An ultrasonic array is a single transducer that contains a number of individually connected elements. Recent years have seen a dramatic increase in the use of ultrasonic arrays for non-destructive evaluation. Arrays offer great potential to increase inspection quality and reduce inspection time. Their main advantages are their increased flexibility over traditional single element transducer methods, meaning that one array can be used to perform a number of different inspections, and their ability to produce immediate images of the test structure. These advantages have led to the rapid uptake of arrays by the engineering industry. These industrial applications are underpinned by a wide range of published research which describes new piezoelectric materials, array geometries, modelling methods and inspection modalities. The aim of this paper is to bring together the most relevant published work on arrays for non-destructive evaluation applications, comment on the state-of the art and discuss future directions. There is also a significant body of published literature referring to use of arrays in the medical and sonar fields and the most relevant papers from these related areas are also reviewed. However, although there is much common ground, the use of arrays in non-destructive evaluation offers some distinctly different challenges to these other disciplines.

Ultrasonic arrays for non-destructive evaluation: A review

Advanced post-processing for scanned ultrasonic arrays: Application to defect detection and classification in non-destructive evaluation

Ultrasonic arrays are increasingly widely used in nondestructive evaluation (NDE) due to their greater flexibility and potentially superior performance compared to conventional monolithic probes. The characterization of small defects remains a challenge for NDE and is of great importance for determining the impact of a defect on the integrity of a structure. In this paper, a technique for characterizing reflectors with subwavelength dimensions is described. This is achieved by post-processing the complete data set of time traces obtained from an ultrasonic array using two algorithms. The first algorithm is used to obtain information about reflector orientation and the second algorithm is used to distinguish between point-like reflectors that reflect uniformly in all directions and specular reflectors that have distinct orientations. Experimental results are presented using a commercial 64-element, 5-MHZ array on two aluminum test specimens that contain a number of machined slots and side-drilled holes. The results show that the orientation of 1-mm-long slots can be determined to within a few degrees and that the signals from 1-mm-long slots can be distinguished from that from a 1-mm-diameter circular hole. Techniques for quantifying both the orientation and the specularity of measured signals are presented and the effect of processing parameters on the accuracy of results is discussed.

Advanced Reflector Characterization with Ultrasonic Phased Arrays in NDE Applications

It has a pivotal role in medical science and in industry to concentrate the acoustic energy created with piezoelectric transducers (PTs) into a specific area. However, previous researches seldom consider the focal resolution, whose focal size is much larger than one wavelength. Furthermore, there is to date no such design method of PTs that allows a large degree of freedom to achieve designed focal patterns. Here, an active and configurable planar metasurface PT prototype is proposed to manipulate the acoustic focal pattern and the focal resolution freely. By suitably optimized ring configurations of the active metasurface PT, we demonstrate the manipulation of focal patterns in acoustic far fields, such as the designed focal needle and multi foci. Our method is also able to manipulate and improve the cross-sectional focal resolution from subwavelength to the extreme case: the deep sub-diffraction-limit resolution. Via the acoustic Rayleigh-Sommerfeld diffraction integral (RSI) cum the binary particle swarm optimization (BPSO), the free manipulation of focusing properties is achieved in acoustics for the first time. Our approach may offer more initiatives where the strict control of acoustic high-energy areas is demanding.

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Manipulation of acoustic focusing with an active and configurable planar metasurface transducer

Development of an ultra sonic phased array system for nondestructive tests of nuclear power plant components

An ultrasonic phased array transducer has been developed and demonstrated for the nondestructive evaluation of steel structures. The number of array elements is 64 and the center frequency is about 5 MHz. This phased array transducer is designed to use with the phased array system that does steering, transmission focusing and dynamic receive focusing. Each of the array elements is individually excited according to the focal laws and steering angles. Measurements of ultrasonic beam profiles for the array transducer in a reference steel block are presented and compared with theoretical predictions. Some of the phased array transducer design concepts for the application in steel structures are discussed. The two-dimensional ultrasonic images of the sample steel block including flat bottom holes and side drilled holes are presented. Experimental and theoretical results demonstrate excellent feasibility of the utility of the phased array transducer in imaging and detection of defects in steel structures.

Ultrasonic phased array transducers for nondestructive evaluation of steel structures

An intelligent ultrasonic phased array system is being developed to obtain real time flaw images and to characterize flaws in steel structures. The system uses zone-based transmission focusing and dynamic receiver focusing to produce the ultrasonic images and an A-scan signal for a selected angle of incidence. For the optimized design of rectangular phased array transducers, a complete 3-D radiation beam model based on the boundary diffraction wave model is developed to predict near- and far-acoustic fields while radiated beams are focused and steered with phase delay. A time domain RF signal of a focused beam is predicted by the inverse Fourier transform of frequency-domain solutions.

Development of an intelligent ultrasonic phased array system for NDT of steel structures

A digital ultrasonic image construction system was developed for the nondestructive detection of cracks in water distribution pipes. The system consists of PC based ultrasonic testing system and a scanning device. The PC based ultrasonic system has an ultrasonic pulse/receive board for the generation and reception of ultrasonic signals, an analogue to digital conversion board for the digitization of the received ultrasonic signals, and transducers for the ultrasonic sensors. Using this system, the digitized ultrasonic signals were properly constructed in accordance with the position information obtained by scanning device that moves an ultrasonic transducer along the outer surface of pipes. In the construction of the ultrasonic signals, signal processing concepts, such as spatial average and array concept, were considered to enhance the resolution of ultrasonic images of pipe wall. Using the developed system, crack detection experiments were performed in both laboratory and field, which shows promise for crack detection in the water distribution system.

https://eeer.org/upload/eer-11-2-99-5.pdf

You Hyun Jang

Papers

Development of an ultra sonic phased array system for nondestructive tests of nuclear power plant components

Ultrasonic phased array transducers for nondestructive evaluation of steel structures

Development of an intelligent ultrasonic phased array system for NDT of steel structures

Application of digital ultrasonic image construction system for the detection of cracks in water distribution system