EMI Shield with Dielectric Layer for Implantable Devices
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Solution Overview
Problem
Implantable medical devices, such as cardiac stimulus devices, face challenges in mitigating the effects of electromagnetic interference (EMI) from various sources, including self-generated noise and external electrical devices, which can lead to nonlinear electrical conduction issues like corona discharge, affecting the operation of internal circuitry.
Innovation Solution
An implantable medical device design featuring an EMI shield with an inner conductive layer coupled to a reference voltage and an outer conductive layer exposed to the interior of the housing, separated by a dielectric layer, to prevent air gaps from causing corona discharge, using conductive metals like silver or copper and incorporating metallized tape to eliminate voltage across air gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an EMI shield is used to block electromagnetic interference, then shielding effectiveness is improved, but air gaps between the shield and housing can cause corona discharge
Solution Approach 1:
A conductive adhesive layer is introduced as an intermediary between the EMI shield and the housing interior. This adhesive layer eliminates air gaps while maintaining electrical conductivity, thereby preventing corona discharge. The adhesive serves as a mediator that simultaneously provides mechanical bonding and electrical continuity, resolving the contradiction between achieving effective EMI shielding and avoiding corona discharge hazards.
2Reliability
If the outer conductive layer is exposed to the interior of the housing, then corona discharge is prevented, but electrical connection to the housing is required
Solution Approach 1:
The mechanical attachment function and electrical connection function are merged into a single conductive adhesive layer. This adhesive simultaneously bonds the EMI shield to the housing and provides the necessary electrical connection to eliminate air gaps and prevent corona discharge. By combining these two functions into one element, the design avoids additional complexity while achieving reliable corona discharge prevention.
3Power
If large voltage pulses are delivered for defibrillation, then therapeutic effect is achieved, but nonlinear electrical conduction and system resets occur
Solution Approach 1:
The conductive adhesive layer acts as a preventive measure that cushions against the harmful effects of high voltage pulses before they can cause damage. By eliminating air gaps in advance, the design prevents corona discharge and nonlinear electrical conduction that would otherwise occur during defibrillation pulse delivery. This prior cushioning ensures system reliability is maintained even when delivering high power therapeutic pulses.
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
The solution effectively reduces corona discharges and minimizes system resets during high voltage pulse delivery, maintaining linear response and reducing current spikes, thereby enhancing the reliability and performance of implantable medical devices.
Implementation Method 1
The inner and outer conductive layers, which may be formed of conductive metals, for example, silver or copper, are separated by a dielectric layer
Implementation Method 2
By exposing the outer conductive layer to contact with the interior of the housing, air gaps between the outer conductive layer and the housing are prevented from becoming sources for nonlinear electrical conduction such as corona discharge
Data Source
AI summary
EMI shields for use in implantable medical devices that include inner and outer metal layers separated by a dielectric layer. When assembled as medical devices, the outer metal layer of an illustrative EMI shield is placed into electrical contact with a conductive inner surface of an associated canister for an implantable medical device.