The use of complexly modulated signals during ultrasonic testing of articles with high integral ultrasonic attenuation is substantiated. On the basis of concepts of the optimal-filtering theory, ...phase-manipulated and frequency-modulated signals most suitable for ultrasonic testing are chosen and the main characteristics of various complexly modulated signals are analyzed. The advantage of using phase-manipulated and frequency-modulated signals in ultrasonic flaw detection for ensuring a high testing resolution and a high sensitivity is shown. It has been revealed that the application of state-of-the-art circuitry components allows the use of various properties of complexly modulated signals and creation of new ultrasonic methods and devices on this basis.
Some problems that are encountered in the ultrasonic pulse-echo thickness gauging of large concrete building structures with high frequency-dependent ultrasound attenuation and a complicated ...nonuniform structure are considered. It has been shown that ultrasonic signals with complex modulation with further optimal filtering of echo signals should be used in single-channel testing to increase the sensitivity during the testing of concrete articles and to enhance echo signals in the presence of white noise. Synchronous detection of echo signals is advisable to increase the precision of measurements. Multichannel spatial–temporal signal processing via thickness measurements at several neighboring points of an article and further coherent summation of partial measurement results should be used to enhance ultrasonic echo signals in the presence of structural noise. However, it is recommended that the multichannel testing of concrete articles with a nonuniform volumetric distribution of physicomechanical properties be performed with the summation of partial echo-signal envelopes after their synchronous detection due to the broad spread of ultrasonic signal velocities in neighboring regions.
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.
We report on a direct search for sub-GeV dark photons (A^{'}), which might be produced in the reaction e^{-}Z→e^{-}ZA^{'} via kinetic mixing with photons by 100 GeV electrons incident on an active ...target in the NA64 experiment at the CERN SPS. The dark photons would decay invisibly into dark matter particles resulting in events with large missing energy. No evidence for such decays was found with 2.75×10^{9} electrons on target. We set new limits on the γ-A^{'} mixing strength and exclude the invisible A^{'} with a mass ≲100 MeV as an explanation of the muon g_{μ}-2 anomaly.
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.
New methods and devices for acoustic testing of large-size (>1.5 m) concrete building structures (foundations, walls of buildings, airfield pavements, bridge pillars, slabs, blocks, beams, etc.) ...based on the use of methods of free and forced vibrations are reviewed. Problems of inspection of large-size compact concrete building structures by the impact-echo method are considered.
A new method of measuring the velocity of acoustic waves in large-size concrete products is considered, based on the use of eigenfrequency methods. It is shown that it is necessary to monitor the ...velocity at several points on the surface of the article with subsequent calculation of the degree of cross correlation of the experimental and theoretical spectral characteristics for each measurement.
Methods for extracting ultrasonic echo signals from interferences (electroacoustic interference and structural noise) correlated with a probing signal are studied in detail. These methods are based ...on the frequency separation of the spectra of the informative signal and noise. Frequency-separation methods involving lock-in signal detection are considered. Various aspects of using a lock-in detector in flaw detection and tomography of complexly structured articles are analyzed. Examples of applying the frequency decorrelation of signals in ultrasonic testing of large old cast bronze bells of the Ivan the Great Bell Tower in the Moscow Kremlin and large bells of the Cathedral of Christ the Savior in Moscow are considered.
The main principles of spatiotemporal processing of signals during ultrasonic testing of articles manufactured from complexly structured materials with high signal attenuation are considered. ...Features of ultrasonic low-frequency testing limiting the application of the simplest algorithms for spatiotemporal signal processing in both ultrasonic flaw detection and ultrasonic tomography of articles manufactured from complexly structured materials are analyzed.
It is shown that the quality of transformation of ultrasonic signals in a broadband transducer is affected by not only the amplitude-frequency but also the spatial characteristics of broadband ...probes. To evaluate the quality of transformation of ultrasonic broadband signals, integral spatiotemporal characteristics of a broadband probe are introduced, viz., the correlation field distribution and the correlation directivity characteristic. The experimental correlation spatiotemporal characteristics of a mosaic low-frequency broadband transducer are presented.
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