This work presents an experimental investigation of a stand alone directional structural health monitoring (SHM) system based on a frequency-steerable acoustic transducer (FSAT) operating in pulse–echo mode. A single transducer bonded at the center of a 1000 × 1000 × 1 mm aluminum plate was used to perform damage detection and localization by exploiting the frequency-dependent beam steering characteristics of the FSAT. Directional scanning of the surrounding structure was achieved without mechanical movement or phased-array electronics. Damage detection employed baseline comparison using a root mean square metric applied to reflected Lamb wave signals. Both directional detection at fixed actuation frequencies and spatial scanning via frequency sweeps were experimentally demonstrated. The system successfully detected and localized multiple damage types, including drilled holes and attached disk masses with a diameter of 10 mm, with characteristic dimensions as small as 3 mm. Progressive detection and discrimination of single, double, and triple damage scenarios at distinct angular locations validated the FSAT’s capability for complex multidamage monitoring. The localization accuracy was consistent with the transducer’s angle–frequency calibration, and time-of-flight measurements provided the radial distance estimation capabilities. Compared to conventional omnidirectional sensor networks or phased-array systems, the presented solution offers reduced system complexity, lower sensor density, and improved scalability, while remaining compatible with existing ultrasonic sensor networks. These results demonstrate the potential of the FSAT for simpler, lighter, and more scalable autonomous SHM systems, with enhanced inspection flexibility and localization accuracy suitable for industrial applications.
Reyes et al. (Fri,) studied this question.