Beam Steering with Segmented Annular Arrays

Two-dimensional (2-D) arrays of squared matrix have maximum periodicity in their main directions; consequently, they require half wavelength (λ/2), interelement spacing to avoid grating lobes. This condition gives rise to well-known problems derived from the huge number of array elements and from their small size. In contrast, 2-D arrays with curvilinear configuration produce lower grating lobes and, therefore, allow the element size to be increased beyond λ/2. Using larger elements, these arrays have the advantage of reducing the number of elements and of increasing the signal-to-noise ratio (SNR). In this paper, the beamforming properties of segmented annular phased arrays are theoretically analyzed and compared with the equivalent squared matrix array. In the first part, point-like elements are considered in order to facilitate the field analysis with respect to the array structure. Afterward, the effect of the element size on the steered beam properties also is presented. In the examples, it is shown that the segmented annular array has notably lower grating lobes than the equivalent squared matrix array and that it is possible to design segmented annular arrays with interelement distance higher than λ whose beam characteristics are perfectly valid for volumetric imaging applications.This paper received the support of the Education and Science Ministry of Spain under its DPI2002-01583, DPI2004-06470, and DPI2004-06756 projects.Peer reviewe

The Use of Instantaneous Phase for Improving Saft Images

6 páginas, 3 figuras. Proceedings of the 2013 International Congress on Ultrasonics (ICU 2013). 2-5 may 2013, SingaporeIn the SAFT technique (Synthetic Aperture Focusing Technique) each element operates in pulse-echo mode, requiring only on e transmit/receive channel. The generated beam pattern can present grating lobes, even if the pitc h is half wavelength, which are related to image quality. By considering the instantaneous phase of the signals detected by each transducer, it is possible to estimate if the signal used in the delay-and-sum algorithm, for each combination of array element and image pixel, is due to a reflector or if it is noise, improving the contrast and reducing the grating lobes effects.The authors would like to thank the financial support from FAPESP (2010/02240-0, 2010/16400- 0), Capes and CNPq as well as the government of Spain (CICYT - DPI 2010 19376).Peer reviewe

The Effect of Anisotropic Focusing of Lamb Modes on a Carbon-Epoxy Plain Woven Fabric Composite Plate

10 páginas, 8 figuras, 1 tabla. 6th International Symposium on NDT in Aerospace, 12-14th November 2014, Madrid, SpainThe medium anisotropy give rise to interesting effects in the physics of wave propagation: the angular dependence of the group velocity, the skew angle between pha se and group velocities, and the elastic focusing leading to the concentration of wave energy in dete rminated directions. All these effects are mode dependent and must be taken into account to choose the ad equate propagating mode in NDE or SHM applications. In this article the dispersion curves of p hase and group velocities, and the patterns of wave focusing for the A0 and S0 modes are theoretically obt ained and verified experimentally. The angular dependence of the group velocity and the effect of the anisotropic elastic focusing is studied in a 1.97 mm-thickness multilayer carbon-epoxy plain woven fab ric composite. The time traces are obtained by scanning the plate with the aid of a retro-reflective film st uck to the surface using a laser Doppler vibrometer. A good agreement between the theory and the expe rimental results was obtained. The Maris factor corresponding to the A0 mode shows smoother angular v ariation than that of the S0 mode which depends much more on the direction.The authors wish to thank to the CAPES Foundation, Ministry of Education of Brazil and to the Ministerio de Economía y Competitividad del Gobierno de Esp aña (project FIS2013-46829-R) for partially support the work, and to the Alltec Materiais Compostos for preparing the laminate samples.Peer reviewe

Towards a non-invasive ultrasound method for the diagnosis of neonatal and infant meningitis

Lumbar Puncture (LP) is currently used to draw a sample of cerebrospinal fluid (CSF) and test for potentially lethal Bacterial Meningitis (BM) in infants (<1yr). Increased CSF cellularity is highly indicative of BM and triggers medication for the patient. In developed countries, 95% of LPs for BM in infants return negative. In developing countries, LPs are rarely available, with 50% of infants with BM dying from the disease. We propose using high-frequency ultrasounds (HFUS) to non-invasively determine CSF cell concentration through the fontanel. The aim of this study is to assess the capabilities of HFUS on a fontanel phantom involving mock CSF with varying leukocyte concentration and pig tissue.This work was supported in part by the Consejería de Educación, Juventud y Deporte de la Comunidad de Madrid (Spain) through the Madrid-MIT M+Visión ConsortiumPeer reviewe

Low attenuation frequency bands for Lamb waves immersed in viscous fluids: theoretical analysis and experimental validation.

6 páginas, 3 figuras. Proceedings of the 2013 International Congress on Ultrasonics (ICU 2013). 2-5 may 2013, SingaporeThe application of Lamb waves is a promising technique i n ultrasonic NDE techniques for inspection and fluid characterization due to multi modal and dispersive characteristics. When a plate is in contact with a viscous fluid these waves are strongly attenuated. However, for most of the Lamb wave modes there is a low at tenuation frequency band that could be used for non-destructive testing or fluid characteriz ation. In order to explore this feature the phase velocity and attenuation curves of Lamb modes are expe rimentally measured in these low attenuation frequency bands, showing good agreement with theory .The present work was supported by the Brazilian National Council for Scientific and Technological Development – CNPq and the Spanish Ministery of Economy and Competitivity through the projects 560825/2010-2 and PIB2010BZ-00570, respectively.Peer reviewe

Diseño e implementación de un sistema de imagen ultrasonica 3D

8 páginas. 4 figuras. 1 Tabla -- PACS: 43.35.Zc. -- Comunicación presentada en: 44º Congreso Español de Acústica - TecniAcustica 2013. Encuentro Ibérico de Acústica. EAA European Symposium on Environmental Acoustics and Noise Mapping, Valladolid, 1 - 4, Octubre, 2013[EN] In this paper the design process of an ultrasonic volumetric imaging system based on synthetic aperture focusing technique is presented. Based on minimum redundancy coarray of 2D aperture an d parallel processing techniques for beamforming an experimental system is developed to operate with a 2D array (3Mhz and 11x11 elements).[ES] Este trabajo describe el proceso de diseño e implementación de un sistema de imagen ultrasónica basado en la composición del coarray de mínima redundancia para aperturas 2D. Esta técnica de adquisición en combinación con la generación de imagen por apertura sintética, implementada por GPGPU, permite diseñar un sistema de imagen 3D con un número reducido de recursos. Se presentan resultados experimentales del sistema implementado sobre un equipo de imagen ultrasónica convencional para una apertura bidimensional de 3Mhz y 11x11 elementos.Este trabajo está financiado por el Gobierno de España a partir del Plan Nacional de I+D+i dentro del marco del proyecto DPI2010-19376.Peer reviewe

Cheetah: A Library for Parallel Ultrasound Beamforming in Multi -Core Systems

6 páginas, 2 figuras, 4 tablasDeveloping new imaging methods needs to establish some proofs of concept before implementing them on real -time scenarios. Nowadays, the high computational power reached by multi-core CPUs and GPUs have driven the development of software-based beamformers. Taking this into account, a library for the fast generation of ultrasound images is presented. It is based on Synthetic Aperture Imaging Techniques (SAFT) and it is fast because of the use of parallel computing techniques. Any kind of transducers as well as SAFT techniques can be defined although it includes some pre-built SAFT methods like 2R -SAFT and TFM. Furthermore, 2D and 3D imaging (slicebased or full volume computation) is supported along with the ability to generate both rectangular and angular images. For interpolation, linear and polynomial schemes can be chosen. The versatility of the library is ensured by interfacing it to Matlab, Python and any programming language over different operating systems. On a standard PC equipped with a single NVIDIA Quadro 4000 (256 cores), the library is able to calculate 262,144 pixels in ≈ 105 ms using a linear transducer with 64 elements, and 2,097,152 voxels in ≈ 5 seconds using a matrix transducer with 121 elements when TFM is applied.This work has been supported by the Spanish Government and the University of Alcalá under projects DPI2010- 19376 and CCG2014/EXP -084, respectively.Peer reviewe

Development of an ultrasonic dry-coupling inspection wheel for Online NDI composite application

8 páginas, 5 figuras. 6th International Symposium on NDT in Aerospace, 12-14th November 2014, Madrid, SpainT he application of ultrasonic waves to the inspection of aeronautic compone nts is based on the use of couplants (water, gel, etc...) to facilitate the propagation of the sensi ng wave through the material. Although several solutions have been designed to integrate the use of these couplants and the NDT operations in different stages of component life (from production to in-service operation) its use incre ases the complexity of the process and the cost of the inspection because in some cases special infrastr uctures may become necessary. Some of the research effort developed in the last decades has been a ddressed to reduce the necessity of couplant gel or fluids. In this sense, the development of ultrasonic inspection w heels based on special rubbers with a high degree of humidity has been proposed and is being commercialized nowadays. How ever, its use is not allowed in applications where the condition of completely dry coupling is imperative. Other tools based on air-coupling have been also developed but they mainly operate in through transmission arrange ments and its use is limited to low frequencies. T his work examines a new wheel-based tool which can operate in dry condit ion . It has been developed in the context of the ICARO Project (Innovación en Composites Avanzados y Rear- End Optimizado) to provide a nondestructive inspection solution to be integrated into an Out of Autoclave ( OoA) composite manufacturing process based on electron beam curing technology layer by layer. T he solution requires be able to inspect very thin composite specimens (from 0.5mm) in clean and dry conditions compatibl e with the manufacturing process. T o overcome these conditions, a special inspection wheel prototype has bee n developed that integrates a 5MHz ultrasonic array transducer composed by 128 elements mounted in a particula r wedge. T his aperture operates in pulse-echo and generates an ultrasonic image based on linear scanning beam forming process and a synthetic aperture acquisition procedure known as 2R-SAFT . Inspection results obtained from reference standard of different thic kness are presented. T hese results are compared with conventional immersion UT inspections and show the high potentia l of this inspection wheel for this special applications.Peer reviewe

White Paper on Digital and Complex Information

Information is one of the main traits of the contemporary era. Indeed there aremany perspectives to define the present times, such as the Digital Age, the Big Dataera, the Fourth Industrial Revolution, the fourth Paradigm of science, and in all ofthem information, gathered, stored, processed and transmitted, plays a key role.Technological developments in the last decades such as powerful computers, cheaperand miniaturized solutions as smartphones, massive optical communication, or theInternet, to name few, have enabled this shift to the Information age. This shift hasdriven daily life, cultural and social deep changes, in work and personal activities,on access to knowledge, information spreading, altering interpersonal relations orthe way we interact in public and private sphere, in economy and politics, pavingthe way to globalizationPeer reviewe

Arrays de Anillos Segmentados para la generación de imagen ultrasónica 3D

Nowadays ultrasonic imaging is one of the methods more frequently employed in clinical diagnosis and NDT applications. Ultrasonic commercial systems are mainly based on bidimensional images. Development of volumetric imaging systems based on array transducers has started at R&D laboratories a decade ago. An array transducer is electronically controlled in order to steer the ultrasonic beam in any direction, avoiding mechanical scanning systems. Mainly rectangular MxN monolithic arrays have been proposed for 3D imaging. Unfortunately, these apertures need a large amount of elements (they can reach several thousands) to produce good quality images. For this reason, a great research effort has been addressed to develop subsampling techniques in order to reduce the number of active elements. But these techniques produce a drastic reduction of the emitted energy, so the image contrast is seriously limited. In this thesis 2D annular-segmented arrays are proposed as an alternative to the more common rectangular patterns. Annular segmented arrays have two main advantages: first, they present axial symmetry so the ultrasonic field shows almost invariant properties at any steered azimuth direction and a great symmetry with respect to the steering axis. Second, elements have a lower periodicity degree than rectangular arrays, and therefore grating lobes level is reduced. Consequently, we can increase the elements size holding at the same time a good quality in the acoustic field. With the purpose of reducing the number of elements with a full-active aperture, one of the objectives of this work is to find a criterion for array designing, in order to determine which is the aperture geometry that gives a good image quality with minimum electronic resources. Due to the scarce previous work devoted to 2D annular-segmented arrays, this thesis proposes innovative methods in the following aspects: • Computational methods valid for complex apertures. An exact solution based on the spatial impulse response, for the ultrasonic field radiated by annular sector transducers is presented. Nevertheless, due to the high computational cost associated to the exact solution, other approximated methods and algorithms are developed that reduce the computational cost in more than one order of magnitude. • Innovative methods to describe the field of annular-segmented arrays for several conditions of the aperture geometry, radiated pulse, field point position, etc. Quantitative and qualitative rules have been obtained to describe lateral response, side lobes and grating lobes in these conditions. • Designing rules for annular-segmented arrays. The influence of several array-designing parameters on the field quality is studied. The following parameters are studied: the elements interspacing, the aperture dimensions, the number and shape of the elements, the UT pulse, etc. From previous results, a theoretical comparative study between annular-segmented arrays and 2D rectangular apertures is presented. And finally, experimental work is done which validates theoretical results.Peer reviewe