A sickle-shaped metamaterial (SSM) based biochemical sensor with multiple resonances was investigated in the terahertz frequency range. The electromagnetic responses of SSM were found to be four resonances, namely dipolar, quadrupolar, octupolar and hexadecapolar plasmon resonances. They were generated from the interactions between SSM and perpendicularly incident terahertz waves. The sensing performances of SSM-based biochemical sensors were evaluated by changing ambient environments and analyte varieties. The highest values of sensitivity and figure of merit (FOM) for SSM covered with analyte thin-films were 471 GHz/RIU (refraction index unit) and 94 RIU⁻¹, respectively. In order to further investigate the biosensing ability of the proposed SSM device, dielectric hemispheres and microfluidic chips were adopted to imitate dry and hydrous biological specimens, respectively. The results show that the sensing abilities of SSM-based biochemical sensors could be enhanced by increasing either the number of hemispheres or the channel width of the microfluidic chip. The highest sensitivity was 405 GHz/RIU for SSM integrated with microfluidic chips. Finally, three more realistic models were simulated to imitate real sensing situations, and the corresponding highest sensitivity was 502 GHz/RIU. The proposed SSM device paves the way to possible uses in biochemical sensing applications.

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.

A design of a tunable terahertz (THz) programmable device by using wrench-shape metamaterial (WSM) is presented, which is composed of a Au layer fabricated on a Si substrate. The size of the WSM unit cell is 30 μm×30 μm, and the distance between each WSM is 20 μm. The electromagnetic response of the THz programmable device exhibits the switch function for single-band resonance and dual-band resonance at the transverse electric mode and transverse magnetic mode. The resonance spans from 3.00 to 8.00 THz and is insensitive to the angle of the incident THz wave. While changing the incident angle of the THz wave, the bandwidth of the resonance becomes broader and the transmission spectrum decreases gradually. By configuring the unit cell from single-atom to quad-atom, WSM exhibits optical-logic behaviors with programmable characteristics and anti-interference. Such results are very suitable for use for an ultra-narrowband filter, single-/dual-band switch, polarization switch, and programmable device. It could potentially provide all-optical logical devices with multichannel data processing at higher bit rates.