J. Zhang, T. Xia, Q. Chen, Q. Sun, Y. Deng, C. Wang,
https://link.springer.com/article/10.1007/s10812-018-0616-6
The characteristic absorption spectra of paraformaldehyde and metaldehyde in the terahertz frequency region are obtained by terahertz time-domain spectroscopy (THz-TDS). In order to reduce the absorption of terahertz (THz) wave by water vapor in the air and the background noise, the measurement system was filled with dry air and the measurements were conducted at the temperature of 24°C. Meanwhile, the humidity was controlled within 10% RH. The THz frequency domain spectra of samples and their references from 0 to 2.5 THz were analyzed via Fourier transform. The refractive index and absorption coefficients of the two aldehydes were calculated by the model formulas. From 0.1 to 2.5 THz, there appear two weak absorption peaks at 1.20 and 1.66 THz in the absorption spectra of paraformaldehyde. Only one distinct absorption peak emerges at 1.83 THz for metaldehyde. There are significant differences between the terahertz absorption coefficients of paraformaldehyde and metaldehyde, which can be used as "fingerprints" to identify these substances. Furthermore, the relationship between the average absorption coefficients and mass concentrations was investigated and the average absorption coefficient–mass concentration diagrams of paraformaldehyde and metaldehyde were shown. For paraformaldehyde, there is a linear relationship between the average absorption coefficient and the natural logarithm of mass concentration. For metaldehyde, there exists a simpler linear relationship between the average absorption coefficient and the mass concentration. Because of the characteristics of THz absorption of paraformaldehyde and metaldehyde, the THz-TDS can be applied to the qualitative and quantitative detection of the two aldehydes to reduce the unpredictable hazards due to these substances.
Zhang Y1,
Qiao S1,
Liang S2,
Wu Z1,
Yang Z1,
Feng Z2,
Sun H1,
Zhou Y1,
Sun L1,
Chen Z3,
Zou X3,
Zhang B4,
Hu J3,
Li S3,
Chen Q5,
Li L1,
Xu G1,
Zhao Y1,
Liu S1.
- 1†Terahertz Science Cooperative Innovation Center, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China.
- 2‡National Key Laboratory of Application Specific Integrated Circuit, Hebei Semiconductor Research Institute, Shijiazhuang 050000, China.
- 3§National Key Laboratory of Communication, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China.
- 4∥School of Electronics Engineering, University of Electronic Science and Technology of China, Chengdu 610054, P. R. China.
- 5⊥Suzhou Institute of Nano-tech and Nano-bionics, Chinese Academy of Sciences, Suzhou 215123, P. R. China.
http://www.ncbi.nlm.nih.gov/pubmed/25919444
The past few decades have witnessed a substantial increase in terahertz (THz) research. Utilizing THz waves to transmit communication and imaging data has created a high demand for phase and amplitude modulation. However, current active THz devices, including modulators and switches, still cannot meet THz system demands. Double-channel heterostructures, an alternative semiconductor system, can support nanoscale two-dimensional electron gases (2DEGs) with high carrier concentration and mobility and provide a new way to develop active THz devices. In this Letter, we present a composite metamaterial structure that combines an equivalent collective dipolar array with a double-channel heterostructure to obtain an effective, ultrafast, and all-electronic grid-controlled THz modulator. Electrical control allows for resonant mode conversion between two different dipolar resonances in the active device, which significantly improves the modulation speed and depth. This THz modulator is the first to achieve a 1 GHz modulation speed and 85% modulation depth during real-time dynamic tests. Moreover, a 1.19 rad phase shift was realized. A wireless free-space-modulation THz communication system based on this external THz modulator was tested using 0.2 Gbps eye patterns. Therefore, this active composite metamaterial modulator provides a basis for the development of effective and ultrafast dynamic devices for THz wireless communication and imaging systems.
