Global Constraint for Temperature Compensation for Dynamic Time Warping of Guided Wave Ultrasound Signals

The paper explores Structural Health Monitoring (SHM) using ultrasonic guided waves, to detect structural damage. Guided waves are highly sensitive to changes in material properties and environmental and operating conditions (EOCs), with temperature being a significant factor. A key challenge in guided waves based SHM is differentiating between damage and temperature-induced changes. This paper focuses on warping-based methods for temperature compensation. Dynamic Time-Warping (DTW) encounters challenges due to its quadratic complexity. However, applying constraints to DTW accelerates the warping process by limiting the scope of the warping path to specified areas. The applied constraint should align with the characteristics of the signal. In this paper, we propose a global constraint for temperature compensation of guided waves, referred to as the Triangular global constraint (Tri-DTW). The performance of the proposed method will be compared with the Sakoe-Chiba global constraint (SC-DTW). Tri-DTW performs well, demonstrating better warping performance with four times reduced computational complexity. The analysis also includes comparisons of warping performance, warping performance with respect to temperature and damage detection performance.