This paper presents a novel non-contact method for evaluating the resonant frequency of a microstructure, Firstly, the microstructure under test is excited by ultrasonic waves. This excitation method does not impose a...This paper presents a novel non-contact method for evaluating the resonant frequency of a microstructure, Firstly, the microstructure under test is excited by ultrasonic waves. This excitation method does not impose any undefined load on the specimen like the electrostatic excitation and also this is the first actual use of ultrasonic wave for exciting a microstructure in the literature. Secondly, the amplitudes of the microstructure are determined by image edge detection using a Mexican hat wavelet transform on the vibrating images of the microstructure. The vibrating images are captured by a CCD camera when the microstructure is vibrated by ultrasonic waves at a series of discrete high frequencies (〉30 kHz). Upon processing the vibrating images, the amplitudes at various excitation frequencies are obtained and an amplitude-frequency spectrum is obtained from which the resonant frequency is subsequently evaluated. A micro silicon structure consisting of a perforated plate (192 × 192 μm) and two cantilever beams (76 × 43 μm) which is about 4 μm thickness is tested. Since laser interferometry is not required, thermal effects on a test object can be avoided. Hence, the setup is relatively simple. Results show that the proposed method is a simple and effective approach for evaluating the dynamic characteristics of microstructures.展开更多
Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3...Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.展开更多
A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing mag...A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing magnetic levitation and a rotary oscillator(R_TO)performing electromagnetic coupling through a stator and a rotor.Both oscillators,coupled by magnetic forces generated by a set of arc permanent magnets,radially magnetized and centro-symmetrically fixed onto the R_LO and the rotor of the R_TO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion.Specifically,the dual resonator is able to convert stochastic reciprocating motion into controllable rotation,provide intrinsic frequency up-conversion,use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting.While solely focusing on developing a dual resonator provides substantial benefits,its dynamic behavior is unclear,thus electromagnetic-dynamic governing equations are derived,and a curve fitting model of restoring torque of R_TO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system.Power analysis is carried out for providing aquantitative guidance of customizing the harvester to achieve an optimal power density.展开更多
In order to improve the surface hydrophobicity, silicone rubber (SIR) samples were exposed to CF4 radio frequency (RF) capacitively coupled plasma (CCP). Attenuated total reflection Fourier transform infrared (ATR-FTI...In order to improve the surface hydrophobicity, silicone rubber (SIR) samples were exposed to CF4 radio frequency (RF) capacitively coupled plasma (CCP). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum and X-ray photoelectron spectroscopy (XPS) were used to observe the variation of the functional groups of the modified SIR. Static contact angle (SCA) was employed to estimate the change of hydrophobicity of the modified SIR. The surface energy of SIR is reduced largely from 27.37 mJ/m2 of original SIR sample to 2.94 mJ/m2 of SIR sample treated by CF4 CCP modification at RF power of 200 W for a treatment time of 5 min. According to the XPS, ATR-FTIR and surface energy analysis, it is suggested that the improvement of hydrophobicity on the modified SIR surface is mainly ascribed to the decrease of surface energy, which is caused by the cooperation of the fluosilicic structure of Si—F or Si—F2 and the fluoric groups of C—CFn induced by the methyl replacement reaction and residual methyl groups of SIR surface.展开更多
The effects of back gate bias(BGEs) on radio-frequency(RF) performances in PD SOI n MOSFETs are presented in this paper. Floating body(FB) device, T-gate body-contact(TB) device, and tunnel diode body-contact(TDBC) de...The effects of back gate bias(BGEs) on radio-frequency(RF) performances in PD SOI n MOSFETs are presented in this paper. Floating body(FB) device, T-gate body-contact(TB) device, and tunnel diode body-contact(TDBC) device, of which the supply voltages are all 1.2 V, are compared under different back gate biases by different figures of merit, such as cut-off frequency( fT), maximum frequency of oscillation( fmax), etc. Because of the lack of a back gate conducting channel, the drain conductance(gd) of TDBC transistor shows a smaller degradation than those of the others, and the trans-conductance(gm) of TDBC is almost independent of back gate bias. The values of fT of TDBC are also kept nearly constant under different back gate biases. However, RF performances of FB and TB each show a significant degradation when the back gate bias is larger than ~ 20 V. The results indicate that TDBC structures could effectively improve the back gate bias in RF performance.展开更多
Using environmental random vibration as the excitation,traditional accelerometer method,non-contact video method and non-contact laser method were employed to determine the natural frequency of Kunyu River footbridge....Using environmental random vibration as the excitation,traditional accelerometer method,non-contact video method and non-contact laser method were employed to determine the natural frequency of Kunyu River footbridge.All the results of these three methods are close to 2.70 Hz,which are concordant with each other and hence credible.展开更多
Using molten Pb-Sn-Bi alloy, the meniscus shape under high frequency magnetic field of φ100 mm round billet caster was investigated. The effect of some parameters on meniscus shape was studied. The results show that ...Using molten Pb-Sn-Bi alloy, the meniscus shape under high frequency magnetic field of φ100 mm round billet caster was investigated. The effect of some parameters on meniscus shape was studied. The results show that for a mold with 12 segments, the meniscus shape is relatively stable. With increasing power input, the menis- cus height increases with intensification of fluctuation. For the given caster, the reasonable power input is about 70 kW. The coil should be near to the top of mold and/or the initial meniscus should be near to the center of the coil. The lower the frequency, the higher is the meniscus height. With increasing frequency, the free surface is more flattened and meniscus becomes more stable. In practice, the power input should be increased simultaneously with frequency. The optimal frequency is about 20 kHz.展开更多
A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displa...A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.展开更多
Atomistic quantum simulation is performed to compare the performance of zero-Schottky-barrier and doped source-drain contacts carbon nanotube field effect transistors(CNTFETs) with strain applied. The doped source-dra...Atomistic quantum simulation is performed to compare the performance of zero-Schottky-barrier and doped source-drain contacts carbon nanotube field effect transistors(CNTFETs) with strain applied. The doped source-drain contact CNTFETs outperform the Schottky contact devices with and without strain applied. The off-state current in both types of contact is similar with and without strain applied. This is because both types of contact offer very similar potential barrier in off-state. However, the on-state current in doped contact devices is much higher due to better modulation of on-state potential profile, and its variation with strain is sensitive to the device contact type. The on/off current ratio and the inverse subthreshold slope are better with doped source-drain contact, and their variations with strain are relatively less sensitive to the device contact type. The channel transconductance and device switching performance are much better with doped source-drain contact, and their variations with strain are sensitive to device contact type.展开更多
Based on the fractal theory,a normal contact stiffness model is established.In the model,the asperity is initially in elastic deformation under contact interference.As the interference is increased,a transition from e...Based on the fractal theory,a normal contact stiffness model is established.In the model,the asperity is initially in elastic deformation under contact interference.As the interference is increased,a transition from elastic to elastoplastic to full plastic deformation occurs in this order.The critical elastic interference,the first elastoplastic critical interference and the second elastoplastic critical interference are scale-dependent.According to the truncated asperity size distribution function,the relations between the total normal contact stiffness and the total contact load are obtained.The results show the total normal contact stiffness depends on the range of frequency indexes of asperities.The normal contact stiffness in elastic deformation is major contribution to the total normal contact stiffness.When the first six frequency indexes are less than the critical elastic frequency index,the dimensionless load-stiffness relation approximately isF^*r^(K^*r)^3.When the initial frequency index is greater than the critical elastic frequency index,the dimensionless load-stiffness relation approximately isF^*r^K^*r.The comparison between the theoretical results and the experimental results indicates that the theoretical results are consistent with the experimental data;therefore,the present fractal model of contact stiffness is reasonable.展开更多
In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to ...In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to the piecewise homogeneous body model with utilizing the three-dimensional linearized theory of elastic waves in initially stressed bodies(TLTEWISB).The materials of the body are chosen to be linearly elastic,homogeneous,and isotropic.The interface between the layers is assumed to be imperfect,and is simulated by the spring-layer model.A similar degree of imperfection on the interface is realized in the normal and tangential directions.The mathematical model for the problem under consideration is designed,and the system of the equations of motion is approximately solved by employing the finite element method(FEM).The numerical results explaining the influence of the parameter that characterizes the degree of corresponding imperfectness on the dynamic response of the plate-strip are presented.In particular,we demonstrate that the distributions of the normal stress become flat,as the normal-spring parameter increases.展开更多
The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for ...The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for thermal resistance of contact (<i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.05 m). The impact of heat exchange coefficients on the front face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0 m) and the rear face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.1 m) on these resistors is shown.</span>展开更多
基金supported by the National Natural Science Foundation of China(10772086 and 10727201)the National University of Singapore(R-265-000-140-112)
文摘This paper presents a novel non-contact method for evaluating the resonant frequency of a microstructure, Firstly, the microstructure under test is excited by ultrasonic waves. This excitation method does not impose any undefined load on the specimen like the electrostatic excitation and also this is the first actual use of ultrasonic wave for exciting a microstructure in the literature. Secondly, the amplitudes of the microstructure are determined by image edge detection using a Mexican hat wavelet transform on the vibrating images of the microstructure. The vibrating images are captured by a CCD camera when the microstructure is vibrated by ultrasonic waves at a series of discrete high frequencies (〉30 kHz). Upon processing the vibrating images, the amplitudes at various excitation frequencies are obtained and an amplitude-frequency spectrum is obtained from which the resonant frequency is subsequently evaluated. A micro silicon structure consisting of a perforated plate (192 × 192 μm) and two cantilever beams (76 × 43 μm) which is about 4 μm thickness is tested. Since laser interferometry is not required, thermal effects on a test object can be avoided. Hence, the setup is relatively simple. Results show that the proposed method is a simple and effective approach for evaluating the dynamic characteristics of microstructures.
基金Project supported by the National Basic Research Program of China(Grant Nos.2016YFA0300601,2017YFA0304700,and 2015CB921402)the National Natural Science Foundation China(Grant Nos.11527806,91221203,11174357,91421303,and 11774405)+1 种基金the Strategic Priority Research Program B of the Chinese Academy of Sciences(Grant Nos.XDB07010100 and XDB28000000)the Beijing Municipal Science&Technology Commission,China(Grant No.Z191100007219008)
文摘Recently,a contact-resistance-measurement method was developed to detect the minigap,hence the Andreev bound states(ABSs),in Josephson junctions constructed on the surface of three-dimensional topological insulators(3D TIs).In this work,we further generalize that method to the circumstance with radio frequency(rf)irradiation.We find that with the increase of the rf power,the measured minigap becomes broadened and extends to higher energies in a way similar to the rf power dependence of the outer border of the Shapiro step region.We show that the corresponding data of contact resistance under rf irradiation can be well interpreted by using the resistively shunted Josephson junction(RSJ)model and the Blonder–Tinkham–Klapwijk(BTK)theory.Our findings could be useful when using the contact-resistancemeasurement method to study the Majorana-related physics in topological insulator-based Josephson junctions under rf irradiation.
基金partially supported by the U.S.Office of Navy Research (No.N000141410230)partially supported by the Department of Energy ARPA-E (No. DOE-AR0000531)
文摘A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is reported.The dual resonator consists of a rectilinear oscillator(R_LO)performing magnetic levitation and a rotary oscillator(R_TO)performing electromagnetic coupling through a stator and a rotor.Both oscillators,coupled by magnetic forces generated by a set of arc permanent magnets,radially magnetized and centro-symmetrically fixed onto the R_LO and the rotor of the R_TO achieve the reciprocating-to-rotary motion conversion and frequency up-conversion.Specifically,the dual resonator is able to convert stochastic reciprocating motion into controllable rotation,provide intrinsic frequency up-conversion,use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy harvesting.While solely focusing on developing a dual resonator provides substantial benefits,its dynamic behavior is unclear,thus electromagnetic-dynamic governing equations are derived,and a curve fitting model of restoring torque of R_TO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical system.Power analysis is carried out for providing aquantitative guidance of customizing the harvester to achieve an optimal power density.
基金Project(05JT1034) supported by the Plan of Science and Technology Bureau of Hunan Province,China
文摘In order to improve the surface hydrophobicity, silicone rubber (SIR) samples were exposed to CF4 radio frequency (RF) capacitively coupled plasma (CCP). Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrum and X-ray photoelectron spectroscopy (XPS) were used to observe the variation of the functional groups of the modified SIR. Static contact angle (SCA) was employed to estimate the change of hydrophobicity of the modified SIR. The surface energy of SIR is reduced largely from 27.37 mJ/m2 of original SIR sample to 2.94 mJ/m2 of SIR sample treated by CF4 CCP modification at RF power of 200 W for a treatment time of 5 min. According to the XPS, ATR-FTIR and surface energy analysis, it is suggested that the improvement of hydrophobicity on the modified SIR surface is mainly ascribed to the decrease of surface energy, which is caused by the cooperation of the fluosilicic structure of Si—F or Si—F2 and the fluoric groups of C—CFn induced by the methyl replacement reaction and residual methyl groups of SIR surface.
文摘The effects of back gate bias(BGEs) on radio-frequency(RF) performances in PD SOI n MOSFETs are presented in this paper. Floating body(FB) device, T-gate body-contact(TB) device, and tunnel diode body-contact(TDBC) device, of which the supply voltages are all 1.2 V, are compared under different back gate biases by different figures of merit, such as cut-off frequency( fT), maximum frequency of oscillation( fmax), etc. Because of the lack of a back gate conducting channel, the drain conductance(gd) of TDBC transistor shows a smaller degradation than those of the others, and the trans-conductance(gm) of TDBC is almost independent of back gate bias. The values of fT of TDBC are also kept nearly constant under different back gate biases. However, RF performances of FB and TB each show a significant degradation when the back gate bias is larger than ~ 20 V. The results indicate that TDBC structures could effectively improve the back gate bias in RF performance.
基金Ministry of Science and Technology of China for sponsoring the"Cooperation Research on the Dynamic Safety and Serviceability of Public Structures Servicing for Human"(No.2010DFB74280)between Beijing Institute of Technology and Ruhr-University Bochum
文摘Using environmental random vibration as the excitation,traditional accelerometer method,non-contact video method and non-contact laser method were employed to determine the natural frequency of Kunyu River footbridge.All the results of these three methods are close to 2.70 Hz,which are concordant with each other and hence credible.
文摘Using molten Pb-Sn-Bi alloy, the meniscus shape under high frequency magnetic field of φ100 mm round billet caster was investigated. The effect of some parameters on meniscus shape was studied. The results show that for a mold with 12 segments, the meniscus shape is relatively stable. With increasing power input, the menis- cus height increases with intensification of fluctuation. For the given caster, the reasonable power input is about 70 kW. The coil should be near to the top of mold and/or the initial meniscus should be near to the center of the coil. The lower the frequency, the higher is the meniscus height. With increasing frequency, the free surface is more flattened and meniscus becomes more stable. In practice, the power input should be increased simultaneously with frequency. The optimal frequency is about 20 kHz.
基金Project(2013CB632305)supported by the National Basic Research Program of ChinaProject(51375108)supported by the National Natural Science Foundation of China
文摘A line contact model of elastic coated solids is presented based on the influence coefficients(ICs) of surface displacement and stresses of coating-substrate system and the traditional contact model. The ICs of displacement and stresses are obtained from their corresponding frequency response functions(FRF) by using a conversion method based on fast Fourier transformation(FFT). The contact pressure and the stress field in the subsurface are obtained by employing conjugate gradient method(CGM) and discrete convolution fast Fourier transformation(DC-FFT). Comparison of the contact pressure and subsurface stresses obtained by the numerical method with the exact analytical solutions for Hertz contact is conducted, and the results show that the numerical solution has a very high accuracy and verify the validity of the contact model. The effect of the stiffness and thickness of coatings is further numerically studied. The result shows that the effects on contact pressure and contact width are opposite for hard and soft coatings and are intensified with the increase of coating thickness; the locations of crack initiation and propagation are different for soft and hard coatings; the risk of cracks and delaminations of coatings can be brought down by improving the lubrication condition or optimizing the non-dimensional parameter h/bh. This research offers a tool to numerically analyze the problem of elastic coated solids in line contact and make the blindness and randomness of trial-type coating design less.
文摘Atomistic quantum simulation is performed to compare the performance of zero-Schottky-barrier and doped source-drain contacts carbon nanotube field effect transistors(CNTFETs) with strain applied. The doped source-drain contact CNTFETs outperform the Schottky contact devices with and without strain applied. The off-state current in both types of contact is similar with and without strain applied. This is because both types of contact offer very similar potential barrier in off-state. However, the on-state current in doped contact devices is much higher due to better modulation of on-state potential profile, and its variation with strain is sensitive to the device contact type. The on/off current ratio and the inverse subthreshold slope are better with doped source-drain contact, and their variations with strain are relatively less sensitive to the device contact type. The channel transconductance and device switching performance are much better with doped source-drain contact, and their variations with strain are sensitive to device contact type.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51105304,51475364)the China Postdoctoral Science Foundation funded project(Grant No.2014M552467).
文摘Based on the fractal theory,a normal contact stiffness model is established.In the model,the asperity is initially in elastic deformation under contact interference.As the interference is increased,a transition from elastic to elastoplastic to full plastic deformation occurs in this order.The critical elastic interference,the first elastoplastic critical interference and the second elastoplastic critical interference are scale-dependent.According to the truncated asperity size distribution function,the relations between the total normal contact stiffness and the total contact load are obtained.The results show the total normal contact stiffness depends on the range of frequency indexes of asperities.The normal contact stiffness in elastic deformation is major contribution to the total normal contact stiffness.When the first six frequency indexes are less than the critical elastic frequency index,the dimensionless load-stiffness relation approximately isF^*r^(K^*r)^3.When the initial frequency index is greater than the critical elastic frequency index,the dimensionless load-stiffness relation approximately isF^*r^K^*r.The comparison between the theoretical results and the experimental results indicates that the theoretical results are consistent with the experimental data;therefore,the present fractal model of contact stiffness is reasonable.
基金supported by Research Fund of Kastamonu University under project number KUBAP-01/2016-4.
文摘In this paper,we present our report on the forced vibration of a bi-layered plate-strip with initial stress resting on a rigid foundation induced by a time-harmonic force.The investigation is carried out according to the piecewise homogeneous body model with utilizing the three-dimensional linearized theory of elastic waves in initially stressed bodies(TLTEWISB).The materials of the body are chosen to be linearly elastic,homogeneous,and isotropic.The interface between the layers is assumed to be imperfect,and is simulated by the spring-layer model.A similar degree of imperfection on the interface is realized in the normal and tangential directions.The mathematical model for the problem under consideration is designed,and the system of the equations of motion is approximately solved by employing the finite element method(FEM).The numerical results explaining the influence of the parameter that characterizes the degree of corresponding imperfectness on the dynamic response of the plate-strip are presented.In particular,we demonstrate that the distributions of the normal stress become flat,as the normal-spring parameter increases.
文摘The study is carried out in imperfect contact with a concrete slab wall attached to a panel based on rice straw compressed in a dynamic frequency regime. We will propose the characterization of thermal insulation for thermal resistance of contact (<i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.05 m). The impact of heat exchange coefficients on the front face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0 m) and the rear face (</span><i><span style="font-family:Verdana;">x</span></i><span style="font-family:Verdana;"> = 0.1 m) on these resistors is shown.</span>