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Fiber optic technology transformed how data is transferred, making the switch from electric current to light. Fiber optic technology encodes information in light which allows for longer transmission distances with less signal loss and faster transfer rates. While fiber optics signals themselves are immune to electromagnetic interference (EMI), the system itself relies heavily on electronics that require proper shielding for the network to function1.
Fiber optic networks rely on standard electronics such as switches, receivers, routers, power supplies and converters to operate. When discussing EMI issues within fiber optic networks, the discussion is centered around protecting this equipment. The environment where fiber optic equipment is set up contains multiple sources of EMI, so the strategy to maintain network integrity is to shield the equipment properly.
More specifically, fiber optic network equipment is often situated near HVAC controllers, electrical substations, transformers, variable frequency drives and industrial automation equipment that all produce interference. Radiated and conducted electromagnetic signals can inadvertently couple with neighboring network equipment, causing malfunction.
Consequences of EMI in Fiber Optic Networks
EMI from nearby equipment can disrupt critical network infrastructure like transceivers and switching interconnects (ICs) which can result in loss of connection and signal instability. EMI also disturbs timing and increases noise output in high-speed fiber equipment which has downstream effects like reduced throughput and higher latency.
In telecom systems like voice over internet protocol (VOIP) or video streaming, EMI interferes as optical signals convert to electrical, resulting in poor audio/visual quality or delays. In fiber transceivers, EMI disrupts modulation accuracy and clock recovery circuits which subsequently leads to synchronization failure.
Solutions for Shielding Fiber Optic Equipment from EMI
The standard approach to reduce the effects of EMI exposure is to surround sensitive electronics within a Faraday cage. The Faraday cage protects circuits by reflecting and absorbing incoming electromagnetic signals, preventing them from penetrating and coupling with the circuitry within the cage. Figure 1 below depicts graphically how the Faraday cage works.
Figure 1: Graphical depiction of a Faraday cage interacting with an incoming electromagnetic wave
For circuits, the housing unit is what attenuates the interference. Classically, housing units were fabricated with aluminum which blocks well over 99.99% of electromagnetic signals; however, due to the weight and cost imposed by using this material, designers switched to housing units made with plastics like ABS and polycarbonate. The issue with these materials is their high electrical insulation, so circuit designers now had to metallize these parts for electromagnetic compliance (EMC).
Electrically Conductive Paint as a Shielding Material
Though conductive foils and meshes are effective materials to block EMI, application is cumbersome and labor intensive. Foils are prone to tearing which creates gaps in the shield where radiation can leak into and out of. A better option that quickly and effectively metallizes plastic parts is electrically conductive paint.
Electrically conductive paint uses metallic filler like graphite, copper, nickel and silver dispersed in common polymer systems like acrylic, polyurethane and epoxy. The paint applies as liquid and cures to a solid plastic finish, conforming to edges and other fine contours of housing interiors. Application effort is minimal; the coating is highly durable and provides attenuation ranging from 20 to 100 dB across a broad frequency range.
MG Chemicals Electrically Conductive Paint
MG Chemicals has developed a full line of electrically conductive paint that effectively shields against EMI. The line comprises acrylic, epoxy and water-based polyurethane products pigmented with highly conductive metal flakes. For plastic housing units situated in controlled environments, the AR series conductive paints are most suitable as they are easy to apply and adhere well to plastics.
The choice of which product to use will depend heavily on what level of shielding is needed within what frequency range. The metal flake used governs the system’s shielding attenuation as is evident from figure 2.
Figure 2: Comparison of different conductive filler with respect to shielding attenuation
While fiber optic signals themselves are immune from the effects of EMI, the supporting infrastructure remains vulnerable when in close proximity to electrical equipment. To mitigate common EMI-related issues such as latency and signal instability, the circuitry that powers fiber optic networks must be surrounded by electrically conductive materials.
Electrically conductive paint provides designers with a clean, simple solution to metallize plastic. The paint is highly durable, cost-effective and conforms to the intricate geometry of housing units. The paint provides attenuation across a wide frequency range and enables design flexibility to reduce cost, weight and complexity.
- Senior, John M.; Jamro, M. Yousif (2009). Optical fiber communications: principles and
practice. Pearson Education, 7–9.
