Metamaterials are artificial materials with unique electromagnetic properties not found in nature and could exhibit a strong electromagnetic resonance with frequency. These characteristics depending on the geometry, dimensions, compositions of the structure, and even the symmetry. In this study, we demonstrated a highly sensitive detection method of glycerol-water solutions using terahertz metamaterials fabricated on silicon substrate with metal arrays of the asymmetric double split-ring resonator structure. We measured the transmitted spectra of the metamaterial to detect the water-glycerol solutions at different concentrations by the terahertz time-domain spectroscopy system. With the increasing of glycerol concentration, resonant dips of metamaterial exhibit the blue-shift phenomena and transmittance at the resonance frequency simultaneously enhance. The movement of resonant dips and the change of transmittance shows that these resonators are sensitive to the variation of glycerol concentration. The finite-difference time-domain simulation agree well with the experimental data, and the simulation of surface current and electric field distribution at resonance dips can further understand the resonance modes in transmission spectra. Our study provides new prospect into the application of terahertz metamaterials in detecting glycerol proportions of solution.
In recent years, terahertz metamaterials have attracted great attention due to their widely application in frequency selector, filter, and other optical devices. Vanadium dioxide as the promising thermal memory material, has been used in making terahertz modulation device because of its well-known insulator-to-metal transition triggered by thermal, optical, and electrical. Here, we designed a composite metamaterial with three rings structure, where outer and inner rings are set to be ideal metallic gold and the middle ring is replaced by VO2. Using finite-difference time-domain method, we theoretically studied the variety of THz transmitted spectra during the insulator-to-metal transition of VO2 and its influence on the resonance coupling effect. When VO2 is in insulating phase, there are two resonant dips in spectrum. However, as VO2 undergoes an insulator-to-metal transition, the low-frequency resonance gradually moves to high frequency and finally splits into two. Our obtained results indicate the reversible terahertz modulation can be achieved by combining metamaterials with phase transition material.
Recently, the terahertz biosensors based on metamaterials have attracted much attention due to the fact that metamaterials are sensitive to the local enhancement of electromagnetic field and the changes of the surrounding dielectric environment. In order to obtain the resonances with the high quality factor for biosensing, here we designed, simulated, and fabricated the metamaterial structures composed of a series of the asymmetric “double” circular arc (DASR) structures. The experimental data show there are three sharp resonance dips named Fano resonance in the terahertz transmission spectra. In the previous study of asymmetric double rings, we studied the effect of different cutting widths on the transmission characteristics of terahertz when the samples were placed at 0 degrees. Here, the spectral characteristics and polarization conversion characteristics of the samples after 90 degrees were studied. We found that when the sample rotated by 90 degrees only two resonance dips exist in the transmission spectrum. As the separation of asymmetric arcs gradually increases, two resonance frequencies also show blue-shift. To further analyze the reasons for the changes in the transmission spectrum at different angles of sample placement, we present the surface currents and the electromagnetic field distributions in those structures. Our obtained results indicate the terahertz metamaterial has great potential in application of biosensing field.
The spectral characteristics of the asymmetric double-wire structures have been investigated in the terahertz (THz) range. Based on the THz time-domain spectroscopy system, the spectral of the samples has been measured. It is shown that a transparent peak appears in the transmission spectrum which indicate that a resonance coupling exist between the two metal bars. Furthermore, we study the optical modulation properties when the pump light irradiates on the sample by using optical pump-terahertz probe technique (OPTP). The measured results indicate that the pump light can realize an optical switch effect to modulate the transmittance of THz wave. When adjusting the time delay between the optical pump and the terahertz probe pulses, the transmittance of THz wave varies, indicating the photoexcited carriers in the substrate have great influence on the resonance characteristics of the structure. Our obtained results indicate optical modulation method could provide the functionally potential applications in the terahertz modulators and filters.
The absorption spectra of two kinds of important functional oligosaccharides were firstly acquired based on Fourier transform infrared spectroscopy in the range of 0.15-10THz. The simulation results of their infrared spectra were given based on Gaussian software, which were in good agreement with the experiment results. The rotation spectra and some perssad vibration spectra of these molecules were analyzed, and their absorption peaks were exactly identified. The components information was obtained by comparing the simulation results of different molecules.
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