Polarization sensing of mechanical strain in THz stereo-metamaterials using compact polarimetric terahertz time-domain spectroscopy

A flexible and reflective stereo-metamaterial (SMM) was fabricated in a strain-sensitive soft backing layer of polydimethylsiloxane and polyimide (PI-PDMS-PI) substrate. The SMM consists of coupled copper rings designed to interact with terahertz (THz) radiation. Up to 5.5% compressive strain was applied to change the resonant frequencies of Cu-coupled metamaterial rings detected through polarization status. Upon application of compressive strain, a blueshift was observed in the frequency-switching response related to the ellipticity of the reflected THz waves. This shift indicates that the SMM structure's resonant properties are sensitive to mechanical deformation. To characterize the polarization state of the reflected THz waves, the four individual Stokes parameters (S₀, S₁, S₂, S₃) and their normalized forms were investigated and analyzed using polarimetric THz time-domain spectroscopy (P-THz-TDS). These characteristics, along with the device's ability to recover when relaxed, suggest potential applications in areas such as structural health monitoring, wearable electronics, and adaptive THz optics.