Elektromanyetik Alanlar ve Mikrodalga Tekniği Anabilim Dalı
Middle East Technical University2
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Kablosuz metamalzemeden ilham alınan dönüş algılayıcıları
Recently steel construction structures have been attracting increasingly more attention due to the speed and ease of their construction. However, to detect potential damages in these structures, long-term and cost-effective health monitoring solutions are required. A rotation-based bending movement, which typically occurs in the load carrying elements of these structures (such as beams), is an example of the aforementioned potential damage. In this thesis, for measuring small bending rotations (10−4 ∼ 10−5 radians) in the structures made of materials such as steel, a novel wireless rotation sensing system with a high level of sensitivity and resolution is proposed and demonstrated. This system consists of two elements: an interrogating antenna and an interdigital double-layer sensor. The proposed sensing system operates based on the principle of near-field coupling between the antenna and the sensor. Briefly, by rotating one layer with respect to the other, the electromagnetic coupling between the layers changes and the resonance frequency is consequently shifted. This frequency shift can be recorded by tracking the resonance dips in the S11 response of the antenna. In the thesis work, various experiments were systematically performed to characterize the sensing system. A high rotation resolution of 20 µ-radians, an excellent sensitivity level of 28 MHz/degree, and a large dynamic range extending over 40◦ were measured. Furthermore, the validity of measurement results was verified by using full-wave electromagnetics simulator and applying digital image correlation (DIC) method for 2D measurements.
Alternatif j-sınıfı yaklaşımı ile GaN teknolojisi temelligeniş bant yüksek verimli güç yükselteci uygulamaları
RF power amplifiers have been the essential elements of any transmit/receive block. Especially in the transmit chain, some applications require high RF power, such as radar, jammer, telecommunication signals targeting a wide range of coverage. High power requirements in RF broadcast mean high supply power to feed RF PA. The efficiency parameter of a high-power transmission system becomes an issue due to heating problems and performance degradation depending on rising temperatures. The heating problem is commonly solved using active cooling plants. Cooling plants add extra cost demanding discrete power supplies and considerable amount of design labor. With these problems at hand, industrial and academic environments have turned to look for more efficient amplifier topologies. In this thesis, modified class-J schemes proposed to enhance operating bandwidth are studied. A modification called "normalized resistive-reactive class-J" (NRRCJ) approach is proposed. Detailed parametric analysis is presented. The effects of parameters in governing equations are discussed. A related engineering design procedure is demonstrated with an ultra-broadband GaN PA. Prototype PA operating at 400-3200 MHz capable of at least 10 W saturated output power is fabricated. Measured efficiency values of %53-%69.8 are obtained at saturated output power. The average efficiency is calculated as %62.45. The measurement results, theoretical aspects, and expectations are compared. It is shown that the resistive termination of harmonics in a systematic way makes it possible to achieve a broadband and relatively high efficiency performance, simultaneously. The final prototype achieves remarkable compatibility with a practical RF system, compared with similar examples in the literature, in terms of size, gain, efficiency, output power and operating frequency band.