Boosting nonlinear ultrasonic detection performance: a framework combining coded excitation and sequence filtering for weak nonlinear feature enhancement

Ultrasonic techniques are widely employed in ensuring structural safety. Traditional ultrasonic techniques are effective for detecting macro-damage yet struggle with early-stage micro-damage. Nonlinear ultrasonic techniques offer promising technical solutions for early-stage micro-damage detection and imaging in structural components. However, the intrinsic weakness of nonlinear features may lead to measurement inaccuracies or imaging artifacts, hindering practical engineering applications. To combat this, a framework integrating pulse compression with coded excitation is proposed to enhance nonlinear acoustic field energy. Specifically, complementary Golay sequences are employed for phase-coded excitation, boosting average transmitting power without increasing peak power. While considering the need to retain the nonlinear features, a sequence filter is used to replace the conventional matched filter to preserve the second harmonic component during signal decoding. Simulations and experiments validate the method’s efficacy in material nonlinearity assessment and micro-damage imaging, demonstrating improved nonlinear feature extraction, artifact suppression, and imaging quality. This work applies coded excitation/decoding techniques to the field of nonlinear ultrasound, significantly enhancing micro-damage detection performance and paving a promising way for early damage assessment in practical engineering structures.