An improved higher-order delay multiply and sum beamforming method for ultrasound real-time nondestructive testing

To improve the contrast and signal-to-noise ratio of nondestructive testing images with low computational complexity, this paper proposes a nonlinear ultrasound imaging method, called the improved high-order delay multiply and sum (IDMAS) beamforming method. The method uses a generalized high-order nonlinear coherence factor to estimate the high-order spatial coherence of echo signals based on the distribution characteristics of the target and noise signals in nondestructive testing and combines with a high-order nonlinear method to obtain the beamforming outputs. The process can not only eliminate low-coherence clutter but also significantly suppress high-coherence artefacts. In this paper, the effectiveness and robustness of the method are verified through four experiments, including the steel block, aluminium block, steel rail and steel plate weld inspection. The experimental results indicate that compared with the traditional delay and sum (DAS) method, the proposed method reduces the array performance index (API) by 67.3%, increases the contrast ratio (CR) by 251.2% and improves the signal-to-noise ratio (SNR) by 34 dB on average. Due to the differences in material properties, the effectiveness of the proposed methods varies. Based on this, the standard deviations of the improvement percentages for different experiments are calculated: compared with DAS, the standard deviations of API, CR and SNR are 8.8%, 83.7% and 38.1%, respectively. In addition, this paper analyzes the real-time performance of the method from two aspects of computational complexity and computation time: compared with the computational complexity of O ( N n ) for high-order delay multiply and sum, the computational complexity of the proposed method is only the order of O ( N ); and its computation time is similar to that of DAS, satisfying the requirements of real-time nondestructive testing.