What Is EMI Shielding? What Does 70 dB Really Mean?

In electronic device design, electromagnetic interference shielding is no longer optional. Whether you are developing smartphones, EV electronics, communication equipment, or industrial control systems, poor shielding can lead to signal instability, noise interference, data loss, and EMC compliance failures.

Yet many engineers still struggle to interpret shielding specifications:

• What does 70 dB shielding effectiveness mean?
• How big is the difference between 60 dB and 90 dB?
• How much EMI shielding does a product actually need?

This guide explains the fundamentals of electromagnetic shielding, how shielding effectiveness is measured, and how to select the right shielding materials for real-world applications.

If you are still unfamiliar with the major categories of shielding materials, start with this article first:
Types of EMI Shielding Materials: Complete Selection Guide

What Is Electromagnetic Shielding?

Electromagnetic shielding refers to the use of conductive or magnetic materials to block, reflect, or absorb electromagnetic waves, preventing interference between electronic systems.

In EMC (Electromagnetic Compatibility) engineering, shielding plays a central role in controlling:

The principle is straightforward:

When electromagnetic waves reach a shielding material, part of the energy is reflected, part is absorbed and dissipated inside the material, and only a small portion passes through.

This is why emi shielding materials are widely used in modern electronics.

Common Electromagnetic Shielding Applications

• Shielding cans above smartphone chipsets
• EMI films behind laptop displays
• Conductive foam gaskets on communication cabinets
• Shielded enclosures and EMC chambers in laboratories
• PCB grounding structures in automotive electronics

For a deeper understanding of conductive foam shielding structures, see:
What Is EMI Foam? A Complete Guide to EMI Foam

How Is Shielding Performance Measured?

The performance of electromagnetic interference shielding is measured using:

Shielding Effectiveness (SE)
Unit: dB (decibel)

dB is a logarithmic unit, not a linear one. This means a small increase in dB can represent a massive improvement in shielding performance.

Shielding Effectiveness Conversion Table

Key Rule to Remember

Every additional 20 dB improves shielding capability by approximately 10×.

That means the difference between 70 dB and 90 dB is not small — it represents roughly 10 times greater attenuation capability.

What Does 70 dB EMI Shielding Mean?

A shielding effectiveness of 70 dB means electromagnetic wave energy is reduced to approximately one ten-millionth of its original strength.

In practice, 70 dB shielding is already sufficient for most commercial and industrial electronic systems.

Typical Shielding Requirements by Industry

So when a supplier claims that a conductive foam gasket provides 70 dB EMI shielding, it already meets the requirements of many automotive and communication systems.

However, there is one important detail:

Shielding effectiveness changes with frequency.

A material may perform extremely well at 100 MHz but degrade significantly at 5 GHz. This is why professional suppliers provide full shielding effectiveness curves rather than a single data point.

For high-frequency design considerations, you may also reference:
EMI RFI Shielding Materials: Avoid 4 Costly 5G Mistakes

Key Factors That Affect EMI Shielding Performance

Shielding effectiveness depends on far more than the material itself.

1. Material Conductivity

Higher conductivity generally delivers better shielding performance.

This is why gold-plated conductive foam usually performs better and more consistently than standard nickel-plated materials.

2. Contact Quality

Even tiny gaps can become EMI leakage paths.

This is one reason conductive foam gaskets are often more reliable than flat conductive fabrics — their elasticity compensates for uneven surfaces and maintains stable contact pressure.

3. Compression Ratio

For elastic shielding materials such as conductive foam, compression directly affects shielding performance.

Recommended compression ratio:

• Typically 25%–30%

Too little compression causes poor electrical contact.
Too much compression may permanently damage the material.

4. Frequency Range

Different materials behave differently across frequency bands.

For example:

• Copper foil performs exceptionally well at lower frequencies
• Absorber materials are often more effective in high-frequency 5G applications

How to Choose the Right EMI Shielding Material

Once you understand shielding effectiveness, material selection becomes much easier.

Scenario 1: Cost-Sensitive Consumer Electronics

Recommended:

• Standard FOF conductive foam
• Conductive fabric

Typical shielding:

• 60–70 dB

Best for:

• Smartphones
• Tablets
• Consumer electronics

Scenario 2: Automated PCB Assembly

Recommended:

• SMT conductive foam gaskets

Advantages:

• Reflow soldering compatible
• Automated placement
• Stable grounding performance
• Shielding effectiveness ≥75 dB

Learn more here:
What Is an SMT EMI Shielding Gasket?

Scenario 3: High-Frequency 5G Applications

Recommended:

• Hybrid designs combining absorber materials and conductive foam

Key consideration:

• Full-frequency shielding curve performance

Scenario 4: Harsh Automotive or Aerospace Environments

Recommended:

• Gold-plated conductive foam
• Conductive silicone rubber

Advantages:

• 90+ dB shielding
• High-temperature resistance
• Salt spray resistance
• Vibration durability

FAQ

Q1: Is electromagnetic shielding the same as soundproofing?

No.

Electromagnetic shielding blocks electromagnetic waves, while soundproofing controls acoustic waves. The materials and engineering principles are completely different.

Q2: What is the difference between a shielding room and a shielding box?

• A shielding room is typically used for full-system EMC testing
• A shielding box is a compact enclosure for module-level testing

Both use conductive enclosures to isolate electromagnetic interference.

Q3: What is the best EMI shielding material?

There is no universal “best” material.

Each option involves trade-offs between:

• Shielding effectiveness
• Mechanical flexibility
• Assembly process
• Cost

Copper foil provides extremely high shielding but lacks elasticity. Conductive foam offers cushioning and gap filling but slightly lower peak shielding performance.

Q4: Are electric field shielding and magnetic field shielding the same?

No.

The physical mechanisms are completely different.

About Konlida

Founded in 2006, Konlida Precision Electronics is a leading manufacturer of EMI shielding and thermal management solutions.

Our conductive foam products achieve shielding effectiveness exceeding 90 dB and are widely used in consumer electronics, automotive electronics, communication systems, and medical devices.

Konlida operates advanced EMC laboratories capable of providing complete 30 MHz–3 GHz shielding effectiveness curves, helping engineers evaluate real-world material performance instead of relying on isolated peak values alone.