We embed diodes as active circuit elements within a metamaterial to implement a switchable metamaterial reflector/absorber at microwave frequencies. Diodes are placed in series with the unit cells of the metamaterial array. This results in just a pair of control lines to actively tune all the diodes in a metamaterial. Diodes can be tuned on and off to switch the function of the metamaterial between a perfect absorber and a reflector. The design, simulation, and experimental results of a switchable reflector/absorber in 2–6 GHz range are presented.

We present the design of a tunable metamaterial element that can serve as the building block for a dynamically reconfigurable aperture. The element-a complimentary electric-LC (cELC) resonator-is patterned into the upper conductor of a microstrip transmission line, providing both a means of exciting the radiating metamaterial element as well as independent access for biasing circuitry. PIN diodes are connected across the capacitive gaps of the cELC and a DC bias current is used to switch the junction between conducting and insulating states. The leakage of RF signal through the bias line is mitigated by integration of a radial decoupling stub. The proposed design and operation of the element are demonstrated through full-wave electromagnetic simulations. We discuss the potential application of the cELC element as a building block for metamaterial apertures capable of dynamic beam-forming, imaging, or security screening applications. Index Terms-Aperture antennas, metamaterials, tunable circuits and devices

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Dielectric and ohmic losses in metamaterials are known to limit their practical use. In this paper, an all-electronic approach for loss compensation in metamaterials is presented. Each unit cell of the meta-material is embedded with a cross-coupled transistor pair based negative differential resistance circuit to cancel these losses. Design, simulation and experimental results for Split Ring Resonator (SRR) metamaterials with and without loss compensation are presented. Results indicate that the quality factor (Q) of the SRR improves by over 400% at 1.6 GHz, showing the effectiveness of the approach. The proposed technique is scalable over a broad frequency range and is limited only by the maximum operating frequency of transistors, which is reaching terahertz in today's semiconductor technologies.

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