Abstract-Experimental and theoretical investigations of tartaric acid isomers by terahertz spectroscopy and density functional theory

Tao Chen, Qin Zhang, Zhi Li, Xianhua Yin, Fangrong Hu,

https://www.sciencedirect.com/science/article/pii/S1386142518306334

The terahertz (THz) absorption spectra of l-, d-, and dl-tartaric acid have been measured in the frequency range from 0.2 to 2.0 THz by terahertz time-domain spectroscopy (THz-TDS). The characteristic absorption peaks of these three tartaric acid isomers were obtained, which showed remarkable difference between enantiomers (l- and d-tartaric acid) and the racemic compound (dl-tartaric acid) in their peak frequencies. In parallel with the experimental study, theoretical calculations on isolated-molecule and unit cell of tartaric acids using density functional theory (DFT) were also performed for simulating the experimental THz spectrum features, which were in good agreement with the experimental data. Results demonstrate that THz-TDS can distinguish the tiny diversity between tartaric acid chiral isomers and its racemic compound, and provided an effective method for molecular identification in biological and biomedical engineering.

Abstract-Highly Sensitive Detection of Carbendazim by Using Terahertz Time-Domain Spectroscopy Combined With Metamaterial

 Binyi Qin,  Zhi Li,  Fangrong Hu,  Cong Hu,  Tao Chen,  Huo Zhang,   Yonghong Zhao

http://ieeexplore.ieee.org/document/8252737/

The rapid and sensitive detection of pesticide residue is essential for ensuring the food safety of consumers. However, there are many disadvantages for current approaches to detect pesticide residue, such as complex pre-treatment and low sensitivity. In this paper, we demonstrate a highly sensitive carbendazim detection method by using terahertz time-domain spectroscopy (THz-TDS) combined with metamaterial. The metamaterial composed of metal ohm ring arrays, is applied in detecting different concentrations of carbendazim. Resonant peaks of metamaterial move to a lower frequency as the concentration increases. The results illustrate that metamaterial can detect trace amounts of carbendazim, as small as 5 mg/L, which is about 104 times enhancement compared to the squash method for THz-TDS detection. It also means that metamaterial combined with THz-TDS is a potential new approach for food quality and safety control.

Abstract-Analog of Electromagnetically Induced Transparency at Terahertz Frequency Based on Bilayer-Double-H-Metamaterials

Yuee Wang, Zhi Li, Fangrong Hu, 

http://iopscience.iop.org/article/10.1088/1361-6463/aa9ba0/pdf

We design a bilayer-double-H-metamaterials (BDHM) composed of two layers of metallic and two layers of dielectric to analog a spectral response of electromagnetically induced transparency (EIT) at terahertz frequency. By changing the incident angle, the BDHM exhibits the EIT-like spectral response. The tunable spectral performances and modulation mechanism of transparent peak are theoretically investigated using a full-wave electromagnetic simulation software. The physical mechanism of the EIT-like effect is based on the constructive and destructive interference between the induced electrical dipoles. Our work provides a new way to realize the EIT-like effect only by changing the incident angles of metamaterials. The potential applications include tunable filter, sensor, attenuator, switches, and so on.

Abstract-Identification of genetically modified cotton seeds by terahertz spectroscopy with MPGA-SVM

• Binyi Qin^a, b, 
• Zhi Li^a, c,  
• Tao Chen^c, 
• Yu Chen^d

• ^a School of Mechano-Electronic Engineering, Xidian University, Xi’an, Shanxi 710071, China
• ^b School of Electronics and Communication Engineering, Yulin Normal University, Yulin, Guangxi 537000, China
• ^c Guangxi Key Laboratory of Automatic Detecting Technology and Instruments, School of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin, Guangxi 541004, China
• ^d SZU-NUS Collaborative Innovation Center for Optoelectronic Science & Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China

http://www.sciencedirect.com/science/article/pii/S003040261730699X

The purpose of this paper was to propose a method that combines support vector machine (SVM) and multi-population genetic algorithm (MPGA) for identifying Genetically modified (GM) cotton seeds with THz spectroscopy. The parameters of SVM were tuned by using MPGA. Comparing previous reports of THz-TDS for GM crops detection, we used a larger sample size and more evaluation criterions (i.e. confusion matrix, average accuracy and 95th percentile of accuracy) in the experiment. Principal component analysis (PCA) was utilized to reduce dimensions of THz absorbance spectra, and then used the result of PCA as the input of different classifiers. When the input dimensionality of MPGA-SVM was 12, recall, precision and F-score were more than 97.9%, 96% and 0.9796, respectively, and accuracy was 99%. To further study the performance of MPGA-SVM with different input dimensionality, different number of principal components (ranged from 2 to 16 at intervals of 2) was selected. In addition, the proposed method was compared with traditional classifiers (decision trees (DT), k-nearest neighbor (KNN) and discriminant analysis (DA)). All the results showed that MPGA-SVM has better performance than other classifier. Thus, MPGA-SVM combined with THz spectroscopy is a potential identification tool for GM cotton seeds detection.

Abstract-Wavelength Selection for Quantitative Analysis in Terahertz Spectroscopy Using a Genetic Algorithm

Zhi Li ; 
The author is with the College of Information Science and Engineering and the Key Laboratory of Grain Information Processing and Control, Ministry of Education, Henan University of Technology, Zhengzhou 450001, China. (email: lizhi@haut.edu.cn).

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=5725169008357305447

In the quantitative analysis of the components of mixtures based on terahertz time-domain spectroscopy (THz-TDS), wavelength selection of the spectra holds great importance for quantitative accuracy. The raw spectrum obtained in the experiments contains both high signal-to-noise ratio (SNR) and low SNR information, along with many types of noise, such as the scattering effect and random disturbances. Usually, the frequency band used for analysis is determined over multiple attempts to obtain the most satisfactory results. Currently, there is no common method for selecting the appropriate frequencies. In this paper, a wavelength selection method for the THz absorption spectra based on a genetic algorithm is presented, with the main focus on quantitative analysis by THz-TDS. Using this method, most of the useful data with high SNR were retained. The comparison between quantitative analysis errors obtained by the raw spectra and by the wavelength-selected spectra showed that this method could significantly decrease quantitative errors. After wavelength selection, the quantitative analysis errors of 12 mixture samples with widely differing concentrations are predominantly below 6% with a standard deviation of 0.0344.

Abstract-The terahertz spectrum detection of transgenic food

• Jianjun Liu^a, , 
• Zhi Li^a, b

• ^a School of Mechano-Electronic Engineering, Xidian University, Xi’an, Shanxi 710071, PR China
• ^b School of Electronic Engineering and Automation, Guilin University of Electronic Technology, Guilin, Guangxi 541004, PR China

http://www.sciencedirect.com/science/article/pii/S0030402614011139

Received 13 July 2013, Accepted 5 January 2014, Available online 4 November 2014

This paper presents the optical characteristic of the four transgenic foods in the terahertz (THz) by means of electro-optic sampling. The transmission spectra and complex refractive index of the four transgenic foods are obtained. This paper finds that transgenic maize (TGM), transgenic rice (TGR), transgenic soybean (TGS) and transgenic potato (TGP) all have absorption within the frequency range of 0.2 and 2.5 THz. It can be seen that the TGM and TGR have obvious absorption peaks at 1.08 and 1.82 THz respectively, the TGS has a plurality of absorption peak in this frequency band, compared to the other three samples, and the TGP is slow. The unique absorption properties in THz of four transgenic foods show that the time-resolved terahertz spectroscopy can be applied to detect and identify transgenic food.

Abstract-Characterization of cocrystals formed by grinding amino acids through terahertz time-domain spectroscopy

• Xiaoyan Zhao, 
• Haixia Su, 
• Zhaohui Zhang, 
• Zhi Li, 
• Han Zhang, 
• Tianyao Zhang

http://link.springer.com/article/10.1007%2Fs11434-014-0432-1

In this paper, we used terahertz time-domain spectroscopy (THz-TDS) over a range of 0.3–2.5 THz to investigate the formation of solid-state cocrystals of amino acids, formed by grinding mixtures of two different kinds of amino acids. For comparison, we prepared dual-layer samples, combined by pressing two single-component pellets together without grinding. In the ground-mixture samples, some extra absorption peaks appeared, different from the characteristic peaks of the pure components, but these peaks did not appear in the dual-layer samples. Thus, these extra absorption peaks in the THz range are unique features of cocrystals. From our results, we believe that THz-TDS is a promising technique to characterize cocrystals.

Article & Abstract-Design of a polarization insensitive multiband terahertz metamaterial absorber

Fangrong Hu, Li Wang, Baogang Quan, Xinlong Xu, Zhi Li, Zhongan Wu,  Xuecong Pan
My Note: you can read the entire article here:
http://m.iopscience.iop.org/0022-3727/46/19/195103/

We design a terahertz (THz) metamaterial absorber having four narrowband high absorptivities of 98%, 97%, 98% and 97% at frequencies of 0.68 THz, 1.27 THz, 2.21 THz and 3.05 THz, respectively. The absorber consists of three metallic layers, which are separated by two dielectric spacers. The absorption performances are simulated using a commercialized full-wave electromagnetic simulation software, and the mechanism of absorption is theoretically investigated. The result shows that the absorber is insensitive to the polarization of THz wave and the position of every absorption peak can be effectively tuned by the geometries of the absorber. The potential applications of the absorber include spectrally selective detecting, THz sensing and thermal imaging.