Carlos J. Martín

2D array design based on Fermat spiral for ultrasound imaging

The main challenge faced by 3D ultrasonic imaging with 2D array transducers is the large number of elements required to achieve an acceptable level of quality in the images. Therefore, the optimisation of the array layout, in order to reduce the number of active elements in the aperture, has been a research topic in the last years. Nowadays, array technology has made viable the production of 2D arrays with larger flexibility on elements size, shape and position, allowing to study other configurations different to the classical matrix organisation, such as circular, archimedes spiral or polygonal layout between others. In this work, the problem of designing an imaging system array with large apertures and a very limited number of active elements (N(e)=128 and N(e)=256) using the Fermat spiral layout has been studied. As summary, a general discussion about the most interesting cases is presented.

Using GPUs for beamforming acceleration on SAFT imaging

SAFT techniques are based on the sequential activation, in emission and reception, of the array elements and the post-processing of all the received signals to compose the image. Thus, the image generation can be divided into two stages: (1) the excitation and acquisition stage, where the signals received by each element or group of elements are stored; and (2) the beamforming stage, where the signals are combined together to obtain the image pixels. The use of Graphics Processing Units (GPUs), which are programmable devices with a high level of parallelism, can accelerate the computations of the beamforming process, that usually includes different functions such as dynamic focusing, band-pass filtering, spatial filtering or envelope detection. This work shows that using GPU technology can accelerate, in more than one order of magnitude with respect to CPU implementations, the beamforming and post-processing algorithms in SAFT imaging.

Damage characterization using guided- wave linear arrays and image compounding techniques

In this work, a high-resolution imaging method for the inspection of isotropic plate-like structures using linear arrays and Lamb waves is proposed. The evaluation of these components is limited by the low dynamic range resulting from main lobe and side lobe field patterns, and from the narrowband nature of the Lamb waves. Based on a full matrix array, synthetic aperture technique using all emitter-receiver combinations, different images from the same object are obtained by using different apodization coefficients, which are related to a trade-off between main lobe width and relative side lobe level. Several image compounding strategies have been tested and a new algorithm, based on apodization and polarity diversities between signals, is proposed. However, some effects, such as the dead zone close to the array and reverberations caused by interactions of the wavefront and defects, still limit the quality of the images. The use of spatial diversity, obtained by an additional array, introduces complementary information about the defects and improves the results of the proposed algorithm, producing high-resolution, high-contrast images. Experimental results are shown for a 1-mm-thick isotropic aluminum plate with artificial defects using linear arrays formed by 30 piezoelectric elements, with the low dispersion symmetric mode S0 at the frequency of 330 kHz.

Reduction of grating lobes in SAFT images

In this work we present a new synthetic aperture technique, derived from the conventional SAFT, where only one element in emission and two in reception are used (2R-SAFT). This new technique suppresses the grating lobes of the conventional SAFT and allows obtaining images with a better contrast and signal-noise ratio, at the same time that minimizes the hardware requirements of the imaging systems and maintains a high frame rate.

P3R-3 Design and Characterization of Air Coupled Ultrasonic Transducers Based on MUMPs

This paper deals with the design and characterization of several capacitive micromachined ultrasonic transducer (cMUT) cells for the future design of an air-coupled transducer for non destructive testing (NDT). Each design was manufactured using the multi-user MEMS process (MUMPs). Special boundary conditions were used to obtain high efficiency: two opposite sides of the 150 mum square shaped membranes are free while the other sides are anchored to a fixed layer of the process. Using these designs a large displacement of the membrane and a higher surface contact is obtained in spite of their mechanical losses

Field modelling acceleration on ultrasonic systems using graphic hardware

Abstract Field modelling is a common practice in the area of ultrasonic non-destructive evaluation (NDE) because it is a useful tool for assessing NDE imaging. However, it is a very time consuming task because of its complexity and data volume, making difficult its use in systems demanding real time responses. Recently, graphics processing units (GPUs) have experienced an extraordinary evolution in both computing performance and programmability, leading to greater use on non-rendering applications. This work shows that the use of GPU technology, which has a high level of parallelism, accelerates the ultrasonic field simulation, reducing the computing time in more than one order of magnitude respect to CPU implementations.

P4M-2 A Linear CMUT Air-Coupled Array For NDE Based on MUMPS

In this paper, the design and characterization of a linear cMUT array based on MUMPS technology is presented. The array has 33 elements having each element 68times2 cMUT cells electrically connected in parallel. The single cell consists of a 130 mum square shaped polysilicon membrane, a gold top electrode, silicon nitride as the isolation layer between conductors and heavily doped silicon which works as the bottom electrode. The central frequency is 720 kHz. Electrical and optical measurements were performed and compared with FEM calculations. These results were used to study the mechanical and electrical behaviour of the device.

Improving synthetic aperture image by image compounding in beamforming process

In this work, signal processing techniques are used to improve the quality of image based on multi‐element synthetic aperture techniques. Using several apodization functions to obtain different side lobes distribution, a polarity function and a threshold criterium are used to develop an image compounding technique. The spatial diversity is increased using an additional array, which generates complementary information about the defects, improving the results of the proposed algorithm and producing high resolution and contrast images. The inspection of isotropic plate‐like structures using linear arrays and Lamb waves is presented. Experimental results are shown for a 1‐mm‐thick isotropic aluminum plate with artificial defects using linear arrays formed by 30 piezoelectric elements, with the low dispersion symmetric mode S0 at the frequency of 330 kHz.

LINEAR SCANNING METHOD BASED ON THE SAFT COARRAY

This work presents a method to obtain B‐scan images based on linear array scanning and 2R‐SAFT. Using this technique some advantages are obtained: the ultrasonic system is very simple; it avoids the grating lobes formation, characteristic in conventional SAFT; and subaperture size and focussing lens (to compensate emission‐reception) can be adapted dynamically to every image point. The proposed method has been experimentally tested in the inspection of CFRP samples.

Coarray Synthesis Based on Polynomial Decomposition

Synthetic aperture (SA) techniques have been frequently used to reduce the volume and complexity of the imaging systems. A useful tool for designing synthetic aperture configurations is the coarray. This is the virtual aperture that produces in one way the same beam pattern as the SA system in emission and reception. In this correspondence, we propose a new algorithm, based on the polynomial decomposition, that allows to obtain any wanted coarray on a linear array using whatever synthetic aperture configuration. With this fast and simple algorithm, the desired coarray is decomposed into a set of sub-apertures, whose length is determined by the requirements and resources of the system. The result is the set of weights that have to be applied on the sub-apertures to get the desired coarray, and consequently, the wanted beam pattern.