Fabrications and dielectric performances of novel composites: Calcium copper titanate / Polyvinylidene fluoride

Wang J.J.,Deng Q.J.,He Y.Y.,Feng Y.N.,Kang M.P.,Duan X.L.,Yang Y.L. 한국물리학회 2022 Current Applied Physics Vol.39 No.-

CCTO (Calcium copper titanate) powder as inorganic filler was synthesized by the Sol-gel method firstly. CCTO/ PVDF (Polyvinylidene fluoride) composite was fabricated by solution mixing based on high temperature resistance of PVDF and insulated property of CCTO. The composite of CCTO/PVDF were characterized by X-ray diffraction, Fourier Transform infrared spectroscopy, Scanning Electron Microscope and impedance analysis. The results showed that the addition of CCTO and increasing in its content did not affect the phase- and microstructure of the composites,but the increase of CCTO content can induce the generation of C–F new bonds. PVDF/CCTO composites were enhanced in performance of thermal and frequency-depended stability with increasing in the fraction of CCTO. The dielectric constant of CCTO/PVDF composite materials with 50% CCTO achieved to a maximum value of 50 almost, which is 5 times higher the pure PVDF. The conductivity felled into 10-8 to 10-1 S m-1 during the frequency of 102–108 Hz. The composite material would be expected to be applied in the field of integrated circuit.

Application of structural health monitoring in civil infrastructure

M. Q. Feng 국제구조공학회 2009 Smart Structures and Systems, An International Jou Vol.5 No.4

The emerging sensor-based structural health monitoring (SHM) technology has a potential for costeffective maintenance of aging civil infrastructure systems. The author proposes to integrate continuous and global monitoring using on-structure sensors with targeted local non-destructive evaluation (NDE). Significant technical challenges arise, however, from the lack of cost-effective sensors for monitoring spatially large structures, as well as reliable methods for interpreting sensor data into structural health conditions. This paper reviews recent efforts and advances made in addressing these challenges, with example sensor hardware and health monitoring software developed in the author’s research center. The hardware includes a novel fiber optic accelerometer, a vision-based displacement sensor, a distributed strain sensor, and a microwave imaging NDE device. The health monitoring software includes a number of system identification methods such as the neural networks, extended Kalman filter,and nonlinear damping identificaiton based on structural dynamic response measurement. These methods have been experimentally validated through seismic shaking table tests of a realistic bridge model and tested in a number of instrumented bridges and buildings.

Numerical investigation on residual stress in photovoltaic laminates after lamination

Q. Z. Zhang,B. F. Shu,M. B. Chen,Q. B. Liang,C. Fan,Z. Q. Feng,P. J. Verlinden 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.2

A series of simulations were carried out to investigate the residual stress induced in the photovoltaic laminate during the cooling processafter lamination with a global model and several submodels. The simulations focus separately on the effects of the cooling rate, thecell layout and anisotropy on the residual stress and deformation of the photovoltaic laminate in a comparative manner with the finiteelement method. The results have shown that significant stress concentration and twist occurs in the interconnection region in the cell. Inaddition, different cooling rates, cell layouts and anisotropy only influence the largest stress rather than the stress distribution and deformation. Therefore, the results of a uniform stationary isotropic model with fewer cells can provide enough insight into the stress distributionin real photovoltaic laminates and the modified largest first principal stress can be used for design and verification.

A 2D hybrid stress element for improved prediction of the out-of-plane fields using Fourier expansion

M. L. Feng,M.Dhanasekar,Q.Z.Xiao 국제구조공학회 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.14 No.6

A 2D hybrid stress element for improved prediction of the out-of-plane fields using Fourier expansion

Feng, M.L.,Dhanasekar, M.,Xiao, Q.Z. Techno-Press 2002 Structural Engineering and Mechanics, An Int'l Jou Vol.13 No.5

Recently we formulated a 2D hybrid stress element from the 3D Hellinger-Reissner principle for the analysis of thick bodies that are symmetric to the thickness direction. Polynomials have typically been used for all the displacement and stress fields. Although the element predicted the dominant stress and all displacement fields accurately, its prediction of the out-of-plane shear stresses was affected by the very high order terms used in the polynomials. This paper describes an improved formulation of the 2D element using Fourier series expansion for the out-of-plane displacement and stress fields. Numerical results illustrate that its predictions have markedly improved.

Application of structural health monitoring in civil infrastructure

Feng, M.Q. Techno-Press 2009 Smart Structures and Systems, An International Jou Vol.5 No.4

The emerging sensor-based structural health monitoring (SHM) technology has a potential for cost-effective maintenance of aging civil infrastructure systems. The author proposes to integrate continuous and global monitoring using on-structure sensors with targeted local non-destructive evaluation (NDE). Significant technical challenges arise, however, from the lack of cost-effective sensors for monitoring spatially large structures, as well as reliable methods for interpreting sensor data into structural health conditions. This paper reviews recent efforts and advances made in addressing these challenges, with example sensor hardware and health monitoring software developed in the author's research center. The hardware includes a novel fiber optic accelerometer, a vision-based displacement sensor, a distributed strain sensor, and a microwave imaging NDE device. The health monitoring software includes a number of system identification methods such as the neural networks, extended Kalman filter, and nonlinear damping identificaiton based on structural dynamic response measurement. These methods have been experimentally validated through seismic shaking table tests of a realistic bridge model and tested in a number of instrumented bridges and buildings.

Improvement of lower hybrid current drive systems for high-power and long-pulse operation on EAST

Wang M.,Liu L.,Zhao L.M.,Li M.H.,Ma W.D.,Hu H.C.,Wu Z.G.,Feng J.Q.,Yang Y.,Zhu L.,Chen M.,Zhou T.A.,Jia H.,Zhang J.,Cao L.,Zhang L.,Liang R.R.,Ding B.J.,Zhang X.J.,Shan J.F.,Liu F.K.,Ekedahl A.,Gonich 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.11

Aiming at high-power and long-pulse operation up to 1000 s, some improvements have been made for both 2.45 GHz and 4.6 GHz lower hybrid (LH) systems during the recent 5 years. At first, the guard limiters of the LH antennas with graphite tiles were upgraded to tungsten, the most promising material for plasma facing components in nuclear fusion devices. These new guard limiters can operate at a peak power density of 12.9 MW/m2 . Strong hot spots were usually observed on the old graphite limiters when 4.6 GHz system operated with power >2.0 MW [B. N. Wan et al., Nucl. Fusion 57 (2017) 102019], leading to a reduction of the maximum power capability. With the new limiters, 4.6 GHz LH system, the main current drive (CD) and electron heating tool for EAST, can be operated with power >2.5 MW routinely. Long-pulse operation up to 100 s with 4.6 GHz LH power of 2.4 MW was achieved in 2021 and the maximal temperature on the guard limiters measured by an infrared (IR) camera was about 540 C, much below the permissible value of tungsten material (~1200 C). A discharge with a duration of 1056 s was achieved and the 4.6 GHz LH energy injected into the plasma was up to 1.05 GJ. Secondly, the fully-activemultijunction (FAM) launcher of 2.45 GHz system was upgraded to a passive-active-multijunction (PAM), for which the density of optimum coupling was relatively low (below the cut-off value). Good coupling with reflection coefficient ~3% has been achieved with plasma-antenna distance up to 11 cm for the new PAM. Finally, in order to eliminate the effect of ion cyclotron range of frequencies (ICRF) wave on 4.6 GHz LH wave coupling, the location of the ICRF launcher was changed to a port that is located 157.5 toroidally from the 4.6 GHz LH system and is not magnetically connected

Development of the 3.7 GHz LHCD System on HL-2A

B. Lu,M. Huang,H. Zeng,X. Y. Bai,X. H. Mao,Z. H. Lu,J. Liang,Z. H. Kang,M. W. Wang,K. Feng,H. Wang,C. Wang,J. Q. Wang,S. Wei,T. Yao,Y. N. Bu,J. Feng,G. Y. Cheng,S. D. Song,D. H. Xia,J. Rao 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.8

A 2 MW-3.7 GHz lower hybrid current drive (LHCD) system is under development for physicsexperiments on the HL-2A device. The RF Power is generated by four TH2103A klystron amplifiersand propagates in the TE10 mode through WR284 waveguides. The transmission lines with a lengthof 20 m to 30 m are pressurized with 2 bars of nitrogen to decrease the possibility of arcing. Thelauncher, based on the passive-active multi-junction (PAM) concept, has been developed and iscurrently being realized. It was designed for a power spectrum peaked at Nk = 2.75 with goodcoupling properties over a wide range of plasma parameters. The four klystrons are fed by ahigh-voltage power supply (HVPS) based on the pulse step modulation (PSM) concept with a fastswitch-off time of less than ten μs. This system is expected to be in operation within 1 years and willexplore many international thermonuclear experimental reactor (ITER) related LH experiments inthe following years.

A First-Principles Study of the Thermodynamic Properties of GaAs under Intense Electronic Excitation

S. Q. Feng,H. N. Li,B. M. Li,X. L. Cheng 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.11

In this paper, we present the phonon dispersion curves of Gallium arsenide (GaAs) at different electronic temperatures. Based on the phonon spectra, we further investigated the thermodynamic properties of GaAs under intense electronic excitation. The phonon entropy, phonon heat capacity and phonon contribution to the Helmholtz free energy and the internal energy as functions of temperature at different electronic temperatures are calculated. A sudden change in the phonon entropy-temperature curve from T e = 1.25 to 1.5 eV provides an indication of GaAs undergoing a phase transition from a solid to a liquid. This can be considered as collateral evidence for the non-thermal melting of GaAs under electronic excitation.

Two-dimensional ZrSe2/ZrS2 heterobilayer tuned by electric field for optoelectronic devices

Zhang L. M.,Zhang W. B.,Qiao S.,Yang Y.,Shang J. M.,Feng S. Q. 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.80 No.7

Constructing two-dimensional heterostructures can obtain more desirable device performance. In this work, we discuss the electronic properties and optical absorption of ZrSe2/ ZrS2 van der Waals (vdW) heterobilayer by density function theory. ZrSe2/ ZrS2 heterobilayer presents an intrinsic type-II band alignment, and the electrons and holes can be separated in different layers of ZrSe2/ ZrS2 heterobilayer, which can improves its carrier lifetime in photovoltaic devices. The electric field can effectively adjust the electronic properties of heterostructures. By applying a certain electric field, the band alignment can realize the transition from type-II to type-I, which is very beneficial to optical emission devices. To understand the inherent physical mechanism of electric field modulation, we analyze the variation trends of the band gap and band offset with external field in detail. In addition, ZrSe2/ ZrS2 heterostructure presents much stronger light absorption than isolated monolayers. Our results suggest that ZrSe2/ ZrS2 heterostructure can provide more potential application in optoelectronic devices.