Shielding Physics (Schelkunoff Theory)
Understand the mathematical relationships determining Shielding Effectiveness (SE). SE combines Absorption Loss (A), Reflection Loss (R), and correction factors. Use the tool below to calculate Skin Depth (δ), the depth at which RF energy is attenuated by ~63%.
Skin Depth Calculator
Schelkunoff Equations
Where A = Absorption, R = Reflection, B = Re-reflection correction.
Performance Comparison: Skin Depth vs. Frequency
Metal Foils & Adhesive Impedance
While foil thickness (e.g., 1 oz vs 2 oz Copper) defines theoretical performance, the Conductive PSA (Pressure Sensitive Adhesive) is often the weak link. Transfer impedance of the adhesive can create slot antenna effects at frequencies >1 GHz.
Copper (ED)
Standard for high SE. Solderable. Excellent H-field attenuation.
Aluminum (1145)
Cost-effective. Galvanically compatible with Al enclosures. Not solderable.
Adhesive Risk
Acrylic PSA degrades over time. "Embossed" foil (mechanical bite) is preferred for long-term reliability.
Fabrics & Coatings Durability
Flexible shielding materials degrade with handling and environmental exposure. This section analyzes SE degradation over wash cycles and the Percolation Threshold required for conductive paints to function.
SE Degradation (Wash Cycles)
Paint Loading: Percolation Threshold
Galvanic Corrosion Alert
Mixing Silver-plated fabrics with Aluminum enclosures in humid environments creates a high galvanic potential (> 0.85V).
This leads to rapid oxidation of the aluminum and loss of shielding bond.
Recommendation: Use Nickel/Copper (Ni/Cu) gaskets or Monel mesh for aluminum chassis.
Standards & High-Frequency Applications
Comparing test methods (ASTM D4935 vs IEEE 299) and addressing modern challenges like 5G mmWave and HEMP hardening.
| Feature | ASTM D4935 | IEEE 299 |
|---|---|---|
| Target | Planar Materials (Fabric, Plastic) | Full Enclosures / Rooms |
| Frequency | 30 MHz - 1.5 GHz | 9 kHz - 18 GHz (+) |
| Dynamic Range | Limited (~80-100 dB) | High (>120 dB possible) |
HEMP Hardening (MIL-STD-188-125)
High-Altitude Electromagnetic Pulse protection requires handling massive E1 pulse currents without saturation.
- Mu-Metal: Fails (Saturates)
- Steel (1010): Excellent (No Saturation)