Patent Abstract:
A circuit board anti-tamper mechanism comprises a circuit board having a frangible portion, a trigger having a trigger spring, a trigger arming mechanism actuated by the trigger wherein the trigger arming mechanism is initially non-actuated, a force producing mechanism, a latch providing mechanical communication between the trigger arming mechanism and the force producing mechanism, wherein the latch initially retains the force producing mechanism in a refracted position. Arming pressure applied to the trigger sufficient to overcome the trigger spring force will actuate the trigger arming mechanism, causing the anti-tamper mechanism to be armed. Subsequent tampering with the anti-tamper mechanism results in a decrease of pressure on the trigger below the trigger spring force, thereby causing the trigger arming mechanism to actuate the latch, thereby releasing the force producing mechanism to apply force to the frangible portion of the circuit board, thereby breaking the circuit board.

Full Description:
RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit under 35 USC 119(e) of U.S. Provisional Patent Application No. 62/000,629, filed on May 20, 2014 and entitled “Secure RFID Tag Or Sensor With Self-Destruction Mechanism Upon Tampering”, the entirety of which is incorporated herein by reference. 
     
    
     CONTRACTUAL ORIGIN OF THE INVENTION 
       [0002]    The United States Government has rights in this invention pursuant to Contract DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates generally to an anti-tamper mechanism configured to destroy the contents of an enclosure if the enclosure is tampered with or detached from a mounting surface, and more particularly to a mechanism configured to destroy a printed circuit board containing an RFID circuit or sensor if tampering or removal is attempted. 
       DESCRIPTION OF THE PRIOR ART 
       [0004]    Passive RFID tags are a convenient means for monitoring the location of critical or high-value items, since no batteries are required for tag function and fixed and/or mobile interrogation devices can be used to query the tags. Maintaining tag security is often accomplished by hiding the tag inside the item being monitored, or in the case of a tag secured to a surface, it is well known in the art to adhere the tag in such a fashion as to ensure tag destruction by shearing or tearing if the tag is removed from the surface of the item. Tag destruction results in a failure to respond to tag interrogation, which can then cause an alarm condition. The former approach works best with items that are radio-transparent in the frequencies used for tag interrogation, and the latter approach works best with small flexible tags of the printed foil variety. 
         [0005]    More sophisticated RFID tags may incorporate printed circuit boards and circuitry containing data storage, data manipulation or encryption technologies, and may have antennas designed for data reception and transmission over greater distances and for more power than the simpler and more common RFID tags. Such tags are larger, more electrically and physically complex, and are not fabricated as small flexible structures. Tamper-proofing through tag destruction for this style of tag often requires the cutting of wires or circuit traces or actual breakage of the circuit board, which may require a portion of the circuit board to be scored, selectively perforated, or otherwise intentionally weakened to facilitate controlled breakage and thus the permanent removal of circuit function. Other anti-tampering strategies for rendering electronic circuits inoperative are also well known in the art, using such means as permanently changing a circuit&#39;s electrical characteristics, and using relatively high voltage or current to destroy components. Since RFID tags of this level of sophistication are most likely used to monitor exceptionally critical or high-value items, tamper-proofing is essential and tag destruction must be ensured with the assistance of specific actuation triggers, as well as means including mechanical force amplification such as spring mechanisms. Tags of this variety often require a housing or enclosure for environmental protection and concealing of the tamper-proofing function. Ideally, the item being monitored could serve as such an enclosure, but if the item is made of a material that is not radio-transparent such as a metal container, then a separate external enclosure is needed for the tag. Further, the contents of the item may not be compatible with the electrical circuitry of the RFID tag, or opening the item to install the tag may be difficult, impractical, or even hazardous. Thus, in many cases it is necessary to mount the more sophisticated RFID tag to the outside of the item being monitored. 
         [0006]    External mounting of an RFID tag raises the challenges of environmental sealing, and of tamper or removal prevention. It is desirable for the tag to be easy to attach to the item being monitored, while being difficult to remove. It is also desirable for the tag anti-tamper mechanism to be easy to activate and extremely difficult or impossible to deactivate. 
         [0007]    U.S. Pat. No. 8,710,991 entitled DISPOSABLE AND TAMPER RESISTANT RFID LOCK teaches a housing containing an RFID tag and a spring-loaded mechanism which includes a locking or ratcheting stem engaged by a connector such that tampering either causes the stem or the connector to break and release the spring, which then expands to drive a puncturing element through a functional portion of the RFID tag and thereby render it nonfunctional. The &#39;991 patent also teaches means to crush or sever portions of the RFID tag, and also teaches adhesive means for attaching the housing to an object. However, while the &#39;991 patent teaches the use of a releasable spring mechanism to destroy an RFID tag in response to tampering, and the spring expansion is sudden and destructive, there is no discrete trigger, and the device is not unitary and requires the user to first attach the multiple parts of the housing to an object through openings in such a way as to arm it, and then install the RFID tag into the armed housing. 
         [0008]    U.S. Pat. No. 8,274,389 entitled DISPOSABLE AND TAMPER RESISTANT RFID LOCK teaches a housing containing a foil type RFID tag and a spring-loaded mechanism which includes a locking or ratcheting stem engaged by a connector such that tampering either causes the stem to break or the connector to loosen and release the spring, which then expands to crush the RFID tag and render it nonfunctional. However, while the spring expansion is sudden and destructive, the device taught by the &#39;389 patent requires the user to first attach the multiple parts of the housing to an object through openings in such a way as to arm it, and then install the RFID tag into the armed housing. There is no means taught for environmentally sealing the opening through which the RFID tag is installed, and specific mechanical attachment features must be present on the item being monitored. Further, the mechanism is designed to work with a small flexible RFID tag, not an RFID tag with a rigid circuit board and a more sophisticated antenna. 
         [0009]    U.S. Pat. No. 7,800,504 entitled DISPOSABLE AND TAMPER RESISTANT RFID LOCK teaches a housing containing an RFID tag and a spring-loaded mechanism which includes a ratcheting stem retained such that tampering causes the stem to break and release the spring, which then expands to drive a cutting blade through the RFID tag, cutting it in half and rendering it nonfunctional. However, the device taught by the &#39;504 patent requires the user to first attach a portion of the housing to an object through openings in such a way as to arm it, and then install the RFID tag into the armed housing portion, and then finish assembling the housing. Specific mechanical attachment features must be present on the item being monitored, and further, the mechanism is designed to work with a small flexible RFID tag, not an RFID tag with a rigid circuit board and a more sophisticated antenna. 
         [0010]    U.S. Pat. No. 5,898,370 entitled SECURITY MONITORING SYSTEM AND METHOD teaches an RFID tag that can include a circuit built on a substrate that is scored or otherwise rendered breakable along a predetermined axis or in a predetermined direction. Thus, when the tag is subject to manipulation or other mechanical tampering, the circuit substrate will break and the tag is rendered inoperable. However, the device taught by the &#39;370 patent lacks any trigger or spring or means to control or amplify the breaking forces resulting from tampering. 
         [0011]    U.S. Pat. No. 4,097,894 entitled SECURED SCRAMBLE DECODER FILTER teaches a circuit mounted on a fragile substrate in a housing containing an anti-tamper mechanism. The mechanism is triggered by attempts to remove the housing from the surface it has been attached to. When triggered, the mechanism releases a torsion spring which snaps against the fragile substrate, breaking it and destroying the circuit. Installation of the filter requires a special tool, and the filter can only be mounted to surfaces that a screw can be driven into. Unfortunately, anyone with access to the special tool or with the ability to manufacture a reasonably close substitute will be able to remove the filter without triggering the destruct feature. 
         [0012]    U.S. Patent Application No. 20100283578 entitled TRANSPONDER BOLT SEAL AND A HOUSING FOR A TRANSPONDER teaches an RFID circuit and antenna enclosed within a housing intended to lock to a bolt. The bolt may be placed through a shipping container door or similar lock hasp and secured through the housing, thus serving to lock the door. The housing contains a mechanism which is armed by the bolt insertion, wherein any attempts to remove the bolt or pry loose the housing will activate a trigger which releases a spring which will destroy the RFID circuit. However, the mechanism taught by the &#39;578 application is very specific to a bolt insertion and removal through a specific container geometry, and further, the bolt and housing are separate parts which must be joined by the user. 
         [0013]    A more robust, capable and easy-to-install tamper-proof RFID tag or other wireless sensor would include a simple and reliable means for permanently attaching the monitoring device to an item without requiring separate hardware or specific mechanical attachment features, a means for automatically arming the monitoring device during attachment, an enclosure providing full environmental protection while being radio-transparent, a specific triggering mechanism to be actuated by tampering or removal attempts, a means to prevent false triggering from mechanical shock, impact, or vibration, and a destruct mechanism with sufficient force to positively destroy the RFID tag in a difficult-to-repair fashion if the triggering mechanism is actuated. 
       SUMMARY 
       [0014]    A circuit board anti-tamper mechanism comprises a circuit board comprising at least a frangible portion containing electronic circuitry, a trigger having a trigger spring which applies a release force to the trigger, a trigger arming mechanism actuated by the trigger wherein the trigger arming mechanism is initially non-actuated, a force producing mechanism, a latch providing mechanical communication between the trigger arming mechanism and the force producing mechanism, the latch initially retaining the force producing mechanism in a retracted position, wherein arming pressure applied to the trigger sufficient to overcome the release force will actuate the trigger arming mechanism, causing the anti-tamper mechanism to be armed, and wherein subsequent tampering with the anti-tamper mechanism results in a decrease of pressure on the trigger below the pressure of the release force, thereby causing the trigger arming mechanism to actuate the latch, thereby releasing the force producing mechanism, thereby permitting the force producing mechanism to apply force to the circuit board, thereby fragmenting the circuit board and rendering the electronic circuit portion non-functional. 
         [0015]    According to another aspect of the present invention, attaching the anti-tamper mechanism to a surface causes the trigger to actuate the trigger arming mechanism. 
         [0016]    According to yet another aspect of the present invention, a portion of the circuit board is made frangible by features selected from the group consisting of holes, slots, and grooves. The frangible portion contains active circuitry, thereby substantially increasing the difficulty of repairing the RFID circuit if the anti-tamper mechanism is actuated. The active circuitry includes circuitry from the group consisting of RFID circuits, microcontrollers, microprocessors, sensor circuits, signal processing circuits, and wireless device circuits. 
         [0017]    According to still another aspect of the present invention, the range of trigger motion necessary to actuate the trigger arming mechanism is the trigger arming travel and the range of trigger motion necessary to result in the actuation of the latch is the trigger release travel, and the trigger arming travel is greater than the trigger release travel. The trigger arming travel is in the range of approximately 0.180″ to 0.220″ and the trigger release travel is in the range of approximately 0.050″ to 0.070″. 
         [0018]    According to yet still another aspect of the present invention, the circuit board anti-tamper mechanism further comprises an enclosure wherein at least the majority of the anti-tamper mechanism including the circuit board is enclosed within the enclosure, which provides environmental protection and visual concealment to the anti-tamper mechanism and the circuit board, wherein a portion of the trigger protrudes outside of the enclosure, and the enclosure includes means for environmentally sealing around the protruding portion of the trigger, while permitting the trigger to move as required for arming and release. The means for environmental sealing comprises the protruding portion of the trigger being enclosed in an opaque flexible sheath sealed to the enclosure, thereby permitting external arming and release of the trigger while maintaining environmental protection and visual concealment of the contents of the enclosure. The enclosure at least partially comprises a base and a cover, and an adhesive covering at least a portion of the base for the purpose of attaching the enclosure to a surface. The adhesive may be a continuous ring of VHB tape approximately bordering the periphery of the base, with the adhesive thereby enclosing a region of the base when the base is attached to a surface, the adhesive thereby providing an environmental seal to the enclosed region of the base when the base is attached to a surface, and wherein the protruding portion of the trigger is disposed within the enclosed region of the base when the base is attached to a surface. The base may be made of a lightweight durable metal and the cover may be made of a durable polymer, and the cover may be permanently affixed and environmentally sealed to the base with a structural adhesive. Attaching the enclosure to a surface with the adhesive causes the trigger arming mechanism to be actuated. Removing the attached enclosure from a surface causes the trigger arming mechanism to actuate the latch, thereby actuating the anti-tamper mechanism and fragmenting the circuit board. Once the anti-tamper mechanism is armed, the anti-tamper mechanism cannot be disarmed. 
         [0019]    According to a further aspect of the present invention, the latch includes means for preventing accidental actuation caused by mechanical shock, impact or vibration. The means for preventing accidental actuation comprises requiring the force producing mechanism to have an increase in stored mechanical energy before release of the force producing mechanism can occur. 
       OBJECTS AND FEATURES OF THE INVENTION 
       [0020]    It is an object of the present invention to provide an RFID tag or sensor in a tamper-proof enclosure including a destruct mechanism actuated by tampering or removal attempts. 
         [0021]    It is another object of the present invention that the tamper-proof enclosure be environmentally rugged. 
         [0022]    It is yet another object of the present invention that the tamper-proof enclosure be environmentally sealed. 
         [0023]    It is still another object of the present invention that the tamper-proof enclosure be mountable to a surface without using any mechanical hardware. 
         [0024]    It is a further object of the present invention that once the destruct mechanism is armed, it cannot be disarmed. 
         [0025]    It is a feature of the present invention that the tamper-proof enclosure be formed from a lightweight metal base and a radio-transparent polymer cover. 
         [0026]    It is another feature of the present invention that the enclosure base and cover be permanently joined with adhesive. 
         [0027]    It is yet another feature of the present invention that the enclosure base be ringed with a VHB tape in order to provide a means for attachment to a surface. 
         [0028]    It is still another feature of the present invention that a trigger pin protrudes from the enclosure base. 
         [0029]    It is a further feature of the present invention that the trigger pin is enclosed in a flexible sheath which is sealed to the enclosure base. 
         [0030]    It is a yet further feature of the present invention that the action of pressing the enclosure base and the VHB tape against a surface also serves to depress the trigger pin, thereby arming the destruct mechanism. 
         [0031]    It is a still further feature of the present invention that the action of lifting the enclosure base away from a surface that it has been pressed against will allow the trigger pin to extend, thereby actuating the destruct mechanism. 
         [0032]    It is an additional feature of the present invention that the trigger pin travel required to actuate the destruct mechanism is substantially less than the trigger pin travel required to arm the destruct mechanism. 
         [0033]    It is a yet additional feature of the present invention that the destruct mechanism is configured to resist accidental actuation due to mechanical shock, impact, or vibration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The present version of the invention will be more fully understood with reference to the following Detailed Description in conjunction with the drawings of which: 
           [0035]      FIG. 1  is a perspective view of a secure RFID tag enclosure; 
           [0036]      FIG. 2  is a bottom perspective view of a secure RFID tag enclosure; 
           [0037]      FIG. 3  is an elevation view of a secure RFID tag enclosure; 
           [0038]      FIG. 4  is a perspective view of a secure RFID tag enclosure with the enclosure cover removed; 
           [0039]      FIG. 5  is a perspective view of a secure RFID tag enclosure with the first antenna portion, insulating standoffs, and antenna fasteners removed. 
           [0040]      FIG. 6  is a perspective view of the enclosure base plate and destruct mechanism; 
           [0041]      FIG. 7  is a perspective view of the destruct mechanism with the circuit board; 
           [0042]      FIG. 8  is a perspective view of the destruct mechanism without the circuit board; 
           [0043]      FIG. 9  is a bottom perspective view of the destruct mechanism; 
           [0044]      FIG. 10  is a side section view of the unarmed destruct mechanism; 
           [0045]      FIG. 11  is a side section view of the armed destruct mechanism; 
           [0046]      FIG. 12  is a side section view of the triggered destruct mechanism; 
           [0047]      FIG. 13  is a side section view of the triggered destruct mechanism with the driver block forward; 
           [0048]      FIG. 14  is a side section view of the triggered destruct mechanism with the breaker bar pivoted up; and 
           [0049]      FIG. 15  shows a side section view of the latch engagement geometry. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0050]      FIGS. 1-3  show the present invention secure RFID tag enclosure  10 , which is approximately 7″ wide by 6″ high by 1″ deep. It is within the scope of the present invention for the enclosure  10  to be realized with different dimensions too. Preferably the tag enclosure footprint is as small as is practical. The enclosure cover  12  is preferably made from a polymer such as injection molded polycarbonate for durability, ease of manufacturing, ease of adhering to the base plate, and radio transparency. The enclosure base  14  is preferably made from a lightweight durable metal such as aluminum for strength, rigidity, low weight and ease in manufacturing. For use in a wide variety of environments, the enclosure base  14  is preferably coated with an environmentally rugged finish such as a military-grade anodized hardcoat. A ring of adhesive  16  is preferably applied to the enclosure base  14  and used to secure the enclosure  10  to a surface. The adhesive  16  is preferably a Very High Bond (VHB) structural tape, where the thickness of the adhesive is calculated into the function of the triggering mechanism, thus providing the correct travel for both arming and actuating the destruct mechanism. This VHB tape preferably approximately follows the periphery of the enclosure base  14 . A structural adhesive such as epoxy, acrylic or urethane is preferably used to attach the enclosure cover  12  to the enclosure base  14 , providing an environmentally sealed tag. At the center of the enclosure base  14  is a flexible sheath  18  for environmental sealing of a trigger. The flexible sheath  18  is a preferred means of environmentally sealing the protruding portion of the trigger, however any means for environmentally sealing around the protruding portion of the trigger, while permitting the trigger to move as required for arming and release, is seen as being within the scope of the present invention. If the adhesive  16  forms a continuous ring surrounding the protruding portion of the trigger, attaching the enclosure  10  to an appropriately sealed surface may serve to environmentally seal the trigger, even if other means for environmental sealing are not present. 
         [0051]    The flexible sheath  18  is preferably molded from an elastomer and secured into the enclosure base  14  with a conformal and flexible sealing adhesive such as a liquid, gel or VHB tape. Preferably, the flexible sheath  18  is opaque in order to conceal the contents of the enclosure  10 . A portion of the trigger protrudes from the enclosure base  14  inside the flexible sheath  18  and is depressed inwards to arm the destruct mechanism when the enclosure base  14  and adhesive  16  are pressed against a surface. The trigger and the flexible sheath  18  are preferably centered under the enclosure base  14 , and the enclosure  10  itself as shown is preferably as close as possible to square in shape so that the lift angle for triggering is equal in all four directions. Alternatively, a circular enclosure with the trigger centered would also provide equal lift angle in all directions. It is within the scope of the present invention to use an enclosure with any approximately radially symmetrical shape, as long as the trigger may be approximately centered. 
         [0052]      FIG. 4  shows the secure RFID tag  10  with the cover  12  removed. A first antenna portion  24  is mounted on insulating standoffs  28  and is attached to the antenna support  38  portion of the enclosure base  14  with antenna fasteners  30 . The circuit board  20  and a frangible portion of the circuit board  22  are visible through an opening in the first antenna portion  24 . The circuit board weakening feature  54  is visible between the circuit board  20  and the frangible portion of the circuit board  22 . The opening in the first antenna portion  24  permits the destruct mechanism to pivot upwards far enough to ensure full board breakage. Preferably, active circuitry such as transistors, integrated circuits or hybrid modules are included on the frangible portion of the circuit board  22  so that breakage of the circuit board  20  will become substantially more difficult to repair after a tampering attempt. Preferably, the functionality of the active circuitry included on the frangible portion of the circuit board  22  may include RFID circuits, microcontrollers, microprocessors, sensor circuits, signal processing circuits, and wireless device circuits. 
         [0053]      FIG. 5  shows the secure RFID tag  10  with the first antenna portion  24  removed. The circuit board  20  extends from one edge of the second antenna portion  26  which here is also at least partially composed of circuit board material. It is within the scope of the present invention for the circuitry on the circuit board  20  to be any type of RFID circuits, microcontrollers, microprocessors, sensor circuits, signal processing circuits, and wireless devices configured to send and/or receive a signal. The second antenna portion  26  is supported by the antenna support  38 , and the elements of the second antenna portion  26  are held together by the antenna block fasteners  32 . The breaker bar  34  portion of the destruct mechanism  80  supports the end of the circuit board  20 . The latch  36  is visible under the circuit board  20  and the pivot guides  52  for the breaker bar  34  are visible on either side of the breaker bar  34  and the latch  36 . The board weakening feature  54  is the target area for breakage, wherein the circuit board  20  is laid out to have a critical portion of the circuitry on the frangible portion of circuit board  22  which will be broken off, thus rendering the circuit both inoperative and also very difficult to rapidly repair. Numerous prior art patents for tamper-proof RFID tags teach the severing of an antenna from an RFID circuit. The destruct mechanism of the present invention preferably severs numerous conductive paths in the actual RFID and signal processing circuitry, preferably with some active circuitry critical to circuit function on the severed portion of the circuit board. Further, no separate wires or other conductive means are needed, thus simplifying the electronic portion of the device and increasing reliability. The target area of the circuit board  20  is in this case rectangular although that is not an absolute requirement. In fact, it is not an absolute requirement for either section of the circuit board  20  or the antenna portions to be rectangular. The fiberglass and other composite materials commonly used for fabricating pc boards are designed to resist breakage. The frangible portion of circuit board  22  as shown is aided in breaking by the circuit board weakening features  54  which in the preferred embodiment are a row of perforations which may be circular, oval and slot-shaped, approximately in line with the pivoting point of the breaking mechanism, preferably as well as a V-groove cut into the board on one side approximately at the pivoting point. A V-groove can only be employed on one side of the board if surface traces are needed to make electrical contact between the circuit on the end portion and the rest of the circuit. However, if a multilayer board is employed it is possible to run all traces internally and have V-grooves on both surfaces. Ideally, the single V-groove depth is between ⅓ and ½ the thickness of the board. Rows of perforations and V-grooves are both well-known methods of producing breakaway regions on circuit boards, generally for panel separation. Additionally, the circuit board  20  is approximately 0.031″ thick because thinner pc boards are easier to break. Note that any combination of break aiding features including the perforations, V-grooves, and thin substrate may be employed. The fragility of the frangible portion of circuit board  22  must be controlled to prevent a board which is too easily broken and thus prone to accidental failure. 
         [0054]      FIG. 6  shows the destruct mechanism  80  mounted on the enclosure base  14 , with the antennas and circuit board completely removed. Preferably, standard fasteners such as screws are used for the mounting.  FIG. 7  shows the destruct mechanism  80  with the frangible portion of the circuit board  22  held in the breaker bar  34 , while  FIG. 8  shows the destruct mechanism  80  without any circuit boards.  FIG. 9  shows the underside of the destruct mechanism  80 . The frangible portion of circuit board  22  is supported by the circuit board support  58  portion of the breaker bar  34 , and held in place by the circuit board retainer tabs  60 . When not actuated, the breaker bar  34  is in a first bar position which serves to support and protect the frangible portion of the circuit board  22 . Stop tabs  82  keep the breaker bar vertical against the pivot brackets  52 , and provide a means for preventing uncontrolled rotation during non-tampering conditions. The spring block  50  serves to anchor the trigger  40  and a pair of trigger springs  44  which are preferably paired torsion springs, and to limit the upward motion of the front of the trigger  40  with the trigger retainer bar  70  to prevent the trigger  40  from having contact with the antenna assembly. The base  14  also constrains the motion of the trigger springs  44 . The spring block  50  also provides channels for the guide rods  48  which guide the driver springs  46  which are preferably paired compression springs which produce the actual destructive force for breaking the frangible portion of circuit board  22 , and the spring block  50  further serves as a backstop for the driver springs  46 . The latch  36  has a pair of latch pivot arms  56  which rotate on two pivot pins in the pivot guides  52 . The latch  36  can also be described as a pivoting latch bar having a latch portion, two latch pivot arms  56  and a pivot axis. The latch  36  engages the driver block  68  which rides on the guide rods  48  and is driven forward by the driver springs  46  when released. On top of the latch  36  the ratchet  42  is fastened. Preferably, an anti-friction plate  84  made of a relatively hard, smooth plastic such as polyester is inlaid flush into the enclosure base  14  in order to reduce sliding friction between the driver block  68  and the enclosure base  14  when the mechanism is actuated. The driver block  68  is preferably wedge shaped as shown in the present invention, in order to contact the edge of the breaker bar  34  furthest from the breaker bar pivots  76  which are shown in  FIG. 10 , and thereby exert the maximum torque on the breaker bar  34  to produce the maximum breaking force. The breaker bar pivots  76  are also held in the pivot guides  52 . The driver springs  46  are compressed during initial assembly of the mechanism and remain so until triggering occurs. Similarly, the trigger springs  44  are compressed but only to an initial degree during assembly of the mechanism. The driver springs  46 , driver block  68 , and breaker bar  34  in combination form a force producing mechanism which functions to break the circuit board  20 . When static, the components of this force producing mechanism are in first positions, and when actuated, the components of this force producing mechanism move rapidly to second positions wherein destructive action is performed. The ratchet  42  includes an attachment section which is preferably fastened to the latch  36  with screws, a resilient portion  86  in the middle, and a barb  66  at the end furthest from the attachment section. The trigger  40  has a trigger pin  62  at a first end and a trigger step  64  at a second end, where the trigger step  64  is configured to engage the barb  66  during actuation of the mechanism. 
         [0055]      FIGS. 10-14  show side section views of the destruct mechanism  80 , as the mechanism is static, then armed, and then triggered. In  FIG. 10 , the mechanism is static. Trigger pin  62  is fully extended by the trigger springs  44  and the trigger  40  is stopped in a first trigger position by the trigger retainer bar  70 . The latch  36  in a first latch position holds the driver block  68  back against the force of the driver springs  46 , in a first driver block position. The trigger step  64  is above the sloped barb  66  of the ratchet  42 , and the trigger step  64  in combination with the ratchet  42  form the trigger arming mechanism. The frangible portion of the circuit board  22  is held in the breaker bar  34  and retained by the circuit board retainer tabs  60 . The breaker bar pivot  76  is represented by a dashed circle to show how the upper surface of the circuit board  20  coincides with the center of the breaker bar pivots  76 . The circuit board weakening feature  54  also is centered over the breaker bar pivots  76 . The trigger  40  rotates on trigger pivot  72  which is held in the spring block  50 , and the trigger springs  44  act upon the trigger  40  and rotate on the trigger spring liners  74  through which the trigger pivot  72  is inserted. Preferably for most efficient operation, the trigger  40 , the trigger springs  44  and the latch pivot arms  56  all share a common axis of rotation. 
         [0056]      FIG. 11  shows the mechanism armed, with the trigger pin  62  pushed up and the trigger step  64  having been rotated below the barb  66  of the ratchet  42 , where the barb  66  has snapped back into place to engage the trigger step  64 . The ratchet  42  is preferably injection molded from a durable polymer with a good mixture of flexibility and rigidity, such as polycarbonate. During the trigger pin  62  upward rotation, the downward rotation of the trigger step  64  will cause the curved face of the trigger step  64  to push against the sloped face of the barb  66 , thereby bending the resilient portion  86  to move the barb  66  laterally so that the trigger step  64  can rotate to below the barb  66 . Preferably, the rotation of the trigger step  64  is approximately adjacent and tangent to the middle or resilient portion  86  of the ratchet  42 . The mechanism is configured to permit some overtravel by the trigger  40  in order to accommodate tolerances in parts manufacturing, assembly and use. Once the trigger step  64  has rotated past the barb  66  and the barb  66  has snapped back into place, the trigger  40  is in the second trigger position and the mechanism is armed. Since the tag enclosure  10  is sealed, once the mechanism is armed it cannot be disarmed. 
         [0057]      FIG. 12  shows the mechanism starting to actuate. The act of removing the attached enclosure  10  from a surface causes the trigger arming mechanism to actuate the latch, thereby actuating the anti-tamper mechanism. The trigger pin  62  has been allowed to rotate downwards, a result of force against the trigger pin  62  becoming less than the force exerted by the trigger springs  44 . As the trigger  40  thus rotates, the trigger step  64  rotates upwards and lifts the barb  66  and thus the ratchet  42 . The ratchet  42  is attached to the latch  36  which is thus lifted too, rotating around the axis of the latch pivot arms  56 . Given the location of the latch  36  and the driver block  68  contact faces relative to the location of the pivot axis, the driver block  68  is initially forced to move backwards against the driver springs  46  to allow the latch  36  to clear the top of the driver block  68 . Once the latch  36  clears the top of the driver block  68 , the latch  36  is in the second latch position and the driver block  68  will be driven forward by the driver springs  46  towards a second driver block position. The mechanism has been designed with enough space between the latch  36  plus the ratchet  42  and the underside of the circuit board  20  that the latch  36  plus the ratchet  42  can rotate upwards successfully to clear the driver block  68 . 
         [0058]    There are two critical ratios for the mechanism to operate properly. The first critical ratio is trigger arming travel vs. trigger release travel. Ideally the trigger arming travel is in the range of 0.180″ to 0.220″, allowing safe handling and ease of application to a surface, plus approximately 0.020″ to 0.030″ of overtravel when arming as a safety margin. This safety margin accommodates manufacturing, assembly and use tolerances. Ideally the trigger release travel is in the range of 0.050″ to 0.070″, being enough travel to prevent any accidental triggering during application of the tag to a surface, but preventing tampering with the trigger during tag removal attempts. In the structure of the tag of the present invention, this translates to a lift angle of less than 2 degrees. 
         [0059]    The second critical ratio is latch pivot location and latch engagement depth versus the driver block backwards travel to release. This means for preventing accidental actuation comprises requiring the force producing mechanism to have an increase in stored mechanical energy before release of the force producing mechanism can occur.  FIG. 15  shows the latch tab  88  portion of the latch  36  latching to and retaining the driver block  68 . The area of retaining contact on the driver block  68  is the latch engagement region  90 . By placing the latch pivot axis  92  below the latch engagement region  90 , raising the latch  36  forces the driver block  68  to travel backwards a very small distance against the driver springs  44 . This geometric relationship is further illustrated by the latch pivot reference line  94 , which is seen as being below the latch engagement area  90 . Therefore, more than just friction is holding the latch  36  in engagement with the driver block  68 , and this required back motion serves to resist accidental release of the latch  36  against mechanical shock, impact, or vibration. Preferably, the trigger pivot  72  and the latch pivot axis  92  are coaxial. The length of the latch pivot arms  56  and engagement depth of the latch  36  with the driver block  68  are also critical factors in determining the distance the driver block  68  will have to move backwards in order to allow the latch  36  to release. An ideal latch engagement depth was found to be in the range of 0.065″ to 0.085″, and an ideal amount of driver block backwards travel was found to be in the range of 0.003″ to 0.011″, where the mechanism of the present invention as fabricated has approximately 0.007″ of driver block  68  backwards travel. Having the trigger  40 , the trigger springs  44  and the latch  36  share a common axis aids in reducing wasteful force components that could interfere with the desired rotational forces. 
         [0060]    Without careful design and fabrication, the friction of the engagement between the latch  36  and the driver block  68  can easily become too much for the trigger springs  44  to overcome, resulting in a stalled mechanism when actuation is needed. The trigger springs  44  can be strengthened but that will reach a point of diminishing returns, and excessive back pressure on the trigger pin  62  may cause a mounting adhesive failure or flexible sheath  18  failure. Careful tradeoffs must be made between the trigger spring  44  force and the driver spring  46  force. Control of the friction between the latch  36  and the latch engagement region  90  of the driver block  68  is best accomplished by polishing the contacting surfaces of the latch engagement region  90 , radiusing the contacting edges by approximately 0.005″-0.010″, and applying a thick lubricant such as white lithium grease to the contacting surfaces. A small amount of lubricant is preferably applied to the guide rods  48  as well. The anti-friction plate  84  also improves the driver block  68  travel. 
         [0061]    An additional mechanical constraint in the present invention is the need for the destruct mechanism  80  to be as low profile as possible to fit under the antenna assembly and not cause the full tag assembly to become excessively tall. The portion of the destruct mechanism which fits under the antenna assembly is less than or equal to 0.375″ tall. 
         [0062]      FIG. 13  shows the mechanism in mid-actuation. Once free of the latch  36 , the driver block  68  is driven forward by the driver springs  46  and contacts the bottom edge of the breaker bar  34 . In  FIG. 14  the destruct action is complete, with the driver block  68  continuing to be driven forwards by the driver springs  46  towards a second driver block position and thus forcing the breaker bar  34  to pivot upwards towards a second bar position, resulting in a broken circuit board  78 . The breaker bar  34  is capable of rotating at least but preferably more than 90 degrees, which adds to the assurance that the frangible portion of circuit board  22  will be fully detached and all conductive traces will be severed. The sequence of events in  FIGS. 12-14  are rapid and violent, and can be clearly heard outside the secure RFID tag enclosure  10 . 
         [0063]    The destruct mechanism  80  parts are preferably made of stainless steel for the fasteners, rods and pivot pins, spring steel for the torsion and compression springs, and high strength aluminum for the other metal parts except for the trigger spring liners  74  located between the trigger pivot pin  72  and the trigger springs  44 . The trigger spring liners  74  are preferably made of brass. 
         [0064]    One unique benefit of the mechanism of the present invention is the ability to provide a significant amount of impact force in a very low-profile device, and have that force easily translated into a different plane, up to 90 degrees or greater from the direction of the primary impact force. The utility of the destruct mechanism of the present invention is not limited to breaking circuit boards and can provide a straight-line impact or as taught herein for circuit board breaking, may also be used to provide impact at an angle of 90 degrees or greater from the primary spring force direction in order to break frangible items such as glass tubes, glass plates, or any other suitably configured frangible item. In such a circumstance the end of the breaker bar  34  furthest from the breaker bar pivots  76  would preferably provide the impact. 
         [0065]    Alternate embodiments of the present invention may include a reinforced polymer or composite enclosure base, different antenna geometries, and a circuit board that is separate from the antenna. 
         [0066]    Alternate embodiments of the destruct mechanism may include multiple trigger pins, alternate triggering mechanisms, greater or lesser amounts of trigger arming and actuating travel, means for adjusting the trigger arming and actuating travel, means for safely disarming the trigger, transmission of impact force to break multiple items, and angled transmission of impact force over a distance inside the enclosure. 
         [0067]    Having described herein illustrative embodiments and best mode of the present invention, persons of ordinary skill in the art will appreciate various other features and advantages of the invention apart from those specifically described above. It should therefore be understood that the foregoing is only illustrative of the principles of the invention, and that various modifications and additions can be made by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, the appended claims shall not be limited by the particular features that have been shown and described, but shall be construed also to cover any obvious modifications and equivalents thereof.

Technology Classification (CPC): 8