Limited Number Of Transducers Research Articles

An Inspection Technique for Steel Pipes Wall Condition Using Ultrasonic Guided Helical Waves and a Limited Number of Transducers.

This research utilizes Ultrasonic Guided Waves (UGW) to inspect corrosion-type defects in steel pipe walls, providing a solution for hard-to-reach areas typically inaccessible by traditional non-destructive testing (NDT) methods. Fundamental helical UGW modes are used, allowing the detection of defects anywhere on the pipe's circumference using a limited number of transducers and measurements on the upper side of the pipe. Finite element (FE) modeling and experiments investigated generating and receiving UGW helical waves and their propagation through varying corrosion-type defects. Defect detection is based on phase delay differences in the helical wave's signal amplitude peaks between defective and defect-free regions. Phase delay variations were noted for the different depths and spatial dimensions of the defects. These results highlight the phase delay method's potential for NDT pipeline inspection.

Flush Airdata System on a Flying Wing Based on Machine Learning Algorithms

By using an array of pressure sensors distributed on the surface of an aircraft to measure the pressure of each port, the flush airdata sensing (FADS) system is widely applied in many modern aircraft and unmanned aerial vehicles (UAVs). Normally, the pressure transducers of the FADS system should be mounted on the leading edge of the aircraft, where they are sensitive to changes in pressure. For UAVs, however, the leading edge of the nose and wing may not be available for pressure transducers. In addition, the number of transducers is limited to 8–10, making it difficult to maintain accuracy in the normal method for FADS systems. An FADS system model for an unmanned flying wing was developed, and the pressure transducers were all located outside the regions of the leading edge areas. The locations of the transducers were selected by using the mean impact value (MIV), and ensemble neural networks were developed to predict the airdata with a very limited number of transducers. Furthermore, an error detection method was also developed based on artificial neural networks and random forests. The FADS system model can accurately detect the malfunctioning port and use the correct pressure combination to predict the Mach number, angle of attack, and angle of sideslip with high accuracy.

Deep Neural Network-Based Sinogram Super-Resolution and Bandwidth Enhancement for Limited-Data Photoacoustic Tomography.

Photoacoustic tomography (PAT) is a noninvasive imaging modality combining the benefits of optical contrast at ultrasonic resolution. Analytical reconstruction algorithms for photoacoustic (PA) signals require a large number of data points for accurate image reconstruction. However, in practical scenarios, data are collected using the limited number of transducers along with data being often corrupted with noise resulting in only qualitative images. Furthermore, the collected boundary data are band-limited due to limited bandwidth (BW) of the transducer, making the PA imaging with limited data being qualitative. In this work, a deep neural network-based model with loss function being scaled root-mean-squared error was proposed for super-resolution, denoising, as well as BW enhancement of the PA signals collected at the boundary of the domain. The proposed network has been compared with traditional as well as other popular deep-learning methods in numerical as well as experimental cases and is shown to improve the collected boundary data, in turn, providing superior quality reconstructed PA image. The improvement obtained in the Pearson correlation, structural similarity index metric, and root-mean-square error was as high as 35.62%, 33.81%, and 41.07%, respectively, for phantom cases and signal-to-noise ratio improvement in the reconstructed PA images was as high as 11.65 dB for in vivo cases compared with reconstructed image obtained using original limited BW data. Code is available at https://sites.google.com/site/sercmig/home/dnnpat.

IWSHM 2017: Structural health monitoring of the loosening in a multi-bolt structure using linear and modulated nonlinear ultrasound acoustic moments approach

Applying highly accurate clamp loads in bolted joints during assembly and inspections is essential for estimation of the integrity of a joint and reduction of disastrous failures. Non-destructive post-assembly and in-service inspections of joint integrity are vital and significantly reduce maintenance and associated repair costs. Therefore, a bolt control technology able to provide precise direct measurement of bolt loosening state during assembly and in-service is needed. This work proposes an in situ structural health monitoring approach based on the evaluation of linear and nonlinear modulated acoustic moments for the assessment of the loosened state of bolts in a multi-bolted structure. Linear and nonlinear ultrasound methods’ detection accuracy and robustness can be highly dependent on correct frequency selection. The structural health monitoring method suggested uses material resonance and a frequency sweep methodology coupled with a cross-correlation method which identifies significant frequency pairs or higher harmonics used to determine bolt loosening. The proposed approach was tested and successfully validated on three different bolted structures showing that loosening of the structure can be identified accurately with a limited number of transducers. The solution provides a qualitative solution, which identifies degradation in the torque of a bolted structure; furthermore, the developed structural health monitoring method has the potential to become an automatic tool for monitoring the loosened state of bolts in critical complex structural components.

Quantitative tomographic visualization for irregular shape defects by guided wave long range inspection

Ultrasonic guided waves have been proven as a promising tool for structure health monitoring due to their capability of interrogating a large structure from a single transducer position. This study presents the guided wave tomographic imaging in structural health monitoring for detecting cracks and visualization by reconstruction algorithm for the probabilistic inspection of damage. The variable shape factor is suggested for quantitative defect shape and sizing by reconstruction image. The defect of irregular boundary imaging with variable shape factor is precisely reconstructed by advanced RAPID algorithm with limited number of transducers. The particular application of interest is defect imaging of symmetric wave modes with irregular shape defect in plate-like structures. A preliminary study of tomographic imaging by guided waves in a plate-like structure provides guidelines for the quantitative defect imaging.

Embedded ultrasonic transducers for active and passive concrete monitoring.

Recently developed new transducers for ultrasonic transmission, which can be embedded right into concrete, are now used for non-destructive permanent monitoring of concrete. They can be installed during construction or thereafter. Large volumes of concrete can be monitored for changes of material properties by a limited number of transducers. The transducer design, the main properties as well as installation procedures are presented. It is shown that compressional waves with a central frequency of 62 kHz are mainly generated around the transducer’s axis. The transducer can be used as a transmitter or receiver. Application examples demonstrate that the transducers can be used to monitor concrete conditions parameters (stress, temperature, …) as well as damages in an early state or the detection of acoustic events (e.g., crack opening). Besides application in civil engineering our setups can also be used for model studies in geosciences.

On the development and testing of a guided ultrasonic wave array for structural integrity monitoring

The prototype of a guided ultrasonic wave array for the structural integrity monitoring of large, plate-like structures has been designed, built, and tested. The development of suitably small transducers for the excitation and measurement of the first antisymmetric Lamb wave mode Ao is described. The array design consists of a ring of 32 transducers, permanently bonded to the structure with a protective membrane, in a compact housing with the necessary multiplexing electronics. Using a phased addition algorithm with dispersion compensation and deconvolution in the wavenumber domain, a good dynamic range can be achieved with a limited number of transducers. Limitations in the transducer design and manufacture restricted the overall dynamic range achieved to 27 dB. Laboratory measurements for a steel plate containing various defects have been performed. The results for standard defects are compared to theoretical predictions and the sensitivity of the array device for defect detection has been established. Simulated corrosion pitting and a defect cut with an angle grinder simulating general corrosion were detected.

Localization of isolate flaws by combination of noised signals detected from perpendicular transducers

Two signal processing methods for ultrasonic localization of isolate flaws, with low computational cost, using a procedure based on a very limited number of transducers, are presented and compared. Both methods produce flaws representation with a better signal-to-noise ratio than the original ultrasonic traces. A theoretical study of the signal-to-noise ratio enhancement obtained in each case is presented. The results of this study are confirmed by simulation techniques. In the last part of the paper, a prototype for generation of broadband ultrasound and signal collection in the Megahertz range, specially designed for testing these methods, is applied to the acquisition of real measurements from a testing piece containing an isolated flaw. Results of processing these measurements confirm the validity of the procedure and give information about the overall performance of both methods in practical conditions.

An Optimization Method for Ultrasonic Beamforming with a Synthetic Aperture

Ultrasonic beamforming with a synthetic aperture is widely used in underwater and underground visualizations, but often suffers from visualization results with elliptically symmetric artifacts, due to lack of measurement points or transducers. We propose a newly-developed optimization method for ultrasonic beamforming. The aim of this method is to sharpen the distribution of the point spread function with a limited number of transducers. The characteristic of the point spread function is useful for evaluating the beamforming performance. This optimized beamforming method employs a visualization result by the conventional beamforming method as the initial guess. In the recursive calculation of this optimization method, the initial visualization result is modified by reducing and enhancing the weights of the discretized points in the measurement area. To evaluate this method, we tested it using a computer simulation and an actual measurement experiments, with a limited number of transducers. As the results of the experiments, this method successfully derives a sharp distribution of the point spread function.

Imaging of passive targets in shallow‐water using an ambient noise acoustic imaging system.

This paper will describe an experiment on the detection of passive targets in shallow water using ambient noise as the sole source of insonification. Glegg and Olivieri [Noise‐Con 95, p. 1179] proposed a broadband signal processing technique to achieve this type of passive acoustic detection using a limited number of transducers. An array has been developed to apply this technique in a shallow‐water environment. This paper will describe an experiment carried out in Summer 1995 off the Boca Raton inlet in which a target was successfully detected. The size of the target chosen for this test was 1.8×1.2 m and it was placed 40 m from the array. The acoustic field was imaged with and without the target present and both passive and active detection of the target was obtained. The measurements were carried out in low sea states when the primary source of ambient noise was biological and strongly anisotropic. [Work supported by ONR.]