Changyou Li

Recursive matrix schemes for composite laminates under plane-wave and Gaussian beam illumination

A full-wave computational model of electromagnetic scattering by composite laminates made of dielectric panels reinforced by periodically arranged circular cylindrical fibers parallel to one another is proposed. Incident plane waves, with plane of incidence possibly differing from the plane orthogonal to the fibers’ axes, and Gaussian beams are assumed. Approaches based on transfer matrices and scattering matrices are developed in parallel, the latter being shown more stable in the present study as expected. In practice, Rayleigh’s and mode-matching methods yield scattering matrices that are cascaded between layers to provide reflection and transmission coefficients, producing power reflection and transmission coefficients from Poynting’s theorem. Typical numerical results, with emphasis on graphite-fiber and glass-fiber laminates, are proposed, completed by results about photonic crystals.

Full-Wave Computational Model of Electromagnetic Scattering by Arbitrarily Rotated 1-D Periodic Multilayer Structure

A full-wave computational model of electromagnetic scattering of conically incident plane waves by arbitrarily rotated 1-D periodic multilayer structure is proposed. Each layer in the structure (overall sandwiched between two half-spaces) consists of a dielectric material within which an infinite chain of periodically arranged and arbitrarily orientated circular cylinders is embedded. The orientations of the cylinder arrays in different layers are arbitrary with respect to one another, offering full generality. The above is a model of fiber-reinforced composite laminates as in industry but also of multilayered photonic crystals. Combining Rayleighs method and mode-matching produces scattering matrices for each layer cascaded from the top to the bottom in order to relate the reflection/transmission coefficients to the incident field. Power reflection and transmission coefficients follow from Poyntings theorem. The mathematical derivation insists on modal representations and building up proper S-matrices. Numerical simulations show that the model is accurate, known results on woodpile structures in photonics are in particular recovered. The model is also versatile in terms of illuminations, geometries, and material parameters. The results could also be used as benchmarks in view of lack of data in present-day literature on such arbitrarily orientated layerings. Calculations of pertinent dyadic Green functions is one of possible extensions in view of the imaging methods of possibly damaged multilayer structures.

Scattering of Obliquely Incident Electromagnetic Plane Waves by Composite Panel Involving Periodic Arrays of Circular Fibers

Electromagnetic scattering of a single-layer periodic composite panel is investigated. The panel is reinforced by a periodic array of infinite circular cylindrical fibers. A planar wave illuminates the panel with its wave vector orientated obliquely versus the fibers axes. In this 2.5-D scattering case, full-wave field representation from multipole and plane-wave expansions yield reflection and transmission coefficients of the longitudinal field components, which is achieved by mode matching at the boundaries. Power reflection and transmission coefficients are obtained from time-averaged Poynting vectors. The work is a prerequisite for modeling electromagnetic nondestructive testing of composite panels, approaching a multilayered structure made by stacking periodic slabs one over the other being the next step.

Electromagnetic modeling of a periodic array of fibers embedded in a panel with multiple fibers missing

Our goal is to detect defects in composite materials composed by multi-layer planar plates with a periodic set of circular cylindrical fibers embedded within each layer. As a starter, the work presented is electromagnetic (EM) modeling and imaging of missing fibers in a fiber array standing in air. The multiple scattering method is utilized to analyze the electromagnetic behavior, and the corresponding imaging model is established directly from Lippman-Schwinger integral formulation. With the imaging model, standard MUltiple SIgnal Classification (MUSIC), and the proposed joint sparsity which borrows the idea from sparsity theory, are applied to retrieve the locations of missing fibers. Various numerical results are provided to illustrate availability and accuracy of the modeling and imaging.

Electromagnetic retrieval of missing fibers in periodic fibered laminates via sparsity concepts

Electromagnetic modeling and imaging of fibered laminates with some fibers missing is investigated, this extending to similarly organized photonic crystals. Parallel circular cylinders are periodically set in a homogeneous layer (matrix) sandwiched between two homogeneous half-spaces. Absent fibers destroy the periodicity. An auxiliary periodic structure (supercell) provides a subsidiary model considered using method tailored to standard periodic structures involving the Floquet theorem to decompose the fields. Imaging approaches from the Lippman-Schwinger integral field formulation as one-shot MUltiple SIgnal Classification (MUSIC) with pointwise scatterers assumptions and an iterative, sparsity-constrained solution are developed. Numerical simulations illustrate the direct model and imaging.

Fast Full-Wave Analysis of Damaged Periodic Fiber-Reinforced Laminates

A computationally efficient modeling approach to analyze transverse magnetic and transverse electric electromagnetic scattering from periodic fiber-reinforced laminates is introduced, when they suffer from missing, shrunk/expanded, displaced fibers, and inclusions. Such damages inside the initially periodic structure (the fibers as organized in a given matrix) are seen as undamaged zones with fictitious line sources properly set inside them, and the field results as a summation of responses to the exterior source and equivalent ones. Then, methods for periodic structures can readily be used. Various numerical results are proposed which are evidencing the interest of this approach.

Electromagnetic Modeling of Damaged Single-Layer Fiber-Reinforced Laminates

Computational modeling of a composite laminate made of a homogeneous planar slab wherein circular cylindrical fibers are periodically embedded is carried out when various damages affect the structure and destroy periodicity. Methods based on the Floquet theorem are inapplicable in direct manner. Supercell methodology yields a fictitious periodic structure, so as the electromagnetic field solution everywhere in space can be accurately modeled, provided that the supercell is large enough. Damages include missing, displaced, shrinked and/or expanded fibers, and cylindrical homogeneous inclusions. Plane-wave and line-source illuminations are accounted for in both TE and TM polarizations. Since often a prerequisite to imaging of damages, Green’s functions are considered in detail and computed with the array scanning method. A set of simulations is proposed, with comparison with a standard finite-element approach, and modeling accuracy and efficiency are discussed.

Electromagnetic near-field imaging of missing fibers in periodic fiber-reinforced laminates

Summary form only given. Much work has been and is being carried out about the electromagnetic behavior of planar laminates (and in parallel, due to similarities of organization, of some particular photonic crystals) which are involving within each layer a periodic array of commonly orientated fibers, as it is underlined in wherein many references on the topic can also be found, both in electromagnetics (and photonics) and elasticity.

Full-wave model and numerical study of electromagnetic plane-wave scattering by multilayered, fiber-based periodic composites

Advanced composite materials are widely applied in aerospace, naval and automotive industries particularly due to their light weight, high stiffness and resistance to corrosion. The building block of the material is a composite slab composed of two parts, matrix and reinforcement. The reinforcement, such as graphite or glass fibers, is embedded inside the background matrix and periodically arranged while the matrix, such as epoxy, binds the reinforcement together. All fibers inside are then orientated into the same direction. Stacking up single layers yields multi-layer composite laminates, the orientations of the fibers in different layers usually differing from one to the other in order to provide strength and stiffness in all directions (C. Alexander et al., Journal of Applied Physics, 114, 2013, 1 – 10).

Design of ETL Process on Spatio-temporal Data and Study of Quality Control

In order to use the space-time data mining technology to conduct operation research in WuLiangSuHai Eutrophication, the water quality sensor parameters of heterogeneous data which reflect the characteristics should set up a spatial data warehouse through ETL process, and water quality sensors for quality control of spatial and temporal data plays a vital role in building an effective analytical environment. The paper designs the ETL process from the data and water quality sensors artificial duty and other heterogeneous data sources spatial data, and proposes data quality control strategy based on the incremental frequency rule engine and the space the inverse distance weighting on the Combination. Experiments show that the incremental frequency rule engine could more effectively find the missing sensor data and abnormal, Space inverse distance weighting method can find the missing data and outliers in the errors within the allowed interpolation processing, ETL procedure is effective and feasible.