Shielding Vent Window

How to Boost Magnetic Shielding Without Losing Airflow

Low‑frequency magnetic fields are a different animal. High‑frequency RF hits a conductive surface and reflects. Low‑frequency magnetic fields? They just plow through.

Aluminum honeycomb works great for RF. But at 50 Hz, 100 Hz – it's nearly transparent. Standard aluminum honeycomb at 100 Hz might give you 5 dB. That's basically nothing.

If you need to block low‑frequency magnetic fields, you can't just add depth. That kills airflow. You need a smarter approach.

Here's what works.

Switch Materials – From Conductive to Magnetic

Aluminum conducts electricity great. But it's almost non‑magnetic. Low‑frequency magnetic fields travel through magnetic paths, not electrical paths.

So you need high‑permeability materials. Steel. Permalloy. Nickel‑iron alloys.

Steel honeycomb: Cold‑rolled steel gives 60+ dB magnetic shielding at low frequencies. Same thickness, steel beats aluminum by 20‑40 dB.

Tin‑plated steel: At 1‑inch thickness, tin‑plated steel honeycomb gives 80+ dB low‑frequency magnetic attenuation.

Permalloy / nickel‑iron: For extreme requirements. High initial permeability. Outperforms ordinary steel by a wide margin.

These materials redirect magnetic flux lines instead of trying to block them. Aluminum can't do that.

And airflow? Same open area, same depth – steel flows about the same as aluminum. The material changed. The holes didn't.

Optimize Depth‑to‑Opening Ratio – Geometry Over Bulk

Deeper cells give better low‑frequency attenuation. But blindly adding depth chokes airflow.

The key is depth‑to‑opening ratio. Rule of thumb: opening ≤ 3 mm, depth ≥ 3× opening. For low frequencies, go harder – depth at least 5× the opening.

Example: drop cell size from 3.2 mm to 1.6 mm. Push depth to 8 mm or more (5× opening). Low‑frequency magnetic attenuation jumps. Open area barely changes. Airflow stays under control.

The logic: make holes smaller, make them deeper, but don't kill open area. Open area = airflow.

Double‑Layer Offset Honeycomb – More Attenuation Without More Depth

Single‑layer honeycomb has limits. Two thin layers offset from each other – the magnetic field has to travel a longer, twisted path. Attenuation jumps.

A 6.35 mm double‑layer offset honeycomb gives 94 dB at 2 GHz. Single‑layer 12.7 mm gives 96 dB. Half the thickness, similar shielding, much better airflow.

For low‑frequency magnetic attenuation, double‑layer thin structures beat single‑layer thick ones every time. Less airflow restriction, more shielding.

Grounding and Installation – Don't Let Bad Work Ruin Good Design

Best material, best geometry – install it wrong and it leaks.

Ground the frame. The vent frame must bond to the shielded room wall. No paint, no oxide, no gap.

Conductive gasket. Beryllium copper fingers or silver‑filled silicone. Contact pressure: 80‑100 N/m.

Screw spacing. 50 mm or less. Too far apart, the gasket bulges in the middle. Gap = leak.

Torque. Too loose, no contact. Too tight, frame warps. Follow the spec.

These cost nothing but attention. Skip them and your design is wasted.

To improve low‑frequency magnetic attenuation without sacrificing airflow, the core strategy is simple:

Use magnetic materials to redirect flux. Use geometry to lengthen the path. Don't just stack depth.

That's what we do.