Developing an optimal acoustic reflector for air-coupled impact-echo sensor

The objectives of this study were to investigate interaction of a parabolic acoustic reflector with leaky stress waves in air-coupled IE testing, and to develop an optimal geometry of the acoustic reflector. The resulting acoustic reflector will be used as a part of an air-coupled impact-echo device for delamination detection in concrete bridge decks. The study was conducted on a series of 2D finite element (FE) models. The models included both solid concrete plate and air domains. The models were developed to investigate interaction of leaky stress waves (in particular, S ₁ resonance mode in Lamb waves) with a parabolic reflector. A series of parametric studies was conducted to determine the optimal geometry of parabolic reflectors (cylinders). The main variables were the rim angle and the width of the reflectors, and location of air-coupled sensors. Furthermore, numerical simulations using 2D FE models, including delamination defects in concrete decks, were conducted to verify the optimal parabolic reflector is effective in enhancing the amplitude of S ₁ resonance modes in Lamb waves corresponding to the various depths of delamination defects. Finally, the results clearly demonstrate that the optimal parabolic domes can significantly improve signal-to-noise ratio in the air-coupled IE measurements. This will increase the feasibility of air-coupled sensing in actual impact echo testing on concrete bridge decks.