The integration of a high-performance metamaterial (MM) onto mechanically flexible and deformable substrates offers significant promise in flexible electronics. Here, we propose two types of stretchable infrared (IR) MMs to design a tunable perfect absorber with a ring-shape (PA-RS) and a cross-shape (PA-CS) on a PDMS/Au/PDMS substrate, respectively. By stretching devices along different directions, PA-RS and PA-CS exhibit ultra-narrowband, polarization-dependent/independent, and switchable characterizations in the IR wavelength range. The tuning ranges are 2.37 μm and 2.36 μm for PA-RS and PA-CS with the deformation quantity of 2.50 μm along two-dimensional directions, respectively, without extra power supply. In this deformation range, most of the incident light is perfectly absorbed for PA-RS design operated at a wavelength of 4.31 μm and PA-CS design operated at a wavelength of 4.24 μm. The corresponding Q-factors of two devices are 98 and 118 for PA-RS and PA-CS, respectively. Such results are very suitable for high-performance refractive index sensor applications. Furthermore, two devices exhibit the functionalities of s-polarization switches and s-/p-polarization switches. To further investigate the characterizations of devices deformed by a tensile force, PA-CS could be actively tuned by bending devices at a certain angle. In the future, these proposed stretchable IR MMs could potentially possess high portability, applicability, and cost-effectiveness for wearable electronic devices in a variety of sensor fields.

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We present and demonstrate a MEMS-based tunable terahertz metamaterial (TTM) composed of inner triadius and outer electric split-ring resonator (eSRR) structures. With the aim to explore the electromagnetic responses of TTM device, different geometrical parameters are compared and discussed to optimize the suitable TTM design, including the length, radius, and height of TTM device. The height of triadius structure could be changed by using MEMS technique to perform active tunability. TTM shows the polarization-dependent and electromagnetic induced transparency (EIT) characteristics owing to the eSRR configuration. The electromagnetic responses of TTM exhibit tunable characteristics in resonance, polarization-dependent, and electromagnetically induced transparency (EIT). By properly tailoring the length and height of the inner triadius structure and the radius of the outer eSRR structure, the corresponding resonance tuning range reaches 0.32 THz. In addition to the above optical characteristics of TTM, we further investigate its potential application in a refraction index sensor. TTM is exposed on the surrounding ambient with different refraction indexes. The corresponding key sensing performances, such as figure of merit (FOM), sensitivity (S), and quality factor (Q-factor) values, are calculated and discussed, respectively. The calculated sensitivity of TTM is 0.379 THz/RIU, while the average values of Q-factor and FOM are 66.01 and 63.83, respectively. These characteristics indicate that the presented MEMS-based TTM device could be widely used in tunable filters, perfect absorbers, high-efficient environmental sensors, and optical switches applications for THz-wave optoelectronics.

We present an electromechanically rotatable infrared (IR) cross-shaped metamaterial (CSM) in the mid-IR wavelength range. The CSM configuration is composed of double gold layers with cross-shaped nanostructures. To investigate the fano-resonance within CSM nanostructures, the aspect ratios and length ratios of CSM are compared and discussed. The electromagnetic responses exhibit the characteristics of large tuning range, tunable broad and narrow bandwidths. By properly tailoring the aspect ratio of CSM, the resonance can be tuned with bidirectional tuning in the range of 650 nm. CSM with different length ratios exhibit narrowband resonances around the wavelength of 4.6 μm and broadband resonances in the wavelength range of 5.0 μm to 6.5 μm. These characteristics of CSM with different aspect ratios and length ratios could be potentially used in IR narrowband and broadband filter. To further increase the flexibility of proposed electromechanically rotatable CSM, an actively tunable narrowband and broadband filter in the mid-IR wavelength range is performed. This study provides a unique approach to realizing an IR filter, with high flexibility.

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