Investigation of an Air-Coupled Nondestructive Testing System for Composite Structures Using Electrodynamic Acoustic Transducer and Laser Vibrometry

This study investigates an air-coupled acoustic excitation system combined with laser Doppler vibrometry for nondestructive testing of composite materials. The original air-coupled system based on a modified electrodynamic acoustic transducer was characterized. The proposed approach features a pulsed operating mode in which the transducer’s peak power substantially exceeds its nominal rating (by approximately a factor of 400). The radiated sound field was quantified in terms of sound-pressure amplitude ( $$ \geqslant {\kern 1pt} 0.2$$ Pa at a distance of ~10 cm from the source) and directivity pattern. In addition, it was demonstrated that varying the discharge-circuit resistance provides effective control over both the peak power and the spectral content of the generated acoustic waves. An experimental modal analysis was performed on a small-scale ( $$5 \times 5$$ mm) model specimen in the form of a thin multilayer plate, and defect detection was carried out on a large-scale ( $$200 \times 200$$ mm) composite sandwich panel with a honeycomb core. Analysis of the experimental data confirmed the feasibility of using electrodynamic transducers for pulsed acoustic excitation in defect detection and nondestructive testing over a frequency range of 3 Hz to 50 kHz. It is shown that combining air-coupled acoustic excitation with laser vibrometry overcomes the limitations of contact-based excitation and vibration measurement methods, significantly extending the applicability of acoustic techniques in defect detection and nondestructive testing.