Time-Domain Topological Energy Imaging Method of Concrete Cavity Defect by Lamb Wave

Wen-Fa Zhu,Shu-Bin Zheng,Guo-Peng Fan,Wei Shao,Le-Le Peng,Xing-Jie Chen,Hai-Yan Zhang

doi:10.1155/2019/6294603

Abstract

This paper presents an ultrasonic Lamb wave imaging method based on time-domain topological energy to address artifacts in the results of traditional ultrasound imaging methods. This method is based on topological theory and the calculation of the direct and adjoint sound fields in a defect-free reference medium. It focuses the direct and adjoint sound fields at the cavity defect using time reversal and their time-domain topological energy as the pixel values of the image to reduce the artifacts. The physical mechanism of time-domain topological energy (TDTE) imaging is revealed by finite element simulation and experiment. The feasibility of this method for multilayer concrete cavity defect imaging is verified. Compared with the traditional synthetic aperture focusing technique (SAFT) imaging method, the numerical simulation and experimental results show that the method can overcome the influence of ultrasonic Lamb wave dispersion and locate cavity defects with high accuracy and few artifacts. These features indicate the potential of the method in imaging damage concrete structures.

Highlights

Concrete is the most widely used material in highway, highspeed railway, and other traffic engineering structures
An ultrasonic Lamb wave high-precision imaging method for realizing multilayer concrete cavity defects using time-domain topological energy (TDTE) is proposed. e method is based on the calculation of direct and adjoint sound fields in the defect-free reference medium, and the excitation signal of the sensor is used as the source calculation. en, in the sound field, the Lamb wave scattering signal caused by the cavity defect is used as the sound source to calculate the adjoint sound field
The direct sound field is multiplied by the adjoint sound field to obtain the time-domain topological energy value as the imaged pixel value. e TDTE method is much better for multilayer structure as it is based on the focusing effect of the forward acoustic field and the adjoint acoustic field

Summary

Introduction

Concrete is the most widely used material in highway, highspeed railway, and other traffic engineering structures. E difference in acoustic impedance between layers cannot be neglected in cavity defects in highways and high-speed rail structures [13, 14] In this case, the assumption of a single constant shear wave velocity will inevitably lead to detection errors. Is study establishes a finite element model and constructs an experimental system to stimulate the generation of ultrasonic Lamb waves in concrete and obtain ultrasonic scattering signals. If the excitation signal xn(t) is applied at the nth element of the linear array and received at each point in the imaging region of the reference plate, the sound field of the entire imaging region can be obtained through calculation, which is called the direct sound field U(x, y, t). According to the propagation model of the Lamb wave, the adjoint sound field V(x, y, t) in the reference plate can be obtained: V(x, y, t) Dcp􏽮z0(t); tω − tp􏽯,. E complex acoustic wave propagation in a three-dimensional model can be simulated by using this method. e upper and bottom surfaces of the model are free, while the remaining four sides are absorbing. e sample is a twolayer concrete bonding structure. e size of the first layer is 1000 × 1000 × 50 mm, and the physical parameters are as

Intedrleafyeecrt cavity

Ultrasonic transmitting and receiving instrument

Conclusion