Abstract
The ability to image strain fields in composite materials is an indispensable necessity for structural health monitoring. Embedded electromagnetic metamaterials sensitive to applied stresses and operating in the terahertz regime have been proposed as a solution, but they have traditionally relied on slight amplitude or frequency shifts of their terahertz spectral resonance relative to a presumably unchanging, unstrained reference spectral map. Here, we demonstrate a facile, reference-free imaging technique to map the currently active local strain throughout a composite structure using a reversible passive terahertz metamaterial laminate with a tailored polarimetric signature. Only two orthogonal polarizations and a few frequencies are required to measure this strong terahertz response, from which the local strain environment may be rapidly and quantitatively mapped over large areas.
Highlights
Opaque high-performance structural composite materials, including glass and carbon fiber-reinforced polymer matrix materials and high-temperature thermoplastics used in the aerospace, automotive, and defense industries, have been widely adopted because of their strength, durability, and reduced weight and cost, providing significant advantages over metallic alternatives1
Inspired by this reference-free technique for mapping strain history using polarization-dependent signals19–21, we introduce a reference-free polarimetric technique for sensing current strain in composite materials, featuring an embedded passive terahertz MM laminate composed of symmetric crossbased antennas with small (∼5 μm) gaps between adjacent meta-atoms
A reference-free polarimetric technique is reported for the visualization of active strain fields in composite materials using embedded reversible terahertz metamaterials
Summary
Opaque high-performance structural composite materials, including glass and carbon fiber-reinforced polymer matrix materials and high-temperature thermoplastics used in the aerospace, automotive, and defense industries, have been widely adopted because of their strength, durability, and reduced weight and cost, providing significant advantages over metallic alternatives. A spatial distribution of the sample strain history was obtained by ellipsometric mapping at the MM resonant frequency, but the signature was irreversible and only recorded where local strain exceeded that threshold Inspired by this reference-free technique for mapping strain history using polarization-dependent signals, we introduce a reference-free polarimetric technique for sensing current strain in composite materials, featuring an embedded passive terahertz MM laminate composed of symmetric crossbased antennas with small (∼5 μm) gaps between adjacent meta-atoms. We show that for a simple one dimensional stretch, the polarization-dependent reversible MM response can be utilized in a self-referential manner to probe the currently active strain state reliably and quantitatively This polarimetric technique opens up a route to facile multidimensional strain imaging of opaque, composite materials without the impractical apriori requirement of an unchanging, unstrained reference spectral map
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