Abstract:
Implantable heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric charge, to abnormally beating hearts. Critical parts in these devices include the capacitors that store and deliver the bursts of electric charge. Some devices use flat aluminum electrolytic capacitors have cases with right-angle corners which leave gaps when placed against the rounded interior surfaces of typical device housings. These gaps and voids not only waste space, but ultimately force patients to endure implantable devices with larger housings than otherwise necessary. Accordingly, the inventors devised several capacitor structures that have curved profiles conforming to the rounded interior surfaces of device housings. Some exemplary capacitor embodiments include two or more staggered capacitor elements, and other embodiments stagger capacitors of different types and/or sizes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. Application Ser. No. 10/287,285, filed on Nov. 4, 2002, now issued as U.S. Pat. No. 6,674,634, which is a division of U.S. Application Ser. No. 09/705,976, filed on Nov. 3, 2000, now issued as U.S. Pat. No. 6,522,525, the specifications of which are incorporated by reference herein. 
   This application is related to U.S. Application Ser. No. 09/706,447, filed on Nov. 3, 2000, now issued as U.S. Pat No. 6,699,265, entitled FLAT CAPACITOR FOR AN IMPLANTABLE MEDICAL DEVICE, which is incorporated herein by reference in its entirety. 

   TECHNICAL FIELD 
   This invention relates generally to electrolytic capacitors and, more particularly to flat electrolytic capacitors for use in implantable heart monitors. 
   BACKGROUND OF THE INVENTION 
   Since the early 1980s, thousands of patients prone to irregular and sometimes life threatening heart rhythms have had miniature heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, implanted in their bodies. These devices detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric current, to their hearts. When the bursts of electric current are properly sized and timed, they restore normal heart function without human intervention, sparing patients considerable discomfort and often saving their lives. 
   The typical implantable heart-monitoring device includes a set of electrical leads, which extend from a sealed housing for implantation into the inner walls of a heart. The housing itself is typically somewhat flat and rectangular with rounded edges and corners to reduce stress on surrounding tissues after implantation. Within the housing are a battery for supplying power, heart-monitoring circuitry for monitoring the heart and detecting abnormal rhythmic conditions, and two or more capacitors for delivering bursts of electric current through the leads to the heart. 
   In many instances, each capacitor takes the form of a flat aluminum electrolytic capacitor. This type of capacitor generally includes a vertical stack of several flat D-shaped capacitor elements, or modules, with each module comprising at least one D-shaped paper separator sandwiched between D-shaped sheets of aluminum foil. The capacitor modules are electrically coupled together to provide a total capacitance and then housed in a D-shaped case made of aluminum or another metal compatible with the foil. 
   The aluminum case, which conforms closely to the shape of the vertical stack of D-shaped capacitor modules, has vertical sidewalls that are parallel to the vertical faces of the stack. The case also has D-shaped top and bottom portions that meet its vertical sidewalls to form approximate right-angle joints and corners along its top and bottom edges. 
   Two or more such capacitors are sometimes stacked on top of each other within the housing of an implantable device. When stacked, the walls of the D-shaped capacitors are aligned with each other, effectively forming a single vertical wall the combined height of the capacitors. 
   One problem with these types of flat capacitors and their stacked arrangement in implantable device housings is that the walls of the cases are incompatible with the rounded edges and corners of implantable device housings. Juxtaposing these vertical walls and right-angle corners against the rounded interior portions of the housings inevitably leaves gaps or voids between the cases and housings. These voids not only waste space, but ultimately force patients to endure implantable devices with larger housings than otherwise necessary. 
   Accordingly, there is a need for flat capacitors that better conform to the rounded portions of implantable medical-device housings. 
   SUMMARY 
   To address this and other needs, the inventors devised new capacitor structures, new capacitor shapes, and new capacitor assemblies to conform better with the housings of implantable medical devices. One exemplary capacitor includes three or more capacitive modules that are sized and stacked so that their edges on at least one side are staggered relative each other in one or two dimensions to define a curved profile that conforms generally with a rounded, interior surface of a capacitor case. 
   The inventors also devised new capacitor shapes, some of which incorporate one or more rounded corners. One exemplary capacitor includes a main portion and two peninsular portions extending from one side of the main portion, defining a “U”. Terminals extend from the end of one of the peninsular portions. One innovative use of this shape entails placing a battery or other component of an implantable medical device in the region between the two peninsular portions. 
   Additionally, the inventors devised new capacitor assemblies. One exemplary capacitor assembly includes two or more separate capacitors of different sizes. In some embodiments, one or more of these capacitors include a curved profile and/or are staggered relative each other. In other embodiments, two or more capacitors of the same size are staggered relative each other. 
   Other aspects of the invention include an implantable medical device, such as a pacemaker, defibrillator, cardioverter-defibrillator, or congestive-heart-failure device, that has a housing with at least one rounded surface abutting the rounded portion of a capacitor. The capacitor includes a capacitive stack with a curved profile and/or includes a pair of peninsular portions spaced to receive a battery or other component. Other implantable devices include one or more of the new capacitive assemblies. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial cross-sectional view of an exemplary capacitor  100  having capacitor modules with edges staggered in a first dimension to define a curved profile  106 ; 
       FIG. 2  is a partial cross-sectional view of capacitor  100  showing that its capacitor modules are staggered in a second dimension to define another curved profile  108 ; 
       FIG. 3  is a partial cross-sectional view of an exemplary implantable heart monitor  300  including a monitor housing  310  and two capacitors  320  and  330  having curved profiles that abut interior curved portions of the monitor housing. 
       FIG. 4  is a perspective view of an exemplary capacitor-battery assembly  400  including two stacked U-shaped capacitors  410  and  420  and a battery  430  nested within the capacitors. 
       FIG. 5  is a front view of the  FIG. 4  assembly without the battery. 
       FIG. 6  is a side view of the  FIG. 4  assembly. 
       FIG. 7  is a top view of the  FIG. 4  assembly. 
       FIG. 8  is a partial cross-sectional view of an exemplary capacitor assembly  800 . 
       FIG. 9  is a partial cross-sectional view of an exemplary capacitor assembly  900 . 
       FIG. 10  is a partial cross-sectional view of an exemplary capacitor assembly  1000 . 
       FIG. 11  is a block diagram of an implantable heart monitor  1100 . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The following detailed description, which references and incorporates the above-identified figures, describes and illustrates one or more specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art. 
   As used herein, the term “profile” refers to the general outline of a portion of an object taken in or projected onto a plane generally perpendicular to a major surface of the object. Thus, for example, in some flat capacitors, profile means the outline of the capacitor case and/or the capacitor stack taken in a plane perpendicular to the major surfaces of the case or the capacitor stack. 
   As used herein, the term “staggered” refers to the existence of an offset between respective adjacent surfaces of two or more juxtaposed or proximate objects. Thus, for example, the offset can result from offsetting one of the objects relative the other object or controlling the relative size and placement of the objects. 
     FIG. 1  shows a portion of an exemplary capacitor  100  incorporating the present invention. Capacitor  100  includes a stack  102  of two or more electrically coupled capacitor modules  102   a ,  102   b ,  102   c ,  102   d , and  102   e  within a capacitor case  104 . Modules  102   a - 102   e  are staggered so that their edges generally (or at least a portion of side of the stack) define a profile  106  that generally conforms or is substantially congruent to an adjacent curved interior portion  104   a  of capacitor case  104 . 
     FIG. 2 , a section view of capacitor  100  taken along line  2 — 2  shows that modules  102   a - 102   e  are staggered in two dimensions. In this view, capacitor modules  102   a - 102   e  define a profile  108 , which is generally congruent to a curved portion  104   b  of case  104 . Although profiles  106  and  108  are quite distinct in this exemplary embodiment, other embodiments make profiles  106  and  108  substantially congruent. 
   In the exemplary embodiment, each capacitor module includes a three-layer etched and/or perforated anode, a cathode, and at least one electrolyte-carrying separator between the anode and the cathode. The anode and cathode comprise foils of aluminum, tantalum, hafnium, niobium, titanium, zirconium, or combinations of these metals. Additionally, each capacitor module is sandwiched between two pairs of electrolyte-carrying separators, with the separators extending beyond the anode and cathode to prevent undesirable shorting with the case. Alternatively, separate insulative layer can be placed between the capacitor modules and the case interior walls to prevent shorting. Exemplary separators comprise kraft paper, and exemplary electrolytes include ethylene-glycol base combined with butrylactone. 
   In other embodiments, the capacitor modules take other forms having different numbers of anode layers and separators. For example, in some embodiments, the anodes, cathode, and separators in one or more of the capacitor modules are staggered to define curved module faces that confront the interior surfaces  104   a  or  104   b  of the case. Also, in some embodiments, one or more of the anodes or cathodes are coupled to the case, making it either anodic or cathodic. 
   To define the staggered edge faces and thus the curved profile, some embodiments which provide the curved profile in a single dimension, use a set of generally congruent modules of different sizes. For example, one embodiment includes four generally D-shaped modules, each with a common width and height, but with four successively smaller lengths. The modules are stacked, each module having at least one edge aligned vertically with the corresponding edges of adjacent modules. 
     FIG. 3  shows an exemplary implantable heart monitor  300  including a monitor housing  310  and two capacitors  320  and  330 . Monitor housing  310  includes curved portions  312  and  314  and adjoining straight portions  316  and  318 . Capacitor  320  includes case  322  and eleven capacitor modules  324 . Case  322  includes a curved portion  322   a  and a straight portion  322   b , respectively confronting curved portion  312  and straight portion  316  of housing  310 . 
   Capacitor modules  324  include a set of staggered modules  324   a  and a set of unstaggered modules  324   b . The set of staggered modules  324   a  confront curved portion  322   a  of case  322  and have edges arranged to define a curved profile  326  generally congruent to the profile of curved portion  322 . Modules  324   b , which are vertically aligned, confront straight portion  322   b  of case  322 . 
   Similarly, capacitor  330  includes case  332  and eleven capacitor modules  334 . Case  332  includes curved portion  332   a  and a straight portion  332   b , which confront respective portion  314  and  318  of housing  310 . Capacitor modules  334  include staggered modules  334   a , which confront curved portion  332   a  of case  332 , have front edges arranged to define a curved profile  336  generally congruent to the profile of curved portion  332   a . Modules  334   b  confront straight portion  332   b  of case  332 . 
   Notably, the exemplary embodiment provides each of modules  324  and  334  with three anodes placed between one or more separators and at least one cathode placed adjacent one of the separators. ( FIG. 3  shows the separators cross-hatched.) However, the invention is not limited to any particular module arrangement. Indeed, some embodiments of the invention use other (greater or lesser) numbers of anodes as well as modules. Moreover, some embodiments mix modules of different arrangements within the same capacitor case. This allows greater flexibility in exploiting the space available in the case as well as the housing. For more details, see co-assigned and co-pending U.S. patent application Ser. No. 09/706,447, filed on Nov. 3, 2000, now issued as U.S. Pat. No. 6, 699,265, which is incorporated herein by reference. 
   Additionally, other embodiments of the invention construct capacitor cases  322  and  332  as a single case having two adjacent compartments with a common wall. Modules  324  and  334  are each placed in a respective compartment. The cathodes in modules  324  and the anodes of modules  334  are electrically coupled to the case; an external anode terminal is coupled to the anodes of module  324 ; and an external cathode terminal is coupled to the cathodes of module  334 , thereby effecting a series connection of the two capacitors using two external terminals instead of the four that are conventionally provided. 
   This arrangement can be made by providing two (first and second) aluminum case bodies having the desired curved portions, placing capacitor modules in the first case body, and welding a cover to the first case body. Other capacitor modules can then be stacked and placed in the second case body. The cover of the first case body is then put on the opening of the second case body and welded in place. For further details, see co-pending and co-assigned U.S. patent application Ser. No. 09/706,447, filed on Nov 3, 2000, now issued as U.S. Pat. No. 6,699,265, and which is incorporated herein by reference. 
     FIG. 4  shows a perspective view of an exemplary capacitor-battery assembly  400  including two stacked U-shaped capacitors  410  and  420  and a battery  430  nested within the capacitors. For sake of brevity, capacitor  420 , which is of substantially identical size, shape, and structure as capacitor  410  in this exemplary assembly, is not described separately. However, the invention is not so limited. Capacitor  410  includes legs  412  and  414 , respective middle (or intermediate) portions  416 , and terminals  418 . Legs  412  and  414 , which are parallel in the exemplary embodiment, include respective curved surfaces  412   a  and  414   a , and respective flat end surfaces  412   b  and  414   b.    
     FIG. 5 , a front view of assembly  400  without battery  430 , shows that curved surfaces  412   a  and  414   b  are generally congruent to each other and to respective curved profile  502  and  504  defined by capacitor modules  500 . Further, it shows a housing  510  (in phantom) having a curved or concave portions  512  and  514  generally congruent with or conformant to curved (or convex) surfaces  412   a  and  414   a . In the exemplary embodiment, curved profiles  502  and  504  are quarter segments of an ellipse or circle, and surfaces  412   a  and  414   a  are portions of an ellipsoid or sphere. The exemplary embodiment provides the modules with one or more of the single or multiple anode structures noted previously. Thus, modules  500  may include modules with differing anode structures as desired to fit a given height. 
     FIG. 6 , a side view of assembly  400 , shows that the curved surfaces  412   a  and  414   a  are generally perpendicular to end surfaces  412   a  and  412   b . Middle portion  416  is also shown as having a curved portion  416   a  which is congruent to a curved profile  506  defined by capacitor modules  500  and a curved portion  516  of monitor housing  510 . 
     FIG. 7  is a top view of assembly  400 , showing the general U-shape of capacitor modules  500 . This figure also shows that battery  430  includes terminals  432 . 
     FIGS. 8 ,  9 , and  10 , all cross-sectional views, show respective four- capacitor assemblies, each illustrating a flexible capacitor-level approach to reducing the voids in implantable-device housings. In a mass-production context, the capacitor-level approach allows one to prefabricate a set of capacitors of different sizes, different curvatures, and even of different capacitor technologies, and then to assemble the capacitors to conform to the available space within a housing. 
   In particular,  FIG. 8 , a cross-sectional view, shows an exemplary capacitor assembly  800 . Capacitor assembly  800  includes a monitor housing  810  and four separate capacitors  820 ,  830 ,  840 , and  850 . Housing  810  includes curved portions  810   a ,  810   b ,  810   c , and  810   d . Capacitors  820 ,  830 ,  840 , and  850  include respective capacitor cases  822 ,  832 ,  842 , and  852 , and respective terminals pairs  824 ,  834 ,  844 , and  854 . (For clarity, the figure omits the internals of these capacitors.) Cases  822 ,  832 ,  842 , and  852  have respective curved portions  822   a ,  832   a ,  842   a , and  852   a  that are generally congruent to and confront respective curved portions  810   a ,  810   b ,  810   c , and  810   d  of housing  810 . The cases also have respective widths (or heights) W 1 , W 2 , W 3 , and W 4  Each of capacitors terminal pairs  824 ,  834 ,  844 , and  854  includes an anode terminal and a cathode terminal. Though not shown, the exemplary embodiment interconnects the terminals to achieve a series connection of two capacitances. 
   This exemplary embodiment provides the four capacitors with a common width. However, other embodiments provide one or more of the capacitors with a different width. For example, in some embodiments, widths W 1  and W 4  are equal, and widths W 2  and W 3  are equal, but different from widths W 1  and W 2 . Additionally, two or more of the capacitors, for example, capacitors  820  and  830  or capacitors  820  and  830 , can be combined into a single capacitor. And, still other embodiments use different numbers of capacitors, such as three, five, or six. Thus, the invention is not limited to an particular number of capacitors. 
     FIG. 9 , a cross-sectional view, shows an exemplary capacitor assembly  900 . Capacitor assembly  900  includes a monitor housing  910  and four separate capacitors  920 ,  930 ,  940 , and  950 . Housing  910  includes curved portions  910   a  and  910   b . Capacitors  920 ,  930 ,  940 , and  950  include respective capacitor cases  922 ,  932 ,  942 , and  952 , which have respective widths (or heights) W 1 , W 2 , W 3 , and W 4 , and respective lengths L 1 , L 2 , L 3 , and L 4 . Cases  922  and  932  have respective end walls  922   a  and  932   a  which confront curved portion  910   a ; and cases  942  and  952  have respective end walls that confront curved portion  910   b.    
   In this exemplary embodiment, the capacitors lack individual curved profiles, but have different sizes to reduce voids between their respective cases and the monitor housing. More precisely, one or more of the capacitors has a different width and/or length. As shown, lengths L 1  and L 4  are equal to a length LA, and lengths L 2  and L 3  are equal to a different length LB. Also, widths W 2  and W 3  are equal to a width WA, and widths W 1  and W 4  are not equal to each other or to the width WA. However, in some embodiments, the capacitors have a common width. 
     FIG. 10 , a cross-sectional view, shows an exemplary capacitor assembly  1000 . Capacitor assembly  1000  includes a monitor housing  1010  and four separate capacitors  1020 ,  1030 ,  1040 , and  1050 . Housing  1010  includes curved portions  1010   a  and  1010   b . Capacitors  1020 ,  1030 ,  1040 , and  1050  include respective capacitor cases  1022 ,  1032 ,  1042 , and  1052 . Cases  1022 ,  1032 ,  1042 , and  1052  have respective widths W 1 , W 2 , W 3 , and W 4 , and respective lengths L 1 , L 2 , L 3 , and L 4 . Additionally, cases  1022 ,  1032 ,  1042 , and  1052  are offset from a common reference plane P by respective offsets O 1 , O 2 , O 3 , and O 4 . 
   In this exemplary embodiment, widths W 1 , W 2 , W 3 , and W 4  are equal, and lengths L 1 , L 2 , L 3 , and L 4  are equal. Further, offsets O 1  and O 4  are equal, and offsets O 2  and O 3  are equal but larger than offsets O 1  and O 4 . In other embodiments, each of the offsets is larger than the previous offset, creating descending steps. 
   In the exemplary embodiments of  FIGS. 8-10 , the four capacitors are aluminum electrolytic capacitors, with each capacitor including one or more capacitor modules of similar or dissimilar structures (as previously described for other exemplary capacitors.) However, other embodiments provide the four capacitors as wet-tantalum, ceramic, dry-film capacitors, or other types of capacitors. Still other embodiments provide combinations of different numbers of capacitors and different types of capacitors. 
     FIG. 11  is a block diagram of implantable heart monitor  1100  which incorporates one or more teachings of the present invention. Specifically, monitor  1100  includes a housing  1110 , lead system  1120 , which after implantation electrically contact strategic portions of a patient&#39;s heart, a monitoring circuit  1130  for monitoring heart activity through one or more of the leads of lead system  1120 , and a therapy circuit  1140 . Circuit  1140  includes a component  1142  which incorporates one or more capacitors, such as capacitors  100  and  300 , capacitor-battery assembly  400 , or one or more of capacitor assemblies  800 ,  900 , or  1000 . Monitor  1100  operates according to well known and understood principles to perform defibrillation, cardioversion, pacing, and/or other therapeutic functions. 
   In addition to its application to implantable heart monitors, or cardiac rhythm management devices, the teachings of the present invention are applicable to photographic flash equipment. Indeed, these teachings are pertinent to any application where small, high-energy capacitors are desirable. 
   CONCLUSION 
   In furtherance of the art, the present inventors have devised several new capacitor structures having curved profiles and capacitor assemblies for reducing voids in implantable medical devices. The curved profiles generally facilitate efficient use of curved capacitor cases and curved housings for implantable medical devices. In some exemplary embodiments, the capacitors include staggered capacitor modules or elements to define the curved profiles, and in other embodiments, the capacitors themselves are staggered. 
   The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the following claims and their equivalents.