Low ESR Filter Capacitor for AIMD MRI RF Protection
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Solution Overview
Problem
Active implantable medical devices (AIMDs) face significant challenges during magnetic resonance imaging (MRI) procedures due to induced RF energy, leading to overheating and potential tissue damage at the distal tip electrode-to-tissue interface, with existing solutions failing to adequately redirect RF energy and provide effective EMI protection.
Innovation Solution
The development of low equivalent series resistance (ESR) filter capacitors and circuits, specifically designed for AIMDs, which utilize a low dielectric constant material to increase the number of electrode plates, effectively decoupling RF energy from implanted leads and redirecting it to the device housing for safe dissipation, thereby minimizing overheating and protecting sensitive electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional filter capacitors with high dielectric constant materials are used in AIMDs, then the capacitor size can be reduced, but the equivalent series resistance (ESR) increases leading to inadequate RF energy redirection and tissue overheating
Solution Approach 1:
The patent changes the dielectric constant parameter from high (conventional) to low (specifically <1000, preferably <100), which fundamentally alters the capacitor's electrical characteristics. This parameter change reduces the ESR and enables effective RF energy redirection while preventing tissue overheating during MRI procedures
Solution Approach 2:
The low ESR capacitor is pre-configured within the AIMD housing before MRI exposure, establishing a low-impedance pathway that proactively redirects RF energy away from the lead-tissue interface before overheating can occur. This preliminary protective measure ensures safety during subsequent MRI procedures
2Reliability
If the number of electrode plates is increased to reduce ESR, then the capacitor complexity increases, but the RF energy filtering effectiveness improves
Solution Approach 1:
The capacitor is segmented into multiple thin electrode plates stacked in series, where each plate contributes to the overall capacitance while the low dielectric constant material between them minimizes ESR. This segmentation allows achieving low ESR with a compact structure that fits within the AIMD housing
Solution Approach 2:
The patent uses a composite structure combining multiple conductive electrode plates with a low dielectric constant material (such as air, vacuum, or specialized ceramics with k<1000). This composite approach optimizes the balance between capacitance, ESR, and physical size
3Device complexity
If existing filter solutions are used, then the device structure remains simple, but EMI protection during MRI is insufficient leading to potential device malfunction
Solution Approach 1:
The patent converts the harmful RF energy induced during MRI into a beneficial protective mechanism by using the low ESR capacitor to deliberately redirect this energy to the device housing where it can be safely dissipated, preventing it from causing damage at the vulnerable lead-tissue interface
Solution Approach 2:
The low ESR capacitor acts as an intermediary element between the lead conductor and the device housing, providing a controlled pathway for RF energy to pass through to the housing rather than allowing it to accumulate at the tissue interface. This intermediary structure mediates the energy flow to protect sensitive components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly reduces the equivalent series resistance of the capacitors, allowing for efficient redirection of RF energy away from the distal tip electrodes, minimizing tissue overheating and ensuring the safe operation of AIMDs during MRI procedures while protecting sensitive electronics from electromagnetic interference.
Implementation Method 1
A filter capacitor is disposed within the conductive housing on the device side. The filter capacitor includes a dielectric body supporting at least two active electrode plates interleaved with at least two ground electrode plates
Implementation Method 2
The filter capacitor also has a dielectric body with a dielectric constant less than 1000. The filter capacitor is configured for EMI filtering of MRI high RF pulsed power by a low equivalent series resistance (ESR), wherein the ESR is the sum of a dielectric loss plus an ohmic loss
Implementation Method 3
the ESR is the sum of a dielectric loss plus an ohmic loss, wherein the ESR of the filter capacitor at an MRI RF pulsed frequency or range of frequencies is less than 2.0 ohms
Data Source
AI summary
An AIMD includes a conductive housing, an electrically conductive ferrule with an insulator hermetically sealing the ferrule opening. A conductive pathway is hermetically sealed and disposed through the insulator. A filter capacitor is disposed on a circuit board within the housing and has a dielectric body supporting at least two active and two ground electrode plates interleaved, wherein the at least two active electrode plates are electrically connected to the conductive pathway on the device side, and the at least two ground electrode plates are electrically coupled to either the ferrule and/or the conductive housing. The dielectric body has a dielectric constant less than 1000 and a capacitance of between 10 and 20,000 picofarads. The filter capacitor is configured for EMI filtering of MRI high RF pulsed power by a low ESR, wherein the ESR of the filter capacitor at an MRI RF pulsed frequency or range of frequencies is less than 2.0 ohms.