Fixed-phase Resonance Tracking for Fast Nonlinear Resonant Ultrasound Spectroscopy

Researchers Jan Kober, Radovan Zeman, and Marco Scalerandi have developed a fixed-phase resonance tracking method for Nonlinear Resonant Ultrasound Spectroscopy (NRUS) that dramatically accelerates material characterization. Traditional NRUS relies on repeated full frequency sweeps, which are slow and sensitive to evolving material parameters due to fast and slow dynamic effects. The new method defines resonance through a prescribed phase relationship between excitation and response, then uses a linearized frequency-phase model to iteratively update the excitation frequency in real-time. This eliminates the need for complete sweeps, reducing measurement time significantly—potentially by an order of magnitude—while maintaining high accuracy.

The approach includes optional feedforward correction to suppress transient wave buildup, further stabilizing measurements. Demonstrated on sandstone bar samples, the method provided reliable estimates of resonance frequency and damping, with comparisons showing that measurement speed and mode stability critically influence nonlinear indicators. The framework is not limited to nonlinear acoustics; it can be applied to any resonant system with slowly evolving parameters, such as structural health monitoring or medical ultrasound. This breakthrough enables faster, more consistent material testing, which is crucial for industries like aerospace, civil engineering, and biomedical diagnostics where real-time monitoring is essential.