EMC shielding refers to measures for reducing electromagnetic interference between electrical and electronic systems. The goal of EMC shielding is to ensure electromagnetic compatibility. Electromagnetic compatibility means that a device does not emit impermissible electromagnetic interference and at the same time is sufficiently immune to external interference.
EMC shielding is a central topic in electrical engineering, electronics, mechanical engineering, the automotive industry, medical technology and industrial electronics. With increasing integration density, higher switching frequencies and progressive digitalization, the importance of EMC shielding continues to grow.
Technical properties and fundamentals
Electromagnetic interference
Electromagnetic interference is generated by time-varying electric currents and voltages. Typical sources of interference are:
- Switch-mode power supplies
- Frequency converters
- Power electronics
- High-speed digital circuits
- Electric motors and relays
Interference can occur as conducted or field-coupled interference. EMC shielding primarily addresses field-coupled interference.
Operating principle of EMC shielding
EMC shielding is based on three physical effects:
- Reflection of electromagnetic waves
- Absorption of field energy in the shielding material
- Deflection of field lines
The effectiveness of the shielding depends on frequency, field type and material properties. Low-frequency magnetic fields place considerably higher demands on shielding than high-frequency electric fields.
Types of EMC shielding
Electric shielding
Electric shielding serves to reduce electric fields. It is typically realized through conductive materials.
Typical features:
- High electrical conductivity
- Good grounding and contact concepts
- Effective mainly at high frequencies
Electric shielding is comparatively easy to implement but requires continuous conductivity.
Magnetic shielding
Magnetic shielding aims to reduce magnetic fields. It is technically more demanding.
Typical features:
- Materials with high magnetic permeability
- Effect especially in the low-frequency range
- Strong dependence on geometry and material thickness
Magnetic shielding is frequently used in sensitive measurement or control applications.
Combined shielding
In many applications, combined electric and magnetic shielding is required. This is realized through multi-layer systems or composite materials.
The effectiveness results from the overall system, not from individual components.
Materials for EMC shielding
Metals
Metals are the most commonly used shielding materials.
Typical properties:
- High electrical conductivity
- Good reflection of electromagnetic waves
- High mechanical stability
Aluminium, copper and steel are used depending on the frequency range and mechanical requirements.
Conductive plastics
Conductive plastics combine electrical conductivity with low weight.
Typical properties:
- Reduced shielding effectiveness compared to metals
- Good processability
- Integration into enclosures possible
The conductivity is produced by fillers and is material-dependent.
Shielding films and fabrics
Shielding films and metallized fabrics are used when flexible or thin shields are required.
Typical properties:
- Low profile
- Good conformability
- Dependence on contact and surface coverage
These materials are often used in cables, enclosures or sealing systems.
Composite materials
Composite materials combine mechanical stability with shielding effectiveness.
Typical properties:
- Combination of metal and polymer
- Integration of functions
- Application-dependent effectiveness
The design is strongly system-dependent.
Design implementation of EMC shielding
Enclosure shielding
Enclosures form the primary shielding of many devices. Decisive factors are:
- Continuous conductive surfaces
- Minimization of openings
- Electrical connection of all enclosure parts
Gaps, ventilation openings or joints can significantly reduce the shielding effectiveness.
Contacting and grounding
A shield is only effective if it is correctly contacted.
Important aspects are:
- Low-impedance connections
- Avoidance of contact resistances
- Appropriate grounding concepts
Faulty grounding can increase susceptibility to interference.
Cable and interface shielding
Cables and interfaces are frequent weak points of EMC shielding.
Typical measures:
- Shielded cables
- 360-degree contacting of the shield
- Short, low-impedance ground connections
An interrupted shield loses its effectiveness.
Applications and use cases
EMC shielding is mandatory in many areas:
- Industrial electronics
- Automation technology
- Automotive and rail technology
- Medical technology
- Communications technology
- Power electronics
The requirements vary considerably depending on the environment and applicable standards.
Distinction from EMC filter measures
EMC shielding reduces field-coupled interference. EMC filters act on conducted interference. In practice, both measures are combined.
A shield does not replace filtering and vice versa.
Limits of EMC shielding
EMC shielding is subject to technical limits:
- Frequency-dependent effectiveness
- Openings and gaps
- Contacting problems
- Mechanical and thermal restrictions
One hundred percent shielding is technically not achievable.
GOBA Takeaway
EMC shielding is a central element for ensuring the electromagnetic compatibility of technical systems. The effectiveness results from the interplay of material, geometry, contacting and grounding.
Successful EMC shielding requires systematic design from the early development phase. Individual measures without an overall concept frequently fail to deliver the desired result.