Project: Synthetic Aperture with Phase-coherence for Real-time Imaging in NDT

The manufacture of heavy machines, components, industrial parts and critical structures requires the highest possible quality control during the manufacturing and in its service life. The purpose of Non Destructive Evaluation (NDE/NDT) techniques is to reduce the possibility of a flaw under the prolonged stress which, eventually, cause the part fatigue and the consequent fissure, fracture and/or other structural damage. The resulting damages, risk of accidents, delays and associated costs have called for more rigorous, accurate and cost effective methods of early detection of such flaws. One such method, the ultrasonic testing (UT) uses high frequency sound waves to conduct material examinations. Nowadays, it's one of the most extended and probably the most important NDT used worldwide. At present, we can differentiate between the Pulse-Echo testing by single or twin element transducers, Time-of-Flight-Diffraction (TOFD) and Phased Array (PA) technologies. These methods normally allow the inspection of parts and components assuring their structural integrity as well as the absence of any serious structural flaws, cracks and other damages, whether superficial or within the component. _x000D__x000D_However, there are some materials that are difficult or also impossible to inspect with these standard technologies. That is the case of the so called “coarse-grained materials”, whose microstructure appears as a large number of small reflectors that generate back scattered echoes. These signals interfere with each other, and when received by the ultrasound transducer, give rise to a certain level of the so called "grain" or "structural" noise that may hide the presence of flaws or, at least, preclude the damage assessment. Materials commonly used in industry such as austenitic steel, composites and titanium alloys typically present grain noise while being UT inspected. As grain-noise level depends on the relationship between the grain size and the ultrasound wavelength, it is a common practice to reduce the transducer frequency to decrease the grain-noise at the expenses of a resolution loss. The last has a negative impact on the inspection quality, because small cracks and defects may reCO undetected. If the structural integrity of the part cannot be ensured within an acceptable confidence level using lower frequency and resolution, more expensive and complex techniques become necessary. X-rays, for example, are less sensitive to grain-noise. However, these techniques normally have their own associated limitations and drawbacks, among others the use of ionizing radiation, equipment weight and the lack of information about the defects depth. _x000D__x000D_The structural or grain noise arises from the mutual interference among unresolved scatterers in a resolution volume. The grain noise, thus, may hide the presence of flaws or, at least, preclude the damage assessment. The CO problem is that the grain noise is within the same frequency band of the flaw indications, so that it cannot be removed by conventional means (filtering, averaging, etc.). Although some techniques, like Split Spectrum Processing (SSP) [1], have been proposed in the past to address this problem, they rely on a complex tuning processes to gain some dBs in the flaw-to-grain noise ratio. This has prevented their use in real applications, reCOing rather as an academic field of research._x000D__x000D_Due to the these considerations, the present project proposes a brand new method, called Phase Coherence Imaging, whose implementation could provide an application oriented NDE technology. Together with a Synthetic Aperture approach, it will achieve real-time 3D imaging with an unprecedent quality for the inspection of grained materials._x000D__x000D_The goal is to overcome the above stated limitations and, in particular, those of the existing PA imaging techniques, still based on conventional approaches, which are inappropriate for grain noise removal. The principal characteristics of the new 3D imaging technology will be improved resolution and contrast, automatic grain noise removal without any tuning process, suppression of indications due to reverberations, side and grating lobes, and a faster operation by means of a parallel beamforming capability. Given the market requirements, the cost of the corresponding high-performance equipment should be competitive with that of the currently available PA technology, offering identical imaging capabilities with increased resolution and at no additional cost._x000D__x000D_The Ps feel that the joint phase coherence and synthetic aperture imaging technologies will represent a significant step forward in the relevant market, setting up a new industrial standard when it comes to the NDT ultrasonic applications, especially for difficult-to-inspect materials._x000D__x000D_[1] V. L Newhouse, N.M. Bilgutay, J. Saniie and E. S. Furgason, “Flaw-to-grain echo enhancement by split-spectrum processing”, Ultrasonics, 20, 2, pp. 59-68, 1982.

Acronym	SAPHARI (Reference Number: 6771)
Duration	01/03/2012 - 28/02/2015
Project Topic	The so called "coarse-grained" materials are difficult or impossible to inspect with the standard UT technologies. The present project introduces a brand new and patented technology called Phase Coherence Imaging which will introduce an adequate and cost effective solution.
Project Results (after finalisation)	The SAPHARI project explored the SAFT algorithm improvement to the ”Non Destructive Technique” and the benefits of the 3D rendering of an acoustic image through a graphical display. The CO 3D rendering improvement is related to the “human readability” of the acoustic object acquired. Using a graphic display it is easy to look at the object from different points of view in order to better understand the relations between the external surfaces (that represent the CO discontinuity in the homogeneity in the acoustic echo path) and the other elements on the image that are highlighted as eventual flaws, cracks, discontinuities or inclusions into the object under analyses. The reduced cost compared with the other NDT technologies, the absence of risks present in the X–Ray analysis and the easier and faster way to acquire an acoustic echo image let this technique to be really affordable even for a screening phase only. The SAFT analysis benefit is less evident due to the complexity of the focalization law that deeply depends on the object geometry. Not all the objects are able to take advantages from this technique but with the improvement in the acoustic probe technologies, the capability to perform a dynamic and continuous focalization can become useful to explore larger block of materials obtaining the acoustic image faster and well focalized at all the depths into the material. A further result of the project is that we have analysed the differences in the probe technologies (Piezoelectric vs CMUT) and developped a software independent of the acquisition hardware. The CMUT technology performances have demonstrated to be comparable at least to the piezoelectric technology performances. The CMUT technology is a relatively new technology and his performance has a potential big improvement, it has a wider bandwidth that can work with a wider range of frequencies and can use higher maximum signal frequency that means better spatial resolutions. Independently of the probe technology selected, the system is able to improve the “Non Destructive Analysis” by using a light system obtaining an immediate improvement in the material analysis. The data acquired and eventually processed by using the SAFT algorithm can be immediately evaluated to check the material consistency and eventually perform a further acquisition. The CMUT technology was provided by Roma 3 University (DUNE sub-contractor in the SAPHARI project.
Network	Eurostars
Call	Eurostars Cut-Off 7

Project partner

Number	Name	Role	Country
3	CITEND	Partner	Spain
3	Dasel S.L.	Coordinator	Spain
3	Dune S.r.l.	Partner	Italy