Electromagnetic Environment (5.14) Quiz

Electromagnetic Environment (5.14) Learning Objectives

• Understand how to minimize or prevent EMI/RFI from being generated by devices.
• Explain the influence of EMC (electromagnetic compatibility) on maintenance practices for electronic systems (Level 2).
• Explain the influence of EMI (electromagnetic interference) on maintenance practices for electronic systems (Level 2).
• Explain the influence of HIRF (high intensity radiated field) on maintenance practices for electronic systems (Level 2).
• Describe the influence of lightning and lightning protection on maintenance practices for electronic systems (Level 2).

Electromagnetic Interference in Electrical Systems

• Electromagnetic Environment (EME): The totality of electromagnetic phenomena at a given location.
• Electromagnetic Compatibility (EMC): Equipment or systems can operate in their intended operational electromagnetic environment at designed levels of efficiency without degradation due to electromagnetic interference.
• Electromagnetic Interference (EMI): A disturbance that disrupts, obstructs, degrades, or limits the effective performance of electronic or electrical equipment (defined by NATO).
• High-Intensity Radiated Field (HIRF): Man-made sources of electromagnetic radiation generated externally to aircraft.

Avionic Frequency Bands

• Aviation frequency bands span a range from kilohertz to gigahertz.
• VOR (VHF Omnidirectional Range): A radio beacon for point-to-point navigation (108 to 118 MHz).
• Glideslope Systems (328-335 MHz): Used during landings.
• DME (Distance Measuring Equipment): Measures distance; operates above 1 GHz.
• Other systems operate above 1 GHz, including global positioning, collision avoidance, and cockpit weather radar.

Personal Electronic Devices (PEDs)

• PEDs operate at frequencies from 10 kHz to 400 MHz.
• The emitted frequencies from PEDs cover almost the entire range of navigation and communication frequencies on aircraft.
• PEDs are a single class of EMI emitters.
• Shielding of avionics equipment is important to protect against EMI from PEDs.

Electromagnetic Interference (EMI) Permeation

• Inadequate shielding, damaged shielding, or degradation due to corrosion can increase the resistance of the electrical connection to ground, allowing wires to easily pick up interfering signals.
• Aircraft with antennas outside the aircraft skin can pick up EMI through unshielded openings (e.g., passenger windows).

Effects of EMI

• EMI can disrupt sensitive equipment, burn out electric circuits (e.g., cockpit fuel gauge), and can lead to an uncommanded dive or shut down a flight critical avionics system.

Electromagnetic Compatibility (EMC)

• EMC is the ability of equipment to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbances to other electrical devices in that environment

Elements of an EMC Problem

• Source: An electromagnetic phenomenon
• Receptor: A component that cannot properly function due to the electromagnetic phenomenon
• Path: A connection that allows the source to interfere with the receptor

Coupling Path

• EMI is coupled to a receptor through:
• Conducted (electric current)
• Inductively (magnetic field)
• Capacitively (electric field)
• Radiated (electromagnetic field)

Electric and Magnetic Fields

• Electric fields have only one pole, whereas magnetic fields have two poles.
• Electric force travels in straight lines from the center of its origin.
• Electric and magnetic fields combine to create electromagnetic fields at a distance.

Leakage and Antenna Effects of Conductors

• Common usage frequencies (AC supply, audio, radio, TV, mobile phones)
• Devices like mains rectifiers, motor drives, and power converters can emit noise at harmonics of fundamental frequencies.
• Conductors can act as antennas, converting electrical signals into electromagnetic fields and vice-versa.

High-Intensity Radiated Field (HIRF)

• HIRF is a man-made electromagnetic radiation source outside the aircraft.
• Includes radar, high power AM/FM broadcast systems, TV transmitters, airport/weather radars, and surveillance radar.
• HIRF is differentiated from other EMI due to its origin outside the aircraft and its high potential for interference in systems.

EMI Management

• Addressing EMI involves identifying the mechanism of energy transfer (radiation, conduction, induction).
• Options for dealing with radiated EMI include: removing/reducing the source, hardening the target, or separating devices.

EMI Shielding

• Techniques include shielding materials (foil, braided), absorbing interference, and shunting EMI to ground.
• Cable shielding (conductive materials) prevents EMI from reaching conductors or reflects it away.
• Structure shielding (e.g., Faraday cage) uses enclosed conductive materials (like the fuselage) to protect circuits.
• Continuous ground planes on circuit boards reduces EMI and emissions.

Static Discharging

• Static build-up is discharged via low-resistance paths to the atmosphere (e.g., static wick dischargers at wing/tail).
• Preventing static interference protects and minimizes interference to critical avionics equipment.

General Precautions

• Filters (e.g., capacitors) minimize noise from critical components.
• Maintaining clean brushes and commutators on rotating machinery is essential to prevent arcing and interference.
• Safe spacing of electronic components that create or are susceptible to EMI is essential.

Antennas

• Antenna placement impacts EMI.
• Physical separation, directional antennas, limited bandwidth, and suppression techniques control radiated EMI.

Fiber Optics

• Fiber optics are immune to electromagnetic interference.

Test your understanding of the electromagnetic environment and its impact on electronic systems. This quiz covers key concepts such as EMI, EMC, HIRF, and lightning protection, particularly focusing on their implications for maintenance practices. Perfect for students learning about electromagnetic compatibility and interference.