Accurate inversion is vital for quantitative imaging, including ultrasonic guided wave tomography, where thickness maps of plate-like structures are reconstructed to quantify corrosion damage. The dispersive properties of guided waves are often exploited to enable thickness maps to be produced from wave speed reconstructions. Ray tomography, diffraction tomography and a hybrid algorithm combining their features were investigated to reconstruct wave speed. Test data produced from simple defects of different sizes using a realistic full elastic guided wave model and the equivalent idealized acoustic model were passed to the imaging algorithms, generating wave speed maps, and, from these, thickness maps. For both datasets, ray tomography exhibited poor resolution. Diffraction tomography performed better, but was limited to shallow, small defects. The hybrid algorithm achieved the best results, giving a resolution around 1.5–2 wavelengths from the realistic test data compared to half wavelength from the idealized case. These results were validated with experimental data, and also extended to a realistic corrosion patch confirming the trends demonstrated with simple defects. The resolution loss with realistic data compared with idealized data indicates the acoustic model cannot accurately capture guided wave scattering and an alternative approach is necessary for better resolution reconstructions.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.2014.0063

Evaluation of inversion approaches for guided wave thickness mapping

A method for examining the interior material of an object, such as a pipeline or a human body, from a surface of an object using ultrasound having a frequency of at least 100 KHz, wherein the ultrasound is supplied to the interior material of the object. The reflectiLons and/or diffractions of the ultrasound from the interior material of the object are received using ultrasonic receivers which are acoustically coupled to the surface of the object at positions which are distributed in two dimensions of the surface of the object, at different points in time or not, wherein, with each of the feelers, a receiving signal is generated, wherein the receiving signals are processed in combination in order to determine, according to the principie of inverse wave field extrapolation, where in the interior material of the object reflections and/or diffractions occur.

/pdf/method-and-apparatus-for-examining-the-interior-material-of-3hka38szds.pdf

Method and apparatus for examining the interior material of an object, such as a pipeline or a human body from a surface of the object using ultrasound

Fatigue resistance of the deck plate in steel orthotropic deck structures

A comparison and extensions of algorithms for quantitative imaging of laminar damage in plates. I. Point spread functions and near field imaging

Non-destructive ultrasonic testing (UT) of materials is used for monitoring critical parts in power plants, aeronautics, oil and gas industry, and space industry. Due to a vast amount of time needed for a human expert to perform inspection it is practical for a computer to take over that task. Some attempts have been made to produce algorithms for automatic UT scan inspection mainly using older, non-flexible analysis methods. In this paper, two deep learning based methods for flaw detection are presented, YOLO and SSD convolutional neural networks. The methods' performance was tested on a dataset that was acquired by scanning metal blocks containing different types of defects. YOLO achieved average precision (AP) of 89.7% while SSD achieved AP of 84.5 %.

Flaw Detection from Ultrasonic Images using YOLO and SSD

A system for extracting one or more acoustic signals from a plurality of source signals emitted by a plurality of sources, respectively, in an environment, the system comprising an array of microphone receivers for receiving the one or more acoustic signals from the environment and transmitting the signal to a signal processor, wherein the signal processor is arranged to estimate the plurality of source signals using the data received by array of receivers, the signal processor is further arranged to perform an operation on the data received by the array of receivers with the estimated source signals to provide an estimate of the impulse response of the environment, wherein the data received by the array of receivers is input to the estimate of the impulse response of the environment to provide an output comprising a plurality of channels, wherein one or more of the channels correspond to the one or more acoustic signals from one of the plurality of sources, respectively.

System and method for extracting acoustic signals from signals emitted by a plurality of sources

Corrosion is one of the industries major issues regarding the integrity of assets. Currently inspections are conducted at regular intervals to ensure a sufficient integrity level of these assets. Both economical and social requirements are pushing the industry to even higher levels of availability, reliability and safety of installations. The concept of predictive maintenance using permanent sensors that monitor the integrity of an installation is an interesting addition to the current method of periodic inspections reducing uncertainty and extending inspection intervals. Guided wave travel time tomography is a promising method to monitor the wall thickness quantitatively over large areas. Obviously the robustness and reliability of such a monitoring system is of paramount importance. Laboratory experiments have been carried out on a 10″ pipe with a nominal wall thickness of 8 mm. Multiple, inline defects have been created with a realistic morphology. The depth of the defects was increased stepwise from 0.5 mm to 2 mm. Additionally the influences of the presence of liquid inside the pipe and surface roughness have been evaluated as well. Experimental results show that this method is capable of providing quantitative wall thickness information over a distance of 4 meter, with a sufficient accuracy such that results can be used for trending. The method has no problems imaging multiple defects.

/pdf/experimental-results-of-guided-wave-travel-time-tomography-1qt9tfrp19.pdf

Experimental results of guided wave travel time tomography

Manual inspection of ultrasonic evaluation images can not only be a time-consuming and therefore expensive task, it can also suffer from operat or performance. In this work we apply image processing techniques to automatically inspect ultraso nic C-scan images. Our method is based on the comparison of a C-scan image with a reconstructed reference image. The method was tested on a set of C-scan images with known defect s and was able to detect all defects. The number of false detections is still high and will be addr essed in future research.

Image processing techniques for ultrasonic inspection

Risk based inspection strategies rely on detailed knowledge of the performance of inspection techniques. It is well known that every inspection technique has limitations in terms of reliability and effectiveness. Moreover, these are influenced by many factors. E.g. it depends on operator skills, inspection procedure, defect and object geometry as well as technique specific instrument properties and settings. The objective of the "POD generator" project is to develop a numerical modeling approach to assess inspection effectiveness for a specific technique and situation flexibly and reliably yet at acceptable costs. Besides the models to simulate various degradation mechanisms, numerical models have been developed and validated for accurately simulating the physics of inspection techniques. Also the human factor is taken into account. These numerical models are then used to generate quantitative probability of detection (POD) curves. This will be illustrated for ultrasonic time-of-flight-diffraction (TOFD) inspection of fatigue cracks. © 2009 American Institute of Physics.

/pdf/pod-generator-project-development-of-numerical-modeling-3rfczmsy1q.pdf

Pod generator project, development of numerical modeling tools for quantitative assessment of the performance of non‐destructive inspection techniques

With a linear array of microphones, 'virtual microphones' can be created with good results on isolating, tracking and separating sources of sound. This technique could be used for command control and speech recognition purposes in an operating theatre.

Arjan Mast

Papers

System and method for extracting acoustic signals from signals emitted by a plurality of sources

Experimental results of guided wave travel time tomography

Image processing techniques for ultrasonic inspection

Pod generator project, development of numerical modeling tools for quantitative assessment of the performance of non‐destructive inspection techniques

Virtual microphones in the operating theatre