I. Core Principles: How Materials “Lock” Electromagnetic Waves

1. Reflection Attenuation: Free electrons on the surface of conductive materials (e.g., metals) generate a reverse electromagnetic field under the action of an electromagnetic field, directly reflecting more than 80% of electromagnetic waves, similar to light reflecting off a mirror. High-frequency scenarios (e.g., WiFi, mobile phone signals) mainly rely on this mechanism, requiring materials with high conductivity (e.g., copper, silver).
2. Absorption and Dissipation: Materials with high magnetic permeability or loss characteristics (e.g., ferrites) convert the remaining electromagnetic waves that penetrate the reflection layer into thermal energy, just like a sponge absorbing water. Low-frequency magnetic fields (e.g., electromagnetic radiation from equipment) require such materials for mitigation.
3. Continuous Shielding Principle: Any gap will become a “weak point” for signals. It is necessary to coordinate materials and structures to form an unbroken enclosed space, which is the key to achieving a shielding effectiveness of over 99.9%.

II. Key Material Systems and Selection Guide

(I) Metal-based Shielding Materials: Main Force for High-Frequency Reflection

(II) Flexible Composite Shielding Materials: Protection for Gaps and Irregular Shapes

1. Conductive Cloth/Gaskets: Three-layer structure of polyester fiber cloth plated with nickel-copper, SE 40–60 dB, wear-resistant up to 5 million times. Used for shielding curtains and equipment joints; conductive adhesive must be used during installation to ensure close contact.
2. Conductive Rubber: Silicone rubber added with silver/silver-plated copper particles, SE up to 90–120 dB, with both sealing and moisture-proof functions. Suitable for communication equipment interfaces and gaps in medical instruments.
3. Conductive Coating: Resin carrier mixed with copper/silver particles, forming a 20–25 μm conductive film after spraying. It can turn plastic enclosures into shielding bodies, applicable to civil equipment such as routers and remote controls. The film resistance ≤ 0.025 Ω/m².

(III) Emerging Functional Materials: Breakthroughs in High-End Scenarios

1. Graphene Coating: Sheet resistance < 1 Ω/sq, thickness only in the micron level, with significant lightweight advantages. However, the cost is as high as 3,000 CNY/kg, and it is currently used in precision electronic cabins of spacecraft.
2. Ferrite Bricks and Tiles: Specialized for absorbing low-frequency magnetic fields (30 Hz–100 kHz), often compounded with metal plates to build multi-layer shielding bodies, improving full-frequency band protection capabilities.
3. Metallized Fiber Fabric: Polyester cloth with nickel plating, good air permeability, SE 40–60 dB. It is the core material for shielding curtains in classified meeting rooms and radiation-proof work clothes.

III. Key Technologies for System Protection: Coordination of Materials and Structures

Gap Sealing Treatment

1. Install beryllium copper finger springs or conductive rubber gaskets at door frames and panel joints, with a compression amount ≥ 3 mm to ensure contact resistance < 0.1 Ω.
2. Prioritize laser continuous welding for welding; use silver-filled conductive adhesive for non-welded areas. The overlapping width of joints ≥ 20 mm to form a labyrinth attenuation path.

Shielding Schemes for Special Parts

1. Ventilation Openings: Adopt honeycomb waveguide windows with an aperture ≤ λ/10 (e.g., aperture ≤ 10 mm for 3 GHz) and a length ≥ 3 times the aperture to achieve cut-off attenuation.
2. Cable Interfaces: Install RF filters on all incoming and outgoing lines; use cables with double shielding layers and 360° lap joint; optical cables need metal armoring and terminate in the shielding box.
3. Observation Windows: Double-layer tempered glass with metal wire mesh, light transmittance ≥ 70% and SE ≥ 40 dB, with edges sealed by conductive adhesive strips.

Grounding and System Integration

IV. Material Application Schemes for Typical Scenarios

Classified Computer Rooms (SE ≥ 60 dB)

1. Walls: 0.5 mm galvanized steel sheet welding + inner layer ferrite bricks; lay copper foil grounding grid on the ground.
2. Supporting Facilities: Waveguide ventilation windows + power filters + plug-in type shielding doors (SE ≥ 80 dB).

Internal Shielding of Electronic Equipment

1. PCB Boards: SMT patch foam (nickel-copper coating + solder layer) for grounding and buffering, with heat resistance suitable for reflow soldering processes.
2. Enclosure Gaps: Conductive cloth gaskets or conductive silica gel dispensing molding, resistant to high and low temperatures (-55℃ ~ +125℃).

Personal Privacy Protection

1. Space: Modify existing rooms with conductive coating wallpaper (containing silver particles), and match with shielding curtains to block WiFi signals.
2. Equipment: Mobile phone signal shielding bags adopt an aluminum foil + conductive cloth composite structure, with SE ≥ 50 dB.

V. Effectiveness Evaluation and Common Misunderstandings

Professional Indicators

Typical Misunderstandings

1. Believing that “a single material can shield all frequencies”: Low frequencies require high magnetic permeability materials (permalloy), high frequencies require high conductivity materials (copper), and full-frequency bands require multi-layer composites.
2. Ignoring structural integrity: Due to improper gap treatment, the actual SE of DIY shielding rooms may be less than 20 dB, far lower than the claimed value.
3. Credulously believing in “health care effects”: Electromagnetic shielding only prevents information leakage and has no scientific correlation with the treatment of “electromagnetic radiation sickness”.