As the operating frequency becomes much higher the electromagnetic interference turns to the critical issue in the metal cases of electronic devices. The electromagnetic wave absorber has been mounted on the cases in order to suppress the interference. Authors measured the attenuation of the electromagnetic wave in the waveguides simulating the metal case, lined with the synthetic rubber absorber, 0.5 to 3mm in thickness, bearing Fe-7Cr-9Al soft-magnetic powder, 15 micrometer in diameter and 8 to 40% in volume. The reflection losses of the rubber absorbers were also measured and compared with the attenuation. In 10 GHz, the both losses reach maximum at the 25% and 1.5/1.7mm thick sheet. However, the attenuation and reflection losses show different characteristics in 22GHz. In 22GHz, although the reflection loss reach maximum at the 12 vol.% and 1.1mm thick sheet, the maximum attenuation is at the 20 vol.% and 1.1mm thick sheet. In 25GHz, although the reflection loss reach maximum at the 23 vol.% and 0.7mm thick sheet, but the maximum attenuation is at the 35 vol.% and 0.7mm thick sheet. The results imply the design of the absorber should be based on the fine and delicate analysis of the suppression of the interference in the metal cases.
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