Design And Construction Of Ultrasonic Wireless Transmission System Across Metal Medium

In application scenarios such as modern defense and nuclear industries,it is necessary to use closed metal structures to store equipment and substances.In order to monitor its internal environment in real time,the technology of cross-metal communication is increasingly important.Among them,wired transmission through wires is the simplest way,but it will destroy the airtightness of the metal wall.Due to the electromagnetic shielding effect,the traditional communication methods using electromagnetic waves as the medium is also inapplicable.Ultrasonic has the advantages of good directionality and high energy concentration,and at the same time,as a mechanical wave,it can communicate across metals without using physical drilling.This paper firstly analyzes the research status of using ultrasonic to communicate across metals,and studies the feasibility of using ultrasonic to transmit audio information through metal.In addition,through the research on the characteristics of the transducer,the piezoelectric ultrasonic transducer is selected to convert between the electrical signal and the mechanical signal,and the impedance characteristic and the resonance frequency point of the transducer are measured by an impedance analyzer.By comparing the echo characteristics of the transducers,the transducers with small echo dispersion were selected for the subsequent experiments.Through the measurement of implementation complexity and communication rate,the 2ASK modulation method is finally selected,and a communication system is built based on it.The sending end includes the ADC for analog audio signal,ASK modulation circuit,DDS carrier generation circuit,signal amplifying circuit and voltage follower.The receiving end includes AGC circuit,envelope demodulation circuit,DAC module and audio power amplifier circuit.The communication rate of the communication system reaches 76.8Kbps while the bit error rate is low,and it can transmit audio information across metals.In order to further improve the communication rate of the system,a scheme to eliminate echo is designed.Firstly,the channel model is established,and the transfer parameters of the channel subsystem are systematically identified.After the transfer function is obtained,the pre-correction filter is simulated and realized.The experiment shows that the communication rate can be increased to 115.2Kbps.However,this method requires high experimental conditions and cannot completely eliminate the echo,which has certain limitations.Secondly,an adaptive impedance matching circuit is designed to improve the power transmission efficiency of ultrasonic waves.Finally,the reliability of the whole communication system is tested.Under the conditions of changing the thickness of the metal,the center deviation of the transducer and the metal material,the communication rate and bit error rate of the system is tested.