Fundamental Properties and Practical Application of Active Microwave Metamaterials Incorporating Gain Devices
Technical Report,30 Sep 2013,30 Mar 2016
Arizona Univ Board Of Regents Tucson Tucson United States
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Metamaterials are artificially designed composite materials which can exhibit unique and unusual properties such as the negative refractive index, negative phase velocity, etc. The concept of metamaterials becomes prevalent in the electromagnetic society since the first experimental implementation in the early 2000s. Many fascinated potential applications, e.g. super lens, invisibility cloaking, and novel antennas that are electrically small, have been proposed based on metamaterials. However, most of the applications still remain in theory and are not suitable for practical applications mainly due to the intrinsic loss and narrow bandwidth large dispersion determined by the fundamental physics of metamaterials. In this program, we have incorporated active gain devices into conventional passive metamaterials to overcome loss and even provide gain. Two types of active gain negative refractive index metamaterials have been proposed, designed and experimentally demonstrated, including an active composite left-right-handed transmission line and an active volumetric metamaterial. These designs have been extended to THz frequency range. In addition, we have investigated the non-Foster circuits for broadband matching of electrically small antennas. A rigorous way of analyzing the stability of non-Foster circuits by normalized determinant function has been proposed. We have studied the practical factors that may affect the stability of non-Foster circuits, including the device parasitics, DC biasing, layouts and load impedance. A stable floating negative capacitor has been designed, fabricated and tested. Moreover, it is important to resolve the sign of refractive index for active gain media which can be quite challenging. We have investigated the analytical solution of a gain slab system, and applied the Nyquist criterion to analyze the stability of a causal gain medium.
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