Terahertz response of microfluidic-jetted fabricated 3D flexible metamaterials

Conventional materials exhibit some restrictions on their electromagnetic properties. Especially in terahertz region, for example, materials that exhibit magnetic response are far less common in nature than materials that exhibit electric response. However, materials can be designed, namely artificial man-made metamaterials that exhibit electromagnetic properties that are not found in natural materials by adjusting, for example, the dielectric, magnetic or structural parameters of the constituent elements. This dissertation demonstrates the use of new fabrication techniques to construct metamaterials in THz range via a material deposition system. The metamaterials are fabricated by stacking alternative layers with conventional designs such as single ring- split ring resonators (SRR) and microstrips to form a 3D metamaterial structure. Conductive nano-particle Ag, Cu and semiconductor polymer fluids are used as structural mediums. The metamaterials are fabricated on polyimide substrate. Their flexible nature will be advantageous in future device innovations. In order to obtain electromagnetic resonance in the terahertz range, the dimensions of the single ring-SRR and microstrips are first approximated by analytical methods and then confirmed by numerical simulation. The fabricated metamaterials are then characterized in transmission mode using Time-domain THz Spectroscopy (THz-TDS) in the 0.1 to 2 THz range

New frontiers in microwave metamaterials : magnetic-free non-reciprocal devices based on angular-momentum-biasing and negative-index metawaveguides

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.Electrical and Computer Engineerin

Reconfigurable and multi-functional antennas

This thesis describes a research into multi-frequency and filtering antennas. Several novel antennas are presented, each of which addresses a specific issue for future communication systems, in terms of multi-frequency operation, and filtering capability. These antennas seem to be good candidates for implementation in future multiband radios, cognitive radio (CR), and software defined radio (SDR). The filtering antenna provides an additional filtering action which greatly improves the noise performance and reduces the need for filtering circuitry in the RF front end. Two types of frequency reconfigurable antennas are presented. One is tunable left-handed loop over ground plane and the second is slot-fed reconfigurable patch. The operating frequency of the left handed loop is reconfigured by loading varactor diodes whilst the frequency agility in the patch is achieved by inserting switches in the coupling slot. The length of the slot is altered by activating the switches. Compact microstrip antennas with filtering capabilities are presented in this thesis. Two filtering antennas are presented. Whilst the first one consists of three edge-coupled patches, the second filtering antenna consists of rectangular patch coupled to two hairpin resonators. The proposed antennas combine radiating and filtering functions by providing good out of band gain suppression

RF MEMS technology for millimeter-wave radar sensors

The dissertation discusses RF MEMS technology for millimeter-wave radar sensors. RF MEMS, which stands for radio frequency micro-electromechanical system, and radar sensor fundamentals are briefly introduced. Of particular interest are: Firstly, a self-aligned fabrication process for capacitive fixed-fixed beam RF MEMS components is disclosed. It enables scaling of the critical dimensions and reduces the number of processing steps by 40% as compared with a conventional RF MEMS fabrication process. Scaling of the critical dimensions of RF MEMS components offers the potential of submicrosecond T/R switching times. RF MEMS varactors with beam lengths of 30 μm are demonstrated using the self-aligned fabrication process, and the performance of a 4 by 4 RF MEMS varactor bank is discussed as well. At 20 GHz, the measured capacitance values range between 180.5 fF and 199.2 fF. The measured capacitance ratio is 1.15, when a driving voltage of 35 V is applied, and the measured loaded Q factor ranges between 14.5 and 10.8. The measured cold-switched power handling is 200 mW. The simulated switching time is 354.6 ns. Secondly, an analog RF MEMS slotline TTD phase shifter is disclosed, for use in conjunction with ultra wideband (UWB) tapered slot antennas, such as the Vivaldi aerial and the double exponentially tapered slot antenna. It is designed for transistor to transistor logic (TTL) bias voltage levels and exhibits a measured phase shift of 28.2°/dB (7.8 ps/dB) and 59.2°/cm at 10 GHz, maintaining a 75 Ω; differential impedance match (S11dd ≤ -15.8 dB). The input third-order intercept point (IIP3) is 5 dBm at 10 GHz for a Δf of 50 kHz, measured in a 100 Ω differential transmission line system.Ph.D.Electrical EngineeringUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/61348/1/vcaeken.pd

Chirality as Generalized Spin-Orbit Interaction in Spintronics

This review focuses on the chirality observed in the excited states of the magnetic order, dielectrics, and conductors that hold transverse spins when they are evanescent. Even without any relativistic effect, the transverse spin of the evanescent waves are locked to the momentum and the surface normal of their propagation plane. This chirality thereby acts as a generalized spin-orbit interaction, which leads to the discovery of various chiral interactions between magnetic, phononic, electronic, photonic, and plasmonic excitations in spintronics that mediate the excitation of quasiparticles into a single direction, leading to phenomena such as chiral spin and phonon pumping, chiral spin Seebeck, spin skin, magnonic trap, magnon Doppler, and spin diode effects. Intriguing analogies with electric counterparts in the nano-optics and plasmonics exist. After a brief review of the concepts of chirality that characterize the ground state chiral magnetic textures and chirally coupled magnets in spintronics, we turn to the chiral phenomena of excited states. We present a unified electrodynamic picture for dynamical chirality in spintronics in terms of generalized spin-orbit interaction and compare it with that in nano-optics and plasmonics. Based on the general theory, we subsequently review the theoretical progress and experimental evidence of chiral interaction, as well as the near-field transfer of the transverse spins, between various excitations in magnetic, photonic, electronic and phononic nanostructures at GHz time scales. We provide a perspective for future research before concluding this article.Comment: 136 pages, 60 figure

Broken passivity and time-reversal-symmetry bounds in acoustics devices

We collect information about the world through our senses, two of which, hearing and touch, are attuned to the mechanical vibrations travelling around us. Scientists and engineers have learned to control these acoustic waves, and in so doing they have opened new possibilities in how we interact with each other and the natural world. One area of rapid progress is acoustic metamaterials, which are architected structures that can shape sound waves in ways that go beyond what is possible with natural materials. Given the potential of these new materials, it is important to consider their limits and identify the underlying physical principles responsible for them. In this dissertation we examine limitations in the response of acoustic materials and devices due to passivity and time-reversal symmetry. An important constraint that arises due to time-reversal symmetry is reciprocity. Reciprocity must be broken to create devices that allow sound through in only one direction. This work explores acoustic nonreciprocity with particular attention to applications in surface acoustic wave devices and topological acoustic demonstrations. One way to achieve acoustic nonreciprocity is with fluid flow. Based on this technique, we present an acoustic Mach-Zehnder isolator and nonreciprocal leaky-wave antenna. A different but equally fundamental and important constraint in acoustics technology is the trade-off between the size, efficiency, and bandwidth of a small resonator. By considering arbitrary stored and radiated sound fields surrounding a compact source, we derive a theoretical lower bound on the quality factor of a passive acoustic radiator. This work discusses opportunities to overcome this constraint by considering active resonators. We experimentally demonstrate a three-fold bandwidth improvement to the passive case by synthesizing a non-Foster circuit load for a piezoelectric sonar transducer. By using a Green’s function approach and by connecting the physics of a disordered array to the statistical theory of random walks, we also explore the physics of near-zero-index materials, and leverage their unusual sound-matter interactions to enable robust and highly directive acoustic sources. This work introduces an entirely new way to achieve highly directional sound beyond traditional techniques.Mechanical Engineerin

Resonant excitation of a nanowire quantum dot and optical frequency shifting via electro-optic modulation

The ability to create pairs of entangled photons is a requirement for many near-future quantum technologies. Despite this, the current state-of-the-art entangled photon sources are fundamentally limited in their performance by their probabilistic nature. Recently, semiconductor quantum dots have gained a great deal of interest as candidates for next-generation entangled photon sources. Quantum dots can produce photon pairs deterministically, and therefore do not suffer from the same limitation. In addition, certain emission properties such as the emission direction, lifetime and spectral linewidth can be greatly improved by embedding the quantum dot within a nanostructure. The results in this thesis are from two separate, but related, techniques relating to the performance of an InAsP quantum dot embedded in an InP photonic nanowire. The first technique is resonant two-photon excitation of the quantum dot, a scheme of optically exciting the quantum dot which is expected to outperform all other optical excitation methods. Quantum dots use the biexciton-exciton cascade to generate entanglement, and the performance of the source depends on how the biexciton is generated within the dot. By directly populating the biexciton state of the quantum dot through two-photon excitation, the charge noise is decreased, which reduces both re-excitation of the dot and dephasing over the lifetime of the excited state. Using this method of excitation, we measure single photon purities of 0.9979(3) and 0.9985(2) for the emitted biexciton and exciton photons, respectively. Furthermore, quantum state tomography of the emitted pairs reveals a peak concurrence of 0.87(4), with a count-averaged concurrence of 0.52(3). This represents the first ever quantum state tomography measurement of a nanowire quantum dot excited with this excitation scheme. One downside of quantum dot-based photon sources is there tends to be some asymmetry introduced unintentionally in the fabrication process. This leads to an energy difference between the intermediate states of the biexciton-exciton cascade, called the fine structure splitting. The fine structure splitting causes the state to precess, so that the state emitted depends on the time between the first and second exciton recombinations. The second technique investigated in this thesis is an all-optical method of eliminating the fine structure splitting. This proposed method uses a pair of electro-optic modulators to shift the energy of the emitted photons and recover the state emitted by a quantum dot without any fine structure splitting. In this thesis, we demonstrate a lithium niobate electro-optic modulator capable of both increasing and decreasing the energy of photons, depending on their polarization. We show up-conversion of right circularly polarized light with 83.7% efficiency and down-conversion of left circularly polarized light with 80.7% efficiency. This demonstration shows that an all-optical fine structure eraser is feasible, and leaves us well-positioned for an experimental demonstration in the near future

Tatsuo Itoh : discurs llegit a la cerimònia d'investidura celebrada a la Sala d'Actes del Rectorat el dia 14 d'octubre de l'any 2015

Tatsuo Itoh va ser investit doctor honoris causa per la UAB per les seves rellevants contribucions a l'enginyeria de radiofreqüència/microones i de les telecomunicacions.Nomenament 19/03/2015. A proposta de l'Escola d'Enginyeria. L'acte d'investidura va tenir lloc el 14 d'octubre de 201