135 research outputs found
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
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Scanning Probe and Spectroscopic Investigations Of Polarization-Driven Electronic Interactions at the Inorganic/Organic Interface of 2D Materials
My thesis focuses on understanding the changes in electronic properties of two-dimensional materials produced by surface interactions not limited to charge exchange. Recent work from our group demonstrated that both small molecules and polymers can function as effective charge dopants for monolayered 2D materials such as MoS2 and graphene, changing the Fermi energy by either donating or accepting electron density to/from the 2D material. Additionally, the underlying support material was found to play a significant role, where higher dielectric constant supports result in larger magnitude of Fermi energy shift of the 2D material because less of the dopant interaction is lost polarizing the support. This work here was motivated by the desire to understand in greater detail how electronic properties of 2D materials can be tailored by exploiting different types of surface interactions, and how the properties can be characterized in a manner which is both specific to the 2D layer, and insightful with respect to the impact of different environmental factors. To this end, two questions were asked: 1) How significant is polarization of the 2D layer in determining electronic properties, compared to charge exchange? 2) What is the role of the overlayer and the underlayer (support) in electronic properties vs. the determined properties?
The questions were addressed using two experimental platforms. In the first, we employed a zwitterionic polymer to test the response of graphene to permanent surface dipoles. The interaction was probed using Kelvin probe force microscopy to detect changes in the Fermi energy, electrostatic force microscopy to detect changes in surface charges and polarizability and was examined from the graphene side and the polymer side by employing a unique inverted sample construction along with a normal orientation sample. This allowed us to probe the source of changes in the Fermi energy, disentangling dipole effects from those of charge exchange, and to observe the magnitude of electric charge screening present in the graphene layer. In the second platform, we used a polymer with perfluorinated linear alkyl side chains to examine the role of fluorine and surface dipole formation in the p-doping of MoS2, using a second unfluorinated polymer as a control. In the system, the photoluminescence signatures of three body excited states (trions, i.e., charged excitons) were used to unambiguously determine changes in the MoS2 carrier density which was compared with Kelvin probe force microscopy measurements of changes in the Fermi energy.
Our goal was to elucidate the role dipoles and surface polarization play in the electronic properties of 2D materials and provide tools to approach the doping and characterization of these materials. We probed phosphorylcholine containing zwitterionic polymer coatings of graphene, and fluorinated polymer coatings of MoS2 using a combination of Kelvin probe force microscopy, electrostatic force microscopy, and photoluminescence. Our key findings were that polarization, both due to the presence of surface dipoles or due to dipole formation in response to fluorinated groups, strongly influences the Fermi energy and can have a larger impact than the exchange of charge. We found that charge exchange accounted for only about 10% of the 261 meV shift in the Fermi energy of graphene due to phosphorylcholine polymers. Additionally, we found that graphene has an astounding electrical ‘opacity’. When viewing a surface interaction through graphene, charge screening within graphene reduces the observed magnitude of the interaction by a factor of ~26. We found that perfluoropolymers are capable of both destabilizing trions and shifting the Fermi energy in MoS2, by ~40x more than the calculated reduction in charge would predict. These findings underline the significance of surface interactions in driving the electronic properties of 2D materials, particularly those involving dipoles, and demonstrate methods of exploiting them to tailor the Fermi energy and photoluminescence properties of two prototypical materials in graphene and MoS2. Further, the way multiple scanning probe techniques can be incorporated into chemical analysis is demonstrated, along with the combination of photoluminescence with scanning probe measurements
Energy-Sustainable IoT Connectivity: Vision, Technological Enablers, Challenges, and Future Directions
Technology solutions must effectively balance economic growth, social equity,
and environmental integrity to achieve a sustainable society. Notably, although
the Internet of Things (IoT) paradigm constitutes a key sustainability enabler,
critical issues such as the increasing maintenance operations, energy
consumption, and manufacturing/disposal of IoT devices have long-term negative
economic, societal, and environmental impacts and must be efficiently
addressed. This calls for self-sustainable IoT ecosystems requiring minimal
external resources and intervention, effectively utilizing renewable energy
sources, and recycling materials whenever possible, thus encompassing energy
sustainability. In this work, we focus on energy-sustainable IoT during the
operation phase, although our discussions sometimes extend to other
sustainability aspects and IoT lifecycle phases. Specifically, we provide a
fresh look at energy-sustainable IoT and identify energy provision, transfer,
and energy efficiency as the three main energy-related processes whose
harmonious coexistence pushes toward realizing self-sustainable IoT systems.
Their main related technologies, recent advances, challenges, and research
directions are also discussed. Moreover, we overview relevant performance
metrics to assess the energy-sustainability potential of a certain technique,
technology, device, or network and list some target values for the next
generation of wireless systems. Overall, this paper offers insights that are
valuable for advancing sustainability goals for present and future generations.Comment: 25 figures, 12 tables, submitted to IEEE Open Journal of the
Communications Societ
Probing quantum devices with radio-frequency reflectometry
Many important phenomena in quantum devices are dynamic, meaning that they cannot be studied using time-averaged measurements alone. Experiments that measure such transient effects are collectively known as fast readout. One of the most useful techniques in fast electrical readout is radio-frequency reflectometry, which can measure changes in impedance (both resistive and reactive) even when their duration is extremely short, down to a microsecond or less. Examples of reflectometry experiments, some of which have been realized and others so far only proposed, include projective measurements of qubits and Majorana devices for quantum computing, real-time measurements of mechanical motion, and detection of non-equilibrium temperature fluctuations. However, all of these experiments must overcome the central challenge of fast readout: the large mismatch between the typical impedance of quantum devices (set by the resistance quantum) and of transmission lines (set by the impedance of free space). Here, we review the physical principles of radio-frequency reflectometry and its close cousins, measurements of radio-frequency transmission and emission. We explain how to optimize the speed and sensitivity of a radio-frequency measurement and how to incorporate new tools, such as superconducting circuit elements and quantum-limited amplifiers into advanced radio-frequency experiments. Our aim is threefold: to introduce the readers to the technique, to review the advances to date, and to motivate new experiments in fast quantum device dynamics. Our intended audience includes experimentalists in the field of quantum electronics who want to implement radio-frequency experiments or improve them, together with physicists in related fields who want to understand how the most important radio-frequency measurements work
Radiation Tolerant Electronics, Volume II
Research on radiation tolerant electronics has increased rapidly over the last few years, resulting in many interesting approaches to model radiation effects and design radiation hardened integrated circuits and embedded systems. This research is strongly driven by the growing need for radiation hardened electronics for space applications, high-energy physics experiments such as those on the large hadron collider at CERN, and many terrestrial nuclear applications, including nuclear energy and safety management. With the progressive scaling of integrated circuit technologies and the growing complexity of electronic systems, their ionizing radiation susceptibility has raised many exciting challenges, which are expected to drive research in the coming decade.After the success of the first Special Issue on Radiation Tolerant Electronics, the current Special Issue features thirteen articles highlighting recent breakthroughs in radiation tolerant integrated circuit design, fault tolerance in FPGAs, radiation effects in semiconductor materials and advanced IC technologies and modelling of radiation effects
Development of a chipless RFID based aerospace structural health monitoring sensor system
Chipless Radio Frequency Identification (RFID) is modern wireless technology that has been earmarked as being suitable for low-cost item tagging/tracking. These devices do not require integrated circuitry or a battery and thus, are not only are cheap, but also easy to manufacture and potentially very robust. A great deal of attention is also being put on the possibility of giving these tags the ability to sense various environmental stimuli such as temperature and humidity.
This work focusses on the potential use of chipless RFID as a sensor technology for aerospace Structural Health Monitoring. The project is focussed on the sensing of mechanical strain and temperature, with an emphasis placed on fabrication simplicity,
so that the final sensor designs could be potentially fabricated in-situ using existing printing technologies.
Within this project, a variety of novel chipless RFID strain and temperature sensors have been designed, fabricated and tested. A thorough discussion is also presented on the topic of strain sensor cross sensitivity, which places emphasis on issues like, transverse strain, dielectric constant variations and thermal swelling. Additionally, an exploration into other key technological challenges was also performed, with a focus on challenges such as: accurate and reliable stimulus detection, sensor polarization and multi-sensor support.
Several key areas of future research have also been identified and outlined, with aims related to: Enhancing strain sensor fabrication simplicity, enhancing temperature sensor sensitivity and simplicity and developing a fully functional interrogation system
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
Micro/Nano Structures and Systems
Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field
Antennas and Electromagnetics Research via Natural Language Processing.
Advanced techniques for performing natural language processing (NLP) are being utilised to devise a pioneering methodology for collecting and analysing data derived from scientific literature. Despite significant advancements in automated database generation and analysis within the domains of material chemistry and physics, the implementation of NLP techniques in the realms of metamaterial discovery, antenna design, and wireless communications remains at its early stages. This thesis proposes several novel approaches to advance research in material science. Firstly, an NLP method has been developed to automatically extract keywords from large-scale unstructured texts in the area of metamaterial research. This enables the uncovering of trends and relationships between keywords, facilitating the establishment of future research directions. Additionally, a trained neural network model based on the encoder-decoder Long Short-Term Memory (LSTM) architecture has been developed to predict future research directions and provide insights into the influence of metamaterials research. This model lays the groundwork for developing a research roadmap of metamaterials. Furthermore, a novel weighting system has been designed to evaluate article attributes in antenna and propagation research, enabling more accurate assessments of impact of each scientific publication. This approach goes beyond conventional numeric metrics to produce more meaningful predictions. Secondly, a framework has been proposed to leverage text summarisation, one of the primary NLP tasks, to enhance the quality of scientific reviews. It has been applied to review recent development of antennas and propagation for body-centric wireless communications, and the validation has been made available for comparison with well-referenced datasets for text summarisation. Lastly, the effectiveness of automated database building in the domain of tunable materials and their properties has been presented. The collected database will use as an input for training a surrogate machine learning model in an iterative active learning cycle. This model will be utilised to facilitate high-throughput material processing, with the ultimate goal of discovering novel materials exhibiting high tunability. The approaches proposed in this thesis will help to accelerate the discovery of new materials and enhance their applications in antennas, which has the potential to transform electromagnetic material research
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