Invisibility cloaking devices constitute a unique and potentially disruptive technology, but only if they can work over broad bandwidths for electrically-large objects. So far, the only known scheme that allows for broadband scattering cancellation from an electrically-large object is based on an active implementation where electric and magnetic sources are deployed over a surface surrounding the object, but whose ‘switching on’ and other characteristics need to be known (determined) a priori, before the incident wave hits the surface. However, until now, the performance (and potentially surprising) characteristics of these devices have not been thoroughly analysed computationally, ideally directly in the time domain, owing mainly to numerical accuracy issues and the computational overhead associated with simulations of electrically-large objects. Here, on the basis of a finite-difference time-domain (FDTD) method that is combined with a perfect (for FDTD’s discretized space) implementation of the total-field/scattered-field (TFSF) interface, we present detailed, time- and frequency-domain analyses of the performance and characteristics of active cloaking devices. The proposed technique guarantees the isolation between scattered- and total-field regions at the numerical noise level (around −300 dB), thereby also allowing for accurate evaluations of the scattering levels from imperfect (non-ideal) active cloaks. Our results reveal several key features, not pointed out previously, such as the suppression of scattering at certain frequencies even for imperfect (time-delayed) sources on the surface of the active cloak, the broadband suppression of back-scattering even for imperfect sources and insufficiently long predetermination times, but also the sensitivity of the scheme on the accurate switching on of the active sources and on the predetermination times if broadband scattering suppression from all angles is required for the electrically-large object.

中文翻译：

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电大物体主动隐身的时域有限差分分析

隐形隐身设备构成了一种独特的且具有潜在破坏性的技术，但前提是它们可以在较大的带宽上工作以处理大型电气物体。到目前为止，唯一允许从大型电气物体消除宽带散射的已知方案是基于一种主动实现方式，其中在物体周围的表面上部署了电磁源，但是其“接通”和其他特性需要被先验（确定），在入射波撞击水面之前。然而，直到现在，这些设备的性能（以及可能令人惊讶的）特性还没有得到完整的计算分析，理想情况下直接在时域中进行了分析，这主要是由于数值精度问题和与电大物体的仿真相关的计算开销。在此，基于有限差分时域（FDTD）方法与总场/散场（TFSF）接口的完美实现（对于FDTD的离散空间），我们提供了详细的时间-主动隐身装置的性能和特征的频域分析。所提出的技术保证了在数值噪声水平（-300 dB左右）下散射区域和总场区域之间的隔离，因此，还可以准确评估不完美（非理想）的活动披风的散射程度。我们的结果揭示了一些以前未曾指出的关键特征，例如，即使对于活动披风表面上的不完美（时间延迟）源，也可以在某些频率上抑制散射，甚至对于不完善的源也可以对宽带进行反向散射抑制。足够长的预定时间，但如果电大物体需要从各个角度抑制宽带散射，则该方案对于精确接通有源电源和预定时间的灵敏度也很高。