Automatic simultaneous measurement of phase velocity and thickness in composite plates using iterative deconvolution

A new method for the automatic and simultaneous measurement of phase velocity and thickness for thin composite plates was developed based on Ping He's method, without any need of a priori knowledge of the material parameters. Two composites were analyzed: a block of clean epoxy and a thin specimen of glass-fiber reinforced plastic produced by resin transfer molding. The proposed method combines cross-correlation functions and iterative deconvolution for accurate measurement of times of flight and gating. The new method has demonstrated to be more accurate than conventional Ping He's method, and can be implemented automatically thus saving processing time and increasing accuracy.This research was funded by a Project IN-SMART, Grant no. VP1-3.1SMM-10-V-02-012 and by the Spanish Ministerio de Ciencia e Innovacion (TEC2011-23403).Rodriguez Martinez, A.; Svilainis, L.; Dumbrava, V.; Chaziachmetovas, A.; Salazar Afanador, A. (2014). Automatic simultaneous measurement of phase velocity and thickness in composite plates using iterative deconvolution. NDT and E International. 66:117-127. https://doi.org/10.1016/j.ndteint.2014.06.001S1171276

Analysis of piezomotor driver for laser beam deflection

A mechanical laser beam deflection using piezoactuator is analyzed in the paper. Wide angular range was required therefore mechanical mirror positioning using a multilayer piezoceramics friction drive configuration was chosen. The paper reports on research results of the deflection system parameters. Dynamic and static motion parameters such as angular speed, breaking displacement, positioning repeatability and angular resolution have been analyzed. For this purpose the measurement equipment have been designed and manufactured. Analysis of breaking characteristics has revealed that breaking angular displacement is dependant on driving voltage. Conducted positioning repeatability experiments indicate that the relative error between steps was about 1 %. Analysis of the complex electrical impedance of the piezoactuator over frequency range under varying load conditions was conducted. The equipment for measurement of electrical parameters has been described. Experimental research results of the actuator complex impedance are presente

Ultrasonic System Models for Pulse Trains Excitation Tuning

Quality of the ultrasonic imaging depends on probing signal. Application of the spread spectrum (SS) signals offers significant advantage over conventional signals: higher signal-to-noise ratio can be achieved and spectral content can be programmed. Yet, such SS signals like chirp and coded sequences suffer for the sidelobes which are induced by compression processing. Arbitrary position and width pulse (APWP) trains is a new class of SS signals which are expected to maintain advantages of the square pulse and the SS signals. Usual approach of SS signals application does not assume signal optimization. The novelty of the APWP approach is the optimization of the APWP train accounting of the signal transmission through system. In order to speed up the optimization iterations, a mathematical model of the APWP signal transmission through ultrasonic system is needed: instead of doing the iterations in real environment, those can be accomplished mathematically, using the system transmission model in order to sustain the experiment conditions. The development of the transmission model of the system is presented; the models are compared using the correlation properties. The results of the investigation are presented

Comparison of spread spectrum and pulse signal excitation for split spectrum techniques composite imaging

[EN] Ultrasonic imaging of composites was investigated. Glass and carbon fiber reinforced plastic produced by resin transfer molding and prepreg forming were analyzed. In some of the samples air bubbles were trapped during RTM (resin transfer molding) process and interlayer gaps were present in prepreg technology samples. One of the most expected techniques to apply in such case is the Split Spectrum processing. On the other hand such signals require specific processing to reliably reconstruct the temporal position of the defect reflection. Correlation processing can be used for signal compression or Wiener filtering can be applied for spectral content equalisation. Pulse signals are simple to generate, but lack the possibility to alter the signal’s spectrum shape. Spread spectrum signals offer a powerful tool for signal energy over frequency band increase and resolution enhancement. CW (continuous wave) burst has high energy but lacks the bandwidth needed for SSP (spread spectrum processing). The aim of the investigation was to compare the performance of the above signals in case of composite imaging, when various Split Spectrum Processing techniques are used with preceding Wiener processing for spectral content compensation. Resulting composite signals and images obtained are presented. Structural noise removal performance was evaluated as Receiver Operating Characteristics (ROC).This research (acquisition system and spread spectrum signals) was funded by a grant (No. MIP058/2012) from the Research Council of Lithuania. SSP part was supported by PROMETEO 2010/40.Svilainis, L.; Kitov, S.; Rodriguez Martinez, A.; Vergara Domínguez, L.; Dumbrava, V.; Chaziachmetovas, A. (2012). Comparison of spread spectrum and pulse signal excitation for split spectrum techniques composite imaging. IOP Conference Series: Materials Science and Engineering. 42:5-9. https://doi.org/10.1088/1757-899X/42/1/012007S594

Ultrasound-Based Density Estimation of Composites Using Water-Air Interface

[EN] In this paper we present a new method to obtain the density of solid composites using ultrasound. The method exploits the relation between density and acoustic impedance and only requires the measurement of a reference signal form the interface water-air. Once made in a controlled environment, it can be used for any material, and does not require any additional measurement or set-up, so that with a simple calculus it can be used with automatic ultrasonic measurements to calculate the density and therefore elastic constants of the composite for its complete characterization. The method is applied to 3 different materials: two composites based on epoxy and polyester resins respectively with unknown final properties and a common methacrylate sample used as reference. Results show good concordance between obtained and expected results.This research was partly funded by a grant ADECON by Kaunas University of Technology and by the Spanish Ministerio de Economia y Competitividad (TEC2014-58438-R).Aleksandrovas, A.; Rodriguez Martinez, A.; Svilainis, L.; Casa, MADL.; Salazar Afanador, A. (2016). Ultrasound-Based Density Estimation of Composites Using Water-Air Interface. Elektronika ir Elektrotechnika. 22(6):28-32. doi:10.5755/j01.eie.22.6.17219S283222

Approximation performance of model functions for blind deconvolution of ultrasonic reflections

Comparison of the approximation performance of the ultrasonic reflections by simple model functions used in blind deconvolution is presented. New model function was proposed where causality of the signal is easily modelled without the need for piecewise-linear equations. Parameter estimation technique was developed. Performance investigation was done for three model functions using four experimentally collected ultrasonic signals under different signal filtering conditions

Miniature ferroelectret microphone design and performance evaluation using laser excitation

Miniature microphones suitable for measurements of ultrasonic wave field scans in air are expensive or lack sensitivity or do not cover the range beyond 100 kHz. It is essential that they are too large for such fields measurements. The use of a ferroelectret (FE) film is proposed to construct a miniature, needle-style 0.5-mm-diameter sensitive element ultrasonic microphone. FE has an acoustic impedance much closer to that of air compared with other alternatives and is low cost and easy to process. The performance of the microphone was evaluated by measuring the sensitivity area map, directivity, ac response, and calibrating the absolute sensitivity. Another novel contribution here is that the sensitivity map was obtained by scanning the focused beam of a laser diode over the microphone surface, producing thermoelastic ultrasound excitation. The electroacoustic response of the microphone served as a sensitivity indicator at a scan spot. Micrometer scale granularity of the FE sensitivity was revealed in the sensitivity map images. It was also demonstrated that the relative ac response of the microphone can be obtained using pulsed laser beam thermoelastic excitation of the whole microphone surface with a laser diode. The absolute sensitivity calibration was done using the hybrid three-transducer reciprocity technique. A large aperture, air coupled transducer beam was focused onto the microphone surface, using the parabolic off-axis mirror. This measurement validated the laser ac response measurements. The FE microphone performance was compared with biaxially stretched polyvinylidene difluoride (PVDF) microphone of the same construction