Miguel A. Rodriguez-Hernandez

Ultrasonic non-destructive evaluation with spatial combination of Wigner–Ville Transforms

Abstract This paper introduces a novel ultrasonic signal combination technique to be applied in detection systems based on multiple transducers. The technique uses a spatial combination approach that considers the specimen inspection from several apertures located in different planes. Information received from transducers is fused in a common integrated pattern with a signal to noise ratio (SNR) improvement. The result of the combination is a high quality image of the inspected material obtained from simple A-scans. The method is based on digital signal processing techniques, more concretely time–frequency analysis. Combination is performed by means of the Wigner–Ville Transform preserving temporal and frequencial information. Temporal techniques for combination are presented and the results obtained from both techniques are compared using the SNR.

Noise reduction using wavelet cycle spinning: analysis of useful periodicities in the z-transform domain

Cycle spinning (CS) and a’trous algorithms are different implementations of the undecimated wavelet transform (UWT). Both algorithms can be used for UWT and even though the resulting wavelet coefficients are different, they keep a correspondence. This paper describes an analysis of the CS algorithm performed in the z-transform domain, showing the similarities and differences with the a’trous implementation. CS generates more wavelet coefficients than a’trous, but the number of significative and different coefficients is the same in both cases because of the occurrence of a periodic repetition in CS coefficients. Mathematical expressions for the relationship between CS and a’trous coefficients and for CS coefficient periodicities are provided in the z-transform domain. In some wavelet denoising applications, periodicities (present in the coefficients of the CS procedure) can also be found in the performance measure of the processed signals. In particular, in ultrasonic CS denoising applications, periodicities have been appreciated in the signal-to-noise ratio (SNR) of the ultrasonic denoised signals. These periodicities can be used to optimize the number of CS coefficients for an efficient implementation. Two examples showing the periodicities in the SNR are included. A selection of several reduced sets of CS wavelet coefficients has been utilized in the examples, and the SNRs resulting after denoising are analyzed.

Flaw location from perpendicular NDE ultrasonic transducers using the wavelet packet transform

Ultrasonic inspection of materials from different planes is a technique that produces complementary information of the same piece using different echographic traces. The combination of these traces in order to obtain an improved representation of the inspected area is a problem that can be solved by means of digital signal processing techniques. A new method for the combination of the traces coming from perpendicular transducers is presented in this paper. The method is based on the undecimated wavelet packet transform and it is applied to the localization of isolated flaws in a plastic piece.

Ultrasonic system for remote non-destructive testing using mobile telephony

In distributed non-destructive testing (NDT), the acquisition of ultrasonic measurements occasionally has to be performed at different locations distant from the central station, where the ultrasonic data must be analysed and displayed. In this paper, the design details of an ultrasonic system with such objective are described. The system aims to perform remote acquisitions and transmit them to a central station using mobile telephony. Ultrasonic and telecommunication sub-systems involved in this system are described. The practical implementation here depicted combines own-designed modules with some low-cost commercial devices. Some design consideration and the block schemes of each subsystem are detailed. Finally, a laboratory prototype, developed for design viability purposes, is presented. This development includes stages for: transducer driving by means of a high-voltage pulse generator, broad-band amplification, acquisition, multiplexing and A/D conversion of signals, ultrasonic data transmission by mobile telephony, and the control of telemetering aspects by remote and local software.

Virtual Laboratory for QoS Study in Next-Generation Networks With Metro Ethernet Access

Teaching in university engineering departments is currently facing a number of challenges, especially for those involved in the most innovative and dynamic areas of information and communication technology. Learning model developments that place greater weight on laboratory activities require investment in specific equipment that is often very expensive, difficult to manage, and soon obsolete. This paper describes a virtual laboratory education platform, QoSLab, for training in and research into quality-of-service (QoS) mechanisms used for Metro Ethernet access in next-generation networks (NGNs). QoSLab integrates three experiments and 21 tasks with a pedagogical model to help students achieve learning goals; it also promoting student teamwork, iteration with lecturers, and autonomy. QoSLab was developed using OMNeT++, an open-source framework environment that allows students to run the code on their personal computers. Evaluations have shown that since 2013, QoSLab has produced a significant increase in student grades on NGN-related topics, as well as good results in student satisfaction surveys.

Shift selection influence in partial cycle spinning denoising of biomedical signals

Abstract Denoising of biomedical signals using wavelet transform is a widely used technique. The use of undecimated wavelet transform (UWT) assures better denoising results but implies a higher complexity than discrete wavelet transform (DWT). Some implementation schemes have been proposed to perform UWT, one of them is Cycle Spinning (CS). CS is performed using the DWT of several circular shifted versions of the signal to analyse. The reduction of the number of shifted versions of the biomedical signal during denoising process used is addressed in the present work. This paper is about a variant of CS with a reduced number of shifts, called Partial Cycle Spinning (PCS), applied to ultrasonic trace denoising. The influence of the choice of PCS shifts in the denoised registers quality is studied. Several shifts selection rules are proposed, compared and evaluated. Denoising results over a set of ultrasonic registers are provided for PCS with different shift selection rules, CS and DWT. The work shows that PCS with the appropriate choice of shifts could be the best option to denoise biomedical ultrasonic traces.

Telecom services design in Smart-Hospital communications

The introduction of new diagnosis treatment systems and devices in hospital environments presents an enormous challenge in terms of strategies and operational planning. These systems, which are generally interconnected, generate huge volumes of information of a heterogeneous nature that may be processed using resources that are external to the hospital. Correct design of hospital communications would result in a better quality of service, and reductions in costs, especially in environments with convergent communication networks where all communication shares a common infrastructure. The analytical dimensioning of a Smart-Hospital telecommunications is a complex task due to the large number, and heterogeneity, of the devices involved. In this case, the use of simulation tools to dimension these communications gives better flexibility and can be carried out at a reasonable cost. A tool has been designed for the specific simulation of hospital communications which makes use of an arbitrary collection of connected services with Metro-Ethernet access. This present work evaluates the communication dimensioning of a hypothetical hospital offering a range of medical services. The results obtained: loss of information, delay and jitter will be used to design capacities and types of service contracted from the telecommunications carrier.

Denoising of hepatic signals with Partial Cycle Spinning

Partial Cycle Spinning (PCS) is a technique that allows denoising of signals with lower complexity than Cycle Spinning (CS). PCS is a simplified version of CS, in which only a subset of the shifts used in CS is used. The results obtained with PCS show some variability depending on the shifts chosen. The quality of the processed signals can be improved by taking advantage of this variability. This paper presents a study of the influence of the choice of shifts on the PCS algorithm for medical signal denoising applications, to be more precise for hepatic signals of ultrasonic origin. The results obtained, both for synthetic signals and ultrasonic hepatic signals, show how the choice of shifts in the PCS algorithm influences the quality of the final processed signal.

Wavelet denoising of ultrasonic A-scans by random partial cycle spinning

Wavelet shrinkage schemes are applied for reducing noise in synthetic and experimental ultrasonic A-scans, using the Discrete Wavelet Transform (DWT) and a cycle-spinning (CS) implementation of Undecimated Wavelet Transform (UWT). A new wavelet-based denoising procedure, which we call Random Partial Cycle Spinning (RPCS) is presented and its performance is compared with that of DWT and a CS implementation of UWT. Three well known threshold selection rules (Universal, Minimax and Sure), with decomposition level dependent threshold selection, are used in all cases. Denoising using the UWT has previously shown a robust and usually better performance than denoising using DWT but with a much higher computational cost. In this work, it is shown that the alternative procedure RPCS provides a good robust performance, close to CS performance, but with a much lower computational cost.

Wavelet-based 2D fusing of ultrasonic pulse-echo traces measured from two arrays radiating orthogonal beams

Ultrasonic measurements using orthogonal collimated beams provide both complementary and redundant information about internal parts of pieces or structures being tested, which must be fused. In this paper, a new wavelet-based digital-processing technique which fuses ultrasonic pulse-echo traces obtained from several transducers located in two perpendicularly coupled arrays is proposed. This is applied to accurately visualize the location of a small internal reflector by means of two-dimensional (2D) displays. A-scans are processed in a wavelet domain and fused in a common 2D pattern. A mathematical expression of the resulting 2D signal-to-noise ratio (SNR) is derived, and its accuracy is confirmed using benchmark tests performed with simulated registers and real measurements acquired using a multi-channel laboratory prototype. The measurement system consists of two properly coupled perpendicular arrays comprising four square pulsed transducers and electronic driving circuitry. This technique improves the 2D-SNR by a factor of twice the number of bands. In addition, good reflector location is obtained, since submillimeter 2D resolution is achieved, despite only requiring eight ultrasonic channels. This good performance is confirmed by comparing the new wavelet fusing method with the two previously described techniques.