Non-Contact Acoustic Excitation and Sensing for Nondestructive Testing of Concrete Structures

date February 8, 2013
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Friday, February 8, 2013 4:00 p.m. in ETC 4.150

Professor Jinying Zhu and Xiaowei Dai
Department of Civil, Architectural and Environmental Engineering
The University of Texas at Austin

Air‑coupled sensing has shown great potential for rapid nondestructive sensing and scanning of concrete infrastructure. However, the current air‑coupled sensing method has two limitations: (1) the air‑couple sensor (a microphone) has low sensitivity, which results in low signal‑to‑noise ratio (SNR) for testing in the field and (2) a mechanical contact impact source is needed to excite elastic waves in concrete. In this presentation, we present a fully air-coupled acoustic excitation and sensing system to address these challenges. To improve the SNR, a parabolic reflector is used to focus the incident plane wave radiated from the concrete specimen, and a microphone located at the focal point of reflector receives the amplified signals. An analytical solution has been derived to optimize the geometry of the reflector for this purpose. Experimental studies and finite element simulations validate the improved sensitivity and SNR. To realize non‑contact excitation, an acoustic spark source with an ellipsoidal reflector has been proposed to excite wave motion in concrete. Analogous to shock wave lithotripter devices, the spark is located at the near focus and generates an outgoing wave that is then focused at the far focus of the reflector which is aligned at the air-concrete interface. Applications of the air-coupled system for Rayleigh wave, zero‑group velocity Lamb wave (impact‑echo) and through‑transmission tests on a concrete slab are presented.