The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this wor...The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.展开更多
Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suita...Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.展开更多
This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi...This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.展开更多
Stab-resistant textiles play a critical role in personal protection,necessitating a deeper understanding of how structural and layering factors influence their performance.The current study experimentally examines the...Stab-resistant textiles play a critical role in personal protection,necessitating a deeper understanding of how structural and layering factors influence their performance.The current study experimentally examines the effects of textile structure,layering,and ply orientation on the stab resistance of multi-layer textiles.Three 3D warp interlock(3DWI)structures({f1},{f2},{f3})and a 2D woven fabric({f4}),all made of high-performance p-aramid yarns,were engineered and manufactured.Multi-layer specimens were prepared and subjected to drop-weight stabbing tests following HOSBD standards.Stabbing performance metrics,including Depth of Trauma(DoT),Depth of Penetration(DoP),and trauma deformation(Ymax,Xmax),were investigated and analyzed.Statistical analyses(Two-and One-Way ANOVA)indicated that fabric type and layer number significantly impacted DoP(P<0.05),while ply orientation significantly affected DoP(P<0.05)but not DoT(P>0.05).Further detailed analysis revealed that 2D woven fabrics exhibited greater trauma deformation than 3D WIF structures.Increasing the number of layers reduced both DoP and DoT across all fabric structures,with f3 demonstrating the best performance in multi-layer configurations.Aligned ply orientations also enhanced stab resistance,underscoring the importance of alignment in dissipating impact energy.展开更多
Three different kinds of PELE(the penetrator with lateral efficiency) were launched by ballistic artillery to impact the multi-layer spaced metal target plates.The lmpact velocities of the projectiles were measured by...Three different kinds of PELE(the penetrator with lateral efficiency) were launched by ballistic artillery to impact the multi-layer spaced metal target plates.The lmpact velocities of the projectiles were measured by the velocity measuring system.The damage degree and process of each laye r of target plate impacted by the three kinds of projectiles were analyzed.The experimental results show that all the three kinds of projectiles have the effect of expanding holes on the multi-layer spaced metal target plates.For the normal structure PELE(without layered) with tungsten alloy jacket and the radial layered PELE with tungsten alloy jacket,the diameters of holes on the seco nd layer of plates are 3.36 times and 3.76 times of the diameter of the projectile,re spectively.For radial layered PELE with W/Zr-based amorphous composite jacket,due to the large number of tungsten wires dispersed after the impact,the diameter of the holes on the four-layer spaced plates can reach 2.4 times,3.04 times,5.36 times and 2.68 times of the diameter of the projectile.Besides,the normal structure PELE with tungsten alloy jacket and the radial layered PELE whit tungsten alloy jacket formed a large number of fragments impact marks on the third target plate.Although the number of fragments penetrating the third target plate is not as large as that of the normal structure PELE,the area of dispersion of fragments impact craters on the third target plate is larger by the radial layered PELE.The radial layered PELE with W/Zr-based amorphous composite jacket released a lot of heat energy due to the impact of the matrix material,and formed a large area of ablation marks on the last three target plates.展开更多
Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based o...Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green＇s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green＇s function can be divided into two parts： primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.展开更多
The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and mi...The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.展开更多
High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,tempe...High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.展开更多
Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling(HIR).To improve the heating speed of asphalt pavement in HIR,based on the numerical analysis model of asphalt mixture heating ...Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling(HIR).To improve the heating speed of asphalt pavement in HIR,based on the numerical analysis model of asphalt mixture heating process,a new multi-layer low-temperature heating method(MLHM)was proposed.Considering input heat flux,the thermal capacity and thermal resistance of asphalt mixture,the heat transfer model was established based on energy conservation law.By heating the asphalt mixture in layers,it changes the situation that the heat energy can only be input from the upper surface of the asphalt mixture pavement.Through the simulation of the heating method of asphalt mixture in the existing technology,the result shows that the existing heating methods lead to serious aging or charring of the asphalt mixture.By MLHM,the upper and the bottom of the asphalt mixture are heated at the same time,and the heating temperature is lower than other heat methods,which not only reduces the heating thickness and increases the heating area of the asphalt mixture pavement,but also improves the heating speed,saves the energy resource and ensures the heating quality.Especially,by MLHM,the heating uniformity is better and speed is faster.展开更多
Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The result...Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.展开更多
Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small vol...Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.展开更多
The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-...The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-doped TiO2-based varistor ceramics were fabricated by sintering at 1 250 ℃ for 0.5-5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cma decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 1l5 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0-3.0 h considering both nonlinear electrical behavior and dielectric properties.展开更多
The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diff...The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of B203 causes the increase of the contents of [BO3], [BO4] and [SiO4], which deduces the increase of CaB204 and a-SiO2 and the decrease of CaSiO3 correspondingly. No new phase is observed throughout the entire experiments. A bulk density of 2.54 g/cm3, a thermal expansion coefficient value of 11.95× 10-6 ℃-1 （20-500℃）, a dielectric constant er value of 6.42 and a dielectric loss tanδ value of 0.000 9 （measured at 9.7 GHz） are obtained for CBS glass ceramics containing 35%-B203 （mass fraction） sintered at 850 ℃ for 15 min.展开更多
The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was sign...The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was significantly reduced under nano-gap conditions and the optimal discharge voltage was 2 kV.Then,the anodic bonding and dielectric barrier discharge activated bonding were performed in comparison experiments,and the bonding strength was characterized by tensile failure test.The results showed that the bonding strength was higher under the nano-gap dielectric barrier discharge.This process completed 110°C ultra-low temperature anodic bonding and the bonding strength reached 2 MPa.Finally,the mechanism of promoting bonding after activation is also discussed.展开更多
Under the scenario of dense targets in clutter, a multi-layer optimal data correlation algorithm is proposed. This algorithm eliminates a large number of false location points from the assignment process by rough corr...Under the scenario of dense targets in clutter, a multi-layer optimal data correlation algorithm is proposed. This algorithm eliminates a large number of false location points from the assignment process by rough correlations before we calculate the correlation cost, so it avoids the operations for the target state estimate and the calculation of the correlation cost for the false correlation sets. In the meantime, with the elimination of these points in the rough correlation, the disturbance from the false correlations in the assignment process is decreased, so the data correlation accuracy is improved correspondingly. Complexity analyses of the new multi-layer optimal algorithm and the traditional optimal assignment algorithm are given. Simulation results show that the new algorithm is feasible and effective.展开更多
CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning ...CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.展开更多
Considering the fact that in some complex cases,plate anchors are buried in multi-layered geotechnical materials,the ultimate dynamic analysis was performed to investigate the uplift capacity and failure mechanism of ...Considering the fact that in some complex cases,plate anchors are buried in multi-layered geotechnical materials,the ultimate dynamic analysis was performed to investigate the uplift capacity and failure mechanism of shallow strips and circular plate anchors in multi-layered soils.The nonlinear strength criterion and non-associated flow rule of geotechnical materials were introduced to investigate the influence of nonuniformity on the pullout performance and failure mechanism of shallow plate anchors.The expressions of the detaching curves or surfaces were obtained to reflect the failure mechanism,which can be used to figure out the ultimate uplift capacity and failure range.The results are generally in agreement with the numerical simulations and previous research.The effects of various parameters on the ultimate uplift capacity and failure mechanism of plate anchors in multi-layered soils were investigated,and it is found that the ultimate uplift capacity and failure range of shallow anchors increase with the increase of initial cohesion and dilatancy coefficient,but decrease with the unit weight,axial tensile stress and nonlinear coefficient.展开更多
This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the cha...This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the charge,a peak overpressure prediction model for the composite charge under singlepoint detonation and simultaneous detonation was established.The effects of the charge structure and initiation method on the overpressure field characteristics were investigated in AUTODYN simulation.The accuracy of the prediction model and the reliability of the numerical simulation method were subsequently verified in a series of static explosion experiments.The results reveal that the mass of the inner charge was the key factor determining the peak overpressure of the composite charge under single-point detonation.The peak overpressure in the radial direction improved apparently with an increase in the aspect ratio of the charge.The overpressure curves in the axial direction exhibited a multi-peak phenomenon,and the secondary peak overpressure even exceeded the primary peak at distances of 30D and 40D(where D is the charge diameter).The difference in peak overpressure among azimuth angles of 0-90°gradually decreased with an increase in the propagation distance of the shock wave.The coupled effect of the detonation energy of the inner and outer charge under simultaneous detonation improved the overpressure in both radial and axial directions.The difference in peak overpressure obtained from model prediction and experimental measurements was less than 16.4%.展开更多
The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential ther...The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.展开更多
The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approach...The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.展开更多
基金National Natural Science Foundation of China (52302140)Major Scientific and Technological Innovation Project of Wenzhou (ZG2023040, ZG2023042)Joint Funds of the National Natural Science Foundation of China Key Program (U21B2068)。
文摘The feldspar-based microwave dielectric ceramic with low relative permittivity(εr)and excellent mechanical properties has attracted much attention in the fifth-generation wireless communication technology.In this work,a series of microwave dielectric ceramic SrAl_(2-x)Ga_(x)Si_(2)O_(8)(0.1≤x≤2.0)was synthesized using the traditional solid-state method.X-ray diffraction pattern indicates that Ga^(3+)can be dissolved into Al^(3+),forming a solid solution.Meanwhile,substitution of Ga^(3+)for Al^(3+)can promote the space group transition from I2/c(0.1≤x≤1.4)to P21/a(1.6≤x≤2.0)with coefficient of thermal expansion(CTE)increasing from 2.9×10^(-6)℃^(-1) to 5.2×10^(-6)℃^(-1).During this substitution,the phase transition can significantly improve the structural symmetry to enhance the dielectric properties and mechanical properties.Rietveld refinement results indicate that Ga^(3+)averagely occupied four Al^(3+)compositions to form solid solution.All ceramics have a dense microstructure and high relative density above 95%.An ultralower of 5.8 was obtained at x=1.6 composition with high quality factor(Q´f)of 50700 GHz and negative temperature coefficients of resonant frequency(tf)of approximately−35×10^(-6)℃^(-1).The densification temperature can be reduced to 940℃by adding 4%(in mass)LiF,resulting in good chemical compatibility with Ag electrode.Meanwhile,negativetf can be tuned to near-zero(+3.7×10^(-6)℃^(-1))by adding CaTiO_(3) ceramic.
基金Student Training Program for Innovation and Entrepreneurship of Hangzhou Institute for Advanced Study,UCAS(CXCY20230305)Chinese Academy of Sciences Key Project(ZDRW-CN-2021-3-1-18)。
文摘Ceramic dielectric materials with high dielectric strength and mechanisms of their internal factors affecting dielectric strength are significantly valuable for industrial application,especially for selection of suitable dielectric materials for high-power microwave transmission devices and reliable power transmission.Pure magnesium oxide(MgO),a kind of ceramic dielectric material,possesses great application potential in high-power microwave transmission devices due to its high theoretical dielectric strength,low dielectric constant,and low dielectric loss properties,but its application is limited by high sintering temperature during preparation.This work presented the preparation of a new type of multiphase ceramics based on MgO,which was MgO-1%ZrO_(2)-1%CaCO_(3-x)%MnCO_(3)(MZCM_(x),x=0,0.25,0.50,1.00,1.50,in molar),and their phase structures,morphological features,and dielectric properties were investigated.It was found that inclusion of ZrO_(2) and CaCO_(3) effectively inhibited excessive growth of MgO grains by formation of second phase,while addition of MnCO_(3) promoted the grain boundary diffusion process during the sintering process and reduced activation energy for the grain growth,resulting in a lower ceramic sintering temperature.Excellent performance,including high dielectric strength(Eb=92.3 kV/mm)and quality factor(Q×f=216642 GHz),simultaneously accompanying low dielectric loss(<0.03%),low temperature coefficient of dielectric constant(20.3×10^(–6)℃^(–1),85℃)and resonance frequency(–12.54×10^(–6)℃^(–1)),was achieved in MZCM1.00 ceramics under a relatively low sintering temperature of 1350℃.This work offers an effective solution for selecting dielectric materials for high-power microwave transmission devices.
基金Projects(42477162,52108347,52178371,52168046,52178321,52308383)supported by the National Natural Science Foundation of ChinaProjects(2023C03143,2022C01099,2024C01219,2022C03151)supported by the Zhejiang Key Research and Development Plan,China+6 种基金Project(LQ22E080010)supported by the Exploring Youth Project of Zhejiang Natural Science Foundation,ChinaProject(LR21E080005)supported by the Outstanding Youth Project of Natural Science Foundation of Zhejiang Province,ChinaProject(2022M712964)supported by the Postdoctoral Science Foundation of ChinaProject(2023AFB008)supported by the Natural Science Foundation of Hubei Province for Youth,ChinaProject(202203)supported by Engineering Research Centre of Rock-Soil Drilling&Excavation and Protection,Ministry of Education,ChinaProject(202305-2)supported by the Science and Technology Project of Zhejiang Provincial Communication Department,ChinaProject(2021K256)supported by the Construction Research Founds of Department of Housing and Urban-Rural Development of Zhejiang Province,China。
文摘This study proposes a general imperfect thermal contact model to predict the thermal contact resistance at the interface among multi-layered composite structures.Based on the Green-Lindsay(GL)thermoelastic theory,semi analytical solutions of temperature increment and displacement of multi-layered composite structures are obtained by using the Laplace transform method,upon which the effects of thermal resistance coefficient,partition coefficient,thermal conductivity ratio and heat capacity ratio on the responses are studied.The results show that the generalized imperfect thermal contact model can realistically describe the imperfect thermal contact problem.Accordingly,it may degenerate into other thermal contact models by adjusting the thermal resistance coefficient and partition coefficient.
文摘Stab-resistant textiles play a critical role in personal protection,necessitating a deeper understanding of how structural and layering factors influence their performance.The current study experimentally examines the effects of textile structure,layering,and ply orientation on the stab resistance of multi-layer textiles.Three 3D warp interlock(3DWI)structures({f1},{f2},{f3})and a 2D woven fabric({f4}),all made of high-performance p-aramid yarns,were engineered and manufactured.Multi-layer specimens were prepared and subjected to drop-weight stabbing tests following HOSBD standards.Stabbing performance metrics,including Depth of Trauma(DoT),Depth of Penetration(DoP),and trauma deformation(Ymax,Xmax),were investigated and analyzed.Statistical analyses(Two-and One-Way ANOVA)indicated that fabric type and layer number significantly impacted DoP(P<0.05),while ply orientation significantly affected DoP(P<0.05)but not DoT(P>0.05).Further detailed analysis revealed that 2D woven fabrics exhibited greater trauma deformation than 3D WIF structures.Increasing the number of layers reduced both DoP and DoT across all fabric structures,with f3 demonstrating the best performance in multi-layer configurations.Aligned ply orientations also enhanced stab resistance,underscoring the importance of alignment in dissipating impact energy.
基金supported by National Natural Science Foundation of China(Grant No.11802141)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX18_0465)。
文摘Three different kinds of PELE(the penetrator with lateral efficiency) were launched by ballistic artillery to impact the multi-layer spaced metal target plates.The lmpact velocities of the projectiles were measured by the velocity measuring system.The damage degree and process of each laye r of target plate impacted by the three kinds of projectiles were analyzed.The experimental results show that all the three kinds of projectiles have the effect of expanding holes on the multi-layer spaced metal target plates.For the normal structure PELE(without layered) with tungsten alloy jacket and the radial layered PELE with tungsten alloy jacket,the diameters of holes on the seco nd layer of plates are 3.36 times and 3.76 times of the diameter of the projectile,re spectively.For radial layered PELE with W/Zr-based amorphous composite jacket,due to the large number of tungsten wires dispersed after the impact,the diameter of the holes on the four-layer spaced plates can reach 2.4 times,3.04 times,5.36 times and 2.68 times of the diameter of the projectile.Besides,the normal structure PELE with tungsten alloy jacket and the radial layered PELE whit tungsten alloy jacket formed a large number of fragments impact marks on the third target plate.Although the number of fragments penetrating the third target plate is not as large as that of the normal structure PELE,the area of dispersion of fragments impact craters on the third target plate is larger by the radial layered PELE.The radial layered PELE with W/Zr-based amorphous composite jacket released a lot of heat energy due to the impact of the matrix material,and formed a large area of ablation marks on the last three target plates.
文摘Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green＇s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green＇s function can be divided into two parts： primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.
基金Project(2010GXNSFA013029) supported by the Natural Science Foundation of Guangxi Province,ChinaProject(101059529) supported by National Undergraduate Innovation Program of the Ministry of Education of China
文摘The influences of BaCu（B2O5） （BCB） addition on sintering, microstructure and microwave dielectric properties of Li2MgTi308 ceramics were investigated using X-ray diffractometry, scanning electron microscopy and microwave dielectric measurements. The experimental results show that a small amount of BaCu（B2O5） addition can effectively reduce the sintering temperature to 900℃, and induce only a limited degradation of the microwave dielectric properties. Typically, the best microwave dielectric properties of er24.5, Q×f =24 622 GHz, rf=4.2×10-6℃ -1 are obtained for 1.0% BCB-doped Li2MgTi3O8 ceramics sintered at 900℃ for 3 h. The BCB-doped Li2MgTi3O8 ceramics can be compatible with Ag electrode, which may be a strong candidate for low temperature co-fired ceramics applications.
基金Project(11174077)supported by the National Natural Science Foundation of ChinaProject(11JJ3079)supported by the Hunan Provincial Natural Science Foundation of ChinaProjects(12C0237,11C0844)supported by the Science Research Program of Education Department of Hunan Province,China
文摘High intensity focused ultrasound(HIFU)therapy is an effective method in clinical treatment of tumors,in order to explore the bio-heat conduction mechanism of in multi-layer media by concave spherical transducer,temperature field induced by this kind of transducer in multi-layer media will be simulated through solving Pennes equation with finite difference method,and the influence of initial sound pressure,absorption coefficient,and thickness of different layers of biological tissue as well as thermal conductivity parameter on sound focus and temperature distribution will be analyzed,respectively.The results show that the temperature in focus area increases faster while the initial sound pressure and thermal conductivity increase.The absorption coefficient is smaller,the ultrasound intensity in the focus area is bigger,and the size of the focus area is increasing.When the thicknesses of different layers of tissue change,the focus position changes slightly,but the sound intensity of the focus area will change obviously.The temperature in focus area will rise quickly before reaching a threshold,and then the temperature will keep in the threshold range.
基金Project(2017JM5077)supported by the Natural Science Basic Research Plan in Shaanxi Province,ChinaProjects(300102259109,300102259306)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Asphalt mixture pavement reheating is one of the important steps in hot in-place recycling(HIR).To improve the heating speed of asphalt pavement in HIR,based on the numerical analysis model of asphalt mixture heating process,a new multi-layer low-temperature heating method(MLHM)was proposed.Considering input heat flux,the thermal capacity and thermal resistance of asphalt mixture,the heat transfer model was established based on energy conservation law.By heating the asphalt mixture in layers,it changes the situation that the heat energy can only be input from the upper surface of the asphalt mixture pavement.Through the simulation of the heating method of asphalt mixture in the existing technology,the result shows that the existing heating methods lead to serious aging or charring of the asphalt mixture.By MLHM,the upper and the bottom of the asphalt mixture are heated at the same time,and the heating temperature is lower than other heat methods,which not only reduces the heating thickness and increases the heating area of the asphalt mixture pavement,but also improves the heating speed,saves the energy resource and ensures the heating quality.Especially,by MLHM,the heating uniformity is better and speed is faster.
基金Project(2013JSJJ002)supported by the Faculty Research Fund of Central South University,China
文摘Graphite oxide(GO) was prepared by the pressurized oxidation method and incorporated into polyimide(PI) matrix to fabricate high-k composite films by in-situ polymerization and subsequent thermal treatment. The results show that the as-prepared GO had good dispersion and compatibility in PI matrix due to the introduction of abundant oxygen-containing functional groups during the oxidation. The residual graphitic domains and the thermal treatment induced reduction of GO further enhanced the dielectric permittivity of the resulting GO–PI composites. The dielectric permittivity of the GO–PI composites exhibited a typical percolation behavior with a percolation threshold of 0.0347 of volume ratio and a critical exponent of 0.837. Near the percolation threshold, the dielectric permittivity of the GO–PI composite increased to 108 at 10~2 Hz and was 26 times that of the pure PI.
基金Project(202045007) supported by the Start-up Funds for Outstanding Talents in Central South University,China。
文摘Nanocomposite dielectrics show great promising application in developing next generation wearable all-solidstate cooling devices owing to the possessed advantages of high cooling efficiency, light-weight and small volume without the induced greenhouse effect or serious harm to ozone layer in the exploited refrigerants. However, low electrocaloric strength in nanocomposite dielectric is severely restricting its wide-spread application because of high applied operating voltage to improve electrocaloric effect. After addressing the chosen optimized ferroelectric ceramic and ferroelectric polymer matrix in conjunction with the analysis of crucial parameters, recent progress of electrocaloric effect(ECE) in polymer nanocomposites has been considerably reviewed. Subsequently, prior to proposing the conceptual design and devices/systems in electrocaloric nanocomposites, the existing developed devices/systems are reviewed. Finally, conclusions and prospects are conducted, including the aspects of materials chosen, structural design and key issues to be considered in improving electrocaloric effect of polymer nanocomposite dielectrics for flexible solidstate cooling devices.
基金Project(50872001) supported by the National Natural Science Foundation of ChinaProjects(KJ2007B132, KJ2009A006Z) supported by the Scientific Research Foundation of Education Department of Anhui Province, ChinaProject(XJ200907) supported by the Foundation of Construction of Quality Project of Anhui University, China
文摘The influence of soaking time on the nonlinear electrical behavior and dielectric properties of TiO2-based varistor ceramics was investigated. Based on single sintering process, six disk samples of （Sr, Bi, Si, Ta）-doped TiO2-based varistor ceramics were fabricated by sintering at 1 250 ℃ for 0.5-5.0 h. The samples were characterized by X-ray diffraction, voltage-current characteristics, energy spectra, metallographs, breakdown voltages, and apparent dielectric constant. It is found that the breakdown electrical field intensity at a current density of 10 mA/cma decreases from 5.5 to 4.1 V/mm first and then increases to 7.0 V/mm, the nonlinear coefficient increases from 2.39 to 2.62 first and then decreases to 2.42, and the apparent dielectric constant increases from 98 200 to 1l5 049 first and then decreases to 73 865 with the soaking time increasing from 0.5 to 5.0 h. These indicate that the optimal soaking time is 2.0-3.0 h considering both nonlinear electrical behavior and dielectric properties.
基金Project(2007AA03Z0455) supported by the National High-Technology Research and Development Program of ChinaProject(BE2009168) supported by the Natural Science Foundation of Jiangsu Province in ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institution,China
文摘The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 （CBS） glass ceramics were investigated by Fourier transform infrared spectroscopy （FTIR）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. The results show that the increasing amount of B203 causes the increase of the contents of [BO3], [BO4] and [SiO4], which deduces the increase of CaB204 and a-SiO2 and the decrease of CaSiO3 correspondingly. No new phase is observed throughout the entire experiments. A bulk density of 2.54 g/cm3, a thermal expansion coefficient value of 11.95× 10-6 ℃-1 （20-500℃）, a dielectric constant er value of 6.42 and a dielectric loss tanδ value of 0.000 9 （measured at 9.7 GHz） are obtained for CBS glass ceramics containing 35%-B203 （mass fraction） sintered at 850 ℃ for 15 min.
基金Project(6140863020216JW30001)supported by the General Armaments Department Pre-research Fund,China。
文摘The article improves the process of dielectric barrier discharge(DBD)activated anode bonding.The treated surface was characterized by the hydrophilic surface test.The results showed that the hydrophilic angle was significantly reduced under nano-gap conditions and the optimal discharge voltage was 2 kV.Then,the anodic bonding and dielectric barrier discharge activated bonding were performed in comparison experiments,and the bonding strength was characterized by tensile failure test.The results showed that the bonding strength was higher under the nano-gap dielectric barrier discharge.This process completed 110°C ultra-low temperature anodic bonding and the bonding strength reached 2 MPa.Finally,the mechanism of promoting bonding after activation is also discussed.
基金This project was supported by the National Natural Science Foundation of China (60672139, 60672140)the Excellent Ph.D. Paper Author Foundation of China (200237)the Natural Science Foundation of Shandong (2005ZX01).
文摘Under the scenario of dense targets in clutter, a multi-layer optimal data correlation algorithm is proposed. This algorithm eliminates a large number of false location points from the assignment process by rough correlations before we calculate the correlation cost, so it avoids the operations for the target state estimate and the calculation of the correlation cost for the false correlation sets. In the meantime, with the elimination of these points in the rough correlation, the disturbance from the false correlations in the assignment process is decreased, so the data correlation accuracy is improved correspondingly. Complexity analyses of the new multi-layer optimal algorithm and the traditional optimal assignment algorithm are given. Simulation results show that the new algorithm is feasible and effective.
基金Project(2007AA03Z0455) supported by the National High Technology Research and Development Program of ChinaProject(BE2010194) supported by Science&Technology Pillar Program of Jiangsu Province, China+1 种基金Project(KF201103) supported by the State Key Laboratory of New Ceramic and Fine Processing, Tsinghua University, ChinaProject supported by the Priority Academic Development of Jiangsu Higher Education Institutions, China
文摘CaO-B203-SiO2 （CBS） glass powders are prepared by conventional glass melting method at different melting temperatures whose properties and microstructures are characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 ℃ to 1 500 ℃ and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 ℃ could be sintered from 830 ℃ to 930 ℃ and the bulk densities of the samples are all higher than 2.4 g/cm^3. From the points of the properties and energy conservation, the melting temperature of 1 450 ℃ is the optimal melting temperature. The glass ceramic sintered at 850 ℃ exhibits better dielectric properties： er=6.33, tan6=2.2×10^-3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.
基金Project(51874202) supported by the National Natural Science Foundation of ChinaProject(2017JQ0003) supported by the Sichuan Youth Fund,China。
文摘Considering the fact that in some complex cases,plate anchors are buried in multi-layered geotechnical materials,the ultimate dynamic analysis was performed to investigate the uplift capacity and failure mechanism of shallow strips and circular plate anchors in multi-layered soils.The nonlinear strength criterion and non-associated flow rule of geotechnical materials were introduced to investigate the influence of nonuniformity on the pullout performance and failure mechanism of shallow plate anchors.The expressions of the detaching curves or surfaces were obtained to reflect the failure mechanism,which can be used to figure out the ultimate uplift capacity and failure range.The results are generally in agreement with the numerical simulations and previous research.The effects of various parameters on the ultimate uplift capacity and failure mechanism of plate anchors in multi-layered soils were investigated,and it is found that the ultimate uplift capacity and failure range of shallow anchors increase with the increase of initial cohesion and dilatancy coefficient,but decrease with the unit weight,axial tensile stress and nonlinear coefficient.
基金funded by the National Natural Science Foundation of China(Grant No.11972018,No.12002336)China Postdoctoral Science Foundation(Grant No.2021M701710)。
文摘This article investigates the characteristics of shock wave overpressure generated by multi-layer composite charge under different detonation modes.Combining dimensional analysis and the explosion mechanism of the charge,a peak overpressure prediction model for the composite charge under singlepoint detonation and simultaneous detonation was established.The effects of the charge structure and initiation method on the overpressure field characteristics were investigated in AUTODYN simulation.The accuracy of the prediction model and the reliability of the numerical simulation method were subsequently verified in a series of static explosion experiments.The results reveal that the mass of the inner charge was the key factor determining the peak overpressure of the composite charge under single-point detonation.The peak overpressure in the radial direction improved apparently with an increase in the aspect ratio of the charge.The overpressure curves in the axial direction exhibited a multi-peak phenomenon,and the secondary peak overpressure even exceeded the primary peak at distances of 30D and 40D(where D is the charge diameter).The difference in peak overpressure among azimuth angles of 0-90°gradually decreased with an increase in the propagation distance of the shock wave.The coupled effect of the detonation energy of the inner and outer charge under simultaneous detonation improved the overpressure in both radial and axial directions.The difference in peak overpressure obtained from model prediction and experimental measurements was less than 16.4%.
基金Project(2007AA03Z0455) supported by the National High Technology Research and Development Program of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institution, China
文摘The effects of Al2O3 addition on both the sintering behavior and microwave dielectric properties of PbO-B203-SiO2 glass ceramics were investigated by Fourier transform infrared spectroscope （FTIR）, differential thermal analysis （DTA）, X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The results show that with the increase of Al2O3 content the bands assigned to [SiO4] nearly disappear. Aluminum replaces silicon in the glass network, which is helpful for the formation of boron-oxygen rings. The increase of the transition temperature Tg and softening temperature Tf of PbO-B2O3-SiO2 glass ceramics leads to the increase of liquid phase precipitation temperature and promotes the structure stability in the glasses, and consequently contributes to the decreasing trend of crystallization. Densification and dielectric constants increase with the increase of Al2O3 content, but the dielectric loss is worsened. By contrast, the 3% （mass fraction） Al2O3-doped glass ceramics sintered at 725℃ have better properties of density p=2.72 g/cm3, dielectric constant Er=6.78, dielectric loss tan8=2.6×10^-3 （measured at 9.8 GHz）, which suggest that the glass ceramics can be applied in multilayer microwave devices requiring low sintering temperatures.
文摘The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.
