9. Modeling of Actuators and Sensors for SHM

This chapter presents computational techniques for the simulation of guided wave generation in plate structures. Generation is here considered as achieved by surface mounted piezoelectric patches of various shapes and characteristics. This computationally costly task is performed through the application of semi-analytical techniques, which involve the solution of the governing elasto-dynamic equations in the frequency/wavenumber domain, and the evaluation of the structure (plate) response in the far-field. Such techniques are presented and further extended to illustrate their joint application with the Finite Element solution of the interface stress between a surface mounted patch and the structural substrate. These methodologies are subsequently applied for the analysis of directional wave generation through actuator arrays. The concept of beam steering through phase control of the array elements, and through their spatial arrangement is presented for the simple case of a linear, one-dimensional array. The basic principles are then applied to the case of a two-dimensional configuration which has the ability to generate beam steering through proper tuning of the excitation frequency. The concept of “frequency-based" steering is discussed in detail as an effective and efficient means for directional wave generation and for focusing of the acoustic energy. The chapter ends with the presentation of methodologies for wave sensing. Most of the presented procedures illustrate the reciprocity between sensing and actuation, along with the opportunity for optimal sensing/generation through proper shaping and/or spatial distribution of the patch elements.