Department of Mechanical Engineering
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The Virginia Tech Mechanical Engineering Department serves its students, alumni, the Commonwealth of Virginia, and the nation through a variety of academic, research and service activities.
Our missions are to: holistically educate our students for professional leadership as creative problem-solvers in a diverse society, conduct advanced research for societal advancement, train graduate students for scholarly inquiry, and engage with alumni, industry, government, and community partners through outreach activities. In order to produce engineers prepared for success across a range of career paths, our academic program integrates training in engineering principles, critical thinking, hands-on projects, open-ended problem solving, and the essential skills of teamwork, communication, and ethics.
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Browsing Department of Mechanical Engineering by Department "Center for Energy Harvesting Materials and Systems (CEHMS)"
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- Combinatory Finite Element and Artificial Neural Network Model for Predicting Performance of Thermoelectric GeneratorKishore, Ravi Anant; Mahajan, Roop L.; Priya, Shashank (MDPI, 2018-08-24)Thermoelectric generators (TEGs) are rapidly becoming the mainstream technology for converting thermal energy into electrical energy. The rise in the continuous deployment of TEGs is related to advancements in materials, figure of merit, and methods for module manufacturing. However, rapid optimization techniques for TEGs have not kept pace with these advancements, which presents a challenge regarding tailoring the device architecture for varying operating conditions. Here, we address this challenge by providing artificial neural network (ANN) models that can predict TEG performance on demand. Out of the several ANN models considered for TEGs, the most efficient one consists of two hidden layers with six neurons in each layer. The model predicted TEG power with an accuracy of ±0.1 W, and TEG efficiency with an accuracy of ±0.2%. The trained ANN model required only 26.4 ms per data point for predicting TEG performance against the 6.0 minutes needed for the traditional numerical simulations.
- Defect and adsorbate induced ferromagnetic spin-order in magnesium oxide nanocrystallitesKumar, Ashok; Kumar, Jitendra; Priya, Shashank (AIP Publishing, 2012-05-01)We report the correlation between d(0) ferromagnetism, photoluminescence (PL), and adsorbed hydrogen (H-) species in magnesium oxide (MgO) nanocrystallites. Our study suggests that the oxygen vacancies, namely singly ionized anionic vacancies (F+) and dimers (F-2(2+)) induce characteristic photoluminescence and the room-temperature ferromagnetic spin-order. Nanocrystallites with low population of oxygen vacancies have revealed diamagnetic behavior. Intriguingly, on adsorption of hydrogen (H-) species in the MgO nanocrystallites, ferromagnetic behavior was either enhanced (in the case of highly oxygen deficient nanocrystallites) or begun to percolate (in the case of nanocrystallite with low population density of oxygen vacancies). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712058]
- Direct and converse effect in magnetoelectric laminate compositesCho, Kyung-Hoon; Priya, Shashank (AIP Publishing, 2011-06-01)In this letter, we analyze the direct and converse effect in laminate composites of magnetostrictive and piezoelectric materials. Our results deterministically show that direct magnetoelectric (ME) effect is maximized at antiresonance frequency while the converse ME effect is maximized at resonance frequency of the laminate composite. We explain this phenomenon by using piezoelectric constitutive equations and combining it with resonance boundary conditions. The dominant factor controlling the position of peak ME coefficient was found to be frequency dependent capacitance of piezoelectric layer. This study will provide guidance toward the development of magnetic field sensors based on direct effect and communication components based on converse effect. (C) 2011 American Institute of Physics. [doi:10.1063/1.3584863]
- Discovery and ramifications of incidental Magnéli phase generation and release from industrial coal-burningYang, Yi; Chen, Bo; Hower, James C.; Schindler, Michael; Winkler, Christopher; Brandt, Jessica E.; Di Giulio, Richard T.; Ge, Jianping; Liu, Min; Fu, Yuhao; Zhang, Lijun; Chen, Yu-ru; Priya, Shashank; Hochella, Michael F. Jr. (Nature Publishing Group, 2017-01-12)Coal, as one of the most economic and abundant energy sources, remains the leading fuel for producing electricity worldwide. Yet, burning coal produces more global warming CO2 relative to all other fossil fuels, and it is a major contributor to atmospheric particulate matter known to have a deleterious respiratory and cardiovascular impact in humans, especially in China and India. Here we have discovered that burning coal also produces large quantities of otherwise rare Magneli phases (Ti; x; O2x–1 with 4 ≤ x ≤ 9) from TiO2 minerals naturally present in coal. This provides a new tracer for tracking solid-state emissions worldwide from industrial coal-burning. In its first toxicity testing, we have also shown that nanoscale Magneli phases have potential toxicity pathways that are not photoactive like TiO2 phases, but instead seem to be biologically active without photostimulation. In the future, these phases should be thoroughly tested for their toxicity in the human lung. Solid-state emissions from coal burning remain an environmental concern. Here, the authors have found that TiO2 minerals present in coal are converted into titanium suboxides during burning, and initial biotoxicity screening suggests that further testing is needed to look into human lung consequences.
- Dual-phase self-biased magnetoelectric energy harvesterZhou, Yuan; Apo, Daniel J.; Priya, Shashank (AIP Publishing, 2013-11-01)We report a magnetoelectric energy harvester structure that can simultaneously scavenge magnetic and vibration energy in the absence of DC magnetic field. The structure consisted of a piezoelectric macro-fiber composite bonded to a Ni cantilever. Large magnetoelectric coefficient similar to 50 V/cm Oe and power density similar to 4.5 mW/cm(3) (1 g acceleration) were observed at the resonance frequency. An additive effect was realized when the harvester operated under dual-phase mode. The increase in voltage output at the first three resonance frequencies under dual-phase mode was found to be 2.4%, 35.5%, and 360.7%. These results present significant advancement toward high energy density multimode energy harvesting system. (C) 2013 AIP Publishing LLC.
- Effect of intensive and extensive loss factors on the dynamic response of magnetoelectric laminatesCho, Kyung-Hoon; Park, Chee-Sung; Priya, Shashank (AIP Publishing, 2010-11-01)We report the correlation between intensive and extensive losses in piezoelectric materials with the frequency dependent response of layered magnetoelectric (ME) composites. Three different piezoelectric compositions were synthesized to achieve varying loss characteristics allowing a systematic interpretation of changes in ME coupling in terms of loss components. We clearly demonstrate that intensive dielectric and piezoelectric loss play an important role in controlling the ME sensitivity of layered composites in sub-resonance low frequency range while extensive mechanical loss is dominant factor at resonance condition. Further, the maximum in ME response is obtained at antiresonance frequency of piezoelectrics. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3511285]
- Electromechanical behavior of 001 -textured Pb(Mg1/3Nb2/3)O-3-PbTiO3 ceramicsYan, Yongke; Wang, Yu. U.; Priya, Shashank (AIP Publishing, 2012-05-01)[001]-textured Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT) ceramics were synthesized by using templated grain growth method. Significantly high [001] texture degree corresponding to 0.98 Lotgering factor was achieved at 1 vol. % BaTiO3 template. Electromechanical properties for [001]-textured PMN-PT ceramics with 1 vol. % BaTiO3 were found to be d(33) = 1000 pC/N, d(31) = 371 pC/N, epsilon(r) 2591, and tan delta = similar to 0.6%. Elastoelectric composite based modeling results showed that higher volume fraction of template reduces the overall dielectric constant and thus has adverse effect on the piezoelectric response. Clamping effect was modeled by deriving the changes in free energy as a function of applied electric field and microstructural boundary condition. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712563]
- Energy band alignment of atomic layer deposited HfO2 on epitaxial (110)Ge grown by molecular beam epitaxyHudait, Mantu K.; Zhu, Y.; Maurya, Deepam; Priya, Shashank (AIP Publishing, 2013-03-01)The band alignment properties of atomic layer HfO2 film deposited on epitaxial (110)Ge, grown by molecular beam epitaxy, was investigated using x-ray photoelectron spectroscopy. The cross-sectional transmission electron microscopy exhibited a sharp interface between the (110)Ge epilayer and the HfO2 film. The measured valence band offset value of HfO2 relative to (110)Ge was 2.28 +/- 0.05 eV. The extracted conduction band offset value was 2.66 +/- 0.1 eV using the bandgaps of HfO2 of 5.61 eV and Ge bandgap of 0.67 eV. These band offset parameters and the interface chemical properties of HfO2/(110)Ge system are of tremendous importance for the design of future high hole mobility and low-power Ge-based metal-oxide transistor devices. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4794838]
- Enhanced piezoelectricity and nature of electric-field induced structural phase transformation in textured lead-free piezoelectric Na0.5Bi0.5TiO3-BaTiO3 ceramicsMaurya, Deepam; Pramanick, Abhijit; An, Ke; Priya, Shashank (AIP Publishing, 2012-04-01)This letter provides a comparative description of the properties of textured and randomly oriented poly-crystalline lead-free piezoelectric 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO(3) (NBT-BT) ceramics. A high longitudinal piezoelectric constant of (d(33)) similar to 322 pC/N was obtained in (001)(PC) textured NBT-7BT ceramics, which is almost similar to 2x times the d(33) coefficient reported for randomly oriented ceramics of the same composition. In situ neutron diffraction experiments revealed that characteristically different structural responses are induced in textured and randomly oriented NBT-BT ceramics upon application of electric fields (E), which are likely related to the varying coherence lengths of polar nanoregions and internal stresses induced by domain switching. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4709404]
- Enhanced torsional actuation and stress coupling in Mn-modified 0.93(Na0.5Bi0.5TiO3)-0.07BaTiO(3) lead-free piezoceramic systemBerik, Pelin; Maurya, Deepam; Kumar, Prashant; Kang, Min-Gyu; Priya, Shashank (Taylor & Francis, 2017-01-01)
- Ferroelectric properties and dynamic scaling of < 100 > oriented (K0.5Na0.5)NbO3 single crystalsGupta, Sanjay; Priya, Shashank (AIP Publishing, 2011-06-01)In this letter, we report the dielectric and ferroelectric (FE) characteristics of potassium sodium niobate (K0.5Na0.5NbO3) single crystals grown by flux method. Orientation analysis of as-grown cubical-shaped crystals was conducted by electron backscattered diffraction technique revealing the < 100 > crystallographic orientation of two opposing major faces. Annealed crystals were found to exhibit FE orthorhombic to FE tetragonal transition temperature of 200 degrees C and Curie temperature of 407 degrees C. Poled < 100 > oriented crystals had longitudinal piezoelectric constant of 148 pC/N. Dielectric measurement as a function of temperature was conducted to determine the second order parameter in Gibbs free energy expansion. Dynamic hysteresis analysis on these crystals showed the power law relations to be of the form < A > proportional to f(0.47Eo-0.85)E(o)(1.45f0.14) and < A > proportional to f(0.04)E(o) below and above the coercive field. (C) 2011 American Institute of Physics. [doi:10.1063/1.3600058]
- Flexible Margin Kinematics and Vortex Formation of Aurelia aurita and RobojellyVillanueva, Alex A.; Vlachos, Pavlos P.; Priya, Shashank (PLOS, 2014-06-06)The development of a rowing jellyfish biomimetic robot termed as “Robojelly”, has led to the discovery of a passive flexible flap located between the flexion point and bell margin on the Aurelia aurita. A comparative analysis of biomimetic robots showed that the presence of a passive flexible flap results in a significant increase in the swimming performance. In this work we further investigate this concept by developing varying flap geometries and comparing their kinematics with A. aurita. It was shown that the animal flap kinematics can be replicated with high fidelity using a passive structure and a flap with curved and tapered geometry gave the most biomimetic performance. A method for identifying the flap location was established by utilizing the bell curvature and the variation of curvature as a function of time. Flaps of constant cross-section and varying lengths were incorporated on the Robojelly to conduct a systematic study of the starting vortex circulation. Circulation was quantified using velocity field measurements obtained from planar Time Resolved Digital Particle Image Velocimetry (TRDPIV). The starting vortex circulation was scaled using a varying orifice model and a pitching panel model. The varying orifice model which has been traditionally considered as the better representation of jellyfish propulsion did not appear to capture the scaling of the starting vortex. In contrast, the pitching panel representation appeared to better scale the governing flow physics and revealed a strong dependence on the flap kinematics and geometry. The results suggest that an alternative description should be considered for rowing jellyfish propulsion, using a pitching panel method instead of the traditional varying orifice model. Finally, the results show the importance of incorporating the entire bell geometry as a function of time in modeling rowing jellyfish propulsion.
- Giant energy density in 001 -textured Pb(Mg1/3Nb2/3)O-3-PbZrO3-PbTiO3 piezoelectric ceramicsYan, Yongke; Cho, Kyung-Hoon; Maurya, Deepam; Kumar, Amit; Kalinin, Sergei; Khachaturyan, Armen G.; Priya, Shashank (AIP Publishing, 2013-01-01)Pb(Zr,Ti)O-3 (PZT) based compositions have been challenging to texture or grow in a single crystal form due to the incongruent melting point of ZrO2. Here we demonstrate the method for achieving 90% textured PZT-based ceramics and further show that it can provide highest known energy density in piezoelectric materials through enhancement of piezoelectric charge and voltage coefficients (d and g). Our method provides more than similar to 5x increase in the ratio d(textured)/d(random). A giant magnitude of d.g coefficient with value of 59 000 x 10(-15) m(2) N-1 (comparable to that of the single crystal counterpart and 359% higher than that of the best commercial compositions) was obtained. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789854]
- Giant magnetoelectric coupling in laminate thin film structure grown on magnetostrictive substratePark, Chee-Sung; Khachaturyan, Armen G.; Priya, Shashank (AIP Publishing, 2012-05-01)Highly dense 1 mu m-thick piezoelectric film was deposited on magnetostrictive substrate [platinized nickel-zinc ferrite (NZF)]. A strong magnetic coupling between the piezoelectric film and magnetostrictive NZF substrate was measured exhibiting the maximum magnetoelectric (ME) coefficient on the order of 140 mV/cm Oe at the conditions of H-DC = 50 Oe and H-AC = 1Oe at f = 1 kHz. This giant ME coupling under low DC magnetic field condition is attributed to effective elastic coupling. A rotation-type dynamic strain distribution was observed on the PZT film surface which provides information about the nature of elastic coupling. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4712132]
- Giant self-biased magnetoelectric coupling in co-fired textured layered compositesYan, Yongke; Zhou, Yuan; Priya, Shashank (AIP Publishing, 2013-02-01)Co-fired magnetostrictive/piezoelectric/magnetostrictive laminate structure with silver inner electrode was synthesized and characterized. We demonstrate integration of textured piezoelectric microstructure with the cost-effective low-temperature co-fired layered structure to achieve strong magnetoelectric coupling. Using the co-fired composite, a strategy was developed based upon the hysteretic response of nickel-copper-zinc ferrite magnetostrictive materials to achieve peak magnetoelectric response at zero DC bias, referred as self-biased magnetoelectric response. Fundamental understanding of self-bias phenomenon in composites with single phase magnetic material was investigated by quantifying the magnetization and piezomagnetic changes with applied DC field. We delineate the contribution arising from the interfacial strain and inherent magnetic hysteretic behavior of copper modified nickel-zinc ferrite towards self-bias response. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4791685]
- Giant strain with ultra-low hysteresis and high temperature stability in grain oriented lead-free K0.5Bi0.5TiO3-BaTiO3-Na0.5Bi0.5TiO3 piezoelectric materialsMaurya, Deepam; Zhou, Yuan; Wang, Yaojin; Yan, Yongke; Li, Jiefang; Viehland, Dwight D.; Priya, Shashank (Springer Nature, 2015-02-26)We synthesized grain-oriented lead-free piezoelectric materials in (K0.5Bi0.5TiO3-BaTiO3-xNa(0.5)Bi(0.5)TiO(3) (KBT-BT-NBT) system with high degree of texturing along the [001]c (c-cubic) crystallographic orientation. We demonstrate giant field induced strain (similar to 0.48%) with an ultra-low hysteresis along with enhanced piezoelectric response (d(33) similar to 190pC/N) and high temperature stability (similar to 160 degrees C). Transmission electron microscopy (TEM) and piezoresponse force microscopy (PFM) results demonstrate smaller size highly ordered domain structure in grain-oriented specimen relative to the conventional polycrystalline ceramics. The grain oriented specimens exhibited a high degree of non-180 degrees domain switching, in comparison to the randomly axed ones. These results indicate the effective solution to the lead-free piezoelectric materials.
- Harvesting Energy from the Counterbalancing (Weaving) Movement in Bicycle RidingYang, Yoonseok; Yeo, Jeongjin; Priya, Shashank (MDPI, 2012-07-30)Bicycles are known to be rich source of kinetic energy, some of which is available for harvesting during speedy and balanced maneuvers by the user. A conventional dynamo attached to the rim can generate a large amount of output power at an expense of extra energy input from the user. However, when applying energy conversion technology to human powered equipments, it is important to minimize the increase in extra muscular activity and to maximize the efficiency of human movements. This study proposes a novel energy harvesting methodology that utilizes lateral oscillation of bicycle frame (weaving) caused by user weight shifting movements in order to increase the pedaling force in uphill riding or during quick speed-up. Based on the 3D motion analysis, we designed and implemented the prototype of an electro-dynamic energy harvester that can be mounted on the bicycle's handlebar to collect energy from the side-to-side movement. The harvester was found to generate substantial electric output power of 6.6 mW from normal road riding. It was able to generate power even during uphill riding which has never been shown with other approaches. Moreover, harvesting of energy from weaving motion seems to increase the economy of cycling by helping efficient usage of human power.
- High thermal stability of piezoelectric properties in (Na0.5Bi0.5TiO3)(x)-(BaTiO3)(y)-(Na0.5K0.5NbO3)(1-x-y) ceramicsGupta, Sanjay; Priya, Shashank (AIP Publishing, 2013-01-01)We report the piezoelectric and ferroelectric properties of (Na0.5Bi0.5TiO3)(x)-(BaTiO3)(y)-(Na0.5K0.5NbO3)(1-x-y) ceramics for Na0.5K0.5NbO3 rich end of composition (x, y <= 0.04 mol. %). These compositions were found to exhibit significantly improved thermal stability of piezoresponse. Variation of dielectric constant as a function of temperature revealed that orthorhombic-tetragonal (To-t) and tetragonal-cubic (T-c) transition temperatures for these compositions were in the vicinity of 0 degrees C and 330 degrees C, respectively. Dynamic scaling and temperature dependent X-ray diffraction analysis were conducted. Results are discussed in terms of intrinsic and extrinsic contributions to the piezoelectric response explaining the temperature dependent behavior. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773983]
- Integration of lead-free ferroelectric on HfO2/Si (100) for high performance non-volatile memory applicationsKundu, Souvik; Maurya, Deepam; Clavel, Michael B.; Zhou, Yuan; Halder, Nripendra N.; Hudait, Mantu K.; Banerji, Pallab; Priya, Shashank (Nature Publishing Group, 2015-02-16)We introduce a novel lead-free ferroelectric thin film (1-x)BaTiO3-xBa(Cu1/3Nb2/3)O3 (x 5 0.025) (BT-BCN) integrated on to HfO2 buffered Si for non-volatile memory (NVM) applications. Piezoelectric force microscopy (PFM), x-ray diffraction, and high resolution transmission electron microscopy were employed to establish the ferroelectricity in BT-BCN thin films. PFMstudy reveals that the domains reversal occurs with 1806 phase change by applying external voltage, demonstrating its effectiveness forNVMdevice applications. X-ray photoelectron microscopy was used to investigate the band alignments between atomic layer deposited HfO2 and pulsed laser deposited BT-BCN films. Programming and erasing operations were explained on the basis of band-alignments. The structure offers large memory window, low leakage current, and high and low capacitance values that were easily distinguishable even after ,106 s, indicating strong charge storage potential. This study explains a new approach towards the realization of ferroelectric based memory devices integrated on Si platform and also opens up a new possibility to embed the system within current complementary metal-oxide-semiconductor processing technology.
- Large piezoresistivity phenomenon in SiCN-(La,Sr)MnO3 compositesKarmarkar, Makarand; Singh, Gurpreet; Shah, Sandeep; Mahajan, Roop L.; Priya, Shashank (AIP Publishing, 2009-02-01)We present the results on SiCN-(La,Sr)MnO3 (LSMO) composites correlating the observed large piezoresistance behavior with the microstructural features and defect chemistry. Scanning electron microscopy characterization revealed the presence of self-assembled periodic microvalleys in the microstructure with width of 1-5 mu m and depth of 600-1000 nm. The microvalleys act as stress concentration points providing change in volume with applied stress. High resolution transmission electron microscopy measurements conducted on composites showed that LSMO grains consist of SiCN phase but no inclusions were observed.