Phase symmetry analysis for nonlinear ultrasonic modulated signals

SummaryNonlinear ultrasonic experiments typically require digital pass‐band filters and advanced signal processing tools to highlight low‐amplitude nonlinear elastic effects such as harmonics, subharmonics, and sidebands, which are used as signatures for the presence of damage. However, current signal processing techniques cannot be used with dual periodic excitation without reducing signal frequency resolution and severely altering measured waveforms. This paper reports the theoretical development of phase symmetry analysis for nonlinear ultrasound with dual periodic transmission. The proposed signal postprocessing technique consists of determining the phase angles of transmitted waveforms that allow filtering modulated nonlinear ultrasonic waves from the measured signal spectrum. Experimental results validated theoretical predictions and revealed that phase symmetry analysis method provides an easy‐to‐implement and reliable procedure to extract sidebands from the measured signal noise. Phase symmetry analysis with dual excitation has, therefore, the potential to enable sensitive and efficient nonlinear ultrasound testing for various materials, damage scenarios, and applications