18 research outputs found
RF micro-systems for 5G front-end signal processing
No full textThe fifth-generation (5G) communication has sparked great research interest in developing the next generation radio frequency (RF) front ends for more stringent requirements on performance, power consumption, and spectral utilization efficiency. More parallel RF bands and paths are added in the same form factor, along with which come more components and tighter integration. Designing portable systems faces the new challenge of reducing component size while still operating at RF, where the path attenuation is low and fading is readily manageable. Satisfactory size reduction is particularly difficult for passive components that rely on the principle of waveguiding and thus scale with electromagnetic (EM) wavelength at RF (typical ~10s cm). Hence, radical size reduction by several orders of magnitude can only be attained by resorting to a physical domain other than EM, namely acoustic waves with wavelengths 4~5 orders of magnitude smaller. In fact, acoustic devices at RF, such as surface or bulk acoustic wave devices, have been widely used for mobile phone applications. Other acoustic elements, such as couplers, correlators, and impedance matching networks, have also shown promising potential to outperform the state-of-the-art EM counterparts. However, the past developments often battled the challenge of efficiently accessing the acoustics over a sufficiently wide bandwidth and subsequently producing application-worthy performance, because of the fundamental limitations from the lack of high electromechanical coupling (k2) and low damping piezoelectric platforms. Recently, thanks to the advances in materials, design, and fabrication, LiNbO3 thin-film has been proved as a promising low-loss, wideband, and frequency-diverse acoustic platform for novel functions toward high-performance 5G front-end signal processing.
Based on acoustic devices in LiNbO3 thin films, this thesis aims to design and demonstrate several classes of novel RF microsystems that can enable conventional signal processing functions with better performance or new tasks for emerging applications. First, the acoustic systems are used as passive signal processing elements for the Internet of Things (IoT) applications. The high figure of merit (FoM) LiNbO3 resonator array is used as the impedance matching element for interfacing with the high impedance CMOS rectifiers in the IoT-inspired wake-up radio. The high FoM, adequately large static capacitance and spurious free performance collectively contribute to a high voltage gain over 20. Another type of microsystem for IoT applications is 1-dB IL acoustic delay lines (ADLs) on the S0 mode in thin-film LiNbO3, showing record-breaking low IL over a larger bandwidth, opening new horizons for low-power RF acoustic signal processing. Second, the miniature nonreciprocal component based on switched high-performance delay elements is demonstrated for full duplex radio. The wideband and long delay featured by the high-performance LiNbO3 ADLs significantly benefit the performance, including the dynamic switching induced IL and intra-modulations, while relaxing the requirements for synthesizing and synchronizing the control signals. The demonstrated 4 port circulator shows a highly symmetric performance across the 4-ports with 18.8 dB nonreciprocal contrast between the IL (6.6 dB) and isolation (25.4 dB) over an FBW of 8.8% at a center frequency 155 MHz, all of which are accomplished with a record low switching frequency of 877.22 kHz. Upon further optimizations, such circulators can potentially outperform ferrite-based devices in loss, bandwidth, and isolation while offering more compact size and reconfigurable operation. Third, low-loss wideband GHz S0 mode ADLs are explored for self-interference cancellation in full-duplex radio. The fabricated miniature acoustic delay lines show a fractional bandwidth of 4% and a minimum IL of 3.2 dB at a center frequency of 0.96 GHz. Various delays ranging from 20 ns to 900 ns have been obtained for digitally addressable delay synthesis. Multiple acoustic delay lines with center frequencies from 0.9 to 2 GHz have been demonstrated. The demonstrated ADLs can potentially provide wide-range and high-resolution reconfigurable delays for future SIC applications. Finally, design and measurement of 5 GHz antisymmetric mode acoustic delay lines for 5G enhanced mobile broadband (eMBB) applications are presented; the demonstrated ADLs significantly surpass the state of the art with similar feature sizes in center frequency. The implemented ADLs at 5 GHz show a minimum insertion loss of 7.94 dB and a fractional bandwidth around 4%. In addition to the remarkable device performance, these designs also point out the opportunities to advance the operation frequencies of acoustic devices toward the wideband and high-frequency signal processing functions required for future 5G applications.
RF acoustic microsystems demonstrated in this thesis have shown promising prospects for 5G front-end signal processing applications. Thanks to the simultaneously low damping and wideband performance at RF, acoustic devices based on LiNbO3 thin films are auspicious candidates to provide the design flexibilities and high performance required for various 5G application scenarios. Further development in high-performance RF acoustic devices may put on the horizon an RF front-end synthesized either purely or predominantly from an RF acoustic component kit.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-12-01The student, Ruochen Lu, accepted the attached license on 2019-09-12 at 09:43.The student, Ruochen Lu, submitted this Dissertation for approval on 2019-09-12 at 10:03.This Dissertation was approved for publication on 2019-09-13 at 16:52.DSpace SAF Submission Ingestion Package generated from Vireo submission #14451 on 2020-02-28 at 17:35:17Made available in DSpace on 2020-03-02T22:38:37Z (GMT). No. of bitstreams: 4
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Previous issue date: 2019-09-13Embargo set by: Seth Robbins for item 113969
Lift date: 2022-03-02T22:39:04Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 113969 on 2022-03-03T10:15:08Z
Thin-Film Lithium Niobate Acoustic Delay Line Oscillators
No full textIn this work, thin-film lithium niobate (LiNbO3) acoustic delay line (ADL) based oscillators are experimentally investigated for the first time for the application of single-mode oscillators and frequency comb generation. The design space for the ADL-based oscillator is first analyzed, illustrating that the key to low phase noise lies in high center frequency (fo), large delay (τ G), and low insertion loss (IL) of the delay. Therefore, two self-sustained oscillators employing low noise amplifiers (LNA) and a low IL, long delay (fo=157MHz, IL =2.9dB, τG= 200-440ns) SH0 mode ADLs are designed for a case study. The two SH0 ADL oscillators show measured phase noise of -109 dBc/Hz and -127 dBc/Hz at 10-kHz offset while consuming 16 mA and 48 mA supply currents, respectively. Although the carrier power of the proposed oscillator is lower than published state-of-the-art ADL oscillators, competitive phase noise performance is still attained thanks to the low IL. Finally, frequency comb generation is also demonstrated with the same delay line and a commercial RF feedback amplifier, showing a comb spacing of 3.4 MHz that matches the open-loop characterization.Accepted Author ManuscriptDynamics of Micro and Nano System
Low-loss and wideband acoustic delay lines
No full text This paper demonstrates low-loss acoustic delay lines (ADLs) based on shear-horizontal waves in thin-film LiNbO 3 for the first time. Due to its high electromechanical coupling, the shear-horizontal mode is suited for producing devices with large bandwidths. Here, we show that shear-horizontal waves in LiNbO 3 thin films are also excellent for implementing low-loss ADLs based on unidirectional transducers. The high acoustic reflections and large transducer unidirectionality induced by the mechanical loading of the electrodes on a LiNbO 3 thin film provide a great tradeoff between delay line insertion loss and bandwidth. The directionality for two different types of unidirectional transducers has been characterized. Delay lines with variations in the key design parameters have been designed, fabricated, and measured. One of our fabricated devices has shown a group delay of 75 ns with an IL below 2 dB over a 3-dB bandwidth of 16 MHz centered at 160 MHz (fractional bandwidth = 10%). The measured insertion loss for other devices with longer delays and different numbers of transducer cells are analyzed, and the loss contributing factors and their possible mitigation are discussed. Accepted Author ManuscriptDynamics of Micro and Nano System
A Multi-Task Learning Based Runoff Forecasting Model for Multi-Scale Chaotic Hydrological Time Series
No full textAccurately predicting runoff is crucial for managing water resources, preventing and mitigating floods, scheduling hydropower plant operations, and protecting the environment. The hydrological dynamic composite system that forms runoff is complex and random, and seemingly random behavior may be caused by nonlinear variables in a simple deterministic system, which poses a challenge to runoff prediction. In this paper, we construct parallel and multi-timescale reservoirs from a chaotic theory perspective to simulate the stochasticity of chaotic systems. We propose a multi-task-based "Decomposition-Integration-Prediction" (Multi-SDIPC) model for runoff prediction. To validate our research results, we use the Catchment Attributes and Meteorology for Large-Sample Studies (CAMELS) dataset and compare our proposed model with 10 baseline models. The results show that our model has an average NSE metric of 0.83 and exhibits higher accuracy, better generalization, and greater stability than the other models in multi-step forecasting. Based on our findings, we recommend wider application of the Multi-SDIPC model in different regions of the world for medium or long-term runoff prediction.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport Engineering and Logistic
Leadership and Management of A Jiangnan Town in Late Qing (1800-1911)
No full text本文的目的在於理解南潯作為一個繁榮的江南市鎮，如何在十九世紀的各個階段得到有效的管理，以及其領導層的組成如何隨著外界的政治經濟變遷而改變。作者選擇市鎮作為研究單位，其目的在於將市場和周邊的村落放在同一單位下檢視，以求更好地在經濟和社會層面認識中國之城鄉連續體的本質。通過細讀地方一手史料（包括地方志、族譜、報紙和文集），本文將不僅從制度的角度，同時也會通過地方權力持有者（包括地方官、下層士紳和商人）的具體活動，來觀察南潯鎮的權力結構。我的主要論點是，雖然地方的領導層從未放棄其自治權，但是該領導層的組成卻能夠靈活地在不同階段（1800-1842，1843-1864，1865-1890，1891-1911）進行重組，這造就了南潯鎮一整個世紀的社會穩定，除了其間遭受外來的太平天國戰爭的打擊。為了經營市場和經營更大的市鎮，地方領袖們成立了不同的組織且運用了不同的策略。概括而論，商人行會的成立是為了協調商業事務，而寺廟和善堂的維護則是為了建立一種社區共同體的意識并消弭潛在的社會衝突。在整個十九世紀，尤其是其後半段，地方領袖們的行政權和執法權都得到了擴張，其代價是官方權力的縮減，但其同時也確保了辛亥革命期間南潯的和平政權更迭。This paper attempts to understand how a prosperous Jiangnan town, Nanxun, was managed in different periods of the 19th century and how its leadership evolved when the broad political and economic environment changed. The choice of a town as the unit for analysis was made under the intention to bring together the marketplace and the surrounding villages for examining the nature of Chinese urban-rural continuum both economically and socially. Through scrutiny of local primary sources, i.e., local gazetteers, genealogies, newspapers and literary collections, I am going to investigate the power structure of Nanxun town not only from an institutional perspective but also through the activities of local power agents, e.g., local officials, lower gentry and merchants. My thesis is that the local leadership never gave up autonomy over town management but its constitution changed flexibly in four stages (1800-1842, 1843-1864, 1865-1890, 1891-1911), resulting in long-term stability throughout the century except the major interruption by the exogenous Taiping war. For running the marketplace and the broad town, local leaders established different institutions and adopted different strategies. Generally speaking, the merchant guilds were founded for coordinating commercial affairs while the temples and charities were maintained for building a sense of community and easing potential conflicts over the town. Through the second half of the century, especially after several major mid-century structural changes, the administrative and enforcement power of local leaders expanded at the expense of official authority and secured the peaceful regime change in the 1911 Revolution.Chen, Ruochen.Thesis M.Phil. Chinese University of Hong Kong 2016.Includes bibliographical references (leaves ).Abstracts also in Chinese.Title from PDF title page (viewed on …).Detailed summary in vernacular field only
Multi-user Diversity Systems with Application to Cognitive Radio
No full textabstract: This thesis aims to investigate the capacity and bit error rate (BER) performance of multi-user diversity systems with random number of users and considers its application to cognitive radio systems. Ergodic capacity, normalized capacity, outage capacity, and average bit error rate metrics are studied. It has been found that the randomization of the number of users will reduce the ergodic capacity. A stochastic ordering framework is adopted to order user distributions, for example, Laplace transform ordering. The ergodic capacity under different user distributions will follow their corresponding Laplace transform order. The scaling law of ergodic capacity with mean number of users under Poisson and negative binomial user distributions are studied for large mean number of users and these two random distributions are ordered in Laplace transform ordering sense. The ergodic capacity per user is defined and is shown to increase when the total number of users is randomized, which is the opposite to the case of unnormalized ergodic capacity metric. Outage probability under slow fading is also considered and shown to decrease when the total number of users is randomized. The bit error rate (BER) in a general multi-user diversity system has a completely monotonic derivative, which implies that, according to the Jensen's inequality, the randomization of the total number of users will decrease the average BER performance. The special case of Poisson number of users and Rayleigh fading is studied. Combining with the knowledge of regular variation, the average BER is shown to achieve tightness in the Jensen's inequality. This is followed by the extension to the negative binomial number of users, for which the BER is derived and shown to be decreasing in the number of users. A single primary user cognitive radio system with multi-user diversity at the secondary users is proposed. Comparing to the general multi-user diversity system, there exists an interference constraint between secondary and primary users, which is independent of the secondary users' transmission. The secondary user with high- est transmitted SNR which also satisfies the interference constraint is selected to communicate. The active number of secondary users is a binomial random variable. This is then followed by a derivation of the scaling law of the ergodic capacity with mean number of users and the closed form expression of average BER under this situation. The ergodic capacity under binomial user distribution is shown to outperform the Poisson case. Monte-Carlo simulations are used to supplement our analytical results and compare the performance of different user distributions.Dissertation/ThesisM.S. Electrical Engineering 201
Savings and Losses of Scarce Virtual Water in the International Trade of Wheat, Maize, and Rice
No full textThe international cereal trade can mitigate global water stress by saving virtual scarce water (VSW). Based on bilateral trade data, this study assessed VSW savings and losses in the international trade of three major cereals (i.e., wheat, maize, and rice) from 2008 to 2017 by incorporating the water stress index (WSI) into a virtual water assessment. We found that the trade in wheat and maize saved a significant amount of VSW, while the rice trade led to increasingly severe losses of VSW. This study identified the top trades of VSW savings and losses for each cereal. Wheat and maize were primarily exported from the countries that are relatively abundant in water resources (e.g., United States, Brazil, Argentina, Russia) to water-scarce countries (e.g., Mexico and Egypt), whereas rice was exported mainly from India and Pakistan, two of the most water-stressed countries. We suggest that policy makers consider VSW savings and losses when making cereal trading decisions to alleviate global water stress
Dynamic Spectrum Sharing in Cognitive Radio and Device-to-Device Systems
No full textabstract: Cognitive radio (CR) and device-to-device (D2D) systems are two promising dynamic spectrum access schemes in wireless communication systems to provide improved quality-of-service, and efficient spectrum utilization. This dissertation shows that both CR and D2D systems benefit from properly designed cooperation scheme.
In underlay CR systems, where secondary users (SUs) transmit simultaneously with primary users (PUs), reliable communication is by all means guaranteed for PUs, which likely deteriorates SUs’ performance. To overcome this issue, cooperation exclusively among SUs is achieved through multi-user diversity (MUD), where each SU is subject to an instantaneous interference constraint at the primary receiver. Therefore, the active number of SUs satisfying this constraint is random. Under different user distributions with the same mean number of SUs, the stochastic ordering of SU performance metrics including bit error rate (BER), outage probability, and ergodic capacity are made possible even without observing closed form expressions. Furthermore, a cooperation is assumed between primary and secondary networks, where those SUs exceeding the interference constraint facilitate PU’s transmission by relaying its signal. A fundamental performance trade-off between primary and secondary networks is observed, and it is illustrated that the proposed scheme outperforms non-cooperative underlay CR systems in the sense of system overall BER and sum achievable rate.
Similar to conventional cellular networks, CR systems suffer from an overloaded receiver having to manage signals from a large number of users. To address this issue, D2D communications has been proposed, where direct transmission links are established between users in close proximity to offload the system traffic. Several new cooperative spectrum access policies are proposed allowing coexistence of multiple D2D pairs in order to improve the spectral efficiency. Despite the additional interference, it is shown that both the cellular user’s (CU) and the individual D2D user's achievable rates can be improved simultaneously when the number of D2D pairs is below a certain threshold, resulting in a significant multiplexing gain in the sense of D2D sum rate. This threshold is quantified for different policies using second order approximations for the average achievable rates for both the CU and the individual D2D user.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201
Quasi-Distribution Appraisal Based on Piecewise Bézier Curves: An Objective Evaluation Method about Finite Element Analysis
No full textA class of quasi-distribution evaluation criteria based on piecewise Bezier curves is proposed to address the issue of the inability to objectively evaluate finite element models. During the optimization design of mechanical parts, finite element modeling is performed on their stress deformation, and the mesh node shape variable values are converted into distribution histogram data for piecewise Bezier curve fitting. Being dealt with area normalization method, the fitting curve could be regarded as a kind of probability density function (PDF), and its variance could be used to evaluate the finite element modeling results. The situation with the minimum variance is the optimal choice for overall deformation. Numerical experiments have indicated that the new method demonstrated the intrinsic characteristics of the finite element models of difference mechanical parts. As an objective appraisal method for evaluating finite element models, it is both effective and feasible
Review of Automotive Thermoelectric Generator Structure Design and Optimization for Performance Enhancement
No full textThermoelectric generator (TEG) has emerged as a critical technology for automotive exhaust energy recovery, yet there is still a lack of reviews analyzing automotive TEG structure design and optimization methods simultaneously. Therefore, this review consolidates structure design and methods for improving thermoelectric conversion efficiency, focusing on three core components: thermoelectric module (TEM), heat exchanger (HEX), and heat sink (HSK). For TEM, research and development efforts have primarily centered on material innovation and structural optimization, with segmented, non-segmented, and multi-stage configurations emerging as the three primary structural types. HEX development spans external geometries, including plate, polygonal, and annular designs, and internal enhancements such as fin, heat pipe, metal foam, and baffle to augment heat transfer. HSK leverages active, passive, or hybrid cooling systems, with water-cooling designs prevalent in automotive TEG for cold-side thermal management. Optimization methods encompass theoretical analysis, numerical simulation, experimental testing, and hybrid methods, with strategies devised to balance computational efficiency and accuracy based on system complexity and resource availability. This review provides a systematic framework to guide the design and optimization of automotive TEG
