Abstract:
In one aspect the present invention comprises a surgical tool. The surgical tool preferably includes a body having a cavity, and RFID electronic assembly, a first layer of first encapsulant formed around the electronic assembly and a housing insertable into the cavity. In accordance with this aspect of the present invention, a second layer of second encapsulant may be formed around the housing to hold it in place in the body cavity. In another aspect, the present invention preferably comprises an orthopedic instrument having a body which includes a cavity. Most preferably, a housing is located within the cavity, the housing preferably comprises a base member, a cap attached to the base and a glass dish attached to the cap, the glass dish being adapted to a loud frequency wave to pass through its body.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention is generally directed to a surgical navigation system. More particularly, this invention is directed to a system for protecting electronic circuitry used in orthopedic instruments that generally comprise a part of the navigation system from contamination, impact and the effects of sterilization. 
         [0003]    2. Description of Related Art 
         [0004]    Surgical navigation systems have become extremely useful tools in operating rooms. Generally, a surgical navigation system consists of one or more trackers. Each tracker is attached to a specific surgical instrument, device or implant. The system also includes a localizer. Each tracker generates one or more specific signals. These signals may be radio signals, other electromagnetic (EM) signals, light signals or ultrasonic signals. The localizer monitors the locations signals that are broadcasted. The tracker&#39;s location-identifying signals obtained by the localizer are forwarded to a processor. Based on the data contained in these signals, including their signal strength and relative phases, the processor generates data indicating the position of the tracker and the attached component. 
         [0005]    Either prior to or at the start of the procedure, the processor is provided with data identifying the relative positions of tissue landmarks at the surgical site. The processor also has data that indicates the location of the surgical site relative to the localizer. Based on the above data, the processor provides information about the location of the surgical component attached to the tracker relative to the surgical site. Often this information is presented on a display that shows the position of the surgical component at a location within the patient. A surgical navigation system thus provides a view of the location of a surgical component at surgical site that, due to the presence of surrounding tissue, otherwise cannot be seen. 
         [0006]    During a surgical procedure, a number of different instruments and other components are typically positioned at a surgical site. For example, during a procedure to implant an orthopedic implant, a first set of tissue cutting devices are used to gain access to the surgical site. A second set of devices are used to remove the bone and surrounding soft tissue that are to be replaced. A third set of devices shape the remaining tissue, typically the bone, so it can accept the implant. Often, trial implants are positioned at the surgical site to determine the appropriate size of implant components that should be permanently fitted to the patient. Then, the positions of the implant components themselves are tracked. Once an implant is fitted, the position of the instruments used to close the surgical site are tracked. Each of these of these instruments, implants and other components has a set of unique physical dimensions. For the surgical navigation system to accurately generate data indicating the location of a component relative to the surgical site, the system processor must have data describing component&#39;s dimensions. 
         [0007]    U.S. patent application Ser. No. 10/214,937, filed Aug. 8, 2002, U.S. Patent Publication No. US 2003/0093103 A1, now U.S. Pat. No. ______, and incorporated herein by reference, discloses one system for providing a surgical navigation unit with data regarding the individual components applied to a surgical site. In the invention of this system, a radio frequency identification device (RFID) is attached to each component. Internal to the RFID is a memory in which data regarding the component are stored. These data identify the component and/or the physical dimensions of the component. The component also includes a coil through which the RFID is capable of exchanging signals. Prior to use, the component is attached to a handpiece. The handpiece is coupled to some a control console or station. The connection between the handpiece and the control console may be a wireless connection. Internal to the handpiece is a coil. The handpiece coil and component coil are in sufficient proximity to allow inductive signal transfer. The control console, through the handpiece, reads the data from the component RFID. These data are transferred from the console to the surgical navigation system. Based on these data, the surgical navigation system processor generates data indicating the position of the component at the surgical site. 
         [0008]    The handpiece and the components must be sterile for use in a surgery. The handpiece and any reusable components are subject to cleaning and sterilized before use and any subsequent reuse. Generally, the most popular process utilized for sterilization is steam autoclaving. The handpiece and the components must also be protected from contamination and impaction. Thus, the electronic components contained within the orthopedic instrumentation, such as the handpiece and the components must be protected from the steam used for autoclaving, cleaning solutions and impaction. 
       SUMMARY AND INVENTION 
       [0009]    The present invention provides a surgical navigation system having components such as a reamer, a burr, a broach, a handle, or a tracker that contain electronic circuits including radio frequency identifiers (RFID). These electronic circuits need to be protected from contamination, impaction and effects of sterilization. These circuits may be housed in packages that in turn are incorporated in the components (orthopedic instruments). The protection of the electronic circuits is achieved by encapsulating them. The present invention may also be applied to rotating couplings. 
         [0010]    Encapsulation of the electronic circuits and the packages thereof may be done using an epoxy. The assembly of RFID and electronics is placed/located into a mold cavity and uncured epoxy is injected around the assembly. The assembly of RFID, chip, antenna and electronics may also be referred to as the transponder. The epoxy is then cured. The molded transponder is placed in a cavity in the orthopedic instrument. Additional epoxy is then injected into the gap between the molded transponder and the instrument cavity and cured. The second epoxy application forms a seal between the encased electronics and instrument. Alternatively, the transponder is positioned directly in the appropriately sized cavity in the orthopedic instrument and uncured epoxy is injected around the transponder and then cured. 
         [0011]    Yet another technique is to use polymeric-epoxy combination. This technique utilizes a polymeric housing and epoxy in combination to provide sufficient protection from contamination, impaction and sterilization. In this technique, a polymeric cap is formed via either a machining or injection molding process. A transponder is then assembled into the cap and fixed in place through the use of an adhesive/epoxy. The cap is then filled with an epoxy and cured to fully encase the transponder. This assembly is then attached to a cavity in the orthopedic instrument utilizing additional epoxy. 
         [0012]    Additionally, to ensure a firm attachment between the transponder and the cavity in the orthopedic instrument, mechanical attachment between them may be provided via suitable methods, for example peening. 
         [0013]    Yet another technique is to use metallic-epoxy combination. In this technique, a metallic “cap” is used in much the same way as the polymeric cap described above. 
         [0014]    Yet another technique is to use all polymeric encapsulation. In all polymeric technique, the base and the cap of an electronic package are made from Ultem or Radel via either machining or molding. The transponder is inserted into the cap, and the cap welded to the base to form a robust seal between the two components. This assembly is then inserted into the cavity in the orthopedic instrument and attached to the orthopedic instrument such as a reamer with a metal ring via laser welding. 
         [0015]    Yet another technique is to use ceramic-metallic combination. In this case, the ceramic material is typically glass or alumina material and the metallic components are typically stainless steel. A thin ceramic disc is bonded to the cap that is formed through conventional machining. The transponder is assembled and bonded to the ceramic disc and cap assembly, this component is then preferably resistance welded to the “base” to complete the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The above and further objects, features and benefits of this invention are discussed in the detailed description below taken in conjunction with the accompanying drawings in which: 
           [0017]      FIG. 1  illustratively depicts a surgical navigation system that may be used in accordance with an aspect of the present invention; 
           [0018]      FIG. 2  is an assembly drawing that illustratively depicts packaging for components used in navigation system of  FIG. 1  in accordance with an aspect of the present invention; 
           [0019]      FIG. 3  shows the assembly of  FIG. 2  mounted in a cavity in a component used in navigation system of  FIG. 1  in accordance with an aspect of the present invention; 
           [0020]      FIG. 3A  shows details of the transponder assembly used in  FIG. 2 . 
           [0021]      FIG. 4  shows a base used in the assembly of  FIG. 2  in accordance with an aspect of the present invention; 
           [0022]      FIG. 5  shows a cap used in the assembly of  FIG. 2  in accordance with an aspect of the present invention; 
           [0023]      FIG. 6  shows a ring used to lock the package of  FIG. 2  in a component used in the surgical navigation system of  FIG. 1  in accordance with an aspect of the present invention; 
           [0024]      FIG. 7  is an assembly drawing that illustratively depicts packaging for components used in navigation system of  FIG. 1  in accordance with an aspect of the present invention; 
           [0025]      FIG. 8  is shows the assembly of  FIG. 7  mounted in a cavity in a component used in navigation system of  FIG. 1  in accordance with an aspect of the present invention; 
           [0026]      FIG. 9  shows a base used in the assembly of  FIG. 7  in accordance with an aspect of the present invention; 
           [0027]      FIG. 10  shows an assembly of the base of  FIG. 9  with bushings and pins in accordance with an aspect of the present invention; 
           [0028]      FIG. 11  is a cap used in the assembly of  FIG. 7  in accordance with an aspect of the present invention; 
           [0029]      FIG. 12  shows a ceramic disc for attachment to the cap of  FIG. 11  in accordance with an aspect of the present invention; 
           [0030]      FIG. 13  is a schematic diagram illustrating the method using the polymeric-epoxy combination in accordance with an aspect of the present invention; 
           [0031]      FIG. 14  is a schematic diagram illustrating peening in accordance with an aspect of the present invention; and 
           [0032]      FIG. 15  is a schematic diagram illustrating use of a metallic attachment ring in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]      FIG. 1  depicts a surgical navigation system  20  in accordance with an aspect of the present invention that obtains data about surgical components  22  and  24  without wire connections to the components. In  FIG. 1 , surgical component  22  is a reamer, but may comprise a broach or burr as is discussed in further detail below. Surgical component  24  is a handle assembly. The proximal end of the handle assembly  24  is attached to a battery operated driver  26  that actuates the reamer  22 . (“Proximal”, it is understood, means away from the surgical site. “Distal” means towards the surgical site.) Not shown is the battery attached to the base of the handgrip of the driver  26  that supplies the energization current for the driver. It should also be understood that the “surgical component” may be any other instrument used to cut, form or shape tissue, a trial implant or an actual implant. Sometimes, the surgical component is alternatively referred to as a “surgical implement.” 
         [0034]    System  20  of this invention includes a tracker  28  attached to handle assembly  24 . Tracker  28  broadcasts signals from one or more emitters. These signals may comprise signals having wavelengths in the electromagnetic spectrum, but are not so limited. Some trackers, for example, emit infra-red light or visible light. Other trackers emit radio frequency (RF) or electromagnetic energy. Still other trackers emit sonic energy. A localizer  30 , also part of system  20 , monitors the position of the tracker  28 . Specifically, the localizer  30  contains one or more receivers capable of receiving the energy emitted by the tracker  28 . The receivers may determine the direction from which the energy is transmitted or the strength of the received energy. 
         [0035]    The localizer receivers send signals representative of the measurements made thereby to a processor  32 , also part of system  20 . Based on the determination of the different locations from which the individual tracker transmitters emit signals or the strength of the received signal or energy, the localizer  30  determines where, in three-dimensional space, the tracker  28  is positioned and the orientation of the tracker. The data representative of the location and orientation of the tracker  28 , or the signals used to determine this information, are forwarded by the localizer  30  to a processor  32  also part of the system  20 . Processor  32 , based on the signals from the localizer  30 , then generates signals representative of the position and orientation of the tracker  28 . A more detailed explanation of how a surgical navigation system operates is contained in U.S. patent application Ser. No. 10/677,874, filed Oct. 2, 2003, U.S. Patent Publication No. US 2004/0073279 A1, now U.S. Pat. No. ______ and incorporated herein by reference. 
         [0036]    As will be discussed in detail below, internal to the reamer  22  and handle assembly  24  are separate data storage devices. Each of these devices stores data that identifies the associated surgical component. These data include data that identify the physical characteristics of the component. When the reamer-handle-tracker sub-assembly is assembled, the tracker  28  reads the data in the storage devices. The tracker  28  transmits signals containing these data. A receiver  34 , typically positioned in the localizer  30 , reads data. The data is transmitted by the receiver  34  to the system processor  32 . 
         [0037]    Prior to the commencement of the procedure in which system  20  is employed, the processor  32  is loaded with data that identifies the location of individual body tissues and organs at the surgical site. During the procedure, the processor  32  is provided with data indicating the location of the surgical site. Based on this data, the data indicating the position and orientation of the tracker  28  and the data identifying the physical characteristics of the surgical components  22  and  24 , processor  32  generates information indicating the position of the surgical components relative to the surgical site. More particularly, the processor generates information indicating the position of the surgical components relative to the body tissue at the surgical site. Typically, this information is presented visually on a display  36 . The surgeon is thus able to view the position of the surgical components that otherwise cannot readily be seen. 
         [0038]    As discussed previously, the orthopedic instrumentation such as the reamer  22 , handle  24  and tracker  28  contain electronic circuits. These circuits may be housed in packages that in turn are incorporated in various types of orthopedic instrumentation. An example of an embodiment of such package is shown in  FIGS. 2-3 . 
         [0039]      FIG. 2  shows a package  50  that encloses a transponder that includes an electronic circuit including a RFID.  FIG. 3  shows the package  50  placed in a cavity in an orthopedic instrument. The electronic circuit and the RFID need to be protected from contamination, impaction and sterilization. The protection of the electronic circuit and the RFID is achieved by encapsulating them using one of the various methods for encapsulation discussed hereafter. 
         [0040]    The package  50  may form a part of the orthopedic instrumentation, for example, the reamer  22 , handle  24  or tracker  28 . The package  50  includes a base  56 , a cap  78  and a transponder  60 .  FIG. 3A  shows details of transponder  60 . Transponder  60  has a core  52 , a flexible circuit  53  attached to the core  52  and a bobbin assembly  54  mounted in the core  52 .  FIG. 4  is a detailed drawing of the base  56 . The base  56  is a cone shaped body  62  having a flat bottom surface  64 . Two holes  66  and  68  are formed in the bottom surface  64 . Holes  66  and  68  are optional and may be included or excluded in a different embodiment. Pins  70  and  72  ( FIG. 2 ) pass from the interior of the body  62  to the exterior via holes  66  and  68 . Pins  70  and  72  may be used to interconnect with other electronics on the orthopedic instrument. A lip  74  is formed at the opposing end from the bottom surface  64 . A slight projection  76  is formed on the top surface of the lip  74 . Projection  76  may aid in attaching a cap  78  ( FIG. 5 ) to the base  56 , for example, via welding or ultrasonic welding. 
         [0041]    Cap  78  has a flat top surface  80  and a cylindrical wall  82  projecting from the top surface  80 . A lip  84  is formed in approximately middle of wall  82 . The bottom surface of lip  84  mates with the top surface of lip  74  when the cap  78  is assembled on the base  56 . The assembly of the cap  78  and base  56  may be achieved by vibrating at ultrasonic frequency the cap  78  relative to the base  56  and melting the interface including the projection  76 . Upon cooling of the interface, the cap  78  is welded to the base  56  forming a sealed interface. The cylindrical wall  82  forms a shallow cup  86  with the top surface  80  forming a base of the cup  86 . 
         [0042]    Prior to welding the base  56  to the cap  78 , the transponder  60  is placed in the cup  86 . The inside surface of the wall  82  and the external surface of cylindrical member  88  of the transponder  60  face each other with a small air gap between them. The transponder  60  is attached to the cap  78  by introducing suitable glue in the air gap. Cylindrical member  88  houses, inter alia, the transponder  60 . The transponder  60  may be encapsulated in its attached position within the cap  78 . Additionally, the entire package  50  may also be encapsulated in a cavity in the orthopedic instrumentation. Alternatively, the package  50  may be held in place by attaching a ring  77  ( FIG. 6 ), for example, via welding to the mouth of the opening in the orthopedic instrument with the package  50  in place in the opening. 
         [0043]    Another embodiment of a package that may house the transponder and may in turn be incorporated in various types of orthopedic instrumentation is shown in  FIGS. 7-8 .  FIG. 7  shows a package  90  that encloses an electronic circuit including a RFID.  FIG. 8  shows the package  90  placed in a cavity in an orthopedic instrument. The transponder  100  need to be protected from contamination, impaction and sterilization. The protection of the transponder  100  is achieved by encapsulating them using one of the various methods for encapsulation discussed hereafter. 
         [0044]    The package  90  may form a part of the orthopedic instrumentation, for example, the reamer  22 , handle  24  or tracker  28 . The package  90  includes a base  96 , a metal cap  98 , a non metallic lid  99  and the transponder  100 .  FIG. 9  is a detailed drawing of the base  96 . The base  96  is a cone shaped body  102  having a flat bottom surface  104 . Two holes  106  and  108  are formed in the bottom surface  104 . Feed throughs  105  and  107  having holes in their center are inserted in holes  106  and  108  respectively. Pins  110  and  112  ( FIG. 10 ) pass from the interior of the body  102  to the exterior via holes in the feed throughs  105  and  107  mounted in holes  106  and  108 . Pins  110  and  112  may be used to interconnect with other electronics on the orthopedic instrument. A lip  114  is formed at the opposing end from the bottom surface  104 . A slight projection  116  is formed on the top surface of the lip  114 .  FIG. 10  shows an assembly of the base  96 , feed throughs  105  and  107  and pins  110  and  112 . Projection  116  may aid in attaching a cap  98  ( FIG. 11 ) to the base  96 , for example, via welding or ultrasonic welding. 
         [0045]    Cap  98  is generally cylindrical and has a larger cylindrical surface  120  and a smaller cylindrical surface  122 . A lip surface  124  is formed at the juncture of cylindrical surface  120  and cylindrical surface  122 . The lip surface  124  is perpendicular to the central axis of cylindrical surface  120  and cylindrical surface  122 . The lip surface  124  mates with the top surface of lip  114  when the cap  98  is assembled on the base  96 . The assembly of the cap  98  and base  96  may be achieved by vibrating at ultrasonic frequency the cap  98  relative to the base  96  and melting the interface including the projection  116 . Upon cooling of the interface, the cap  98  is welded to the base  96  forming a sealed interface. Alternatively, the cap  98  may be welded on to the base  96 . A sapphire glass lid  99  ( FIG. 12 ) is attached on a ring shaped surface  126  formed near the top end of the cap  98 . The lid  99  and cap  98  form a hermetic seal between them. The attachment may be achieved by applying glue to the mating surfaces or any other appropriate means including welding and ultrasonic welding. The cap  98  and lid  99 , when assembled, form a shallow cup with the lid  99  forming a base of the cup. 
         [0046]    Prior to welding the base  96  to the cap  98 , the transponder  100  is placed in the cup formed by the cap  98  and the lid  99 . The inside surface of the cylindrical portion  122  and the external surface of cylindrical member  130  of the transponder  100  face each other with a small air gap between them. The transponder  100  is attached to cap  98  by introducing suitable glue in the air gap. Cylindrical member  130  houses, inter alia, the transponder  100 . The transponder  100  is encapsulated in its attached position within the cap  98 . 
         [0047]    The packages  50  and  90  of the above described exemplary embodiments may be encapsulated in a cavity in the orthopedic instrumentation using any one of the techniques discussed hereafter, or a combination of these techniques. 
         [0048]    Encapsulation of Packages  50  and  90  and similar packages may be done using an Epoxy. Commercially available, autoclave resistant, epoxies such Masterbond EP42 HT-2, Zymet 505/515 and EpoTek 353ND may be used. Uncured epoxy may be formed to any shape due to its ability to flow and conform to complex geometries. The encapsulation of packages  50  and  90  using an Epoxy may be accomplished by one of the two encapsulation methods described below. 
         [0049]    Method 1 (the molded method): When using the molded method, the transponder is placed/located into a mold cavity and uncured epoxy is injected around the assembly. The epoxy is then cured to maximize material properties for resistance to autoclave conditions. The molded assembly is placed in a cavity in the orthopedic instrument. Additional epoxy is then injected into the gap between the molded assembly and the instrument cavity and cured. The second epoxy application forms a seal between the encased electronics and instrument. 
         [0050]    A variation of this method may comprise directly positioning the transponder in an appropriately sized cavity in the orthopedic instrument and uncured epoxy is injected around the transponder and then cured. This cured epoxy then fully encases the transponder were positioned in the instrument cavity. In this method the cup shaped cavity in the instrument serves as the mold for the epoxy. 
         [0051]    Method 2 (the pre-formed method): This method is similar to the molded method above except in this scenario the epoxy is formed/molded into an appropriate shape and cured prior to it contacting transponder. After forming, the formed epoxy is then assembled onto the transponder or into the cavity in the orthopedic instrument to fabricate the necessary encapsulation geometry. Once assembled onto the transponder or into the cavity in the orthopedic instrument, the epoxy is re-cured to complete the encapsulation process. 
         [0052]    Yet another technique is to use polymeric-epoxy combination. This technique utilizes a polymeric housing and epoxy, in combination, to provide sufficient protection from contamination, impaction and sterilization. The combination of materials allows for the polymeric material to provide additional resistance to gross contamination and the epoxy to provide the seal between polymer and metallic instrument. This method minimizes the use of epoxy. 
         [0053]      FIG. 13  is a schematic diagram illustrating the method using the polymeric-epoxy combination. In this technique, a polymeric “cap  140 ” (transponder  60  or  100  described above may serve the function of the cap  140 ) is formed via either a machining or injection molding process. A transponder assembly (assembly  142  hereafter) is then assembled into the cap  140  and fixed in place through the use of an adhesive/epoxy. The cap  140  is then filled with an epoxy and cured to fully encase the assembly  142 . This assembly  142  is then located in an appropriately sized cavity in the orthopedic instrument. Additional epoxy  144  is then injected into the gap between the assembly  142  and the cavity in the orthopedic instrument and cured. Epoxy  144  forms a seal between the assembly  142  and the orthopedic instrument. 
         [0054]    Additionally, to ensure a firm attachment between the assembly  142  and the cavity in the orthopedic instrument, there can be mechanical attachment between them. This mechanical attachment can be achieved through a variety of methods. One potential method involves “peening” the metallic material  146  that is adjacent to the epoxy  144  so that it comes into direct contact with the epoxy  144 . See  FIG. 14 . The metal is deformed during this process, to form a tab  148  that mechanically fixes the assembly  142  in place. Another potential mechanical attachment method is to utilize a metallic ring  150  ( FIG. 15 ) that contacts the polymeric cap  140  and the metallic material  146 . Metallic ring  150  is typically made from stainless steel. Once assembled onto the orthopedic instrument, metallic ring  150  can be welded to mechanically fix the assembly  142  in place. 
         [0055]    Yet another technique is to use metallic-epoxy combination. In this technique, a metallic “cap” is used in much the same way as the polymeric cap  140  described above. In this case, the “cap” is fabricated via machining and the assembly  142  is assembled into the “cap” in much the same manner as described above. Once this is accomplished, the “cap” can be attached to the orthopedic instrument either utilizing epoxy or metal ring as described above. 
         [0056]    Yet another technique is to use all polymeric encapsulation. There are many polymeric materials that have been proven to be resistant to repeated autoclave cycles. Ultem® and Radel® are 2 examples of sterilization-resistant polymeric materials. These materials can be shaped into complex geometries via machining or molding processes making their utility in this application very appealing. The two polymeric components can be joined via several methods but the two most applicable methods are ultrasonic welding and laser welding. 
         [0057]    In all polymeric technique, the base  56  and the cap  78  of  FIG. 2  are made from Ultem or Radel via machining. The assembly  142  is inserted into the cap  78 . The cap  78  is held in the base  56  via interference fit. Next the cap  59  or the base  56  is subjected to ultrasonic energy causing it to vibrate, while the other component is held motionless. The result is localized melting of the polymeric material at the interference point which, upon cooling, amalgamates to form a robust seal between the two components. This assembly is then inserted into the cavity in the orthopedic instrument and attached to the orthopedic instrument such as reamer  22 , by welding a metal ring  150 , as described previously, via laser welding. 
         [0058]    Yet another technique is to use ceramic-metallic combination. In this case the ceramic material is typically glass or alumina material and the metallic components are typically stainless steel. The two materials can be joined in a variety of methods but the two most applicable methods, resistance welding and brazing. The Ceramic-Metallic encapsulation method is constructed from three separate components that are joined to form highly robust (“hermetic”) electronics housing. 
         [0059]    The first of these components is a ceramic disc such as the non-metallic disc  99  of  FIG. 12  that provides a pathway for the RF communication. In addition to being non-metallic, this item must be very thin in cross-section (less than 0.040″—to allow for RF communication) and also able to withstand impaction and repeated sterilization cycles. In this application, a glass (e.g., single crystal sapphire) or ceramic (e.g., Alumina) material can be utilized since they are available in thin cross-sections, can withstand the rigors of sterilization and most importantly, can be readily bonded or brazed onto stainless steel to form a highly robust seal between the two materials. 
         [0060]    The second component in this assembly is a stainless steel “cap” such as cap  98  of  FIG. 11  that serves as the intermediate part of the three piece housing. This component serves two purposes; first, it is used to attach the ceramic disc and second, it provides the connection point for the “base” component. Essentially this component is a flanged ring that is formed thorough conventional machining and includes features to accomplish both purposes mentioned above. 
         [0061]    The third component is the “base” such as the base  96  of  FIG. 9 . This component can be made from a variety of materials but typically is made from a nickel-cobalt alloy (e.g., Kovar) due to its thermal expansion characteristics which allow it to bond efficiently with glass/ceramic materials used for feed-through  105  and  107 . The geometry for this component can be formed using conventional machining. After the electronics assembly  142  is assembled and bonded to the ceramic disc (or glass disc) and “cap” assembly, this component is then resistance welded to the “base” to complete the housing. 
         [0062]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. For example, the invention described herein may also be applied to rotating couplings. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.