EMI AND EMC ON RAD

INTRODUCTION

  • Electromagnetics (EM) is a branch of physics or electrical engineering focused on electric and magnetic phenomena.

  • Electromagnetic interference (EMI): Adverse effects on electrical/electronic equipment performance due to electromagnetic energy manifesting as noise.

  • Electromagnetic compatibility (EMC): Ability of electrical/electronic equipment to function without performance degradation in an environment with EMI.

  • Common methods for noise reduction:

    • Proper equipment circuit design

    • Shielding

    • Grounding

    • Filtering

    • Isolation

    • Separation

    • Orientation

    • Noise cancellation techniques

DEFINITION OF EMI & EMC

  • EMI: Degradation in device performance caused by the electromagnetic environment fields.

  • EMC: Achieved when a device operates satisfactorily without causing disturbances in the electromagnetic environment.

BASIC ELEMENTS OF EMI

  • Coupling Mechanism:

    • Source (Emitter/Culprit)

    • Coupling (Path/Medium)

    • Receiver (Receptor/Victim)

  • Interference occurs when received energy causes unwanted receptor function.

  • Receiver performance depends on the coupling path, source, and victim.

  • The goal is to minimize medium efficiency to reduce interference.

RADIATED INTERFERENCE

  • Narrowband interference: High-frequency interference from intentional transmissions (e.g., radio/TV stations).

    • Example: Proximity effect

  • Broadband interference: Low-frequency interference from incidental sources (e.g., power lines, motors).

    • Example: Skin effect

CONDUCTED INTERFERENCE

  • Caused by physical contact of conductors (conducted electromagnetic interference).

  • Disturbances in the EM field radiate away from the conductor surface.

  • Mutual inductance can lead to EMI between radiated electromagnetic fields.

EMITTERS/RECEIVERS & EFFECTS OF EMI

  • Intra-system EMI: Caused by components like power supplies, mobile radios, etc.

  • Inter-system EMI: Includes sources such as lightning, computers, and TV sets.

  • Effects of EMI:

    • Disturbance in TV/radio reception

    • Computer reset/loss of data

    • Change in control equipment settings

    • Pacemaker failure due to interference

    • Malfunctioning flight systems from passenger devices

    • Potential biological hazards

SOURCES OF EMI

  • Natural Sources: e.g., Lightning

  • Manmade Sources: e.g., Commercial radio/telephone communications

  • Functional EMI: From devices designed to generate electromagnetic energy.

  • Incidental EMI: From unintended sources causing interference.

  • Natural EMI: Caused by natural events (e.g., electrical storms).

EMI CONTROL TECHNIQUES

  • Three common techniques for EMI control:

    • Grounding

    • Shielding

    • Filtering

GROUNDING

  • Establishes an electrically conductive path between points to connect system elements.

  • Ideal ground: Zero-potential, zero-impedance reference for signals.

  • Bonding: Low-impedance path between metal surfaces, protects against shocks, provides return paths for current.

SHIELDING

  • Purpose: Confine radiated energy or prevent it from entering an area.

  • Types of shields: Solid, nonsolid (screens), and braid shields on cables.

  • Shielding Effectiveness (SE): Measure defined as SE = 10 log(incident power density / transmitted power density).

FILTERING

  • Electrical filter network consisting of resistors, inductors, and capacitors that controls frequency passage.

  • Reduces levels of conducted interference.

  • Insertion Loss (IL): Defined as IL = 20 log(V2/V1), comparing output voltages with and without the filter.

ELECTROMAGNETIC COMPATIBILITY (EMC)

  • Studies unintentional generation, propagation, and reception of electromagnetic energy.

  • Goal of EMC: Ensure correct operation of various equipment without interference.

  • A system is EMC compliant if:

    • It doesn't introduce interference to other systems.

    • It's not susceptible to emissions from others.

    • It doesn't interfere with itself.

METHODOLOGIES TO PREVENT EMI

  • Suppress emissions at source: Best method to control EMI.

  • Make coupling paths inefficient.

  • Reduce the receiver's susceptibility to emissions.

COUPLING MECHANISM

  • Noise source, coupling path, and victim arrangement.

    • Source may include electronic devices or natural phenomena.

  • Coupling Mechanisms:

    1. Conductive: Direct contact with conducting body.

    2. Capacitive: Varying electrical fields induce voltage changes.

    3. Inductive: Short distance fields create coupling effects.

    4. Radiative: Occurs over long distances, acting like antennas.

NEED FOR EMC STANDARDS

  • Necessary for co-existence and operational consistency of systems.

  • Manufacturer-user interaction is usually limited, making standards essential.

  • Required to establish harmonized standards for reducing trade barriers and improving product reliability.

EMC STANDARDS

  • Military Standards: Ensure system compatibility in real-time environments, based on MIL-STD 461 and 462.

  • Civilian Standards: Protect broadcast services from interference in commercial applications.

ADVANTAGES OF EMC STANDARDS

  • Increased compatibility, reliability, and maintainability.

  • Provides design safety margins.

  • Ensures satisfactory operation in EMI environments.

  • Enhances product life and profitability.

EMC STANDARDS IN DIFFERENT COUNTRIES

  • International Standards: e.g., CISPR (Europe), FCC (USA), VDE (Germany), ISI (India)

CONCLUSION

  • EMI recognized as a significant practical issue for over 75 years has evolved into a well-researched field.

  • Solutions have advanced beyond trial and error approaches to interdisciplinary methodologies.

  • Continuous research is necessary in areas like interference characterization and measurement techniques.

REFERENCES

  • "EMI Protection for Communication Systems" by Kresimir Malaric.

  • "Elements of Electromagnetics" by Sadiku, 3rd edition.

  • "Applied Electromagnetics and Electromagnetic Compatibility" by Dipak L. Sengupta, Valdis V. Liepa.

  • Relevant online resources including ARRL and Electronics-project-design.com.