Application of Modulation Transfer Effect to Damage Detection

The paper presents investigation of modulation transfer effect. This effect - originally observed in the early nineteen thirties in Luxembourg and in Gorky for radio waves propagation in ionosphere - was manifested by modulation transfer of a weaker wave in presence of a strong amplitude-modulated wave. The research are focused for both, application to damage detection and analysis of possible sources of modulation transfer. The different nonlinear model are analyzed to find the potential source of non-linearities responsible for sidebands transfer form low to high frequency. The models include hysteretic stiffness and quadratic damping. In experimental part of the work, modulated low-frequency signal was used as excitation of cracked beam. Simultaneously the high frequency acoustic wave has been introduced to the structure. This combination of excitations induced a modulation transfer from low-frequency to high-frequency wave in presence of structural damage. Surface bonded piezoceramic transducer and electromagnetic shaker were used to excite the structure. Laser vibrometry was used to acquire the response of the structure. The experimental work presented focuses on the analysis of modulation intensities and damage-related nonlinearities. The paper demonstrates that the method can be used for fatigue damage detection.