Том 61, № 7 (2018)

The shadowing of some regions of a wavy water surface by other regions can significantly influence the backscattered signal not only in the problem of remote monitoring of a water reservoir at grazing angles (e.g., in radar), but also in the problems of underwater vision. In this work, we present the results of a theoretical study of this phenomenon with respect to the model of underwater imaging of the sky (Snell’s window) near the image boundary. The numerical-simulation method is used to develop the statistically mean image of Snell’s window, which allows for the shadowing effects, and the corrected formula of the estimate of a wave parameter, namely, the water-surface slope variance, is obtained using the value of blurring of the boundary of Snell’s window.

Features of detection of a single crack in a plate are experimentally studied by the nonlinear acoustic modulation method provided that single defects (cracks and cavities) are located between a low-frequency (tens of kilohertz) ultrasonic transducer of Lamb waves and a high-frequency (units of megahertz) ultrasonic transducer. It is shown that using modulation of the defect characteristics by a sequence of phase-inverted Lamb waves, by the level of modulation of the high-frequency wave reflected from the defect one can determine its type (a crack or a cavity). Changing step by step the interaction region of low-frequency and high-frequency waves by varying a delay between their radiation, it is possible to study selectively the nonlinear acoustic characteristics of the defects arranged in series on the location path. Based on the obtained results, we created a combined transducer which scans a defect and modulates its characteristics simultaneously in the preset area and which is suitable for moving it by hand on the surface of a plate for seeking hidden cracks.

We propose an analytical solution of the problem of diffraction of a plane electromagnetic wave by a multilayer dielectric (including plasmon) sphere. The solution is obtained using the method of separation of variables. New efficient recurrence relationships are obtained for calculations of the fields in layers, as well as formulas for the fields in the near and far diffraction zones. The novelty of the proposed solution is connected with the way of representing its radial part in the form of normalized functions. It is shown that as the number of the lens layers, which approximate the smooth profile of dielectric permittivity, grows, the electric field at the focusing point increases and reaches the maximum value. This allows one to determine the minimum required number of layers in practical problems. Resonance properties of metal-dielectric nanoparticles are studied in the optical band.