Extremely Low Frequency and Very Low Frequency (ELF/VLF ) Communications for Underground, Underwater, and Hypersonic Flight

Radio frequency (RF) technologies have limitations that cannot fulfill specific requirements. For instance, underground and underwater are challenging environments due to the absorption of high frequency electromagnetic (EM) waves in dense media. For hypersonic communications, Very Low Frequencies (VLF) band signals have large EM wavelengths that can penetrate the plasma sheath layer with minimal loss,…