Power-Efficient ELF Wireless Communications Using Electro-Mechanical Transmitters

Abstract

Ultra-miniaturized and highly power-efficient ELF (0.3-3 kHz) transmitters are desirable for underground and undersea wireless communications. This paper proposes the use of rotating permanently polarized dipoles (magnets or electrets) for such applications. A power-efficient data modulation scheme based on continuous-frequency FSK (CF-FSK) is also proposed for such electro-mechanical transmitters. Theoretical analysis and simulations show that 7-ary CF-FSK is optimal in the sense that it minimizes average mechanical torque on the mechatronic antenna for a given bit rate. Preliminary experimental results from a prototype ELF magnetic-field based transmitter based on a high-strength rare-earth (NdFeB) magnet and small brushless DC (BLDC) motor are presented. The results highlight local environment challenges such as power line interference that affect the choice of data encoding and modulation schemes. Reliable non-lineof-sight (NLOS) communication through concrete barriers at 100 Hz and ∼0.25 bit/sec is demonstrated at distances up to ∼5 m. The proposed mechatronic antenna and modulation scheme can be scaled up in both frequency and transmit power for more challenging applications in surface-to-undersea, surface-to-cave, and other conductive environments that require ELF channels. INDEX TERMS Antennas and propagation, communication systems, electromechanical devices, emergency services, magnetic devices, transmitters.

Magneto-Mechanical Transmitters for Ultralow Frequency Near-Field Data Transfer

“…This power reduction process can be carried on arbitrarily until some practical limits are hit, e.g., the system size becomes too large to be practical, the total inertial mass becomes too large, or the static bearing friction dominates over the drive torque. Importantly, this scaling principle is not available in MMTs that operate using full rotation of the rotors [16]- [21].…”

“…Instead, energy is now only consumed in the physical motion required for producing the harmonic carrier signal, and for the secondary modulation applied for transmitting data, thereby transforming the engineering challenges to different domains. When the carrier signal is generated using full rotation [16]- [21], data can be encoded by varying the rotational speed, resulting in a frequency modulation (FM) method. This modulation typically consumes a significant amount of energy per bit since a slow-down/speed-up operation must be used for data transmission, although regenerative braking methods may be considered.…”

A miniaturized mechanical antenna based on FEP/THV unipolar electrets for extremely low frequency transmission

“…The current distribution and electromagnetic energy of a mechanical antenna are independent of the power supply and more controllable than those of a traditional antenna. This unique radiation mechanism makes the mechanical antenna free from the limitation of antenna size in terms of efficiency, thus achieving high-efficiency ELF electromagnetic radiation with a size much smaller than that of a traditional ELF transmitting antenna 10 – 13 .…”

Research on Ultra-Low-Frequency Communication Based on the Rotating Shutter Antenna

“…The communication system which uses RPMA as the transmitter mostly adopts direct antenna modulation (DAM). For example, we can obtain an OOK signal by controlling the driver switch and an FSK signal by controlling the speed of motion [16][17][18][19][20]. Besides, Refs.…”