Abstract-Non-Destructive Evaluation of Hidden Defects Beneath the Multilayer Organic Protective Coatings Based on Terahertz Technology

Wanli Tu, Shuncong Zhong, Manting Luo, Qiukun Zhang, 

https://www.frontiersin.org/articles/10.3389/fphy.2021.676851/full

An organic protective coating system plays an important role for the corrosion protection of offshore metallic structures. It is of practical importance to detect possible coating defects and evaluate coating performance for corrosion degradation monitoring. Reliable defect identification can provide timely and effective maintenance to avoid serious consequences. This work investigated various multilayer organic coating systems by terahertz pulse imaging technology and aimed to explore the inspection ability of terahertz non-destructive testing (THz NDT) of protective coatings. Several types of defective coating samples were measured. The comparison of measurements obtained for sites with and without defects was provided. The changes in the signals caused by the presence of defects were explained. Structural analysis, quantitative evaluation, and defect identification were carried out in detail. The results of measurements showed that corrosion defects, paint bulge defects, and paint detachment defects can be distinguished and identified in combination with the causes of defects. It can provide effective technical guidance for terahertz technology to be gradually extended to engineering applications.

Abstract-Application of Terahertz Spectroscopy and Imaging in the Diagnosis of Prostate Cancer

Ping Zhang, Shuncong Zhong, Junxi Zhang, Jian Ding, Zhenxiang Liu, Yi Huang, Ning Zhou, Walter Nsengiyumva, and Tianfu Zhang

https://www.osapublishing.org/copp/abstract.cfm?uri=copp-4-1-31

The feasibility of the application of terahertz electromagnetic waves in the diagnosis of prostate cancer was examined. Four samples of incomplete cancerous prostatic paraffin-embedded tissues were examined using terahertz spectral imaging (TPI) system and the results obtained by comparing the absorption coefficient and refractive index of prostate tumor, normal prostate tissue and smooth muscle from one of the paraffin tissue masses examined were reported. Three hundred and sixty cases of absorption coefficients from one of the paraffin tissues examined were used as raw data to classify these three tissues using the Principal Component Analysis (PCA) and Least Squares Support Vector Machine (LS-SVM). An excellent classification with an accuracy of 92.22% in the prediction set was achieved. Using the distribution information of THz reflection signal intensity from sample surface and absorption coefficient of the sample, an attempt was made to use the TPI system to identify the boundaries of the different tissues involved (prostate tumors, normal and smooth muscles). The location of three identified regions in the terahertz images (frequency domain slice absorption coefficient imaging, 1.2 THz) were compared with those obtained from the histopathologic examination. The tissue tumor region had a distinctively visible color and could well be distinguished from other tissue regions in terahertz images. Results indicate that a THz spectroscopy imaging system can be efficiently used in conjunction with the proposed advanced computer-based mathematical analysis method to identify tumor regions in the paraffin tissue mass of prostate cancer.

Abstract-Terahertz phase jumps for ultra-sensitive graphene plasmon sensing

Yi Huang,  Shuncong Zhong,  Yaochun Shen, Yingjie Yu, Daxiang Cui,

https://pubs.rsc.org/en/Content/ArticleLanding/2018/NR/C8NR08672A?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+rss%2FNR+%28RSC+-+Nanoscale+latest+articles%29#!divAbstract

The phase behavior of the reflected terahertz radiation (THz) under surface plasmon resonance (SPR) supported by doped graphene has been comprehensively investigated. For a TM–polarized wave, the dependence of the phase on the angle of incidence has a region with an abrupt jump–like change. We found in particular that the resonance phase dependence would change from step–like contour to Fano lineshape when the system passed through the optimum SPR conditions (i.e., R = 0) in terahertz regime. Monitoring the transformation could provide ultrahigh–sensitive label–free detection of biomolecules. Importantly, the characteristic of phase jumps as a readout response to achieve refractive index sensing that outperforms traditional terahertz–amplitude based attenuated total reflection (ATR) spectroscopy. The results demonstrated a high figure of merit (FOM) of up to 171 based on the terahertz phase information. Moreover, the sensing range could be tuned by changing the surface conductivity of graphene via high doping levels or with few–layer graphene. These terahertz phase response characteristics of graphene plasmon are promising for tunable ultra–sensitivity (bio)chemical sensing applications.

Abstract-Defect feature extraction of marine protective coatings by terahertz pulsed imaging

Tu, Wanli and Zhong, Shuncong and Incecik, Atilla and Fu, Xibin

https://strathprints.strath.ac.uk/63208/

Feature extraction of marine protective coatings using Hilbert transform (HT) and wavelet transform modulus maximum (WTMM) on terahertz pulsed imaging (TPI) of the coatings was proposed. For TPI-based marine protective coating detection, it is difficult to locate exactly the reflected echoes form internal structure of coating system by the faint feature in the time domain due to the interference of background noise. However, those faint features were usually caused by the interface between two different medium layers whose refractive indices are very similar or caused by micro defects beneath the coating. The proposed algorithm was validated by simulated and experimental TPI waveform obtained from marine paint samples with or without defects. To extract the structure feature more clearly and intuitively, Hilbert transform procedure was carried out on detected terahertz signal to get Hilbert envelope for further processing. Subsequently, the modulus maximum of the stationary wavelet transform approximation coefficients were employed as the criteria for feature extraction of internal interfaces and defect features, according to the relationship between WTMM and signal singularity. The results demonstrated that the combination of HT and WTMM algorithms could be used to exactly extract the structure feature and to evaluate the position of defects beneath coatings.

Abstract-Tunable terahertz plasmonics sensor using doped graphene

Yi Huang,  Shuncong Zhong,

http://ieeexplore.ieee.org/document/8068489/

Graphene plasmons exhibit much larger confinement and relatively long propagation distances at terahertz (THz) regime, with the advantage of being highly tunable via electrical and chemical doping. Thus, it provide a suitable alternative to noble-metal plasmons. We investigated the Otto configuration based THz-plasmonics sensor using a continuous suspended monolayer graphene (MLG) and graphene/insulator stacks (GIS) by finite element method (FEM). We revealed that a continuous suspended MLG based sensor has extremely high detection accuracy and promising prospect of application in ultrasensitive THz-plasmonics gas sensing. In addition, more layers of graphene will result in higher detection accuracy, but lower sensitivity and FOM of the sensor using GIS.

Abstract-Terahertz Chiral SSPPs Mode on the Helically Grooved Metal Wire

Haizi Yao, Shuncong Zhong,

https://link.springer.com/chapter/10.1007/978-981-10-4109-9_14

Terahertz wave (λ = 30 μm–3 mm@f = 0.1–10 THz) is such a band of electromagnetic wave that locates between light and microwave. Many chiral biomolecules, such as protein and amino acid, have their own unique structure vibrating frequencies at Terahertz region, therefore they have the “fingerprint” terahertz absorption spectrum. It is meaningful to study the chirality of chiral macromolecules through their terahertz circular dichroism (CD) response which is defined as the differential absorption of two opposite chiral terahertz wave. In the present work, we used the Finite-element-method (FEM) to investigate terahertz spoof surface plasmon polariton (SSPP) wave propagating on the helically grooved metal wire. Different from the metal wire decorated by the periodic grooves the helically grooved metal wire can support a kind of chiral SSPP surface mode. Due to the chirality of helical grooves, the normal degenerate HE1 SSPP mode on helically grooved metal wire decompose into two opposite chiral modes, i.e., HE−1 and HE+1 SSPP surface modes. Mode analysis showed that the dispersion curves of HE+1 mode deviated from that of HE−1 modes, and thus form a broad frequency band where the chiral HE+1 mode could exists exclusively. Super-chiral terahertz field concentration that may be achieved on the helically grooved metal wire through chiral HE+1 mode can find important applications in near-field circular dichroism spectroscopy in terahertz frequencies.

Abstract-Simulation and Experiment of Terahertz Wave Detection of Marine Protective Coating

Wanli Tu, Shuncong Zhong


https://www.springerprofessional.de/en/simulation-and-experiment-of-terahertz-wave-detection-of-marine-/15181602

Terahertz detection of multilayer marine protective coatings on a steel substrate using terahertz pulsed imaging (TPI) system in reflection mode was investigated. The multilayered anticorrosive/antifouling paint on steel substrate with different coating structures were produced as experimental samples for terahertz wave detection. The modeling and numerical simulation to calculate the propagation of THz radiation from marine protective coatings was studied by the finite difference time domain (FDTD) method. The reflected radiation properties in both simulation and experimentation were recorded for further analysis, such as the identification of the defect beneath coating. The results showed that it was able to provide much more detailed information on the position of the defect beneath the coating, such as detachment of large areas where adhesion has failed, or the blistering defect beneath the coating. Therefore, the developed model combined with the experimental analysis was effective and feasible for the detection and structure characterization of marine protective coatings and will provide timely and reliable information for ship maintenance work.

Abstract-Free-standing double-layer terahertz band-pass filters fabricated by femtosecond laser micro-machining

Yanzhang Lin, Haizi Yao, Xuewei Ju, Ying Chen, Shuncong Zhong, and Xiangfeng Wang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-21-25125

We report on the fabrication and transmission properties of free-standing single-layer and double-layer THz bandpass filters. These filters are fabricated on aluminum foils using femtosecond laser micro-machining. The aluminum foils are periodically patterned with cross apertures with a total area of 1.75×1.75 cm2, also known as frequency-selective surfaces. Their terahertz transmission properties were simulated using the FDTD method and measured using a time-domain terahertz spectroscopy system. The simulation results agree with the measurements results very well. The performance of single-layer bandpass filters is as good as the commercial equivalents on the market. The double-layer filters show extraordinary transmission peaks with changing spacing between the two layers. We show the contour map of the electric field distribution across the apertures, and ascribe the new transmission peaks to the interference and coupling of surface plasmon polaritons between the two layers.

© 2017 Optical Society of America

Abstract-Impact of processing conditions on inter‐tablet coating thickness variations measured by terahertz in-line sensing

Lin, Hungyen and May, Robert K. and Evans, Michael J. and Zhong, Shuncong and Gladden, Lynn F. and Shen, Yaochun and Zeitler, J. Axel 

http://strathprints.strath.ac.uk/53773/

A novel in-line technique utilising pulsed terahertz radiation for direct measurement of the film coating thickness of individual tablets during the coating process was previously developed and demonstrated on a production-scale coater. Here, we use this technique to monitor the evolution of tablet film coating thickness and its inter-tablet variability during the coating process under a number of different process conditions that have been purposefully induced in the production-scale coating process. The changes that were introduced to the coating process include removing the baffles from the coater, adding uncoated tablets to the running process, halting the drum, blockage of spray guns and changes to the spray rate. The terahertz sensor was able to pick up the resulting changes in average coating thickness in the coating drum and we report the impact of these process changes on the resulting coating quality.

Abstract- Impact of Processing Conditions on Inter-tablet Coating Thickness Variations Measured by Terahertz In-Line Sensing

1. Hungyen Lin¹, 
2. Robert K. May^1,†, 
3. Michael J. Evans², 
4. Shuncong Zhong^3,‡, 
5. Lynn F. Gladden¹, 
6. Yaochun Shen³ and
7. J. Axel 

1. http://onlinelibrary.wiley.com/doi/10.1002/jps.24503/abstract

Article first published online: 2 JUN 2015

DOI: 10.1002/jps.24503

© 2015 Wiley Periodicals, Inc. and the American Pharmacists Association

A novel in-line technique utilising pulsed terahertz radiation for direct measurement of the film coating thickness of individual tablets during the coating process was previously developed and demonstrated on a production-scale coater. Here, we use this technique to monitor the evolution of tablet film coating thickness and its inter-tablet variability during the coating process under a number of different process conditions that have been purposefully induced in the production-scale coating process. The changes that were introduced to the coating process include removing the baffles from the coater, adding uncoated tablets to the running process, halting the drum, blockage of spray guns and changes to the spray rate. The terahertz sensor was able to pick up the resulting changes in average coating thickness in the coating drum and we report the impact of these process changes on the resulting coating quality. 

© 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci

Abstract-Plasmonic corrugated cylinder–cone terahertz probe

Haizi Yao and Shuncong Zhong  »View Author Affiliations

JOSA A, Vol. 31, Issue 8, pp. 1856-1860 (2014)
http://dx.doi.org/10.1364/JOSAA.31.001856

The spoof surface plasmon polariton (SPP) effect on the electromagnetic field distribution near the tip of a periodically corrugated metal cylinder–cone probe working at the terahertz regime was studied. We found that radially polarized terahertz radiation could be coupled effectively through a spoof SPP into a surface wave and propagated along the corrugated surface, resulting in more than 20× electric field enhancement near the tip of probe. Multiple resonances caused by the antenna effect were discussed in detail by finite element computation and theoretical analysis of dispersion relation for spoof SPP modes. Moreover, the key figures of merit such as the resonance frequency of the SPP can be flexibly tuned by modifying the geometry of the probe structure, making it attractive for application in an apertureless background-free terahertz near-field microscope.

© 2014 Optical Society of America