Abstract
Introduction
In recent years, metamaterials have attracted great attention due to their unique properties[
Ionic solution, such as calcium chloride (CaCl2), plays an essential role in many biochemical processes[
In this work, a novel terahertz photo-excited tunable metamaterial switch is investigated. Its resonant frequencies can be modulated by variation of external light intensity. Furthermore, the gap of this structure can be equivalent to a capacitor, and LC resonance occurs as a result, which is sensitive to its surrounding dielectric environment. Therefore, this structure can also achieve a sensing application by changing the concentration of the injected ionic solution.
1 Structure design and analysis
The schematic diagram of the proposed structure’s unit cell is shown in
Figure 1.Schematic diagram of (a) the proposed photosensitive structure, and (b) laser pump testing configuration
Figure 2.Transmission spectrum of metamaterial structure for various silicon conductivities when electric field of terahertz wave was (a) perpendicular, and (b) parallel to the top two split gaps
Figure 3.
2 Sensing application
The dielectric responses of CaCl2 solutions with different concentrations (up to 3 mol/L) were measured by a typical terahertz time domain spectroscopy system in the range of 0.2~1.5 THz, which are shown in
Figure 4.(a) Real parts (ε’), and (b) imaginary parts (ε’’) of the complex permittivity of CaCl2 solutions with different concentrations
Figure 5.Peak responses of the sensor for different permittivities and the inset figure is the schematic diagram of the proposed structure coated with analyte
Figure 6.Frequency shifts for different CaCl2 molar concentrations
3 Conclusion
In this work, a terahertz photo-excited tunable metamaterial sensor is investigated, and the resonant frequency of this switch can be modulated by variation of external light intensity and changing the permittivity of the surrounding material. This sensor is composed of a hybrid metal-semiconductor structure and a flexible polyimide substrate. Silicon is filled in the gaps of the structure. Simulation results reveal that the conductivity of the semiconductor component can be tuned by changing the external pump light’s power, resulting in resonant peak shift of the composite metamaterial structure. The electric field and current density distributions of this structure under different resonant frequencies are also analyzed. The physical mechanism of this device has been further discussed. Moreover, the resonant peak will be red-shift as the permittivity of CaCl2 increases, and the sensitivity is 11.4 GHz per M. This work will contribute to qualitative and quantitative study in trace sensing in terahertz region, especially for non-destructive testing of low-density or thin-film biological samples.
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