Prediction of directivity characteristics of piezoelectric macro-fiber composite interdigital transducers: a semi-analytical approach

The employment of guided waves for structural health monitoring
applications has attracted substantial attention in recent years. Piezoelectric
transducers are frequently employed in these systems for elastic wave generation and
acquisition. Their dynamic properties, i.e., direction-dependent frequency
characteristics such as directivity patterns, are an important feature for designing a
reliable monitoring strategy. Although analysis of the transducer directivity pattern
can be performed using finite element models, these usually tend to be
computationally very expensive, especially for parametric and optimization studies.
In this paper, a semi-analytical framework is proposed that can predict the farfield
directivity patterns of complex transducers of arbitrary shape and structure
mounted on a substrate. The framework described in this paper integrates analytical
far-field predictions with a local finite element model evaluating the traction field
produced by the transducer. Consequently, the FE model accurately captures nearfield
responses, whereas the analytical component predicts the far-field responses.
The implementation of this semi-analytical framework requires the development
of analytical and numerical approaches. The former includes computation of
dispersion curves of the inspected plate, the stress and displacement profiles of wave
modes, and ultimately, the excitability relations, while the latter includes estimation
of the traction field between the transducer and the plate using the FE model. Owing
to the popularity of piezoelectric macro-fiber composite (MFC) transducers, in this
paper, we apply the proposed method to predict the directivity patterns of MFC
M2807-P2 transducer. To validate the reliability of the proposed method, the
predicted patterns are compared with experimental results obtained using Laser
Doppler Vibrometer.