222 research outputs found
Steve Freear Passes the Torch as the Editor-in-Chief of IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control
No full textAs the New Year starts and after 6 years of serving as the Editor-in-Chief of the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control (UFFC), Steven Freear passes the torch to Peter A. Lewin
Compressive sensing with frequency warped compensation for damage detection in composite plate
No full textThis work focuses on an ultrasonic guided wave structural health monitoring (SHM) system development for composite plate inspection. The development of an in situ health monitoring system that can inspect large areas and communicate remotely to the inspector is highly computational demanding due to both the huge number of piezoelectric sensors needed and the high sampling frequency. To address this problem, a general approach for low rate sampling is developed. Compressive Sensing (CS) has emerged as a potentially viable technique for the efficient acquisition that exploits the sparse representation of dispersive ultrasonic guided waves in the frequency warped basis. The framework is applied to lower the sampling frequency and to enhance defect localization performances of Lamb wave inspection systems. As a result, an automatic detection procedure to locate defect-induced reflections was demonstrated and successfully tested on simulated Lamb waves propagating in a carbon fiber plate using PZFlex software. The proposed method is suitable for defect detection and can be easily implemented for real application to structural health monitoring
Frequency warping compressive sensing for structural monitoring of aircraft wing
No full textThis work focuses on an ultrasonic guided wave structural health monitoring (SHM) system development for aircraft wing inspection. The performed work simulate small, low-cost and light-weight piezoelectric discs bonded to various parts of the aircraft wing, in a form of relatively sparse arrays, for cracks and corrosion monitoring. The piezoelectric discs take turns generating and receiving ultrasonic guided waves. The development of an in situ health monitoring system that can inspect large areas and communicate remotely to the inspector is highly computational demanding due to both the huge number of Piezoelectric sensors needed and the high sampling frequency. To address this problem, a general approach for low rate sampling is developed. Compressive Sensing (CS) has emerged as a potentially viable technique for the efficient acquisition that exploits the sparse representation of dispersive ultrasonic guided waves in the frequency warped basis. The framework is applied to lower the sampling frequency and to enhance defect localization performances of Lamb wave inspection systems. The approach is based on the inverse Warped Frequency Transform (WFT) as the sparsifying basis for the Compressive Sensing acquisition and to compensate the dispersive behaviour of Lamb waves. As a result, an automatic detection procedure to locate defect-induced reflections was demonstrated and successfully tested on simulated Lamb waves propagating in an aluminum wing specimen using PZFlex software. The proposed method is suitable for defect detection and can be easily implemented for real application to structural health monitoring
Separation of Overlapping Linear Frequency Modulated (LFM) Signals Using the Fractional Fourier Transform
No full textLinear frequency modulated (LFM) excitation combined with pulse compression provides an increase in SNR at the receiver. LFM signals are of longer duration than pulsed signals of the same bandwidth; consequently, in many practical situations, maintaining temporal separation between echoes is not possible. Where analysis is performed on individual LFM signals, a separation technique is required. Time windowing is unable to separate signals overlapping in time. Frequency domain filtering is unable to separate signals with overlapping spectra. This paper describes a method to separate time-overlapping LFM signals through the application of the fractional Fourier transform (FrFT), a transform operating in both time and frequency domains. A short introduction to the FrFT and its operation and calculation are presented. The proposed signal separation method is illustrated by application to a simulated ultrasound signal, created by the summation of multiple time-overlapping LFM signals and the component signals recovered with +/-0.6% spectral error. The results of an experimental investigation are presented in which the proposed separation method is applied to time-overlapping LFM signals created by the transmission of a LFM signal through a stainless steel plate and water-filled pipe
Recontando la resistencia: nuevas narrativas míticas e históricas en el teatro de Romero, Resino, Pascual y de Paco Serrano
No full textIn this article we will look at a small but cohesive sample of plays by female dramatists of democratic Spain from the 1980’s to the present, in which the dramatic retelling of history and myth has evolved in time as it accompanied the emergence of stronger female narratives. We will focus on plays that feature female protagonists whom we think we already know from history or mythology and who confront culturally predominant male narratives. In each case, the playwright offers her characters a unique opportunity to deconstruct and re-write these stories, or even to demythify and re-inscribe myth. These writers emphasize the credibility of their female characters as they urge their spectators to question the legitimacy of traditional patriarchal roles for women and to look beyond a purely masculine point of view to a more pertinent and comprehensive view of the problems that exist in the world outside the theater.En este artículo veremos una muestra pequeña pero coherente de obras de dramaturgas de la España democrática, desde los años 80 hasta la actualidad, en las que se ve una relectura de la historia y del mito. Nos centraremos en las obras protagonizadas por mujeres que ya reconocemos de la historia o de la mitología y veremos cómo estas figuras se enfrentan a las narrativas masculinas predominantes. En cada caso, la dramaturga ofrece a sus personajes una oportunidad única para deconstruir y re-escribir estas historias, o incluso para desmitificar y luego re-escribir unos mitos. Estas escritoras enfatizan la credibilidad de sus personajes femeninos mientras piden a su público que cuestione la legitimidad de viejos papeles patriarcales para mujeres, que mire más allá de un punto de vista puramente masculino y que proponga una visión más pertinente y completa de los problemas que existen en el mundo fuera del teatro
Quinary excitation method for pulse compression ultrasound measurements
No full textA novel switched excitation method for linear frequency modulated excitation of ultrasonic transducers in pulse compression systems is presented that is simple to realise, yet provides reduced signal sidelobes at the output of the matched filter compared to bipolar pseudo-chirp excitation. Pulse compression signal sidelobes are reduced through the use of simple amplitude tapering at the beginning and end of the excitation duration. Amplitude tapering using switched excitation is realised through the use of intermediate voltage switching levels, half that of the main excitation voltages. In total five excitation voltages are used creating a quinary excitation system. The absence of analogue signal generation and power amplifiers renders the excitation method attractive for applications with requirements such as a high channel count or low cost per channel. A systematic study of switched linear frequency modulated excitation methods with simulated and laboratory based experimental verification is presented for 2.25 MHz non-destructive testing immersion transducers. The signal to sidelobe noise level of compressed waveforms generated using quinary and bipolar pseudo-chirp excitation are investigated for transmission through a 0.5 m water and kaolin slurry channel. Quinary linear frequency modulated excitation consistently reduces signal sidelobe power compared to bipolar excitation methods. Experimental results for transmission between two 2.25 MHz transducers separated by a 0.5 m channel of water and 5% kaolin suspension shows improvements in signal to sidelobe noise power in the order of 7-8 dB. The reported quinary switched method for linear frequency modulated excitation provides improved performance compared to pseudo-chirp excitation without the need for high performance excitation amplifiers
Fractional Fourier Transform with Pulse Inversion for Second Harmonic Pulse Compression
No full textIn ultrasound harmonic imaging with chirp coded excitation, harmonic matched filtering (HMF) is required on the receiving side to perform second harmonic pulse compression to recover signal axial resolution. In the compressed signal, peak sidelobe levels will grow and the mainlobe width may increase under mismatched or overlap harmonic conditions. In this paper, fractional Fourier transform (FrFT) with pulse inversion is proposed for the second harmonic pulse compression. Experimental results are presented which show a, 13.5%, improvement in the mainlobe width, with comparable peak sidelobe levels, when compared with the conventional HMF technique
Gold nanoparticle nucleated cavitation for enhanced high intensity focused ultrasound therapy
No full textHigh intensity focused ultrasound (HIFU) or focused ultrasound surgery is a non-invasive technique for the treatment of cancerous tissue, which is limited by difficulties in getting real-time feedback on treatment progress and long treatment durations. The formation and activity of acoustic cavitation, specifically inertial cavitation, during HIFU exposures has been demonstrated to enhance heating rates. However, without the introduction of external nuclei its formation an activity can be unpredictable, and potentially counter-productive. In this study, a combination of pulse laser illumination (839 nm), HIFU exposures (3.3 MHz) and plasmonic gold nanorods (AuNR) was demonstrated as a new approach for the guidance and enhancement of HIFU treatments. For imaging, short duration HIFU pulses (10 μs) demonstrated broadband acoustic emissions from AuNR nucleated cavitation with a signal-to-noise ranging from 5–35 dB for peak negative pressures between 1.19–3.19 ± 0.01 MPa. In the absence of either AuNR or laser illumination these emissions were either not present or lower in magnitude (e.g. 5 dB for 3.19 MPa). Continuous wave (CW) HIFU exposures for 15 s, were then used to generate thermal lesions for peak negative pressures from 0.2–2.71 ± 0.01 MPa at a fluence of 3.4 mJ . Inertial cavitation dose (ICD) was monitored during all CW exposures, where exposures combined with both laser illumination and AuNRs resulted in the highest level of detectable emissions. This parameter was integrated over the entire exposure to give a metric to compare with measured thermal lesion area, where it was found that a minimum total ICD of a.u. was correlated with the formation of thermal lesions in gel phantoms. Furthermore, lesion area (mm2) was increased for equivalent exposures without either AuNRs or laser illumination. Once combined with cancer targeting AuNRs this approach could allow for the future theranostic use of HIFU, such as providing the ability to identify and treat small multi-focal cancerous regions with minimal damage to surrounding healthy tissue
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