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Going Beyond Chu's Limit: ULF Radiation with Directly Modulated Spinning Magnet Arrays

  • Author(s): Mysore Nagaraja, Srinivas Prasad
  • Advisor(s): Wang, Yuanxun Ethan
  • et al.
Abstract

The frequencies lying between 300 Hz to 3 KHz have been designated as Ultra Low Fre-

quency (ULF) with corresponding wavelengths from 1000 Km to 100 Km. These frequencies

can penetrate some distance into media like water, soil and rock.Although ULF has very

low bandwidth it is very reliable, penetrating and hard to jam.But if low data rates are

acceptable ULF is an attractive choice for RF denied environments such as underwater and

underground.ULF antennas, if made portable within a diameter of 1m, will operate under

an electrical length of the order of 10?4 to 10?6 wavelengths in free space. Like for any other

electrically small antenna, Chu's limit kicks in and denes the lower bound of the radiation

quality factor. In this study we present an electromechanical radiating system based on

spinning permanent magnets which are not subject to Chu's limit. Based on our simulation

study and experimental results, a spinning magnet array is proposed.

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