为实现金属圆棒的定量无损检测(QNDT)，在经典的Cartesian坐标系超声合成孔径(SAFT)理论指导下，提出了极坐标系下的合成孔径聚焦成像(pSAFT)算法及其环绕式时域合成孔径聚焦技术(ST-SAFT)。基于螺旋扫查自动检测系统推导了采用有效合成孔径弧度(SAR)表示的延时叠加成像表达式；通过制备横孔型人工缺陷试样进行检测实验，将超声检测数据经ST-SAFT处理后成像为圆截面断层扫描图；再运用图像边缘识别法进行定量评价该方法对缺陷检测的定量定位分辨率。结果表明：ST-SAFT孔径测量值与实际值相当；横孔定位准确；成像分辨率显著优于B扫描结果；每圆截面成像速率可达毫秒量级，可与棒材检测一周的机械扫查速率相匹配。该技术可用于提升金属圆棒超声检测设备的技术水平和提高棒材使用安全性保障能力。

Spiral scanning mode, where ultrasonic probes relatively rotate forward around a tested bar, is commonly used in an automatic ultrasonic testing system for metal bar quality control. Current nondestructive testing standards for bars with ultrasonic technology specify that whether the bar is rejected or accepted should be made in accordance with the amplitude of the echo from a defect in the bar. The quality information obtained by the abovementioned standard testing procedure is only the echo from the defect, and it is too simple to characterize the defect in detail and accurately. Therefore, inspection using imagery and quantitative nondestructive testing (QNDT) of bar quality is the development trend of bar quality control technology in the future. In achieving QNDT of metal round bars, a synthetic aperture focusing on imaging algorithm in a polar coordinate system (pSAFT) and its surrounding scan-mode time-domain synthetic aperture focusing technology (ST-SAFT) were proposed in accordance with the classical ultrasonic synthetic aperture focusing technology (SAFT) theory on a Cartesian coordinate system. Based on the signal set collected by the spiral scanning automatic detection system, the formula of time-delay superposition imaging expressed by the effective synthetic aperture radian was deduced to image the defects in the bar with a cross-sectional view. By preparing a transverse-hole artificial defect sample for the testing experiment, ultrasonic testing data were processed by ST-SAFT, and then a circular section tomography was imaged. Image edge recognition was used to quantitatively evaluate the sizing ability and positioning resolution of ST-SAFT for defect detection. Experimental results show that the measured value of artificial defects with ST-SAFT is equivalent to the real value; the positioning of the transverse side-drilled hole is accurate, and the imaging resolution is significantly better than that of B-scan. The imaging speed for each circular section can reach the order of milliseconds, which can match the mechanical scanning speed of bar inspection for one circle. Therefore, this technology can be used to improve the technical level of ultrasonic automatic testing equipment for metal round bars and ensure safety of the application of metal round bars.