EMI, EMC, and Shielding Advanced EMC Topics Informational

How do I design a shielded room for RF testing that meets a specific shielding effectiveness requirement?

Designing a shielded room for RF testing that meets a specific shielding effectiveness (SE) requirement involves: selecting the wall material and construction (for SE > 60 dB from 10 kHz to 18 GHz: use welded steel panels, 2-3 mm thick, with continuous welded seams; for SE > 80 dB: use double-wall construction with an air gap between two layers of welded steel, or clad steel panels with copper or aluminum inner surfaces for high-frequency performance; for SE > 100 dB: use specialized construction with multiple shielded layers and isolated internal ground systems), designing the door (the most critical element: the door must maintain the same SE as the walls when closed; RF shielded doors use: beryllium copper or stainless steel finger stock gaskets around the entire door perimeter, knife-edge contact surfaces for high-frequency sealing, pneumatic or mechanical clamping to maintain consistent pressure on the gaskets, and single-point or multi-point door closure mechanisms), managing penetrations (every cable, pipe, ventilation duct, and utility that passes through the shield wall is a potential leakage path: power lines use power line filters rated for the required SE; signal cables use filtered connectors or waveguide-below-cutoff feedthroughs; ventilation uses honeycomb waveguide-below-cutoff panels; water pipes use isolated sections with waveguide-below-cutoff bypass), and verifying the SE after construction (using IEEE 299 or MIL-STD-285 test procedures: a transmit antenna outside the room and a receive antenna inside measure the shielding at multiple frequencies and locations).

Category: EMI, EMC, and Shielding

Updated: April 2026

Product Tie-In: Shielding, Gaskets, Absorbers, Filters

RF Shielded Room Design and Construction

Shielded rooms (also called Faraday cages or screen rooms) are essential for EMC testing, RF calibration, sensitive signal measurement, and secure communications (TEMPEST). The design must ensure consistent SE across the entire frequency range and prevent degradation over time.

Construction Methods

Welded steel panels: The standard construction for high-performance shielded rooms (SE > 80 dB). Panels are typically 1.5-3 mm galvanized steel, welded with continuous seams. The floor is a steel plate on a raised support structure. Typical SE: 80-100 dB from 200 MHz to 18 GHz, 60-80 dB below 200 MHz
Modular bolt-together panels: Faster installation, lower cost. Panels connect with conductive gaskets at each seam. SE: 60-80 dB depending on gasket quality and maintenance. Requires re-tightening of bolts periodically to maintain SE
Copper foil on wood frame: The least expensive option. Copper foil or mesh is applied to wooden panels. SE: 40-60 dB. Adequate for general-purpose screening but not for high-performance EMC testing

Shielded Room Design Parameters

Shielding effectiveness: SE = 20 log(E_inc/E_trans) [dB]
Steel panel (2mm, f>1MHz): SE > 100 dB (dominated by absorption loss)
SE components: SE = A + R + B where A=absorption, R=reflection, B=re-reflection
Absorption loss: A = 8.686 × t/delta where delta = skin depth
For steel at 1 GHz: delta = 1.5 um, t = 2 mm: A = 11,600 dB (absorption dominant)

Common Questions

Frequently Asked Questions

What is the typical cost of a shielded room?

Small room (3x3x2.5 m) with SE > 80 dB: approximately $50,000-$150,000 including installation and verification. Medium room (5x5x3 m): approximately $100,000-$300,000. Large anechoic chamber (10x6x6 m) with absorber lining: approximately $500,000-$2,000,000. Modular bolt-together rooms are 30-50% less expensive than welded construction. The door and penetration panel typically account for 30-40% of the total cost.

How do I maintain the SE over time?

SE degrades due to: door gasket wear and contamination (clean and replace finger stock gaskets every 2-5 years), corrosion at panel seams (especially in humid environments; apply conductive sealant or re-weld), loose bolts on modular panels (re-torque annually), and new cable penetrations that are improperly filtered. Annual SE verification testing (per IEEE 299) ensures the room continues to meet its specification.

What frequency has the lowest SE?

SE is typically lowest at low frequencies (10 kHz - 1 MHz) where the skin depth is largest and the reflection loss is lowest. At these frequencies: the SE of a 2 mm steel panel is approximately 60-80 dB (adequate for most applications). For higher SE at low frequencies: use thicker panels, higher-permeability materials (mu-metal for magnetic shielding below 100 kHz), or active cancellation systems. At high frequencies (above 1 GHz): SE is very high (> 100 dB) for intact panels but can be limited by aperture leakage at seams, doors, and penetrations.

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