Rf filter for an active medical device (amd) for handling high rf power induced in an associated implanted lead from an external rf field

Abstract

An RF filter for an active medical device (AMD), for handling RF power induced in an associated lead from an external RF field at a selected MRI frequency or range frequencies includes a capacitor having a capacitance of between 100 and 10,000 picofarads, and a temperature stable dielectric having a dielectric constant of 200 or less and a temperature coefficient of capacitance (TCC) within the range of plus 400 to minus 7112 parts per million per degree centigrade. The capacitor's dielectric loss tangent in ohms is less than five percent of the capacitor's equivalent series resistance (ESR) at the selected MRI RF frequency or range of frequencies.

1 . An RF filter for an active implantable medical device (AIMD) for handling high RF power induced in an associated implantable lead from an external RF field at a selected MRI RF center frequency or range of frequencies, comprising:
 at least one capacitor having a capacitance of between 10 and 20,000 picofarads, and a temperature stable dielectric having a dielectric constant of 200 or less and a temperature coefficient of capacitance (TCC) within the range of plus 400 to minus 7112 parts per million per degree centigrade (ppm/° C.);   wherein the capacitor's dielectric loss tangent in ohms is less than five percent of the capacitor's equivalent series resistance (ESR) at the selected MRI center frequency or range of frequencies; and   wherein the capacitance is selected such that heat flow away from the capacitor is maximized.   
     
     
         2 . The RF filter of  claim 1  wherein the capacitor includes at least ten interleaved active and ground electrode plates for minimizing the capacitor's high frequency ESR and to maximize heat flow from the capacitor. 
     
     
         3 . The RF filter of  claim 2  wherein the ground electrode plates are conductively connected to an energy dissipating surface (EDS). 
     
     
         4 . The RF filter of  claim 1 , wherein the capacitor has a capacitance of between 100 and 10,000 picofarads. 
     
     
         5 . The RF filter of  claim 1 , wherein the RF filter comprises a single or multi-element lowpass filter. 
     
     
         6 . The RF filter of  claim 5 , wherein the single or multi-element lowpass filter is electrically coupled with one or more bandstop filters, one or more L-C trap filters, or both, in any order or circuit configuration. 
     
     
         7 . The RF filter of  claim 6 , wherein the lowpass filter, bandstop filter, or L-C trap filter comprises at least one high power handling two-terminal chip capacitor, an MLCC capacitor, a three-terminal feedthrough-type capacitor, a flat-through capacitor, or an X2Y attenuator. 
     
     
         8 . The RF filter of  claim 5 , wherein the multi-element lowpass filter is selected from the group consisting of an L, reverse L, Pi, T, LL, reverse LL, and an n-element filter. 
     
     
         9 . The RF filter of  claim 1 , wherein the high RF power capacitor is disposed at or near a point of the lead's ingress into a housing for the active medical device (AMD), wherein the capacitor is electrically connected in parallel between at least one lead conductor and the AMD housing. 
     
     
         10 . The RF filter of  claim 1 , wherein the RF filter further comprises a bandstop filter connected in series with the lead, and an L-C trap filter connected from the lead electrically in parallel with the AMD housing, wherein the lead is in turn electrically connected to AMD electronic circuits. 
     
     
         11 . The RF filter of  claim 1 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than two ohms. 
     
     
         12 . The RF filter of  claim 1 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than 0.5 ohm. 
     
     
         13 . The RF filter of  claim 1 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than 0.1 ohm. 
     
     
         14 . The RF filter of  claim 1 , wherein the capacitance varies no more than plus or minus one percent from minus 55 degrees C. to plus 125 degrees C. 
     
     
         15 . The RF filter of  claim 1 , wherein the capacitor's dielectric loss tangent is less than two ohms at the selected MRI RF frequency or range of frequencies. 
     
     
         16 . The RF filter of  claim 3 , wherein the energy dissipating surface comprises a housing for the AIMD. 
     
     
         17 . The RF filter of  claim 16 , wherein the energy dissipating surface comprises a conductive ferrule conductively attached to both the capacitor ground electrode plates and the AMD housing. 
     
     
         18 . The RF filter of  claim 2 , wherein the ground electrode plates comprise dual electrode plates. 
     
     
         19 . The RF filter of  claim 2 , wherein the active electrode plates comprise dual electrode plates. 
     
     
         20 . The RF filter of  claim 2 , wherein the ground electrode plates comprise triple or n electrode plates. 
     
     
         21 . The RF filter of  claim 3 , including a thermal-setting conductive adhesive for conductively connecting the ground electrode plates to the energy dissipating surface. 
     
     
         22 . The RF filter of  claim 21 , wherein the thermal-setting conductive adhesive includes conductive particles, silver flakes or conductive flakes, conductive rods, tubes, whiskers, fibers, or nano particles, or any combination thereof. 
     
     
         23 . The RF filter of  claim 2 , wherein said interleaved electrode plates are bounded at one end by a first set of at least one extra ground plate embedded within the dielectric material. 
     
     
         24 . The RF filter of  claim 23 , including a second set of at least one ground plate embedded within the dielectric material and bounding said interleaved electrode plates opposite the first set of ground plates. 
     
     
         25 . The RF filter of  claim 2 , including a plurality of ground electrode plates extending to substantially the periphery of the capacitor. 
     
     
         26 . The RF filter of  claim 25 , including a high thermal conductivity material or a high thermally conductive overlay for attaching at least partially the ground electrode plates to a ferrule. 
     
     
         27 . The RF filter of  claim 26 , wherein the ferrule is connected to an energy dissipation surface. 
     
     
         28 . The RF filter of  claim 27 , wherein the energy dissipation surface is a housing of the AIMD. 
     
     
         29 . The RF filter of  claim 26 , wherein the ferrule comprises an energy dissipating surface. 
     
     
         30 . The RF filter of  claim 29 , including a thermally-conductive overlay extending from the conductive ferrule over the top of the capacitor. 
     
     
         31 . The RF filter of  claim 30 , wherein the thermally-conductive overlay extends across at least a portion of a housing for the active medical device. 
     
     
         32 . The RF filter of  claim 29 , including a hermetic insulator disposed within the conductive ferrule, the hermetic insulator having ground plates conductively coupled to the ferrule. 
     
     
         33 . The RF filter of  claim 30 , including a thermally-conductive liner disposed adjacent to an inside surface of a housing for the active implantable medical device. 
     
     
         34 . The RF filter of  claim 33 , wherein the thermally-conductive liner comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotrophically Enriched Diamond, Graphene, Gold, Silver, or Platinum. 
     
     
         35 . The RF filter of  claim 26 , including a weld shield associated with the conductive ferrule. 
     
     
         36 . The RF filter of  claim 2 , including a thickened metallization layer disposed about the outside perimeter of the capacitor and conductively coupled to the ground electrode plates. 
     
     
         37 . The RF filter of  claim 36 , wherein the thickened metallization layer comprises metal bearing glass frits or Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         38 . The RF filter of  claim 26 , including a thermally conductive ceramic disposed within the conductive ferrule between the capacitor and an alumina ceramic insulator. 
     
     
         39 . The RF filter of  claim 26 , including a thermally conductive washer disposed between the capacitor and a hermetic seal insulator disposed within the conductive ferrule. 
     
     
         40 . The RF filter of  claim 39 , wherein the thermally-conductive washer comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         41 . The RF filter of  claim 26 , wherein the conductive ferrule includes a capture flange for the capacitor. 
     
     
         42 . The RF filter of  claim 26 , wherein the high thermal conductivity material for attaching the ground electrode plates to the conductive ferrule comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         43 . The RF filter of  claim 1 , including a heat conductive structure affixed to a periphery of the capacitor. 
     
     
         44 . The RF filter of  claim 43 , wherein the heat conductive structure comprises a plurality of convection fins. 
     
     
         45 . The RF filter of  claim 1 , wherein a housing for the active medical device is filled with a dielectric fluid. 
     
     
         46 . The RF filter of  claim 1 , including at least one secondary capacitor disposed within a housing for the active medical device at a space location from the at least one capacitor, the secondary capacitor associated with electronic components of the active medical device. 
     
     
         47 . The RF filter of  claim 46 , including at least one secondary energy dissipating surface associated with electronic components disposed within the housing for the active medical device. 
     
     
         48 . An RF filter for an active implantable medical device (AIMD) for handling high RF power induced in an associated implantable lead from an MRI RF pulsed field at a selected center frequency or range of frequencies, comprising:
 at least one capacitor having a capacitance of between 10 and 20,000 picofarads, a temperature stable dielectric having a dielectric constant of  200  or less, and a temperature coefficient of capacitance (TCC) within the range of plus 400 to minus 7112 parts per million per degree centigrade (ppm/° C.);   wherein the capacitor's dielectric loss tangent in ohms is less than five percent of the capacitor's equivalent series resistance (ESR) at the selected center frequency or range of frequencies; and   wherein the equivalent series resistance is selected such that heat flow away from the capacitor is maximized.   
     
     
         49 . The RF filter of  claim 48 , wherein the capacitor includes at least ten interleaved active and ground electrode plates, the ground electrode plates being conductively connected to an energy dissipating surface (EDS). 
     
     
         50 . The RF filter of  claim 49 , wherein the high frequency energy comprises an MRI frequency-induced current in the implantable lead. 
     
     
         51 . The RF filter of  claim 49 , wherein the selected frequency or range of frequencies comprises an MRI frequency. 
     
     
         52 . The RF filter of  claim 51 , wherein said MRI frequency comprises a range of MRI frequencies. 
     
     
         53 . The RF filter of  claim 51 , wherein said MRI frequency in megahertz is selected from the group of frequencies comprising 42.56 times the static magnetic field strength in Teslas of an MRI scanner. 
     
     
         54 . The RF filter of  claim 48  wherein the capacitor has a capacitance of between 100 and 10,000 picofarads. 
     
     
         55 . The RF filter of  claim 48 , wherein the RF filter comprises a single or multi-element lowpass filter. 
     
     
         56 . The RF filter of  claim 55 , wherein the single or multi-element lowpass filter is electrically coupled with one or more bandstop filters, one or more L-C trap filters, or both, in any order or circuit configuration. 
     
     
         57 . The RF filter of  claim 56 , wherein the lowpass filter, bandstop filter, or L-C trap filter comprises at least one high power handling two-terminal chip capacitor, an MLCC capacitor, a three-terminal feedthrough-type capacitor, a flat-through capacitor, or an X2Y attenuator. 
     
     
         58 . The RF filter of  claim 54 , wherein the multi-element lowpass filter is selected from the group consisting of an L, reverse L, Pi, T, LL, reverse LL, and an n-element filter. 
     
     
         59 . The RF filter of  claim 48 , wherein the high RF power capacitor is disposed at or near a point of the lead's ingress into a housing for the active medical device (AMD), wherein the capacitor is electrically connected in parallel between at least one lead conductor and the AMD housing. 
     
     
         60 . The RF filter of  claim 48 , wherein the RF filter further comprises a bandstop filter connected in series with the lead, and an L-C trap filter connected from the lead electrically in parallel with the AMD housing, wherein the lead is in turn electrically connected to AMD electronic circuits. 
     
     
         61 . The RF filter of  claim 48 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than two ohms. 
     
     
         62 . The RF filter of  claim 48 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than 0.5 ohm. 
     
     
         63 . The RF filter of  claim 48 , wherein the equivalent series resistance at the selected MRI center frequency or range of frequencies is less than 0.1 ohm. 
     
     
         64 . The RF filter of  claim 48 , wherein the capacitance varies no more than plus or minus one percent from minus 55 degrees C. to plus 125 degrees C. 
     
     
         65 . The RF filter of  claim 48 , wherein the capacitor's dielectric loss tangent is less than two ohms at the selected MRI RF frequency or range of frequencies. 
     
     
         66 . The RF filter of  claim 49 , wherein the energy dissipating surface comprises a housing for the AIMD. 
     
     
         67 . The RF filter of  claim 66 , wherein the energy dissipating surface comprises a conductive ferrule conductively attached to both the capacitor ground electrode plates and the AMD housing. 
     
     
         68 . The RF filter of  claim 49 , wherein the ground electrode plates comprise dual electrode plates. 
     
     
         69 . The RF filter of  claim 49 , wherein the active electrode plates comprise dual electrode plates. 
     
     
         70 . The RF filter of  claim 49 , wherein the ground electrode plates comprise triple or n electrode plates. 
     
     
         71 . The RF filter of  claim 49 , wherein said interleaved electrode plates are bounded at one end by a first set of at least one extra ground plate embedded within the dielectric material. 
     
     
         72 . The RF filter of  claim 71 , including a second set of at least one ground plate embedded within the dielectric material and bounding said interleaved electrode plates opposite the first set of ground plates. 
     
     
         73 . The RF filter of  claim 49 , including a plurality of ground electrode plates extending to substantially the periphery of the capacitor, and a high thermal conductivity material for attaching the ground electrode plates to a heat sink, wherein the heat sink comprises a conductive ferrule. 
     
     
         74 . The RF filter of  claim 49 , including a thermal-setting conductive adhesive for conductively connecting the ground electrode plates to the energy dissipating surface, wherein the thermal-setting conductive adhesive includes conductive particles, silver flakes or conductive flakes, conductive rods, tubes, whiskers, fibers, or nano particles, or any combination thereof. 
     
     
         75 . The RF filter of  claim 48 , including a thermally-conductive overlay extending from the conductive ferrule over the top of the capacitor, wherein the thermally-conductive overlay extends across at least a portion of a housing for the active medical device. 
     
     
         76 . The RF filter of  claim 48 , including a hermetic insulator disposed within the conductive ferrule, the hermetic insulator having ground plates conductively coupled to the ferrule. 
     
     
         77 . The RF filter of  claim 48 , including a thermally-conductive liner disposed adjacent to an inside surface of a housing for the active medical device, wherein the thermally-conductive liner comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotrophically Enriched Diamond, Graphene, Gold, Silver, or Platinum. 
     
     
         78 . The RF filter of  claim 67 , including a weld shield associated with the conductive ferrule. 
     
     
         79 . The RF filter of  claim 49 , including a thickened metallization layer disposed about the outside perimeter of the capacitor and conductively coupled to the ground electrode plates, wherein the thickened metallization layer comprises metal bearing glass frits or Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         80 . The RF filter of  claim 48 , including a thermally conductive ceramic disposed within the conductive ferrule between the capacitor and an alumina ceramic insulator. 
     
     
         81 . The RF filter of  claim 67 , including a thermally conductive washer disposed between the capacitor and a hermetic seal insulator disposed within the conductive ferrule, wherein the thermally-conductive washer comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         82 . The RF filter of  claim 67 , wherein the conductive ferrule includes a capture flange for the capacitor, wherein the high thermal conductivity material for attaching the ground electrode plates to the conductive ferrule comprises Aluminum, Aluminum Nitride, Beryllium, Copper, Multiwalled Carbon Nanotube, Isotropically Enriched Diamond, Graphene, Gold, Silver, Platinum, or other materials with thermal conductivity greater than 150 watts per meter Kelvin near 300K. 
     
     
         83 . The RF filter of  claim 49 , including a heat conductive structure affixed to a periphery of the capacitor, wherein the heat conductive structure comprises a plurality of convection fins. 
     
     
         84 . The RF filter of  claim 48 , wherein a housing for the active medical device is filled with a dielectric fluid. 
     
     
         85 . The RF filter of  claim 48 , including at least one secondary capacitor disposed within a housing for the active medical device at a space location from the at least one capacitor, the secondary capacitor associated with electronic components of the active medical device. 
     
     
         86 . The RF filter of  claim 85 , including at least one secondary energy dissipating surface associated with electronic components disposed within the housing for the active medical device.