The Ga N high electron mobility transistor(HEMT)has been considered as a potential terahertz(THz)radiation source,yet the low radiation power level restricts their applications.The HEMT array is thought to improve the...The Ga N high electron mobility transistor(HEMT)has been considered as a potential terahertz(THz)radiation source,yet the low radiation power level restricts their applications.The HEMT array is thought to improve the coupling efficiency between two-dimensional(2D)plasmons and THz radiation.In this work,we investigate the plasma oscillation,electromagnetic radiation,and the integration characteristics of Ga N HEMT targeting at a high THz radiation power source.The quantitative radiation power and directivity are obtained for integrated Ga N HEMT array with different array periods and element numbers.With the same initial plasma oscillation phase among the HEMT units,the radiation power of the two-element HEMT array can achieve 4 times as the single HEMT radiation power when the array period is shorter than 1/8electromagnetic wavelength.In addition,the radiation power of the HEMT array varies almost linearly with the element number,the smaller array period can lead to the greater radiation power.It shows that increasing the array period could narrow the main radiated lobe width while weaken the radiation power.Increasing the element number can improve both the radiation directivity and power.We also synchronize the plasma wave phases in the HEMT array by adopting an external Gaussian plane wave with central frequency the same as the plasmon resonant frequency,which solves the problem of the radiation power reduction caused by the asynchronous plasma oscillation phases among the elements.The study of the radiation power amplification of the one-dimensional(1D)Ga N HEMT array provides useful guidance for the research of compact high-power solid-state terahertz sources.展开更多
Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique.Planar eddy-current sensor arrays have several advantages such as good coherence,fast response speed,and high sensitivi...Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique.Planar eddy-current sensor arrays have several advantages such as good coherence,fast response speed,and high sensitivity,which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation.The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions.The principle and characteristics of planar eddy-current sensor arrays are introduced,and a crack length quantification algorithm in different directions is investigated.A damage quantitative detection system is established based on a field programmable gate array and ARM processor.The system is utilized to inspect the micro defect in a metallic material,which is carved to micro crack with size of 7mm(length)×0.1mm(width)×1mm(depth).The experimental data show that the sensor arrays can be used for the length measurement repeatedly,and that the uncertainty of the length measurement is below ±0.2mm.展开更多
Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a ...Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically（in x axis）,and it is 0.55 horizontally（in y axis）.The theoretical model is also simulated,and success of our structured mirror array is achieved.展开更多
The problem of two-dimensional direction of arrival(2D-DOA)estimation for uniform planar arrays(UPAs)is investigated by employing the reduced-dimensional(RD)polynomial root finding technique and 2D multiple signal cla...The problem of two-dimensional direction of arrival(2D-DOA)estimation for uniform planar arrays(UPAs)is investigated by employing the reduced-dimensional(RD)polynomial root finding technique and 2D multiple signal classification(2D-MUSIC)algorithm.Specifically,based on the relationship between the noise subspace and steering vectors,we first construct 2D root polynomial for 2D-DOA estimates and then prove that the 2D polynomial function has infinitely many solutions.In particular,we propose a computationally efficient algorithm,termed RD-ROOT-MUSIC algorithm,to obtain the true solutions corresponding to targets by RD technique,where the 2D root-finding problem is substituted by two one-dimensional(1D)root-finding operations.Finally,accurate 2DDOA estimates can be obtained by a sample pairing approach.In addition,numerical simulation results are given to corroborate the advantages of the proposed algorithm.展开更多
An experimental investigation was performed to investigate two-dimensional axial velocity field at downstream of the 90°double bend pipe with and without inlet swirling condition. The main objectives are to fi...An experimental investigation was performed to investigate two-dimensional axial velocity field at downstream of the 90°double bend pipe with and without inlet swirling condition. The main objectives are to find separation region and observe the influence of inlet swirling flow on the velocity fluctuation using ultrasound technique. The experiments were carried out in the pipe at Reynolds number Re = 1 × 104. In case of inlet swirling flow condition, a rotary swirler was used as swirling generator, and the swirl number was setup S = 1. The ultrasonic measurements were taken at four downstream locations of the second bend pipe. Phased Array Ultrasonic Velocity Profiler (Phased Array UVP) technique was applied to obtain the two-dimensional velocity of the fluid and the axial and tangential velocity fluctuation. It was found that the secondary reverse flow became smaller at the downstream from the bend when the inlet condition on the first bend was swirling flow. In addition, inlet swirling condition influenced mainly on the tangential velocity fluctuation, and its maximum turbulence intensity was 40%.展开更多
The resistance and inductance of a wire array during an implosion are very important parameters of interest to：researchers. A variety of inductances and resistances directly affect the kinetic energy and resistance h...The resistance and inductance of a wire array during an implosion are very important parameters of interest to：researchers. A variety of inductances and resistances directly affect the kinetic energy and resistance heat energy coupled from a pulsed-power generator. In this paper, the inductance and resistance of a planar wire array during the Z-pinch process are analyzed. The inductance is calculated from the data obtained by a time-resolved soft X-ray framed camera, while the resistance is calculated through the voltage and the current of the wire array load combined with the variety of the inductance. The results show that the resistance of the load increases with the development of the implosion, and reaches its maximum at 0.29 ± 0.16Ω near the pinched time.展开更多
Two dynamics modes, named short ablation mode and long ablation mode, are observed in implosion experiments of planar wire array Z pinch on ＇QiangGuang-I＇ facility utilizing an optical streak camera. The long ablati...Two dynamics modes, named short ablation mode and long ablation mode, are observed in implosion experiments of planar wire array Z pinch on ＇QiangGuang-I＇ facility utilizing an optical streak camera. The long ablation mode has a lagged trajectory compared with the short ablation mode. For shot 10035 in a short ablation mode, the initial time of K-shell radiation is consistent with the interaction time for ablation plasma arriving at the centre of wire array, while for shot 10038 in long ablation mode, the initial time of K-shell radiation is about 10 ns earlier. In the two modes, the partial ablation plasma could traverse the wire array plane and then collide in the centre to form a dense plasma column with a diameter of 2.2 mm for shot 10035 and 1.5 mm for shot 10038.展开更多
In recent years, several attempts have been made in designing planar array antennas with high directivity. This paper is aimed at investigating the impact of element spacing on the directivity of planar array of monop...In recent years, several attempts have been made in designing planar array antennas with high directivity. This paper is aimed at investigating the impact of element spacing on the directivity of planar array of monopole antenna. The directivity of antenna with reduced grating lobes can be obtained by carefully varying the inter-element spacing of array antenna. Based on this conception, this paper presents the investigation carried out on the relationship between inter-element spacing and the directivity of planar array of monopole antenna. It went further to highlight the effect on the total fields radiated by the antenna. The inter-element spacing is one of the most important antenna parameters that determine the directivity of the antenna. For a planar array of monopole, the directivity can be improved by varying the inter-element spacing. Four elements uniform planar array antenna and Hadamard matrix method was used to determine element positioning in the array matrix. The simulated results obtained using Matlab, showed that good directivity was obtained by using element spacing between 0.1λ - 0.5λ. Increasing the spacing beyond 0.6λ - 1.0λ also improved the directivity, but generated many grating lobes. As inter-element spacing increased, the grating lobes increased in size, number and levels. The study, therefore, inferred that the best directivity (radiation pattern) can only be obtained when the element spacing is within 0.1 - 0.5λ.展开更多
A novel low-cost 4-element planar array antenna directly fed by a coaxial cable for Ultra-WideBand(UWB) application is presented. The proposed antenna consists of 2×2 bowtie elements and a simple 1:4 power divide...A novel low-cost 4-element planar array antenna directly fed by a coaxial cable for Ultra-WideBand(UWB) application is presented. The proposed antenna consists of 2×2 bowtie elements and a simple 1:4 power divider feeding network. Compared to the basic bowtie element, the impedance bandwidth of the array antenna has a significant improvement that the low cut-off frequency is extended from 6 GHz of the bowtie element to 2 GHz. The measured results show that the proposed antenna has a large bandwidth of 2 GHz to 11 GHz for Voltage Standing Wave Ratio(VSWR)<2, and exhibits a bidirectional radiation pattern and a modest gain across the operating band and a peak gain of about 9 dBi at 11 GHz.展开更多
Gaseous phases of carbon-containing and metastable oxides will be resulted from the carbonization of phenolic resin binders and the reduced reactions between C and oxides at high temperatures in carbon-containing refr...Gaseous phases of carbon-containing and metastable oxides will be resulted from the carbonization of phenolic resin binders and the reduced reactions between C and oxides at high temperatures in carbon-containing refractories. With the in-situ catalysis technique, these gaseous phases can be transformed to one-or two-dimensional bonding phases by deposition,which is favorable for the improvement on strength and toughness of carboncontaining refractories,especially low carbon refractories. The research results reveal that：（ 1） the amorphous carbon resulted from phenolic resin can be transformed to carbon nanotubes,thus,the oxidation peak temperature is raised from 506 to 664. 6 ℃;（ 2） onedimensional whiskers of MgO or Mg Al2 O4 can be in-situ formed in MgO-C refractories, and their CMOR,CCS,rupture displacement and residual CCS（ two water quenching cycles,1 100 ℃） are increased by 66%,47%,13% and 26%,respectively;（ 3） two-dimensional array structure of flake β-SiAlON can be in-situ formed in Al2 O3-C refractories,which improves the material strength by 60% and decreases the residual strength after thermal shock by only 4. 5 MPa. It is believed that the in-situ formation of one-or two-dimensional bonding phases at high temperatures can improvethe comprehensive thermal physical properties of carboncontaining refractories,and will be the developing trend of the strengthening and toughening of low carbon-containing refractories.展开更多
Sparse arrays of telescopes have a limited (u, v)-plane coverage. In this paper, an optimization method for designing planar arrays of an aperture synthesis telescope is proposed that is based on distributed genetic a...Sparse arrays of telescopes have a limited (u, v)-plane coverage. In this paper, an optimization method for designing planar arrays of an aperture synthesis telescope is proposed that is based on distributed genetic algorithm. This distributed genetic algorithm is implemented on a network of workstations using community communication model. Such an aperture synthesis system performs with imperfection of (u, v) components caused by deviations and(or) some missing baselines. With the maximum (u, v)-plane coverage of this rotation-optimized array, the image of the source reconstructed by inverse Fourier transform is satisfactory.展开更多
This paper presents a dual-band planar antenna array for ISM band applications (2.4 GHz and 2.45 GHz). This antenna is proposed for indoor applications and enables adaptive beamforming and angle of arrival (AOA) estim...This paper presents a dual-band planar antenna array for ISM band applications (2.4 GHz and 2.45 GHz). This antenna is proposed for indoor applications and enables adaptive beamforming and angle of arrival (AOA) estimation. An adaptive beamforming algorithm is applied for a planar antenna array, which is able to steer its main beam and nulls in azimuth and elevation planes over a wide frequency band. Planar antenna array operates as a spatial filter in 3D space, processing the received signals with weighting schemes. A planar antenna array is designed for AOA estimation in azimuth and elevation planes by using MUltiple SIgnal Classification (MUSIC) based on subspace algorithm. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. Planar antenna with four elliptical slotted triangular elements (PAFESTE) is used to obtain optimal directivity in four directions in azimuth plane with specific orientation of 30? in elevation plane. It is characterized by half power beamwidth in elevation plane of about 60? and half power beamwidth in azimuth plane of about 90?.展开更多
With the development of the aerospace industry,space missions are becoming more complicated and diversified,and there is a demand for antenna mechanisms with a larger physical aperture.In this paper,a planar deployabl...With the development of the aerospace industry,space missions are becoming more complicated and diversified,and there is a demand for antenna mechanisms with a larger physical aperture.In this paper,a planar deployable mechanism is proposed,which can form a flat reflection surface with a small gap between plates.To this end,a novel large-scale two-dimensional deployable nine-grid planar antenna mechanism is designed.First,two antenna folding schemes and four supporting mechanism schemes are proposed.Through comparison analysis,the antenna configuration scheme with the best comprehensive performance is selected.A kinematic model of the deployable mechanism is established,and its kinematic characteristics are analyzed.Then,the correctness of the kinematic model is verified by comparing the analytical and simulation results of the kinematic model.Subsequently,a finite element model of the antenna is developed.Based on the response surface method,the structural parameters of the support rods of the antenna are optimized,and a set of optimized solutions with lightweight and high fundamental frequency characteristics are obtained.Finally,a prototype of the proposed nine-grid planar antenna is fabricated.The feasibility of the deployment principle and the rationality of the designed mechanism are verified by deployment experiments.展开更多
As the basis of machine vision,the biomimetic image sensing devices are the eyes of artificial intelligence.In recent years,with the development of two-dimensional(2D)materials,many new optoelectronic devices are deve...As the basis of machine vision,the biomimetic image sensing devices are the eyes of artificial intelligence.In recent years,with the development of two-dimensional(2D)materials,many new optoelectronic devices are developed for their outstanding performance.However,there are still little sensing arrays based on 2D materials with high imaging quality,due to the poor uniformity of pixels caused by material defects and fabrication technique.Here,we propose a 2D MoS_(2)sensing array based on artificial neural network(ANN)learning.By equipping the MoS_(2)sensing array with a“brain”(ANN),the imaging quality can be effectively improved.In the test,the relative standard deviation(RSD)between pixels decreased from about 34.3%to 6.2%and 5.49%after adjustment by the back propagation(BP)and Elman neural networks,respectively.The peak signal to noise ratio(PSNR)and structural similarity(SSIM)of the image are improved by about 2.5 times,which realizes the re-recognition of the distorted image.This provides a feasible approach for the application of 2D sensing array by integrating ANN to achieve high quality imaging.展开更多
The concept of difference and sum co-array(DSCA)has become a new design idea for planar sparse arrays.Inspired by the shifting invariance property of DSCA,a specific configuration named here as the improved L-shaped a...The concept of difference and sum co-array(DSCA)has become a new design idea for planar sparse arrays.Inspired by the shifting invariance property of DSCA,a specific configuration named here as the improved L-shaped array is proposed.Compared to other traditional 2D sparse array configurations such as 2D nested arrays and hourglass arrays,the proposed configuration has larger central consecutive ranges in its DSCA,thus increasing the DOF.At the same time,the mutual coupling effect is also reduced due to the enlarged spacing between the adjacent sensors.Simulations further demonstrate the superiority of the proposed arrays in terms of detection performance and estimation accuracy.展开更多
The double layered Radial Line Slot Antenna (RLSA) is a new type of antenna for Ku band Direct Broadcasting Satellite (DBS) reception. This paper presents the structure, aperture field distribution, gain and efficien...The double layered Radial Line Slot Antenna (RLSA) is a new type of antenna for Ku band Direct Broadcasting Satellite (DBS) reception. This paper presents the structure, aperture field distribution, gain and efficiency of the antenna, discusses parameters of slot pair structure and influences of aperture field distribution and suggests calculation of parameters of the slot pairs and the array structure and CAD design procedures.展开更多
The concept of difference and sum(diff-sum)coarray has attracted a lot of attentions in the estimation of direction-of-arrival(DOA)for the past few years,due to its high degrees-of-freedom(DOFs).A vectorized conjugate...The concept of difference and sum(diff-sum)coarray has attracted a lot of attentions in the estimation of direction-of-arrival(DOA)for the past few years,due to its high degrees-of-freedom(DOFs).A vectorized conjugate augmented MUSIC(VCA-MUSIC)algorithm is applied to generate an equivalent signal model which contains the virtual sensor positions of both the difference and sum of the physical sensors in the two-dimensional(2D)arrays,by utilizing both the spatial and temporal information.Besides,an augmented 2D coprime array configuration is presented with the basis on the concept of difference and sum coarray.By compressing the inter-element spacing of one subarray and introducing the proper separation between the two subarrays of 2D coprime array,the redundancy between the difference coarray and the sum one can be reduced so that more virtual sensors in both coarrays can make contributions to the DOFs.As a result,a much larger consecutive area in the diff-sum coarray can be achieved,which can significantly increase the DOFs.Numerical simulations verify the superiority of the proposed array configuration.展开更多
Naturally suited array geometry for 360° coverage is the uniform circular array (UCA). A comparison of two types of uniform circular array configurations is presented in this paper. Due to its symmetrical...Naturally suited array geometry for 360° coverage is the uniform circular array (UCA). A comparison of two types of uniform circular array configurations is presented in this paper. Due to its symmetrical geometry UCA is always targeted which results in minimal change inside lobe levels and beam width when scanned by a phased array antenna. Particle Swarm Optimization and Cuckoo algorithm are used for the calculation of complex weights of the array elements. Comparisons are drawn in the context of adaptive beam forming capabilities. Obtained results suggest that planar uniform circular array (9:10) using Cuckoo algorithm, has better beam forming properties with also reduced side lobe levels when compared to other geometry.展开更多
In this paper,we investigate the end-to-end performance of intelligent reflecting surface(IRS)-assisted wireless communication systems.We consider a system in which an IRS is deployed on a uniform planar array(UPA)con...In this paper,we investigate the end-to-end performance of intelligent reflecting surface(IRS)-assisted wireless communication systems.We consider a system in which an IRS is deployed on a uniform planar array(UPA)configuration,including a large number of reflecting elements,where the transmitters and receivers are only equipped with a single antenna.Our objective is to analytically obtain the achievable ergodic rate,outage probability,and bit error rate(BER)of the system.Furthermore,to maximize the system’s signal-to-noise ratio(SNR),we design the phase shift of each reflecting element and derive the optimal reflection phase of the IRS based on the channel state information(CSI).We also derive the exact expression of the SNR probability density function(p.d.f.)and show that it follows a non-central Chi-square distribution.Using the p.d.f.,we then derive the theoretical results of the achievable rate,outage probability,and BER.The accuracy of the obtained theoretical results is also verified through numerical simulation.Itwas shown that the achievable rate,outage probability,and BER could be improved by increasing the number of reflecting elements and choosing an appropriate SNR regime.Furthermore,we also find that the IRS-assisted communication system achieves better performance than the existing end-to-end wireless communication.展开更多
It is an important theme in nanoscience to control the interval of the ordered array of nanoparticles through modifying the chain length of the passivating molecules of the nanoparticles. The theme runs through most o...It is an important theme in nanoscience to control the interval of the ordered array of nanoparticles through modifying the chain length of the passivating molecules of the nanoparticles. The theme runs through most of the applications of the ordered array of nanoparticles. Though the Langmuir-Blodgett (LB) technique is one of the most important ways to prepare the two-dimensional ordered array of nanoparticles, it has only been used in case that the passivating molecules are short enough (【C12). When the passivating molecules become longer, it is difficult to obtain the ordered array of the particles simply by compressing them on the surface of water. The present work focused on the formation of the two-dimensional array of the octadecyl-amine-passivated gold nanoparticles at the air/water interface. By properly modifying the ordinary LB technique, the long-term two-dimensional ordered array of nanoparticles was successfully achieved. The surface pressure-area isotherms and the electron microscopy展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.92163204,61921002,and 62171098)。
文摘The Ga N high electron mobility transistor(HEMT)has been considered as a potential terahertz(THz)radiation source,yet the low radiation power level restricts their applications.The HEMT array is thought to improve the coupling efficiency between two-dimensional(2D)plasmons and THz radiation.In this work,we investigate the plasma oscillation,electromagnetic radiation,and the integration characteristics of Ga N HEMT targeting at a high THz radiation power source.The quantitative radiation power and directivity are obtained for integrated Ga N HEMT array with different array periods and element numbers.With the same initial plasma oscillation phase among the HEMT units,the radiation power of the two-element HEMT array can achieve 4 times as the single HEMT radiation power when the array period is shorter than 1/8electromagnetic wavelength.In addition,the radiation power of the HEMT array varies almost linearly with the element number,the smaller array period can lead to the greater radiation power.It shows that increasing the array period could narrow the main radiated lobe width while weaken the radiation power.Increasing the element number can improve both the radiation directivity and power.We also synchronize the plasma wave phases in the HEMT array by adopting an external Gaussian plane wave with central frequency the same as the plasmon resonant frequency,which solves the problem of the radiation power reduction caused by the asynchronous plasma oscillation phases among the elements.The study of the radiation power amplification of the one-dimensional(1D)Ga N HEMT array provides useful guidance for the research of compact high-power solid-state terahertz sources.
基金supported by the National Natural Science Foundation of China (No.61171460)
文摘Eddy-current (EC) testing is an effective electromagnetic non-destructive testing (NDT) technique.Planar eddy-current sensor arrays have several advantages such as good coherence,fast response speed,and high sensitivity,which can be used for micro-damage inspection of crucial parts in mechanical equipments and aerospace aviation.The main purpose of this research is to detect the defect in a metallic material surface and identify the length of a crack using planar eddy-current sensor arrays in different directions.The principle and characteristics of planar eddy-current sensor arrays are introduced,and a crack length quantification algorithm in different directions is investigated.A damage quantitative detection system is established based on a field programmable gate array and ARM processor.The system is utilized to inspect the micro defect in a metallic material,which is carved to micro crack with size of 7mm(length)×0.1mm(width)×1mm(depth).The experimental data show that the sensor arrays can be used for the length measurement repeatedly,and that the uncertainty of the length measurement is below ±0.2mm.
基金Project supported by the Shanghai Nanoscience Foundation,China (Grant Nos. 0852nm07000 and 0952nm07000)the National Natural Science Foundation of China (Grant Nos. 10804084 and 91123022)+1 种基金the National Key Technology R & D Program,China (Grant No. 2006BAF06B08)the Specialized Research Fund for the Doctoral Program of Ministry of High Education of China (Grant No. 200802471008)
文摘Direct-write atom lithography,one of the potential nanofabrication techniques,is restricted by some difficulties in producing optical masks for the deposition of complex structures.In order to make further progress,a structured mirror array is developed to transversely collimate the chromium atomic beam in two dimensions.The best collimation is obtained when the laser red detunes by natural line-width of transition 7S3 → 7P40 of the chromium atom.The collimation ratio is 0.45 vertically（in x axis）,and it is 0.55 horizontally（in y axis）.The theoretical model is also simulated,and success of our structured mirror array is achieved.
基金supported by the National Natural Science Foundation of China(Nos.61631020,61971218,61601167,61371169)。
文摘The problem of two-dimensional direction of arrival(2D-DOA)estimation for uniform planar arrays(UPAs)is investigated by employing the reduced-dimensional(RD)polynomial root finding technique and 2D multiple signal classification(2D-MUSIC)algorithm.Specifically,based on the relationship between the noise subspace and steering vectors,we first construct 2D root polynomial for 2D-DOA estimates and then prove that the 2D polynomial function has infinitely many solutions.In particular,we propose a computationally efficient algorithm,termed RD-ROOT-MUSIC algorithm,to obtain the true solutions corresponding to targets by RD technique,where the 2D root-finding problem is substituted by two one-dimensional(1D)root-finding operations.Finally,accurate 2DDOA estimates can be obtained by a sample pairing approach.In addition,numerical simulation results are given to corroborate the advantages of the proposed algorithm.
文摘An experimental investigation was performed to investigate two-dimensional axial velocity field at downstream of the 90°double bend pipe with and without inlet swirling condition. The main objectives are to find separation region and observe the influence of inlet swirling flow on the velocity fluctuation using ultrasound technique. The experiments were carried out in the pipe at Reynolds number Re = 1 × 104. In case of inlet swirling flow condition, a rotary swirler was used as swirling generator, and the swirl number was setup S = 1. The ultrasonic measurements were taken at four downstream locations of the second bend pipe. Phased Array Ultrasonic Velocity Profiler (Phased Array UVP) technique was applied to obtain the two-dimensional velocity of the fluid and the axial and tangential velocity fluctuation. It was found that the secondary reverse flow became smaller at the downstream from the bend when the inlet condition on the first bend was swirling flow. In addition, inlet swirling condition influenced mainly on the tangential velocity fluctuation, and its maximum turbulence intensity was 40%.
基金supported by National Natural Science Fundation of China(No.10905047)
文摘The resistance and inductance of a wire array during an implosion are very important parameters of interest to：researchers. A variety of inductances and resistances directly affect the kinetic energy and resistance heat energy coupled from a pulsed-power generator. In this paper, the inductance and resistance of a planar wire array during the Z-pinch process are analyzed. The inductance is calculated from the data obtained by a time-resolved soft X-ray framed camera, while the resistance is calculated through the voltage and the current of the wire array load combined with the variety of the inductance. The results show that the resistance of the load increases with the development of the implosion, and reaches its maximum at 0.29 ± 0.16Ω near the pinched time.
文摘Two dynamics modes, named short ablation mode and long ablation mode, are observed in implosion experiments of planar wire array Z pinch on ＇QiangGuang-I＇ facility utilizing an optical streak camera. The long ablation mode has a lagged trajectory compared with the short ablation mode. For shot 10035 in a short ablation mode, the initial time of K-shell radiation is consistent with the interaction time for ablation plasma arriving at the centre of wire array, while for shot 10038 in long ablation mode, the initial time of K-shell radiation is about 10 ns earlier. In the two modes, the partial ablation plasma could traverse the wire array plane and then collide in the centre to form a dense plasma column with a diameter of 2.2 mm for shot 10035 and 1.5 mm for shot 10038.
文摘In recent years, several attempts have been made in designing planar array antennas with high directivity. This paper is aimed at investigating the impact of element spacing on the directivity of planar array of monopole antenna. The directivity of antenna with reduced grating lobes can be obtained by carefully varying the inter-element spacing of array antenna. Based on this conception, this paper presents the investigation carried out on the relationship between inter-element spacing and the directivity of planar array of monopole antenna. It went further to highlight the effect on the total fields radiated by the antenna. The inter-element spacing is one of the most important antenna parameters that determine the directivity of the antenna. For a planar array of monopole, the directivity can be improved by varying the inter-element spacing. Four elements uniform planar array antenna and Hadamard matrix method was used to determine element positioning in the array matrix. The simulated results obtained using Matlab, showed that good directivity was obtained by using element spacing between 0.1λ - 0.5λ. Increasing the spacing beyond 0.6λ - 1.0λ also improved the directivity, but generated many grating lobes. As inter-element spacing increased, the grating lobes increased in size, number and levels. The study, therefore, inferred that the best directivity (radiation pattern) can only be obtained when the element spacing is within 0.1 - 0.5λ.
基金Supported by the National High Technology Research and Development Program(No.2012AA121901)
文摘A novel low-cost 4-element planar array antenna directly fed by a coaxial cable for Ultra-WideBand(UWB) application is presented. The proposed antenna consists of 2×2 bowtie elements and a simple 1:4 power divider feeding network. Compared to the basic bowtie element, the impedance bandwidth of the array antenna has a significant improvement that the low cut-off frequency is extended from 6 GHz of the bowtie element to 2 GHz. The measured results show that the proposed antenna has a large bandwidth of 2 GHz to 11 GHz for Voltage Standing Wave Ratio(VSWR)<2, and exhibits a bidirectional radiation pattern and a modest gain across the operating band and a peak gain of about 9 dBi at 11 GHz.
文摘Gaseous phases of carbon-containing and metastable oxides will be resulted from the carbonization of phenolic resin binders and the reduced reactions between C and oxides at high temperatures in carbon-containing refractories. With the in-situ catalysis technique, these gaseous phases can be transformed to one-or two-dimensional bonding phases by deposition,which is favorable for the improvement on strength and toughness of carboncontaining refractories,especially low carbon refractories. The research results reveal that：（ 1） the amorphous carbon resulted from phenolic resin can be transformed to carbon nanotubes,thus,the oxidation peak temperature is raised from 506 to 664. 6 ℃;（ 2） onedimensional whiskers of MgO or Mg Al2 O4 can be in-situ formed in MgO-C refractories, and their CMOR,CCS,rupture displacement and residual CCS（ two water quenching cycles,1 100 ℃） are increased by 66%,47%,13% and 26%,respectively;（ 3） two-dimensional array structure of flake β-SiAlON can be in-situ formed in Al2 O3-C refractories,which improves the material strength by 60% and decreases the residual strength after thermal shock by only 4. 5 MPa. It is believed that the in-situ formation of one-or two-dimensional bonding phases at high temperatures can improvethe comprehensive thermal physical properties of carboncontaining refractories,and will be the developing trend of the strengthening and toughening of low carbon-containing refractories.
基金This project was supported by the High Technology Research and Development Programme of China (2002AA111040).
文摘Sparse arrays of telescopes have a limited (u, v)-plane coverage. In this paper, an optimization method for designing planar arrays of an aperture synthesis telescope is proposed that is based on distributed genetic algorithm. This distributed genetic algorithm is implemented on a network of workstations using community communication model. Such an aperture synthesis system performs with imperfection of (u, v) components caused by deviations and(or) some missing baselines. With the maximum (u, v)-plane coverage of this rotation-optimized array, the image of the source reconstructed by inverse Fourier transform is satisfactory.
文摘This paper presents a dual-band planar antenna array for ISM band applications (2.4 GHz and 2.45 GHz). This antenna is proposed for indoor applications and enables adaptive beamforming and angle of arrival (AOA) estimation. An adaptive beamforming algorithm is applied for a planar antenna array, which is able to steer its main beam and nulls in azimuth and elevation planes over a wide frequency band. Planar antenna array operates as a spatial filter in 3D space, processing the received signals with weighting schemes. A planar antenna array is designed for AOA estimation in azimuth and elevation planes by using MUltiple SIgnal Classification (MUSIC) based on subspace algorithm. The Base Station (BS) equipped with this planar antenna is preferred to be at the center position on the room ceiling to cover all sectors of the room. It is designed to use four directional triangular elements arranged to form a square planar antenna array. Planar antenna with four elliptical slotted triangular elements (PAFESTE) is used to obtain optimal directivity in four directions in azimuth plane with specific orientation of 30? in elevation plane. It is characterized by half power beamwidth in elevation plane of about 60? and half power beamwidth in azimuth plane of about 90?.
基金supported by the National Natural Science Foundation of China(No.52075467).
文摘With the development of the aerospace industry,space missions are becoming more complicated and diversified,and there is a demand for antenna mechanisms with a larger physical aperture.In this paper,a planar deployable mechanism is proposed,which can form a flat reflection surface with a small gap between plates.To this end,a novel large-scale two-dimensional deployable nine-grid planar antenna mechanism is designed.First,two antenna folding schemes and four supporting mechanism schemes are proposed.Through comparison analysis,the antenna configuration scheme with the best comprehensive performance is selected.A kinematic model of the deployable mechanism is established,and its kinematic characteristics are analyzed.Then,the correctness of the kinematic model is verified by comparing the analytical and simulation results of the kinematic model.Subsequently,a finite element model of the antenna is developed.Based on the response surface method,the structural parameters of the support rods of the antenna are optimized,and a set of optimized solutions with lightweight and high fundamental frequency characteristics are obtained.Finally,a prototype of the proposed nine-grid planar antenna is fabricated.The feasibility of the deployment principle and the rationality of the designed mechanism are verified by deployment experiments.
基金This project was financially supported by the Dalian Science and Technology Innovation Fund of China(No.2019J11CY011)the Science Fund for Creative Research Groups of NSFC(No.51621064).
文摘As the basis of machine vision,the biomimetic image sensing devices are the eyes of artificial intelligence.In recent years,with the development of two-dimensional(2D)materials,many new optoelectronic devices are developed for their outstanding performance.However,there are still little sensing arrays based on 2D materials with high imaging quality,due to the poor uniformity of pixels caused by material defects and fabrication technique.Here,we propose a 2D MoS_(2)sensing array based on artificial neural network(ANN)learning.By equipping the MoS_(2)sensing array with a“brain”(ANN),the imaging quality can be effectively improved.In the test,the relative standard deviation(RSD)between pixels decreased from about 34.3%to 6.2%and 5.49%after adjustment by the back propagation(BP)and Elman neural networks,respectively.The peak signal to noise ratio(PSNR)and structural similarity(SSIM)of the image are improved by about 2.5 times,which realizes the re-recognition of the distorted image.This provides a feasible approach for the application of 2D sensing array by integrating ANN to achieve high quality imaging.
基金Supported by the National Natural Science Foundation of China(61801024)。
文摘The concept of difference and sum co-array(DSCA)has become a new design idea for planar sparse arrays.Inspired by the shifting invariance property of DSCA,a specific configuration named here as the improved L-shaped array is proposed.Compared to other traditional 2D sparse array configurations such as 2D nested arrays and hourglass arrays,the proposed configuration has larger central consecutive ranges in its DSCA,thus increasing the DOF.At the same time,the mutual coupling effect is also reduced due to the enlarged spacing between the adjacent sensors.Simulations further demonstrate the superiority of the proposed arrays in terms of detection performance and estimation accuracy.
文摘The double layered Radial Line Slot Antenna (RLSA) is a new type of antenna for Ku band Direct Broadcasting Satellite (DBS) reception. This paper presents the structure, aperture field distribution, gain and efficiency of the antenna, discusses parameters of slot pair structure and influences of aperture field distribution and suggests calculation of parameters of the slot pairs and the array structure and CAD design procedures.
基金Supported by the National Natural Science Foundation of China(61801024)。
文摘The concept of difference and sum(diff-sum)coarray has attracted a lot of attentions in the estimation of direction-of-arrival(DOA)for the past few years,due to its high degrees-of-freedom(DOFs).A vectorized conjugate augmented MUSIC(VCA-MUSIC)algorithm is applied to generate an equivalent signal model which contains the virtual sensor positions of both the difference and sum of the physical sensors in the two-dimensional(2D)arrays,by utilizing both the spatial and temporal information.Besides,an augmented 2D coprime array configuration is presented with the basis on the concept of difference and sum coarray.By compressing the inter-element spacing of one subarray and introducing the proper separation between the two subarrays of 2D coprime array,the redundancy between the difference coarray and the sum one can be reduced so that more virtual sensors in both coarrays can make contributions to the DOFs.As a result,a much larger consecutive area in the diff-sum coarray can be achieved,which can significantly increase the DOFs.Numerical simulations verify the superiority of the proposed array configuration.
文摘Naturally suited array geometry for 360° coverage is the uniform circular array (UCA). A comparison of two types of uniform circular array configurations is presented in this paper. Due to its symmetrical geometry UCA is always targeted which results in minimal change inside lobe levels and beam width when scanned by a phased array antenna. Particle Swarm Optimization and Cuckoo algorithm are used for the calculation of complex weights of the array elements. Comparisons are drawn in the context of adaptive beam forming capabilities. Obtained results suggest that planar uniform circular array (9:10) using Cuckoo algorithm, has better beam forming properties with also reduced side lobe levels when compared to other geometry.
基金supported in part by the Joint Research Fund for Guangzhou University and Hong Kong University of Science and Technology under Grant No.YH202203the Guangzhou Basic Research Program Municipal School(College)Joint Funding Project,the Research Project of Guizhou University for Talent Introduction under Grant No.[2020]61+7 种基金the Cultivation Project of Guizhou University under Grant No.[2019]56the Open Fund of Key Laboratory of Advanced Manufacturing Technology,Ministry of Education under Grant No.GZUAMT2021KF[01]the National Natural Science Foundation of China under Grant Nos.51978089 and 62171119the Key R&D Plan of Sichuan Science and Technology Department under Grant No.22ZDYF2726the Chengdu Normal University Scientific Research and Innovation Team under Grant Nos.CSCXTD2020B09,ZZBS201907,CS21ZC01the Open Project of Intelligent Manufacturing Industry Technology Research Institute under Grant No.ZNZZ2208the National Key Research and Development Program of China under Grant No.2020YFB1807201Key research and development plan of Jiangsu Province under Grant No.BE2021013-3.
文摘In this paper,we investigate the end-to-end performance of intelligent reflecting surface(IRS)-assisted wireless communication systems.We consider a system in which an IRS is deployed on a uniform planar array(UPA)configuration,including a large number of reflecting elements,where the transmitters and receivers are only equipped with a single antenna.Our objective is to analytically obtain the achievable ergodic rate,outage probability,and bit error rate(BER)of the system.Furthermore,to maximize the system’s signal-to-noise ratio(SNR),we design the phase shift of each reflecting element and derive the optimal reflection phase of the IRS based on the channel state information(CSI).We also derive the exact expression of the SNR probability density function(p.d.f.)and show that it follows a non-central Chi-square distribution.Using the p.d.f.,we then derive the theoretical results of the achievable rate,outage probability,and BER.The accuracy of the obtained theoretical results is also verified through numerical simulation.Itwas shown that the achievable rate,outage probability,and BER could be improved by increasing the number of reflecting elements and choosing an appropriate SNR regime.Furthermore,we also find that the IRS-assisted communication system achieves better performance than the existing end-to-end wireless communication.
文摘It is an important theme in nanoscience to control the interval of the ordered array of nanoparticles through modifying the chain length of the passivating molecules of the nanoparticles. The theme runs through most of the applications of the ordered array of nanoparticles. Though the Langmuir-Blodgett (LB) technique is one of the most important ways to prepare the two-dimensional ordered array of nanoparticles, it has only been used in case that the passivating molecules are short enough (【C12). When the passivating molecules become longer, it is difficult to obtain the ordered array of the particles simply by compressing them on the surface of water. The present work focused on the formation of the two-dimensional array of the octadecyl-amine-passivated gold nanoparticles at the air/water interface. By properly modifying the ordinary LB technique, the long-term two-dimensional ordered array of nanoparticles was successfully achieved. The surface pressure-area isotherms and the electron microscopy
