On-demand harmonic wave suppression in non-Hermitian space-time-periodic phased arrays
On-demand harmonic wave suppression in non-Hermitian space-time-periodic phased arrays
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DOI：
10.1088/1361-665x/acd597
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发表时间：
2023-05
影响因子：
4.1
通讯作者：
R. Adlakha;M. Nouh
中科院分区：
文献类型：
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作者：
R. Adlakha;M. Nouh
多年来，相控阵一直是无损评估、声纳通信和医学成像的基石。常规阵列通过在一组换能器上施加静态相位梯度来在期望的方向上操纵自创建的波前来工作。最近，空间时间周期（STP）相控阵列已经在多谐波波束的背景下进行了探索。由于STP相位分布，产生了单频输入的多个散射谐波，这些谐波在不同的方向通道中同时传播。这些通道中的每一个的特征在于可以通过计算预测的主要角度和不同的频率特征。然而，由于时空相位梯度的厄米（真实的）性质，从阵列出射的波仍然必然沿着具有完美对称能量分布的上转换和下转换方向同时传播。寻求推动这一边界，本文提出了一类非厄米STP相控阵列，通过增益，损耗和耦合之间的相互作用，其各个组件之间的发射波行使前所未有的控制程度。在两个特殊的对称性，奇偶校验时间（PT）和反PT，一个复杂的相位分布，使调制的各种谐波的幅度和adapples上，下转换的谐波相同的顺序。我们表明，这些阵列提供按需抑制的上转换或下转换的谐波在一个特殊的点-退化的参数空间中的系统的本征值和本征向量合并。非厄米阵列的实验原型的构建说明选择性的方向抑制通过时间瞬态测量的弹性基板的面外位移，通过激光测振。非厄米相控阵理论及其实验实现为精确的弹性声波操纵提供了丰富的机会，可以为各种工程应用量身定制。
Phased arrays have been a cornerstone of non-destructive evaluation, sonar communications, and medical imaging for years. Conventional arrays work by imparting a static phase gradient across a set of transducers to steer a self-created wavefront in a desired direction. Most recently, space-time-periodic (STP) phased arrays have been explored in the context of multi-harmonic wave beaming. Owing to the STP phase profile, multiple scattered harmonics of a single-frequency input are generated which propagate simultaneously in different directional lanes. Each of these lanes is characterized by a principal angle and a distinct frequency signature that can be computationally predicted. However, owing to the Hermitian (real) nature of the spatiotemporal phase gradient, waves emergent from the array are still bound to propagate simultaneously along up- and down-converted directions with a perfectly symmetric energy distribution. Seeking to push this boundary, this paper presents a class of non-Hermitian STP phased arrays which exercise a degree of unprecedented control over the transmitted waves through an interplay between gain, loss, and coupling between its individual components. A complex phase profile under two special symmetries, parity-time (PT) and anti-PT, is introduced that enables the modulation of the amplitude of various harmonics and decouples up- and down-converted harmonics of the same order. We show that these arrays provide on-demand suppression of either up- or down-converted harmonics at an exceptional point—a degeneracy in the parameter space where the system’s eigenvalues and eigenvectors coalesce. An experimental prototype of the non-Hermitian array is constructed to illustrate the selective directional suppression via time-transient measurements of the out-of-plane displacements of an elastic substrate via laser vibrometry. The theory of non-Hermitian phased arrays and their experimental realization unlock rich opportunities in precise elastoacoustic wave manipulation that can be tailored for a diverse range of engineering applications.