Steering of multiple defect bands in one-dimensional phononic crystals with segmented piezoelectric defects

Phononic crystals (PnCs) can inhibit the propagation of elastic waves within specific frequency ranges, known as band gaps. They can also introduce localized defect bands that enable functionalities such as filtering, sensing, and energy harvesting. However, conventional approaches that use piezoelectric defects combined with external circuits have limitations. While odd-symmetric defect bands can be tuned with synthetic negative capacitors, even-symmetric defect bands remain insensitive due to voltage cancellation. This study introduces a segmented piezoelectric defect concept to overcome this limitation. In this concept, each segment is connected to a synthetic negative capacitor, which eliminates voltage cancellation and enables the simultaneous control of multiple defect bands. An electromechanically coupled transfer-matrix framework is developed in MATLAB to predict defect-band frequencies, defect-mode shapes, and transmittance spectra. Numerical validations performed in the one-dimensional finite element method demonstrate close agreement with the analytical results. The proposed configuration shifts both defect-band frequencies across the band-gap region, tailors the localization patterns of defect modes, and regulates the number and existence of transmission peaks. These results confirm that segmentation expands the design space of defective PnCs and provides a foundation for multifunctional phononic devices.