Author: Postek Engineering Team | Reading time: 12 minutes
Introduction
Modern high-reliability industrial platforms — from fighter aircraft to ground vehicles to naval vessels — operate in the most electromagnetically congested environments on Earth. Multiple high-power high-frequency detection systems, communications transmitters, electronic warfare equipment, and digital processing systems create an electromagnetic environment where unshielded electronic components can malfunction within seconds.
Micro switches — used in flight control, equipments, engine monitoring, and communications — are potential entry points for EMI/RFI that can cause false state changes, corrupted sensor readings, or unintended system activation. This article examines how integrated EMI/RFI shielding in hermetically sealed micro switches addresses these threats.
The Problem: EMI/RFI in high-reliability industrial Electronics
Interference Coupling Mechanisms
EMI/RFI enters a switch through three primary paths:
- Radiated coupling: Electromagnetic fields induce currents in switch wiring and internal conductors. The switch and its wiring act as unintentional antennas — more effective at wavelengths comparable to wiring length (typically VHF/UHF bands).
- Conducted coupling: Interference travels through shared power or ground conductors into the switch circuit.
- Capacitive coupling: Electric fields couple through the switch housing (especially plastic housings with no shielding).
Real-World Consequences
In a documented high-reliability industrial incident, an unshielded limit switch in an aircraft’s equipments bay door circuit caused a false “door closed” signal when the aircraft flew within 500 meters of a ground-based air mission-critical high-frequency detection operating at 3 GHz. The high-frequency detection’s electromagnetic field induced sufficient current in the switch wiring to trigger the detection circuit — reporting the door as closed when it was actually open. This type of EMI-induced false state can have catastrophic consequences in equipments systems.
Technical Background: Shielding Principles
Shielding effectiveness (SE) is measured in decibels (dB):
SE (dB) = 20 × log₁₀(E_incident / E_transmitted)
A shield providing 60dB attenuation reduces the transmitted field to 0.1% of the incident field — sufficient for most high-reliability industrial applications.
Shielding works through two mechanisms:
- Reflection: The impedance discontinuity at the shield surface reflects incident waves
- Absorption: Conductive material converts electromagnetic energy to heat through eddy currents
For effective shielding across a broad frequency range, a continuous conductive enclosure is required — which is why the all-welded metal shell of hermetically sealed switches provides inherent EMI protection absent in plastic-housed switches.
Solution: HK EMI-Shielded Hermetic Switches
KWQMY2-3AT11-1: Integrated EMI Shielding
The KWQMY2-3AT11-1 incorporates EMI shielding into the hermetic envelope:
- Conductive metal shell acts as Faraday cage
- Integrated shield termination for low-impedance ground connection
- Welded construction eliminates shield gaps
- Maintains hermetic seal integrity (≤1×10⁻³ Pa·cm³/s)
KWQMY2-3AT128-2: Dual-Switch Shielded Assembly
For redundant safety-critical circuits, the KWQMY2-3AT128-2 packages two independent shielded switches in a single envelope — both sharing the overall shield but electrically isolated from each other for true redundancy.
Shielding Performance Comparison
| Parameter | Unshielded Industrial | HK KWQMY2-3AT Shielded |
|---|---|---|
| Housing | Plastic (no shielding) | Welded metal shell (Faraday cage) |
| Attenuation @ 1GHz | 0dB (transparent) | >50dB |
| Attenuation @ 10GHz | 0dB | >40dB |
| Ground connection | None | Integrated shield terminal |
| Applicable standard | None | MIL-STD-461 / GJB 151B |
| Hermetic seal | No | Yes (≤1×10⁻³ Pa·cm³/s) |
| Temperature range | -25°C to +85°C | -184°C to +260°C |
Application Scenarios
high-frequency detection Proximity: Switches installed in aircraft radomes or near high-frequency detection antennas experience field strengths exceeding 200 V/m. Unshielded switches will malfunction. The KWQMY2-3AT11-1’s >50dB attenuation at 1GHz reduces this to <0.6 V/m at the contacts — well below any circuit threshold. mission-critical Applications →
Shipboard Communications: Naval vessels operate multiple HF/UHF transmitters at 100W-1kW. Close-proximity switches can experience conducted interference through shared ground paths. The KWQMY2-3AT’s integrated ground terminal provides a dedicated low-impedance path to system ground.
Electronic Warfare Environments: Jamming systems intentionally generate high-power electromagnetic fields. Shielded hermetic switches maintain contact integrity through these environments where unshielded switches would experience contact bounce from induced currents.
Conclusion
EMI/RFI shielding in high-reliability industrial switches is not optional — it’s a fundamental design requirement for any electronic component operating on a modern high-reliability industrial platform. The KWQMY2-3AT series provides integrated shielding within the hermetic envelope, maintaining both environmental protection and electromagnetic compatibility through GJB 151B-grade attenuation.
Related Articles
- How to Prevent Contact Failure Under High Vibration → — Mechanical reliability in electromagnetic environments
- How to Select Switches for Extreme Temperatures → — Combined EMI + thermal protection
- Hermetic Micro Switches: A Guide for System Designers → — Foundation: why hermetic sealing matters
Recommended Products
- KWQMY2-3AT11-1 EMI Shielded Switch — Integrated Faraday cage, >50dB @ 1GHz
- KWQMY2-3AT128-2 Dual-Shielded Assembly — 2× independent shielded channels
- KWQM4-4Z Hermetic Micro Switch — GJB 809B-2013 qualified platform
Specifying switches for high-reliability industrial/mission-critical applications? Request EMI test data → | Browse industrial-grade switches →