Terahertz (THz) waves are characterized by low photon energy, sensitivity to polar molecules, and different spectral responses to many biomolecules, which are of great research and application value in the biomedical field. Metamaterials are very sensitive to changes in the dielectric environment of their surfaces and have great potential in the field of sensing. Aiming at the current needs of terahertz-band biosensors whose sensitivity still needs to be improved, we propose an open-ring resonator biosensor with an asymmetric structure of discontinuous dielectric layers. Simulation results show that the refractive index sensitivity of this discontinuous dielectric layer metamaterial biosensor can reach up to 605 GHz/RIU, it exhibits a figure of merit (FOM) value of 24.2 RIU-1 and a high quality (Q) factor of 79.8, indicating a high Q factor and an ultra-high sensitivity. These characteristics are significant in the design of terahertz ultra-sensitive biosensors, showcasing their valuable application potential.
High performance tunable absorbers for terahertz (THz) frequencies will be crucial in advancing applications such as single-pixel imaging and spectroscopy. Metamaterials provide many new possibilities for manipulating electromagnetic waves at the subwavelength scale. Due to the limited response of natural materials to terahertz radiation, metamaterials in this frequency band are of particular interest.
The realization of a high-performance tunable (THz) absorber based on microelectromechanical system (MEMS) is challenging, primarily due to the severe mismatch between the actuation range of most MEMS (on the order of 1-10 microns) and THz wavelengths on the order of 100-1000 microns. Based on a metamaterial design that has an electromagnetic response that is extremely position sensitive, we combine meta-atoms with suspended at membranes that can be driven electrostatically. This is demonstrated by using near-field coupling of the meta-atoms to create a substantial change in the resonant frequency.
The devices created in this manner are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness ( 1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and with a fast switching speed ( 27 us). In the snap-down state, the resonance shifts by γ >200% of the linewidth (14% of the initial resonance frequency), and the absorption modulation measured at the initial resonance can reach 65%.
Gelatin is an irreversible hydrolyzed form of collagen having similar amino acid composites with its parent collagen. The hydrogen atoms on the side chains of the long peptide strings can weakly bond with their surrounding gelatin as well as water molecules in aqueous environment, forming a cross-linked 3D matrix. Gelatin has been used as a model for soft tissue phantoms in several medical imaging studies including in terahertz imaging. In the terahertz regime, the dielectric property of the gelatin relies largely on its hydration status and the relationship has been shown to be non-linear. It is therefore essential to study the change of the dielectric properties with respect to the hydration status so as to accurately mimic the properties of fresh biological tissues in the terahertz spectrum. In this work, we studied the hydration status of gelatin with a terahertz time-domain spectroscopy system in the reflection setup. Gelatin gels with different molar weights were prepared with the weight concentration varying from 0 to 33.3%. The complex dielectric constants of the samples were calculated and fitted with an effective medium approximation model. The results provide a quantitative knowledge on the total number of the water molecules affected by each gelatin molecule and how the hydration status is influenced by the concentration and the molar weight.
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