852   b  during repulsion. Alternatively, the stoppers  852   a ,  852   b  may be one-way retractable, hinged, flexible, spring-loaded, or the like. 
     Apparatus  900  ( FIG. 13 ) may also include a plurality of stoppers  952   a ,  952   b  in the movement paths of the respective surfaces  10   a ,  10   b . The location of each of the stoppers  952   a,    952   b  may be proportional to the strength of the static field  16  experienced by the two surfaces  10   a ,  10   b . For example, the lowest stopper  952   a  may correspond to a field strength of 20 kV, the next stopper  952   a  may correspond to 30 kV, and so on. In the example of  FIG. 13 , the stoppers  952   a ,  952   b  are shown in phantom when bending to allow passage of the surfaces  10   a ,  10   b  during repulsion. 
     While the indication of repulsion of the two surfaces  10   a ,  10   b  is preferably directly observed, other indication techniques are available. For example, in  FIG. 14 , apparatus  1000  includes an electric circuit  1054  electrically coupled to a battery  1055  and an indicator  1056 . The indicator  1056  is preferably a light. The stoppers  1052   a ,  1052   b  may be contact pads that are electrically coupled to the circuit  1054 . The surfaces  10   a ,  10   b  are shown in the rest position in phantom. Contact between the stoppers  1052   a ,  1052   b  and the respective surfaces  10   a ,  10   b  completes the electric circuit  1054 , thereby enabling electricity to flow through from the battery  1055  to the indicator  1056 . Contacts for the electric circuit  1054  may also be separate from the stoppers  1052   a ,  1052   b . Alternatively, the repulsed surfaces  10   a ,  10   b  may break, rather than enable, the electric circuit  1054 . 
     In certain embodiments, it may be desirable to permit motion by only one of the surfaces  10   a ,  10   b . For example, apparatus  1100  in  FIG. 15  fixes surface  10   a  while the other surface  10   b  is free to move during repulsion in the presence of the static field  16 . The stopper  1152   b  prevents the other surface  10   b  from returning to the rest position. The fixing of one of the surfaces  10   a,    10   b  may also be applicable to many of the other embodiments described herein. 
       FIG. 16  illustrates an apparatus  1200  for detecting a static field  16  in accordance with another preferred embodiment of the present invention. The apparatus  1200  includes a microelectromechanical systems (MEMS) device  1260  having two cantilevered beams  1210   a,    1210   b  of conductive material, which is preferably a doped semiconductor material such as silicon or germanium. The cantilevered beams  1210   a ,  1210   b  can be very small, preferably having a thickness T of 100 nanometers (nm) or less. In the absence of a static field (rest position), the two cantilevered beams  1210   a ,  1210   b  are adjacent and substantially parallel to each other ( FIG. 17 ). In the presence of a static field  16 , the two cantilevered beams  1210   a,    1210   b  repel each other ( FIG. 16 ). The apparatus  1200  further includes at least one sensor  1262  that detects an amount of repulsion of the two cantilevered beams  1210   a ,  1210   b  from each other. 
     The MEMS device  1260  may use conventional circuitry (not shown) for determining position of the cantilevered beams  1210   a ,  1210   b . The sensors  1262  are preferably capacitors, but may also be optical sensors or the like. The sensors  1262  detect displacement of the cantilevered beams  1210   a ,  1210   b  from the rest position, which is used to calculate the repulsion of the cantilevered beams  1210   a ,  1210   b  from one another. A simple example of an algorithm for determining the repulsion of the cantilevered beams  1210   a ,  1210   b  from each other is shown by Table 1 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Measured Beam 
                 Repulsion of Beams 
               
               
                 Measured Beam 1210a 
                 1210b Displacement 
                 1210a, 1210b from 
               
               
                 Displacement from Rest 
                 from Rest 
                 Rest Position 
               
               
                 Position (Units) 
                 Position (Units) 
                 (Units) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 1 
                 2 
               
               
                 2 
                 2 
                 4 
               
               
                 3 
                 3 
                 6 
               
               
                 4 
                 4 
                 8 
               
               
                 5 
                 5 
                 10 
               
               
                   
               
            
           
         
       
     
     The measured displacements of each of the respective cantilevered beams  1210   a ,  1210   b  may be summed to attain the repulsion value. It follows from Table 1 that non-repulsive movement of at least one of the cantilevered beams  1210   a ,  1210   b , as a result of vibrations or other motion, results in a negative displacement value for at least one of the cantilevered beams  1210   a ,  1210   b . In order to prevent false readings of repulsion resulting such motion, the apparatus  1200  may be programmed to ignore negative displacements so that only repulsion (positive displacement by both cantilevered beams  1210   a ,  1210   b ) is reported. 
     The sensors  1262  may continuously determine the amount of repulsion of the two cantilevered beams  1210   a ,  1210   b  from each other, or may determine only whether the amount of the repulsion of the two cantilevered beams  1210   a ,  1210   b  is greater than a predetermined distance. 
     The apparatus  1200  further includes an indicator  1264  connected to an output of the sensor  1262 . When the sensor  1262  continuously determines the amount of repulsion of the cantilevered beams  1210   a ,  1210   b , the indicator  1264  communicates a maximum amount of repulsion of the two cantilevered beams  1210   a ,  1210   b . The amount is preferably converted to a value representing the strength of the static field  16 . When the sensor  1262  determines only whether the amount of repulsion of the cantilevered beams  1210   a ,  1210   b  is greater than a predetermined distance, the indicator  1264  communicates whether the amount of repulsion of the two cantilevered beams  1210   a ,  1210   b  exceeded the predetermined distance. The indicator  1264  may be a light, alphanumeric characters, a memory that is read out by a user, or the like. Additionally, the sensing and indication may be implemented in software. When the apparatus  1200  is used within finished equipment (e.g., a chip in a computer) (not shown), the MEMS device  1260  may be communicatively coupled to the equipment for self-monitoring. The indicator  1264  is also preferably resettable to allow the apparatus  1200  to be reused. 
     In an alternate embodiment, apparatus  1300  shown in  FIG. 18  includes two frangible cantilevered beams  1310   a ,  1310   b . At least one of the two frangible cantilevered beams  1310   a,    1310   b  fractures upon a repulsion of the two beams  1310   a ,  1310   b  from each other by at least a predetermined distance. Fracture may occur at any portion of the respective two beams  1310   a,    1310   b . The apparatus  1300  further includes at least one sensor  1362  to detect a fracturing of at least one of the two beams  1310   a ,  1310   b . An indicator  1364 , similar to those described above, may be used to indicate when fracture of the beams  1310   a ,  1310   b  has occurred. 
     Use of the embodiments of the present invention detailed above will now be described. For simplicity, all embodiments hereinafter will be referred to as static detector  2000 . 
       FIG. 19  illustrates one of the preferred uses of the static detector  2000 . A printed circuit board (PCB)  2070  is shown having the static detector  2000  disposed thereon. The static detector  2000  is preferably adhered or fastened to the PCB  2070 . The static detector  2000  is preferably attached to the PCB  2070  prior to manufacturing or assembly of the PCB  2070 , permitting examination of potentially damaging static fields  16  at each stage. This is particularly useful in determining ESD “hot spots” within manufacturing equipment and permits monitoring of compliance with S20.20 standards. 
     The size of the static detector  2000  may be adjusted to suit the size of the PCB  2070 . It is even contemplated to enable a static detector  2000  to be placed on a single lead (not shown) on the PCB  2070 , for independent monitoring of the most sensitive component thereon. Placement of the static detector  2000  is not limited to PCBs  2070 , but may be placed on all kinds of ESD sensitive devices during manufacture, such as integrated circuits (ICs), wafers and chips. The static detectors  2000  may also be placed within the manufacturing equipment for monitoring, although placement on the PCB  2070  is preferred. 
     The static detector  2000  may also be placed on packaging materials, such as a static shield bag  2072  ( FIG. 20 ) or an IC shipping tube  2074  ( FIG. 21 ). ESD packaging materials are produced with anti-static chemical additives or coatings that minimize the generation or accumulation of static charge within the packaging material. These chemical additives and coatings may lose their effectiveness over time and the packaging becomes susceptible to generating and accumulating charge. The static detector  2000  indicates when the static shield bag  2072 , IC shipping tube  2074 , or the like packaging has degraded to an undesirable condition for ESD sensitive equipment. 
     As shown in  FIG. 22 , the static detector  2000  may also be placed in a container  2076  with a fluid  2077 , such as de-ionized water, which is often used in manufacturing electronics. Generation of carbon dioxide  2078  or other fluid disturbances can cause static buildup, and the static detector  2000  indicates whether the static generated in the fluid  2077  exceeds a desired level. 
       FIG. 23  shows a static detector  2000  positioned near one or more ionizers  2080  that place or remove charge from a material  2082 . The material  2082  may be, for example, a web of sheet plastic. The static detector  2000  provides a much smaller sensor for detecting whether the ionizers  2080  are functioning properly. The static detector  2000 , particularly in MEMS embodiments, could also replace the common charge plate monitor for machines. Currently the smallest charge plate monitors are approximately 1 inch by 1 inch. The relatively small size of the static detector  2000  makes it especially suited for smaller volumes within equipment. 
     For embodiments shown in  FIGS. 4-15 , the static detector  2000  preferably has the appearance to the naked eye of a dot. It may be referred to as a “static dot.” In one preferred embodiment, the static detector  2000  is preferably generally round with a diameter of about 2 to about 3 millimeters (mm). 
     As seen in the drawings, the static detector  2000  may include a number of “active” and “passive” embodiments, that is, embodiments wherein the static detector  2000  requires or does not require power. Passive embodiments include the embodiments shown in  FIGS. 4-7 ,  10 - 13 , and  15 , and active embodiments include the embodiments shown in  FIGS. 8-9 ,  14 , and  16 - 18 , although any of the embodiments shown may be modified to be active or passive. 
     Passive embodiments have the advantage that no power is required, which reduces cost and complexity of the static detector  2000 . One advantage of the active embodiments is the ability to provide a wider range of easily identifiable indicators, such as lights. Power for active embodiments may be supplied, for example, by an internal battery (e.g.  FIG. 14 ), solar cells, connection to an external power supply, radio frequency signals (similar to radio frequency identification (RFID) tags), or the like. 
     From the foregoing, it can be seen that embodiments of the present invention comprise an apparatus for detecting a static field. It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.