Design Of Ultra-low Frequency Communication System Based On Rotating Dipole

High-frequency communication in wireless transmission has the advantages of large bandwidth and high rate,which can meet the transmission requirements of most communication tasks.However,in special environments such as underground and underwater,high-frequency electric small antennas are limited by the skin effect,which leads to large transmission attenuation and short propagation distance.Although the ultralow frequency electromagnetic wave has strong ability of penetration,,small electric antenna in this frequency band has huge size and low radiation efficiency.In order to solve this communication requirement,a new type of mechanical antenna has attracted the attention of researchers in recent years.It generally generates low-frequency FSK signals by rotating permanent magnets or electrets,while having both portability and flexibility.Based on this,this paper proposes a modulation scheme using electromechanical coupling by means of using the shielding structure to control the low-frequency signal strength changing and produce ASK signal,and not changing the magnet speed controlled by the motor meanwhile.This paper realize the trial production of high-efficiency,high-rate miniaturized mechanical antenna prototype working in the ultra-low frequency band(SLF),and complete the design of the communication system with the amplitude modulation.In this paper,the magnetic moment and electromagnetic radiation characteristics of the rotating dipole and vibrating dipole are first studied.The orthogonal vibrating magnetic dipole is used to replace the rotating magnetic dipole model equivalently.Propagation characteristics of the near-field and far-field electromagnetic fields of dipoles are analyzed.The finite element simulation of the radiation model was carried out on the Comsol software,and the distribution characteristics of the time-varying magnetic field in the near region of the rotating dipole were obtained,which verified the feasibility of the rotating magnetic dipole radiation signal.Secondly,the modulation schemes of existing mechanical antennas are studied comparatively.In order to reduce the strict requirements on the mechanical structure of the modulation scheme in the mechanical antenna,an ASK mechanical antenna transmitter and matched modulation communication system using electromechanical coupling are proposed.Considering the modulation signal loading method and the difficulty of engineering implementation,the performance comparison and feasibility analysis of the existing modulation schemes of mechanical antennas were carried out.Finally,according to the rotating dipole radiation model and the modulation scheme of electromechanical coupling,combined with the actual mechanical structure for design and optimization,the prototype of the ASK mechanical antenna based on the rotating magnetic ball and high-speed servo motor was realized.Then The composition and function of this mechanical antenna module was introduced.The prototype model with electrical shielding is theoretically analyzed and experimentally verified.Combined with the electromechanical coupling modulation scheme,the design of the amplitude modulation communication system and the testing of the software platform are completed.Above all,we demonstrate the effectiveness of the ultra-low frequency communication system proposed in this paper.