As budgets continue to be scrutinized, design engineers and managers are looking into semi-permanent, temporary or mobile enclosure options including hard-wall relocation, modular units, and soft-sided tent enclosures. Here are five design requirement considerations for fabric-based EMI RF shielded room enclosures:
1. Existing Space: Will an existing structure be used to house an RF EMI shielded test enclosure? If so, custom sized semi-permanent or temporary full enclosures can be configured to meet the test standard and lab size. Design options include floorless, soft-sided RF shielded enclosures where a metal floor already exists or for low level shielding where equipment cannot be moved. When space is tight, a completely collapsible tent enclosure and frame free up needed space when not in use.
2. Design Cycle: How long will the test structure be needed? A week, a month, on-going? The shorter the time frame, a collapsible or semi rigid enclosure may provide needed shielding, easy disassembly, and storage until the next product design cycle. Another option is a semi-rigid or rigid frame which leaves the frame structure in place while the soft-walled RF enclosure is removed and stored. These options allow testing and may provide cost savings including recouped floor space, use at more than one facility and shared use between departments.
3. Shielding Effectiveness: What frequencies will be tested? What shielding effectiveness is needed to complete the testing at those frequencies? This will determine the amount of shielding necessary and can produce cost savings when included in the design specifications. Examples of Shielding Effectiveness (Select Fabricators’ room enclosure design):
- a. Single Layer configuration of floor, door, four sides, roof, and filter box using standard performance AC voltage line filter: -65 to -70 dB average from 150 kHz to 18 GHz
- b. Double Layer configuration of floor, door, four sides, roof, wall mounted I/O plate with high performance AC voltage line filter: -85 to -90 dB average from 150 kHz to 18 GHz
4. Controlling Entry and Exiting: A vestibule keeps the RF integrity of the test setup by controlling access. A larger size vestibule can be used as a control room where test equipment is calibrated. SFi’s double layer, soft-sided EMI shielding enclosure has -85.7 dB minimum shielding effectiveness from 400 MHz to 18 GHz when an internal vestibule design, high performance I/O plate, and AC voltage line filter are used. Most RF shielded enclosures have options for either an internal or external vestibule.
5. Size: Does the entire room need to be shielded? What size are the objects to be tested? What are the space needs for the test setup? A tabletop RF EMI enclosure or wireless RF testing pouch may be helpful for preliminary design testing. At the other end of the range, automotive and aerospace bay area modular RF enclosures can be custom sized as well as meet additional considerations, for example, anechoic foam installation to meet testing standards.
As time and budgets continue to contract, there are a number of new shielded room designs that make in-house shielded room enclosures more affordable. Deciding what is needed and necessary will make justification and sourcing more effective. Next time I’ll discuss design considerations for I/O plates, anechoic foam, and ventilation.
Continue reading EMI / RF Design Considerations – Part 2