Extremely Low Frequency Communications: Antenna Design, System Design, and Experimental Verification

Wireless communication is the main means of emergency rescue after a disaster. However, electromagnetic waves (EMWs) in commonly used frequency bands experience significant attenuation when passing through obstacles, and traditional extremely low frequency (ELF) antennas are too large to be carried by rescue robots. This paper proposes a new radiation mechanism, which involves changing the current in the solenoid to alter the magnetic field distribution around the solenoid, thereby enabling information loading. This solenoid antenna is capable of emitting a single-cycle sine pulse. To achieve ELF communication using this pulse, this paper presents a joint pulse position and shape modulation (JPPSM) scheme for the transmitter and a flexible delay synchronization (FDS) scheme for the receiver. FDS utilizes distributed pulses to ensure low redundancy and exploits the acquiring and tracking ability to adaptively increase delay to ensure synchronization accuracy. Simulations show that FDS has higher accuracy and faster acquisition than existing schemes. Experiments show that the operating frequency range of the solenoid antenna is from 14 to 165 Hz. The proposed ELF communication system is capable of achieving error-free transmission over a distance of 450 meters.