Complex pressure-node formation and resonances induced by scatterers in a standing-wave acoustic cavity

Acoustic pressure nodes in acoustophoretic devices are crucial for applications in tissue engineering, cell analysis, and particle trapping. Typically, a single primary node forms at the half-wavelength resonance condition, with its shape and position constrained by the channel dimensions. The generation of additional nodes, along with control over their positions and shapes, is highly desirable in biomedical applications and could significantly enhance particle manipulation capabilities. To explore this potential, we numerically demonstrate the formation of additional, complex-shaped nodes, alongside the primary one, induced by a circular scatterer within a rectangular cavity. We identify three distinct types: ring, protuberant, and crescent nodes, whose formation depends on the scatterer's size, its relative placement, and the corresponding resonant frequency. Furthermore, we analyze the impact of the scatterer on acoustic pressure, acoustic energy, and the quality factor. We show that the emergence of additional nodes come at the cost of reduced acoustic pressure and energy in the channel. This study provides foundational insight into generating complex nodes in a standing-wave acoustic cavity at the fundamental frequency, offering new opportunities for noncontact particle and fluidic manipulation in acoustofluidic devices.