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1.
ChemSusChem ; 2019 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-31883308

RESUMO

The diverse nature of organic precursors offers a versatile platform for precisely tailoring the electronic properties of semiconducting polymers. In this study, three fully conjugated sp2 carbon-linked polymers have been designed and synthesized for photocatalytic hydrogen evolution under visible-light illumination, by copolymerizing different C3 -symmetric aromatic aldehydes as knots with the 1,4-phenylene diacetonitrile (PDAN) linker through a C=C condensation reaction. The hydrogen evolution (HER) is achieved at a maximum rate of 30.2 mmol g-1 h-1 over a polymer based on 2,4,6-triphenyl-1,3,5-triazine units linked by cyano-substituted phenylene, with an apparent quantum yield (AQY) of 7.20 % at 420 nm. Increasing the degree of conjugation and planarity not only extends visible-light absorption, but also stabilizes the fully conjugated sp2 -carbon-linked donor-acceptor (D-A) polymer. Incorporating additional electron-withdrawing triazine units into the D-A polymer to form multiple electron donors and acceptors can greatly promote exciton separation and charge transfer, thus significantly enhancing the photocatalytic activity.

2.
Opt Express ; 27(23): 34067-34078, 2019 Nov 11.
Artigo em Inglês | MEDLINE | ID: mdl-31878463

RESUMO

We report a high-resistivity silicon (HR-Si) prism coupled terahertz (THz) spoof surface plasmon polaritons (SSPPs) on flat subwavelength metasurface. Using a high refractive index prism as an external coupler, a more tightly confined SSPPs mode can be excited in a smaller resonant cavity, leading to strong light-matter interaction. Besides, theoretical analysis and experimental results have both indicated that the SSPPs resonance response to the filling patterns of analyte in the resonant cavity are quite different. In particular, we have found that the interaction between analyte and SSPPs wave can be maximized when the analyte filled with the whole resonant cavity and a higher sensitivity for THz sensing can be obtained. A high sensitivity varied from 0.31 THz/RIU to 0.85 THz/RIU is predicted. Furthermore, these SSPPs modes exhibit high Q-factor, and characteristic spectra of water caused by surface plasmon resonance (SPR) are observed, which is significant in promoting the THz-SPR sensing of polar liquids or aqueous analytes with THz metasurfaces.

3.
Opt Express ; 27(18): 25647-25655, 2019 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-31510433

RESUMO

We experimentally demonstrated a corrugated metallic metasurface based tunable perfect absorber for terahertz (THz) frequencies in a total internal reflection geometry. The absorbance is strongly depend on the central layer of this three-layer absorber, which provides a feasible approach to tune the absorption. In particular, there exist an optimal gap that enables a perfect absorption at specific frequency. Due to the simple 1D geometric structure of metasurface, its absorption frequency can be easily tailored over a wide frequency range (0.625-1.499 THz). More importantly, the modulation of the effective refractive index and loss of medium environment can be accepted as an alternative approach for the absorption properties modulation. This prism coupling absorber provides a new route for modulation of the absorption characteristics with potential applications in biological sensing.

4.
Opt Express ; 27(2): 965-979, 2019 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-30696185

RESUMO

We proposed a high-performance optical coherence velocimeter (OCV) based on broadband optical interference which achieves spatial resolution from interference cancellation or enhancement of different components of the broadband light. There is a challengeable issue for OCV that the interference fringes become blurred when the velocity of detected object is relatively large, hindering the pace of OCV application in high-velocity field. To resolve this, the relationship between blurry coefficient and OCV system parameters (e.g., exposure time, central wavelength, bandwidth of source) was derived. It was found that blurry coefficient changed with oscillatory decay form and reached the minimum at each order blurry velocity. It showed that maximum measurable velocity of OCV systems could reach 10th order blurry velocity. The measurement of vibration of the loudspeaker driven by a function signal generator was employed to experimentally verify the velocity measurement performance of the system. The experiment demonstrated that the developed OCV can provide large velocity measurement ranges from static to 25.2 mm/s with nanometer-level precision and maximum measurable vibration frequency of up to 50 kHz. However, in theory, the theoretical maximum measurable velocity can be up to 1.06 m/s for current OCV configuration. The OCV has high precision, large dynamic range, and high-velocity measurement capability, making it attractive for applications in mechanical structure vibration monitoring and acoustic measurement.

5.
Nanoscale ; 10(47): 22466-22473, 2018 Dec 21.
Artigo em Inglês | MEDLINE | ID: mdl-30478462

RESUMO

Phase behavior of the reflected terahertz radiation (THz) under surface plasmon resonance (SPR) supported by doped graphene has been comprehensively investigated via theoretical analysis with simulation verifications. 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 is valuable. 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.

6.
Opt Express ; 25(21): 25125-25134, 2017 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-29041184

RESUMO

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.

7.
Zhongguo Yi Liao Qi Xie Za Zhi ; 41(4): 235-239, 2017 Jul 30.
Artigo em Chinês | MEDLINE | ID: mdl-29862778

RESUMO

Blood pressure is an important index to measure the function of human cardiovascular system. In order to solve the problem of non-invasive continuous measurement of blood pressure in electronic sphygmomanometer, a noninvasive blood pressure measurement method based on EEMD (ensemble empirical mode decomposition) and ANN (artificial neural networks) were proposed. In the experiment, a total of 19 500 pulse wave signals from THE MIMIC DATABASE were analyzed and subsequently the pulse wave was decomposed by EEMD. Furthermore, 10 characteristic parameters of the 4th layer decomposition signal were extracted as the input of ANN. The blood pressure corresponding to the pulse wave was taken as the output of ANN to train the BP (blood pressure) model. The error analysis of the model was carried out. The results indicated that the error of the model meets the standards of the American Association for the advancement of medical instrumentation (AAMI). Therefore, this method can be employed in noninvasive continuous measurement of blood pressure.


Assuntos
Determinação da Pressão Arterial , Pressão Sanguínea , Sistema Cardiovascular , Frequência Cardíaca , Humanos
8.
J Pharm Sci ; 104(8): 2513-22, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26037660

RESUMO

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.


Assuntos
Composição de Medicamentos/métodos , Comprimidos com Revestimento Entérico/química , Automação , Fenômenos Químicos , Técnicas Eletroquímicas , Processamento de Imagem Assistida por Computador , Controle de Qualidade , Reprodutibilidade dos Testes , Propriedades de Superfície
9.
J Opt Soc Am A Opt Image Sci Vis ; 31(10): 2285-93, 2014 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-25401257

RESUMO

Experimental investigations have shown that terahertz pulsed imaging (TPI) is able to quantitatively characterize a range of multilayered media (e.g., biological issues, pharmaceutical tablet coatings, layered polymer composites, etc.). Advanced modeling of the interaction of terahertz radiation with a multilayered medium is required to enable the wide application of terahertz technology in a number of emerging fields, including nondestructive testing. Indeed, there have already been many theoretical analyses performed on the propagation of terahertz radiation in various multilayered media. However, to date, most of these studies used 1D or 2D models, and the dispersive nature of the dielectric layers was not considered or was simplified. In the present work, the theoretical framework of using terahertz waves for the quantitative characterization of multilayered media was established. A 3D model based on the finite difference time domain (FDTD) method is proposed. A batch of pharmaceutical tablets with a single coating layer of different coating thicknesses and different refractive indices was modeled. The reflected terahertz wave from such a sample was computed using the FDTD method, assuming that the incident terahertz wave is broadband, covering a frequency range up to 3.5 THz. The simulated results for all of the pharmaceutical-coated tablets considered were found to be in good agreement with the experimental results obtained using a commercial TPI system. In addition, we studied a three-layered medium to mimic the occurrence of defects in the sample.


Assuntos
Imagem Terahertz/métodos , Modelos Teóricos , Fenômenos Ópticos , Preparações Farmacêuticas
10.
Opt Express ; 22(21): 25149-60, 2014 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-25401547

RESUMO

We report terahertz surface plasmon resonance (SPR) sensing based on prism-coupling to the spoof surface plasmon polariton (SSPP) mode existing on periodically grooved metal films. It was demonstrated that, except for the fundamental mode of the SSPP, there was also a higher mode SSPP wave when the depth of groove was larger. Both fundamental and high-order modes of SSPP could be used for terahertz sensing. We compared the performance of different modes of SSPP on the sensing sensitivity using both reflection amplitude and phase-jump information. The results indicated that the gap distance between the prism base and the metal film had a significant influence on the reflectivity of SPR sensing by affecting the coupling efficiency of an evanescent wave to an SSPP wave; also, high-order mode SSPP-based sensing had a high sensitivity of up to 2.27 THz/RIU, which nearly doubled the sensitivity of the fundamental mode. The application of high-mode SSPP has enormous potential for ultra-sensitive SPR sensing in the terahertz regime.


Assuntos
Metais/química , Ressonância de Plasmônio de Superfície , Radiação Terahertz , Simulação por Computador , Refratometria
11.
J Opt Soc Am A Opt Image Sci Vis ; 31(8): 1856-60, 2014 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-25121543

RESUMO

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.


Assuntos
Microscopia/instrumentação , Refratometria/instrumentação , Ressonância de Plasmônio de Superfície/instrumentação , Radiação Terahertz , Transdutores , Campos Eletromagnéticos , Desenho de Equipamento , Análise de Falha de Equipamento , Luz , Espalhamento de Radiação
12.
J Pharm Sci ; 102(7): 2179-86, 2013 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-23609052

RESUMO

We present terahertz pulsed imaging (TPI) as a novel tool to quantify the hardness and surface density distribution of pharmaceutical tablets. Good agreement between the surface refractive index (SRI) measured by TPI and the crushing force measured from diametral compression tests was found using a set of tablets that were compacted at various compression forces. We also found a strong correlation between TPI results and tablet bulk density, and how these relate to tablet hardness. Numerical simulations of tablet surface density distribution by finite element analysis exhibit excellent agreement with the TPI measured SRI maps. These results show that TPI has an advantage over traditional diametral compression and is more suitable for nondestructive hardness and density distribution monitoring and control of pharmaceutical manufacturing processes.


Assuntos
Comprimidos/química , Imagem Terahertz , Composição de Medicamentos , Análise de Elementos Finitos , Dureza , Refratometria , Propriedades de Superfície
13.
J Pharm Sci ; 100(4): 1535-44, 2011 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-20957746

RESUMO

We present a new in-line measurement technique to determine the coating thickness of individual pharmaceutical tablets during film coating in a pan coating unit using pulsed terahertz technology. Results of these real-time terahertz measurements acquired during a production scale coating run are validated using both off-line high-resolution terahertz pulsed imaging of the whole dosage form as well as weight-gain measurements made on sample tablets removed at discrete time intervals during the process run. The terahertz measurements provide a direct method of determining the coating thickness, and no chemometric calibration models are required for the quantification. The results, and their repeatability, demonstrate that real-time monitoring of pharmaceutical tablet coating is not only possible but also provides substantially more information of the coating quality than the standard quality control method. Rather than providing the average coating thickness of a large number of tablets, the terahertz sensor provides the thickness of up to 100 individual tablet coatings per minute. Using this information, the operator can get additional information about the thickness distribution in the coating pan and adjust the process accordingly. At present, a minimum coating thickness of 40 µm is required to determine the coating thickness. The technique is applicable for coatings up to 1 mm in thickness. Within that range, it provides thickness measurements of sub-micron resolution. Terahertz in-line coating process measurements show considerable potential for applications in real-time release, process analytical technology and quality by design.


Assuntos
Comprimidos com Revestimento Entérico/química , Imagem Terahertz/instrumentação , Composição de Medicamentos/instrumentação , Desenho de Equipamento
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