Microwave Absorbers: Reducing Cavity Resonances

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  • Author: Andrew Sundsmo

After rigorous and costly design, circuit-board engineers often find that their well-devised circuit board does not operate properly when it is integrated with the shielded cavity or chassis. The resonance in shielded microwave cavities is increasingly the cause of the problem. Such resonance can hinder the performance of the circuit board or the overall performance of the system. Microwave cavities have certain resonant frequencies that oscillate. Microwave-absorbing materials are a demonstrated, viable method for eliminating both simple and complex cavity resonances. The energy can be attenuated when lossy magnetic or dielectric materials are introduced into the cavity.

To address resonance problems during testing, engineers often use either microwave-absorbing elastomers or foam products. Magnetically loaded elastomers are the most commonly used. These thin elastomers are nonconductive, so they will not short the microwave circuit. However, less-expensive dielectrically loaded foam materials despite their thickness and conductivity, can also help safeguard circuit boards. Either approach can eliminate cavity resonances.