Electrical Impedance Matching Network For Broadband Ultrasonic Communication Through Metal Wall

Due to the lack of electromagnetic shielding restrictions,the communication system with ultrasonic as the medium can realize wireless transmission of data inside and outside the sealed metal cavity,and has good application prospects in some specific scenarios such as nuclear reactor containment vessels,submarines and large bombs.As expectations for communication rates continue to grow,the bandwidth requirements for such communication systems are correspondingly increasing.Once the ultrasonic transducer is selected,the signal-to-noise ratio outside the available bandwidth can be improved by introducing a suitable impedance matching network,thereby further expanding the available bandwidth of the ultrasonic transducer.At present,the most widely used broadband matching methods include real frequency technology and broadband matching methods based on various optimization algorithms.Among them,the broadband matching method based on the optimization algorithm usually sacrifices the operation speed in order to pursue the optimal matching performance,and the optimal topology cannot be guaranteed.In contrast,the simplified real frequency method in the real frequency method has the advantages of matching performance and operation speed,so this thesis uses the simplified real frequency method to design the ultrasonic transducer broadband matching network.This thesis first introduces the theoretical basis of circuit networks required for wideband matching networks,including Holwitz polynomials,parameter matrices of two-port networks,and transmission power gain of single-port and two-port networks.At the same time,this thesis analyzes and compares the advantages and disadvantages of the four real-frequency technology methods in wideband matching design,and selects the simplified real-frequency method as the design method for this topic.In addition,the Kaur synthesis method for the synthesis of the countermeasure moving point function is analyzed,and the method of denormalization after synthesis is analyzed to obtain the actual circuit parameters.Based on the above theoretical analysis,a Norton transform method is proposed to solve the inconsistency between the Darlington resistance and the target resistance in the circuit.Secondly,this thesis analyzes and compares the impedance changes before and after coupling between the ultrasonic transducer and the metal wall,and designs two sets of matching networks for the impedance after coupling,namely the impedance of the ultrasonic transducer straddling both sides of the metal wall and the design of the broadband impedance matching network of the "transducer-metal wall-transducer" two-port network.In this thesis,the performance of matching networks with and without transformers is analyzed and compared,and the scheme with the best network performance is selected for synthesis.Finally,an experimental system is built for the two impedance matching networks,and the performance of the two matching networks is analyzed and compared by taking the transmission power gain of the system as the evaluation standard.The experimental results show that the impedance matching network of the ultrasonic transducer straddled on both sides of the metal wall can effectively improve the transmission power gain in the considered frequency band and improve the communication bandwidth.The "transducer-metal wall-transducer" two-port network is not ideal because conjugate matching cannot be fully achieved.