Rasmussen Curtis, Rosa Matheus I N, Lewton Jacob, Ruzzene Massimo
P. M. Rady Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO, 80309, USA.
Adv Sci (Weinh). 2023 Oct;10(28):e2301811. doi: 10.1002/advs.202301811. Epub 2023 Aug 16.
The creation of a sink in a lossless wave-bearing medium is achieved using complex frequency signals-harmonic excitations that exponentially grow in time. The wave sink, where incident waves are confined to a point, has attracted interest for imaging and sensing since it may lead to arbitrarily small hotspots that surpass the diffraction limit. However, most methods of creating sinks require careful tuning, such as by impedance matching the sink to free space through the inclusion of loss, which imposes constraints on emerging applications. An alternative method, proposed here, relies on complex frequency excitations, bypassing the need to modify the scattering system by instead shaping the input signal. Eigenvalue zeros derived from a scattering formalism extended to the complex frequency plane reveal operating conditions that induce complete energy trapping under steady-state conditions in a framework generally applicable to 2D and 3D media. To support the developed theory, an experiment is performed where a sink is realized using elastic waves on a plate with a circular cutout. These findings may lead to imaging and sensing applications relying on subwavelength focal points and nonlinear wave generation due to the high amplitudes achieved over short timescales.
在无损波传播介质中通过使用复频率信号（即随时间呈指数增长的谐波激励）来创建一个波阱。波阱可将入射波限制在一个点上，由于它可能会产生超越衍射极限的任意小的热点，因此在成像和传感领域引起了人们的兴趣。然而，大多数创建波阱的方法都需要仔细调整，例如通过引入损耗使波阱与自由空间进行阻抗匹配，这对新兴应用施加了限制。本文提出的一种替代方法依赖于复频率激励，无需通过修改散射系统，而是通过对输入信号进行整形来实现。从扩展到复频率平面的散射形式理论中导出的特征值零点揭示了在稳态条件下能在一般适用于二维和三维介质的框架中诱导完全能量俘获的工作条件。为了支持所提出的理论，进行了一项实验，在带有圆形切口的平板上利用弹性波实现了一个波阱。由于在短时间尺度上能实现高振幅，这些发现可能会推动依赖亚波长焦点和非线性波产生的成像和传感应用的发展。
