  Experimental modal analysis (EMA) is of great importance for the dynamic
characterization of structures. Existing methods typically employ out-of-plane
forces for excitation and measure the acceleration or strain for modal
analysis. However, these methods encountered difficulties in some cases. In
this work, we proposed an in-plane excitation method based on thickness-shear
(d15) piezoelectric transducers. Through the combination of distributed d15 PZT
strips, arbitrary vibration modes can be selectively excited in a wide
frequency range. Both simulations and experiments were conducted and the
results validated the proposed method. Specifically, bending, torsional, and
longitudinal vibration modes of a rectangular bar were selectively excited.
Torsional modes of a shaft were excited without the aid of brackets and bending
modes of a circular plate were excited with actuators placed at nodal lines.
Furthermore, the electromechanical impedance of the PZT-structure system was
measured from which the natural frequency and quality factor were directly
extracted. Due to its simplicity and flexibility, the proposed vibration
excitation method is expected to be widely used in near future.
