Time Reversal Acoustics (TRA) provides a way to focus ultrasound in space and time. Standard TRA focusing system produces tone burst signal with a frequency band lim- ited by the bandwidth of the transducer. For certain medical... more
Time Reversal Acoustics (TRA) provides a way to focus ultrasound in space and time. Standard TRA focusing system produces tone burst signal with a frequency band lim- ited by the bandwidth of the transducer. For certain medical applications, both in therapy and imaging, a wider bandwidth is required. The goal of this study was to explore a possibility to generate shorter pulses less affected by the limited bandwidth of the transducers of the TRA focusing system. We proposed and tested a technique named "pseudo impulse response (pIR) method" which provides significant extension of the TRA focusing system bandwidth. In addition, the suggested method leads to a decrease of the spatial side lobes and also facilitates the task of creating multiple ultrasound foci. Index Terms—Time reversal acoustic, focusing, short pulse, pseudo impulse response.
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Time-reversal acoustic (TRA) focusing systems are typically based on an acoustical resonator (a cavity) in which the multiple reflections of a bouncing acoustic pulse act as a virtual phased array. The efficiency of the TRA focusing... more
Time-reversal acoustic (TRA) focusing systems are typically based on an acoustical resonator (a cavity) in which the multiple reflections of a bouncing acoustic pulse act as a virtual phased array. The efficiency of the TRA focusing system depends on the spectral and temporal parameters of the focused pulse and parameters of the resonator, such as its shape, size, and the relative position of its transducers. The acoustical properties of the resonator material, parameters of the sonicated medium, and the coupling of the TRA resonator and sonicated medium may also affect efficiency. Optimization of such a multiparametric system is a complex problem which is nearly impossible to achieve empirically without an adequate theoretical model. A theoretical model for predicting the efficacy of TRA focusing has been developed and experiments testing theoretical predictions were conducted. The experiments were conducted using a 10-channel TRA system developed in Artann with several broadband resonators in the frequency band of 0.1–2 MHz. The measured dependences of the focused signal on the acoustic pulse spectrum and duration, coupling of the resonator with the sonication medium, and the modes of TRA signal formation (analog or binary) confirmed theoretical predictions. [Work supported by NIH.]
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Research Interests: Mechanical Engineering, Applied Mathematics, Physics, Acoustics, Optics, and 13 moreUltrasound, Impulse response, Deconvolution, Time Reversal, Transfer Function, Frequency Modulation, Ultrasonic Sensor, Amplitude Modulation, Amplitude, Direct Method, Ultrasonic Transducer, Waveform, and piezoelectric sensor
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Concerns about improper use of Unmanned Aerial Vehicles (UAVs, also unmanned aerial systems or UAS) led to the development of various methods for their detection, tracking, and classification. One of the methods is using acoustics.... more
Concerns about improper use of Unmanned Aerial Vehicles (UAVs, also unmanned aerial systems or UAS) led to the development of various methods for their detection, tracking, and classification. One of the methods is using acoustics. Advantages of passive acoustics include the low cost of acoustic systems, finding of the Direction of Arrival (DOA) and localization by simple means; and classification of UAV sounds by acoustic signature. Stevens Institute of Technology has developed and built the Drone Acoustic Detection System (DADS) that can detect, track and classify UAVs based on the propeller noise. The system consists of three or more microphone nodes. The microphones in each node are arranged in a tetrahedron with configurable size. The microphone data is transferred over WiFi in real-time to a central computer, where it is processed. The Stevens DADS system was investigated in numerous field tests together with several other directional arrays including a 16-channel two-tier cross array, the OptiNav 40-microphone phased array, and parabolic and shot gun microphones. Multirotor UAVs of different sizes were employed in testing, including DJI models Phantom 4, M600 and S1000. The test results of the different systems were compared.
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Stevens Institute of Technology has been conducting development and field tests of various underwater passive acoustic systems for several years. Several such systems provided localization of boats and divers triangulation. The new... more
Stevens Institute of Technology has been conducting development and field tests of various underwater passive acoustic systems for several years. Several such systems provided localization of boats and divers triangulation. The new version of SPADES has a tethered low-cost bottom-mounted circular 2.2-m underwater acoustic array with eight custom-built hydrophones. The cost of the array was significantly reduced by manufacturing the hydrophones in-house and utilizing a lightweight and low-cost tether. The tether can provide power and communication up to 1 km away and power to the data acquisition. The software has been developed for real-time direction-finding using Steered Power Response Phase Transform (SRP-PHAT) method, combined with region-zeroing (RZ) approach to multi-source separation and custom noise background estimation subtraction. The array was tested for seven months in the shallow and busy waters of the Hudson River tracking small boat activity. The system’s reliability...
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Stevens Institute of Technology (SIT) designed and built multiple acoustic sensors to detect and track drones using Steered-Response Phase Transform (SRP-PHAT) and classify them using narrow-band frequencies. SIT improved a previously... more
Stevens Institute of Technology (SIT) designed and built multiple acoustic sensors to detect and track drones using Steered-Response Phase Transform (SRP-PHAT) and classify them using narrow-band frequencies. SIT improved a previously built four-microphone system by increasing the number of microphones to seven, modifying the software, and improving the testing algorithm for system performance estimation. The four- and the seven-microphone systems were deployed during several tests conducted with multi-rotor UAVs of different sizes, including the DJI Inspire 2, DJI Mavic 2 Pro, Autel Robotics EVO II Pro, and the Intel Falcon 8 performing flight patterns at various distances, elevations, and speeds. The tests were conducted in an environment with low-flying aircraft and vehicular traffic noise. Acoustic signatures were collected and detection distances were compared for the tested UAVs. The improved seven-microphone system provided farther detection and classification distances than ...
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Stevens Institute of Technology has conducted extensive long-term testing of acoustic systems designed to track low-flying small aircraft in remote location and recorded over 2 years of data. The system consisted of 4 nodes placed in... more
Stevens Institute of Technology has conducted extensive long-term testing of acoustic systems designed to track low-flying small aircraft in remote location and recorded over 2 years of data. The system consisted of 4 nodes placed in difficult remote terrain with separation ranging 1–4 km, each node comprising a pyramid-shaped volumetric cluster of 5 microphones an embedded computer, and a pan-tilt-zoom camera steered to detected targets in real time. and communication device. Each nodes' computer performed direction of arrival finding communicated to a central computer collected that data and processed it to generate tracks and classify targets. The duration and the scale of the deployment allowed to identify and solve many problems, including the effects of propagation delays between station and on cooperative localization and tracking, the seasonal changes in environmental noise, persistent and transient noise sources, and the diversity of targets of opportunity and their sig...
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Stevens Institute of Technology conducted a long-term test of an acoustic system designed to track low-flying small aircraft in remote locations. The system consists of 4 nodes located between 1 and 4 km apart in a mountainous terrain.... more
Stevens Institute of Technology conducted a long-term test of an acoustic system designed to track low-flying small aircraft in remote locations. The system consists of 4 nodes located between 1 and 4 km apart in a mountainous terrain. Each node is comprised of a pyramid-shaped volumetric cluster of 5 microphones, an embedded computer, and a pan-tilt-zoom camera steered to detected targets in real time. A communication device was used to transfer data to a centralized location. Each node estimates the direction of arrival toward the sound sources and sends it along to a central processing computer. The central computer combines the data from all nodes to generate tracks and classify targets. The duration and the scale of the deployment allowed to identify and solve many problems, including the effects of propagation delays between nodes on cooperative localization and tracking, the seasonal changes in environmental noise, persistent and transient noise sources, and the diversity of targets of opportunity and their signatures. The propagation delay effects led to the development of separate trackers for review of target trajectories and for immediate action such as automatically steering the camera.
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Stevens Institute of Technology has been investigating engineering solutions to augment the current inspection process at ports of entry in an effort to minimize the threat posed by invasive species. Stevens has built several sensitive... more
Stevens Institute of Technology has been investigating engineering solutions to augment the current inspection process at ports of entry in an effort to minimize the threat posed by invasive species. Stevens has built several sensitive acoustic systems for detection of tiny acoustic/vibrational signals produced by moving insects and tested them in two US ports of entry and at the USDA APHIS PPQ S&T facility in Buzzards Bay, MA. The system for insect detection in vegetables and herbs uses a soundproofed case where boxes filled with vegetables or herbs were placed during the test. For wood boring insects, sensitive custom-made accelerometers were built. Special algorithms for detection of events connected with insect movement and separating them from the ambient noise were developed. The tests demonstrating the system ability for insect detection were conducted with several representative insects, including: Khapra beetles in rice, Copitarsia larva and Helicoverpa zea in a large box of vegetables, and Asian Longhorned Beetles and Emerald Ash Borers in wood.
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Stevens Institute of Technology has been investigating solutions for instrumental detection of invasive species at ports of entry. Stevens has built several acoustic systems for detection of acoustic/ vibrational signals produced by... more
Stevens Institute of Technology has been investigating solutions for instrumental detection of invasive species at ports of entry. Stevens has built several acoustic systems for detection of acoustic/ vibrational signals produced by insects. This paper presents acoustic signals recorded in tests conducted in APHIS Otis Lab using tree bolts infested by Asian Longhorn Beetle, ALB and Emerald Ash Borer, EAB larvae. The analysis of the recorded sounds extracted the signal features that allowed larval classification. These features include frequencies of the generated pulses, their durations and frequencies of pulse envelops. These features showed a clear separation of ALB and EAB. For example, the main frequency of the ALB sound was in the range of 3.8–4.8 kHz, while for EAB it was between 1.2 and 1.8 kHz. A preliminary algorithm for automated insect signal detection was developed. The algorithm automatically detects pulses with parameters typical for the larva-induced sounds and reject...
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Acoustics methods for Unmanned Aerial Systems (UAS) detection have several advantages. They are low cost and passive, do not radiate any RF signals, and can provide UAS classification. The disadvantages of acoustic methods include shorter... more
Acoustics methods for Unmanned Aerial Systems (UAS) detection have several advantages. They are low cost and passive, do not radiate any RF signals, and can provide UAS classification. The disadvantages of acoustic methods include shorter detection distances and susceptibility to acoustic noise. We present the results of field tests of several acoustic UAS detection methods. The tested systems included the Drone Acoustic Detection System (DADS) that was developed by Stevens Institute of Technology, a 16 microphone cross two-tier acoustic array, directional acoustic microphones (parabolic and shotgun microphones), and the OptiNav ACAM 120 acoustic array. The field tests were conducted to investigate the performance of various acoustic systems for UAS detection and tracking ability of various DJI models. Directional microphones and systems with many microphones did not demonstrate a significant advantage over the lower cost DADS that consists of three nodes, with each node having four...
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Stevens Institute of Technology has applied the cross-correlation method for the detection of low flying aircraft using passive acoustics. A modified cross correlation method was tested for finding the time difference of arrival of... more
Stevens Institute of Technology has applied the cross-correlation method for the detection of low flying aircraft using passive acoustics. A modified cross correlation method was tested for finding the time difference of arrival of acoustic signals from various unmanned aerial vehicles (UAV), collected by NASA’s Langley Research Center. Cross-correlation was applied for UAV detection and for measurements of the time difference of arrival that is used for estimating the direction of arrival. The microphone separation combined with the high speed of the target had led to a significant differential Doppler effect leading to de-correlation of the received signals. For the compensation of those effects, Stevens applied a modified de-skewed short-time correlator (DSTC) approach. The detection ability of the cross-correlation method also depends on the cross correlation properties of ambient noise. The collection was performed in a relatively quiet area, to estimate the performance of the ...
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Stevens Institute of Technology, in cooperation with the DHS Science and Technology Directorate and the U.S. Customs and Border Protection, has been investigating engineering solutions to augment the current inspection process at ports of... more
Stevens Institute of Technology, in cooperation with the DHS Science and Technology Directorate and the U.S. Customs and Border Protection, has been investigating engineering solutions to augment the current inspection process at ports of entry in an effort to minimize the threat posed by invasive species. Stevens has built several sensitive acoustic systems for detection of tiny acoustic/vibrational signals produced by moving insects and tested them in a Laredo, TX port of entry. The system for detection of insects in vegetables and herbs uses a soundproofed case where boxes filled with vegetables or herbs were placed during test. For wood boring insects, sensitive custom-made accelerometers were built. Special algorithms for detection of events connected with insect movement and separating them from the ambient noise were developed. Tests conducted demonstrated reliable detection of Copitarsia larva in a large box of vegetables. Smaller insects similar to Khapra beetles were clear...
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Stevens Institute of Technology in cooperation with the DHS Science and Technology Directorate and the U.S. Customs and Border Protection has been investigating engineering solutions to augment the current inspection process at ports of... more
Stevens Institute of Technology in cooperation with the DHS Science and Technology Directorate and the U.S. Customs and Border Protection has been investigating engineering solutions to augment the current inspection process at ports of entry in an effort to minimize the threat posed by invasive species. This paper presents the initial results of acoustic sensors application detection of rodents and small insects in grains with the goal of improving the accuracy and effectiveness of current manual inspection methods.
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A test bed was developed for Plum Island, NY experimental multi-sensor security surveillance. The system includes broadband radars, cameras, an Automatic Identification System receiver, geophones and underwater passive acoustic sensors.... more
A test bed was developed for Plum Island, NY experimental multi-sensor security surveillance. The system includes broadband radars, cameras, an Automatic Identification System receiver, geophones and underwater passive acoustic sensors. The sensors were grouped into nodes connected to a Command and Control Center via a Wi-Fi network. Some sensors are COTS, some were developed and built by Stevens Institute of Technology. Sensor network was tested for the detection of potential surface and underwater intruders. This paper presents a system description and sensor performance estimations for various targets, including jet skis, small boats, kayaks, and divers. The system design performance versus cost considerations and methods of sensor integration are discussed.
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Standard approach to aircraft classification in acoustic sensor networks is based on propeller blades rotation harmonics and fundamental frequency analysis. However, propeller blades induced sound is not the only sound producing... more
Standard approach to aircraft classification in acoustic sensor networks is based on propeller blades rotation harmonics and fundamental frequency analysis. However, propeller blades induced sound is not the only sound producing mechanism. As a result, aircraft of different classes (small plane, helicopter, and ultralight aircraft) often provide similar acoustic signatures in the spectral domain. We present new feature extraction methods beyond the spectral peaks-based ones. First, general feature extraction considerations are reviewed. Then features are described including harmonic-based feature, a feature based on Lloyd's mirror multi-path propagation effect, and a feature based on sound spikes caused by propeller blades interaction with flow vortices. Experiments are provided to justify the efficiency of the proposed features for target classification.
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The availability of Unmanned Aerial System (UAS) to consumers has increased in the recent years, with it came the potential for negligent or nefarious misuse of them. Stevens Institute of Technology has built a passive acoustic system for... more
The availability of Unmanned Aerial System (UAS) to consumers has increased in the recent years, with it came the potential for negligent or nefarious misuse of them. Stevens Institute of Technology has built a passive acoustic system for low flying aircraft detection, the application of the developed principles and algorithms for UAS acoustic detection and tracking is presented in this paper. The application of the developed principles and algorithms for UAS acoustic detection and tracking is presented in this paper. Several experiments were conducted aiming to establish the characteristics of the emitted noise of UAVs of various sizes while airborne and demonstrate the processing required to detect and find the direction toward the source. The vehicles tested included popular quadrotors: DJI Phantom 2 Vision + , 3DR Solo, DJI Inspire 1 as well as larger semi-professional vehicles: Freefly Alta 6, DJI S1000. The small array of 16 microphones was used for data collection in the test...
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Feature based passive acoustic detection of underwater threats
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Small boats represent a particular challenge to maritime surveillance due to their ubiquity, low radar cross-section, and absence of AIS transmission. We present a review of previously developed acoustic classification methods and... more
Small boats represent a particular challenge to maritime surveillance due to their ubiquity, low radar cross-section, and absence of AIS transmission. We present a review of previously developed acoustic classification methods and demonstrate the importance of both the engine, and propeller as the two sources of small vessel noise. The features used for classification are extracted using various signal processing methods including signal spectra, spectra of Detection of Envelope Modulation on Noise (DEMON), and Cepstrum. The normalization of the features allowing to remove the dependence of the parameters on the distance to a boat and its speed was conducted. Acoustic signatures of six small boats including a panga, a jetski, an electrical boat, a go fast boat and two speed boats of the type common in the United States were collected by Stevens in a large glacial lake in NJ. The sound sources of various tonal components in the signal spectra are discussed. The program for automated extraction of classific...
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Assessments of wind turbine generator (WTG) noise are required to comply with the US Environmental Agency and local governments and avoid legal action that may result of non-compliant operation. Current methods for WTG noise measurements... more
Assessments of wind turbine generator (WTG) noise are required to comply with the US Environmental Agency and local governments and avoid legal action that may result of non-compliant operation. Current methods for WTG noise measurements require the comparison of long-term sound data recorded before and after a WTG installation. These measurements must be conducted during several months for various wind speeds and environmental conditions. Such measurements are complicated due to the presence of multiple sources other than noise not from WTG, including intermittent and fluctuating sources. The application of directional processing can help localize and identify the sources responsible for increased sound levels at any given moment and to estimate the contribution of the other than WTG sources to the whole sound level. Stevens has developed various acoustic systems with several sensors that provide directional processing of sounds that were previously applied for detection, tracking ...
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This paper presents a new method of signal processing for vibro-acoustic modulation (VAM) methods in order to detect damage accumulation in steel samples. Damage in the tested samples was produced by cycle loading, which, with a small... more
This paper presents a new method of signal processing for vibro-acoustic modulation (VAM) methods in order to detect damage accumulation in steel samples. Damage in the tested samples was produced by cycle loading, which, with a small amplitude, was used as a pump wave to modulate an ultrasonic probe wave. Multiple sideband peaks were observed, which were used to characterize the modulation effect. We propose the effectiveness sideband peak number (SPN) method as an indicator of any damage accumulation when the load cycle is applied. Moreover, after comparing the SPN with the previously used modulation index (MI), we concluded that, for some of the samples, the SPN provided better damage indication than the MI. The presented results can be explained by a simple model of bilinear crack nonlinearity. This model demonstrates that the amplitude dependences of the sideband components on the pump and the probe wave amplitudes are very different from the quadratic crack model that is usual...
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The following study presents the acoustic aircraft detection system designed for automated detection, classification and tracking of low-flying aircraft using a network of passive acoustic sensors. The system consists of multiple... more
The following study presents the acoustic aircraft detection system designed for automated detection, classification and tracking of low-flying aircraft using a network of passive acoustic sensors. The system consists of multiple autonomously powered sensor nodes, each equipped with a microphone cluster, cameras and electronics that perform pre-processing and transmit the results wirelessly to a central processing station. The station fuses the data from sensors for finding the direction of arrival (DOA) of aircraft sounds then uses triangulation techniques for the target localisation. The calculated tracks were used for steering the cameras to the acoustically tracked target to capture pictures. The extended test spanning more than two years has uncovered many challenges that are part of such deployment including the impact of the weather, natural and man-made interfering sources of noise, effects of terrain and the variety of types and modes of operation of the targets of interest. During the deployment period, the system detected a significant number of targets of interest. Several control tests with different aircraft providing ground truth GPS for comparison with the acoustic tracking was also conducted.
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The Acoustic Aircraft Detection (AAD) system developed by Stevens Institute of Technology for the detection of small aircraft in remote border areas was tested for tracking small aircraft in the airport. The goal of the test was to... more
The Acoustic Aircraft Detection (AAD) system developed by Stevens Institute of Technology for the detection of small aircraft in remote border areas was tested for tracking small aircraft in the airport. The goal of the test was to demonstrate a proof-of-concept capability for the acoustic sensor when applied to tracking aircraft during take off, landing, or taxing in a small airport. Two AAD nodes with five microphones were used to find the direction of arrival of sound produced by an aircraft using time-difference of arrival to pairs of sensors and to localize those by triangulation in real time. Additionally, a portable acoustic recorder system (PARS) with three microphones arranged in a ground plane was deployed to provide more data for post-processing analysis. The nodes separation varied between 150 and 250 m in different experiments. During the two-day experiment, aircraft activity of regular airport traffic was observed. At least 14 different aircraft were recorded during various movement on airpo...
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ABSTRACT
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The experimental setup for precision acoustic measurements of the elastic tensor of structurally inhomogeneous materials has been designed and fabricated. The achieved accuracy of measurements is high enough for studying a fine structure... more
The experimental setup for precision acoustic measurements of the elastic tensor of structurally inhomogeneous materials has been designed and fabricated. The achieved accuracy of measurements is high enough for studying a fine structure of rocks. It is shown that resonant acoustic spectroscopy is a useful tool for measuring the small content of oriented microcracks that can be used for diagnostics
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The ability of a single-channel time reversal acoustic systems to focus and receive ultrasound radiation is considered. The basic element of these systems is a liquid-filled acoustic reverberator. Two types of the reverberators have been... more
The ability of a single-channel time reversal acoustic systems to focus and receive ultrasound radiation is considered. The basic element of these systems is a liquid-filled acoustic reverberator. Two types of the reverberators have been experimentally studied; one of them is a thin-wall cylindrical balloon used in ultrasound catheters for treatment of cardiac fibrillation, and the other consists of plane-parallel foil layers. It is demonstrated that such systems can effectively focus ultrasound using only one radiation channel. Random deformation of balloon walls and foil layers leads to a noticeable improvement of focusing quality and helps to overcome the limitations imposed by a spatial symmetry of a system. The use of a binary radiation mode increases the focal field intensity as compared to the conventional mode. The possibility of spatial localization of external sources with the use of the time reversal focusing system as a receiver is demonstrated.
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ABSTRACT General approaches to solving the problem of nonlinear acoustic spectroscopy of defects in geomaterials are considered. Expressions that relate the nonlinear response (scattering at combination frequencies) to the position,... more
ABSTRACT General approaches to solving the problem of nonlinear acoustic spectroscopy of defects in geomaterials are considered. Expressions that relate the nonlinear response (scattering at combination frequencies) to the position, orientation, and nonlinear characteristics of narrow cracks are obtained. The expressions describe a broad class of nonlinear interactions at a crack. The nonlinearity caused by the contact of uneven rough edges of a crack is analyzed in detail. The results of the analysis are compared with the results obtained earlier from considering micromechanical models and with experimental data. The satisfactory agreement between the theoretical and experimental values of Landau’s moduli suggests that the mechanism of contact nonlinearity may manifest itself in the process of fracture of polycrystalline rock, when narrow cracks with uneven edges are formed. Numerical examples demonstrate the possibility of determining the orientation and position of a narrow crack. The procedure of solving the problem of crack localization is illustrated by the example of a crack in a thin rod. The importance of taking into account the phase data in the determination of the crack coordinate is pointed out.