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DTSTART;TZID=America/New_York:20220922T130000
DTEND;TZID=America/New_York:20220922T140000
DTSTAMP:20260618T011658
CREATED:20221103T184721Z
LAST-MODIFIED:20221103T184721Z
UID:5924-1663851600-1663855200@ece.northeastern.edu
SUMMARY:Justin Crabb's PhD Proposal Review
DESCRIPTION:“Multiphysics Simulation of Graphene Transistors for On-Chip Plasmonic THz Signal Generation and Modulation” \nAbstract: \nTerahertz communication is envisioned as a key technology not only for the next generation of macro-scale networks (e.g.\, 6G+)\, but also for transformative networking applications at the nanoscale (e.g.\, wireless nanosensor networks and wireless networks on chip). This proposal focuses on the development of a multiphysics simulation platform for a plasmonic THz nanogenerator with on-chip modulation. The in-house developed finite-element-method platform\, which self-consistently solves the hydrodynamic and Maxwell’s equations\, is utilized to provide extensive numerical results demonstrating the device’s functionality along with ultra-wide bandwidth and high modulation index capabilities. \nFirst\, a comprehensive theory of the Dyakonov-Shur (DS) plasma instability in current-biased graphene transistors is presented. Using the hydrodynamic approach\, equations describing the DS instability in the two-dimensional electron fluid in graphene at arbitrary values of electron drift velocity are derived. These non-linear equations together with Maxwell’s equations are used for numerical analysis of the spatial and temporal evolution of the graphene electron system after the DS instability is triggered by random current fluctuations. Conditions necessary for the onset of the DS instability and the properties of the final stationary state of the graphene electron system are analyzed. \nNext\, a detailed numerical analysis of the DS plasma instability in the DC current-biased graphene transistor with the gate shifted with respect to the middle of the transistor conducting channel is presented. The geometric asymmetry is shown to be sufficient to trigger the DS instability in the two-dimensional electron gas in the transistor channel. Sustained plasma oscillations in the instability endpoint are demonstrated and the properties of these oscillations are analyzed for different positions of the gate and at different values of other physical and geometric FET parameters. The obtained results show the possibility of designing a tunable on-chip source of THz electromagnetic radiation based on the graphene transistor with a shifted gate. \nFollowing\, the on-chip THz nano-generator with amplitude and frequency modulation capabilities is presented. The proposed device uses and leverages the tunability of the Dyakonov-Shur instability for the growth and modulation of plasmonic oscillations in the two-dimensional electron gas channel of the graphene transistor. \n  \nCommittee: \nProf. Josep Jornet (Advisor) \nProf. Tommaso Melodia \nProf. Matteo Rinaldi \nProf. Hossein Mosallaei
URL:https://ece.northeastern.edu/event/justin-crabbs-phd-proposal-review/
LOCATION:432 ISEC\, 360 Huntington Ave\, Boston\, MA\, 02115\, United States
GEO:42.3396156;-71.0886534
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END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220923T120000
DTEND;TZID=America/New_York:20220923T130000
DTSTAMP:20260618T011658
CREATED:20221103T181851Z
LAST-MODIFIED:20221103T181851Z
UID:5882-1663934400-1663938000@ece.northeastern.edu
SUMMARY:Eric Robinson's PhD Proposal Review
DESCRIPTION:“Techniques for the Modelling\, Design\, and Fabrication of Ultra-Wideband Dipole Arrays”\nAbstract: \nA novel set of techniques are proposed which advance the state of the art for the modelling\, design\, and fabrication of ultra-wideband dipole arrays. First\, existing techniques and relevant topics in the field are introduced and summarized. These include equivalent circuit and Green’s Function models for the impedance of the infinite dipole array. Challenges for the realization of arrays are discussed\, including finite array effects\, common-mode effects\, and the limitations of different fabrication techniques. Several relevant recent innovations by the author are presented to form the foundation of the proposed work. \nFirst\, a new lossy transmission line model for the infinite dipole array impedance is described which results in highly accurate predictions across wide bandwidths and for large scan angles. The accuracy of the model is demonstrated via comparisons to full-wave simulations\, and the model is used to rapidly design a wide-scanning\, ultra-wideband array to demonstrate its value. Next\, a new technique developed by the author is described for physically realizing complex dipole array geometries with integrated dielectrics. A tightly-coupled array is achieved by 3D-printing an array of elements featuring internal through-cavities in the shape of the radiating elements. The internal surfaces of these cavities are then metallized via a copper deposition\, producing an array of conductive elements within a dielectric shell\, resulting in improved mechanical rigidity\, improved scan performance\, and increased inter-element capacitance for ultrawide bandwidth. \nBuilding on these results\, additional research is proposed for completion of the dissertation. First\, the lossy transmission line model will be extended to other relevant cases\, including the unbalanced feed-structure-fed dipole array and the hybrid slot-dipole array. Second\, a new model will be implemented to describe the effects of surface waves on the active impedance of the tightly-coupled dipole array. Mitigating techniques will be proposed based on the results of this model\, enabling the realization of finite arrays which better conform to the predicted performance of the infinite array. Finally\, each of the aforementioned models and techniques will be leveraged towards the design and fabrication of a notional array for an imaging application\, demonstrating their practical value for array design. \nCommittee: \nProf. Carey Rappaport (Advisor) \nProf. Josep Jornet\nProf. Edwin Marengo Fuentes \nDr. Ian McMichael
URL:https://ece.northeastern.edu/event/eric-robinsons-phd-proposal-review/
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220926T143000
DTEND;TZID=America/New_York:20220926T153000
DTSTAMP:20260618T011658
CREATED:20221103T184922Z
LAST-MODIFIED:20221103T184922Z
UID:5926-1664202600-1664206200@ece.northeastern.edu
SUMMARY:Michele Pirro's PhD Dissertation Defense
DESCRIPTION:“AlScN material characterization for MEMS applications” \nAbstract: \nThe increasing demand for data is pushing the MEMS industry to more performant and area-efficient systems to be used in IOT nodes as sensors and RF-components. In this market\, AlN plays a pivotal role thanks to the piezoelectric properties accompanied with good stability over power and temperature in miniaturized devices. In fact\, AlN is already present in different commercial MEM systems\, such as duplexers\, ultrasound generators\, energy harvesters and so on\, proving a mature mass-production process flow. The required more stringent specifications in terms of bandwidth\, losses and efficiency are pushing towards piezoelectric materials with higher coupling coefficient\, but still in a compatible post-CMOS process flow. Recent works showed how it is possible to enhance the piezoelectric effect by doping AlN with Scandium\, allowing up to 400% increase in the d33 piezoelectric coefficient. The enhanced acoustic transduction along with the recent demonstration of ferroelectric switching and the post-IC compatibility\, is making Sc-doped AlN a new material with the potential not only to replace AlN\, but also to integrate different functionalities within the same component. Academy and industry all over the world are actively researching the actual potential of the material but there is still a lack of information on high-Sc concentration\, which would allow lower-voltage switching along with higher d33. This work has the main objective to show Sc-concentration > 28% and their piezo/ferroelectric response for a new class of microelectromechanical devices.\nI will discuss the advance in the process flow of high Sc-concentrations\, showing the impact of the deposition parameters on the material properties with focus on the ferroelectric behavior. Effect of RF powers on the substrate and on the target are also analyzed\, demonstrating the possibility to properly optimize the AlScN deposition. Last\, I will present MEM devices which exploit the enhanced piezoelectric activity (high frequency resonators and pmut) and the ferroelectric properties (impedance with memory)\, confirming the potential of the material for new multi-functionalities MEMS. \nCommittee: \nProf. Matteo Rinaldi (Advisor) \nProf. Cristian Cassella \nProf. Siddhartha Ghosh
URL:https://ece.northeastern.edu/event/michele-pirros-phd-dissertation-defense/
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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20220929T090000
DTEND;TZID=America/New_York:20220929T220000
DTSTAMP:20260618T011658
CREATED:20221103T185118Z
LAST-MODIFIED:20221103T185118Z
UID:5930-1664442000-1664488800@ece.northeastern.edu
SUMMARY:Priyangshu Sen's PhD Dissertation Defense
DESCRIPTION:Location: ISEC 532 \n“Physical Layer Design for Ultrabroadband Terahertz Communications: From Theory to Experiments” \nAbstract: \nTerahertz (THz)-band (0.1 THz to 10 THz) communication is envisioned as a key technology to meet the demand for faster\, more ubiquitous wireless communication networks for the sixth generation (6G) of wireless systems and beyond. For many years\, the lack of compact\, fast and efficient ways to generate\, modulate\, detect and demodulate THz signals has limited the feasibility of such communication systems. Recent progress within different device technologies is finally closing the terahertz technology gap and enabling\, for the first time\, experimental wireless research in the THz band. \nThis thesis presents the first steps towards advancing the development and bridging the gap between theoretical and experimental THz communication research. At the core of this work\, the TeraNova platform\, i.e\, the first testbed for ultra-broadband wireless communications at THz frequencies in the world\, is designed and built. In terms of hardware\, the platform consists of multiple sets of analog front-ends at three different frequencies between 100 GHz and 1.05 THz and three different digital signal processing back-ends\, able to manipulate tens of GHz of bandwidth. In terms of software\, tailored framing\, time synchronization\, channel estimation\, and single and multi-carrier modulation techniques are implemented in guided by the experimental characterization of the THz hardware and the THz channel. Moreover\, implementation details and early experimental results to demonstrate the platform’s capabilities/limitations are reported. The platform is then used to demonstrate several milestones in the field\, including the first true THz link in the first absorption-defined window above 1 THz (i.e.\, 1-1.05 THz) and the longest multi-kilometer link (2.01 Km) at the 200-240 GHz band. Further\, Knowing the peculiarities of the THz band and the available device technology in the frequency range\, innovative solutions are proposed. Based on the observed behaviors\, M-ary amplitude and phase-shift keying is presented to simultaneously overcome the limitations due to peak to average power ratio (PAPR) and reduce the effective symbol error rate (SER)\, both while using a high-order modulation scheme. Based on the unique molecular absorption at THz frequencies\, two innovative modulation schemes are presented to make the most of the THz channel. First\, to not only overcome but exploit the distance-dependent bandwidth of the THz band\, hierarchical bandwidth modulations are proposed as a suitable candidate for a single transmitter and multiple receiver (STMR) system. Second\, to reliably communicate even in the presence of absorption peaks\, chirp spread spectrum (CSS) based communication is investigated. Specifically\, Chirp-Spread Binary Phase-Shift Keying (CS-BPSK) is proposed over traditional Binary Chirp Spread Spectrum (BCSS) to obtain better BER. Moreover\, beyond the physics\, current spectrum allocations break down the otherwise very large bands into narrow sub-sets to accommodate sensing users. Spectrum sharing is needed to make the most out of the spectral resources. Therefore\, the capability of the direct sequence spread spectrum (DSSS) is explored to illustrate the performance by acknowledging the coexistence between active and passive users. Further\, channel sounding is conducted in diverse indoor and outdoor scenarios to understand the channel statistics and design reliable communication links. As the last contribution in this dissertation\, the channel model and statistics are explored for an ultra-broadband outdoor channel in different weather conditions. Further\, the channel metrics are explored in various indoor scenarios with different structural and geometrical aspects\, occupancy\, and antenna gain at 130 GHz. For this purpose\, a fully tailored signal processing back-end for sliding correlator type channel sounder is developed\, which is capable of capturing multipath profiles to describe the ultra-broadband nature of the link. \nIn a nutshell\, this dissertation presents the technologies and the results\, highlights the challenges\, and defines a path to move forward with innovative solutions toward practical THz ultra-broadband and long-distance communication systems. \nCommittee: \nProf. Josep Jornet (Advisor) \nProf. Tommaso Melodia \nProf. Milica Stojanovic \nProf. Kaushik Chowdhury
URL:https://ece.northeastern.edu/event/priyangshu-sens-phd-dissertation-defense/
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