RF shielding keeps radio-frequency energy where it belongs. In a modern product that means stopping a Wi-Fi, cellular or radar transmitter from de-sensing its own receivers, keeping processor and clock harmonics out of the antenna, and making sure the finished device passes its radiated-emissions test. The tools are a conductive enclosure, RF shielding gaskets on its seams, RF shield cans over individual circuits, and RF absorbers that soak up energy inside cavities. This guide covers how RF energy escapes, which RF shielding materials to use in each frequency band, and a design checklist you can apply before layout is frozen.
Radio frequencies span roughly 3 kHz to 300 GHz, but in electronics RF shielding usually means the range from tens of megahertz to the millimeter-wave bands used by 5G and automotive radar. RF shielding is a subset of EMI shielding: the physics is the same — a conductive barrier reflects and absorbs electromagnetic energy — but at radio frequencies the size of every gap, the dimensions of every cavity and the continuity of every seam start to matter as much as the material itself. For a side-by-side comparison of the two terms, see EMI shielding vs RF shielding.
At RF, a shield is only as good as its largest opening. A slot whose length approaches half a wavelength radiates almost as efficiently as a deliberate antenna, so designers keep the longest dimension of any aperture or unsealed seam well below that. A widely used rule of thumb is one-twentieth of the wavelength at the highest frequency of concern:
| Frequency | Typical application | Wavelength | Max opening (≈ λ/20) |
|---|---|---|---|
| 900 MHz | Sub-GHz IoT, LoRa, cellular | 333 mm | ≈ 17 mm |
| 2.4 GHz | Wi-Fi, Bluetooth | 125 mm | ≈ 6 mm |
| 5.8 GHz | Wi-Fi 5/6, point-to-point links | 52 mm | ≈ 2.6 mm |
| 28 GHz | 5G millimeter wave | 10.7 mm | ≈ 0.5 mm |
| 77 GHz | Automotive radar | 3.9 mm | ≈ 0.2 mm |
The table shows why a housing that passed at 900 MHz can fail at 5.8 GHz with no design change: the same seam is now a much larger fraction of a wavelength. Continuous RF gaskets — fabric-over-foam, conductive elastomer, knitted wire or oriented wire — close those seams electrically, and fastener spacing should be checked against the same rule.
A closed metal box resonates at frequencies set by its internal dimensions. For a simple rectangular shield can, the first resonance can be estimated from its two largest dimensions; a 30 × 20 mm can, for example, has its first mode close to 9 GHz. If a clock harmonic or radio band lands near that frequency, energy builds up inside the can and couples to everything in it — and adding more metal does not help. The fix is loss: a thin cavity resonance absorber applied to the inside of the lid damps the mode, while narrowband absorbers target a single known problem frequency. Our narrowband vs cavity resonance absorber guide explains how to choose between them.
| Band | Typical sources | Usual problem | Shielding approach |
|---|---|---|---|
| Below ~30 MHz | Power conversion, motor drives, magnetics | Magnetic-field coupling | Layout and filtering first; mu-metal or steel where magnetic shielding is needed |
| 30 MHz – 1 GHz | Clocks, memory buses, sub-GHz radios | Seam leakage and cable radiation | Enclosure gaskets, board-level shields, cable shielding |
| 1 – 6 GHz | Wi-Fi, Bluetooth, GNSS, LTE and 5G FR1 | Apertures and circuit-to-circuit coupling | Multi-cavity shield cans, fabric-over-foam or elastomer gaskets, thin absorbers |
| 24 – 40 GHz | 5G millimeter wave, satcom | Tiny apertures, cavity modes | Tight seams, hybrid or machined shields, cavity absorbers |
| 76 – 81 GHz | Automotive and industrial radar | Reflections and multipath inside the module | Absorbers around the antenna and precision housings |
Most RF shield cans are made from tin-plated steel for indoor products or nickel silver where corrosion resistance is required, typically in thicknesses from 0.2 mm (0.008″) to 0.6 mm (0.025″). Copper is used where the can also helps spread heat; beryllium copper and phosphor bronze where spring features are needed. See PCB shield cans: types, materials & sizes for the full table.
Fabric-over-foam gives low closure force for thin housings; conductive elastomers add an environmental seal for outdoor and aerospace hardware; knitted wire suits durable metal-to-metal joints. Match the gasket filler to the flange finish to avoid galvanic corrosion, which raises contact resistance and erodes shielding over time.
Magnetically loaded elastomer sheets are thin and suit the inside of shield cans and housings; carbon-loaded broadband dielectric foam absorbers cover wider bands where space allows; low-frequency RF absorbers address the lower end of the spectrum. Select by frequency band and loss mechanism, not by thickness alone.
RF shielding is the use of conductive enclosures, shield cans, RF gaskets and absorbers to block or absorb radio-frequency energy so that radios, processors and other RF circuits do not interfere with each other or with outside equipment. It is the radio-frequency part of the broader discipline of EMI shielding.
For shield cans, tin-plated steel is the standard for indoor products and nickel silver for outdoor or military use. Enclosure seams are sealed with RF gaskets such as conductive elastomer, fabric-over-foam or knitted wire. Inside cavities, magnetically loaded elastomer or carbon-loaded foam absorbers damp resonance. The best material depends on the frequency band and the leak path.
A common rule of thumb keeps the longest dimension of any opening below about one-twentieth of the wavelength at the highest frequency of concern. That is roughly 6 mm at 2.4 GHz, 2.6 mm at 5.8 GHz and about 0.5 mm at 28 GHz. A slot approaching half a wavelength radiates almost as well as an antenna.
A closed metal can is a resonant cavity. At certain frequencies set by its dimensions — around 9 GHz for a 30 × 20 mm can — energy builds up inside instead of being contained. A thin microwave absorber on the inside of the lid damps that resonance without redesigning the can.
Yes. 3G Shielding Specialties ships free samples of standard board-level shields, RF gaskets and microwave absorbers within 48 hours, and its US-based engineers typically answer RF shielding questions the same business day.
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