Effect of material anisotropy on the first-order vibration of piezoelectric oscillators in circular plate configurations

Valveless piezoelectric pumps are widely used in microfluidic actuation because of their simple structure, ease of integration, absence of electromagnetic interference, minimal valve wear, and absence of frequency–response lag issues. These pumps primarily rely on chamber volume changes, causing most piezoelectric oscillators to operate in the first-order vibration mode. However, recent studies on valveless piezoelectric pumps have observed that many pumps exhibit two flow peaks at similar operating frequencies; the underlying mechanism behind this anomaly remains underexplored. In this study, we investigated the impact of substrate metal on the first-order vibrations of piezoelectric oscillators. By conducting tensile tests on rolled pure copper sheets, we measured Poisson's ratio and the elastic modulus in both the parallel and perpendicular rolling directions. Subsequently, we derived the natural frequencies on the plane. Experimental verification of the theoretical predictions was achieved through amplitude experiments conducted on piezoelectric oscillators in air. The dual-peak flow phenomenon was demonstrated to be solely related to the substrate metal of the piezoelectric oscillator. This is attributed to the presence of two first-order vibration natural frequencies on the plane of the substrate metal, resulting in the generation of two amplitude peaks and consequently the appearance of two flow peaks.