ELF/VLF Micro-Array Transmitters with Fe-Co high-μ core for Space Platforms

Recent laboratory experiments [1–4] demonstrated that a small diameter, large aspect ratio multiloop solenoid antenna with a core of non-conducting high-μ material, could efficiently inject Whistler and EMIC waves in the ELF/VLF frequency range in space plasmas. The small radiation resistance due to the small diameter is compensated with the increase in the magnetic moment by the high-μ core. Initial experiments utilized high-μ ferrite core and are known as Ferrite Loop Antenna (FLA) elements. Subsequent experiments utilized commercial ferrofluids. In this case the high-μ core was due to an ensemble of 10-20 nm magnetite nanoparticles, dispersed in low-viscosity fluids known as Magnetic Nano-Transmitter (MNT) elements. The most important result of these experiments was that a phased two-element crossed dipole FLA or MNT array could generate high-amplitude Whistler and EMIC waves like the ones previously generated by Rotating Magnetic Field (RMF) antennas [5], but with radiation resistance more than 30dB larger. The observed waves had helical phase surfaces described by $\mathrm{e}^{\mathrm{i}(\pm++\mathbf{k z}-\omega t)}$. The combination of a magnetic loop that propagates along $\mathbf{B}_{\mathbf{0}}$ while rotating about it, is known as helicon topology.