Investigation of meta-stacks for thermoacoustic applications

Thermoacoustic devices could offer a sustainable approach to energy harvesting, noise mitigation, and environmental diagnostics but remain constrained by low power-to-volume ratios and narrow operational bandwidths. These limitations hinder their adoption in applications requiring compactness and broadband performance. To address these limitations, metamaterial-inspired stack (meta-stack) designs for thermoacoustic applications are investigatedin this study. Utilizing a standing wave thermoacoustic scheme, various meta-stack configurations are simulated based on Rott's approximation and validated using experiments. Three designs are explored: the helical pore stack (HPS), the helical resonator stacks (HRS), and the pie-slice resonator stacks (PRS). The additively manufactured stacks were optimized for low frequencies (<500 Hz) and broadband response. HPS utilizes helical pore geometries to enhance broadband response. HRS achieves dual-frequency operation due to the presence of two convoluted acoustic paths, improving performance at low frequencies, while PRS features modular sections configurable for a wide frequency range. Experimental results correlate well with numerical predictions, demonstrating the potential to enhance thermoacoustic performance. Further, nonlinear and transient analyses are performed to better understand loss mechanisms. Integrating meta-stacks in thermoacoustic devices could provide a promising means to address their traditional limitations and deliver advancements for multifunctional applications.