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Almantas Vilpisauskas
Ultrasound Research Institute, Kaunas University of Technology, K. Baršausko St. 59, LT-51423 Kaunas, Lithuania

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Journal article
Published: 16 January 2020 in Sensors
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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.

ACS Style

Rymantas J. Kazys; Almantas Vilpisauskas. Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film. Sensors 2020, 20, 516 .

AMA Style

Rymantas J. Kazys, Almantas Vilpisauskas. Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film. Sensors. 2020; 20 (2):516.

Chicago/Turabian Style

Rymantas J. Kazys; Almantas Vilpisauskas. 2020. "Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film." Sensors 20, no. 2: 516.

Journal article
Published: 11 August 2018 in Sensors
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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.

ACS Style

Rymantas J. Kazys; Almantas Vilpisauskas; Justina Sestoke. Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave. Sensors 2018, 18, 2636 .

AMA Style

Rymantas J. Kazys, Almantas Vilpisauskas, Justina Sestoke. Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave. Sensors. 2018; 18 (8):2636.

Chicago/Turabian Style

Rymantas J. Kazys; Almantas Vilpisauskas; Justina Sestoke. 2018. "Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave." Sensors 18, no. 8: 2636.