Resolution Enhancement of Total Focusing Imaging Combining with Autoregressive Spectral Extrapolation

doi:10.3901/JME.2020.22.008

Abstract

Abstract: The defects with close spacing are difficult to be distinguished by ultrasonic imaging with total focusing method(TFM). Autoregressive spectrum extrapolation with low-order and wide effective frequency band is introduced to compress the pulse width in time domain, achieving subwavelength resolution imaging of TFM. Two preset side-drilled holes having 1.8 mm center distance and 1.3 mm diameter in the simulated model of carbon steel are detected by array probe with 2.25 MHz center frequency and 32 elements. Focusing on full matrix capture, taking 2-order and the width of frequency window represented a 14 dB drop from the maximum amplitude of spectrum, and the autoregressive model is established to extrapolate the high-frequency and low-frequency components beyond effective frequency band. Then, the delay-and-sum algorithm is implemented on the processed full matrix capture data to obtain the TFM image. The simulated results indicated that the combination of TFM and autoregressive spectrum extrapolation with low-order and wide effective frequency band had high robustness and accuracy, so as to effectively separate adjacent defects with center distance of 0.7λ (λ is ultrasonic wavelength). The positioning error is no more than 0.73% while retaining the lateral resolution. Finally, side-drilled holes having 1.8 mm center distance are calculated with the same testing parameters in experiment, and the positioning error is no more than 1.06%, effectively improving imaging resolution of TFM.

Key words: ultrasonic detection, total focusing method, autoregressive spectrum extrapolation, imaging resolution

CLC Number:

TG115

LIN Li, SHI Siqi, SUN Xu, MA Zhiyuan, ZHANG Xiaofeng, LIU Lili, JIN Shijie. Resolution Enhancement of Total Focusing Imaging Combining with Autoregressive Spectral Extrapolation[J]. Journal of Mechanical Engineering, 2020, 56(22): 8-13,23.

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