scholarly journals Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film

Sensors ◽  
2020 ◽  
Vol 20 (2) ◽  
pp. 516 ◽  
Author(s):  
Rymantas J. Kazys ◽  
Almantas Vilpisauskas
Keyword(s):  
Evanescent Wave ◽  
Ultrasound Velocity ◽  
Thin Plates ◽  
Destructive Testing ◽  
Low Frequencies ◽  
Plastic Films ◽  
Additional Signal ◽  
Virtual Array ◽  
Thin Plastic ◽  
Coupled Technique

At low frequencies, in thin plates the phase velocity of the guided A0 mode can become slower than that of the ultrasound velocity in air. Such waves do not excite leaky waves in the surrounding air, and therefore, it is impossible to excite and receive them by conventional air-coupled methods. The objective of this research was the development of an air-coupled technique for the reception of slow A0 mode in thin plastic films. This study demonstrates the feasibility of picking up a subsonic A0 mode in plastic films by air-coupled ultrasonic arrays. The air-coupled reception was based on an evanescent wave in air accompanying the propagating A0 mode in a film. The efficiency of the reception was enhanced by using a virtual array which was arranged from the data collected by a single air-coupled receiver. The signals measured at the points corresponding to the positions of the phase-matched array were recorded and processed. The transmitting array excited not only the A0 mode in the film, but also a direct wave in air. This wave propagated at ultrasound velocity in air and was faster than the evanescent wave. For efficient reception of the A0 mode, the additional signal-processing procedure based on the application of the 2D Fourier transform in a spatial–temporal domain. The obtained results can be useful for the development of novel air-coupled ultrasonic non-destructive testing techniques.

scholarly journals Attenuation of a Slow Subsonic A0 Mode Ultrasonic Guided Wave in Thin Plastic Films

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1648 ◽  
Author(s):  
Rymantas Kažys ◽  
Reimondas Šliteris ◽  
Liudas Mažeika ◽  
Olgirdas Tumšys ◽  
Egidijus Žukauskas
Keyword(s):  
Guided Waves ◽  
High Efficiency ◽  
Lamb Waves ◽  
Ultrasonic Transducer ◽  
Plane Waves ◽  
Ultrasound Velocity ◽  
Guided Wave ◽  
Low Frequencies ◽  
Plastic Films ◽  
Thin Plastic

The ultrasonic testing technique using Lamb waves is widely used for the non-destructive testing and evaluation of various structures. For air-coupled excitation and the reception of A0 mode Lamb waves, leaky guided waves are usually exploited. However, at low frequencies (<100 kHz), the velocity of this mode in plastic and composite materials can become slower than the ultrasound velocity in air, and its propagation in films is accompanied only by an evanescent wave in air. To date, the information about the attenuation of the slow A0 mode is very contradictory. Therefore, the objective of this investigation was the measurement of the attenuation of the slow A0 mode in thin plastic films. The measurement of the attenuation of normal displacements of the film caused by a propagating slow A0 mode is discussed. The normal displacements of the film at different distances from the source were measured by a laser interferometer. In order to reduce diffraction errors, the measurement method based on the excitation of cylindrical but not plane waves was proposed. The slow A0 mode was excited in the polyvinylchloride film by a dry contact type ultrasonic transducer made of high-efficiency PMN-32%PT strip-like piezoelectric crystal. It was found that that the attenuation of the slow A0 mode in PVC film at the frequency of 44 kHz is 2 dB/cm. The obtained results can be useful for the development of quality control methods for plastic films.

scholarly journals Air-Coupled Excitation of a Slow A0 Mode Wave in Thin Plastic Films by an Ultrasonic PMN-32%PT Array

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 3156 ◽  
Author(s):  
Rymantas Kazys ◽  
Liudas Mazeika ◽  
Reimondas Sliteris ◽  
Justina Sestoke
Keyword(s):  
Lamb Wave ◽  
Composite Structures ◽  
Guided Waves ◽  
Ultrasound Velocity ◽  
Processing Technique ◽  
Wave Mode ◽  
Destructive Testing ◽  
Plastic Films ◽  
Directivity Patterns ◽  
Thin Plastic

Ultrasonic non-destructive testing techniques (NDT) based on the application of guided waves are already used for inspection of plate-type structures made of various materials, including composite materials. Air-coupled ultrasonic techniques are used to test such structures by means of guided waves. The objective of this research was development and investigation of air-coupled excitation of a slow A0 Lamb wave mode in thin plastic films by a PMN-32%PT ultrasonic array. It is known that when the velocity of the A0 mode in the film is less than the ultrasound velocity in air no leaky wave is observed in a surrounding air. It opens new possibilities for NDT of composite structures. The influence of the airborne wave may be eliminated by 3D filtering in a wavenumbers-frequency domain. A special filter and corresponding signals processing technique were developed in order to obtain directivity patterns and velocity maps of the waves propagating in all directions. The measured ultrasound velocity values prove that, with the proposed method, it is possible to excite a slow A0 Lamb wave mode and to separate it from other parasitic waves propagating in air. Measurements of the parameters of the slow A0 mode, such as the propagation velocity in the plastic film, may be applied for the material characterization.

scholarly journals Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2636 ◽  
Author(s):  
Rymantas Kazys ◽  
Almantas Vilpisauskas ◽  
Justina Sestoke
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Ultrasound Velocity ◽  
Optimization Procedure ◽  
Wave Mode ◽  
Zero Order ◽  
Air Gap ◽  
Thin Plates ◽  
Low Frequencies ◽  
Excitation Method

Air-coupled excitation and reception of ultrasonic guided waves is already used for non-destructive testing and evaluation (NDT & E). Usually for air-coupled NDT & E purposes the lowest zero-order antisymmetric Lamb wave mode A0 is used, because it is most sensitive to internal defects and thickness variations. The velocity of the A0 mode is reduced with a reducing frequency and at low frequencies may become slower than the ultrasound velocity in air. Such a wave is named a slow Lamb wave. The objective of this research was the development and investigation of an air-coupled excitation method of the slow zero-order antisymmetric Lamb wave based on application of a piezoceramic ultrasonic array. We have proposed to excite the A0 mode by a planar air-coupled phased array with rectangular elements. The array is matched to the wavelength of the A0 mode in the film. Performance of such an excitation method was investigated both theoretically and experimentally. Two excitation methods of the array were analysed: when all array elements were excited simultaneously or one by one with a proper delay. In order to reduce crosstalk between array elements via the air gap, we have proposed an optimization procedure based on additional shifts of electric excitation impulses of the array elements. For experimental verification of the proposed approach a prototype of the air-coupled eight element array made of Pz-29 piezoceramic strips was manufactured. Experimental validation confirmed the possibility of exciting the slow A0 Lamb wave mode through the air gap in thin plates and films.

scholarly journals Sea Water Contamination in the Vicinity of the Italian Minor Islands Caused by Microplastic Pollution

Water ◽  
2018 ◽  
Vol 10 (8) ◽  
pp. 1108 ◽  
Author(s):  
Giuseppe de Lucia ◽  
Alvise Vianello ◽  
Andrea Camedda ◽  
Danilo Vani ◽  
Paolo Tomassetti ◽  
...  
Keyword(s):  
Water Contamination ◽  
Sea Water ◽  
Ethylene Vinyl Acetate ◽  
Average Density ◽  
Spectroscopy Analysis ◽  
Policy Makers ◽  
Plastic Films ◽  
Thin Plastic ◽  
Abundance And Distribution ◽  
River Mouths

The abundance and distribution of microplastics (MP) were evaluated in six “clean” sites (Italian minor islands) and in two “polluted” areas (near the mouth of two major Italian rivers). Samples of MP, plankton and persistent organic pollutants (POPs) were collected using a manta trawl (MA) and a plankton net (WP2), both lined with a 333 µm mesh net. MP have been confirmed to be ubiquitous since they were found at each site, showing an average density of 0.3 ± 0.04 items/m3 (values ranged from 0.641 to 0.119 ). When comparing the clean sites with the polluted ones, a significantly higher value of MP was found near the river mouths. The most common types of MP were synthetic filaments (50.24%), followed by fragments (30.39%), thin plastic films (16.98%) and spheres (2.39%). Infrared spectroscopy analysis highlighted that the most abundant polymers were polyethylene (PE-26%), polypropylene (PP-11%), polyethylene-terephthalate/polyester (PET/PEST-8%) and ethylene-vinyl-acetate (EVA-5%). Polychlorinated biphenyls and organochlorine pesticides were detected in all the samples with a high variability among sites and depths. This study adds to the existing information on the distribution of contaminants across the Mediterranean Sea, and is useful to policy makers who wish to implement effective measures to reduce MP pollution.

Thermal Effects on Ultrasonic Joining of Thin Plastic Films Using Torsional Vibrations

2008 ◽  
Vol 47 (8) ◽  
pp. 6431-6436 ◽  
Author(s):  
Kazunari Adachi ◽  
Tsuyoshi Takahashi ◽  
Kenichi Kamehashi ◽  
Kazumi Watanabe ◽  
Kenta Uchiyama ◽  
...  
Keyword(s):  
Thermal Effects ◽  
Torsional Vibrations ◽  
Plastic Films ◽  
Thin Plastic

The environmental degradation of thin plastic films

1993 ◽  
Vol 31 (3) ◽  
pp. 179-198 ◽  
Author(s):  
Philip J. Whitney ◽  
Clare H. Swaffield ◽  
Andrew J. Graffham
Keyword(s):  
Environmental Degradation ◽  
Plastic Films ◽  
Thin Plastic

On the Weathering of Thin Plastic Films

1983 ◽  
Vol 105 (2) ◽  
pp. 149-156 ◽  
Author(s):  
H. Cheng ◽  
R. B. Bannerot
Keyword(s):  
Thermal Effects ◽  
Solar Collector ◽  
Solar Irradiation ◽  
Plastic Film ◽  
Degradation Mechanisms ◽  
Plastic Films ◽  
Mechanical Effects ◽  
Thin Plastic

A program is described for the controlled degradation and evaluation of thin plastic film samples in a set of parallel (in time) exposures. The intent of the various exposures is to separate the effects of identifiable degradation mechanisms associated with each material’s use as a solar collector cover. The mechanisms considered were those due to: (i) environment less solar irradiation (chemical, abrasion, humidity, etc.); (ii) environment including solar irradiation; (iii) thermal effects and (iv) mechanical effects. The procedures described in the program are illustrated by presenting the details for the evaluation of two commonly used plastic films.

Test of Rupture Strength of Thin Plastic Films

1950 ◽  
Vol 21 (5) ◽  
pp. 491-492 ◽  
Author(s):  
Joses J. L. Chen
Keyword(s):  
Rupture Strength ◽  
Plastic Films ◽  
Thin Plastic
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