Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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also absorb infrared (IR) emissions from personnel and equipment to prevent detection by overhead satellites and aircraft. Many of these fire-retardant structures are currently in use in the harsh desert and high mountain environments of Iraq and Afghanistan and are built to be able to handle snow load and high winds with proper anchoring. Tent enclosures are usually constructed from multiple layers of conductive fabric, such as electroless plated silver etched directly on to ripstop nylon fabric. Copper and nickel layers are then plated over the silver along with an outer protective coating for durability. This material provides greater than 90 dB signal attenuation from 10 MHz to 18 GHz. Applications And Considerations Custom-made shielded tents and enclosures can create EMI-quiet environments for situations like product evaluation and testing, electromagnetic susceptibility, and providing secure communications facilities. Portable RF-shielded enclosures are ideal for applications including wireless device development and testing, satellite communications testing and isolation, EMC (electromagnetic compatibility) precompliance, medical and aerospace equipment shielding, cellular and computer forensics, and RFID shielding when needed. Designers of radio devices often need to perform special tests for the RF immunity of parts to be used in a system — tests that must be done in a controlled RF environment or shielded enclosure to prohibit distortion. On a small scale, RF isolation boxes and pouches are now available that make bench-testing procedures convenient and cost-effective, while on the other end of the scale, shielded environments can be made big enough to hold a tractor or even an aircraft. RF signal reduction structures are widely used for command and control operations as well as other applications where strength, weight, collapsibility, and portability are vital to a successful field operation. RF signal-secure portable tent enclosures are purpose-designed for safe communications applications where maximum signal attenuation is required for the flexibility that a freestanding, portable system provides. Portable RF-shielded enclosures are designed to suit a variety of environments. Shelters can be designed to withstand rugged conditions such as 2"/hr of free falling and blowing rain for 30 minutes without intrusion of water into the shelter, 10 lbs/sq.ft. of snow load for 12 hours without damage, steady winds of 55 mph with gusts of up to 65 mph for 30 minutes, temperatures of minus 40˚F to 135˚F, and more than 50 erect/strike cycles without structural damage. These enclosures can also endure blackouts, as they contain interior shelter lights not visible during ingress/egress within 100 meters with the naked eye or within 300 meters with night vision goggles. Considerations when specifying an EMI-proof enclosure include the operational environment, mobility, temperature/humidity, level of attenuation, erection and strike time, transportability, snow load, wind load, moisture permeability, illumination, air- conditioning, type and number of I/O connections, EMI standards, etc. Some materials are available that can withstand explosions and can even be self- healing and sealing to some extent. Custom-required connectors with precision-machined I/O panels and options to suit actual test procedures should be specified to maintain the shielding integrity of the enclosure at the locations of cable penetrations, electronic filters, or shielded cables. Just as the enclosure-shielding design is the last line of defense for radiated EMI control, I/O filtering is the last line of defense for controlling conducted EMI. Higher filter insertion loss levels are often required for military equipment operating in severe electromagnetic environments or mission- critical scenarios. Some designs feature roll-up, drive-through doors with magnetic seals, while other EMI solutions also need to consider shielding effectiveness during the physical entry and exit of an enclosure. Vestibule designs are often employed for walk-in enclosures, since opening the door can degrade immediate shielding effectiveness, resulting in a possible data capture compromise or measurement data corruption. With the addition of a vestibule that is integrated with the enclosure, the shielding environment is kept uncompromised for consistent shielding performance. The vestibule is usually designed with its own separate conductive floor, door, and inner walls apart from the tent itself, which allows maximum isolation for continuous testing or examination. Waveguide ventilation ports, full air conditioning, or a fan and ventilation system also need to be shielded to preserve the EMI-quietness of the structure, while making the environment usable for extended periods in many locations. A double-seal door system, a shielded floor, and a built-in, through-connector panel with filtered power and suitable network connections are also common requirements. LED lighting that does not compromise EMI measurement situations or reduce power and heat issues can also be specified. Technology Electronic Military & Defense Annual Resource, 4th Edition 22