Contactless electromagnetic-acoustic transducers have a set of significant advantages over contact transducers, but at the same time they have significant disadvantages that require the development of effective magnetizing devices. Compared to magnetizing devices that are using permanent magnets, electric current magnetization devices are easily removed from the object of testing and cleaned from contamination by metal particles. Unfortunately, such transducers have significant dimensions and weight.

A transducer containing a magnetic circuit magnetized by an electric current coil and two independent electromagnetic inductors located in the gap between the central part of the magnetic circuit and the object of testing has been developed. Inductors are two flat coils, each of them has form like a butterfly. The inductor conductors located in the working area have mutually perpendicular directions; they allow exciting and receiving the transversely polarized acoustic waves without rearranging the transducer. In order to reduce the overall dimensions and mass of the transducer, the mass and dimensional parameters of the magnetizing device were optimized for operating conditions when the magnetization of the object of testing and measurement are performed during the active measurement phase. During the passive measurement phase, which is three times longer than the active phase in time, the magnetizing device cools down. The cyclic mode with alternating active and passive phases made it possible to reduce the weight of the transducer by more than 3 times. In the working area of the transducer with a size of 15×15 mm, with a gap of 1 mm between the magnetic field concentrator and the object of testing, a field with a normal component of 2.4 T is created. The transducer has protection of the magnetization device from overheating, and the cyclic mode of operation allows for continuous performance of up to 30 measurements per minute at an ambient temperature of 20 °C.

The developed magnetizing device can be used in solving a number of problems of structuroscopy, thickness measurement, flaw detection by electromagnetic-acoustic methods based on accurate measurement of the propagation time of elastic waves in the object of testing.

For widely used LED sources there is a sharp decrease in the illumination of the working plane from the center to the edge. The purpose of this study was to analyze the effectiveness of Fresnel lenses usage as a fairly simple and technological element to increase the uniformity of illumination created by LED lamps of local lighting.

A method has been developed for calculating of the distribution of illumination created by the combination of “LED matrix – Fresnel lens” when the distance between the lens and the matrix is less than the focal length of the lens. Comparison of the calculation results and experiments for the case when the lens is located at a distance of 50 cm from the working plane indicates the correctness of the developed calculation method. This made it possible to use this technique to solve the problem of improved uniformity of illumination distribution in the working plane of local lighting LED sources.

It was found that the change in the distance between the matrix and the lens in the range of 0.5–1.5 cm affects the maximum illumination and its uniformity to a lesser extent than the change in focal lengths in the range of 10–100 cm. Analytical dependences of the uniformity of the working surface illumination as a function of the Fresnel lens focal length and its distance to the LED matrix were obtained for three cases. In the first case one lens is used for the entire matrix while the axes of symmetry of the light intensity curves of LEDs are parallel to the axis of the lens. In the second case one lens is also used for the entire matrix, but the continuations of the axes of symmetry of the light intensity curves pass through the front focus of the lens. In the third one an individual Fresnel lens is used for each LED. It is established that for all three cases dependencies have almost the same character. Therefore, the choice of using one of these three options may be due to manufacturability, cost-effectiveness, thermal stability, and other considerations.

Calculations using the above-mentioned analytical dependences made it possible to determine values of the parameters of the “LED matrix – Fresnel lens” system at which the indicators of illumination and uniformity meet the standards’ requirements.

Water area pollution by microplastic particles smaller than 5 mm is a serious environmental problem. Usually, studies of water pollution are carried out by taking water samples with their further analysis in the laboratory. Therefore, study of the water areas for the presence of plastic with the identification of extensive pollution sites in real time is actual.

The project of an autonomous unmanned research vehicle operating in water area and transferring the research data to the information processing center is discussed in the article. The device produces laser probing of the aquatic environment to detect polyethylene microparticles and to build maps of pollution sites in the studied water area.

To implement the proposed project, the following tasks are solved:

• detection of plastic microparticles in the studied volume of the water environment where particle sizes are several orders of magnitude smaller than the studied water volume;
• identification of microparticles in presence of particles of other types of substances in the investigated water environment volume;
• estimation of the number particles’ in the studied water environment

A new approach which consists in creating an autonomous microboat that explores the water area along a route set from a control center located on the shore is proposed. The study involves the detection of microparticles in a certain volume of liquid flowing through a research tube installed in the bottom of the boat. There is a Schauberger tube in the central part of which particles are concentrated inside the tube. It makes possible to search for particles by laser probing with a wavelength about 3.5 μm, on which the peak absorption of light by polyethylene many times exceeds the water absorption.

To ensure the energy efficiency of the microboat it is proposed to use a scheme for laser pulses combining using a fiber-optic delay line. This makes it possible to reduce the power consumption of the laser by almost an order of magnitude. The proposed project of the boat will make it possible to conduct studies of large water areas with the detection of plastic microparticles’ pollution sites. Examples of the used optical fiber, photodetector and laser source for the problem being solved are derived in the article.

Study of the stress field in a plastic imprint and around it is of great practical importance. Processes similar to indentation are used in shot blasting to harden the surface of materials and generate compressive stresses in the surface layers. The purpose of this work was to study the change in the stress-strain state in the area of the plastic imprint with increasing load, in the transition from small to large deformations, as well as to study the change in stress at different strain rates.

X-ray diffraction method was used to study the field of residual stresses generated on the surface of a plastically deformed region – in the zone of an imprint formed when a spherical indenter is pressed into the metal. An analysis of the change in the stress distribution with increasing load in the range of plastic imprint depths of 10–60 µm for steels and aluminum was made. Influence of the loading rate on the change in the values of residual stresses under normal contact of colliding bodies was studied. It is shown that the stress distribution has a complex character with areas of compression and tension of the metal and is determined by the ratio of the indentation depth to its diameter.

The obtained experimental data make it possible to determine the choice of optimal modes of shot blasting, including for increasing the endurance limit of products.

Diagnostic methods applied in the industry do not allow to control the state of electrical machines windings in working condition and to fix the defect formation in them at the early stages of development. The aim of the work was to develop a method and construct a device that allows measuring interturn resistances in the electrical machines’ windings without the need to remove it from the technological process, and thereby assess its current and future performance.

A block diagram of a device for measuring of interturn resistances in the electrical machines’ windings has been developed, a method has been described, and an algorithm for carrying out diagnostic procedures has been developed. Also, as a result of the study, mathematical dependencies were determined that characterize the main operations performed by the device and a mathematical model was developed for obtaining of the interturn resistance value in the diagnosed windings from the value of the measured phase difference for the AIR63V4U3 asynchronous motor.

The developed method and a device based on it allow measuring interturn resistances in the electrical machines’ windings without the need to remove it from the technological process and fix the beginning of defect formation, and, thereby, evaluate its current and future performance in real time.

Surface electric potential measurements are widely used in non-destructive inspection and testing of precision surfaces, for example, in the production of semiconductor devices and integrated circuits. Features of the construction and application of devices for measuring the surface electric potential using an immovable reference electrode are considered. Despite the need to increase the area of the probe compared to devices with a vibrating probe, measurement techniques with an immovable probe have a number of advantages and could expand the scope of surface electric potential measurements in the inspection of samples with precise surfaces. Models of the formation of a measuring signal in the presence of a spatial inhomogeneity of surface electric potential are presented and discussed.

Highly loaded transmission gears are cemented and hardened. An important parameter of the hardened cemented layer is its effective thickness h_ef . Metal banding and the unavoidable instrumental error in hardness measuring have a great influence on the reliability of h_ef determination. The purpose of this article was to develop a methodology to improve the reliability of determining of the effective thickness h_ef of the hardened layer in steel after carburizing and quenching.

The value of h_ef is the distance h from the surface of the product to the hardness zone of 50 HRC. The article substantiates that approximation of hardness change from the distance h to the product surface will allow to obtain a more reliable dependence of hardness change in the investigated area when making hardness measurements in a wider range of distance h. Therefore, to increase the reliability of h_ef determination, results of the HV0.5 hardness measurement in an extended range of changes in h in the vicinity of the analyzed zone were used. The HV0.5 measurement results are converted to HRC hardness values using the formula recommended by the international standard. The HRC(h) distribution of HRC hardness values in the measurement area is interpolated by a second-degree polynomial which physically correctly reflects the change in metal hardness in the analyzed area. The resulting polynomial is used to determine of the distance h_ef at which the hardness takes on a value of 50 HRC. The methodology was used to determine the h_ef of an 18KhGT steel gear wheel after carburizing and quenching. It is shown that results of two independent measurements of the h_ef sample differ from each other by 0.003 mm. This is significantly less than the permissible error of 0.02 mm of the h_ef determination according to the standard technique. The error of hef determination is reduced by extending the range of variation of h and statistically valid interpolation of the monotonic change in hardness with the distance from the surface of the item in the measurement area. The developed method of determining the effective thickness h_ef of the hardened steel layer consists in determining the distribution of its hardness in the expanded vicinity of the h_ef area, approximating the obtained dependence by a polynomial of the second degree and solving the square equation obtained with its use. The technique provides a significant reduction in the influence of the structural banding of the metal and the inevitable error in measuring hardness on the result of determining the h_ef . Its application will allow to optimize the cementation regimes of gear wheels to increase their service life.