Two-dimensional periodic actuators for frequency-based beam steering

The paper investigates innovative designs of piezoelectric actuators for structural health monitoring (SHM). Periodic configurations are proposed as an effective means to provide actuators and sensors with strong, frequency dependent directional characteristics, which allow beam steering through a sweep of the excitation frequency. The concept has the potential to enable in situ monitoring of critical components through strongly focused actuation (and/or sensing) and directional scanning capability, which may be achieved with very limited hardware requirements. Beam steering is achieved by exploiting interference phenomena generated by the spatial periodicity of the array and the simultaneous activation of its components. Such interference phenomena produce waves with frequency dependent directional characteristics, which allow directional scanning to be performed simply through a frequency sweep. The need for beam-forming algorithms and associated hardware is thus avoided. The concept is illustrated by considering 2D arrays of point sources of various topologies. The case of a thin membrane supporting the propagation of SV waves is first presented to provide a simple frame work of analysis. The case of Lamb waves in a thin plate is then considered to demonstrate the validity and the practicality of the proposed approach.