V. K. Kachanov

APPLICATION OF SIGNAL PROCESSING METHODS TO ULTRASONIC NON-DESTRUCTIVE TESTING OF ARTICLES WITH HIGH STRUCTURAL NOISE

This article describes the methodology of signal processing in ultrasonic nondestructive testing of materials with structural heterogeneities. Reflections of probing signal from these heterogeneities entail appearance of a peculiar interference a structural noise witb the same spectral composition as the probing signal. Therefore, it is hard to overcome these interferences. The article also discusses the methodology of recognising the signal on the background of structural noise in ultrasonic non-destructive testing using spatially dispersed transducers, focusing antennae, antennae with synthesised aperture, and the most efficient method spatialtemporal signal processing, which suggests multichannel reception of probing signal combined with optimal signal filtration in each channel.

Problems of extracting ultrasonic signals from structural noise during inspection of articles produced from materials with complex structures

Problems of ultrasonic testing of materials with complex structures are considered. Such problems arise owing to a correlated interference—structural noise (SN). The simplest models describing the formation of SN are analyzed, and static noise characteristics are determined for them. The main concepts that define the parameters of SN are introduced. The requirements imposed on the procedure of discriminating echo signals from a flaw against a correlated-noise background are determined.

The Fundamentals of the Theory of Spatiotemporal Signal Processing as Applied to Problems of Ultrasonic Flaw Detection of Articles from Complexly Structured Materials

The basic propositions of spatiotemporal signal processing as applied to the problems of ultrasonic testing of complex-structure articles with a high attenuation of acoustic signals are considered. Different algorithms of extracting informational echo signals from white and structural noise during multichannel spatiotemporal signal processing are studied.

Development of a broadband low-frequency mosaic ultrasonic piezoelectric transducer with a limited aperture

Broadband low-frequency mosaic ultrasonic piezoelectric transducers with apertures comparable with acoustic wavelengths, which are designed as sets of acoustically coupled piezoelectric elements of different heights, are considered. Examples of small-aperture broadband mosaic transducers and their production technology are presented.

Ultrasonic structural probing of products based on materials with a complex structure by analyzing the statistical characteristics of the structural noise

It is shown that during ultrasonic control of products that are made of materials with a complex structure (cast iron, concrete, and bronze) the use of ultrasonic signals with a wavelength that is comparable to the sizes of the acoustic irregularities in a material induces the combined reflection of an ultrasonic probing signal from structural irregularities, which masks the reflections from the initial defects of the product. The combined reflected signal is correlated with the probing signal; in ultrasonic defectoscopy of products it has to be considered as interference that masks the echo signals from the initial defects of the product. At the same time, it provides information on the structural state of a studied material. In this work we consider the model of a complex material with a random structural irregularity distribution, for which the statistical characteristics of the combined reflected signal, viz., the density of the structural-noise probability, dispersion, and energy spectrum, are determined. We propose a new method for defining the structural state of a complex material by analyzing the statistical characteristics (energy spectrum and dispersion) of the structural noise.The experimental results on the analysis of the statistical characteristics of the structural noise are discussed for cast-iron products, allowing the structural state to be detected and monitored during their operation.

Detection of reflecting planes in ultrasonic tomography of concrete building structures

The features of algorithms for identifying the configurations of reflecting objects (points, spheres, planes, cylinders, etc.) in ultrasonic tomography of complexly structured concrete products are considered. The results of a practical solution to the problem of recognizing a pattern and determining the coordinates of a flat reflector using ultrasonic phased antenna arrays are presented for the example of applying the algorithm of focusing to a plane.

Choosing parameters of space-time signal processing in ultrasonic structuroscopy of cast-iron molds subjected to thermal cycling

It is shown that in order to improve the accuracy of measuring the speed of ultrasonic vibrations in cast-iron products by echo-pulse method, one should use noise-immune space-time echosignal processing methods that improve signal–to–pattern-noise ratio. Signal parameters should also be adapted for characteristics of the test object. Requirements for the choice of probing-signal parameters have been established as well as optimum displacement step of a double-crystal transducer. The value of the speed of ultrasound at a time moment that precedes the destruction of cast-iron mold has been determined.

Adaptive instruments for ultrasonic nondestructive testing of large objects with complex structures

An ultrasonic multifunctional adaptive measuring complex, which is built on the basis of a personal computer and algorithmically generates various simple and complexly modulated probing signals, is described. This system implements various radio-engineering algorithms for processing echo signals (storage, optimal filtering, synchronous detection, etc.) and provides adaptation of the signal parameters to the characteristics of inspected objects. Using the example of a frequency-modulated signal, it is shown that an adaptive measuring complex can increase the testing reliability and provide high sensitivity and high resolution owing to both the adaptive adjustment of the parameters of a probing signal and the compensation for distortions in the received signal in the electroacoustic path.

Comparison of the features of composite and mosaic piezotransducers for the ultrasonic testing of products with a high attenuation level of ultrasonic signals

The problem of the creation of stacked (mosaic and composite) broadband transducers that simultaneously provide a broad band and a high electroacoustic transduction efficiency is analyzed. The mosaic technology is shown to be optimal for the practical implementation of ultrasonic broadband low-frequency electroacoustic transducers. Being functionally flexible, the mosaic technology allows the development of numerous variants of electroacoustic transducers for the solution of different ultrasonic testing problems and, first of all, for the undistorted transduction of signals.

Synthesis of low-frequency broadband ultrasonic mosaic transducers with nondistorting spatiotemporal characteristics

It is shown that the spatial distribution of the acoustic field of a broadband transducer may influence the degree of distortion of ultrasonic signals. The principle for forming a uniform acoustic-field distribution within the directivity characteristic of a low-frequency broadband transducer based on the chosen topology of a mosaic transducer is proposed. The comparative spatiotemporal characteristics of mosaic broadband transducers with optimized and nonoptimized mosaic topologies are obtained as a result of simulation. It is shown that for an optimized topology uniform field distributions can be obtained in both far- and near-field zones of the broadband transducers.