Research on Detection of Food additives Based on Terahertz Spectroscopy and Analytic Hierarchy Process

Terahertz time-domain spectroscopy is a kind of far-infrared spectroscopy technology,and its spectrum reflects the internal properties of substances with rich physical and chemical information,so the use of terahertz waves can be used to qualitatively identify food additives containing nitrogen elements.Analytic hierarchy process(AHP)was originally used to solve evaluation-type problems,and this paper introduces it into the field of terahertz spectral qualitative analysis,proposes a terahertz time-domain spectral qualitative identification method combined with analytic hierarchy process,and verifies the feasibility of the method by taking four common food additives(xylitol,L-alanine,sorbic acid,and benzoic acid)and two illegal additives(melamine,and Sudan Red No.I)as the objects of study.Firstly,the collected terahertz time-domain spectral data were pre-processed and transformed into a data set consisting of peaks,peak positions,peak numbers and overall trends;then,the data were divided into comparison and test sets,and a qualitative additive identification model incorporating analytic hierarchy process was constructed and parameter optimisation was performed.The results showed that the qualitative identification accuracies of additives based on single factors,i.e.,overall trend,peak value,peak position,and peak number,were 80.23%,70.93%,67.44%,and 40.70%,respectively,whereas the identification accuracy of the analytic hierarchy process qualitative identification method based on multi-factors could be improved to 92.44%.In addition,the fuzzy characterisation of the absorption spectrum data was binarised in the data pre-processing stage and used as the base data for the overall trend,and the recognition accuracy was improved to 94.19%by combining the fuzzy characterisation method of such data with the hierarchical analysis qualitative recognition model.The results show that it is feasible to use terahertz technology to identify different varieties of additives,and this paper constructs a hierarchical analytical qualitative model with better effect,which provides a new means for food additives detection,and the method is simple in steps,with a small demand for samples,which is suitable for the rapid detection of small samples.

Measurements and analysis of water content in winter wheat leaf based on terahertz spectroscopy

Wheat is a major grain crop in China.Water is one of the most important factors which influence the lifecycle and yield of wheat.It is of great significance to study the water content at the key stages of wheat growth in order to make irrigation decision to raise its yield.As Terahertz(THz)spectroscopy is a brand new sensing technology and sensitive to water absorption,the relationship between terahertz spectra and water content in winter wheat leaf was investigated and a preliminary result was presented in this paper.Forty winter wheat leaves samples with diverse range of water content(42.8%-72.5%)were collected.The Terahertz time domain spectra(THz-TDS)were first obtained and then transformed into Frequency-domain amplitude with the Fast Fourier Transformation(FFT)method.The absorption and refractive index spectra were then calculated.The spectra were linearly fitted to obtain the slope and intercept used for building a calibration model.The partial least squares(PLS)method and linear regression were employed to establish models to determine leaf water content in the winter wheat.The predicted correlation coefficient and the root mean square error of the optimal model established with the Frequency-domain amplitude parameter at 0.3 THz by linear regression were 0.812%and 4.4%,respectively.The results showed that terahertz spectroscopy performed well in water content prediction and could be an effective and potential method for leaf water content measurement in winter wheat.

Leakage detection of oil tank using terahertz spectroscopy

The necessity for safety in oil-gas storage and transportation has led to increasing technical requirements for on-line monitoring of damaged pores and oil leakage from tanks. In this study, the severity of damage of the oil tank at the micron level was detected by terahertz time-domain spectroscopy(THz-TDS), which is of great significance for the early detection and prevention of oil leakage. The THz amplitude(EP) was related to the severity of damaged according to the THz-TDS measurement of oil tanks with various degrees of damage, including intact, partially damaged, completely damaged, and seriously damaged points.Absorption and scattering effects co-occurred when the THz wave penetrated the tanks, with the collective tendencies being used to expressly monitor oil leakage from tanks. When the oil tank was damaged to form micron-level pores and the crude oil had not overflowed, the pore size was close to THz wavelength and the Mie scattering effect was obvious. After further destruction of the pores, the crude oil gradually spilled over and the scattering effect was gradually transformed from Mie scattering to Rayleigh scattering. In addition, the polar molecules in crude oil have strong resonance under the irradiation of THz wave, and the THz wave has strong attenuation. Eventually, surface tension of the oil flattens the surface of the tank, the scattering effect is gradually suppressed and replaced by the absorption effect. Absorption and scattering caused by THz waves passing through tanks coexist and have competing relationships. The change rule of EPcan successfully prove the phenomenon and can be considered as an important alternative for application to predict the degree of tank damage. Therefore, in this study, the detection of pores as small as micrometers on the oil tank was expected to greatly prevent oil leakage accidents and improve the safety of oil and gas storage and transportation.

Preliminary study on qualitative and quantitative detection of norfloxacin based on terahertz spectroscopy

Norfloxacin is a kind of quinolone bactericide which is widely used in food industry,livestock feed and medicine area.At present,how to develop a rapid,convenient and accurate technique for qualitative and quantitative detection of norfloxacin is still a challenge.In this study,Terahertz Time-domain Spectroscopy technology(THz-TDS)was used to explore qualitative and quantitative analysis of norfloxacin.Forty-five norfloxacin samples with different levels were prepared.The pure norfloxacin powder was mixed with polyethylene(PE)powder together and made into tablets by tablet-making machine.The minimum detection concentration was 10%and the maximum detection concentration evaluated in the paper was 90%.Then,terahertz(THz)spectra of each sample were measured on K15 THz-TDS equipment.The multiple linear regressions and the partial least squares regression algorithms were used to establish a model to make quantitative analysis.From the results,two typical fingerprint peaks of norfloxacin in terahertz band were observed at 0.944 THz and 1.206 THz,and the correlation coefficient and the root mean square error of the established model reached 0.9908 and 0.0481,respectively,which showed that the model performed well for the prediction.This preliminary study indicates that THz spectroscopy has great potential for future screening applications to detect the presence of norfloxacin residues in food,livestock feed and medicine industries.

Feasibility of terahertz spectroscopy for hybrid purity verification of rice seeds

The purity of hybrid rice seeds reflects the typical consistency of seed varieties in characteristics.The accuracy and reliability of seed purity detecting are of great significance to ensure the quality of seeds.In this study,the feasibility of identifying the purity of hybrid rice seeds,Xinong 1A/89,by terahertz(THz)time-domain spectroscopy system combined with chemometrics was explored.Three quantitative identification models for testing the purity of Xinong 1A/89 hybrid rice seed were developed and compared by THz absorption spectroscopy with extreme learning algorithm(ELM),Principal cComponent Regression(PCR)and Partial Least Squares Regression(PLSR).Experimental results showed that comparing with classical PLSR and PCR models,ELM presents a better feasibility and stability.For the testing set,the quantitative prediction result of ELM(ELoo=2.005×10^(-5),R^(2)=96.75%)is significantly better than those of PCR(ELoo=7.346×10^(-5),R^(2)=88.10%)and PLSR(ELoo=8.007×10^(-5),R^(2)=87.03%).The results highlight the feasibility of THz spectroscopy combined with ELM as an efficient and reliable method for verification of hybrid rice seeds.

Time of flight improved thermally grown oxide thickness measurement with terahertz spectroscopy

As a nondestructive testing technique,terahertz time-domain spectroscopy technology is commonly used to measure the thickness of ceramic coat in thermal barrier coatings(TBCs).However,the invisibility of ceramic/thermally grown oxide(TGO)reflective wave leads to the measurement failure of natural growth TGO whose thickness is below 10μm in TBCs.To detect and monitor TGO in the emergence stage,a time of flight(TOF)improved TGO thickness measurement method is proposed.A simulative investigation on propagation characteristics of terahertz shows the linear relationship between TGO thickness and phase shift of feature wave.The accurate TOF increment could be acquired from wavelet soft threshold and cross-correlation function with negative effect reduction of environmental noise and system oscillation.Thus,the TGO thickness could be obtained efficiently from the TOF increment of the monitor area with different heating times.The averaged error of 1.61μm in experimental results demonstrates the highly accurate and robust measurement of the proposed method,making it attractive for condition monitoring and life prediction of TBCs.

Time-resolved terahertz spectroscopy of charge carrier dynamics in the chalcogenide glass As_(30)Se_(30)Te_(40)[Invited]

Broadband(1.6–18 THz) terahertz time-domain spectroscopy(THz-TDS) and time-resolved terahertz spectroscopy(TRTS) were performed on a 54 μm thick chalcogenide glass(As_(30)Se_(30)Te_(40)) sample with a two-color laser-induced air plasma THz system in transmission and reflection modes, respectively. Two absorption bands at 2–3 and 5–8 THz were observed. TRTS reveals an ultrafast relaxation process of the photoinduced carrier response, well described by a rate equation model with a finite concentration of mid-bandgap trap states for self-trapped excitons.The photoinduced conductivity can be well described by the Drude–Smith conductivity model with a carrier scattering time of 12–17 fs, and we observe significant carrier localization effects. A fast refractive index change was observed 100 fs before the conductivity reached its maximum, with 2 orders of magnitude larger amplitude than expected for the optically induced THz Kerr effect, indicating that free carriers are responsible for the transient index change.

Modulated orientation-sensitive terahertz spectroscopy

Intramolecular vibrations of large macromolecules reside in the terahertz range. In particular, protein vibrations are closely spaced in frequency, resulting in a nearly continuous vibrational density of states. This density of vibrations interferes with the identification of specific absorption lines and their subsequent association with specific functional motions. This challenge is compounded with the absorption being dominated by the solvent and local relaxational motions. A strategy for removing the isotropic relaxational loss and isolating specific vibrations is to use aligned samples and polarization-sensitive measurements. Here, we demonstrate a technique to rapidly attain the anisotropic resonant absorbance using terahertz time domain spectroscopy and a spinning sample. The technique, modulated orientation-sensitive terahertz spectroscopy(MOSTS), has a nonzero signal only for anisotropic samples, as demonstrated by a comparison between a silicon wafer and a wire grid polarizer. For sucrose and oxalic acid molecular crystals, the MOSTS response is in agreement with modeled results for the intermolecular vibrations. Further, we demonstrate that, even in the presence of a large relaxational background, MOSTS isolates underlying vibrational resonances.

Investigation of spoilage in salmon by electrochemical impedance spectroscopy and time-domain terahertz spectroscopy

In this study,Spoilage of salmon was investigated using electrochemical impedance spectroscopy(EIS)and ter-ahertz time-domain spectroscopy(TDS).Salmon tissues were continuously observed for more than 20 h,from fresh to full spoilage.The complex impedance(Z)and phase shift(θ)of the salmon samples were derived based on the EIS signal.Critical frequency changes,phase shifts,and impedance variations with time at different fre-quencies were extracted from the data and used as indicators of the freshness of salmon.In the THz TDS analysis,time-domain spectra were recorded in transmission and reflection modes.Four stages of fish spoilage were clearly observed in both the EIS and THz TDS spectra.Although EIS is more sensitive under the current experimental conditions,THz TDS in reflection mode provides a non-invasive and non-destructive way to monitor salmon spoilage,which is practically beneficial for the food quality control industry.

Measurement Method of Internal Residual Stress in Plastic Parts Using Terahertz Spectroscopy

Since internal residual stress in polymers causes dimension errors over time,a measurement method for residual stress in polymers,especially in opaque engineering plastics,is strongly required.In this study,we propose to utilize terahertz(THz)spectroscopy to non-destructively measure internal residual stress in polymers.To verify the validity of the proposed method,we manufactured polytetrafluoroethylene ring samples with and without residual stress,and studied them with THz time domain spectroscopy system.THz spectra of samples without residual stress showed almost no polarization difference,whereas spectra of samples with residual stress showed clear polarization difference.Dimension changes between the samples with and without residual stress were also estimated and it was found that the change had a correlation with THz polarization difference.These experimental analyses confirm the validity for the proposed non-destructive measurement of residual stress in polymer.

Broadband terahertz time-domain spectroscopy and fast FMCW imaging: Principle and applications

We report a broadband terahertz time-domain spectroscopy(THz-TDS)which enables twenty vibrational modes of adenosine nucleoside to be resolved in a wide frequency range of 1-20 THz.The observed spectroscopic features of adenosine are in good agreement with the published spectra obtained using Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy.This much extended bandwidth leads to enhanced material characterization capability as it provides spectroscopic information on both intra-and inter-molecular vibrations.In addition,we also report a low-cost frequency modulation continuous wave(FMCW)imaging system which has a fast measurement speed of 40000 waveforms per second.Cross-sectional imaging capability through cardboard has also been demonstrated using its excellent penetration capability at a frequency range of 76-81 GHz.We anticipate that the integration of these two complementary imaging technologies would be highly desirable for many real-world applications because it provides both spectroscopic discrimination and penetration capabilities in a single instrument.

Time-domain terahertz spectroscopy in high magnetic fields

There are a variety of elementary and collective terahertz-frequency excitations in condensed matter whose magnetic field dependence contains significant insight into the states and dynamics of the electrons involved.Often,determining the frequency,temperature,and magnetic field dependence of the optical conductivity tensor,especially in high magnetic fields,can clarify the microscopic physics behind complex many-body behaviors of solids.While there are advanced terahertz spectroscopy techniques as well as high magnetic field generation techniques available,a combination of the two has only been realized relatively recently.Here,we review the current state of terahertz time-domain spectroscopy(THz-TDS)experiments in high magnetic fields.We start with an overview of time-domain terahertz detection schemes with a special focus on how they have been incorporated into optically accessible high-field magnets.Advantages and disadvantages of different types of magnets in performing THz-TDS experiments are also discussed.Finally,we highlight some of the new fascinating physical phenomena that have been revealed by THz-TDS in high magnetic fields.

Review of theoretical methods and research aspects for detecting leaf water content using terahertz spectroscopy and imaging

The water content in vegetative leaves is an important indicator to plant science.It reveals the physiological status of plants and provides valuable information in irrigation management.Terahertz(THz)as a state-of-the-art technology shows great potential in measuring and monitoring the water status in plant leaves.This paper reviewed the theoretical models for calculating water content in the plant leaves,the methods for eliminating the scattering loss caused by the surface roughness of leaf,the applications of THz spectroscopy and THz imaging for monitoring leaf water content and describing leaf water distribution.The survey of the researches presents the considerable advantages of this emerging and promising THz technology in agriculture.

Guest Editorial TTA Special Section on Applications of Terahertz Time Domain Spectroscopy

Terahertz(THz)radiation,whose frequency ranges from 0.1 THz to 10.0 THz,has rich science,but limited technology.It has long been considered the last remaining scientific gap in the electromagnetic spectrum.Far from being fully exploited,it offers great opportunities in science,innovation,new technology,and potential applications.

Isotopic analysis based on terahertz spectrum

As a new promising detection technology in the terahertz research field,the terahertz time-domain spec-troscopy(THz-TDS)has very broad application potential in many fields because its advantage on the characteristic spectrum,wide spectrum and non-destructive analysis of interested substances.In this paper,the terahertz absorption spectra of gases mixed with 12 CO and 13 CO in the spec-trum range of 0.5–2.5 THz are measured by terahertz time-domain spectroscopy for the first time.Several isotopo-logues can be clearly distinguished based on the difference in their rotational energies and the consequent terahertz spectrum.The experimental results show that 12 CO and 13 CO have obvious characteristic absorption peaks in the spectrum range of 0.5–2.5 THz due to the difference in rotational energy,and the rotational constant B can be calculated according to the experimental values to distin-guish the two gaseous isotopologues.The frequency posi-tions of the characteristic absorption peak measured by this experiment and the rotation constant B calculated accord-ing to the experimental values are compared with those previous theoretical calculations and experimental results,and they are in good agreement.This result lays a foun-dation for developing more sophisticated terahertz instru-ments to the detection of different isotopologues.

Integrated system of traditional THz time-domain spectroscopy and asynchronous optical sampling

Terahertz time-domain spectroscopy(THz-TDS)system,as a new means of spectral analysis and detection,plays an increasingly pivotal role in basic scientific research.However,owing to the long scanning time of the traditional THz-TDS system and the complex control of the asynchronous optical scanning(ASOPS)system,which requires frequent calibration,we combine traditional THz-TDS and ASOPS systems to form a composite system and propose an all-fiber trigger signal generation method based on the time overlapping interference signal generated by the collinear motion of two laser pulses.Finally,the time-domain and frequency-domain spectra are obtained by using two independent systems in the integrated systems.It is found that the full width at half maximum(FWHM)of the time-domain spectra and the spectral width of the frequency-domain spectra are almost the same,but the sampling speed of the ASOPS system is significantly faster than that of the traditional THz-TDS system,which conduces to the study of the transient characteristics of substances.

Spectroscopy Studies on Stream Sediments in the Terahertz Range

In order to study stream sediments in the terahertz range, we have measured six reference stream sediment samples by terahertz time-domain spectroscopy (THz-TDS). We obtained the absorption coefficients and refractive indexes. By analyzing the spectra, we got different drops in amplitude and delays in time. The absorption and refractive properties of samples changed with its components and types. In addition, we also found there was a nearly linear relationship between the absorption coefficient and the frequency. We calculated the slope value (K) of each sample by linear fitting, and find the K was corresponding to the contents of the samples. The results showed THz-TDS was an effective method to the analysis of stream sediments.

Terahertz Spectroscopic Characterization and Thickness Evaluation of Internal Delamination Defects in GFRP Composites

The use of terahertz time-domain spectroscopy(THz-TDS)for the nondestructive testing and evaluation(NDT&E)of materials and structural systems has attracted significant attention over the past two decades due to its superior spatial resolution and capabilities of detecting and characterizing defects and structural damage in non-conducting materials.In this study,the THz-TDS system is used to detect,localize and evaluate hidden multi-delamination defects(i.e.,a three-level multi-delamination system)in multilayered GFRP composite laminates.To obtain accurate results,a wavelet shrinkage de-noising algorithm is used to remove the noise from the measured time-of-flight(TOF)signals.The thickness and location of each delamination defect in the z-direction(i.e.,through-the-thickness direction)are calculated from the de-noised TOF signals considering the interaction between the pulsed THz waves and the different interfaces in the GFRP composite laminates.A comparison between the actual and the measured thickness values of the delamination defects before and after the wavelet shrinkage denoising process indicates that the latter provides better results with less than 3.712%relative error,while the relative error of the non-de-noised signals reaches 16.388%.Also,the power and absorbance levels of the THz waves at every interface with different refractive indices in the GFRP composite laminates are evaluated based on analytical and experimental approaches.The present study provides an adequate theoretical analysis that could help NDT&E specialists to estimate the maximum thickness of GFRP composite materials and/or structures with different interfaces that can be evaluated by the THz-TDS.Also,the accuracy of the obtained results highlights the capabilities of the THz-TDS for the NDT&E of multilayered GFRP composite laminates.

Characterization and evaluation of oil shale based on terahertz spectroscopy: A review

Oil shale is a fine-grained sedimentary rock rich in organic kerogen,which is a national strategic reserve resource and supplementary energy and shale oil and pyrolysis gas can be obtained through carbonization and pyrolysis.Due to the diversity of main components in oil shale and the complexity of the occurrence relationship between organic matter and minerals,the current understanding of the oil generation potential of oil shale and the dy-namic process of organic matter pyrolysis is still unclear,leading to the relatively backward level of its devel-opment technology.The development of new theories and methods for efficient utilization of oil shale resources has great strategic significance.The rotation and vibration frequency of macromolecules in oil shale occur in the terahertz(THz)band,so the THz optical parameters of oil shale can reflect the physical properties of kerogen.In this review,the experimental work progress in THz spectroscopy for characterization and evaluation of oil shale is provided.Oil shale is high anisotropic,resulting that the anisotropy in THz optical parameters strongly depends on the oil yield which is an effective selection for evaluating the oil yield to avoid the problem of environmental pollution in traditional detection.The heterogeneous distributions of organics on the oil shale surface,e.g.,the existence of kerogen-rich and kerogen-poor areas,was evaluated by THz amplitude imaging.In addition,the thermal THz analysis technology was developed to determine the pyrolysis process of kerogen and establish the pyrolysis model of kerogen,and the optimization of oil shale pyrolysis process was realized using THz parameters.Moreover,kerogen in oil shale displays a characteristic absorption peak in the THz range,which provides a new insight into the research of kerogen in the micro and nano scale.The pyrolysis oil shale at high temperature absorbs THz radiation strongly due to the decomposition of pyrite in oil shale.These recent works suggest that THz spectroscopy can realize rapid and non-contact detection of oil shale.At last,we propose the prospects and challenges of the THz technology in future as a new method for optimizing oil shale processing technology and improving the utilization efficiency of oil shale.

Optically tuned dielectric characteristics of SrTiO_(3)/Si thin film in the terahertz range

Active control of the optical parameters in strontium titanate(SrTiO_(3),STO)thin films is highly desirable for tunable terahertz(THz)integrated devices such as filters,phase modulators,and electro-optical devices.In this work,optically tuned dielectric parameters of a STO thin film epitaxially grown on a silicon wafer were characterized in the THz region with an 800 nm laser pump-THz detection system.The refractive index,extinction coefficient,and complex dielectric constant of the STO thin film were calculated using thin-film parameter extraction.Owing to carrier transportation and soft-mode oscillation,the above optical parameters changed notably with the pump power of the external laser.This study is of great significance for rapid and non-contact THz phase-modulation technology and may serve as a powerful tool to tune the dielectric properties of the STO thin films.