The moving part of an electromagnetic device such as a relay, buzzer, or loudspeaker.

电枢：电磁装置的移动部分，如继电器，蜂音器或扬声器。

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Electromagnetic waves or energy passed through the air from one device to the other.

VOA: special.2010.12.08

The power needed to operate the device is sufficiently small that it can get all the juice it needs from stray (or transmitted) electromagnetic radiation or miniature solar collectors.

FORBES: Electronic Devices Packaged in Synthetic Skin