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04/2011; , ISBN: 978-953-307-239-5
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ABSTRACT: This paper presents a strict timing-coherent digital signal processing architecture. The main requirement is that programmable events can be produced within predictable time intervals with tight accuracy (timing errors <; 1 ns). This characteristic is essential to ultrasound beamforming. The followed approach defines a modular and scalable architecture (AMPLIA), which is configured as a multibranch pipeline. This arrangement guarantees timing coherence along all the system, independent of the number of processing modules. An important element of the architecture is the interface and control unit (ICU), which decouples the asynchronous communication channel with a host computer to the strictly timing-coherent domain of the signal processing system. Furthermore, in the beamforming application, several elements have a great impact on system timing resolution, particularly when dynamic focusing is involved. This paper addresses the issues of coded excitation, analog-to-digital (A/D) conversion, and signal interpolation in achieving dynamic focusing by progressive focusing correction with processing rates of several gigasamples per second and tight timing accuracy.
IEEE Transactions on Instrumentation and Measurement 11/2010; · 1.21 Impact Factor
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ABSTRACT: This work addresses three key subjects to the image quality with phased arrays: timing accuracy, beamforming strategy and post-processing for increased resolution and suppression of grating and side lobes. Timing accuracy is achieved by defining a modular and scalable architecture which guarantees low timing errors, whatever is the system size. The proposed beamforming methodology follows the progressive focusing correction technique, which keeps low focusing errors, provides a high information density and has a simple implementation for real-time imaging in modular architectures. Then, phase coherence imaging is defined to suppress grating and sidelobe indications, simultaneously increasing the lateral resolution.
Ultrasonics 09/2009; 50(2):122-6. · 1.84 Impact Factor
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ABSTRACT: A new method for grating and side lobes suppression in ultrasound images is presented. It is based on an analysis of the phase diversity at the aperture data. Two coherence factors, namely the phase coherence factor (PCF) and the sign coherence factor (SCF), are proposed to weight the coherent sum output. Different from other approaches, phase rather than amplitude information is used to perform the correction action.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 06/2009; · 1.69 Impact Factor
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ABSTRACT: This paper introduces the fast focal law calculator (FFLC), a Newton-Raphson based algorithm that performs such task accurately at high speed. It is especially well suited for dynamic focusing through arbitrary geometry interfaces, where other algorithms are order of magnitude slower. In spite of the high speed of the FFLC, errors are kept very small, typically within a few tens of picoseconds. Besides a short background theory, the paper compares the results of the FFLC with regard to exact solutions (for planar interfaces) and those based on search algorithms. Field simulations are performed to assess the correctness of the method. Also, experiments are carried out with a curved interface showing the advantages of the FFLC for dynamic focusing to improve the image quality and the flaw detection and evaluation capabilities.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: This work presents an ultrasonic non-destructive technique for in service railway wheels inspection. To overcome the problem of accessibility to critical regions where cracks may appear this method uses phased-array with immersion coupling, which allows carrying out the inspection process on non-dismantled wheels sets. The acquired frames are subjected to compound imaging methods in order to improve the automatic detection of cracks. The proposed method provides low inspection time, high image quality and reliable crack detection capabilities.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: In this work, a novel procedure that considerably simplifies the fabrication process of ferro electret-based multi-element array transducers is proposed and evaluated. Also, the potential of ferro electrets as active material for air-coupled ultrasonic transducer design is demonstrated. The new construction method of multi-element transducers introduces two distinctive improvements, first, the active ferro electret material is not discretized into elements and, second, the need of structuring upper and lower electrodes in advance of the permanent polarization of the film is removed. In order to validate the procedure, two linear array prototypes of 32 elements were built and evaluated. A low crosstalk among elements, below -30 dB, was measured by interferometry. Likewise, a homogeneous response of the array elements, with a maximum deviation of plusmn1.8 dB, was obtained. Acoustic beam steering measurements were accomplished at different deflection angles using a calibrated microphone. The ultrasonic beam parameters, namely lateral resolution, side lobes level, grating lobes and focus depth, were congruent with theory. The proposed procedure simplifies the manufacturing of multi-dimensional arrays with arbitrary shape elements and not uniformly distributed. Furthermore, this concept can be extended to non-flat arrays as long as the transducer substrate conforms to a developable surface.
Ultrasonics Symposium, 2008. IUS 2008. IEEE; 12/2008
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ABSTRACT: A simple input protection circuit for ultrasound pulse-echo applications is described. Its performance is analyzed with regard to other widely used arrangements. Besides the primary function of showing high impedance during the transducer excitation time and a low impedance path to the amplifier in reception, issues of harmonic distortion, insertion losses, bandwidth, power dissipation, transient response, and noise are addressed. It is shown that the proposed circuit has many advantages, operating without any control signals or bias voltages. It is small and can be considered a good general-purpose protection circuit alternative.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2008; 55(5):1160-4. · 1.69 Impact Factor
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ABSTRACT: This work presents a strict timing-coherent digital signal processing architecture. The fundamental requirement is that programmable events can be produced within predictable time intervals with tight accuracies (timing errors <1 ns). There are several application fields where this characteristic is essential, as in ultrasound beamforming, where the system spreads over several processing modules. The followed approach defines a modular and scalable architecture (AMPLIA), configured as a multi-branch pipeline. This arrangement guarantees timing coherence along all the system, independently of the number of processing modules. The latency introduced by every module is automatically compensated and clock synchronization is achieved by Digital Clock Managers inside FPGAs. Furthermore, AMPLIA is a very simple to use architecture, involving a 32-bit data bus and only 8 control lines. An important element of the architecture is the Interface and Control Unit (ICU). This element couples the asynchronous communications with a host computer to the strictly timing- coherent domain of the system. Besides, it automatically performs the operations of parameter programming, triggering of acquisition-processing cycles, housekeeping functions and result retrieval, all within well defined time intervals. In the beamforming application, high timing resolution is achieved in emission by clock multiplication and by Lagrange interpolation in reception. This allows operating the overall system at the lower sampling clock frequency. Dynamic focusing is performed by Progressive Focusing Correction and processing rates of several Gsamples/s are achieved.
Intelligent Signal Processing, 2007. WISP 2007. IEEE International Symposium on; 11/2007
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ABSTRACT: This work presents a beamformer based on standard LVDS 12-bit analog-to-digital converters, which deliver the samples serially over a differential pair. The bit stream is synchronized and converted to a sequence of words in a FPGA. Beamforming is then carried out following the progressive focusing correction technique described in a previous work. The low pin count of serial converters and the FPGA ball grid array package allowed a high level of board integration. A scalable architecture allows many different configurations. Some of the possible applications are: phased array, linear scan, multi-channel ultrasound systems, SAFT imaging and TOFD techniques. The configuration is changed by software or just installing more modules in a back-plane. This work describes the system architecture, analog and digital preprocessing and assesses the performance with experimental images from a test block and tissue phantoms
Ultrasonics Symposium, 2006. IEEE; 11/2006
