Electromagnetic wave control using the concept of a reflecting surface is first studied as a near-field and a far-field problem. Using a secondary source present in a wireless communication environment, such as a backscatter tag, it is possible to leverage the incoming radiation from the source as a reference-wave to synthesize the desired wavefront across the reflecting surface, radiating a field of interest. In this geometry, the phase grating, which is synthesized using an array of sub-wavelength unit cells, is calculated by interacting the incident reference-wave with the desired wavefront, similar to a hologram. When illuminated by the reference-wave, the reflected wavefront from the calculated phase grating is guaranteed to constructively add in the direction of the desired radiation (beam-steering in the far-field) and also focus at the intended depth (beam-focusing in the radiative near-field). Next, leveraging a dynamic modulation mechanism in the context of an intelligent reflective surface (IRS) illuminated by a backscatter tag, we demonstrate that one can selectively focus and defocus at an arbitrarily positioned receiver within the 3D field of view of the reflecting surface. This enables the control of the amplitude of the radiated electric field at the receiver location, paving the way for a spatial modulation mechanism by means of reconfiguring the reflecting surface in a backscattered wireless communication environment. In addition to the phase modification approach on a unit cell level to reconfigure the aperture radiated wavefronts, we finally present a time varying IRS concept making use of a time-delay based approach relying on a delay adjustment between the reflection coefficients of the IRS’ unit cell lattices.

中文翻译：

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具有空间调制的智能反射表面：电磁学的视角

首先，研究了使用反射面概念的电磁波控制作为近场和远场问题。使用存在于无线通信环境中的辅助源（例如反向散射标签），可以利用来自源的入射辐射作为参考波来合成穿过反射面的所需波前，从而辐射出感兴趣的场。在这种几何形状中，类似于全息图，通过使入射参考波与所需波前相互作用，可以计算出使用亚波长单位单元阵列合成的相位光栅。当被参考波照射时，保证了从计算出的相位光栅反射的波前在所需辐射的方向上进行结构性相加（远场中的光束转向），并且还聚焦在预期的深度上（在辐射性近场中进行光束聚焦）。接下来，在由后向散射标签照亮的智能反射表面（IRS）的背景下，利用动态调制机制，我们演示了可以在反射表面的3D视场内的任意放置的接收器上选择性地聚焦和散焦。这使得能够控制接收器位置处的辐射电场的幅度，从而通过在反向散射无线通信环境中重新配置反射表面，为空间调制机制铺平了道路。