Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78712, USA.
Department of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden.
Phys Rev Lett. 2018 Apr 6;120(14):143901. doi: 10.1103/PhysRevLett.120.143901.
Extraction of electromagnetic energy by an antenna from impinging external radiation is at the basis of wireless communications and wireless power transfer (WPT). The maximum of transferred energy is ensured when the antenna is conjugately matched, i.e., when it is resonant and it has an equal coupling with free space and its load. This condition, however, can be easily affected by changes in the environment, preventing optimal operation of a WPT system. Here, we introduce the concept of coherently enhanced WPT that allows us to bypass this difficulty and achieve dynamic control of power transfer. The approach relies on coherent excitation of the waveguide connected to the antenna load with a backward propagating signal of specific amplitude and phase. This signal creates a suitable interference pattern at the load resulting in a modification of the local wave impedance, which in turn enables conjugate matching and a largely increased amount of extracted energy. We develop a simple theoretical model describing this concept, demonstrate it with full-wave numerical simulations for the canonical example of a dipole antenna, and verify experimentally in both near-field and far-field regimes.
天线从外部入射辐射中提取电磁能量是无线通信和无线功率传输 (WPT) 的基础。当天线共轭匹配时，即当它谐振且与自由空间及其负载具有相等的耦合时，可确保传输的能量最大。然而，这种情况很容易受到环境变化的影响，从而阻止 WPT 系统的最佳运行。在这里，我们引入相干增强 WPT 的概念，该概念允许我们绕过此困难并实现功率传输的动态控制。该方法依赖于通过具有特定幅度和相位的反向传播信号来相干地激励与天线负载相连的波导。该信号在负载处产生合适的干涉图案，从而导致局部波阻抗发生变化，这反过来又允许共轭匹配并大大增加提取的能量。我们开发了一个简单的理论模型来描述这个概念，并用全波数值模拟对典型的偶极天线示例进行了演示，并在近场和远场两种情况下进行了实验验证。
