Research of oscillation mode in automated pulsed eddy current testing systems

The formation and analysis of eddy current probe signals obtained in pulsed excitation mode is considered. The proposed method of implementing pulsed eddy current testing with the formation of attenuating harmonic oscillations is more resistant to the effects of noise and interference that accompany the process of inspected object parameters evaluation. The equivalent scheme of the system “test object–eddy current probe” is developed and analyzed. The obtained mathematical model of the eddy current probe signals allowed proposing the natural frequency and the attenuation as informative signals parameters, which are determined from signals phase and amplitude characteristics. Developed algorithm and the proposed methodology was implemented for evaluation of eddy current signals parameters and related characteristics of testing objects. This method was experimentally verified on a series of different test specimens. The obtained results confirm the possibility to apply the proposed informative signals to solve some problems concerned with automated eddy current testing. The formation and analysis of eddy current probe signals obtained in pulsed excitation mode are considered. The proposed method of implementing pulsed eddy current testing with the formation of attenuating harmonic oscillations is more resistant to the effects of noise and interference that accompany the process of automated eddy current testing. The equivalent scheme of the system “test object–eddy current probe” is developed and analyzed. The obtained mathematical model of the eddy current probe signals allows proposing the natural frequency and the attenuation as informative signals parameters, which are determined from signal phase and amplitude characteristics. Methods of increasing the accuracy of determining the eddy current probe signals attenuation and frequency using trends of signals phase and amplitude characteristics are considered. The proposed signal processing method was verified by modeling the process of determining the eddy current probe signals attenuation and the frequency from the signal with Gaussian noise. Algorithmic and software were developed based on the simulation results and the proposed improved methodology was implemented for determining signals parameters and related parameters and characteristics of testing objects.

Gallium arsenide buffer amplifier

The circuitry of a buffer amplifier (BA) implemented on gallium arsenide n-channel field-effect transistors with a control p-n junction and gallium arsenide bipolar p-n-p transistors is considered. The results of computer simulation of the amplitude characteristics of the BA in the LTspice environment are presented. The proposed circuit solutions are recommended for use in RC filters of the Sallen Key family

Gallium arsenide buffer amplifier

The circuitry of a buffer amplifier (BA) implemented on gallium arsenide n-channel field-effect transistors with a control p-n junction and gallium arsenide bipolar p-n-p transistors is considered. The results of computer simulation of the amplitude characteristics of the BA in the LTspice environment are presented. The proposed circuit solutions are recommended for use in RC filters of the Sallen Key family

Methodology for Designing Hardware for Measuring Parameters of a Digital Signal

In the production of various devices, various problems can arise, leading to the appearance of defects, both explicit and latent. This may be due to both poor quality materials and imperfect technology. To identify defects, devices are tested. If the device uses a digital signal transmission at high frequencies, it is usually considered sufficient to check the functioning of the individual components using technological programs. But at high transmission frequencies, or due to defects, the digital signal is distorted, and in devices where there is no error control, violations of the signal integrity during transmission can lead to failures and failures. Moreover, under normal conditions, the signal can meet the requirements, and in difficult conditions, go beyond the permissible limits. If an individual instance of a device can be susceptible to such failures, this can be identified in more detail by examining the signals flowing through its circuits. The most obvious way requires an oscilloscope, on the screen of which a person looks at the parameters of such a signal, time and amplitude characteristics. This is a very slow operation, so optimization might be the next step. For example, the use of flying probes, or probes with commutation, recording and automatic comparison of oscillograms with the exemplary one. In any case, these tests require equipment operating at frequencies much higher than the circuit itself, which means that at high baud rates, such equipment starts to be expensive.

Analysis of the engineering mathematical model of the physical properties of a three-layer hydroacoustic screen with anisotropic components

A numerical-analytical technique for analyzing the physical effects of the formation of fields of hydroacoustic waves in the area in front of a flat three-layer hydroacoustic screen and in the space behind the screen at normal incidence of a stationary hydroacoustic wave on it is presented. The engineering model of the screen uses the assumption that its components are made of anisotropic functional-gradient materials with exponential inhomogeneity in thickness, and thin, absolutely flexible, inextensible coatings can be applied to the outer and contact surfaces of the layers. The technique is based on the analytical integration of the equations of wave deformation of the screen components and obtaining complex amplitude characteristics for the reflected and generated hydroacoustic waves behind the screen when solving a system of algebraic equations with a functional matrix, which follows from the boundary conditions for the investigated problem. Parametric descriptions for the characteristics of the investigated physical fields are obtained and examples of numerical analysis of the considered engineering model are presented.

Studying the unsteady characteristics of a laminar transonic buffet depending on the angle of attack

Laminar transonic buffet on the airfoil for low Reynolds numbers of 0.5-0.7⋅106 was experimentally studied. Basic experiments were performed using high-speed schlieren imaging. The unsteady flow structure was investigated using various methods. It was found that shock wave oscillations can be significantly different from the turbulent case. The frequency and amplitude characteristics of oscillations from the angle of attack were found.

Dynamic modeling and simulation of a flexible-rotor ball bearing system

This work proposes a comprehensive numerical dynamic model of a flexible-rotor bearing system based on the Hertzian and cubic polynomial nonlinear contact force methods. The model can consider the influences of the nonlinear bearing contact forces and unbalanced force caused by the rotor offset. The displacements and spectrums of the flexible-rotor bearing system from the Hertzian and cubic polynomial nonlinear contact force methods are discussed. The influences of the radial clearance, eccentricity, mass, and deformation of the rotor on the frequency–amplitude characteristics of the flexible-rotor bearing system considering a large speed range are analyzed. The results show that the dynamic and vibration characteristics of the flexible-rotor bearing system from the Hertzian and cubic polynomial nonlinear contact force methods are different. The differences of the frequency–amplitude characteristics between the flexible- and rigid-rotor bearing system are small in a lower speed stage; however, their differences are very large in a higher speed stage. This method can be applied to the nonlinear dynamic modeling and simulation of the flexible-rotor bearing system, which can predict the dynamics and prevent the system failures during the design processing of rotor system.