Research On Automatic Testing Techiques Of Acoustic Field Characteristic For Ultrasonic Transducers

As an effective means for quality control, ultrasonic non-destructive testing technology is widely used in modern industry, national economy, national defense construction and other fields. And ultrasonic transducer is the core component of this technology, whose performance, especially acoustic field distribution characteristic, has an important effect on the coverage of ultrasonic detection, the defect resolution and the range of ultrasonic detection. Therefore, it is of great practical significance for the development and application of ultrasonic transducer to carry out the research on its acoustic field distribution characteristic. The acoustic field of ultrasonic transducer, however, is a physical quantity with spatial distribution. So the acoustic field distribution characteristic testing must be conducted through spatial search and location, which requires large amount of workload and high accuracy. Besides, the existing artificial detection means has been difficult to meet the demand of quantitative evaluation for acoustic field of ultrasonic transducer. For the purpose, combined with the National Natural Science Foundation Project "Research on theory and practice of automatic online ultrasonic nondestructive testing with high performance based on rotating acoustic field (NO.51175465)", the research on automatic testing techniques of acoustic field characteristic for ultrasonic transducer was put forward in this dissertation. Based on the research of ultrasonic transducer sound beam parameters automatic testing technique, three-dimensional acoustic field reconstruction technique and test-results visualization representation technique, an automatic acoustic field characteristic detection system for ultrasonic transducers was successfully developed, which meets the needs of quantitative detection of the ultrasonic transducer acoustic field characteristics and provides an technical means for the development and application of ultrasonic transducers. The detailed contents of this dissertation were presented as follows:Chapter 1, the research significance of acoustic field distribution characteristic testing was illustrated comprehensively. And the research status and development trends of the acoustic field characteristic testing techniques were summarized synthetically. On the basis of analyzing the technical barriers of acoustic field characteristic testing, the research direction of this dissertation was pointed out.Chapter 2, the radiated acoustic field model of ultrasonic transducer was established, and the energy distribution and sound beam feature parameters were discussed. Besides, the goals and the diagram of the automatic acoustic field characteristic testing system were also proposed.Chapter 3, by using the Rayleigh integral calculation result of the measured two-dimensional sound pressure data to adaptively predict the special position of the ultrasonic transducer focus point, the sound beam target points were acquired and tracked effectively. And an automatic testing technique for ultrasonic transducers, based on the resample algorithm, was developed to detect the sound beam feature parameters and balance the effectiveness and accuracy of the detection. Meanwhile, a special frequency domain model of sound angle spectrum propagation was established, and the acoustic field reconstruction accuracy was improved by selecting suitable spacial sample interval and aperture and de-noising in the spacial frequency domain. In addition, combined with the angle spectrum method based on three-dimensional FFT with time domain information, a kind of technique was proposed to reconstruction the three-dimensional acoustic field accurately.Chapter 4, On the basis of linear interpolation and normalization preprocessing for the acoustic field testing data and using multi-mode color mapping relationship to image preprocessing result data, the detection result of ultrasonic transducer acoustic field characteristic was acquired real-time and shown automatically. Besides, by using the Matching Cubes Algorithm to extract isosurfaces and combining with the acoustic field reconstruction technique, the testing result of ultrasonic transducer acoustic field characteristic was friendly and visually represented with three-dimensional images.Chapter 5, adopting the distributed architecture and modular design strategy, an automatic testing system for ultrasonic transducer acoustic field characteristic was successfully developed, whose key modules include hardware components, software components, motion control components and mechanical scanning devices. Meanwhile, some experiments were carried out by this system to validate its performance level and the techniques proposed in this dissertation.Chapter 6, the research results and the innovative points of this dissertation were summarized, and the future research works were also forecast.