There are two main styles of panels used for shielded-room construction: pan-type panels and laminated or cell-type panels. Either style can meet the specified compliance tests. However, AR/Comtest pan-type panels provide several distinct advantages over the laminated type. This application note will discuss the benefits of pan shielding, covering four main aspects: mechanical construction, shielding effectiveness (SE), installation, and durability.
Laminate panels are composed of an insulative substrate, typically wood. Both sides are then covered with zinc-plated steel, as shown in Figure 1.
This method leads to several problems due to the limitations of a compression fit. See Figure 2 for an illustration.
Pan-type panels are composed of a single piece of 2 mm thick plated steel. The edges are precision cut and rolled over to form a U channel, as in Figure 3.
Corners are welded to provide maximum shielding by eliminating any seams. See Figure 4.
The U channel design of pan-type panels provides exceptional strength and stability. The mating of the two panels forms an I-beam style of structural support. See Figure 5.
Structural integrity is an important factor influencing the long-term shielding effectiveness of the chamber. Cell-type compression fittings are susceptible to shear forces that diminish the reliability of the shield seam, as seen in Figure 6. Pan-type design is resistant to any disruption of its shielding effectiveness.
The foremost reason to choose pan-type shielding is the overall advantage provided to shielding effectiveness. For the purpose of this document, shielding effectiveness is defined as the ratio of the magnitude of the incident electric field to the magnitude of electric field on the other side of chamber wall. Put simply, all energy is reflected or absorbed. Undeniably, the weakest SE parts of any chamber are at the seams, penetrations, and doors. Every panel must maintain SE 360° around its edges. Corners are especially prone to poor SE. See Figure 7.
The mating surface area of a pan-type panel is considerably larger than that of a cell-type panel. The folded and welded design assures that the mating surface remains uniformly flat, allowing for a better RF seal. Every seam of an AR/Comtest chamber is 100% sealed and includes double-row shielding gaskets. Corner seams are overlapped, ensuring a tight RF seal. See Figure 8.
Cell-type chamber design is inherently poor at meeting SE requirements. Malformation of the sheet at its edges and corners lowers SE performance. Wadding and copper tape are frequently employed to overcome its failures, as seen in Figure 9. This usually involves disassembly of the panel and multiple attempts to meet the SE requirement, greatly increasing installation time and final acceptance. The assembly of the pan-type panels uses a bolt-up connection that does not penetrate the shield, as it would with a cell-type shield. The pan-type shield also includes a double-row gasket that creates an RF seal on either side of the bolts used.
Cell-type panels require custom cutting, resulting in significant dust and noise. As noted above, re-work is very likely. Because of this, assembly time is multiplied, resulting in multiplied costs. The modular design of pan-type panels allows for a clean and rapid installation. Post-installation SE mitigation is rare. Panels are precision cut and require very little on-site customization.
The preparation of the panels for assembly is also a significant difference between these two types of shield designs. On a cell-type shield, all eight surfaces that make contact with one another need to be cleaned, but the pan-type panels have only two surfaces to clean for reliable electrical continuity. This represents additional time in installation for cell-type shields.
The substrates of laminate panels have differing expansion coefficients and can easily be prone to moisture absorption, causing distortion and reduced SE. If an enclosure needs to be disassembled and moved, cell-type panels will often require replacement. Seams are degraded over time due to corrosion. AR/Comtest panels are plated with state-of the-art materials, resulting in very low oxidation. Their single-piece design maintains its form and durability over time. Re-assembly is as simple as the installation. Panels can simply be reused, with only the gasket material and possibly the hardware needing to be replaced.
|Mechanical construction||Pan-type: one-piece construction, I-beam structural support, precision modular design||Cell-type: compression joints, weak structural reliability|
|Shielding effectiveness||Pan-type: double-row EMI gasket, wide mating surface, fast track to full compliance||Cell-type: poor contact, requires mitigation techniques|
|Installation||Pan-type: precision-cut modules allow for fast and clean installation||Cell-type: requires custom fitting, on-site disruptions|
|Durability||Pan-type: single material and advanced plating reduce corrosion and warpage||Cell-type: composite degradation, sheet malformation, very poor disassembly reliability|