Tunable origami metastructure based on liquid crystal for curvature sensing in terahertz band

This paper introduces an origami metastructure (OMST), which realizes the conversion of electromagnetically induced transparency (EIT) to electromagnetically induced absorption (EIA), and realizes the liquid crystal adjustable curvature sensing (CS) function using EIA. The OMST consists of an upper resonator (resonator 1) and a lower resonator (resonator 2). Resonator 1 achieves the EIT phenomenon when 0–2 THz is excited by an electromagnetic wave (EMW), and a transparent window appears at 0.883 THz. When resonator 2 is introduced, the phase of OMST is regulated and the EIT phenomenon changes to EIA. The absorption peak is 0.998 THz, and the peak value is 0.937. OMST uses the flexible material polyimide, and the liquid crystal injected between the resonators 1 and 2 layers is a nematic liquid crystal (HTW114200-100). The metastructure is used on cylindrical surfaces of CS to measure their curvature. In the initial liquid crystal state, when EMW incident, the OMST resonance frequency changes from 0.998 to 1.006 THz, and the corresponding absorptivity changes from 0.937 to 0.650 (from 0.924 to 0.613 in the bias liquid crystal state). Regarding CS, OMST can be used for curvature detection in the micrometer class, with a detection range of 0–0.02 μm. The maximum curvature measurement sensitivity is 32.230 (33.690), and the quality-factor is 41.859 (40.840). Traditional CS is usually made of optical fiber, but because of the fragility of optical fiber sensors, it is difficult to directly apply to the curvature measurement of various objects. However, OMST's design overcomes this shortcoming and is simple to manufacture. OMST has a high detection accuracy and can be used to detect the curvature of small objects, which has a potential application value in flatness detection and intelligent robots.