Bradley Department of Electrical and Computer Engineering

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https://hdl.handle.net/10919/18738

From pervasive computing, to smart power systems, Virginia Tech ECE faculty and students delve into all major areas of electrical and computer engineering. The main campus is in Blacksburg, and the department has additional research and teaching facilities in Arlington, Falls Church, and Hampton, Virginia.

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1 kV GaN-on-Si Quasi-Vertical Schottky Rectifier
Qin, Yuan; Xiao, Ming; Zhang, Ruizhe; Xie, Qingyun; Palacios, Tomás; Wang, Boyan; Ma, Yunwei; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Srijanto, Bernadeta R.; Zhang, Yuhao (IEEE, 2023-07)
This work demonstrates quasi-vertical GaN Schottky barrier diodes (SBDs) on 6-inch Si substrate with a breakdown voltage (BV) over 1 kV, the highest BV reported in vertical GaN-on-Si SBDs to date. The deep mesa inherently in quasi-vertical devices is leveraged to form a self-aligned edge termination, and the mesa sidewall is covered by the p-type nickel oxide (NiO) as a reduced surface field (RESURF) structure. This novel termination enables a parallel-plane junction electric field of 2.8 MV/cm. The device also shows low turn-on voltage of 0.5 V, and low specific on-resistance of 1.1 m ·cm2. Moreover, the device exhibits excellent overvoltage robustness under the continuous 800 V stress in the unclamped inductive switching test. These results show the good promise of the low-cost vertical GaN-on-Si power diodes.
1 kV Self-Aligned Vertical GaN Superjunction Diode
Ma, Yunwei; Porter, Matthew; Qin, Yuan; Spencer, Joseph; Du, Zhonghao; Xiao, Ming; Wang, Yifan; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Udrea, Florin; Tadjer, Marko; Wang, Han; Zhang, Yuhao (IEEE, 2024-01)
This work demonstrates vertical GaN superjunction (SJ) diodes fabricated via a novel self-aligned process. The SJ comprises n-GaN pillars wrapped by the charge-balanced p-type nickel oxide (NiO). After the NiO sputtering around GaN pillars, the self-aligned process exposes the top pillar surfaces without the need for additional lithography or a patterned NiO etching which is usually difficult. The GaN SJ diode shows a breakdown voltage (B V) of 1100 V, a specific on-resistance ( RON) of 0.4 mΩ⋅ cm2, and a SJ drift-region resistance ( Rdr) of 0.13 mΩ⋅ cm2. The device also exhibits good thermal stability with B V retained over 1 kV and RON dropped to 0.3 mΩ⋅ cm2 at 125oC . The trade-off between B V and Rdr is superior to the 1D GaN limit. These results show the promise of vertical GaN SJ power devices. The self-aligned process is applicable for fabricating the heterogeneous SJ based on various wide- and ultra-wide bandgap semiconductors.
10-kV Ga₂O₃ Charge-Balance Schottky Rectifier Operational at 200 ^◦C
Qin, Yuan; Xiao, Ming; Porter, Matthew; Ma, Yunwei; Spencer, Joseph; Du, Zhonghao; Jacobs, Alan G.; Sasaki, Kohei; Wang, Han; Tadjer, Marko; Zhang, Yuhao (IEEE, 2023-08)
This work demonstrates a lateral Ga2O3 Schottky barrier diode (SBD) with a breakdown voltage (BV) over 10 kV, the highest BV reported in Ga2O3 devices to date. The 10 kV SBD shows good thermal stability up to 200◦C, which is among the highest operational temperatures reported in multi-kilovolt Ga2O3 devices. The key device design for achieving such high BV is a reduced surface field (RESURF) structure based on the p-type nickel oxide (NiO), which balances the depletion charges in the n-Ga2O3 channel at high voltage. At BV, the chargebalanced Ga2O3 SBD shows an average lateral electric field (E-field) over 4.7 MV/cm at 25 ◦C and over 3.5 MV/cm at 200◦C, both of which exceed the critical E-field of GaN and SiC. The 10 kV SBD shows a specific on-resistance of 0.27 ·cm2 and a turn-on voltage of 1 V; at 200◦C, the former doubles and the latter reduces to 0.7 V. These results suggest the good potential of Ga2O3 devices for mediumand high-voltage, high-temperature power applications.
2 kV, 0.7 mΩ·cm² Vertical Ga₂O₃ Superjunction Schottky Rectifier with Dynamic Robustness
Qin, Yuan; Porter, Matthew; Xiao, Ming; Du, Zhonghao; Zhang, Hongming; Ma, Yunwei; Spencer, Joseph; Wang, Boyan; Song, Qihao; Sasaki, Kohei; Lin, Chia-Hung; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Tadjer, Marko; Wang, Han; Zhang, Yuhao (IEEE, 2023)
We report the first experimental demonstration of a vertical superjunction device in ultra-wide bandgap (UWBG) Ga2O3. The device features 1.8 μm wide, 2×1017 cm-3 doped n-Ga2O3 pillars wrapped by the charge-balanced p-type nickel oxide (NiO). The sidewall NiO is sputtered through a novel self-align process. Benefitted from the high doping in Ga2O3, the superjunction Schottky barrier diode (SJ-SBD) achieves a ultra-low specific on-resistance (RON,SP) of 0.7 mΩ·cm2 with a low turn-on voltage of 1 V and high breakdown voltage (BV) of 2000 V. The RON,SP~BV trade-off is among the best in all WBG and UWBG power SBDs. The device also shows good thermal stability with BV > 1.8 kV at 175 oC. In the unclamped inductive switching tests, the device shows a dynamic BV of 2.2 kV and no degradation under 1.7 kV repetitive switching, verifying the fast acceptor depletion in NiO under dynamic switching. Such high-temperature and switching robustness are reported for the first time in a heterogeneous superjunction. These results show the great potential of UWBG superjunction power devices.
2012 CPES Annual Report
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2012)
The Center for Power Electronics Systems at Virginia Tech is a research center dedicated to improving electrical power processing and distribution that impact systems of all sizes – from battery – operated electronics to vehicles to regional and national electrical distribution systems. Our mission is to provide leadership through global collaborative research and education for creating advanced electric power processing systems of the highest value to society. CPES, with annual research expenditures about $4-5 million US dollars, has a worldwide reputation for its research advances, its work with industry, and its many talented graduates. From its background as an Engineering Research Center for the National Science Foundation during 1998 - 2008, CPES has continued to work towards making electric power processing more efficient and more exact in order to reduce energy consumption. Power electronics is the “enabling infrastructure technology” that promotes the conversion of electrical power from its raw form to the form needed by machines, motors and electronic equipment. Advances in power electronics can reduce power conversion loss and in turn increase energy efficiency of equipment and processes using electrical power. This results in increased industrial productivity and product quality. With widespread use of power electronics technology, the United States would be able to cut electrical energy consumption by 33 percent. This energy savings in the United States alone is estimated to be the equivalent of output from 840 fossil fuel based generating plants. This savings would result in enormous economic, environmental and social benefits.
2013 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2013)
The CPES industrial consortium is designed to cultivate connectivity among researchers in academia and industry, as well as create synergy within the network of industry members. The CPES industrial consortium offers: The best mechanism to stay abreast of technological developments in power electronics; The ideal forum for networking with leadingedge companies and top-notch researchers; The CPES connection provides the competitive edge to industry members via: Access to state-of-the-art facilities, faculty expertise, top-notch students; Leveraged research funding of over $4-10 million per year; Industry influence via Industry Advisory Board and research champions; Intellectual properties with early access for Principal Plus and Principal members via CPES IPPF (Intellectual Property Protection Fund); Technology transfer made possible via special access to the Center’s multi-disciplinary team of researchers, and resulting publications, presentations and intellectual properties; Continuing education opportunities via professional short courses offered at a significant discount. The CPES industrial consortium offers the ideal forum for networking with leading-edge companies and top-notch researchers and provides the best mechanism to stay abreast of technological developments in power electronics.
2014 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2014)
Over the past two decades, CPES has secured research funding from major industries, such as GE, Rolls-Royce, Boeing, Alstom, ABB, Toyota, Nissan, Raytheon, and MKS, as well as from government agencies including the NSF, DOE, DARPA, ONR, U.S. Army, and the U.S. Air Force, in research pursuing high-density system design. CPES has developed unique high-temperature packaging technology critical to the future powerelectronic industry. In the HDI mini-consortium, the goal of high power density will be pursued following two coupled paths, both leveraging the availability of wide-bandgap power semiconductor, as well as high-temperature passive components and ancillary functions. The switching frequency will be pushed as high as component technologies, thermal management, and reliability permit. At the same time, the maximum component temperatures will be pushed as high as component technologies, thermal management, and reliability permit. The emergence of wide‐bandgap semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) makes it possible to realize power switches that operate at frequency beyond 5 MHz and temperature beyond 200° C. As the switching frequency increases, switching noise is shifted to higher frequency and can be filtered with small passive components, leading to improved power density. Higher operating temperatures enable increased power density and applications under harsh environments, such as military systems, transportation systems, and outdoor industrial and utility systems.
2015 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2015)
In its efforts to develop power processing systems to take electricity to the next step, CPES has developed research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power conversion systems; (4) Renewable energy systems. In 2015, CPES sponsored research totaled approximately $2.2 million. The following abstracts provide a quick insight to the current research efforts.
2016 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2016)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power converter systems; and (4) High-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.1 million. The following abstracts provide a quick insight to the current research efforts.
2017 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2017)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) power management for information and communications technology; (2) point-of-load conversion for power supplies; (3) vehicular power converter systems; and (4) high-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.4 million. The following abstracts provide a quick insight to the current research efforts.
2018 CPES Annual Report
(Virginia Tech, 2018)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) power management for information and communications technology; (2) point-of-load conversion for power supplies; (3) vehicular power converter systems; and (4) high-power conversion systems. In 2018, CPES sponsored research totaled approximately $2.9 million. The following abstracts provide a quick insight to the current research efforts.
3D printed graphene-based self-powered strain sensors for smart tires in autonomous vehicles
Maurya, Deepam; Khaleghian, Seyedmeysam; Sriramdas, Rammohan; Kumar, Prashant; Kishore, Ravi Anant; Kang, Min-Gyu; Kumar, Vireshwar; Song, Hyun-Cheol; Lee, Seul-Yi; Yan, Yongke; Park, Jung-Min (Jerry); Taheri, Saied; Priya, Shashank (2020-10-26)
The transition of autonomous vehicles into fleets requires an advanced control system design that relies on continuous feedback from the tires. Smart tires enable continuous monitoring of dynamic parameters by combining strain sensing with traditional tire functions. Here, we provide breakthrough in this direction by demonstrating tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis. Ink of graphene based material was designed to directly print strain sensor for measuring tire-road interactions under varying driving speeds, normal load, and tire pressure. A secure wireless data transfer hardware powered by a piezoelectric patch is implemented to demonstrate self-powered sensing and wireless communication capability. Combined, this study significantly advances the design and fabrication of cost-effective smart tires by demonstrating practical self-powered wireless strain sensing capability. Designing efficient sensors for smart tires for autonomous vehicles remains a challenge. Here, the authors present a tire-integrated system that combines direct mask-less 3D printed strain gauges, flexible piezoelectric energy harvester for powering the sensors and secure wireless data transfer electronics, and machine learning for predictive data analysis.
6G Enabled Smart Infrastructure for Sustainable Society: Opportunities, Challenges, and Research Roadmap
Imoize, Agbotiname Lucky; Adedeji, Oluwadara; Tandiya, Nistha; Shetty, Sachin (MDPI, 2021-03-02)
The 5G wireless communication network is currently faced with the challenge of limited data speed exacerbated by the proliferation of billions of data-intensive applications. To address this problem, researchers are developing cutting-edge technologies for the envisioned 6G wireless communication standards to satisfy the escalating wireless services demands. Though some of the candidate technologies in the 5G standards will apply to 6G wireless networks, key disruptive technologies that will guarantee the desired quality of physical experience to achieve ubiquitous wireless connectivity are expected in 6G. This article first provides a foundational background on the evolution of different wireless communication standards to have a proper insight into the vision and requirements of 6G. Second, we provide a panoramic view of the enabling technologies proposed to facilitate 6G and introduce emerging 6G applications such as multi-sensory–extended reality, digital replica, and more. Next, the technology-driven challenges, social, psychological, health and commercialization issues posed to actualizing 6G, and the probable solutions to tackle these challenges are discussed extensively. Additionally, we present new use cases of the 6G technology in agriculture, education, media and entertainment, logistics and transportation, and tourism. Furthermore, we discuss the multi-faceted communication capabilities of 6G that will contribute significantly to global sustainability and how 6G will bring about a dramatic change in the business arena. Finally, we highlight the research trends, open research issues, and key take-away lessons for future research exploration in 6G wireless communication.
Aberrant Calcium Signaling in Astrocytes Inhibits Neuronal Excitability in a Human Down Syndrome Stem Cell Model
Mizuno, Grace O.; Wang, Yinxue; Shi, Guilai; Wang, Yizhi; Sun, Junqing; Papadopoulos, Stelios; Broussard, Gerard J.; Unger, Elizabeth K.; Deng, Wenbin; Weick, Jason; Bhattacharyya, Anita; Chen, Chao-Yin; Yu, Guoqiang; Looger, Loren L.; Tian, Lin (Elsevier, 2018-07-10)
Down syndrome (DS) is a genetic disorder that causes cognitive impairment. The staggering effects associated with an extra copy of human chromosome 21 (HSA21) complicates mechanistic understanding of DS pathophysiology. We examined the neuronastrocyte interplay in a fully recapitulated HSA21 trisomy cellular model differentiated from DS-patientderived induced pluripotent stem cells (iPSCs). By combining calciumimaging with genetic approaches, we discovered the functional defects of DS astroglia and their effects on neuronal excitability. Compared with control isogenic astroglia, DS astroglia exhibited more-frequent spontaneous calcium fluctuations, which reduced the excitability of co-cultured neurons. Furthermore, suppressed neuronal activity could be rescued by abolishing astrocytic spontaneous calcium activity either chemically by blocking adenosine-mediated signaling or genetically by knockdown of inositol triphosphate (IP3) receptors or S100B, a calcium binding protein coded on HSA21. Our results suggest a mechanism by which DS alters the function of astrocytes, which subsequently disturbs neuronal excitability.
Abnormal Behavior Detection Based on Traffic Pattern Categorization in Mobile Cellular Networks
De Almeida, J. M.; Pontes, C. F. T.; DaSilva, Luiz A.; Both, C. B.; Gondim, J. J. C.; Ralha, Celia G.; Marotta, M. A. (IEEE, 2021-01-01)
Abnormal behavior in mobile cellular networks can cause network faults and consequent cell outages, a major reason for operational cost increase and revenue loss for operators. Nonetheless, network faults and cell outages can be avoided by monitoring abnormal situations in the network and acting accordingly. Thus, anomaly detection is an important component of self-healing control and network management. Network operators may use the detected abnormal behavior to quantify numerically their intensity. The quantification of abnormal behavior assists the characterization of potential regions for infrastructure updates and to support the creation of public policies for local connectivity enhancements. We propose an unsupervised learning solution for anomaly detection in mobile networks using Call Detail Records (CDR) data. We evaluate our solution using a real CDR data set provided by an Italian operator and compare it against other state-of-the-art solutions, showing a performance improvement of around 35%. We also demonstrate the relevance of considering the distinct traffic patterns of diverging geographic areas for anomaly detection in mobile networks, an aspect often ignored in the literature.
Acoustic Energy Harvesting and Sensing via Electrospun PVDF Nanofiber Membrane
Shehata, Nader; Hassanin, Ahmed H.; Elnabawy, Eman; Nair, Remya; Bhat, Sameer A.; Kandas, Ishac (MDPI, 2020-05-31)
This paper introduces a new usage of piezoelectric poly (vinylidene fluoride) (PVDF) electrospun nanofiber (NF) membrane as a sensing unit for acoustic signals. In this work, an NF mat has been used as a transducer to convert acoustic signals into electric voltage outcomes. The detected voltage has been analyzed as a function of both frequency and amplitude of the excitation acoustic signal. Additionally, the detected AC signal can be retraced as a function of both frequency and amplitude with some wave distortion at relatively higher amplitudes and within a certain acoustic spectrum region. Meanwhile, the NFs have been characterized through piezoelectric responses, beta sheet calculations and surface morphology. This work is promising as a low-cost and innovative solution to harvest acoustic signals coming from wide resources of sound and noise.
Acoustic X-wave reflection and transmission at a planar interface: Spectral analysis
Shaarawi, Amr M.; Besieris, Ioannis M.; Attiya, Ahmed M.; El-Diwany, Essam (Acoustical Society of America, 2000-01-01)
The spectral structure of a three-dimensional X-wave pulse incident on a planar surface of discontinuity is examined. Introducing a novel superposition of azimuthally dependent pulsed plane waves, it is shown for oblique incidence that the reflected pulse has a localized wave structure. On the other hand, the transmitted field maintains its localization up to a certain distance from the interface, beyond which it starts disintegrating. An estimate of the localization range of the transmitted pulse is established; also, the parameters affecting the localization range are identified. The reflected and transmitted fields are deduced for X-waves incident from either a slower medium or a faster one. For the former case the evanescent fields in the second medium are calculated and their explicit time dependence is deduced for a normally incident X-wave. Furthermore, at near-critical incidence the transmitted pulse exhibits significant pulse compression and focusing.
Acousto-optic modulators integrated on-chip
Beller, Jared; Shao, Linbo (Springer Nature, 2022-07-29)
Acousto-optic devices that use radio frequency mechanical waves to manipulate light are critical components in many optical systems. Here, the researchers bring acousto-optic devices on-chip and make them more efficient for integrated photonic circuits.
Acousto-Optics: introduction to the feature issue
Poon, Ting-Chung; Tsai, C. S.; Voloshinov, V. B.; Chatterjee, M. R. (Optical Society of America, 2009-03-01)
This Acousto-Optics feature celebrates the scientific careers of two remarkable scientists, Antoni Sliwinski and Adrian Korpel. The feature includes original papers based on a representative selection of topics that were presented at the Tenth Spring School on Acousto-Optics held in Poland in May 2008. (C) 2009 Optical Society of America
Active suppression of acoustic radiation from impulsively excited structures
Baumann, William T.; Saunders, William R.; Robertshaw, Harry H. (Acoustical Society of America, 1991-12-01)
The objective is to use active control to suppress the acoustic energy that is radiated to the far field from a structure that has been excited by a short-duration pulse. The problem is constrained by the assumption that the far-field pressure cannot be directly measured. Therefore, a method is developed for estimating the total radiated energy from measurements on the structure. Using this estimate as a cost function, a feedback controller is designed using linear quadratic regulator theory to minimize the cost. Computer simulations of a clamped-clamped beam show that there is appreciable difference in the total radiated energy between a system with a controller designed to suppress vibrations of the structure and a system with a controller that takes into account the coupling of these vibrations to the surrounding fluid. The results of this work provide a framework for a general, model-based method for actively suppressing transient structural acoustic radiation that can also be applied to steady, narrow, or broadband disturbances.

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