Interconnecting the electrical systems in your aircraft is a crucial part of certification. Aircraft EWIS requirements are mandated by US Federal Aviation Regulations (FAR) Part 25 - Subpart H for all transport type planes. To best avoid the risk of part failure, designers must now consider component design limitations, functionality, and susceptibility. One such important element of electrical wiring interconnect systems is shielding, that of which is used to control the electromagnetic interference characteristics of subsystems and equipment. While shielding is a crucial part of many electrical assemblies, some aircraft wiring will require shielding, while other wires will not. This blog will shed light on the several considerations that will help you determine when you should shield aircraft wiring. To begin, let us understand why we need aircraft shielding for wiring in the first place.
Electromagnetic interference (EMI) is a major concern for many industries. It can disrupt electronic devices, equipment, and systems used in critical aviation applications or military and commercial aircraft. Aircraft wires are especially susceptible to EMI that sources from lightning, solar flares, electrostatic discharge, and other forms of electric current. These EMI disruptions can cause short circuits that result in electrical fires onboard a plane. Thus, having a shield in place can limit the impact of electromagnetic interference on system performance. However, just because shielding is required, one cannot add a shield to every wire used in the aircraft. Several factors must be considered while selecting shielding material, such as how the shielding will affect a wire’s bend radius, weight, and installation/repair time. There are two different methods for protecting an electrical system from EMI with shielding, and we will briefly discuss each below.
Shielding Signal Wires
Signal cables are the key to data integrity in an aircraft as they send signals with low voltage and high speeds. This means that any interference can be detrimental to these sensitive components, leading to them being damaged or altered by external factors such as electrical noise from aircraft equipment. It is always important to protect the internal sections of signal wires to ensure the accuracy of information.
To ensure data is never interrupted by interference, the wires inside a cable must be shielded. This means attaching an outer layer or "screen," which will stop any EMI from getting through while allowing frequency signals to pass unhindered. The decision to shield the individual wires inside a cable is dependent on data rates. Wires transferring high frequencies generate more EMI, so they are more susceptible and should receive additional protection through shielding that can be optimized for their specific needs—the outer layer will act as generalized prevention against outside interference. At the same time, the innermost layer shields the frequencies carried by the internal wires. There are also several benefits of shielding signal wires, such as establishing isolation for the transmitted data of each system. There is a wide range of shielded cables to choose from, so you should have no problem finding one that meets your needs.
Shield Power Wires
Another way of protecting wires from unwanted EMI is by shielding the power wires instead of signal wires. Since there are often less power wires in an aircraft as compared to signal wires, it can be easier to shield them. With the latest trends in power systems, there are several options that provide equipment control through pulse width modulation and wide frequency generation. Each of these has benefits from an EMI perspective, but they also create new challenges for signal wire proximity due to electromagnetic flux (EMF) being generated when there are high-frequency current changes with modulated pulses occurring near signal wires. If this happens, it could impact performance or cause damage over time if EMF is not blocked properly. On the other hand, several benefits of shielding power wires include reducing EMI sources all over the aircraft, reducing noise for sensitive electronic equipment. In addition, power wire shielding provides chafe protection for cables.
Shielding has been an integral part of aircraft design for generations, but it has become even more necessary with modern-day advances in electronics. Many strategies can be used to accomplish the goal of wire protection, and some may provide better performance than others, depending on your specific needs and desired frequencies.
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