Conformity Magazine - December 2008 - (Page 40)

Product Focus Microwave Absorbers Common Uses and a Comparison by Scott Stephan, Laird Technologies s the performance and speed of today’s electronic devices increase, so does the emitted frequency. Standard shielding materials such as finger stock, fabric-over-foam, and board-level shields work well at lower frequencies, but become less effective at increased speeds. Today, more and more manufacturers are using microwave absorbing materials to enhance shielding performance at higher frequencies. Microwave absorbers are specifically designed to attenuate or absorb microwave energy, address frequencies from 500 MHz to 77 GHz, and act as coatings with modified electrical or magnetic properties that allow absorption of microwave energy at discrete or broadband frequencies. Absorbers are used for radar cross section (RCS) reduction, electromagnetic interference (EMI) reduction, suppression of surface waves, and transmission line applications, as well as carbon dielectric foam absorbers for radome lining and antenna side lobe reduction. The two main applications for microwave absorbing materials are EMI and RCS reduction in military and commercial electronics, such as high-frequency consumer electronics, notebook computers, wireless LAN devices, network servers and switches, wireless antenna systems, and cellular phone base stations. Material Selection A wide variety of absorber materials are utilized in EMI and RCS reduction. To optimize their use in a design, three sets of 0 Conformity DeCember 2008 A parameters should be critically analyzed: electrical, physical, and application. For optimal absorber use, the following questions should be asked: • What frequency bands need coverage? • Is coverage needed over the entire region or just at specific frequencies? For example, if coverage cannot be achieved over the entire two to 18 GHz region, will absorption at specific frequencies provide enough protection? • What is the order of importance in coverage? Perhaps at F0, 20 dB absorption is needed; however, only 12 dB is needed at F1 and 7 dB is acceptable at F2. By setting these priorities, a design can be more easily reached. • Will the absorber be used to absorb specular energy, or is the application at such high angles of incidence radiation that surface waves must be attenuated? By answering these questions, the various tradeoffs in electrical performance can be examined, and an optimum absorber solution derived. Electrical Performance Guidelines In addition, it is also important to keep the following guidelines in mind when evaluating the electrical performance of various absorber materials:

Table of Contents Feed for the Digital Edition of Conformity Magazine - December 2008

Conformity Magazine - December 2008 Contents Editor's Note FCC Warns Regulatory Fee Payers About Potential "Phishing" Commission Prowls the Web to Enforce Its Regulations First DTV Rollout Initiated in Wilmington, NC New Standards List Released for the EU's Directive on the Safety of Toys ESD Association Call for Papers ESDA. JEDEC Announce Standards Development Cooperation Commission Releases Data on Local Telephone Competition The Future of ESD Testing ESD Open Forum Emerging Issues in Standards: China RoHS: One Year and Counting Challenges in Testing: Revisiting 10-Meter and 3-Meter Radiated Emission Measurements Design Fundamentals: Meeting the Shielding Challenges of Injection-Molded Plastics Focus On...Microwave Absorbers Buyer's Guide FDA Recalls Automated External Defibrillators FDA Revises Guidance on Medical Device Tracking Guidance Document Safety of Passive Implants Released FDA Offers Guidance on Marketing Diagnostic Ultrasound Systems EU Commission Issues Correction on Machinery Directive Standards Other CPSC Actions in the News Product Reviews IEC Standards Update UL Standards Update Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - December 2008

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