Design of Broadband Matching Circuit for Underwater Acoustic Communication Transducer

Abstract

The design of matching circuit for broadband underwater acoustic transducer is a key technology in sonar system. Matching circuit can reduce the energy loss of the power amplifier, extend the system bandwidth and improve the distortion of the transmitted waveform. In this paper, the theory of real frequency direct computational technique (RFDT) is discussed. Then, we design the matching circuit for a tubular transducer. Finally, the match performance is tested in anechoic pool. The results illustrate that the broadband matching circuit can expand the bandwidth and improve the efficiency of the transmitter. Compared with the transmitter without matching, the sound source level of the system increased about 10dB. Compared with the single inductor matching circuit, the work bandwidth is extended. The whole design process of broadband matching circuit completed with computer and without the equivalent circuit of the transducer, so the RFDT is fit for practical project. Introduction At present, the high speed underwater acoustic communications and underwater remote detection technology have been rapidly developed. The broadband signal technology is widely used in sonar equipment. The broadband transducer, wideband transmit system has become an important part of the sonar system, how to expand the operating frequency bandwidth and ensure the waveform with less distortion has become a key technology. In some sonar equipment which powered with battery, such as underwater acoustic buoy, portable communication sonar which has the limited energy that requires the transmit system with high work efficiency. Therefore the actual transmit system in the sonar equipment not only has a flat frequency response but also has a higher power factor and ideal waveform [1]. For the realization of sonar transmit system with high efficiency, a matching circuit must be used between the transducer and the power amplifier. In general, sonar system use linear power amplifier which has fixed output impedance, when determined the output power. For a piezoelectric ceramic transducer, the impedance varies with the frequency and difficult to be expressed by the analytical function, so it is difficult to achieve good broadband matching performance in a wide frequency range. At present, underwater acoustic transducer broadband matching circuits often used single inductor to get the available bandwidth or construct several resonance peaks to complete the matching circuit design in the transducer work band using multi-resonance method. But the actual matching effect cannot achieve the desired effect, it is difficult to satisfy the needs of broadband sonar [2] [3] [4] [5]. In recent years, the theory and method of broadband matching has been well developed, combined with computer aided (CAD) technology, a series of broadband matching numerical methods such as the direct optimization method, the real frequency method and genetic algorithm which widely applied in the antenna broadband matching and microwave amplifier design. Haiying Huang and Daniel Paramo [6] have described a method to estimation equivalent parameter with an ultrasonic piezoelectric transducer and completed the broadband matching circuit with Smith chart. International Conference on Intelligent Systems Research and Mechatronics Engineering (ISRME 2015) © 2015. The authors Published by Atlantis Press 2298 Yongshi [7] has described a computer-aided method to design the broadband FET amplifiers in microwave monolithic integrated circuit. Jianfei [8] has used genetic algorithm to design the matching network in a broadband ultrasonic transducer array. The above methods have got good matching results. Real frequency direct computational technique The real frequency technique is a kind of broadband matching methods of computer aided design. Its main idea is that the matching network impedance is described with the driving point function, while the transducer power (TPG) of the system can be expressed in a simple form of function by the driving point function and the actual data of the transducer. Use a nonlinear curve-fitting algorithm to optimize the TPG as high and flat as possible in the band of operation. Finally obtains the driving point function which optimized, synthesis the matching network which can be easy to realize in real engineering implementation. The real frequency technique without the load equivalent circuit model and analytical expression, also without selecting the topological structure and the analytical expression of the transfer function of the matching network, only need the initial value of the driving point function. The whole calculation is completed by the computer. Therefore, this method is suitable for practical engineering transducer with multi-resonant mode which the equivalent circuit parameters are difficulty to determine. The real frequency technology mainly includes the real frequency method, the real frequency direct computational technique (RFDT), simplified real frequency technique (SRFT) and parameter method. The basic idea of the above methods is the same, however, the computation complexity and computation stability are different [9].