An Electromagnetic Sensor with a Metamaterial Lens for Nondestructive Evaluation of Composite Materials.

Adriana Savin,Roman Šturm,Rozina Steigmann,Alina Bruma

doi:10.3390/s150715903

Abstract

This paper proposes the study and implementation of a sensor with a metamaterial (MM) lens in electromagnetic nondestructive evaluation (eNDE). Thus, the use of a new type of MM, named Conical Swiss Rolls (CSR) has been proposed. These structures can serve as electromagnetic flux concentrators in the radiofrequency range. As a direct application, plates of composite materials with carbon fibers woven as reinforcement and polyphenylene sulphide as matrix with delaminations due to low energy impacts were examined. The evaluation method is based on the appearance of evanescent modes in the space between carbon fibers when the sample is excited with a transversal magnetic along z axis (TMz) polarized electromagnetic field. The MM lens allows the transmission and intensification of evanescent waves. The characteristics of carbon fibers woven structure became visible and delaminations are clearly emphasized. The flaws can be localized with spatial resolution better than λ/2000.

Highlights

In the past several decades, a number of nondestructive evaluation (NDE) techniques have been developed for detecting effect of damages/embedded objects in inhomogeneous media
Considering the fiber reinforced polymer composites (FRPC) as illuminated with a plane wave, transversal magnetic along z axis (TMz) polarized, at normal incidence, the magnetic field being parallel with the y axis such that Hx = Hz = 0 and Hy ≠ 0, in the very near field, evanescent wave can appear between carbon fibers similar with metallic strip gratings [31,52] and the eigenmodes between the carbon fibers playing the role of object for the detection system from Figure 1
At the scanning of the selected region of sample, the image delivered by the assembly sensor-equipment is amplified. This is due to the diffraction on the aperture of the evanescent waves generated by scattering on the woven carbon fibers

Summary

Introduction

In the past several decades, a number of nondestructive evaluation (NDE) techniques have been developed for detecting effect of damages/embedded objects in inhomogeneous media. The presence of material inhomogeneities (voids, inclusions, cracks, with lower electrical conductivity) will disturb induced eddy currents and will change the apparent impedance of sensors At this time, eNDE of FRPC is carried out by using eddy current sensors with ferrite core probes [22,23] or pancake coils [24], with and without shielding and metamaterial (MM) sensors used for improvement of electromagnetic image quality of microscopic discontinuities in conductive pieces as FRPC composites as well as metallic strip gratings from flexible printed circuits can be made using evanescent modes generated in slits, in spaces between carbon fibers and respectively in cracks [25]. The possibility to manipulate the evanescent waves that appear in the space between carbon fibers allow for an improvement of the spatial resolution to at least λ/2000, exceeding the limit imposed by diffraction

Constitutive Parameters of Conical Swiss Rolls

Functioning Principle of a MM Lens Sensor

Physical Realization of MM Lens Sensor

Studied Samples and Experimental Set-Up

Experimental Results

Conclusions