Aviation Electronics Card Lightning Protection via Shield Capacitance
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Solution Overview
Problem
Electronic equipment in aircraft faces challenges from increasing indirect lightning effects and electromagnetic radiation due to non-conductive fuselage materials, requiring effective protection without using bulky and expensive surge-suppressing components.
Innovation Solution
The electronics card features a stack of printed circuit layers with conductive tracks and two electromagnetic shields, comprising a grid and a plate, connected to mechanical and electrical grounds respectively, forming a voltage divider to reduce voltage during lightning strikes and minimizing capacitance to reduce electromagnetic radiation emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional surge-suppressing peak-clipping diode circuits are used to protect against lightning, then protection reliability is improved, but device complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the bulky protective circuits based on surge-suppressing peak-clipping diodes by utilizing the inherent capacitance properties of the electromagnetic shields and stray capacitances to form a voltage divider, thereby achieving protection without additional complex components
Solution Approach 2:
The electromagnetic shields and stray capacitances within the card structure itself are utilized to form the voltage divider, allowing the card to protect itself against lightning without requiring external protective components
2Object-generated harmful factors
If ground planes are connected to mechanical ground to discharge electrical charge, then electromagnetic radiation emission is reduced, but voltage during lightning strikes increases
Solution Approach 1:
The invention changes the electrical parameters of the ground connection by introducing a capacitive coupling instead of direct connection, allowing the system to maintain low electromagnetic radiation while limiting voltage during lightning strikes through the voltage divider effect
Solution Approach 2:
The electromagnetic shields with controlled capacitance act as an intermediary between the internal circuit ground and the external mechanical ground, mediating the trade-off between electromagnetic radiation control and lightning voltage protection
3Weight of moving object
If fuselage uses non-conductive materials for weight reduction, then weight is reduced, but Faraday cage protection against lightning is weakened
Solution Approach 1:
The invention converts the harmful indirect lightning effects that penetrate through non-conductive fuselage materials into a manageable voltage condition by using the capacitance-based voltage divider to reduce the voltage applied to sensitive circuits
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 configuration effectively reduces the voltage applied to input/output connections during lightning strikes, allowing the use of lower-performance components for protection while maintaining reliability and minimizing electromagnetic interference.
Implementation Method 1
reducing the capacitance of the capacitor formed by the electromagnetic shields for protecting the card against external electromagnetic radiation and for creating stray capacitances within the card
Implementation Method 2
the voltage divider constituted by the plane capacitor formed by the grids and the stray capacitances formed between the printed circuit layers reduces the voltage to which the printed circuits and the input/output connection of the card are subjected
Implementation Method 3
two electromagnetic shields extending respectively over a top face and over a bottom face of the stack... designed to be connected to the mechanical ground of the device in which the card is mounted in order to form a shield against external electromagnetic radiation
Data Source
Figure 1~2
AI summary
An electronics card comprising a stack (9) of printed circuit layers (10), each comprising an electrically insulating support (12) having at least one conductive track (11) extending thereon, and two electromagnetic shields (13) extending respectively over a top face and over a bottom face of the stack, each shield comprising a grid (14) and a plate (16) that are superposed and electrically conductive, each extending over an electrically insulating support (15, 17), and the conductive tracks being obtained by solid copper type etching. The invention also provides a device including such a card, and a method of protecting such a card of such a device against a lightning strike and against electromagnetic radiation.