【作者】 王志宇；

【导师】 冉立新； Marin Solja(?)i(?)；

【作者基本信息】 浙江大学 ， 电子科学与技术， 2013， 博士

【摘要】 本文结合Maxwell-Garnett等效媒质理论和人工媒质的有源构造方法,分别进行了具有强非线性和旋电效应的有源人工微波媒质研究。自然媒质在微波频段通常只呈现极其微弱的非线性效应。对比类别丰富的空间光学非线性应用,微波频段的非线性应用通常局限于微波电路中实现。基于等效媒质理论,本文研究、设计和实现了具有强空间非线性电磁响应的有源人工微波媒质,在微瓦级空间微波照射下观测到了清晰的空间谐波产生和频谱调制等非线性效应,并从实验测量数据中有效地提取了上述人工微波媒质的等效非线性特征本构参数。在上述工作基础上,本文提出并实验演示了微波源的非线性空间成像和远场重构,得到了超过Abbe衍射极限(Abbe diffraction limit)的空间分辨率。在Maxwell理论中,电磁波的传播满足互易原理,并在能量守恒的条件下遵循局部时间反演对称(Local time-reversal symmetry)。仅在外加偏置场的条件下,自然存在的少量回旋(Gyrotropic)媒质,如磁化等离子体和铁氧体,可以呈现微弱的非互易旋电或旋磁效应。本文创新地利用微波电路中常见的单向元件,提出了无需外加偏置磁场即可呈现强旋电效应的有源人工媒质构造方法。通过将有源元件的单向性转化为等效媒质的非互易电磁响应,物理实现了仅需直流电压偏置的人工旋电微波媒质,并采用逆问题优化算法提取了对应的等效特征本构参数。在进一步的实验研究中,本文清晰观测到了具有显著极化角度偏转的法拉第极化旋转效应,验证了电磁波在上述人工媒质传播中不对称的局部时间反演。本文研究所得的两种人工微波媒质从原理上避免了相应的自然存在媒质在微波频段的性能局限,具有很好的潜在应用前景。更多还原

【Abstract】 In this dissertation, assisted by Maxwell-Garnett effective medium theory and the construction approach with active elements, research on active metamaterials with strong microwave responses of nonlinearity and gyroelectricity were conducted.At the microwave frequencies, natural media usually exhibit extremely weak nonlinear effects. Compared with diverse spatial nonlinear optical applications, nonlinear applications at microwave frequencies are usually limited to microwave circuits. Based on the effective medium theory, we designed and realized an active metamaterial with strong spatial nonlinear electromagnetic (EM) responses. Under the illumination of a micro-Watt spatial microwave, strong nonlinear EM responses, like spatial harmonic generation and spectrum modulation, were clearly observed. After that, the effective nonlinear constitutive parameters of the active metamaterial were successfully retrieved from measured data. Based on above research, we proposed and experimentally demonstrated the imaging of microwave sources. Spatial resolutions exceeding the Abbe diffraction limit were achieved.In Maxwell’s theory, EM waves propagating in most natural media satisfy the reciprocal theory. When energy conservation is satisfied, this propagation exhibits a local time-reversal symmetry. Few naturally occurring gyrotropic media, such as magnetized plasma and ferrite, behave relatively weak non-reciprocal, gyroelectric or gyromagnetic phenomena only when external bias magnetic fields are applied. In this dissertation, by innovatively introducing unidirectional devices commonly used in active microwave circuits, we proposed a construction method of the active metamaterial with strong gyroelectric effects in the absence of an external magnetic bias. By translating the property of a unidirectional active device into the non-reciprocal response of effective media, we realized a gyroelectric metamaterial that only depends on a DC-voltage bias. Effective constitutive parameters were retrieved by using an optimization algorithm. In further experiments, strong non-reciprocal Faraday rotations with large deflected polarization angles were observed, breaking the local time-reversal symmetry.The obtained active metamaterials fundamentally avoided the inherent performance limits of the corresponding naturally occurring media at microwave frequencies, showing a wide range of potential applications in the future.更多还原