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The increasing threat of Electromagnetic Interference

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Electromagnetic interference (EMI) also called radio-frequency interference (RFI) is a disturbance generated by unwanted electrical signals from electronic devices or natural occurrences which can have harmful effects on equipment. These unwanted signals may reduce the performance of the equipment and can even stop it from functioning. These disturbances can occur in various flight-critical applications including communication and military flight control systems, medical applications, and telecommunications.

Design engineers need a way to filter out the unwanted electrical signal, so it doesn't harm additional components. In order to protect modern electronic systems from the abundance of EMI sources in today’s environments, a combination of approaches are implemented: shielding, filtering, and reduction of EMI at the source (if possible). This blog focuses on filtering methods of the signal.

Design Concepts for EMI filter Connectors:

Sophisticated filter connector technology addresses EMI/RFI filtering, and transient protection to meet demanding high intensity radiated field (HIRF) requirements. EMI filter connectors use multi-layer ceramic capacitor arrays together with inductive materials to realize robust, high performance low pass filter networks. Where required, protection can be provided against high energy transients from direct lightning strikes, standard EMP, high altitude EMP (HEMP), non-nuclear EMP (NNEMP) and electromagnetic interference (EMI).

Advantages of EMI Filter Connectors:

  • A single capacitor array can provide multiple capacitance values
  • Most space efficient method of packaging EMI/RFI and EMP transient protection
  • Connector shell protects capacitor array & diodes from environmental, mechanical and thermal damage
  • Transient voltage suppressors integrated into the connector offer EMP transient protection to sensitive circuitry
  • System weight is reduced by integrating the filters and diodes into the connector
  • Modular design techniques reduce the overall package size and improve maintainability
  • ​Monolithic capacitor arrays are the most reliable method of EMI/RFI filtering
  • Tested and documented using automatic test equipment
  • Plug and go solution

 

Tubular Capacitors Chip Capacitors Planar Capacitor Array
  • Capacitor takes the form of a cylinder with axial leads
  • Tubular capacitors were the first to be incorporated into EMI filters
  • Not available in higher capacitance values
  • Can fail quickly in extreme shock and vibration environments
  • Cannot withstand higher voltages due to wall thickness
  • Tubular capacitors still have a significant market share, but are being phased out
  • These capacitors mount on the surface of the PCB
  • Much greater range of capacitance values compared to tubular capacitors
  • Can be removed and replaced from the PCB to modify the capacitor value with minimal cost
  • Less susceptible to shock and vibration compared to tubular capacitors
  • Has a resonance frequency of 120 MHz, may be problematic for some applications
  • Low cost and easily to source
  • This capacitor is constructed out of a ceramic disk
  • Disk can contain different capacitor values for each pin, unfiltered (feed through) pins, and ground pins
  • Best technology to use in high shock and vibration environments
  • Lowest rate of failure
  • No resonance frequency
  • Can handle up to 1000 VDC working voltage

Transient Protection using Surface Mount Technology (SMT) Diodes:

Where required, transient suppression can be combined with EMI/RFI filtering to provide maximum protection. Transients are temporary spikes or surges in voltage that can impact components or circuits to the point of failure.  Transient protection solutions can be embedded within the filter connector shell by utilizing SMT diodes. The incorporation of SMT diodes can offer space and weight savings to a varying degree dependent on connector application requirements.

Advantages of Surface Mount Technology (SMT) Diodes:

  • Significant reduction in board space and connector weight
  • Low incremental surge resistance
  • Fast response time, typically less than 1.0ps
  • Low Zener diode impedance values
  • Better thermal conductivity for high power dissipation requirements
  • Increased flexibility in design limits
  • Increased mean time between failures (MTBF)
  • Improved shock and vibration resistance

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