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RF filter on a circuit board for an active medical device (AMD) for handling high RF power induced in an associated implanted lead from an external RF field

  • US 9,764,129 B2
  • Filed: 05/24/2016
  • Issued: 09/19/2017
  • Est. Priority Date: 03/01/2011
  • Status: Active Grant
First Claim
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1. An active implantable medical device (AIMD), comprising:

  • a) a device housing containing electronic circuits for the AIMD, the device housing defining a body fluid side and a device side, wherein the body fluid side is located outside the device housing and the device side is located inside the device housing;

    b) an electrically conductive ferrule sealed in a housing opening in the device housing, the ferrule defining a ferrule opening extending from a ferrule device side to a ferrule body fluid side;

    c) an insulator at least partially residing in the ferrule opening where a first hermetic seal connects the insulator to the ferrule, wherein the insulator extends from an insulator body fluid side to an insulator device side, and wherein at least one insulator passageway extends through the insulator from the insulator device side to the insulator body fluid side;

    d) a conductive pathway disposed in the insulator passageway where a second hermetic seal connects the conductive pathway to the insulator in a non-conductive relation with the ferrule and the device housing, wherein the conductive pathway extends from a conductive pathway body fluid side to a conductive pathway device side;

    e) a circuit board residing inside the device housing;

    f) at least one filter capacitor disposed on the circuit board, the filter capacitor comprising;

    i) a dielectric having a dielectric constant greater than zero up to 200 and a temperature coefficient of capacitance (TCC) within the range of plus 400 to minus 7112 parts per million per degree centigrade (ppm/°

    C.);

    ii) at least two active electrode plates and at least two ground electrode plates interleaved in the dielectric in a capacitive relationship with each other; and

    iii) an active metallization connected to the at least two active electrode plates and a ground metallization connected to the at least two ground electrode plates; and

    g) an active electrical connection material electrically coupling the active metallization of the filter capacitor to the conductive pathway device side; and

    h) a ground electrical connection material electrically coupling the ground metallization of the filter capacitor to the ferrule or the device housing or, to both the ferrule and the device housing,i) wherein the filter capacitor has;

    i) a capacitance of between 10 and 20,000 picofarads,ii) wherein an equivalent series resistance (ESR) is the sum of a dielectric loss plus an ohmic loss, and the capacitor'"'"'s dielectric loss tangent measured in ohms at an MRI RF pulsed frequency or range of frequencies is less than five percent of the capacitor'"'"'s ESR, andiii) wherein the capacitor'"'"'s ESR at the MRI RF pulsed frequency or range of frequencies is greater than zero, but less than 2.0 ohms, andj) wherein the filter capacitor is the first filter capacitor electrically connected to the conductive pathway device side and to the ferrule or the device housing or, to both the ferrule and the device housing.

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