Browsing by Subject "Circulator"

Now showing 1 - 4 of 4

Engineering exotic linear and nonlinear electromagnetic responses using spatial and spatiotemporal modulation
(2019-05) Tymchenko, Mykhailo; Alù, Andrea; Belkin, Mikhail; Bank, Seth R.; Wasserman, Daniel; Khanikaev, Alexander B.
Periodicity and modulation lie at the heart of modern electromagnetic, acoustic and mechanical engineering, dramatically altering the way in which waves interact with periodically structured media. The main idea driving the intense research into periodic systems is the fact that periodicity breaks the dependence on natural properties of constituent media and instead allows one to blend the responses of various materials and leverage their geometric shapes to obtain collective responses on demand. In the realm of electromagnetics, over the past two decades there has been an explosive surge of interest to artificially engineered time-invariant periodic structures thanks to numerous fascinating linear and nonlinear effects they enable. In this dissertation, I will present some transformative developments in the area of efficient nonlinear generation and wave mixing in thin 2D periodic structures based on multi-quantum-wells, as well as show the possibility to engineer to the great extent the dispersion topology of surface waves propagating along ideally thin conducting sheets with 1D spatial periodicity such as graphene ribbons. In parallel with the progress in obtaining desired responses in time-invariant periodic structures, significant progress is being made in applying temporal and synchronous spatial and temporal modulation to engage new degrees of freedom and extend the spectrum of achievable electromagnetic phenomena even further. In this dissertation, I will also show that spatiotemporal modulation applied to electronic networks holds a key to obtain ultrawideband and extremely compact delays far beyond those achievable in time-invariant systems. Spatiotemporal modulation also allows for all kinds of nonreciprocal devices to be seamlessly integrated in an electronic chip by overcoming the size and magnetic material incompatibility constraints. This fact holds a truly groundbreaking potential for future electronic devices and wireless systems by enabling their simultaneous transmit-and-receive operation. Finally, I will show that spatiotemporal modulation enables a direct translation of some of the most advanced and intricate concepts of condensed matter physics – topological insulators – to the realm of classical electronic circuits. Compared to standalone nonreciprocal devices, topologically-nontrivial electronic circuits provide an even larger toolbox to obtain various nonreciprocal functionalities by enforcing a wideband unidirectional transmission robust to defects and imperfections
Magnetless circulators based on linear time-varying circuits
(2019-06-18) Kord, Ahmed; Alù, Andrea; Gharpurey, Ranjit; Wasserman, Daniel; Vishwanath, Sriram; Krishnaswamy, Harish
In a crowded electromagnetic spectrum with an ever‐increasing demand for higher data rates to enable multimedia‐rich applications and services, an efficient use of the available wireless resources becomes crucial. For this reason, full‐duplex communication, which doubles the transmission rate over a certain bandwidth compared to currently deployed half-duplex radios by operating the uplink and the downlink simultaneously on the same frequency, has been brought back into the spotlight after decades of being presumed impractical. This long‐held assumption has been particularly due to the lack of high performance low-cost and small-size circulators that could mitigate the strong self-interference at the RF frontend interface of full-duplex transceivers while, at the same time, permitting low-loss bi-directional communication using a single antenna. Traditionally, such non-reciprocal components were almost exclusively based on magnetic biasing of rare-earth ferrite materials, which results in bulky and expensive devices that are not suitable for the vast majority of commercial systems. Despite significant research efforts over the past few decades, none of the previous works managed to eliminate the magnet while satisfying all the challenging requirements dictated by the standards of real systems. In this dissertation, we introduce several newly invented magnetless circulators based on linear time-varying circuits that can overcome for the first time the limitations of all previous approaches. We analyze the presented circuits rigorously and validate them through simulations and measurements, showing unprecedented performance in all relevant metrics, thus holding the promise to enable full-duplex radios in the near future
New frontiers in microwave metamaterials : magnetic-free non-reciprocal devices based on angular-momentum-biasing and negative-index metawaveguides
(2015-08) Estep, Nicholas Aaron; Alù, Andrea; Gharpurey, Ranjit; Ling, Hao; Shvets, Gennady; Wang, Zheng
In this work, metamaterial concepts are applied to improve the design and realization of microwave components of a new generation. Conventional radiation sources, despite the mature and efficient development over the past century, maintain fundamental limitations. Slow-wave structures, such as backward-wave oscillators and traveling-wave tubes, function on the order of several operational wavelengths, leading to bulky architectures. Cherenkov radiation-based detectors are constrained to forward propagation, where the detection or diagnostic scheme may be damaged by energetic particles. Metamaterial concepts, specifically negative-index structures, provide new opportunities for these applications. In this context, we developed a detailed design of a negative-index metamaterial conducive to microwave generation. We experimentally validated a negative-index waveguide based on patterned plates of complementary split ring resonators. The design is conducive to interaction between particles and waves; it maintains a scalable negative-index band along with a longitudinal electric field component for particle interaction. The sub-wavelength resonant nature of the metamaterial allows for a compact design. In a different field of research, there is also significant need to squeeze the dimensions of microwave components. We have developed magnet-less, non-reciprocal, microwave circulators based on angular-momentum-biasing, which allow the realization of non-reciprocal devices that do not require magnets, and therefore lead to cheaper, lighter and significantly smaller devices. Angular-momentum-biasing, theoretically proposed recently in our research group, effectively mimics the collective alignment of electron spins seen in a ferromagnetic medium under a magnetic bias. Through spatiotemporal modulation, one can generate electrical rotation, leading to strong nonreciprocal response without magnetism. We have experimentally proven the theory on lumped element circulators and proposed transmission-line variations, providing over 50 dB of isolation in a range of frequency bands. This method provides efficient, easily tunable, fully integrable, compact devices that may revolutionize the future of integrated components. We have developed rigorous design principles that not only provide guidance for designs based on desired performance metrics, but also proves the passive nature of the concept. Furthermore, we have crafted mechanisms to enhance the bandwidth performance and improve linearity.
Using real time traveler demand data to optimize commuter rail feeder systems
(2012-08) Yu, Yao, Ph. D.; Machemehl, Randy B.; Leite, Fernanda; Kendrick, David A.; Boyles, Steve; Zhang, Zhanmin
Commuter rail systems, operating on unused or under-used railroad rights-of-way, are being introduced into many urban transportation systems. Since locations of available rail rights-of-way were typically chosen long ago to serve the needs of rail freight customers, these locations are not optimal for commuter rail users. The majority of commuter rail users do not live or work within walking distance of potential commuter rail stations, so provision of quick, convenient access to and from stations is a critical part of overall commuter decisions to use commuter rail. Minimizing access time to rail stations and final destinations is crucial if commuter rail is to be a viable option for commuters. Well-designed feeder routes or circulator systems are regarded as potential solutions to provide train station to ultimate destination access. Transit planning for main line or feeder routes relies upon static demand estimates describing a typical day. Daily and peak-hour demands change in response to the state of the transport system, as influenced by weather, incidents, holiday schedules and many other factors. Recent marketing successes of “smart phones” might provide an innovative means of obtaining real time data that could be used to identify optimal paths and stop locations for commuter rail circulator systems. Such advanced technology could allow commuter rail users to provide real-time final destination information that would enable real time optimization of feeder routes. This dissertation focuses on real time optimization of the Commuter Rail Circulator Route Network Design Problem (CRCNDP). The route configuration of the circulator system – where to stop and the route among the stops – is determined on a real-time basis by employing adaptive Tabu Search to timely solve an MIP problem with an objective to minimize total cost incurred to both transit users and transit operators. Numerical experiments are executed to find the threshold for the minimum fraction of travelers that would need to report their destinations via smart phone to guarantee the practical value of optimization based on real-time collected demand against a base case defined as the average performance of all possible routes. The adaptive Tabu Search Algorithm is also applied to three real-size networks abstracted from the Martin Luther King (MLK) station of the new MetroRail system in Austin, Texas.