The Ultra-Compact ELF Magneto-Mechanical Transmission Antenna With the Speed Modulated EM Signal Based on Three-Phase Induction Motor

Abstract

An extremely low-frequency (ELF) magnetomechanical antenna with the size of one-millionth wavelength based on a three-phase induction motor is reported, whose working frequency is no longer limited by the resonant wavelength. The rotating three-phase induction motor with nonmagnetic material shell is just equivalent to a rotating magnetic dipole with 1.5 times magnetic dipole moment. It can transmit the modulated electromagnetic (EM) signal by modulating the rotating speed of the motor. A near-field ELF EM signal transmission experiment system is constructed based on the magnetomechanical antenna with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Phi 10$ </tex-math></inline-formula> cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times50$ </tex-math></inline-formula> cm size, and the transmitted EM signals were received by a 200-turn coil, which is 10–200 m far away from the transmitter. The EM signal frequency is almost the same as the rotating speed of the motor, and it varies with the rotating speed too. With arbitrary waveform generator and variable-frequency drive (VFD) modulating the rotating speed of the motor, a near-field ELF transmitter with modulating EM signal is built, and the sawtooth wave (STW)-modulated EM signal was transmitted and received clearly during 10–200 m. The square wave (SW)-modulated EM signal was communicated too. The proposed magnetomechanical antenna has a compact size and is very suitable for ELF remote wireless communication.