Research overview
This paper presents a reference-free way to image the strain currently acting inside composite materials, an important need for structural health monitoring of visually opaque composites. Earlier terahertz metamaterial strain sensors relied on small amplitude or frequency shifts measured against an unstrained reference map. Here, a reversible, passive metamaterial based on a symmetric Jerusalem-cross design is embedded in a stretchable host, giving a tailored polarimetric signature. Measuring the ratio of terahertz transmission for two orthogonal polarizations at a few frequencies near the resonance (around 0.4 THz) gives a quantitative measure of local strain. Hyperspectral THz time-domain imaging, with wire-grid polarizers ensuring pure s- or p-polarization, mapped strain fields across the laminate at global strains of 0–6%. The approach could be applied to high-performance composites used in aerospace, automotive and defence.
Key findings
- Reference-free mapping of active strain using an embedded terahertz metamaterial laminate
- Polarimetric signature from a Jerusalem-cross metamaterial gives a quantitative strain measure
- Only two orthogonal polarizations and a few frequencies near 0.4 THz required
- Strain fields imaged by hyperspectral THz-TDS at global strains of 0–6%
