ISSN 
2009 Vol. 38, No. 5
2009, 38(5): 481-486.
doi: 10.3969/j.issn.1001-0548.2009.05.001
Abstract:
Scientists found that half of the cosmic background radiation from the Big Bang is in the THz part of the spectrum, This fact seems unbelievable but it is the nature. It shows how much science involved in the THz frequency regime. The unique characteristics and great technological potential in physics , chemistry, biomedical engineering, astronomy, materials science and environment engineering of THz are presented in this paper，and the recent development of THz S&T is introduced. The rapid progresses and the urgent need result in the combination and mergence of the related basic research, development and the industrial applications of the THz S&T.
Scientists found that half of the cosmic background radiation from the Big Bang is in the THz part of the spectrum, This fact seems unbelievable but it is the nature. It shows how much science involved in the THz frequency regime. The unique characteristics and great technological potential in physics , chemistry, biomedical engineering, astronomy, materials science and environment engineering of THz are presented in this paper，and the recent development of THz S&T is introduced. The rapid progresses and the urgent need result in the combination and mergence of the related basic research, development and the industrial applications of the THz S&T.
2009, 38(5): 487-494.
doi: 10.3969/j.issn.1001-0548.2009.05.002
Abstract:
Photonic crystal fibers (PCFs) have many unique advantages as a new generation of optical fibers when compared with conventional optical fibers. Hence, study on fiber-optic sensors based on PCFs has become one of the hot topics in the field of optical fiber sensing. In this paper, a series of fiber-optic Fabry-Perot interferometric (FFPI) sensors based on PCFs are reported for the first time to our knowledge, including FFPI strain and temperature sensors based on hollow core PCF; FFPI temperature and refractive index sensors based on solid core single-mode PCF; FFPI high temperature strain sensor based on solid core PCF fabricated by fs and 157nm lasers. These novel PCF-based FFPI sensors have many outstanding advantages, such as insensitive to temperature change, high accuracy, good reliability, capability to operate in harsh environments, etc. It is anticipated that they would find important applications in many areas, such as energy, transportation, aerospace, biochemical, etc.
Photonic crystal fibers (PCFs) have many unique advantages as a new generation of optical fibers when compared with conventional optical fibers. Hence, study on fiber-optic sensors based on PCFs has become one of the hot topics in the field of optical fiber sensing. In this paper, a series of fiber-optic Fabry-Perot interferometric (FFPI) sensors based on PCFs are reported for the first time to our knowledge, including FFPI strain and temperature sensors based on hollow core PCF; FFPI temperature and refractive index sensors based on solid core single-mode PCF; FFPI high temperature strain sensor based on solid core PCF fabricated by fs and 157nm lasers. These novel PCF-based FFPI sensors have many outstanding advantages, such as insensitive to temperature change, high accuracy, good reliability, capability to operate in harsh environments, etc. It is anticipated that they would find important applications in many areas, such as energy, transportation, aerospace, biochemical, etc.
2009, 38(5): 495-504.
doi: 10.3969/j.issn.1001-0548.2009.05.003
Abstract:
The history of electromigration (EM) modeling of IC interconnects is briefly reviewed. The widely used one-dimension (1-D) EM-induced back flow model is introduced. Based on the conception of atomic flux divergence (AFD), the EM modeling can also be mainly grouped into two approaches. One is the conventional diffusion path approach, which has explained many important phenomena in traditional Al on-chip metallization. However, the microelectronic industry has turned to Cu/low-k interconnects in need of better performances of the shrinking chip, and three-dimensional (3-D) integrated circuit technology is also introduced. In this trend, the driving force approach is developed, which can help to understand many phenomena in narrow interconnection. The finite element modeling (FEM) is used more and more in the driving force formalism.
The history of electromigration (EM) modeling of IC interconnects is briefly reviewed. The widely used one-dimension (1-D) EM-induced back flow model is introduced. Based on the conception of atomic flux divergence (AFD), the EM modeling can also be mainly grouped into two approaches. One is the conventional diffusion path approach, which has explained many important phenomena in traditional Al on-chip metallization. However, the microelectronic industry has turned to Cu/low-k interconnects in need of better performances of the shrinking chip, and three-dimensional (3-D) integrated circuit technology is also introduced. In this trend, the driving force approach is developed, which can help to understand many phenomena in narrow interconnection. The finite element modeling (FEM) is used more and more in the driving force formalism.
2009, 38(5): 505-523.
doi: 10.3969/j.issn.1001-0548.2009.05.004
Abstract:
The spintronics refers to the research area where electron spins, in additional to or sometimes in place of electron charges, are controlled and manipulated to give rise to an array of properties. Spintronic devices have already found applications in computer hard drive and magnetic random access memory, profoundly changed the information technology industry. These applications utilize the spin polarized transport where electron with fixed spin direction transverse through magnetic heterostructures. More recently, investigation of spin dynamics in spintronic device relates microwave with spin polarized transport, offering significant potential for novel microwave devices with dimension far less than the microwave wavelength. In this “review-like” article, we first briefly introduce the concept of spintronic devices. Microwave experiments with spintronic devices are discussed next in the context of microwave assisted switching and spin pumping phenomenon. The former has potential for developing high density computer hard disk, the latter, with the development of direct electronic detection, could lead to miniaturized and passive microwave detector.
The spintronics refers to the research area where electron spins, in additional to or sometimes in place of electron charges, are controlled and manipulated to give rise to an array of properties. Spintronic devices have already found applications in computer hard drive and magnetic random access memory, profoundly changed the information technology industry. These applications utilize the spin polarized transport where electron with fixed spin direction transverse through magnetic heterostructures. More recently, investigation of spin dynamics in spintronic device relates microwave with spin polarized transport, offering significant potential for novel microwave devices with dimension far less than the microwave wavelength. In this “review-like” article, we first briefly introduce the concept of spintronic devices. Microwave experiments with spintronic devices are discussed next in the context of microwave assisted switching and spin pumping phenomenon. The former has potential for developing high density computer hard disk, the latter, with the development of direct electronic detection, could lead to miniaturized and passive microwave detector.
2009, 38(5): 524-530.
doi: 10.3969/j.issn.1001-0548.2009.05.005
Abstract:
Polymer assisted deposition (PAD) is a new thin film deposition technique which has been developed recently. In this technique, aqueous solutions of metal precursors and water-soluble polymers are combined together. This results in homogenous and steady solutions by binding the metal ions to the polymers. After coating the solutions on the substrates, the precursor films will go through a heat treatment to pyrolyze the polymer and form solid films, In this paper, we show some representative oxide and nitride films grown by PAD, including simple oxide/nitride such as TiO32, GaN, AlN and complex oxide/nitride such as (Ba,Sr)TiO33 and Ti1?xAlxN. X-ray diffraction, transmission electron microscopy, dielectric measurement, and optics measurement are used to characterize structural and physical properties of the films. Effects of substrates and growth conditions on structural and physical properties are discussed. These results indicate that PAD can be used widely to prepare high quality oxide and nitride thin films.
Polymer assisted deposition (PAD) is a new thin film deposition technique which has been developed recently. In this technique, aqueous solutions of metal precursors and water-soluble polymers are combined together. This results in homogenous and steady solutions by binding the metal ions to the polymers. After coating the solutions on the substrates, the precursor films will go through a heat treatment to pyrolyze the polymer and form solid films, In this paper, we show some representative oxide and nitride films grown by PAD, including simple oxide/nitride such as TiO32, GaN, AlN and complex oxide/nitride such as (Ba,Sr)TiO33 and Ti1?xAlxN. X-ray diffraction, transmission electron microscopy, dielectric measurement, and optics measurement are used to characterize structural and physical properties of the films. Effects of substrates and growth conditions on structural and physical properties are discussed. These results indicate that PAD can be used widely to prepare high quality oxide and nitride thin films.
2009, 38(5): 531-536.
doi: 10.3969/j.issn.1001-0548.2009.05.006
Abstract:
Bounds relation between the dynamic magnetic parameters (e.g.the real and imaginary part of the microwave permeability, or the cutoff frequency) and the intrinsic magnetic parameters is a key issue for the high frequency magnetic structures. In the past decades, the bounds relation is developed with the fast development of high frequency magnetic structures, as the theoretical support of material design and the guidance of future development. This paper reviews the development and recent progress of both high frequency magnetic structure and bounds relation, focusing on their relationship and study methods. At last, suggestions about future study and existing problems are given.
Bounds relation between the dynamic magnetic parameters (e.g.the real and imaginary part of the microwave permeability, or the cutoff frequency) and the intrinsic magnetic parameters is a key issue for the high frequency magnetic structures. In the past decades, the bounds relation is developed with the fast development of high frequency magnetic structures, as the theoretical support of material design and the guidance of future development. This paper reviews the development and recent progress of both high frequency magnetic structure and bounds relation, focusing on their relationship and study methods. At last, suggestions about future study and existing problems are given.
2009, 38(5): 537-543.
doi: 10.3969/j.issn.1001-0548.2009.05.007
Abstract:
Community structure is a very important property of complex networks. Detecting communities in networks is of great importance in biology, computer science, sociology and so on. In recent years, a lot of community discovery algorithms have been proposed aiming at different kinds of large scale complex networks. In this paper, we review some latest representative algorithms, focusing on the improved methods based on the modularity function, the algorithms which can detect overlapping and hierarchical community structure in networks, and the benchmark in detecting communities. Finally, some future directions are pointed out.
Community structure is a very important property of complex networks. Detecting communities in networks is of great importance in biology, computer science, sociology and so on. In recent years, a lot of community discovery algorithms have been proposed aiming at different kinds of large scale complex networks. In this paper, we review some latest representative algorithms, focusing on the improved methods based on the modularity function, the algorithms which can detect overlapping and hierarchical community structure in networks, and the benchmark in detecting communities. Finally, some future directions are pointed out.
2009, 38(5): 550-554.
doi: 10.3969/j.issn.1001-0548.2009.05.009
Abstract:
Several key techniques of brain computer-interface based on motor imagery are introduced. For the feature extraction, emphasized are the common spatial patterns (CSP) and discriminative spatial patterns (DSP) filters; for the pattern recognition, stressed are the Bayesian linear discriminant analysis (BLDA) employed large probabilistic test samples to expand the training set, the transductive support vector machines (TSVM), the manifold-based Laplacian support vector machine (LapSvm), and the hierarchical Bayesian linear discriminant analysis. For on-line system realization, amplifier designing and the idle-state detection are described. Finally, the potential future directions are discussed.
Several key techniques of brain computer-interface based on motor imagery are introduced. For the feature extraction, emphasized are the common spatial patterns (CSP) and discriminative spatial patterns (DSP) filters; for the pattern recognition, stressed are the Bayesian linear discriminant analysis (BLDA) employed large probabilistic test samples to expand the training set, the transductive support vector machines (TSVM), the manifold-based Laplacian support vector machine (LapSvm), and the hierarchical Bayesian linear discriminant analysis. For on-line system realization, amplifier designing and the idle-state detection are described. Finally, the potential future directions are discussed.
2009, 38(5): 555-561.
doi: 10.3969/j.issn.1001-0548.2009.05.010
Abstract:
Fast correlation attack is the best method for analysing the stream cipher combination generators, its idea is transforming the decryption of the combination stream cipher to a decoding problem, and realizing its attack using decoding techniques in error-correcting codes. In past few years, there are important developments and applications in stream cipher fast correlation attack based on error correcting codes, so it has important scientific and applied values to summarizing the development of the fast correlation attack and propose and analyze the new problems. In this paper, we apply the stream cipher fast correlation attack model to error-correcting codes and propose firstly the new direction for joint design of stream cipher and error-correcting codes. The research results may resolve the reliable communication under the lower SNR. According to the principles of the fast correlation attack, four kind primary fast correlation attack algorithms and their performances are analysed. In the end, the general applicable rules has been drawed, and open problems and future works of fast correlation attack are proposed.
Fast correlation attack is the best method for analysing the stream cipher combination generators, its idea is transforming the decryption of the combination stream cipher to a decoding problem, and realizing its attack using decoding techniques in error-correcting codes. In past few years, there are important developments and applications in stream cipher fast correlation attack based on error correcting codes, so it has important scientific and applied values to summarizing the development of the fast correlation attack and propose and analyze the new problems. In this paper, we apply the stream cipher fast correlation attack model to error-correcting codes and propose firstly the new direction for joint design of stream cipher and error-correcting codes. The research results may resolve the reliable communication under the lower SNR. According to the principles of the fast correlation attack, four kind primary fast correlation attack algorithms and their performances are analysed. In the end, the general applicable rules has been drawed, and open problems and future works of fast correlation attack are proposed.
2009, 38(5): 562-567.
doi: 10.3969/j.issn.1001-0548.2009.05.011
Abstract:
The code with quasi-three-dimensional electromagnetic particle-in-cell plus Monte Carlo collision (PIC/MCC) method is proposed for the research of ionization process of argon electron cyclotron resonance (ECR) discharge. The electron energy distributions in different regions of ECR reactor are obtained when the steady state of ECR discharge attains, and the variations of these distributions with neutral pressure and external magnetic field are also discussed. As the neutral pressure increases, the low energy electrons decrease and the high energy ones increase at the region away from ECR layer, while the variations of electron energy distribution with neutral pressure are opposite at ECR layer. In the far downstream region, the electron energy confinements are better with the mirror-type magnetic configuration than with the convergence-type one. The simulation results and discussions are useful for the optimization of the ECR plasma applied in deposition, etching or other micro-electronic fabrications.
The code with quasi-three-dimensional electromagnetic particle-in-cell plus Monte Carlo collision (PIC/MCC) method is proposed for the research of ionization process of argon electron cyclotron resonance (ECR) discharge. The electron energy distributions in different regions of ECR reactor are obtained when the steady state of ECR discharge attains, and the variations of these distributions with neutral pressure and external magnetic field are also discussed. As the neutral pressure increases, the low energy electrons decrease and the high energy ones increase at the region away from ECR layer, while the variations of electron energy distribution with neutral pressure are opposite at ECR layer. In the far downstream region, the electron energy confinements are better with the mirror-type magnetic configuration than with the convergence-type one. The simulation results and discussions are useful for the optimization of the ECR plasma applied in deposition, etching or other micro-electronic fabrications.
2009, 38(5): 568-578.
doi: 10.3969/j.issn.1001-0548.2009.05.012
Abstract:
A brief review of the early work, current research areas, and future development of computational electromagnetics in the computational electromagnetics laboratory (CEMLAB) at University of Electronic Science and Technology of China (UESTC) is described. The time-domain and frequency-domain numerical methods are developed to improve simulation efficiency while maintaining the same accuracy for transmission, radiation and scattering problems. The neural network with knowledge-based neurons and generalized transmission line equation techniques are adopted for electromagnetic modeling as CAD tools with high performance. Efficient electromagnetic optimization methods, such as jumping genes genetic algorithm and space mapping technique, are also proposed to optimize antennas and microwave passive components.
A brief review of the early work, current research areas, and future development of computational electromagnetics in the computational electromagnetics laboratory (CEMLAB) at University of Electronic Science and Technology of China (UESTC) is described. The time-domain and frequency-domain numerical methods are developed to improve simulation efficiency while maintaining the same accuracy for transmission, radiation and scattering problems. The neural network with knowledge-based neurons and generalized transmission line equation techniques are adopted for electromagnetic modeling as CAD tools with high performance. Efficient electromagnetic optimization methods, such as jumping genes genetic algorithm and space mapping technique, are also proposed to optimize antennas and microwave passive components.
2009, 38(5): 579-586.
doi: 10.3969/j.issn.1001-0548.2009.05.013
Abstract:
With the improvement of high temperature superconducting (HTS) material technology, HTS linear motors (LM) which are built using HTS bulks and HTS tapes have been realized. In this paper, different types of the developed HTS LMs are summarized with their structure models. The electromagnetic characteristics of these HTS LMs are studied with the results obtained by using magnetic field finite element method. Superiorities of the HTS LM technology are also verified with its applications in transportation field such as maglev and electromagnetic aircraft launcher.
With the improvement of high temperature superconducting (HTS) material technology, HTS linear motors (LM) which are built using HTS bulks and HTS tapes have been realized. In this paper, different types of the developed HTS LMs are summarized with their structure models. The electromagnetic characteristics of these HTS LMs are studied with the results obtained by using magnetic field finite element method. Superiorities of the HTS LM technology are also verified with its applications in transportation field such as maglev and electromagnetic aircraft launcher.
2009, 38(5): 587-596.
doi: 10.3969/j.issn.1001-0548.2009.05.014
Abstract:
Intrusion detection is an extremely important aspect of network security. The Anomaly intrusion detection research is one of highlighted topics of intrusion detection. The relationship between intrusion detection and network security model is reviewed. The concept of intrusion detection and the abstract model of intrusion detection system are introduced. Three developing technologies including network data based anomaly detection, system call based anomaly detection, and system call arguments based anomaly detection are discussed in detail. Most important research methods of those three technologies are summarized. Finally, the future development of this research domain is presented.
Intrusion detection is an extremely important aspect of network security. The Anomaly intrusion detection research is one of highlighted topics of intrusion detection. The relationship between intrusion detection and network security model is reviewed. The concept of intrusion detection and the abstract model of intrusion detection system are introduced. Three developing technologies including network data based anomaly detection, system call based anomaly detection, and system call arguments based anomaly detection are discussed in detail. Most important research methods of those three technologies are summarized. Finally, the future development of this research domain is presented.
2009, 38(5): 597-602.
doi: 10.3969/j.issn.1001-0548.2009.05.015
Abstract:
The preconcentrator is a front-end sampling and concentrating device that can significantly improves the detection limit of a microanalytical system. The micromachined preconcentrators with reduced thermal mass can raise the temperature much faster at lower power compared with the conventional desorption tubes, thus realizing a much higher concentration factor. In this paper, the state-of-the-art of the microfabricated preconcentrators are systematically summarized, with especial emphasise on the structure of the micro-preconcentrators from the point of view of adsorption area, gas flux, temperature rising, fluid channel design, and so on. The principles of phased heater array and preconcentrator with integrated micro-valves are also introduced.
The preconcentrator is a front-end sampling and concentrating device that can significantly improves the detection limit of a microanalytical system. The micromachined preconcentrators with reduced thermal mass can raise the temperature much faster at lower power compared with the conventional desorption tubes, thus realizing a much higher concentration factor. In this paper, the state-of-the-art of the microfabricated preconcentrators are systematically summarized, with especial emphasise on the structure of the micro-preconcentrators from the point of view of adsorption area, gas flux, temperature rising, fluid channel design, and so on. The principles of phased heater array and preconcentrator with integrated micro-valves are also introduced.
2009, 38(5): 603-608.
doi: 10.3969/j.issn.1001-0548.2009.05.016
Abstract:
The high strength, high modulus, high thermal stable properties, and special functionalized methods of bisphthalonitrile polymers are discussed. The functional design on chemical reaction of polymer systhesis is mainly studied through some special bisphthalonitrile monomer. The thermosetting resin which is easy to process and convenient to cure could be supplied as the high performance matrix resin. The ferrocene group was bonded to bisphthalonitrile resin by molecure structure design methods. The cured polymer exhibits good electrochemistry properties. The polymer magnetic materials with courier temperature beyond 300oC was obtained. The magnetic functional composites containing organic-inorganic hybrid materials were obtained according to the reactivity between bisphthalonitrile and metal or metal salt. The nano functional composite materials were prepared by the surface nitrilized of carbon nanotubes. The hyperbranch Cu-phthalocyanine with high permittivity and PEN dielectric film with high strength were realized by the chemical control systhesis. The electric, magnetic, and shear stress field influences of polymer microstructure are studied. These functionalized research efforts broad the research, development and application region of the bisphthalonitrile polymer.
The high strength, high modulus, high thermal stable properties, and special functionalized methods of bisphthalonitrile polymers are discussed. The functional design on chemical reaction of polymer systhesis is mainly studied through some special bisphthalonitrile monomer. The thermosetting resin which is easy to process and convenient to cure could be supplied as the high performance matrix resin. The ferrocene group was bonded to bisphthalonitrile resin by molecure structure design methods. The cured polymer exhibits good electrochemistry properties. The polymer magnetic materials with courier temperature beyond 300oC was obtained. The magnetic functional composites containing organic-inorganic hybrid materials were obtained according to the reactivity between bisphthalonitrile and metal or metal salt. The nano functional composite materials were prepared by the surface nitrilized of carbon nanotubes. The hyperbranch Cu-phthalocyanine with high permittivity and PEN dielectric film with high strength were realized by the chemical control systhesis. The electric, magnetic, and shear stress field influences of polymer microstructure are studied. These functionalized research efforts broad the research, development and application region of the bisphthalonitrile polymer.
2009, 38(5): 609-617.
doi: 10.3969/j.issn.1001-0548.2009.05.017
Abstract:
Voltage-controlled devices based on tunable dielectric thin film materials are attractive for microwave applications for their excellent high frequency performance, power handling capability, and fast tuning speed. Dielectric voltage-controlled microwave devices offer advantages over semiconductor varactor diodes, ferrite, and MEMS devices with potential integration with microelectronic circuits, small power consumption, low cost, and high reliability. In this paper, based on the recent work of the authors, the recent development of tunable dielectric thin film materials and voltage-controlled microwave devices is introduced. Besides the intensively investigated BaxSr1-xTiO3 (BST) thin films, the alternative tunable Bi1.5MgNb1.5O7 (BMN) thin films with cubic pyrochlore structure are introduced due to relatively high tunability, low loss dielectric loss (~0.002), moderate permittivity (~86), and small temperature coefficient. BMN thin films may be one of potential tunable materials for microwave applications.
Voltage-controlled devices based on tunable dielectric thin film materials are attractive for microwave applications for their excellent high frequency performance, power handling capability, and fast tuning speed. Dielectric voltage-controlled microwave devices offer advantages over semiconductor varactor diodes, ferrite, and MEMS devices with potential integration with microelectronic circuits, small power consumption, low cost, and high reliability. In this paper, based on the recent work of the authors, the recent development of tunable dielectric thin film materials and voltage-controlled microwave devices is introduced. Besides the intensively investigated BaxSr1-xTiO3 (BST) thin films, the alternative tunable Bi1.5MgNb1.5O7 (BMN) thin films with cubic pyrochlore structure are introduced due to relatively high tunability, low loss dielectric loss (~0.002), moderate permittivity (~86), and small temperature coefficient. BMN thin films may be one of potential tunable materials for microwave applications.
2009, 38(5): 618-623.
doi: 10.3969/j.issn.1001-0548.2009.05.018
Abstract:
Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), are considered to be excellent candidates for high power, high frequency and high temperature applications in the commercial and military power distribution and conversion systems. The advantages of wide bandgap materials over the conventional Si and GaAs include wide bandgap, high saturation electron velocity, and high critical electric field. In this paper, the recent progress in the development of high-voltage SiC and GaN power switching devices is reviewed. The experimental performance of various rectifiers and transistors, which have been demonstrated, is discussed. Market and technical challenges on SiC and GaN power devices are also described. The future trends in device development and commercialization are pointed out.
Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), are considered to be excellent candidates for high power, high frequency and high temperature applications in the commercial and military power distribution and conversion systems. The advantages of wide bandgap materials over the conventional Si and GaAs include wide bandgap, high saturation electron velocity, and high critical electric field. In this paper, the recent progress in the development of high-voltage SiC and GaN power switching devices is reviewed. The experimental performance of various rectifiers and transistors, which have been demonstrated, is discussed. Market and technical challenges on SiC and GaN power devices are also described. The future trends in device development and commercialization are pointed out.
2009, 38(5): 624-628.
doi: 10.3969/j.issn.1001-0548.2009.05.019
Abstract:
Ultrasound and microbubbles have been widely used for diagnostic imaging in clinical fields without producing significant adverse effects for many decades. To further improve the image contrast, development of targeted microbubbles is becoming the hot subject of ultrasound medicine in recent years. The goal of this brief review is to illustrate selected examples of targeted microbubbles that have been applied to the arenas of atherosclerosis, thrombosis, and vascular biology. The adhesion interactions of targeted microbubbles-endothelial cells under shear flow are also reviewed. The overall characterization of targeted microbubbles in vitro will be helpful for the clinic applications in the future.
Ultrasound and microbubbles have been widely used for diagnostic imaging in clinical fields without producing significant adverse effects for many decades. To further improve the image contrast, development of targeted microbubbles is becoming the hot subject of ultrasound medicine in recent years. The goal of this brief review is to illustrate selected examples of targeted microbubbles that have been applied to the arenas of atherosclerosis, thrombosis, and vascular biology. The adhesion interactions of targeted microbubbles-endothelial cells under shear flow are also reviewed. The overall characterization of targeted microbubbles in vitro will be helpful for the clinic applications in the future.
2009, 38(5): 629-633.
doi: 10.3969/j.issn.1001-0548.2009.05.020
Abstract:
A technique for designing the transceiver front-part system module for Ka-band full coherent radar is proposed. By good frequency programming, circuits designing and the perfect use of DDS, phase locked loop(PLL) and FPGA devices, the better performances of spectrum purity (phase noise and spur lever) and converting time are obtained, and a high-performance transceiver front-part module is developed. The measurement results show that in S/C band, when the minimum frequency step is 15M Hz and the bandwidth is 480 MHz, the measured transmitter spur is less than ?65 dBc, the corresponding receiver spur is less than ?70 dBc, the measured phase noise is less than ?94 dBC/Hz@1 kHz, and the maximum frequency switching time is less than 15 μs.
A technique for designing the transceiver front-part system module for Ka-band full coherent radar is proposed. By good frequency programming, circuits designing and the perfect use of DDS, phase locked loop(PLL) and FPGA devices, the better performances of spectrum purity (phase noise and spur lever) and converting time are obtained, and a high-performance transceiver front-part module is developed. The measurement results show that in S/C band, when the minimum frequency step is 15M Hz and the bandwidth is 480 MHz, the measured transmitter spur is less than ?65 dBc, the corresponding receiver spur is less than ?70 dBc, the measured phase noise is less than ?94 dBC/Hz@1 kHz, and the maximum frequency switching time is less than 15 μs.
2009, 38(5): 634-638.
doi: 10.3969/j.issn.1001-0548.2009.05.021
Abstract:
Magneto-optic fiber gratings are a class of special fiber gratings with magneto-optical effects, which are useful for intrinsic magnetic field sensing and realizing magnetic controlled photonic information processing. The magnetic field sensitivity of polarization-dependent loss for left-/right-handed circularly polarized light in sectional magneto-optic fiber Bragg gratings (MFBGs) is analyzed by using the piecewise-uniform grating model and it is shown that the central section of uniform MFBGs is most sensitive to magnetic field. The F-P structure of sectional MFBGs is presented, which is superior to the corresponding uniform MFBGs for measuring the polarization-dependent loss in the range of small magnetic field.
Magneto-optic fiber gratings are a class of special fiber gratings with magneto-optical effects, which are useful for intrinsic magnetic field sensing and realizing magnetic controlled photonic information processing. The magnetic field sensitivity of polarization-dependent loss for left-/right-handed circularly polarized light in sectional magneto-optic fiber Bragg gratings (MFBGs) is analyzed by using the piecewise-uniform grating model and it is shown that the central section of uniform MFBGs is most sensitive to magnetic field. The F-P structure of sectional MFBGs is presented, which is superior to the corresponding uniform MFBGs for measuring the polarization-dependent loss in the range of small magnetic field.
2009, 38(5): 639-643.
doi: 10.3969/j.issn.1001-0548.2009.05.022
Abstract:
In order to enhance channel estimation performance of NC-OFDM systems in the case of lacking enough pilot symbols, a novel channel estimation scheme with modified noise reduction in transform domain is proposed. Channel multipath fading coefficients are estimated by inverse discrete Fourier transform (IDFT) in time domain based on the relationship between time and frequency domain expressions of the channel fading coefficients of NC-OFDM systems. Noise reduction filtering is performed in time domain. Finaly, the channel fading coefficients are obtained in frequency domain by discrete Fourier transform (DFT) without interpolation. Simulation results show the proposed channel estimation scheme outperforms the conventional LS estimation with a gain of about 4dB.
In order to enhance channel estimation performance of NC-OFDM systems in the case of lacking enough pilot symbols, a novel channel estimation scheme with modified noise reduction in transform domain is proposed. Channel multipath fading coefficients are estimated by inverse discrete Fourier transform (IDFT) in time domain based on the relationship between time and frequency domain expressions of the channel fading coefficients of NC-OFDM systems. Noise reduction filtering is performed in time domain. Finaly, the channel fading coefficients are obtained in frequency domain by discrete Fourier transform (DFT) without interpolation. Simulation results show the proposed channel estimation scheme outperforms the conventional LS estimation with a gain of about 4dB.
2009, 38(5): 644-650.
doi: 10.3969/j.issn.1001-0548.2009.05.023
Abstract:
The competitive and shared wireless channel is vulnerable by random backoff attacks from malicious nodes (or selfish nodes). As a consequence, the channel resource can be occupied unfairly, or the private benefit can be enhanced selfishly. This paper proposes a novel central limit theorem (CLT) based algorithm to detect medium access control (MAC) misbehaviors of malicious nodes. This algorifhm is able to decrease the computational complexity, adjust the efficiency and the accuracy of detection on-demand, and implement the collaborated detection in a distributed manner. In order to improve the detection correctness of malicious nodes, the CLT based algorithm can be further enhanced by the Markov chain detection model. Compared with the traditional detection methods, the CLT based algorithm has the characteristics with lower misdiagnose probability and more detection efficiency. Simulation experiments show that the CLT based algorithm is superior to the DOMINO algorithm for diagnosing backoff attacks misbehaviors, in terms of detection correctness and convergence speed.
The competitive and shared wireless channel is vulnerable by random backoff attacks from malicious nodes (or selfish nodes). As a consequence, the channel resource can be occupied unfairly, or the private benefit can be enhanced selfishly. This paper proposes a novel central limit theorem (CLT) based algorithm to detect medium access control (MAC) misbehaviors of malicious nodes. This algorifhm is able to decrease the computational complexity, adjust the efficiency and the accuracy of detection on-demand, and implement the collaborated detection in a distributed manner. In order to improve the detection correctness of malicious nodes, the CLT based algorithm can be further enhanced by the Markov chain detection model. Compared with the traditional detection methods, the CLT based algorithm has the characteristics with lower misdiagnose probability and more detection efficiency. Simulation experiments show that the CLT based algorithm is superior to the DOMINO algorithm for diagnosing backoff attacks misbehaviors, in terms of detection correctness and convergence speed.
2009, 38(5): 651-655.
doi: 10.3969/j.issn.1001-0548.2009.05.024
Abstract:
Simulation of polarization synthetic aperture radar (SAR) imaging of sea wave has great significance on sea surface scattering. According to the theory of random ocean wave, rough ocean surface is modeled in this paper. Random rough ocean surface which contains swell is constructed using the two-scale-model. This treatment takes both the large scale and small scale surface into account. By using the Bragg scattering model and the geometry optical approximation method, polarization SAR images of the modeled ocean surface at different wind speeds are simulated. The effects of the parameters of ocean waves and the parameters of SAR system are analyzed. Finally, some useful conclusions are drawn, which are helpful for extracting the information of ocean surface.
Simulation of polarization synthetic aperture radar (SAR) imaging of sea wave has great significance on sea surface scattering. According to the theory of random ocean wave, rough ocean surface is modeled in this paper. Random rough ocean surface which contains swell is constructed using the two-scale-model. This treatment takes both the large scale and small scale surface into account. By using the Bragg scattering model and the geometry optical approximation method, polarization SAR images of the modeled ocean surface at different wind speeds are simulated. The effects of the parameters of ocean waves and the parameters of SAR system are analyzed. Finally, some useful conclusions are drawn, which are helpful for extracting the information of ocean surface.
2009, 38(5): 656-668.
doi: 10.3969/j.issn.1001-0548.2009.05.025
Abstract:
The forthcoming semantic Web evolving from the current World Wide Web is designed to define the semantics of information and services on the web, thereby endowing the web with intelligence to automatically reason about the web contents. Description logics (DLs) play a substantial role in the semantic Web, since they underlie the W3C-recommended Web ontology language (OWL), which is derived from ontology research in artificial intelligence (AI) in order to achieve the goal of the semantic Web. However, the knowledge and data in the Semantic Web are large-scale, dispersive, multi-authored, and therefore usually inconsistent. It is reasonable and imperative to develop practical reasoning techniques for inconsistent ontologies. This paper proposes a new type of paraconsistent description logics based on Hunter's quasi-classical logic (QCL), which are termed as quasi-classical description logics (QCDLs). QCDLs avoid logical explosion. A semantic tableau calculus is constructed in QCDLs for the reasoning on the knowledge bases with acyclic TBox. Furthermore, a sound, complete and decidable consequence relation based on the calculus is defined. These enable a complete framework for paraconsistent reasoning in the Semantic Web. A comparison with other key paraconsistent description logics is also given. It is shown that QCDLs possess more expressive semantics and stronger reasoning capability, and that its connectives behave classically at the object level.
The forthcoming semantic Web evolving from the current World Wide Web is designed to define the semantics of information and services on the web, thereby endowing the web with intelligence to automatically reason about the web contents. Description logics (DLs) play a substantial role in the semantic Web, since they underlie the W3C-recommended Web ontology language (OWL), which is derived from ontology research in artificial intelligence (AI) in order to achieve the goal of the semantic Web. However, the knowledge and data in the Semantic Web are large-scale, dispersive, multi-authored, and therefore usually inconsistent. It is reasonable and imperative to develop practical reasoning techniques for inconsistent ontologies. This paper proposes a new type of paraconsistent description logics based on Hunter's quasi-classical logic (QCL), which are termed as quasi-classical description logics (QCDLs). QCDLs avoid logical explosion. A semantic tableau calculus is constructed in QCDLs for the reasoning on the knowledge bases with acyclic TBox. Furthermore, a sound, complete and decidable consequence relation based on the calculus is defined. These enable a complete framework for paraconsistent reasoning in the Semantic Web. A comparison with other key paraconsistent description logics is also given. It is shown that QCDLs possess more expressive semantics and stronger reasoning capability, and that its connectives behave classically at the object level.
2009, 38(5): 669-677.
doi: 10.3969/j.issn.1001-0548.2009.05.026
Abstract:
Model checking is a promising approach to verifying safety properties of trusted computing systems in the design phase of system-level. Dynamic model checking is the model checking in which the model changes frequently along the design process. A serious problem for dynamic model checking is that the cost of re-checking is too expensive due to model being changed trivially, so a key issue of the problem is to seek invariance in order to avoid the checking repeatedly. An invariance is a true predicate that will remain true throughout a sequence of model checking. In this paper, a formal framework of dynamic model checking is constructed, and an invariance theory is proposed based on an iterative design process of flow control oriented systems described by Moore machines. It is proved that some non-trivial computation tree logic (CTL) properties can be preserved in the iteration.
Model checking is a promising approach to verifying safety properties of trusted computing systems in the design phase of system-level. Dynamic model checking is the model checking in which the model changes frequently along the design process. A serious problem for dynamic model checking is that the cost of re-checking is too expensive due to model being changed trivially, so a key issue of the problem is to seek invariance in order to avoid the checking repeatedly. An invariance is a true predicate that will remain true throughout a sequence of model checking. In this paper, a formal framework of dynamic model checking is constructed, and an invariance theory is proposed based on an iterative design process of flow control oriented systems described by Moore machines. It is proved that some non-trivial computation tree logic (CTL) properties can be preserved in the iteration.
2009, 38(5): 678-686.
doi: 10.3969/j.issn.1001-0548.2009.05.027
Abstract:
The application of wearable computing in industry domain is a hot research topic. A brief review is first given to the research status of wearable computing in some typical industry application domains. Then, the paper discusses and analyzes some key problems which have an direct impact on the popularization and application of wearable computing, including wearability and usability, wearable human-computer interaction, software architecture and support pattern. At last, a novel workshop information environment pattern -“Aware Workshop” and wearable on-site task assistant system, which aim at the application of wearable computing in industry domain, are presented.
The application of wearable computing in industry domain is a hot research topic. A brief review is first given to the research status of wearable computing in some typical industry application domains. Then, the paper discusses and analyzes some key problems which have an direct impact on the popularization and application of wearable computing, including wearability and usability, wearable human-computer interaction, software architecture and support pattern. At last, a novel workshop information environment pattern -“Aware Workshop” and wearable on-site task assistant system, which aim at the application of wearable computing in industry domain, are presented.
2009, 38(5): 687-692.
doi: 10.3969/j.issn.1001-0548.2009.05.028
Abstract:
Neural networks have the capability of approaching nonlinear function with any accuracy. Time-serial prediction model can perfectly show the nonlinear tendency of information. In this paper, the genetic algorithm (GA) with global search capability is adopted to improve traditional back propagation (BP) neural networks, based on analyzing defect of BP neural networks. At the same time, the theory of optimizing initial weights and threshold of neural networks by means of GA method is discussed in detail. In the course of explaining prediction method, two examples are taken to analyze GA-BP neural networks prediction performance and characteristics. The result of prediction shows that the prediction accuracy and adaptability of GA-BP neural networks was better than that of traditional BP neural networks.
Neural networks have the capability of approaching nonlinear function with any accuracy. Time-serial prediction model can perfectly show the nonlinear tendency of information. In this paper, the genetic algorithm (GA) with global search capability is adopted to improve traditional back propagation (BP) neural networks, based on analyzing defect of BP neural networks. At the same time, the theory of optimizing initial weights and threshold of neural networks by means of GA method is discussed in detail. In the course of explaining prediction method, two examples are taken to analyze GA-BP neural networks prediction performance and characteristics. The result of prediction shows that the prediction accuracy and adaptability of GA-BP neural networks was better than that of traditional BP neural networks.
2009, 38(5): 693-695.
doi: 10.3969/j.issn.1001-0548.2009.05.029
Abstract:
The importance of the loaded Q are analyzed on the basis of phase noise equation of Leeson model in feedback oscillator, the formula of loaded Q is derived by the analysis of Pierce oscillator circuit, and we can draw a conclusion that the larger C1 is, the higher loaded Q becomes. Based on this conclusion, a design of the prototype 120 MHz AT-cut crystal oscillator is presented and the experiments are carried out. The measurement results of phase noise are ?130 dBc/Hz@100 Hz, ?142 dBc/Hz@220 Hz, ?155 dBc/Hz@1 kHz and the phase noise floor better than ?175 dBc/Hz. Experimental results show that it is feasible to design low phase noise crystal oscillators based on improving the loaded Q.
The importance of the loaded Q are analyzed on the basis of phase noise equation of Leeson model in feedback oscillator, the formula of loaded Q is derived by the analysis of Pierce oscillator circuit, and we can draw a conclusion that the larger C1 is, the higher loaded Q becomes. Based on this conclusion, a design of the prototype 120 MHz AT-cut crystal oscillator is presented and the experiments are carried out. The measurement results of phase noise are ?130 dBc/Hz@100 Hz, ?142 dBc/Hz@220 Hz, ?155 dBc/Hz@1 kHz and the phase noise floor better than ?175 dBc/Hz. Experimental results show that it is feasible to design low phase noise crystal oscillators based on improving the loaded Q.
2009, 38(5): 696-699.
doi: 10.3969/j.issn.1001-0548.2009.05.030
Abstract:
The fault self-diagnosis and fault monitoring can improve the maintainability and reliability of wireless sensor network (WSN) and prolong the lifetime of WSN. In this paper, a novel method of fault self-diagnosis for the nodes of WSN is brought forward. The attribute reduction for decision-making of fault diagnosis is obtained based on mutual information algorithm for reduction of knowledge in rough set theory. A set of node's fault self-diagnosis techniques based on attribute matching in WSN are built. Finally, the faults for each module of nodes in WSN are diagnosed and located in detail. The simulation shows that this method only needs a little expenditure of communication, very low energy of nodes in WSN and low misdiagnosis rate when fault self-diagnosis is implemented in WSN.
The fault self-diagnosis and fault monitoring can improve the maintainability and reliability of wireless sensor network (WSN) and prolong the lifetime of WSN. In this paper, a novel method of fault self-diagnosis for the nodes of WSN is brought forward. The attribute reduction for decision-making of fault diagnosis is obtained based on mutual information algorithm for reduction of knowledge in rough set theory. A set of node's fault self-diagnosis techniques based on attribute matching in WSN are built. Finally, the faults for each module of nodes in WSN are diagnosed and located in detail. The simulation shows that this method only needs a little expenditure of communication, very low energy of nodes in WSN and low misdiagnosis rate when fault self-diagnosis is implemented in WSN.
2009, 38(5): 700-706.
doi: 10.3969/j.issn.1001-0548.2009.05.031
Abstract:
Evaluating ecological security is very important to the construction of the ecological security. The technologies of remote sensing (RS), geographical information system (GIS), and analytical hierarchy process (AHP) are used to evaluate Sichuan ecological security. The appraisal index system suitable for Sichuan is created at first, which is composed of three layers such as object, rule, and index. The 14 indexes indicate respectively the status of nature, human culture, society and environmental pollution. The indexes are obtained and calculated by using RS and GIS. The weights of the indexes are determined by using AHP. The relative models are created for evaluating the ecological security. Finally, the indexes of the natural ecological environment, human culture society pressure security, environmental pollution pressure security, and regional ecological security are calculated and graded by using the relative models and GIS. It is shown that: the regional ecological security can be effectively evaluated by using RS, GIS and AHP.
Evaluating ecological security is very important to the construction of the ecological security. The technologies of remote sensing (RS), geographical information system (GIS), and analytical hierarchy process (AHP) are used to evaluate Sichuan ecological security. The appraisal index system suitable for Sichuan is created at first, which is composed of three layers such as object, rule, and index. The 14 indexes indicate respectively the status of nature, human culture, society and environmental pollution. The indexes are obtained and calculated by using RS and GIS. The weights of the indexes are determined by using AHP. The relative models are created for evaluating the ecological security. Finally, the indexes of the natural ecological environment, human culture society pressure security, environmental pollution pressure security, and regional ecological security are calculated and graded by using the relative models and GIS. It is shown that: the regional ecological security can be effectively evaluated by using RS, GIS and AHP.
2009, 38(5): 707-711.
doi: 10.3969/j.issn.1001-0548.2009.05.032
Abstract:
The introduction of inversion of soil moisture content, Simulating backscattering coefficients of winter wheat based on Water Cloud and IEM model and methods to measuring backscattering coefficients of winter wheat is proposed. In order to test the inversion result and the measure result, the backscattering coefficients of winter wheat were measured by FM-CW Ground-based Scattermeter at L-band, S-band, C-band, and X-band, the LAI、biomass、soil moisture contents and so on relevant coefficients were gathered, the date on condition that the different time and different wave band and different polarized were compared, the different factors, such as incidence angle, polarization and wave length, that affect backscattering coefficients are discussed. The inversion of soil moisture content is indential the experiment results.
The introduction of inversion of soil moisture content, Simulating backscattering coefficients of winter wheat based on Water Cloud and IEM model and methods to measuring backscattering coefficients of winter wheat is proposed. In order to test the inversion result and the measure result, the backscattering coefficients of winter wheat were measured by FM-CW Ground-based Scattermeter at L-band, S-band, C-band, and X-band, the LAI、biomass、soil moisture contents and so on relevant coefficients were gathered, the date on condition that the different time and different wave band and different polarized were compared, the different factors, such as incidence angle, polarization and wave length, that affect backscattering coefficients are discussed. The inversion of soil moisture content is indential the experiment results.
2009, 38(5): 712-715.
doi: 10.3969/j.issn.1001-0548.2009.05.033
Abstract:
Compared with ordinary digital signature, the designated verifier signature scheme makes it possible for a signer to convince a designated verifier that she has signed a message in such a way that the designated verifier cannot transfer the signature to a third party. In designated verifier signature scheme, no third party can even verify the validity of a designated verifier signature since it must use the designated verifier's secret key in verification. Recently, an ID-based strong designated verifier scheme, ID-based designated verifier proxy signature scheme, and partial cryptanalysis ware proposed. In this paper, we show that the designated verifier signature scheme is delegatable, and the designated verifier proxy signature is forgeable since construction of the proxy scheme is unreasonable.
Compared with ordinary digital signature, the designated verifier signature scheme makes it possible for a signer to convince a designated verifier that she has signed a message in such a way that the designated verifier cannot transfer the signature to a third party. In designated verifier signature scheme, no third party can even verify the validity of a designated verifier signature since it must use the designated verifier's secret key in verification. Recently, an ID-based strong designated verifier scheme, ID-based designated verifier proxy signature scheme, and partial cryptanalysis ware proposed. In this paper, we show that the designated verifier signature scheme is delegatable, and the designated verifier proxy signature is forgeable since construction of the proxy scheme is unreasonable.
2009, 38(5): 716-720.
doi: 10.3969/j.issn.1001-0548.2009.05.034
Abstract:
Traditional field programmable gate array (FPGA) test schemes confront many problems, such as memory depth not large enough to meet requirement of configuration of many times, I/O pin counts usually less than needed, manual configuration generation and download, no position of fault sites, etc. A new approach to test FPGA based on SoC HW/SW co-verification technology is proposed and verified in the paper. This test scheme has taken advantage of flexibility and observability of software in conjunction with high-speed simulation of hardware. As a result, efficiency and reliability of the test can be enhanced without manual work. In the experiment, the proposed test approach has been applied to a Xilinx 4010 FPGA to implement automatic configuration, test as well as location of fault sites.
Traditional field programmable gate array (FPGA) test schemes confront many problems, such as memory depth not large enough to meet requirement of configuration of many times, I/O pin counts usually less than needed, manual configuration generation and download, no position of fault sites, etc. A new approach to test FPGA based on SoC HW/SW co-verification technology is proposed and verified in the paper. This test scheme has taken advantage of flexibility and observability of software in conjunction with high-speed simulation of hardware. As a result, efficiency and reliability of the test can be enhanced without manual work. In the experiment, the proposed test approach has been applied to a Xilinx 4010 FPGA to implement automatic configuration, test as well as location of fault sites.
2009, 38(5): 721-724.
doi: 10.3969/j.issn.1001-0548.2009.05.035
Abstract:
The phenomenon of printed circuit board (PCB) bonding finger surface discoloration was explained by analyzing the diffusion of copper atoms，that was, the copper atoms diffused from copper substrate to PCB bonding finger surface, then was oxidized. At the same time, the inherent driving force of copper atoms diffusion in the PCB bonding finger was analyzed. In addition, the diffusion flux and concentration distribution expressions of copper atoms in the PCB bonding finger were drawn by analyzing Fick's Law combined with actual conditions, which provided a theoretical basis for preventing diffusion of copper atoms in the PCB bonding finger.
The phenomenon of printed circuit board (PCB) bonding finger surface discoloration was explained by analyzing the diffusion of copper atoms，that was, the copper atoms diffused from copper substrate to PCB bonding finger surface, then was oxidized. At the same time, the inherent driving force of copper atoms diffusion in the PCB bonding finger was analyzed. In addition, the diffusion flux and concentration distribution expressions of copper atoms in the PCB bonding finger were drawn by analyzing Fick's Law combined with actual conditions, which provided a theoretical basis for preventing diffusion of copper atoms in the PCB bonding finger.
2009, 38(5): 725-729.
doi: 10.3969/j.issn.1001-0548.2009.05.036
Abstract:
A new crosshatching technology on polyimide flexible substrate is described using chemical etching method. The etching solution is composed of Potassium hydroxide, Sodium hydroxide, and additives. The window of demanding is crosshatched in certain conditions on polyimide flexible substrate. The technology process and mechanism of etching are also discussed in detail with examples of hollowing board process. The demerits of the pre-investment and maintenance costs too high or precision too low to traditional crosshatching process are conquered. The new crosshatching technology on polyimide flexible substrate can be applied in the small and high-density FPCB products that have high added value.
A new crosshatching technology on polyimide flexible substrate is described using chemical etching method. The etching solution is composed of Potassium hydroxide, Sodium hydroxide, and additives. The window of demanding is crosshatched in certain conditions on polyimide flexible substrate. The technology process and mechanism of etching are also discussed in detail with examples of hollowing board process. The demerits of the pre-investment and maintenance costs too high or precision too low to traditional crosshatching process are conquered. The new crosshatching technology on polyimide flexible substrate can be applied in the small and high-density FPCB products that have high added value.
2009, 38(5): 730-733.
doi: 10.3969/j.issn.1001-0548.2009.05.037
Abstract:
Phosphor doped (n-type) hydrogenated amorphous silicon (a-Si:H) thin films were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The refractive index, extinction coefficient, optical bandgap and hydrogen content of the testing films were investigated by means of ellipsometry and Fourier transform infrared spectra (FTIR) with gas pressure varied from 20 Pa to 80 Pa. The microstructural changes of a-Si:H thin films caused by different gas pressure were studied and discussed using Raman spectra along with optical property measurement. The results show that the optical bandgap and the hydrogen content of a-Si:H thin films increase with the rise of gas pressure in PECVD system, while the refractive index and the extinction coefficient decrease gradually. In the mean time, the ordering of amorphous network of the testing thin films on the short and intermediate scales is getting worse as the gas pressure goes up.
Phosphor doped (n-type) hydrogenated amorphous silicon (a-Si:H) thin films were deposited by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). The refractive index, extinction coefficient, optical bandgap and hydrogen content of the testing films were investigated by means of ellipsometry and Fourier transform infrared spectra (FTIR) with gas pressure varied from 20 Pa to 80 Pa. The microstructural changes of a-Si:H thin films caused by different gas pressure were studied and discussed using Raman spectra along with optical property measurement. The results show that the optical bandgap and the hydrogen content of a-Si:H thin films increase with the rise of gas pressure in PECVD system, while the refractive index and the extinction coefficient decrease gradually. In the mean time, the ordering of amorphous network of the testing thin films on the short and intermediate scales is getting worse as the gas pressure goes up.
2009, 38(5): 734-736.
doi: 10.3969/j.issn.1001-0548.2009.05.038
Abstract:
From the point of view of the principle of special relativity, it can be known that under the Lorentz transformation of space and time, the electromagnetic field vectors are different with the inertial frames, but the forms of the Maxwell equations are invariant. According to Faraday's law of electromagnetic induction and Ampere's law based on Maxwell's hypothesis of displacement current, the expressions for relativity of time-varying electromagnetic field in resourceless free space to inertial frames which move relatively in low speed are derived concisely. In addition, the form invariance of the basic equations of time-varying electromagnetic field based on the obtained expressions is discussed. The gained results are very important to help ones understand and apply Maxwell's equations of time-varying electromagnetic field.
From the point of view of the principle of special relativity, it can be known that under the Lorentz transformation of space and time, the electromagnetic field vectors are different with the inertial frames, but the forms of the Maxwell equations are invariant. According to Faraday's law of electromagnetic induction and Ampere's law based on Maxwell's hypothesis of displacement current, the expressions for relativity of time-varying electromagnetic field in resourceless free space to inertial frames which move relatively in low speed are derived concisely. In addition, the form invariance of the basic equations of time-varying electromagnetic field based on the obtained expressions is discussed. The gained results are very important to help ones understand and apply Maxwell's equations of time-varying electromagnetic field.
