Research On Underwater Wireless Communication Technology Based On Magnetic Induction

With the increasing frequency of human exploration of the ocean,in order to ensure the safe conduct of ocean exploration activities and the transmission of related exploration information,higher and higher requirements for communication capabilities are put forward.The existing underwater wireless communication methods include hydroacoustic communication,optical communication,electromagnetic wave communication and magnetic communication.Among them,hydroacoustic communication is the current mainstream underwater communication method,but its huge antenna size,slow communication speed and delay cannot meet the requirements.Communication needs in some special occasions.Optical communication has the advantages of fast communication speed and large bandwidth,but it needs to achieve high-precision alignment in harsh underwater environments,and the communication distance is limited by the light attenuation performance of water,which is not suitable for some environments with poor water quality.Because the electromagnetic wave attenuates very sharply underwater,it is difficult for electromagnetic wave communication to be applied underwater.As a new type of near-field communication,magnetic communication has many advantages such as high speed,low delay,low power,simple antenna structure,etc.The non-propagation of magnetic field enables magnetic signals to be transmitted in complex and harsh underwater environments and across water-air interfaces.When showing great advantages.This paper conducts theoretical simulation research on underwater and cross-medium interface magnetic communication transmitting and receiving systems,exploring the laws of magnetic signal transmission in underwater magnetic communication,developing receiving and transmitting systems,and realizing underwater and cross-medium magnetic communication.Firstly,the theoretical research on underwater magnetic communication technology is carried out.According to the distance between the observation point and the field source,the magnetic field is divided into the near field,the radiation field and the far field,and the near field is selected as the communication range of the magnetic communication.The magnetic signal transmission model was established,and the influence of coil parameters and placement position on mutual inductance was studied by simulation;the influence factors of induced electromotive force were studied according to Faraday’s law of electromagnetic induction;the air and underwater environments with different conductivity were simulated based on COMSOL Attenuation of magnetic signal transmission.Secondly,the common signal modulation and demodulation methods are analyzed,and the binary digital amplitude modulation is determined according to their characteristics.The signal modulation method of the experimental system for this subject is determined.The basic structure of the magnetic communication circuit system is designed.According to the basic principles of each part of the circuit,the basic functions of signal modulation and demodulation are simulated using Multisim circuit,and the basic functions of the transmission power amplifier circuit,the signal amplifier circuit at the receiving end,and the frequency reduction circuit are studied and analyzed.Function,and analyze the design parameters of each part of the components.Thirdly,the transmitting and receiving and signal processing hardware circuits of the magnetic communication system are designed and developed.The transmitted signal uses the TTL level output by the microcontroller serial port as the baseband,and the10 MHz analog sine wave signal generated by the digital modulation synthesizer AD9850 is used as the carrier;the power amplifier circuit uses a field effect tube to form a transformer coupled push-pull amplifier circuit.The signal receiving end adopts an automatic control gain circuit,so that when the input signal amplitude changes,the peakto-peak output voltage is stable at 1.6V;a heterodyne frequency reduction circuit is used to reduce the frequency of the amplitude modulation signal from 10 MHz to 1MHz,which effectively improves the signal Detection sensitivity;signal demodulation adopts fullwave precision detection circuit,which can realize 5μs pulse amplitude modulation signal demodulation.Finally,series resonant antenna is designed,which improved the signal-to-noise ratio of the transmitted signal and the received signal;built a magnetic communication experimental system,and carried out the magnetic communication experimental research under three conditions of air,underwater and across the water-air interface.The transmission of underwater text information and picture information,and the transmission of text information across the water and air interface.