Butt welding is extensively applied in long-distance oil and gas pipelines, and it is of great significance to conduct non-destructive ultrasonic testing of girth welds in order to avoid leakage and safety accidents during pipeline production and operation. In view of the limitations of large transducer size, single fixed beam angle, low detection resolution and high cost of conventional ultrasonic inspection technologies, a 16-channel piezoelectric micro ultrasonic transducer (PMUT) array probe was developed through theoretical analysis and structural optimization design. After the probe impedance characterization, the experimental results show that the theoretical model can effectively guide the design of the ultrasonic transducer array, offering the maximum operating frequency deviation of less than 5%. The ultrasonic echo performance tests indicate that the average −6 dB bandwidth of the PMUT array probe can be up to 77.9%. In addition, the fabricated PMUT array probe has been used to successfully detect five common internal defects in pipeline girth welds. Due to the multiple micro array elements, flexible handling of each element, large bandwidth and high resolution of defect detection, the designed PMUT array probe can provide a good application potential in structural health monitoring and medical ultrasound imaging fields.
This paper addresses the bandwidth problem of ultrasonic transducers, and a frequency band broadening technique based on multi-frequency impedance network coupling is proposed. Based on the extended BVD circuit model, three coupled circuits including one first-order and two second-order are designed. The inductor-capacitor value and series-parallel connection method are reasonably chosen for tuning to achieve multi-peak resonance to improve the operating bandwidth of the transducer. The results show that for each order increase of the LC circuit, the resonance peak will increase by one, and the bandwidth will be broadened accordingly. Finally, the bandwidth of the first-order coupling circuit is increased by 50.45% and the bandwidth of the second-order coupling circuit is increased by 88.29%.
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