Optoelectronics, Instrumentation and Data Processing

In this paper, we propose a solution to the problem of designing a combined output control system for a nonlinear nonaffine plant with a delay in the control loop under a priori parametric uncertainty and external interference. Simulation results confirm the performance of the control system, and the resulting controller provides tracking of the plant to the reference signal.

Application of the method of layer-by-layer selective laser sintering of a metal powder for depositing capillary-porous coatings with a prescribed porosity onto heat-releasing surfaces is considered. Implementation of this method in experimental investigations of the boiling process on modified surfaces allows broad-range variations of the main parameters of microstructured capillary-porous coatings and other three-dimensional structures: material, porosity, amplitude (height), thickness of the residual layer and wavelength of capillary-porous coatings, and size and shape of three-dimensional ordered microtextures. It is demonstrated that the use of this technology can increase the heat transfer coefficient the case of boiling on the surface with a capillary-porous coating by several times as compared to the uncoated surface.

Based on an analysis of differences between the experimentally measured temperature dependence of the current-voltage characteristic (I-V curve) of a laser diode bar (LDB) with AlGaAs/GaAs heterostructure and the dependence obtained in accordance with the well-known model of light-emitting diodes, assumptions were made about the sources of these differences. The agreement between the experimental and modeled dependences is significantly improved by taking into consideration the change in the resistance of LDB layers caused by temperature change. It is shown that when the injection current is known, the measured voltage drop across the LDB can be used to estimate the temperature of the diode active region in order to implement thermal stabilization for solid-state laser pumping systems based on high-power laser diodes.

Several approaches to the use of neural networks for object detection on spatially inhomogeneous backgrounds are considered. A method for constructing a classifier for object detection directly from observed fragments has been developed. An approach consisting of a combination of matched linear filtering and convolutional neural networks is proposed. It is shown that this approach reduces the false alarm probability while maintaining the object detection probability.

A method of fast bandwidth selection in a nonparametric algorithm of pattern recognition corresponding to the maximum a posteriori probability criterion is proposed. The algorithm is based on the results of studying the asymptotic properties of the nonparametric estimate of the separation surface equation and probability densities in solving a two-alternative problem of pattern recognition. The proposed method is compared with the traditional approach based on minimizing the classification error probability estimate.

Modern aviation industry solves the problem of developing multifunction engines capable of flying both at subsonic and supersonic speeds. An important part in such engines is a variable area nozzle, which allows varying the geometry of the engine exhaust unit and, accordingly, its technical characteristics. This study touches upon an computer vision based optical noncontact method for reconstructing a nozzle shape. The reconstruction requires data recorded by two optical three-dimensional recorders directed toward the inner part of the nozzle when the engine is subjected to ground tests. The diagnosis is complicated by the presence of a hot jet being in the way of the sensor vision, the regime-dependent variation of the nozzle glow brightness, and intense mechanical vibrations. The performed bench tests confirm the efficiency of the proposed method. According to their results, in a low-gas regime, the standard deviation of the diagnosed diameters of the exhaust unit and critical sections for each frame does not exceed 0.3% of the corresponding sizes. The data obtained as a result of this diagnosis can be taken into account when upgrading the exhaust unit of the engine and the thrust control system of a gas turbine engine.

A diffraction Fresnel method of precision measurement of diameters of circular metallic cylinders in the range from several units to hundreds of millimeters with an arbitrary coefficient of light reflection from the cylinder surface is developed. The method is based on determining the position of the first maximum in the Fresnel pattern of the object formed in the free space. An expression for the diffraction Fresnel pattern of a plane model of a cylinder fragment is derived in the class of special functions (Fresnel integrals). Based on this expression, a formula is found for taking into account the displacement of the position of the first maximum of the field as a function of the light reflection coefficient. By using an appropriate correcting additive, the measurement error component induced by this factor can be reduced by more than an order of magnitude. The results of the present study can be used for the development of optical-electronic systems of precision dimensional inspection of cylindrical articles.

A new method for image reconstruction from a series of digital holograms obtained by stepped phase shift with random values of phase shifts is under consideration. It is shown that images reconstructed from a digital hologram in a Fresnel region at a distance matching a distance from the object to the hologram consist of two parts, one of which is a clear image of the object and the other one being formed by incorrect phase shifts consists of a set of defocused images of the object. At the same time, the quality of the reconstructed image is slightly reduced. This effect eliminates the necessity to use precision systems for setting the phase shift and significantly reduces requirements for stabilizing the optical device.