Experimental demonstration of directional GW generation through wavenumber-spiral Frequency Steerable Acoustic Actuators

Directional inspection using guided waves (GWs) is a convenient approach for Structural Health Monitoring (SHM) of large 2D regions. While beam steering is conventionally achieved through phased arrays, often at the cost of a considerable hardware and software complexity, a single, differential-channel actuator is employed in this work to send GWs in arbitrary directions by properly choosing the excitation frequency. This frequency-steerable directional scanning is achieved through an angle-dependent wavelength tuning provided by the peculiar shape of the piezoelectric patch which forms the transducer. Although the underlying theoretical framework of Frequency-Steerable Acoustic Transducers (FSATs) encompasses both directional generation and sensing of GWs, directional actuation has only been predicted by simulations so far. This paper presents for the first time an experimental study of directional GW generation on an aluminum plate through an FSAT fabricated by inkjet printing of the electrodes on a PVDF substrate and previously operated in sensing mode.