Shielding Solutions Provide EM Isolation and Protection

Part of developing an effective EMI/RFI shielding solution is understanding the nature of an electronic design’s radiated or conducted EMI and RFI, and how susceptible the design is to EMI and RFI from other sources. Test equipment to understand the EMI/RFI characteristics of a device under test (DUT) includes an EMI receiver, spectrum analyzer, near-field EM probes, and a line impedance stabilization network (LISN) to isolate a DUT from its own power source (which could be an EMI or RFI source).

Testing typically takes two different forms during the development cycle of an electronic product: pre-compliance testing, which is performed early in the development of a DUT to detect any circuit or system EMI/RFI issues, and testing, which is performed later in the product’s development to meet regulatory compliance requirements for the product’s application area.

The EMC of a design can be determined according to regulations established by national and international standards organizations, such as the Federal Communications Commission (FCC) in the USA, the European Union (EU) in Europe, and the International Special Committee on Radio Interference (ICMC).CISPR) for global coverage.

Standards such as the FCC’s Part 15 regulations for most commercial electronic products and the FCC’s Part 18 rules for industrial-scientific-medical (ISM) electronic equipment are examples of standards that help ensure compatibility and harmonization among electronic devices in everyday life. The number of these electronic products that transmit and receive EM and RF energy continues to grow and requires efficient and effective shielding solutions, whether as small as Faraday cages or as large as full equipment enclosures.

Shielding Covers Everything from Small Enclosures to Room-Size Containers

Shielding solutions range from small, component-sized enclosures to room-sized enclosures, where the element or elements to be shielded and the design strategy determine the type of shielding to be used. The continued miniaturization of electronic designs in portable devices and the increased use of higher wireless frequencies are leading to denser packaged circuits in smaller designs, creating more challenging EMI/RFI shielding challenges.

When PCBs are tested for EMI and RFI and problems arise, layout designers often consider changes to signal paths, even additional circuit layers and ground planes, before adding shielding materials. However, failing to address a minor EMI/RFI issue can lead to a more expensive, enclosure-sized solution.

Shielding solutions include Faraday cages, grounding contacts, gaskets, conductive foam, and conductive adhesives such as epoxy, which allow you to surround a component on six sides (including the PCB ground plane). Shielding is typically applied at the circuit, board, or enclosure level, and costs are minimized by adding shielding as close to the noise source as possible.

Shielding individual components and devices at the circuit level is important in situations where radiation from that device could interact with nearby components on the same circuit. A Faraday cage or shield has long been a way to block EMI and RFI. It surrounds a component or device in an enclosure that prevents EM/RF energy from escaping the device or reaching the device from outside the enclosure.

Lider Technology Inc. Offers a wide range of board-level shielding solutions, such as the CBS Series, based on the Faraday cage. Available in standard sizes from 0.5×0.5” to 12×24”, the two-piece EMI shields consist of a fence and a removable cover (Figure 1).