The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the ...The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.展开更多
A hybrid method combining finite difference time domain(FDTD)with topology network was presented to treat with electromagnetic couplings and transmissions in large spaces A generalized matrix euqation expressing th...A hybrid method combining finite difference time domain(FDTD)with topology network was presented to treat with electromagnetic couplings and transmissions in large spaces A generalized matrix euqation expressing the relations among wave vectors at every port of the network nodes was give Scattering characteristics and electromagnetic distributions of every node was calculated independently using FDTD A structure of irises in a waveguide was taken as numerical examples This hybrid method has more advantages than the traditional FDTD method which includes saving calculation time,saving memory spaces and being flexible in setting up FDTD grids展开更多
The cluster-shaped plasmonic nanostructures are used to manage the incident light inside an ultra-thin silicon solar cell.Here we simulate spherical,conical,pyramidal,and cylindrical nanoparticles in a form of a clust...The cluster-shaped plasmonic nanostructures are used to manage the incident light inside an ultra-thin silicon solar cell.Here we simulate spherical,conical,pyramidal,and cylindrical nanoparticles in a form of a cluster at the rear side of a thin silicon cell,using the finite difference time domain(FDTD)method.By calculating the optical absorption and hence the photocurrent,it is shown that the clustering of nanoparticles significantly improves them.The photocurrent enhancement is the result of the plasmonic effects of clustering the nanoparticles.For comparison,first a cell with a single nanoparticle at the rear side is evaluated.Then four smaller nanoparticles are put around it to make a cluster.The photocurrents of 20.478 mA/cm2,23.186 mA/cm2,21.427 mA/cm2,and 21.243 mA/cm2 are obtained for the cells using clustering conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.These values are 13.987 mA/cm2,16.901 mA/cm2,16.507 mA/cm2,17.926 mA/cm2 for the cell with one conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.Therefore,clustering can significantly improve the photocurrents.Finally,the distribution of the electric field and the generation rate for the proposed structures are calculated.展开更多
Noble metal nanoantenna could effectively enhance light absorption and increase detection sensitivity. In this paper,we propose a periodic Ag diamond nanoantenna array to increase the absorption of thin-film solar cel...Noble metal nanoantenna could effectively enhance light absorption and increase detection sensitivity. In this paper,we propose a periodic Ag diamond nanoantenna array to increase the absorption of thin-film solar cells and to improve the detection sensitivity via localized surface plasmon resonance. The effect of nanoantenna arrays on the absorption enhancement is theoretically investigated using the finite difference time domain（FDTD） method with manipulating the spectral response by geometrical parameters of nanoantennas. A maximum absorption enhancement factor of 1.51 has been achieved in this study. In addition, the relation between resonant wavelength（intensity reflectivity） and refractive index is discussed in detail. When detecting the environmental index using resonant wavelengths, a maximum detection sensitivity of about 837 nm/RIU（refractive index unit） and a resolution of about 10-3RIU can be achieved. Moreover, when using the reflectivity, the sensitivity can be as high as 0.93 AU/RIU. Furthermore, we also have theoretically studied the effectiveness of nanoantennas in distinguishing chemical reagents, solution concentrations, and solution allocation ratios by detecting refractive index. From the results presented in this paper, we conclude that this work might be useful for biosensor detection and other types of detections.展开更多
An FDTD system associated with uniaxial perfectly matched layer（UPML） for an electromagnetic scattering problem in two-dimensional space in polar coordinates is considered.Particularly the FDTD system of an initial-...An FDTD system associated with uniaxial perfectly matched layer（UPML） for an electromagnetic scattering problem in two-dimensional space in polar coordinates is considered.Particularly the FDTD system of an initial-boundary value problems of the transverse magnetic（TM） mode to Maxwell＇s equations is obtained by Yee＇s algorithm,and the open domain of the scattering problem is truncated by a circle with a UPML.Besides,an artificial boundary condition is imposed on the outer boundary of the UPML.Afterwards,stability of the FDTD system on the truncated domain is established through energy estimates by the Gronwall inequality.Numerical experiments are designed to approve the theoretical analysis.展开更多
A hybrid algorithm is presented for nonuniform lossy multiconductor transmission lines (MTL) connected by arbitrary linear load networks. The networks are characterized by a state-variable equation which allows a gene...A hybrid algorithm is presented for nonuniform lossy multiconductor transmission lines (MTL) connected by arbitrary linear load networks. The networks are characterized by a state-variable equation which allows a general characterization of dynamic elements in the cascade networks. The method is achieved by the finite difference-time domain (FDTD) algorithm for the MTL, and the skin effect is taken into account, the more accurate method is used to compute the skin effect. And this method is combined with the computation of the nonuniform transmission lines. Finally, several numerical examples are given, these results indicate that: the current of the lossy MTL is smaller than the lossless of the MTL; and when the load networks contain the dynamic element, the transition time of the current is longer than the MTL connected by resistance only.展开更多
The factors affecting one dimensional （1D） and two dimensional （2D） photonic crystals （PhCs） are systemically analyzed in this paper by numerical simulation. Transfer matrix method （TMM） is employed for 1D PCs...The factors affecting one dimensional （1D） and two dimensional （2D） photonic crystals （PhCs） are systemically analyzed in this paper by numerical simulation. Transfer matrix method （TMM） is employed for 1D PCs, both finite difference time domain method （FDTD） and plane wave expansion method （PWE） are employed for 2D PCs. The result shows that the photonic bandgaps （PBG） are directly affected by crystal type, crystal lattice constant, modulation of refractive index and periodicity, and it is should be useful for design of different type photonic crystals with the required PBG and functional devices. Finally, as an example, a near-IR 1D PCs narrow filter was designed.展开更多
In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-...In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-node acoustic fluid elements. The vibration characteristics of the structure in the finite fluid domain are calculated combining structure FEM mass matrix. By writing relevant programs, the numerical analysis on vibration characteristics of a submerged cantilever rectangular plate in finite fluid domain and loaded ship model is performed. A modal identification experiment for the loaded ship model in air and in water is conducted and the experiment results verify the reliability of the numerical analysis. The numerical method can be used for further research on vibration characteristics and acoustic radiation problems of the structure in the finite fluid domain.展开更多
We investigate optical properties of a bowtie-shaped aperture using the finite difference time domain method to optimize its geometric parameters for specific incident lights. The influence of the parameters on local ...We investigate optical properties of a bowtie-shaped aperture using the finite difference time domain method to optimize its geometric parameters for specific incident lights. The influence of the parameters on local field enhancement and resonant wavelength in the visible frequency range is numerically analysed. It is found that the major resonance of the spectrum is exponentially depended on the bowtie angle but independent of the whole aperture size. The simulation also demonstrates that increasing the aperture size raises the local field intensity on the exit plane due to an enlarged interaction area between the light and the metal medium. And the near-field spot size is closely related to the gap. Based on these results, the design rules of the bowtie structure can be optimized for specific wavelengths excited.展开更多
An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the...An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells,i.e.used memory,while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer.The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions.To demonstrate the efficiency of the parallelized FDTD model,a mirrored cavity is analyzed.The analysis shows that the proposed model reduces computation time and memory cost,and the parallel computation result matches the theoretical model.展开更多
By utilizing a Fabry–Perot （FP） nanocavity adjacent to T-shaped gap waveguide ports, spectrally selective filtering is realized. When the wavelength of incident light corresponds to the resonance wavelength of the ...By utilizing a Fabry–Perot （FP） nanocavity adjacent to T-shaped gap waveguide ports, spectrally selective filtering is realized. When the wavelength of incident light corresponds to the resonance wavelength of the FP nanocavity, the surface plasmons are captured inside the nanocavity, and light is highly reflected from this port. The resonance wavelength is determined by using Fabry–Perot resonance condition for the nanocavity. For any desired filtering frequency the dimension of the nanocavity can be tailored. The numerical results are based on the two-dimensional finite difference time domain simulation under a perfectly matched layer absorbing boundary condition. The analytical and simulation results indicate that the proposed structure can be utilized for filtering and splitting applications.展开更多
A unidirectional surface plasmon polaritons(SPPs) generator with greatly enhanced generation efficiency is proposed. The SPPs generator consists of an asymmetric single nanoslit coated with a polyviny alcohol(PVA) fil...A unidirectional surface plasmon polaritons(SPPs) generator with greatly enhanced generation efficiency is proposed. The SPPs generator consists of an asymmetric single nanoslit coated with a polyviny alcohol(PVA) film and a silver rectangle block. The generation efficiency of this SPPs generator is investigated using the finite difference time domain method. Due to the presence of the silver rectangle block, the SPPs generation efficiency of the asymmetric single nanoslit with PVA film can be greatly enhanced and the corresponding wavelength with the maximum enhancement factor can be tuned flexibly. The influence of the structural parameters on the generation efficiency is also investigated for the enhanced unidirectional SPPs generator.展开更多
In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain（FDTD） simulat...In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain（FDTD） simulation method.By simulating reflectance spectra,electric field distribution,and charge distribution,we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light,in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity.A coaxial waveguide mode TE11 will exist in these annular cavities,and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities.These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss.The formation of an absorption peak can be explained from the aspect of phase matching conditions.We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps,gap surface topography.Meanwhile,different lengths of the cavity may cause the shift of resonance dips.Also,we study the field enhancement at different vertical locations of the slit.In addition,dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths,which make the annular cavities good candidates for refractive index sensors.The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity.Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates,refractive index sensors,nano-lasers,and optical trappers.展开更多
The bowtie aperture surrounded by concentric gratings(the bull’s eye structure) integrated on the near-field scanning optical microscopy(NSOM) probe(aluminum coated fiber tip) for nanolithography has been investigate...The bowtie aperture surrounded by concentric gratings(the bull’s eye structure) integrated on the near-field scanning optical microscopy(NSOM) probe(aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain(FDTD) method.By modifying the parameters of the bowtie aperture and the concentric gratings,a maximal field enhancement factor of 391.69 has been achieved,which is 18 times larger than that obtained from the single bowtie aperture.Additionally,the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength.The superiority of the combination of the bowtie aperture and the bull’s eye structure is confirmed,and the mechanism for the electric field enhancement in this derived structure is analyzed.展开更多
基金Project supported partly by the Open Research Program in State Key Laboratory of Millimeter Waves of China(Grant No.K200802)partly by the National Natural Science Foundation of China(Grant No.60971122)
文摘The transmission coefficients of electromagnetic （EM） waves due to a superconductor-dielectric superlattice are numerically calculated. Shift operator finite difference time domain （SO-FDTD） method is used in the analysis. By using the SO-FDTD method, the transmission spectrum is obtained and its characteristics are investigated for different thicknesses of superconductor layers and dielectric layers, from which a stop band starting from zero frequency can be apparently observed. The relation between this low-frequency stop band and relative temperature, and also the London penetration depth at a superconductor temperature of zero degree are discussed, separately. The low-frequency stop band properties of superconductor-dielectric superlattice thus are well disclosed.
文摘A hybrid method combining finite difference time domain(FDTD)with topology network was presented to treat with electromagnetic couplings and transmissions in large spaces A generalized matrix euqation expressing the relations among wave vectors at every port of the network nodes was give Scattering characteristics and electromagnetic distributions of every node was calculated independently using FDTD A structure of irises in a waveguide was taken as numerical examples This hybrid method has more advantages than the traditional FDTD method which includes saving calculation time,saving memory spaces and being flexible in setting up FDTD grids
文摘The cluster-shaped plasmonic nanostructures are used to manage the incident light inside an ultra-thin silicon solar cell.Here we simulate spherical,conical,pyramidal,and cylindrical nanoparticles in a form of a cluster at the rear side of a thin silicon cell,using the finite difference time domain(FDTD)method.By calculating the optical absorption and hence the photocurrent,it is shown that the clustering of nanoparticles significantly improves them.The photocurrent enhancement is the result of the plasmonic effects of clustering the nanoparticles.For comparison,first a cell with a single nanoparticle at the rear side is evaluated.Then four smaller nanoparticles are put around it to make a cluster.The photocurrents of 20.478 mA/cm2,23.186 mA/cm2,21.427 mA/cm2,and 21.243 mA/cm2 are obtained for the cells using clustering conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.These values are 13.987 mA/cm2,16.901 mA/cm2,16.507 mA/cm2,17.926 mA/cm2 for the cell with one conical,spherical,pyramidal,cylindrical NPs at the backside,respectively.Therefore,clustering can significantly improve the photocurrents.Finally,the distribution of the electric field and the generation rate for the proposed structures are calculated.
基金Project supported by the International Scientific and Technological Cooperation Projects of Guizhou Province,China(Grant No.20117035)the Program for Innovative Research Team of Guilin University of Electronic Technology,China(Grant No.IRTGUET)
文摘Noble metal nanoantenna could effectively enhance light absorption and increase detection sensitivity. In this paper,we propose a periodic Ag diamond nanoantenna array to increase the absorption of thin-film solar cells and to improve the detection sensitivity via localized surface plasmon resonance. The effect of nanoantenna arrays on the absorption enhancement is theoretically investigated using the finite difference time domain（FDTD） method with manipulating the spectral response by geometrical parameters of nanoantennas. A maximum absorption enhancement factor of 1.51 has been achieved in this study. In addition, the relation between resonant wavelength（intensity reflectivity） and refractive index is discussed in detail. When detecting the environmental index using resonant wavelengths, a maximum detection sensitivity of about 837 nm/RIU（refractive index unit） and a resolution of about 10-3RIU can be achieved. Moreover, when using the reflectivity, the sensitivity can be as high as 0.93 AU/RIU. Furthermore, we also have theoretically studied the effectiveness of nanoantennas in distinguishing chemical reagents, solution concentrations, and solution allocation ratios by detecting refractive index. From the results presented in this paper, we conclude that this work might be useful for biosensor detection and other types of detections.
文摘An FDTD system associated with uniaxial perfectly matched layer（UPML） for an electromagnetic scattering problem in two-dimensional space in polar coordinates is considered.Particularly the FDTD system of an initial-boundary value problems of the transverse magnetic（TM） mode to Maxwell＇s equations is obtained by Yee＇s algorithm,and the open domain of the scattering problem is truncated by a circle with a UPML.Besides,an artificial boundary condition is imposed on the outer boundary of the UPML.Afterwards,stability of the FDTD system on the truncated domain is established through energy estimates by the Gronwall inequality.Numerical experiments are designed to approve the theoretical analysis.
文摘A hybrid algorithm is presented for nonuniform lossy multiconductor transmission lines (MTL) connected by arbitrary linear load networks. The networks are characterized by a state-variable equation which allows a general characterization of dynamic elements in the cascade networks. The method is achieved by the finite difference-time domain (FDTD) algorithm for the MTL, and the skin effect is taken into account, the more accurate method is used to compute the skin effect. And this method is combined with the computation of the nonuniform transmission lines. Finally, several numerical examples are given, these results indicate that: the current of the lossy MTL is smaller than the lossless of the MTL; and when the load networks contain the dynamic element, the transition time of the current is longer than the MTL connected by resistance only.
基金Sponsored by the Ministerial Level Advanced Research Foundation (1006513002060)
文摘The factors affecting one dimensional （1D） and two dimensional （2D） photonic crystals （PhCs） are systemically analyzed in this paper by numerical simulation. Transfer matrix method （TMM） is employed for 1D PCs, both finite difference time domain method （FDTD） and plane wave expansion method （PWE） are employed for 2D PCs. The result shows that the photonic bandgaps （PBG） are directly affected by crystal type, crystal lattice constant, modulation of refractive index and periodicity, and it is should be useful for design of different type photonic crystals with the required PBG and functional devices. Finally, as an example, a near-IR 1D PCs narrow filter was designed.
基金Supported by the National Natural Science Foundation of China （No. 51079027）.
文摘In this paper, the vibration characteristics of the structure in the finite fluid domain are analyzed using a coupled finite element method. The added mass matrix is calculated with finite element method （FEM） by 8-node acoustic fluid elements. The vibration characteristics of the structure in the finite fluid domain are calculated combining structure FEM mass matrix. By writing relevant programs, the numerical analysis on vibration characteristics of a submerged cantilever rectangular plate in finite fluid domain and loaded ship model is performed. A modal identification experiment for the loaded ship model in air and in water is conducted and the experiment results verify the reliability of the numerical analysis. The numerical method can be used for further research on vibration characteristics and acoustic radiation problems of the structure in the finite fluid domain.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10975012)
文摘We investigate optical properties of a bowtie-shaped aperture using the finite difference time domain method to optimize its geometric parameters for specific incident lights. The influence of the parameters on local field enhancement and resonant wavelength in the visible frequency range is numerically analysed. It is found that the major resonance of the spectrum is exponentially depended on the bowtie angle but independent of the whole aperture size. The simulation also demonstrates that increasing the aperture size raises the local field intensity on the exit plane due to an enlarged interaction area between the light and the metal medium. And the near-field spot size is closely related to the gap. Based on these results, the design rules of the bowtie structure can be optimized for specific wavelengths excited.
基金Supported by the Scientific Research Foundation of Nanjing University of Posts and Telecommunications(NY212008,NY213116)the National Science Foundation of Jiangsu Province(BK20131383)
文摘An efficient wavelet-based finite-difference time-domain(FDTD)method is implemented for analyzing nanoscale optical devices,especially optical resonator.Because of its highly linear numerical dispersion properties the high-spatial-order FDTD achieves significant reduction in the number of cells,i.e.used memory,while analyzing a high-index dielectric ring resonator working as an add/drop multiplexer.The main novelty is that the wavelet-based FDTD model is extended in a parallel computation environment to solve physical problems with large dimensions.To demonstrate the efficiency of the parallelized FDTD model,a mirrored cavity is analyzed.The analysis shows that the proposed model reduces computation time and memory cost,and the parallel computation result matches the theoretical model.
基金Project supported by the National Key Basic Research Program of China (Grant No. 2013CB328702)
文摘By utilizing a Fabry–Perot （FP） nanocavity adjacent to T-shaped gap waveguide ports, spectrally selective filtering is realized. When the wavelength of incident light corresponds to the resonance wavelength of the FP nanocavity, the surface plasmons are captured inside the nanocavity, and light is highly reflected from this port. The resonance wavelength is determined by using Fabry–Perot resonance condition for the nanocavity. For any desired filtering frequency the dimension of the nanocavity can be tailored. The numerical results are based on the two-dimensional finite difference time domain simulation under a perfectly matched layer absorbing boundary condition. The analytical and simulation results indicate that the proposed structure can be utilized for filtering and splitting applications.
基金Project supported by the National Natural Science Foundation of China （Grant Nos. 11174237 and 10974161）, the National Basic Research Program of China （Grant No. 2013CB328904）, the Fundamental Research Funds for the Central Universities of Ministry of Education of China （Grant Nos. SWJTU 12CX084 and SWJTU2（/10ZT06）, and the Innovation Fund for Ph.D. Student of Southwest Jiaotong University, China.
文摘A unidirectional surface plasmon polaritons(SPPs) generator with greatly enhanced generation efficiency is proposed. The SPPs generator consists of an asymmetric single nanoslit coated with a polyviny alcohol(PVA) film and a silver rectangle block. The generation efficiency of this SPPs generator is investigated using the finite difference time domain method. Due to the presence of the silver rectangle block, the SPPs generation efficiency of the asymmetric single nanoslit with PVA film can be greatly enhanced and the corresponding wavelength with the maximum enhancement factor can be tuned flexibly. The influence of the structural parameters on the generation efficiency is also investigated for the enhanced unidirectional SPPs generator.
基金Project supported by the National Natural Science Foundation of China(Grant No.61178044)the Natural Science Foundation of Jiangsu Province,China(Grant No.BK20160969)the University Postgraduate Research and Innovation Project of Jiangsu Province,China(Grant No.KYLX 0723)
文摘In this paper,optical properties of two-dimensional periodic annular slot cavity arrays in hexagonal close-packing on a silica substrate are theoretically characterized by finite difference time domain（FDTD） simulation method.By simulating reflectance spectra,electric field distribution,and charge distribution,we confirm that multiple cylindrical surface plasmon resonances can be excited in annular inclined slot cavities by linearly polarized light,in which the four reflectance dips are attributed to Fabry–Perot cavity resonances in the coaxial cavity.A coaxial waveguide mode TE11 will exist in these annular cavities,and the wavelengths of these reflectance dips are effectively tailored by changing the geometrical pattern of slot cavity and the dielectric materials filled in the cavities.These resonant wavelengths are localized in annular cavities with large electric field enhancement and dissipate gradually due to metal loss.The formation of an absorption peak can be explained from the aspect of phase matching conditions.We observed that the proposed structure can be tuned over the broad spectral range of 600–4000 nm by changing the outer and inner radii of the annular gaps,gap surface topography.Meanwhile,different lengths of the cavity may cause the shift of resonance dips.Also,we study the field enhancement at different vertical locations of the slit.In addition,dielectric materials filling in the annular gaps will result in a shift of the resonance wavelengths,which make the annular cavities good candidates for refractive index sensors.The refractive index sensitivity of annular cavities can also be tuned by the geometry size and the media around the cavity.Annular cavities with novel applications can be implied as surface enhanced Raman spectra substrates,refractive index sensors,nano-lasers,and optical trappers.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10974025 and 61137005)
文摘The bowtie aperture surrounded by concentric gratings(the bull’s eye structure) integrated on the near-field scanning optical microscopy(NSOM) probe(aluminum coated fiber tip) for nanolithography has been investigated using the finite-difference time domain(FDTD) method.By modifying the parameters of the bowtie aperture and the concentric gratings,a maximal field enhancement factor of 391.69 has been achieved,which is 18 times larger than that obtained from the single bowtie aperture.Additionally,the light spot depends on the gap size of the bowtie aperture and can be confined to sub-wavelength.The superiority of the combination of the bowtie aperture and the bull’s eye structure is confirmed,and the mechanism for the electric field enhancement in this derived structure is analyzed.
