关键词: phase gradient structure, one-dimensional mechanical adjustment, adjustable focusing

Abstract: Adjustable or programmable metamaterials offer versatile functions, while the complex multi-dimensional regulation increases workload, and hinders their applications in practical scenarios. To address these challenges, we present a mechanically programmable acoustic metamaterial for real-time focal tuning via one-dimensional phase-gradient modulation in this paper. The device integrates a phase gradient structure with concave cavity channels and an x-shaped telescopic mechanical framework, enabling dynamic adjustment of inter-unit spacing (1 mm-3 mm) through a microcontroller-driven motor. By modulating the spacing between adjacent channels, the phase gradient is precisely controlled, allowing continuous focal shift from 50 mm to 300 mm along the $x$-axis at 7500 Hz. Broadband focusing is also discussed in the range 6800 Hz-8100 Hz, with transmission coefficients exceeding 0.5, ensuring high efficiency and robust performance. Experimental results align closely with simulations, validating the design's effectiveness and adaptability. Unlike conventional programmable metamaterials requiring multi-dimensional parameter optimization, this approach simplifies real-time control through single-axis mechanical adjustment, significantly reducing operational complexity. Due to the advantages of broadband focusing, simple control mode, real-time monitoring, and so on, the device may have extensive applications in the fields of acoustic imaging, nondestructive testing, ultrasound medical treatment, etc.

Key words: phase gradient structure, one-dimensional mechanical adjustment, adjustable focusing