发表机构
Imperial College London; Universitat Politècnica de València; Purdue University; Universitat Jaume I; Fudan University（帝国理工学院; 瓦伦西亚理工大学; 普渡大学; 海梅一世大学; 复旦大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出利用非线性虚拟源在结构表面直接产生与目标模式对称性匹配的局域低频源，实现对称保护声学BIC的非侵入式远场激发，在不引入额外辐射通道的前提下保持其高约束特性，为开放系统中的波操控与高灵敏度器件提供了通用策略。
AI 中文摘要
连续谱中的束缚态（BICs）通过相消干涉或对称保护机制，能够在开放系统中实现完全的波约束，从而产生理想化的无限品质因子和极端的场增强效应。然而，其实际应用受到一个根本性悖论的阻碍：抑制辐射的同一机制也阻止了从远场进行高效激发。现有的实验方法通常通过引入外部耦合通道来克服这一限制，但这不可避免地会扰动受保护的状态并降低其约束能力。在此，我们展示了一种通过直接在结构表面产生的非线性虚拟源来实现对称保护声学BIC的非侵入式激发方法。通过将时间调制的超声束聚焦到超反射镜上，非线性解调产生局域化的低频源，其空间相位与目标模式的对称性相匹配，同时避免与谐振器发生任何物理耦合。这种方法在不打开额外辐射通道的情况下将能量注入BIC，从而保持其固有的非辐射特性。我们建立了一个描述该模式形成和对称保护的理论框架，通过对称性约化实现了紧凑的实验装置，并直接测量了受限压力场及其品质因子。我们的研究结果表明，非线性虚拟源为在开放系统中访问对称保护态提供了一条途径，同时保持了其卓越的约束特性，为跨物理平台实现波操控和高灵敏度谐振器件提供了一种通用策略。
英文摘要
Bound states in the continuum (BICs) enable complete wave confinement within open systems through destructive interference or symmetry protection, giving rise to ideally infinite quality factors and extreme field enhancement. Their practical exploitation, however, is hindered by a fundamental paradox: the same mechanism that suppresses radiation also prevents efficient excitation from the far field. Existing experimental approaches typically overcome this limitation by introducing external coupling channels that inevitably perturb the protected state and reduce its confinement. Here we demonstrate the non-invasive excitation of a symmetry-protected acoustic BIC through nonlinear virtual sources generated directly at the surface of the structure. By focusing time-modulated ultrasonic beams onto a metamirror, nonlinear demodulation produces localized low-frequency sources whose spatial phase matches the symmetry of the target mode while avoiding any physical coupling to the resonator. This approach injects energy into the BIC without opening additional radiative channels, preserving its intrinsic non-radiative character. We develop a theoretical framework describing the formation and symmetry protection of the mode, realize a compact experimental implementation through symmetry reduction, and directly measure the confined pressure field and its quality factor. Our results establish nonlinear virtual sources as a route to accessing symmetry-protected states in open systems while maintaining their exceptional confinement properties, providing a general strategy for wave manipulation and high-sensitivity resonant devices across physical platforms.
