Patent Publication Number: US-RE46699-E

Title: Low impedance oxide resistant grounded capacitor for an AIMD

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional application Ser. No. 61/841,419, filed on Jun. 30, 2013. The present application also claims priority to and is a continuation-in-part application of U.S. application Ser. No. 13/873,832, filed on Apr. 30, 2013, the contents of which are incorporated herein by reference. The present application also claims priority to and is a continuation-in-part application of U.S. patent application Ser. No. 13/743,276, filed on Jan. 16, 2013, the contents of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to feedthrough capacitors. More particularly, the present invention relates to a feedthrough capacitor located on the device side with a low impedance and oxide-resistance electrical connection. 
     BACKGROUND OF THE INVENTION 
     Feedthrough capacitors and MLCC chip capacitors are well known in the prior art for active implantable medical devices (AIMDs). One is directed to U.S. Pat. Nos. 5,333,095; 5,905,627; 6,275,369; 6,529,103; and 6,765,780 all of which are incorporated herein by reference. The hermetic seal feedthrough terminal assemblies generally consist of a titanium ferrule into which an alumina hermetic seal is gold brazed. One or more lead wires penetrate through the alumina in non-conductive relationship with the ferrule. Gold brazes are also used to form a hermetic terminal between the one or more leadwires and the alumina ceramic. 
     First, some general information concerning good engineering design practice for electromagnetic interference (EMI) filters. It is very important to intercept the EMI at the point of lead conductor ingress and egress to the AIMD. It would be an inferior practice to put filtering elements down in the circuit board as this would draw EMI energy inside of the AIMD housing where it could re-radiate or cross-couple to sensitive AIMD circuits. A superior approach is to mount one or more feedthrough or MLCC-type capacitors right at the point of leadwire entrance so that it can be coupled to high frequency EMI signals from the lead conductors directly to the AIMD housing, which acts as an energy dissipating surface. 
     There are some interesting design challenges however. The titanium ferrule, which is laser welded into the overall AIMD housing, is at ground potential. Titanium tends to form oxides which act as either insulators or semi-conductors. Accordingly, grounding the feedthrough capacitor electrode plates directly to the titanium ferrule is contra-indicated. Reference is made to U.S. Pat. No. 6,465,779 (which is incorporated with this reference) which describes gold bond pad areas where the feedthrough capacitor external metallization can be directly connected to gold. The gold to which the feedthrough capacitor is directly connected is the braze material used to form the hermetic seal between the alumina and the titanium ferrule. As noted above, the hermetic seal is formed via a brazing process. By attaching the capacitor&#39;s ground plates to the gold, one can be assured that there will be no oxide that will increase the capacitor&#39;s equivalent series resistance (ESR) which can seriously degrade the capacitor&#39;s performance at high frequency. An undesirable aspect of using the gold braze for attachment is that gold is very expensive. Accordingly, there is a need for methods that provide a reliable low impedance ground path which are oxide resistant for grounding of AIMD filter capacitors. The present invention fulfills these needs and provides other related advantages. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment of a hermetically sealed filtered feedthrough assembly for an implantable medical device includes an insulator hermetically sealed to a conductive ferrule or housing. A conductor is hermetically sealed and disposed through the insulator in non-conductive relation to the conductive ferrule or housing between a body fluid side and a device side. A feedthrough capacitor is disposed on the device side. The feedthrough capacitor includes a first and a second end metallization, wherein the first end metallization is connected to at least one active electrode plate and wherein the second end metallization is connected to at least one ground electrode plate. The at least one active electrode plate is interleaved and disposed parallel to the at least one ground electrode plate, wherein the at least one active and at least one ground electrode plates are disposed within a capacitor dielectric. A first low impedance electrical connection is between the first end metallization and the conductor. A second low impedance electrical connection is between the second end metallization and the ferrule or housing. The second low impedance electrical connection includes an oxide-resistant metal addition attached directly to the ferrule or housing and an electrical connection coupling the second end metallization electrically and physically directly to the oxide-resistant metal addition. 
     In other exemplary embodiments the oxide-resistant metal addition may include a different material as compared to the ferrule or housing. The oxide-resistant metal addition may include a noble metal such as gold, platinum, palladium, silver and combinations thereof. The oxide-resistant metal addition may be laser welded to the ferrule or housing. The oxide-resistant metal addition may include a brazed metal such as gold. Possible braze materials include gold, gold-based metal, platinum, platinum based metal, palladium, palladium based metal, silver and silver based metal. Non-limiting noble metal based braze examples are gold-palladium, gold-boron, and palladium-silver. It is anticipated that proprietary brazes such as but not limited to the Pallabraze product family (palladium-containing) and Orobraze product family (gold-containing) offered by Johnson Matthey may be used. The braze material may be a rod, a ribbon, a powder, a paste, a cream, a wire and a preform such as but not limited to stamped washers. 
     A grounding loop may be defined on the device side having the first low impedance electrical connection and the second low impedance connection from the conductor through the feedthrough capacitor to the ferrule or housing. The total resistance of the grounding loop may be less than 1 milliohm. The total inductance of the grounding loop may be less than 10 nanohenries or less than 1 nanohenry. 
     The conductor may include a leadwire having platinum, palladium, silver or gold. 
     The insulator may be flush with the ferrule or housing on the device side. The insulator may include an alumina substrate comprised of at least 96% alumina and the conductor having a substantially closed pore and substantially pure platinum fill disposed within a via hole and extending between the body fluid side and the device side of the alumina substrate. 
     A hermetic seal may be between the platinum fill and the alumina substrate, wherein the platinum fill forms a tortuous and mutually conformal knitline or interface between the alumina substrate and the platinum fill, wherein the hermetic seal has a leak rate that is no greater than 1×10 −7  std cc He/sec. 
     An inherent shrink rate during a heat treatment of the alumina dielectric substrate in a green state may be greater than that of the platinum fill in the green state. 
     The oxide-resistant metal addition may include a wire, a pad, an L-shaped pad or an L-shaped pad with cutouts or combinations thereof. 
     A ground wire may be disposed through both the insulator and the feedthrough capacitor, where the ground wire is not electrically coupled to the at least one active and one ground electrode plate. 
     The ferrule or housing may include an integrally formed conductive peninsula, where the ground wire is electrically coupled to the peninsula. 
     The feedthrough capacitor may have a resonant frequency above 400 MHz. The feedthrough capacitor may have a capacitance of between 300 picofarads and 10,000 picofarads. 
     Other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate the invention. In such drawings: 
         FIG. 1  illustrates a wire-formed diagram of a generic human body showing various types of active implantable and external medical devices currently in use; 
         FIG. 2  is an isometric cut-away view of a unipolar feedthrough capacitor; 
         FIG. 3  is a cross-sectional view of the unipolar capacitor of  FIG. 2  shown connected to the hermetic terminal of an AIMD; 
         FIG. 4  is a schematic diagram of the unipolar feedthrough capacitor shown in  FIGS. 2 and 3 ; 
         FIG. 5  is an exploded view of the cover sheets and internal electrodes of the unipolar capacitor previously described in  FIGS. 2 and 3 ; 
         FIG. 6  is a diagrammatic exploded view of a typical AIMD; 
         FIG. 7  is an isometric view of the quad polar feedthrough capacitor previously described in the prior art pacemaker of  FIG. 6 ; 
         FIG. 8  is a sectional view taken from section  8 - 8  of  FIG. 7  and illustrates the quad polar feedthrough capacitor interior electrode plates; 
         FIG. 9  is an exploded view of the quad polar feedthrough capacitor of  FIG. 7 ; 
         FIG. 10  is the schematic diagram of the quad polar feedthrough capacitor of  FIG. 7 ; 
         FIG. 11  illustrates a prior art quad polar feedthrough capacitor that is rectangular instead of round; 
         FIG. 12  is an isometric view of the feedthrough assembly before the feedthrough capacitor is placed; 
         FIG. 13  is taken from section  13 - 13  from  FIG. 11  showing the four active electrode plates; 
         FIG. 14  is taken from section  14 - 14  from  FIG. 11  and illustrates the ground electrode plate; 
         FIG. 15  is an assembly view taken from  FIGS. 11-14  showing the quad polar rectangular feedthrough capacitor mounted onto the hermetic seal housing and the ferrule; 
         FIG. 16  is a sectional view taken from section  16 - 16  from  FIG. 15 ; 
         FIG. 17  is the schematic diagram of the quad polar feedthrough capacitors previously illustrated in  FIGS. 14 and 15 ; 
         FIG. 18  is a perspective view showing gold bond pads used to eliminate the problem of attachment to oxides of titanium between the feedthrough capacitor outside diameter and its ground electrode plate sets; 
         FIG. 19  shows that the electrical connections between the capacitor&#39;s ground metallization is now directly connected to this oxide resistant noble pad; 
         FIG. 20  is a sectional view of the structure of  FIG. 19  taken through lines  20 - 20 ; 
         FIG. 21  is very similar to  FIG. 19 , except that the quad polar capacitor is round which is consistent with the feedthrough capacitor previously illustrated in the cardiac pacemaker of  FIG. 6 ; 
         FIG. 22  is generally taken from section  22 - 22  from  FIG. 21  and illustrates the capacitor&#39;s internal structure including its ground and active electrode plates; 
         FIG. 23  illustrates the schematic diagram of the improved rectangular quad polar feedthrough capacitor of  FIG. 19  and the round quad polar capacitor of  FIG. 21 ; 
         FIG. 24  illustrates attenuation versus frequency comparing the ideal feedthrough capacitor to one that has undesirable ground electrode plate connection to an oxidized surface; 
         FIG. 25  is a perspective view of an exemplary feedthrough capacitor embodying the present invention; 
         FIG. 26  is a sectional view taken along line  26 - 26  of the structure of  FIG. 25 ; 
         FIG. 27  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 27A  is an exploded view of the structure of  FIG. 27  showing the peninsula portion of the ferrule; 
         FIG. 28  is a sectional view taken along line  28 - 28  of the structure of  FIG. 27 ; 
         FIG. 28A  is an enlarged view of a novel embodiment of a similar structure of  FIG. 28  taken along lines  28 A- 28 A; 
         FIG. 28B  is another embodiment of the structure of  FIG. 28A  now showing a rectangular shaped structure attached to the ferrule; 
         FIG. 28C  is a view similar to  27 A except now showing a recess on the ferrule for the wire to fit within; 
         FIG. 29  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 30  is a sectional view taken along line  30 - 30  of the structure of  FIG. 29 ; 
         FIG. 31  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 32  is a sectional view taken along line  32 - 32  of the structure of  FIG. 31 ; 
         FIG. 33  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 34  is a sectional view taken along line  34 - 34  of the structure of  FIG. 33 ; 
         FIG. 35  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 36  is an exploded view of the structure of  FIG. 35  showing the peninsula portion of the ferrule; 
         FIG. 37  is a sectional view taken along line  37 - 37  of the structure of  FIG. 35 ; 
         FIG. 38  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 39  is a sectional view taken along line  39 - 39  of the structure of  FIG. 38  now showing a ground electrode plate; 
         FIG. 40  is an sectional view taken along line  40 - 40  of the structure of  FIG. 38  now showing an active electrode plate; 
         FIG. 41  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 42  is an sectional view taken along line  42 - 42  of the structure of  FIG. 41  now showing a ground electrode plate; 
         FIG. 43  is an sectional view taken along line  43 - 43  of the structure of  FIG. 41  now showing an active electrode plate; 
         FIG. 44  is a sectional view taken along lines  44 - 44  of the structures of both  FIGS. 38 and 41 ; 
         FIGS. 45A, 45B and 45C  are perspective views of various embodiments of the novel ground attachments shown in  FIGS. 38, 41 and 44 ; 
         FIG. 46  is a perspective view of another exemplary feedthrough capacitor embodying the present invention; 
         FIG. 47  is an exploded view of the structure of  FIG. 46  showing the novel ground attachment below the capacitor; 
         FIG. 48  is a perspective view of another exemplary feedthrough embodying the present invention now showing novel rectangular ground attachments in the ferrule; 
         FIG. 49  is a perspective view of another exemplary feedthrough embodying the present invention now showing novel circular ground attachments in the ferrule; 
         FIG. 50  is similar to either  FIG. 48 or 49  now showing the capacitor grounded to the ferrule; 
         FIG. 51  is a sectional view taken along line  51 - 51  of the structure of  FIG. 50  now showing a ground electrode plate; 
         FIG. 52  is a sectional view taken along line  52 - 52  of the structure of  FIG. 50  now showing an active electrode plate; 
         FIG. 53  is a perspective view of another exemplary feedthrough embodying the present invention now showing novel ground attachments around the continuous perimeter of the ferrule; 
         FIG. 54  is an exploded view of another exemplary feedthrough capacitor embodying the present invention now showing novel ground attachment plate; and 
         FIG. 55  is the perspective assembled view of the structure of  FIG. 54  showing the capacitor metallization grounded to the novel plate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a wire-formed diagram of a generic human body showing various types of active implantable and external medical devices  100  that are currently in use.  100 A is a family of external and implantable hearing devices which can include the group of hearing aids, cochlear implants, piezoelectric sound bridge transducers and the like.  100 B includes an entire variety of neurostimulators and brain stimulators. Neurostimulators are used to stimulate the Vagus nerve, for example, to treat epilepsy, obesity and depression. Brain stimulators are similar to a pacemaker-like device and include electrodes implanted deep into the brain for example but not limited to sensing the onset of the seizure and also providing electrical stimulation to brain tissue to prevent the seizure from actually happening, or for treating memory loss, Alzheimer&#39;s and the like. The lead wires that come from a deep brain stimulator are often placed using real time imaging. Most commonly such lead wires are placed during real time MRI.  100 C shows a cardiac pacemaker which is well-known in the art.  100 D includes the family of left ventricular assist devices (LVAD&#39;s), and artificial hearts, including the recently introduced artificial heart known as the ABIOCOR.  100 E includes an entire family of drug pumps which can be used for dispensing of insulin, chemotherapy drugs, pain medications and the like. Insulin pumps are evolving from passive devices to ones that have sensors and closed loop systems. That is, real time monitoring of blood sugar levels will occur. These devices tend to be more sensitive to EMI than passive pumps that have no sense circuitry or externally implanted lead wires.  100 F includes a variety of external or implantable bone growth stimulators for rapid healing of fractures.  100 G includes urinary incontinence devices.  100 H includes the family of pain relief spinal cord stimulators and anti-tremor stimulators.  100 H also includes an entire family of other types of neurostimulators used to block pain.  100 I includes a family of implantable cardioverter defibrillators (ICD) devices and also includes the family of congestive heart failure devices (CHF). This is also known in the art as cardio resynchronization therapy devices, otherwise known as CRT devices.  100 J illustrates an externally worn pack. This pack could be an external insulin pump, an external drug pump, an external neurostimulator, a Holter monitor with skin electrodes or even a ventricular assist device power pack. 
       FIG. 2  is an isometric cut-away view of a unipolar feedthrough capacitor  132 . It has an outside diameter metallization  142  and an inside diameter metallization  144 . Active electrode plates  148  and ground electrode plates  146  are interleaved in the dielectric body. The active electrode plate set  148  is connected to the inside diameter metallization  144 . The ground electrode plate set  146  is connected to the outside diameter metallization  142 . Metallization surfaces  142  and  144  can be glass fritted platinum silver or various types of plating. The metallization surfaces  142  and  144  are very important as it is easy to make electrical connection to these surfaces to other circuit elements. 
       FIG. 3  is a cross-sectional view of the unipolar capacitor of  FIG. 2  shown connected to the hermetic terminal of an active implantable medical device, such as a cardiac pacemaker. Shown is a hermetic seal formed from an insulator  160 , such as an alumina ceramic, glass or the like. A gold braze  162  forms a hermetic seal between the insulator  160  and leadwire  114 ,  111 . The leadwire labeled  114  on the body fluid side is generally directed to an implantable lead that has an electrode contactable to biological cells (not shown). And there is a second gold braze  150  which hermetically connects the outside diameter of the insulator material  160  to a ferrule  112 . In the prior art, the ferrule is generally of titanium. The AIMD housing  116  is also generally of titanium. A laser weld  154  is formed which connects the ferrule  112  to the AIMD housing  116  electrically and mechanically. The laser weld  154  also forms a hermetic seal. The unipolar feedthrough capacitor  132  of  FIG. 2  is shown mounted directly to the hermetic seal insulator. An electrical connection  156  connects the capacitor inside diameter metallization  144  to leadwire  111 . There is also an electrical connection material  152  connected directly to the ferrule  112  as shown. This electrical connection  152  is substantially inferior to the present invention and thus undesirable. As shown, an electrical connection is being made directly to the titanium surface  112 . It is well known that titanium, particularly when brought to elevated temperatures, forms oxides. Oxides of titanium, for example, titanium dioxide is so stable, it&#39;s used as a paint pigment. It is also highly resistive and also has semi-conductive properties. For this reason, this inserts an undesirable series resistance R OXIDE  between the feedthrough capacitor and the ferrule  112  and/or AIMD housing  116 . 
       FIG. 4  is a schematic diagram of unipolar feedthrough capacitor shown in  FIGS. 2 and 3 . Shown is an ideal feedthrough capacitor C. In general, feedthrough capacitors are three-terminal devices in that there is an input side  114  (terminal one), an output side  111  (terminal two) and a ground  116  (terminal three). It is well known that an implanted lead can undesirably act as an antenna and couple to high frequency electromagnetic interference (EMI) energy. This EMI energy may be undesirably coupled along the implanted leadwire conductors to lead  111 , which is directed to sensitive AIMD electronics. It is well known that EMI can disrupt the proper operation of AIMD electronic circuitry. For example, there have been a number of case reports of complete inhibition of cardiac pacemakers when EMI was falsely detected as a normal cardiac rhythm and the pacemaker inhibited. This is immediately life-threatening as its leaves a pacemaker dependent patient without a heart beat during the entire time of the EMI exposure. The feature in the feedthrough capacitor as illustrated in  FIGS. 2 and 3  is to divert incoming EMI energy in the implanted lead and dissipate it to the electromagnetically shielded housing  116  of the AIMD which said EMI energy may be dissipated as a harmless amount of thermal or RF energy. In other words, it is the job of feedthrough capacitors to protect the sensitive AIMD electronics while at the same time freely allowing pacing or therapeutic pulses to pass and also to allow the AIMD to sense biological signals that are generally in the frequency range from zero to 2000 Hz without interruption. The capacitor is also known as a frequency variable impedance element. The capacitive reactance X c  in ohms:
 
X c =1/[2πfc]
 
This inverse relationship with frequency means that, at very low frequencies, the capacitor looks like an open circuit (as if it were not there at all), and at very high frequencies, the capacitor acts as a short circuit where it diverts undesirable RF energy such as emissions from cellular telephones, microwave ovens or the like.
 
     Referring once again to  FIG. 4 , one can see R OXIDE . This resistive element is highly undesirable because it degrades the performance of the feedthrough capacitor all across its frequency range. There is also a great deal of variability in this oxide. During the gold brazing operation or during the formation of the hermetic seal, oxide poisoning may reach any corner or part of the brazing oven. The inventors have experienced some of the parts to be relatively oxide free where others in the lot may have a very thick or heavy oxide build-up. 
       FIG. 5  is an exploded view of the cover sheets  147  and internal electrodes of the unipolar capacitor  132  previously described in  FIGS. 2 and 3 . One can see that there are active electrode plates  148  screened onto dielectric layers  149  and interleaved with ground electrode plates  146 . A number of blank cover sheets  147  are placed on top and bottom for insulative and mechanical strength purposes. 
       FIG. 6  is a diagrammatic explosion of a typical AIMD, such as a cardiac pacemaker  100 C. It has an overall electromagnetic shielded titanium housing  116  along with a polymer header block (connector block)  101 . Shown, are two implantable leads  107  and  107 ′, which in this case are directed to chambers of the heart  124 . There are additional electrodes located at point  109  in the right ventricle and distal electrodes  109 ′ located in the right atrium. In the art, this is known as a simple dual chamber bipolar pacemaker. As shown, EMI can be undesirably coupled to leads  107  and  107 ′ where it can be conductive to the leadwires  114  of the hermetic seal assembly  120 . The feedthrough capacitor element  132  diverts the EMI conducted on leads  114  into the conductive AIMD housing  116  where it is dissipated as eddy currents or RF energy (EMI′) as simply coupled to surrounding body tissues. In any event, the EMI is prevented from reaching the delicate AIMD circuit boards  122 . 
       FIG. 7  is an isometric view of the quad polar feedthrough capacitor  132  previously described in the prior art pacemaker of  FIG. 6 . The quad polar feedthrough capacitor has an outside diameter metallization  142  and four feedthrough holes all of which have inside diameter metallization  144 . 
       FIG. 8  is a sectional view taken from section  8 - 8  of  FIG. 7  and illustrates the quad polar feedthrough capacitor interior electrode plates. There is a ground electrode plate set  146  which is coupled to the outside diameter metallization  142 . There are four different sets of active electrode plates  148  which are each coupled to their own individual feedthrough hole  134 . 
       FIG. 9  is an exploded view of the quad polar feedthrough capacitor of  FIG. 7 . Shown, are the four active electrode plate areas  148  and the ground electrode plates  146 . As previously described, these active and ground electrode plates are in interleaved relationship. There are also a number of blank ceramic cover sheets  147  added on top and bottom for mechanical strength and electrical insulation. Those skilled in the capacitor art will understand that a higher voltage capacitor could be built by interleaving additional blank electrodes between the active and ground electrode plates thereby building up the dielectric thickness. Typically, the dielectric material could be of barium titanate ceramic and could vary in dielectric constant k anywhere from 50 all the way up to several thousand. 
       FIG. 10  is the schematic diagram of the quad polar feedthrough capacitor of  FIG. 7 . Again, as previously described for the unipolar capacitor of  FIG. 2  and  FIG. 4 , there is an undesirable resistance R OXIDE  as shown. Ideally, feedthrough capacitors are three-terminal devices that have no series inductance or series resistance. This is why they make such effective broadband electromagnetic interference filters. In general, a feedthrough capacitor can provide attenuation over a very broad frequency range extending even to 18 to 20 GHz. However, this oxide is highly undesirable as it can seriously degrade filter performance. In general, filter performance is described by the terms insertion loss or by attenuation. Both of these are generally measured in a balanced 50 ohm system with the measurement units in decibels. 
       FIG. 11  illustrates a prior art quad polar feedthrough capacitor that, in this case, is rectangular instead of round. It still has an outside metallization  142 , but in this embodiment, instead of being all around a perimeter or outside diameter, it is shown only over a portion of the rectangular edge of the capacitor. This can actually be done in many ways. One way would be to extend the metallization  142  around the entire perimeter of the capacitor. Feedthrough metallization  144  is provided for each of the four feedthrough holes.  FIG. 11  in combination with  FIG. 12  illustrates an exploded assembly view wherein the capacitor of  FIG. 11  is designed to be mounted atop a prior art quad polar hermetic terminal of  FIG. 12 . The hermetic terminal of  FIG. 12  has four leadwires  111 ,  114 , a hermetic insulator  124  and a ferrule, generally of titanium  112 . There is a gold braze  150  which forms a hermetic joint between the ferrule  112  and the generally alumina ceramic insulator  124 . There are four more gold brazes  162  which join leadwire  111  to the inside diameter holes of the hermetic insulator  124 . 
       FIG. 13  is taken from section  13 - 13  from  FIG. 11 . Shown are the four active electrode plates  148  of the feedthrough capacitor. 
       FIG. 14  is taken from section  14 - 14  from  FIG. 11  and illustrates the ground electrode plate  146  of the feedthrough capacitor. 
       FIG. 15  is an assembly view taken from  FIGS. 11 and 12  showing the quad polar rectangular feedthrough capacitor mounted onto the hermetic seal housing and the ferrule  112 . An electrical connection  152  is generally made with a thermal-setting conductive adhesive between the capacitor metallization  142  directly to the ferrule  112 . 
       FIG. 16  is a sectional view taken from section  16 - 16  from  FIG. 15 . This sectional view goes through one of the leadwires  111  and shows the interior ground electrode plate set  146  and the active electrode plate set  148 . The ground electrode plates  146  make electrical and mechanical contact to the capacitor ground metallization  142 . There is an electrical connection  152  shown directly to the top surface of the titanium ferrule  112 . There is a cross-hatched area  164  which shows the formation of a very undesirable layer of titanium oxides. For simplicity, this layer is shown only on the top surface, but in reality, it would coat all of the surfaces of the titanium cross-section. As previously mentioned, the formation of this oxide can happen during initial gold brazing, during subsequent storage and handling of the overall filter feedthrough subassembly, or during laser welding of the ferrule  112  into the AIMD housing  116 . One particular problem is that the thermal-setting conductive adhesive  152  always contains a certain amount of available oxygen. When a laser weld is formed to the AIMD housing, which is positioned to be placed in slot  163 , this significantly raises the temperature of thermal-setting conductive adhesive  152 . This is why a thermal-setting conductive polyimide is the connection material of choice, as a conductive polyimide is stable at temperatures well above 300 degrees C. This is in comparison to most epoxies which are only rated to about 230 degrees C. When this assembly is raised through laser welding to high temperature, oxygen can be released from a thermal-setting conductive material  152  and then be formed as a titanium dioxide or trioxide  164  on the ferrule  112  of the hermetic seal. 
       FIG. 17  is the schematic diagram of the quad polar feedthrough capacitors previously illustrated in  FIGS. 11, 15 and 16 . Shown, is the undesirable R OXIDE  which is shown in series between the ideal feedthrough capacitor and ground, which is the same electrical potential as the AIMD housing  116 . As will be shown, the presence of this resistive oxide seriously degrades the filter performance. 
       FIG. 18  is taken from FIG. 20 of U.S. Pat. No. 6,765,779 which describes gold bond pads to eliminate the problem of attachment to oxides of titanium between the feedthrough capacitor outside diameter and its ground electrode plate sets. Referring to  FIG. 18 , one can see that there are novel gold braze pads  165  that have been added. Referring to  FIG. 12 , one can see that these gold braze pads  165  are not present. 
       FIG. 19  shows that the electrical connections  152  between the capacitor&#39;s ground metallization  142  is now directly made to this non-oxidizable noble pad. U.S. Pat. No. 6,765,779 is incorporated herein by reference. As is shown in this &#39;779 patent, a preferred material for the oxide resistant pad  165  is gold. In a particularly preferred embodiment, this gold pad  165  is continuous and is co-formed at the same time the hermetic seal (gold braze) is made to the alumina ceramic insulator  160 . In fact, this is a limitation of U.S. Pat. No. 6,765,779 in that the gold bond pad  165  is always formed as part of the co-braze to the alumina ceramic insulator  160 . 
       FIG. 20  is generally taken from section  20 - 20  from  FIG. 19 . It is very similar to  FIG. 16  except that the gold braze area  165  has been enlarged to include the gold bond pad area  165 . Pure gold has a high melting point (1064° C.) which is above the allotropic transformation temperature of titanium (883° C.). Titanium is soluble in gold, particularly more so at elevated temperature. Elevated temperature maximizes titanium dissolution into gold. As previously noted, titanium is highly reactive to air readily forming surface oxides. Brazing to titanium, therefore, is generally performed at high vacuum. At high vacuum brazing temperatures, when a gold brazed joint  164  165 is formed between, for example, a gold braze preform and a titanium ferrule, the titanium reacts with the gold to form a direct metallurgical bond to the titanium ferrule  112 . As this direct metallurgical bond is gold-rich, it essentially retains the high conductivity of the gold and its oxide resistant properties. In this regard, the enlarged gold braze area surface, that is, the bonding pad that is formed is part of the oxide-resistant metallurgical bond. This enlarged gold braze area serves as the, electrical connection material that is connectable to the capacitor ground metallization  142 . To summarize, a continuous electrical connection that is consistent in its conductivity over the service life of the device is made. The electrical connection is between the titanium ferrule  112  and the filter capacitor ground metallization  142  via the electrical connection material  152  directly to the non-oxidizable gold bond pad  165 . 
       FIG. 21  is very similar to  FIG. 19 , except in this case, the quad polar capacitor is round which is consistent with the feedthrough capacitor  132  previously illustrated in the cardiac pacemaker of  FIG. 6 . 
       FIG. 22  is generally taken from section  22 - 22  from  FIG. 21  and illustrates the capacitor&#39;s internal structure including its ground and active electrode plates. Importantly, outside diameter electrical connection material  152 , which connects the outside diameter metallization  142  to the ferrule  112 , is directly attached to the gold braze material  165 . The fact that some of this overlaps onto the titanium surface is not important. What is critical is that a suitable amount of the electrical connection material  152  is directly attached to an oxide resistant noble surface, such that an undesirable resistance can never develop. 
       FIG. 23  illustrates the schematic diagram of the improved rectangular quad polar feedthrough capacitor of  FIG. 19  and the round quad polar capacitor of  FIG. 21 . One can see that we now have insignificant resistance in the connection from the feedthrough capacitor to ground  116 , which is the overall shielded equipotential surface of the electromagnetically shielded housing  116 . 
       FIG. 24  is attenuation versus frequency curves which compares the ideal feedthrough capacitor to one that has undesirable ground electrode plate connection to an oxidized surface. One can see that the feedthrough capacitor with the resistive oxide R OXIDE  has greatly reduced attenuation all across the frequency band as compared to the ideal feedthrough capacitor. 
       FIG. 25  illustrates a filtered feedthrough assembly of the present invention  210 . Illustrated is a ferrule  216  of the hermetic seal. The ferrule is generally of titanium. In this case, it has a continuous slot  217 , which can receive the can halves of an active implantable medical device, such as a cardiac pacemaker. These titanium can halves are then laser welded to the titanium ferrule  216 . In general, a feedthrough capacitor  212  would be oriented towards the inside of the can to protect it from body fluids. In this case, there are novel round platinum iridium wires  218 , which have been laser welded  220  directly to the ferrule  216 . Laser weld  220  could also be replaced by a resistance weld or a secondary braze operation at a lower temperature using for example, but not limited to, copper based brazing materials such as Cu—SiI or Ti—Cu—SiI, silver based brazing materials such as SiIvaloy (Ag—Cu—Zn) or Gapasil (Ag—Pd—Ga), gold based brazing materials such as Au—Cu, Au—Cu—Ag, or Au—Cu—Ni, or palladium based braze materials such as Pd—Ni—Si. A capacitor ground metallization  223  is attached using solder or thermal-setting conductive adhesives  222  to the platinum iridium wire  218 . The platinum iridium wire can actually be of any noble material including platinum, gold and its alloys, palladium and its alloys, silver and its alloys and combinations thereof. Leadwires  214  through  214 ′″ pass through the feedthrough capacitor and through the hermetic seal. This is best understood by referring to  FIG. 26 , which is taken from section  26 - 26  from the structure of  FIG. 25 . 
       FIG. 26  illustrates the laser weld  220 , the noble wire  218  and the solder or thermal-setting conductive adhesive  222 . In  FIG. 26 , one can see the capacitor interior electrode plate stacks. A ground electrode plate stack  230  and an active electrode plate stack are designated by  232 ′ and  232 ′″ which are connected respectively to terminal pins  214 ′ and  214 ′″. (The preformed capacitor feedthrough hole, inside diameter metallization of the capacitor feedthrough hole and electrical connection material has been omitted for clarity. It is understood by one skilled in the art that various structures and techniques are used to connect the active electrode plates to the lead wires. In this case, the active electrodes  232  are shown directly contacting the lead  214 ′. It will be appreciated that these other features which have been omitted incorporate part of the invention.) On the body fluid side of the capacitor, one can see gold brazes  226  and  228 . Gold braze  226  connects the ferrule  216  to the alumina insulator  224  providing a robust mechanical and hermetically sealed joint. Gold braze  228  forms a robust mechanical and hermetic seal between the alumina ceramic  224  and the leads  214 . 
     Referring once again to  FIGS. 25 and 26 , one can see that the leadwire  218  provides a very novel feature, that is, electrical connection material  222  does not directly attach to the ferrule  216 . The reason for this is that the ferrule is typically of titanium, which commonly forms titanium oxides. Titanium oxides are very resistive and can also act as semiconductors. This means that a direct connection to titanium would degrade the effectiveness of the capacitor ground electrode plate stack. The noble wire  218  acts as an intermediate surface. By laser welding it to the titanium ferrule  216 , one forms a very strong oxide resistant metallurgical bond. Now, the surface on wire  218  is relatively oxide free. For example, it could be gold, platinum or the like which are oxide resistant at room temperatures. In fact, it would be preferable if the wire  218  be pure platinum and not platinum iridium. The reason for this is that the iridium can form oxides. 
     Referring once again to  FIG. 26 , shown is that the gold brazes forming the hermetic seals  226  and  228  are on the body fluid side. There are a number AIMD manufacturers that prefer having the gold braze on the body fluid side. By having the gold braze in this location, however, making a connection to the capacitor&#39;s outside perimeter or diameter metallization  223  to the same gold braze surface becomes impossible. In other words, as previously described in  FIG. 18 , there is no possibility to provide the gold bond pad  165 , which is a contiguous part of the hermetic seal braze  226 . This is major driving feature of the present invention in that a methodology is provided so that the feedthrough capacitor can be properly grounded to an oxide resistant surface even when the gold brazes are disposed on the opposite side (the body fluid side). 
       FIGS. 27-28  are similar to  FIGS. 25-26  but now show a peninsula structure  244  formed as part of the ferrule  216 . A ground wire  242  is attached to the peninsula  244 . As can be seen best in the cross-section of  FIG. 28 , the ground wire  242  is not connected to the ground electrode plates  230 . The ground electrode plates are still electrically coupled to the metallization  223  which is then electrically coupled to the ferrule  216  through the weld  220 , the wire  218  and the thermosetting conductive adhesive  222  or solder. 
     Referring once again to  FIG. 27A , one can see that the grounded peninsula  244 , which is a continuous part of the machined ferrule  216 , is electrically attached via material  219  to the grounded pin  242 . The ground material could be a laser weld, a gold braze, a solder, a thermal-setting conductive adhesive or the like. In general, pin  242  is provided as a convenience to the AIMD manufacturer to either ground the internal circuit board, or to provide an addition pacing vector to a conductor of an implanted lead (not shown) or both. The electrical ground attachment from the peninsula  244  to lead  242  is very low in resistivity, meaning that it would also be applicable for high voltage implantable cardioverter defibrillator applications. In such an application, a very light shock current would flow through this ground joint to an external electrode (not shown). 
       FIG. 28A  is an enlarged view of a new embodiment of the structure from  FIG. 28  taken from lines  28 A- 28 A now showing the wire  218  recessed into the ferrule  216 . In this way the wire  218  may be positioned and affixed in a more efficient manner. 
       FIG. 28B  is an enlarged view of another embodiment of the structure from  FIG. 28  taken from lines  28 B- 28 B now showing the rectangular wire  218  recessed into the ferrule  216 . In this way the rectangular wire  218  may be positioned and affixed in a more efficient manner. 
       FIG. 28C  shows a perspective view similar to  FIG. 27A  now with the recess  231  and inserts  233  clearly shown. The inserts  233  are placed in the recess  231  before the wire  218  is placed and may be gold metal, gold brazed or any of the material variations and connection methods already described herein. 
       FIG. 29  is similar to  FIG. 25  and illustrates that the two wires  218  could be replaced by a number of pads  234  as shown. In general, the pads could be formed as a continuous part (not shown) of the machining of the ferrule  216  or they could be added as a subsequent assembly by gold brazing or laser welding  220  as shown. The pads  234  would be of the same noble materials previously described as for the wire  218 . This means that a convenient oxide resistant electrical connection  222  could be made using solder or thermal-setting conductive adhesives. 
     Throughout the invention, the intermediate biostable and oxide resistant intermediate structure, such as lead  218  shown in  FIG. 27  with pad  234  as illustrated in  FIG. 29 , must have the following properties: 1) they must be weldable or brazable to the titanium ferrule  216 ; 2) this weld or braze joint must break through any oxides of titanium and form a metallurgical bond between the structure  218  or  220  and the ferrule  216 ; and 3) the intermediate biostable wire of pad  234  must be connectable to the capacitor&#39;s external metallization  223 . The number of connection methods to the capacitor&#39;s external metallization is limited. This includes solders, solder paste and all types of thermal-setting inductive adhesives. In general, although possible, it is not reliably possible to braze or weld directly to the capacitor&#39;s external metallization  223 , hence this option is not a preferred embodiment. In summary, the biostable wire  218  or pad  234  need not be platinum, but it can consist of a long list of metals that would meet the above criteria. Obvious choices would be gold, palladium, tantalum, and niobium. Additional non-limiting considerations include: tungsten, iridium, ruthenium, rhodium, silver, osmium, or combinations thereof. Other nonlimiting examples include platinum based materials such as platinum-rhodium, platinum-iridium, platinum-palladium, or platinum-gold, and naturally occurring alloys like platiniridium (platinum-iridium), iridiosmium and osmiridium (iridium-osmium). 
       FIG. 30  is a sectional view taken from section  30 - 30  from  FIG. 29  illustrating that the pads  234  and  234 ′ are disposed on both sides of the capacitor. It will be obvious to those skilled in the art that they could also be disposed at the ends of the capacitor (not shown). It will be appreciated to one skilled in the art that the pads could be connected. For example, referring once again to  FIG. 27 , pads  234  and  234 a could be filled in between so that there was one large continuous pad. These pads could also have holes in them to further facilitate the electrical attachment between the pad and the capacitor external ground metallization  223 . 
       FIG. 31  is a perspective view of another embodiment similar to  FIGS. 25-30  now showing a different configuration of pad  234 . Here, pad  234  is shown in an L-shape. There is a hole in the bottom of the pad facilitating the laser weld or braze  220  to the ferrule  216 .  FIG. 32  is a sectional view taken along line  32 - 32  from the structure of  FIG. 31 . 
       FIG. 33  is a perspective view of yet another embodiment of a feedthrough capacitor assembly  210  similar to  FIGS. 25-32 . Here the pad  234  is a long pad that spans the length of the long side of the capacitor  212 . The pad  234  has a large hole to facilitate the placement and bonding of the conductive adhesive  222 .  FIG. 34  is a sectional view taken from lines  34 - 34  from the structure of  FIG. 33 . 
       FIG. 34  is a sectional view taken from section  34 - 34  from  FIG. 33 . It shows the long bracket  234  cross-section along with laser weld  222 . 
       FIG. 35  is similar to  FIG. 25  except in this case there are more terminal pins  214 . Accordingly, it is necessary that the oxide-free biostable wire  220  be longer and have more laser welds  222 . This is because it would be undesirable to have a long distance between a filtered terminal pin and its associated ground. This is because inductance and resistance can build up across an internal ground plane, thereby degrading the RF filtered performance of a distal filtered pin.  FIG. 36  is an exploded view of the structure of  FIG. 35 . In  FIG. 36 , the ground pin  242  is shown laser welded or gold brazed into the ferrule  216  in the peninsula area  244 . In this case, the capacitor is a conventional capacitor wherein the ground electrode plates are terminated  223  with metallization disposed along the two long outside ends of the capacitor  212 . In this case, there is no connection between terminal pin  242  and the capacitor&#39;s ground electrode plate stack  230 . In a different embodiment (not shown), a capacitor&#39;s ground electrode plates could be connected to this grounded pin as completely described in U.S. Pat. No. 6,765,779, the contents of which are incorporated herein by reference. Referring once again to  FIGS. 35-37 , an alternative is given wherein a direct connection to terminal pin  242  and the grounding of the capacitor&#39;s electrode stacks  230  is nonexistent. That is, the electrical connection is between the capacitor metallization  223  and the noble wires  218 . 
       FIG. 37  is a sectional view taken from section  37 - 37  from  FIG. 35  illustrating that any one of the active pins  214  passes through feedthrough holes near the center of the capacitor  212  in a staggered pattern where the pin  214  makes contact with its own individual set of active electrode plates (not shown) or many active electrode plates. The ground electrode plates contact the capacitor&#39;s long-side perimeter metallization  223  and then electrical attachment material, which can be solder or thermal-setting conductive adhesive, attaches the capacitor ground metallization  223  to the noble wire  218 . 
       FIG. 38  is similar to  FIG. 35 , which illustrates an alternative method of grounding the capacitor&#39;s ground electrode stack  230 . Referring back to  FIG. 36 , one can see the novel ferrule pedestal  244  to which ground pin  242  is electrically and mechanically attached. In  FIG. 28 , ground pin  242  is electrically attached to the ferrule  216  and is thereby grounded in a similar manner as shown in  FIG. 36 . A novel L-shaped clip  246 ′ is electrically attached to ground pin  242  and engages a portion of the capacitor&#39;s external ground metallization  223 . This is best illustrated in  FIG. 28 , where the ground clip  246 ′ being electrically connected  222  to the capacitor&#39;s ground metallization  223  is shown. 
     Referring back to  FIG. 38 , illustrated is clip  246 ′ disposed on the top surface of the capacitor  212 . There is an insulating structure  252  that is disposed on top of capacitor  212 . This can be a conformal coating of insulation, an insulation sheet with adhesive layer, or even an alumina ceramic thin sheet of insulation. For the case where this insulation sheet  252  is alumina ceramic, it may have a cut-out pocket so that the clip  246 ′ drops down into it and fits flush with the top of the insulating layer  252 . This would help to hold the clip  246 ′ in place and to index it. 
       FIG. 39  shows the ground electrode plate  230  which does not make contact with the leadwires  214  or the grounded wire  242 . The ground electrode plate  230  makes contact with metallization  223  which is then in electrical contact with novel pad  246 ′. 
       FIG. 40  shows a multitude of active electrode plates  232  electrically coupled to the leadwires  214 . Note that the grounded pin  242  lacks an active electrode plate  232 . 
       FIGS. 41-43  are very similar to  FIGS. 28-30 .  FIGS. 41-43  show a different embodiment of the novel pad  246 a. Pad  246 a is longer along the length of increased metallization  223 . This design would increase filter performance due to the shortened electrical pathways. In this way, the inductance across the ground planes of the capacitor is greatly reduced. This means that outer pins  214  will have improved attenuation and greater insertion loss than the structure previously illustrated in  FIG. 38 . 
       FIG. 44  is a sectional view for both  FIGS. 38 and 41 . One can see better the peninsula or extension that attaches to the ground wire  242 . It will be understood that novel pad  246  could also extend over the opposite side metallization and also make electrical contact. This would further improve filter performance by lowering electrical pathway lengths. 
       FIGS. 45A, 45B and 45C  illustrate various types of L-shaped clips  246 . In  FIG. 45C , one can see the advantage of having a clip with an elliptical hole  247  because this allows electrical connection material  222 , which can be a solder or a thermal-setting conductive adhesive, to be placed on the outside of the clip and also inside the elliptical hole. This increases the electrical contact area and thereby reduces the resistance as well as improves mechanical strength. 
       FIGS. 46 and 47  are an alternative embodiment of clip  246 b previously illustrated in  FIGS. 38 and 41 . The novel clip  246 b is under the capacitor  212  sandwiched between the ferrule  216  and the capacitor  212 . A hole is also in the clip  246 b to facilitate placement of conductive adhesive  222 .  FIG. 47  is an exploded view that best shows the shape of novel clip  246 b. 
     In the alternative embodiment shown in  FIG. 46 , the clip  246  is disposed underneath the capacitor  212  and electrically and mechanically attached directly to the peninsula structure. Having the clip  246 ′ disposed underneath the capacitor  212 , and then coming up on the side as is illustrated, would improve the RF performance of the capacitor. Effectively, this would shorten the ground pin  242  to almost zero thereby reducing the impedance and inductance of the ground clip  246 ′. A notch (not shown) could be put in the ferrule  216  of the hermetic terminal to facilitate the clip coming out through the bottom so that the capacitor  212  still would sit flush on top of the ferrule structure  216 . 
       FIGS. 48-53  are similar to  FIGS. 25-34  except that in this case pockets  248  and noble metal inserts  250  have been formed so that an oxide resistant electrical attachment  222  can be made between the capacitor ground metallization  223  and the ferrule  216 . An alternative embodiment  250 ′ is shown where first, a brazing perform, such as a gold braze perform  250 a, is placed and then a platinum cap  250 b is placed over it. Alternative metals may be used as noted earlier. In addition, instead of a braze  250 a, one could use a resistance weld or lower temperature brazes such as those listed previously with the Cu—SiI or Ti—Cu—SiI examples. Platinum pad  250 b would be slightly longer in the length direction and slightly longer in the width direction than the underlying pre-form  150 A. This overlaying would prevent it from reflowing and leaking out during a gold braze operation. In addition, the pad  250 b would protrude above the surface of the ferrule. This turns out to be very convenient during electrical attachment of the feedthrough capacitor (not shown) outside perimeter metallization  223 . In other words, the protruding pad  250 b would provide a convenient stop for a solder paste, a solder pre-form or a thermal-setting conductive adhesive (dispensed by robot). This is best understood by referring to  FIGS. 48 and 49 , which shows that a pocket  248  and  248 a are first formed at the time of manufacturing the ferrule  216  of the hermetic seal subassembly  210 . These pockets can be rectangular (as shown), can be rectangular with rounded ends or it can be round holes as illustrated as  248 a or even a continuous groove or slot as illustrated in  FIG. 53  as  248 c. Into these pockets or grooves  248  can be placed a noble wire  218  as previously described in  FIG. 25 , or a material  250 , such as CuSiI or TiCuSiI, gold or any other material as disclosed earlier that can form a metallurgically sound bond to titanium while at the same time, providing an oxide resistant surface to which electrical attachment  222  can form a solid bond. 
     Referring once again to  FIG. 49 , one can see that there is an alternative arrangement similar to that previously described in  FIG. 48 . In this case, a circular gold braze pre-form  250 Ab could first be placed into the counter-bore hole  248 a and then a platinum or equivalent cap  250 Aa could be placed over it. These could all be reflowed into place leaving a convenient area to make electrical attachment between the capacitor external ground metallization  223 , through the oxide resistant pad  250 Aa, through the braze material  250 Ab and, in turn, to the ferrule  216 . 
       FIG. 50  is an isometric view of the quad polar feedthrough capacitor  212  shown mounted to the hermetically sealed ferrule assembly previously illustrated in  FIG. 48 . Shown is an electrical attachment material  222  between the capacitor ground metallization  223  that connects to the oxide resistant connection pads  250 ,  250 ′. Referring once again to  FIG. 50 , one can see that there is metallization  223  on both short ends of the capacitor  212 . This metallization  223  could extend along the long sides or, alternatively, along all perimeter sides of the capacitor. In the case where the length of the perimeter metallization  223  is made longer, then additional pockets and oxide resistant pads  250  would be required. 
       FIGS. 51 and 52  illustrate the ground and active electrode plate sets of the capacitor  212  previously illustrated in  FIG. 50 . In  FIG. 51 , shown is that the ground electrode plate  230  does not make contact with any of the terminal pins  214 . The metallization  223  contacts the ground electrode plate set  230  on its left and right ends.  FIG. 52  illustrates the active electrode plates  232 . In this case, the active electrode plates  232  are connected to each one of the feedthrough terminal pins  214 . 
       FIG. 53  is the same ferrule as previously described in  FIGS. 49 and 50  except that instead of a discrete number of machined pads  248 , there is a continuous groove  248 c formed around the entire perimeter of the capacitor. This would be filled with a gold braze, Cu—SiI or Ti—Cu—SiI or other material previously listed to form an oxide resistant connection area for the feedthrough capacitor (not shown). A feedthrough capacitor  212 , in this case, would have perimeter metallization  223  along all four of its perimeter sides and either a continuous or a multiplicity of short electrical connections  222  would be made between the capacitor metallization  223  and the gold braze or equivalent material that has been flowed in the trough  248 c (not shown). 
       FIGS. 54 and 55  are yet another embodiment of the present invention. As shown in  FIG. 54 , gold films  250 b may be placed on top of the ferrule  216 . Then a conductive sheet  254  is laid overtop the gold films  250 b. In a brazing procedure the gold films or plates bond between the conductive sheet  254  and the ferrule  216 . The capacitor  212  can be placed overtop the conductive sheet  254  and then an electrical connection using conductive adhesives  222  can be made between the external metallization  223  and the conductive sheet  254 . As shown in  FIGS. 54 and 55 , the metallization is around the entirety of the capacitor  212 . This design would also reduce both the inductance and equivalent series resistance of the capacitor  212 . 
     Although several embodiments have been described in detail for purposes of illustration, various modifications may be made to each without departing from the scope and spirit of the invention. Various features of one embodiment may be incorporated into another embodiment, as each embodiment is not exclusive of the other features taught and shown herein. Accordingly, the invention is not to be limited, except as by the appended claims.