Conformity Magazine - December 2008 - (Page 42)

• The broader the frequency coverage, the thicker, heavier and more expensive the absorber will be • The lower the minimum frequency coverage, the thicker and heavier the absorber will be. • Normal incidence performance is better than off-normal performance for most types of absorbers, although they can be designed for off-normal performance. • Millimeter-wave materials are now being developed and used. Physical Performance Guidelines Of equal importance to the material’s electrical performance is its physical performance, which includes environmental characteristics, temperature characteristics, and mechanical properties. Again, a series of questions will help clarify the parameters of major importance: • What is the application environment? Will the absorber be enclosed or subjected to an outdoor environment? • What environmental forces will degrade the absorber? Some examples include salt, water, ozone, oxygen, ultraviolet light, fuels, oils, chemicals, nuclear, and stack gases. • Over what temperature range will the material be subjected and within what thermal range must the material perform? • What mechanical stresses will be placed on the absorber? Examples include vibration, thermal shock, elongation or wind. • What is the expected lifetime of the absorber? For example, missile applications may not require the same degree of physical integrity as a shipboard application. Also consider the following situations: • Elastomeric-type (rubber) absorbers have better environmental resistance than the broadband foam types. These have been successfully used on surface ships for over 40 years. • A variety of elastomers are available to aid in designing for specific environments. Hypalon® and similar elastomers are widely used in naval applications because of superior weather resistance and color fastness. Nitrile is used for fuel and oil resistance. Fluoro-elastomers and silicones have excellent operating temperature range. • Broadband absorption is obtainable with the dual-layer elastomeric absorbers. • Broadband foam materials can be used for external environments; however, steps must be taken to protect the absorber. Open-cell foams can be filled with lowloss plastics to make rigid panels for use outdoors and 2 Conformity DeCember 2008 broadband absorbers can be encapsulated in fiberreinforced plastics to form flexible absorber panels that can be draped over reflectors. • The useful temperature range of most absorber material is –65°F to 250°F. Certain materials are available with higher maximum temperatures. Application Considerations and Guidelines A variety of applications in the field create numerous possible solutions for high-performing microwave absorbing materials. Not one material can be broadly used across a platform of products. For example, an open cell foam absorber, which is considered a broadband type, may be used only in a protective environment or in an encapsulated format and can be specifically designed to an insertion loss of three or 10 GHz. This may be used in an outdoor antenna hat or a test box. Elastomeric type materials are widely used outside in corrosive environments such as naval vessels and maritime applications. The two most notable applications for EMI and RCS reduction exist within the military and commercial electronics industries. Military applications have numerous electronics equipment and radar systems that require sophisticated management and protection against enemy vessels. Because of the complex equipment on naval vessels, problems arise that need to be addressed. The two major problems in military applications are false images from self-reflections and system-to-system interference. Military Today’s military vessels are very complicated and utilize high-tech equipment in their electronics systems. Because of the vast amount of equipment required and the size of the structures, false images or “ghosts” are created with the radar subsystem that are actually reflections of the ship’s own structure. This causes a huge issue by creating the possibility of a weapons system locking onto a target that is actually a ghost image and not an enemy target or vessel. One method used to avoid this detrimental situation is highperforming, specifically tuned elastomeric absorbers. When tuned to the frequency of the radar, this material is bonded to ships’ hulls, masts, stacks, and other structures on the ship. When this type of material is located properly, false images or echoes can be reduced by up to 40db. Because of the large amount of high-tech equipment required on warships and the lack of available space, much of the equipment is spaced close together. Many times a signal or harmonics from one piece of equipment will interfere with equipment in the area. This problem has become increasingly challenging with the powerful broadband jamming equipment being deployed. Constructing absorber barriers can help with this issue. Single frequency, dual-frequency or broadband absorbers will be used depending on the system involved.

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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