Surface Microwaves Research Articles

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.

Контроль электрофизических параметров метаматериалов методом поверхностных электромагнитных волн

Development of metamaterials has led to the search and choice of effective methods of radio-wave nondestructive testing of their electrophysical parameters. The existing approaches to testing based on extracted of effective electrophysical parameters of metamaterials from the coefficients of reflection and transmission of an electromagnetic wave have low reliability and don't provide their local control. We present the new radio-wave method of local control of complex dielectric permittivity and magnetic permeability, as well as the thickness of metamaterial plate on a metal substrate with surface microwaves. The method is based on the solution of inverse problem in the determination of effective electrophysical parameters of metamaterial from the frequency dependence of the attenuation coefficient of the field of a slow surface electromagnetic wave excited in a test sample. The electrophysical parameters of the metamaterial are represented as parametric frequency functions in accordance with the Drude-Lorentz models of dispersion, and the solution of the inverse problem is reduced to minimizing the objective function constructed based on the discrepancy between the experimental and design theoretical values of the attenuation coefficients of surface electromagnetic wave fields on a grid of discrete frequencies. The structure of a measuring complex that implements the proposed method of control is proposed. For the numerical and experimental verification of the method, a sample of a metamaterial plate based on SRR elements with a negative refraction region in the frequency band 10.06–10.64 GHz was investigated. Experimental investigations of the metamaterial demonstrated the theoretical capabilities gained with measurement of the local electrophysical parameters with relative error not greater 10 %.

Estimating the Extent of Exfoliation of Dielectric and Magnetodielectric Coatings with Surface Microwaves

We present the results of a study that confirms the high efficiency of using surface microwaves in assessing the extent of exfoliation of dielectric and magnetodielectric coatings from a metal base. The complex coefficient of attenuation of the field of a surface electromagnetic wave along the normal to the coating surface is used as a parameter for estimating the extent of exfoliation. In contrast to the existing approaches, the developed electrodynamic measurement model takes into account the real and imaginary parts of the complex dielectric permittivity and magnetic permeability of the coating with allowance for their frequency dispersion; this improves the accuracy and reliability of estimating the extent of exfoliation. An algorithm is developed for estimating the extent of coating exfoliation based on the search for the maximum joint probability density of the coefficient of attenuation of the field of a surface electromagnetic wave measured at a set of frequencies. We introduce and substantiate a statistical limit of the resolution of two values of exfoliation; this makes it possible to evaluate the possibility of discriminating between two close values of exfoliation depending on the bandwidth of attenuation coefficient measurements, their number, and the signal-to-noise ratio. The structure of a measuring complex that implements the proposed approaches to exfoliation assessment is provided. Numerical and field experiments have shown the fundamental possibility of estimating the value of recorded values of exfoliation of dielectric and magnetodielectric coatings from a metal substrate with a thickness of 20 μm or less in the frequency band of 9–13.5 GHz.

Statistical Analysis of the Potential of a Bathymetric Lidar with Time-of-Flight Matrix Spad Photodetector

The Monte Carlo method is used to solve the nonstationary laser sensing equation for a multicomponent optically dense water medium taking into account the influence of the water-air interface and the contributions of multiple radiation scattering by sea water and of the signal reflection from the sea bottom. Dependences of the signal power recorded with a monostatic lidar equipped with a time-of-flight matrix single-photon avalanche diode (SPAD) photodetector on the water depth and surface microwaves for different field-of-view angles of the receiver are obtained. Results of investigations have shown that the maximum depth of sea bottom detection is 40–50 m given that the optical water thickness does not exceed 3.5–4 m. The dynamic range of lidar signals from water reaches 7–9 orders of magnitude for lidar sensing of sea bottom at limiting depths of 40–50 m in very transparent water in the presence of the Fresnel reflection from the water surface. Results of statistical simulation have shown that the lidar system with the matrix receiver intended for sea water sensing can be realized at the modern technical level. Under favorable conditions, the lidar return signal power provides sensing of sea bottom to depths of 40–50 m.

Microwave formation mechanisms in surface generation of ultra-precision machining

In ultra-precision machining (UPM), surface microwaves have been commonly produced on the machined surface along with lamellar chips. However, the intrinsic characteristics of surface microwave formation in UPM have not been understood well. Therefore, a theoretical and experimental investigation has been conducted into microwave formation mechanisms of surface generation in UPM. The results revealed that in UPM, the lamellar chip formation caused cyclic cutting forces to induce material recovery and tool vibration, namely chip formation induced material recovery and tool vibration. Accordingly, it caused surface microwaves on the machined surface. Further, a theoretical model has been developed qualitatively to represent the relationship between chip formation induced material recovery and tool vibration and surface microwaves. It was well identified by the machined and simulated surface topographies in UPM.

Statistical Estimates of Lidar Signals Reflected from the Ocean Bottom

The Monte Carlo method is used to solve the nonstationary equation of laser sensing of an optically dense, complex, multicomponent aqueous medium with allowance for the water–air interface, the contribution of multiple scattering of radiation by the water column, and reflection of the signal from the bottom. As a result, we have obtained dependences of the return signal of a monostatic lidar from the water column and the surface microwaves for various field-of-view angles of the receiver. The results of our calculations show that a lidar detection depth of the bottom up to 50 m is achievable for water optical thicknesses up to 3.5–4. When sensing the bottom up to the limiting depth of 50 m under conditions of very transparent water and Fresnel reflection from its surface, the dynamic range of the signal from the water column reaches 7–9 orders of magnitude.

Case study of surface micro-waves in ultra-precision raster fly cutting

In ultra-precision raster fly cutting (UPRFC), very high frequency microwaves in the range of 3.42MHz–6.36MHz are found on the machined surface. This study conducted a series of theoretical and experimental investigations to discover the origin of these microwaves and how they might be suppressed. Research results show that: (i) microwaves on the machined surface are caused by the material sliding during the chip formation in UPRFC; (ii) owing to the inconsistent thickness of chips along their length direction, the microwaves accumulate at the surface-exit in each feed length; and (iii) chip thickness and tool wear change the length and distribution of the microwaves. This research provides a deep insight into the formation of microwaves along with suggestion on how to suppress them.

A Finite-Element Analysis of Surface Wave Plasmas

This paper describes a finite-element analysis of surface microwaves coupled to a cold nonmagnetized plasma for chemical vapor deposition (CVD). The microwave-plasma coupling is taken into account by introducing the frequency-dependent permittivity. The computed resonant modes of the surface wave on the interface between the dielectric and plasma in a cylindrical vessel are shown to be in good agreement with the theoretical ones. Moreover, the computed field distribution for a waveguide loaded cylindrical vessel agrees well with that computed by the finite-difference time-domain (FDTD) method.

Axial temperature profile of plasma columns sustained by surface microwaves

The axial profile of the gas temperature along a N~ plasma column excited with surface propagating microwaves is measured by spectroscopy of the rotational emission lines from the N~(C, v = 0 ) states. At 60 W of microwave input power, the gas temperature is in the range 900 K-1300 K along the plasma column. Addition of He cools the gas temperature down to

Resist Ashing Using Surface-Wave – Produced Plasmas

A new type of plasma asher using surface microwaves propagating on a dielectric line is reported. The ashing process is achieved in aflowing afterglow discharge. A high ashing rate of 3.2 µm/Min over a 5-inch wafer at 230°C is obtained, using pure oxygen at pressures close to 130 Pa. Radiation damage on the substrate is minimized by operating in a flowing afterglow where the ion current on the wafer is barely detectable.

Reexamination of recent experimental results in surface-wave-produced argon plasmas at 2.45 GHz: Comparison with the diffusion-recombination model results

In this paper we comment on recently reported experimental data about some characteristic magnitudes of plasma columns produced and maintained by surface microwaves. We then compare them with theoretical values obtained from the diffusion-recombination model of Mateev, Zhelyazkov, and Atanassov [J. Appl. Phys. 54, 3049 (1988)] and Zhelyazkov, Benova, and Atanassov [J. Appl. Phys. 59, 1466 (1986)] for the same magnitudes, in a wide range of operating conditions. Such a comparison allows us to make conclusions about the results of the model and its hypothesis.

Electron energy distributions and excitation rates in high-frequency argon discharges

The electron energy distribution functions and rate coefficients for excitation and ionisation in argon under the action of an uniform high-frequency electric field were calculated by numerically solving the homogeneous Boltzmann equation. The treatment is restricted to situations in which the electrons do not lose appreciable energy during a cycle of field oscillation. Apart from this restriction the calculations cover the whole range of angular frequencies of the HF field from omega << nu c to omega >> nu c, where nu c is the electron-neutral collision frequency for momentum transfer. Typical values of the ratios of the electric field to the gas density and to the angular frequency considered in this work are in the ranges of 10-16<E/N<10-15V cm2 and 10-10<E/ omega <10-8V cm-1s, respectively. Analytic calculations in the limiting cases of omega >> nu c and omega << nu c are also presented and shown to be in very good agreement with the numerical computations. The results reported here are relevant for the modelling of HF discharges in argon and, in particular, for improving recent theoretical descriptions of a plasma column sustained by surface microwaves.