Контроль диэлектрической проницаемости и толщины анизотропных диэлектрических покрытий методом поверхностных электромагнитных волн

The widespread use of anisotropic composite dielectric coatings operating in the microwave range in various science-intensive areas has led to the search and selection of effective methods of radio wave nondestructive testing of their electrophysical parameters. The existing approaches based on the estimation of the reflection and transmission coefficients of electromagnetic waves have low accuracy and reliability of estimating the components of the complex permittivity tensor and the thickness of such coatings, do not take into account their frequency dispersion and placement on a metal base. We present the new method of local measurements of components of the complex permittivity tensor with allowance for their frequency dispersion and a thickness anisotropic dielectric coatings with radial surface microwaves. The method is based on the solution of inverse problem in the determination of components of the complex permittivity tensor and a thickness coatings from the frequency and angular dependence of the attenuation coefficient of the field of a radial surface electromagnetic wave excited in a test sample. A numerical and experimental study show that for a measurement bandwidth of 9–13,5 GHz the errors in estimating the anisotropy coefficients do not exceed 10% with a confidence coefficient of 0.95. We introduce and substantiate a statistical limit of the resolution of the anisotropy of permittivity; this makes it possible to evaluate the possibility of discriminating between two close values any pair of components of the permittivity tensor. Numerical and field experiments have shown that the method can provide their assessment with a difference of 0.2–0.3% or less in the frequency band of 9–13.5 GHz.

uPTI: uniaxial permittivity tensor imaging of intrinsic density and anisotropy

Architecture of biological systems is important for their homeostatic functions and is predictive of pathology. Volumetric imaging of intrinsic density, anisotropy, and 3D orientation of cell and tissue components is informative, but still challenging. These physical properties can be described succinctly by the volumetric distribution of the specimen’s permittivity tensor (PT). We report uniaxial permittivity tensor imaging (uPTI), a novel approach for label-free volumetric imaging with diffraction-limited resolution. uPTI combines the oblique illumination and the polarization imaging with high numerical apertures to encode the specimen’s permittivity tensor into intensity modulations, which are decoded with a novel vector diffraction model and a multi-channel convex optimization. The uPTI volumes of polystyrene beads and laser-fabricated anisotropic glass targets show that 3D uPT measurements are quantitative, with diffraction-limited spatial resolution of 0.23 × 0.23 × 0.8 μm3. Automated 2D and 3D imaging of a mouse brain section reveals anatomy at multiple scales (cm – 250 nm) and demonstrates that uPTI enables analysis of the density, anisotropy, and orientation of axon bundles and single axons. We multiplex uPTI with fluorescence de-convolution microscopy to enable correlative analysis of physical and molecular architecture of iPSC-derived cardiomyocytes. uPTI can be added to an existing widefield microscope as a low cost module. We share our implementation of the forward model and optimization algorithms via open source repository. Collectively, the reported advances in optical design, image formation, reconstruction algorithms, and biological interpretation open multiple avenues to study architecture of organelles, cells and tissue sections, including human cells and tissues that are challenging to label.

Solving the inverse problem for determining the optical characteristics of materials

The paper describes a methodology for determining the optical and physical properties of anisotropic thin film materials. This approach allows in the future designing multilayer thin-film coatings with specified properties. An inverse problem of determining the permittivity tensor and the thickness of a thin film deposited on a glass substrate is formulated. Preliminary information on the belonging of a thin-film coating to a certain class can significantly reduce the computing time and increase the accuracy of determining the permittivity tensor over the entire investigated range of wavelengths and film thickness at the point of reflection and transmission measurement Depending on the goals, it is possible to formulate and, therefore, solve various inverse problems: o determination of the permittivity tensor and specification of the thickness of a thick (up to 1 cm) substrate, often isotropic; o determination of the permittivity tensor of a thin isotropic or anisotropic film deposited on a substrate with known optical properties. The complexity of solving each of the problems is very different and each problem requires its own specific set of measured input data. The ultimate results of solving the inverse problem are verified by comparing the calculated transmission and reflection with those measured for arbitrary angles of incidence and reflection.

Exact and linearized refractive index stress-dependence in anisotropic photoelastic crystals

For the permittivity tensor of photoelastic anisotropic crystals, we obtain the exact nonlinear dependence on the Cauchy stress tensor. We obtain the same result for its square root, whose principal components, the crystal principal refractive index, are the starting point for any photoelastic analysis of transparent crystals. From these exact results we then obtain, in a totally general manner, the linearized expressions to within higher-order terms in the stress tensor for both the permittivity tensor and its square root. We finish by showing some relevant examples of both nonlinear and linearized relations for optically isotropic, uniaxial and biaxial crystals.

Спектры собственных волн анизотропного цилиндрического твердотельного волновода

Dispersion properties of eigenwaves of an anisotropic cylindrical solid-state waveguide without frequency dispersion in permittivity tensor components have been analyzed theoretically. The classification of waves has been performed. E type bulk–surface eigenwaves with negative group velocities have been found. The conditions for their existence have been determined. The existence in the waveguide of E -type surface eigenwaves and pseudo-surface eigenwaves of E- and H -types has been shown.