Terahertz spectroscopic study of optical and dielectric properties of typical electrical insulation materials

Nsengiyumva, Walter, Shuncong Zhong, Bing Wang, Longhui Zheng, Zhenhao Zhang, Qiukun Zhang, Jianfeng Zhong, Manting Luo, and Zhike Peng. "Terahertz spectroscopic study of optical and dielectric properties of typical electrical insulation materials." Optical Materials (2021): 111837.

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0925346721010375

Abstract

Researchers and engineers are constantly developing novel techniques to accurately measure the electromagnetic properties of electrical insulators. These properties provide useful information about the insulators' performance and aging degree, which may help users to take necessary actions to prevent potential risks to the safety and stability of electric power systems. In this study, terahertz (THz) time-domain spectroscopy (THz-TDS) is used to analyze the spectral absorption and dielectric dispersion of five electrical insulation materials viz. epoxy resin (PER), E-glass fiber-reinforced polymer-matrix composite (GFRP), cross-linked polyethylene (XLPE), electrical porcelain (E-PRL), and high temperature vulcanized silicone rubber (HTVSR), in the THz frequency range (0.1 THz-1.8 THz). The refractive index, absorption coefficient, and complex relative permittivity of each sample are experimentally measured using the THz-TDS system and theoretically calculated using the original Debye model (i.e., based on the relaxation process of the individual samples’ dipoles). Experimental and theoretical results of the refractive indices and dielectric constants of the individual samples are highly correlated with 0.22% and 0.17% aggregate maximum errors, respectively. The values of dielectric constants and imaginary permittivities are found to be the highest and the lowest for E-PRL and XLPE, respectively. In terms of dielectric performance, XLPE exhibits the highest and most stable dielectric performance, followed by the E-PRL, whereas PER, HTVSR, and GFRP exhibit fluctuating and slightly less stable dielectric performance. This study shows the great potential of THz nondestructive testing (NDT) and structural health monitoring (SHM) for the defect detection and service life prediction of electrical insulators.

Experimental

… A commercial THz-TDS system (TeraView TPS 4000) was used to measure the dielectric properties of 5 types of electrical insulation materials. Fig. presents a schematic diagram showing the principle of operation of the TeraView TPS4000 

Electrically controllable terahertz metamaterials with large tunabilities and low operating electric fields using electrowetting-on-dielectric cells

Harry Miyosi Silalahi, Yi-Hong Shih, Shih-Hung Lin, Yi-Ting Chen, Wan-Yi Wei, Pei-Ling Chao, and Chia-Yi Huang, "Electrically controllable terahertz metamaterials with large tunabilities and low operating electric fields using electrowetting-on-dielectric cells," Opt. Lett. 46, 5962-5965 (2021).

for full paper see https://www.osapublishing.org/ol/abstract.cfm?uri=ol-46-23-5962

Abstract

A simple method that is compatible with all geometrical structures of terahertz (THz) metamaterials for increasing their frequency tunabilities and decreasing their operating electric fields is proposed. This method uses the displacement of glycerol droplets with various volumes to tune the resonance frequency of a THz metamaterial in an electrowetting-on-dielectric (EWOD) cell. The experimental results reveal that the THz metamaterial has a large frequency tunability of 28% at an operating electric field that is smaller than 0.2 V/µm as the glycerol droplets move in and out of the path of a THz beam. The frequency tunability is large because the near field of the metamaterial “experiences” a large difference between the refractive indices of glycerol and air. The EWOD cell with the THz metamaterial is a great achievement for developing electrically controllable band-stop filters with large frequency tunabilities and small operating electric fields.

… The transmittance spectrum of the EWOD cell is measured using a THz spectrometer (TPS 3000, TeraView) in transmission mode, and the polarized direction of a normally incident THz beam is set parallel to the xaxis of Fig. 1(a). The …

For more information please click here or visit www.teraview.com

Terahertz spectroscopy of antiferromagnetic resonances in YFe1− xMnxO3 0≤ x≤ 0.4 across a spin reorientation transition

Lee, Howon, Taek Sun Jung, Hyun Jun Shin, Sang Hyup Oh, Kyung Ik Sim, Taewoo Ha, Young Jai Choi, and Jae Hoon Kim. "Terahertz spectroscopy of antiferromagnetic resonances in YFe1− xMnxO3 0≤ x≤ 0.4 across a spin reorientation transition." Applied Physics Letters 119, no. 19 (2021): 192903.

for full paper see https://aip.scitation.org/doi/full/10.1063/5.0070952

Abstract

e have conducted a terahertz spectroscopic study of antiferromagnetic resonances in bulk orthoferrite YFe1−xMnxO3  (0≤x≤0.4).  Below TSR, an antiferromagnetic resonance mode emerges and exhibits a large blueshift with decreasing temperature. However, below 50 K, this mode softens considerably, and this tendency becomes stronger with Mn doping. We provide a deeper understanding of such behaviors of the antiferromagnetic resonance modes in terms of the influence of the Mn3+ ions on the magnetocrystalline anisotropy. Our results show that terahertz time-domain spectroscopy is a useful, complementary tool in tracking magnetic transitions and probing the interaction between disparate magnetic subsystems in antiferromagnetic materials with multiple ionic species.

From the experimental section of the paper 

"Our terahertz transmission measurements were conducted on a Teraview TPS3000 (Teraview Ltd., UK) in the frequency range of 0.1–3 THz with the sample temperature controlled over the range of 4–300 K by a helium-free optical cryostat (Cryostation, Montana Instruments, Ltd., USA). All measurements were carried out in dry nitrogen or in vacuum to remove the water-vapor absorption. For transmission measurements, the samples were attached to a holder with a 3 mm hole by using silver paste. Our THz-TDS technique yielded raw data in the form of time-dependent waveforms of electric fields, and these were converted into complex-valued functions of frequency through the fast Fourier transform (FFT). "

For more information please click here or visit www.teraview.com

$d$ is the thickness of the sample.

TeraSolve - a new tool to measure tablet porosity and predict dissolution using THz spectroscopy

 

New wave of growth coming for Cambridge terahertz light pioneers TeraView

10-09-2021

Cambridgeshire & Peterborough Combined Authority Business Board member Professor Aamir Khalid visited a world-first, homegrown Cambridge business to find out how loan support is helping them to take their growth to the next level.

TeraView is a company reflective of the unique business ecosystem which exists in the region. Born as a ‘spin-out’ from Toshiba and the University of Cambridge, it was co-founded by Sir Michael Pepper and Dr Don Arnone in 2001. Twenty years have since been spent developing patents and intellectual property on ways to use terahertz light for a range of commercial purposes.

Prof Khalid was given a tour of TeraView’s new premises at Cambridge Research Park by Dr Arnone. The new base means it now has space to develop its manufacturing function and grow the business. The move from the more central location of St Johns Innovation Park was supported with a £120,000 Growth Fund loan via the Business Board.

While such groundbreaking technology takes time to develop, the company is now well placed to scale and move to full profitability. Currently employing 21, the relocation will be a springboard for a doubling or even tripling of the workforce over the next five years. Dr Arnone’s projections are that the potential for its technology in the automotive, semiconductor and other industrial inspection markets will approach $100 million over time.

TeraView is a world-first company in the application of terahertz light technology. Terahertz light lies between infra-red and microwaves, and as such has unique properties which enables it to pass through objects and to transmit images and compositional (spectroscopic) information that is ordinarily hidden. Terahertz is non-destructive, safe and fast, making it the ideal inspection and imaging modality for many applications across a range of industries. TeraView’s customers include semi-conductor manufacturers and those in the car, food and pharmaceutical industries. Clients have included Ford and Intel, showing the potential to attract global ‘blue chip’ clients.

Asia and the US will continue to be key markets for TeraView, which is predominantly an export business. It is building sales and technical support based in those key markets, but Dr Arnone said it wants to retain its R&D base in Cambridge. New jobs in both its manufacturing and development teams will be created as part of its planned major workforce expansion. Another benefit to the local economy is the use of local suppliers to support the manufacture of its products, where Dr Arnone said they offer both the precision and flexibility needed by TeraView.

Prof Aamir Khalid of the Business Board said: "This is another breakthrough company emerging from the exciting, dynamic business environment we have in Cambridgeshire & Peterborough. To turn a pioneering technology into a viable commercial opportunity is a fantastic achievement and I applaud TeraView for the ingenuity and hard work it has taken to get to this point.

“TeraView was at a key phase where it needed to change locations in order to scale up and I’m glad the Business Board has been able to play a part in helping their move. Visiting their premises it was clear they now have a great platform to accelerate their growth, with both local people and the local supply chain the beneficiaries through more skilled jobs and greater business opportunities.”

Prof Khalid is the Chief Executive of The Welding Institute (TWI Ltd), which is based at Granta Park near Cambridge.

from https://www.cambridgenetwork.co.uk/news/new-wave-growth-coming-cambridge-terahertz-light-pioneers-teraview

Antibodies Processed Using High Dilution Technology Distantly Change Structural Properties of IFNγ Aqueous Solution

Penkov, Nikita. "Antibodies Processed Using High Dilution Technology Distantly Change Structural Properties of IFNγ Aqueous Solution." Pharmaceutics 13, no. 11 (2021): 1864.

for full paper see https://www.mdpi.com/1999-4923/13/11/1864

Abstract

Terahertz spectroscopy allows for the analysis of vibrations corresponding to the large-scale structural movements and collective dynamics of hydrogen-bonded water molecules. Previously, differences had been detected in the emission spectra of interferon-gamma (IFNγ) solutions surrounded by extremely diluted solutions of either IFNγ or antibodies to IFNγ without direct contact compared to a control. Here we aimed to analyse the structural properties of water in a sample of an aqueous solution of IFNγ via terahertz time-domain spectroscopy (THz-TDS). Tubes with the IFNγ solution were immersed in fluidised lactose saturated with test samples (dilutions of antibodies to IFNγ or control) and incubated at 37 ◦C for 1, 1.5–2, 2.5–3, or 3.5–4 h. Fluidised lactose was chosen since it is an excipient in the manufacture of drugs based on diluted antibodies to IFNγ. After incubation, spectra were recorded within a wavenumber range of 10 to 110 cm−1 with a resolution of 4 cm−1 . Lactose saturated with dilutions of antibodies to IFNγ (incubated for more than 2.5 h) changed the structural properties of an IFNγ aqueous solution without direct contact compared to the control. Terahertz spectra revealed stronger intermolecular hydrogen bonds and an increase in the relaxation time of free and weakly bound water molecules. The methodology developed on the basis of THz-TDS could potentially be applied to quality control of pharmaceuticals based on extremely diluted antibodies.

Experimental 

2.2. THz-TDS 

In this study, we used the THz-TDS technique. It allows the simultaneous acquisition of absorption and refraction spectra of the test substance to calculate complex dielectric functions without using the Kramers–Kronig transformations. The details of this method are described, for example, in [46]. The spectra were recorded with a TPS Spectra 3000spectrometer (Teraview, Cambridge, UK) in a wavenumber range from 10 to 110 cm−1 with a resolution of 4 cm−1 . To obtain one spectrum, averaging over 2000 scans was performed. The humidity of the air in the room during the measurements was controlled and was approximately 35%. The spectra of solutions were recorded in two identical cuvettes with different distances between the windows: 50.02 µm and 100.17 µm. The spectrum of the solution in the first cuvette was considered to be the background spectrum, and the spectrum of the same solution in the second cell was considered to be the spectrum of the sample. 

for more information click here or visit https://teraview.com/sales/

Papers at IRMMW 2021 using TeraView systems

The following papers were presented at this year IRMMW 2021 conference in China. 

Visualizing liquid transport through coated pharmaceutical tablets using terahertz pulsed imaging

Dong, R., and J. A. Zeitler. "Visualizing liquid transport through coated pharmaceutical tablets using terahertz pulsed imaging." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… Above the flow cell, a commercial time-domain terahertz system (TeraPulse 4000, TeraView Ltd, Cambridge, UK) with a reflection probe was used to acquire the terahertz time-domain waveforms while water penetrated the tablet. The beam waist …

Terahertz waveform selection of a pharmaceutical film coating process using a recurrent network 

Li, Xiaoran, Bryan M. Williams, Robert K. May, Michael J. Evans, Shuncong Zhong, Lynn F. Gladden, Yaochun Shen, J. Axel Zeitler, and Hungyen Lin. "Terahertz waveform selection of a pharmaceutical film coating process using a recurrent network." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

Detecting capacity of THz method applied to art painting

Smolyanskaya, Olga A., Sergey V. Sirro, Alexander V. Minin, V. Yu Toropov, Olga V. Kravtsenyuk, Anastasiya A. Lykina, Alessia Portieri et al. "Detecting capacity of THz method applied to art painting." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-1. IEEE.

……The image of paints on canvas was recorded using the TerPulse Lx (TeraView, UK) system with a spectral range 0.06 THz – 6.00 THz …….

Terahertz Response of L-Serine at Low Temperatures

Sanders, T. J., J. L. Allen, J. Horvat, and R. A. Lewis. "Terahertz Response of L-Serine at Low Temperatures." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… At room temperature a terahertz time domain spectrometer (THz-TDS; TeraView TeraPulse 4000) has been employed. Low temperature measurements were taken on a Fourier transform spectrometer (FTS; Bruker IFS 125HR), using a 125 µm mylar …

Quantifying water absorption of hygrothermally aged epoxies with terahertz time-domain spectroscopy

Lin, Hungyen, Benjamin P. Russell, Prince Bawuah, and J. Axel Zeitler. "Quantifying water absorption of hygrothermally aged epoxies with terahertz time-domain spectroscopy." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… We performed transmission THz spectroscopy using a commercial THz-TDS setup (Terapulse 4000, TeraView Ltd., Cambridge, UK). Frequency-dependent optical constants can then be calculated from the measurements and converted to …

Is there a terahertz absorption peak in frozen aqueous solutions of DNA nucleosides?

Tao, Yu Heng, Stuart I. Hodgetts, Alan R. Harvey, Stephen Moggach, and Vincent P. Wallace. "Is there a terahertz absorption peak in frozen aqueous solutions of DNA nucleosides?." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

….Measurements were conducted in a cryostat and measured in a commercial time-domain-spectroscopy (TDS) spectrometer (Terapulse 4000, TeraView Ltd, Cambridge, UK) in transmission mode. The measurements were made within a chamber purged with nitrogen, and the reference was taken with no sample present……

Enhanced THz signal via Au encapsulated in hydrogel gel for non-enzymatic glucose sensing

Zhao, Jingjing, Shaohua Lu, Shuting Fan, and Zhengfang Qian. "Enhanced THz signal via Au encapsulated in hydrogel gel for non-enzymatic glucose sensing." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… A commercial THz-TDS system, TeraPulse 4000 from TeraView Ltd., was used to measure the absorption of the samples. … 

Phase diagram method for efficient THz images reconstructing

Nastasiu, D., M. Bernier, C. Ioana, C. Tréhoult, L. Lyannaz, and F. Garet. "Phase diagram method for efficient THz images reconstructing." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… Experimentally, we used a commercial THz-TDS spectrometer (TeraPulse from Teraview) to perform 10 000 pixels’ images (3 cm x 3 cm – step 300 µm) of geometric patterns with different sizes, printed with conductive ink on dielectric and …

Terahertz Biosensors with high sensitivity for the recognition of neurotransmitter 

Lu, Shaohua, Di Zhou, Jingjing Zhao, Zhengfang Qian, and Shuting Fan. "Terahertz Biosensors with high sensitivity for the recognition of neurotransmitter." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

.... reflection module of a commercial terahertz time domain spectroscopy system (TeraPulse …

THz and IR spectroscopy of H2O@C60 endofullerene 

Melentev, Alexander V., Sergey S. Zhukov, Vasileios Balos, Gabriela Hoffman, Shamim Alom, Mikhail Belyanchikov, Elena Zhukova et al. "THz and IR spectroscopy of H 2 O@ C 60 endofullerene." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… Spectroscopic transmission measurements were carried out in a wide temperature range of 6–300 K using time-domain terahertz spectrometer TeraView TPS Spectra 3000....

Assessing Changes in Human Skin Using in vivo Terahertz Measurements

Lindley-Hatcher, Hannah, A. I. Hernandez-Serrano, Jiarui Wang, Juan Cebrian, Joseph Hardwicke, and Emma Pickwell-MacPherson. "Assessing Changes in Human Skin Using in vivo Terahertz Measurements." In 2021 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), pp. 1-2. IEEE.

… A TeraPulse 4000 system from TeraView Ltd was used to perform in vivo point scans of human skin in a reflection geometry with the skin in contact with a quartz window for the duration of the measurement, as shown in Fig. 1. a). .....

For more information about TeraView click here

Terahertz spectra of a range of liquids

 

We show here the terahertz spectra of liquids.  These parameters can be measured on a terahertz spectrometer such as that provide by TeraView.

TeraView's TeraPulse Lx with sample chamber.

TeraView can provide a complete solution for your terahertz measurements.  The sample chamber can be purged with either dry air or nitrogen.  The software provides you with the 

• Reference and sample time domain signals
• Sample and reference spectrum and phase
• Transmittance
• Transmittance phase
• Absorbance
• Apodization functions
• Background subtraction

With the input of the sample thickness the user is able to obtain 

• Absorption coefficient
• Refractive index
• Complex refractive index

The absorption coefficient of the liquids is shown here

For more information please click here or visit www.teraview.com

Terahertz spectra of a range of window materials

Shown on this page is a selection of window materials that can be used in the terahertz region of the electromagnetic spectrum.  These parameters can be measured on a terahertz spectrometer such as that provide by TeraView.

TeraView's TeraPulse Lx with sample chamber.

TeraView can provide a complete solution for your terahertz measurements.  The sample chamber can be purged with either dry air or nitrogen.  The software provides you with the 

• Reference and sample time domain signals
• Sample and reference spectrum and phase
• Transmittance
• Transmittance phase
• Absorbance
• Apodization functions
• Background subtraction

With the input of the sample thickness the user is able to obtain 

• Absorption coefficient
• Refractive index
• Complex refractive index

Below at the refractive index of a number of window materials that can be used in the terahertz region. 

The absorption of these windows materials are shown here

For more information please click here or visit www.teraview.com

 

Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques

Zhai, Min, D. S. Citrin, and Alexandre Locquet. "Terahertz Nondestructive Stratigraphic Analysis of Complex Layered Structures: Reconstruction Techniques." Journal of Infrared, Millimeter, and Terahertz Waves (2021): 1-18.

for full paper see https://link.springer.com/article/10.1007/s10762-021-00819-1

Abstract

Terahertz (THz) time-of-flight tomography (TOFT), a nondestructive-evaluation technique for the stratigraphic characterization of structures with layers on the micron-to-millimeter scales, has proven to be challenging to apply to samples containing both micron-scale and millimeter-scale layers. In THz TOFT, echoes reflected from distant interfaces and defects are often obscured as they may be immersed in a noisy background as such features in the reflected signal may be weak due to attenuation and dispersion, leading to the loss of valuable information. Moreover, overlapping echoes from any optically thin layers, such as thin coatings on thick specimens, are likely to be mistaken for a single interface in reconstructing the stratigraphy. Thus, layered structures containing both thick and thin layers have proven problematic for THz TOFT characterization. In this paper, a sparse-deconvolution (SD) technique, based on an interior-point method, and including a propagation model accounting for dispersion is demonstrated. The method is shown to be successful in extracting the impulse response of samples that combine the challenges of both thick and thin layers. The robustness and effectiveness of this method are verified numerically and experimentally. While the proposed SD approach does not perform as well as cross-correlation (CC) techniques in terms of the maximum thickness, it can provide a clearer and more accurate reconstruction of moderately thick samples incorporating thin layers.

… It is noted that the bandwidth of the setup (TeraView Ltd. THz-TDS Spectra 3000) extends to 3 THz, corresponding to wavelength ~ 100 µm; however, in practice, accounting for the SNR of the reflected signal, the usable bandwidth in r(t) in these …

for more information about TeraView click here.

Effective Medium Model Applied to Biopolymer Solutions

 Penkov, Nikita V., and Nadezda A. Penkova. "Effective Medium Model Applied to Biopolymer Solutions." Applied Spectroscopy (2021): 00037028211042027.

for full paper see https://journals.sagepub.com/doi/abs/10.1177/00037028211042027

Studying dielectric properties of heterogeneous systems is challenged by a problem of uncertainty of the ratio between dielectric permittivity of the system and dielectric permittivities of its components. Such ratios can be obtained in some cases using theoretical effective medium models. However, such models have not yet been developed for all the systems possible. Particularly, there is no effective medium model with filamentary inclusions. Such a theoretical model elaborated based on the fundamental principles of electrodynamics of continuous media is suggested in the present work. Any point of a filamentary inclusion with a length that is significantly greater than the thickness can be regarded as being located in a long cylinder-like fragment of the inclusion with stochastic direction of the cylinder axis relative to the external electric field. With this regard, electric field strength and electric induction values were averaged across the entire volume of a two-phase dielectric material. As a result, a model linking the dielectric permittivity of the two-phase system and the dielectric permittivities of both phases was elaborated. The model appears to be highly relevant for studying solutions of biopolymers, such as nucleic acids, fibrillar proteins and protein aggregates, polysaccharides, by means of electrical impedance spectroscopy, dielectric spectroscopy, and terahertz time-domain spectroscopy. The suggested theoretical model was successfully validated on a DNA solution within the terahertz region.

Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers

 Shih, Yi-Hong, Xin-Yu Lin, Harry Miyosi Silalahi, Chia-Rong Lee, and Chia-Yi Huang. "Optically Tunable Terahertz Metasurfaces Using Liquid Crystal Cells Coated with Photoalignment Layers." Crystals 11, no. 9 (2021): 1100.

for full paper see https://www.mdpi.com/2073-4352/11/9/1100

Abstract

An optically tunable terahertz filter was fabricated using a metasurface-imbedded liquid crystal (LC) cell with photoalignment layers in this work. The LC director in the cell is aligned by a pump beam and makes angles θ of 0, 30, 60 and 90° with respect to the gaps of the split-ring resonators (SRRs) of the metasurface under various polarized directions of the pump beam. Experimental results display that the resonance frequency of the metasurface in the cell increases with an increase in θ, and the cell has a frequency tuning region of 15 GHz. Simulated results reveal that the increase in the resonance frequency arises from the birefringence of the LC, and the LC has a birefringence of 0.13 in the terahertz region. The resonance frequency of the metasurface is shifted using the pump beam, so the metasurface-imbedded LC cell with the photoalignment layers is an optically tunable terahertz filter. The optically tunable terahertz filter is promising for applications in terahertz telecommunication, biosensing and terahertz imaging.

Experimental

A linearly polarized pump beam (center wavelength = 365 nm) was incident to the metasurface imbedded LC cell from the top substrate. The pump beam with an intensity of 0.3 mW/cm2  irradiated the photoalignment layers for 100 s, aligning the LC director in the cell. The LC director made angles θ of 0, 30, 60 and 90° with respect to the gaps of the SRRs of the metasurface by changing the polarized direction of the pump beam via a polarizer. The metasurface-imbedded LC cell was placed in the chamber of a terahertz spectrometer (TPS 3000, TeraView) for studying the effect of the polarized direction of the pump beam on the resonance frequency of the metasurface. Terahertz waves that were polarized in a direction parallel to the x axis of figure 1a were normally incident to this cell. TPS 3000 had a frequency resolution of 3 GHz in this work.

for more information about TeraView and its products click here.

Optical and electronic properties of iodine and bromine doped chirality enriched (12,1) and (13,2) single-walled carbon nanotubes

 

Abozied, Asmaa M., A. Abouelsayed, A. F. Hassan, A. A. Ramadan, Emad A. Al-Ashkar, and Badawi Anis. "Optical and electronic properties of iodine and bromine doped chirality enriched (12, 1) and (13, 2) single-walled carbon nanotubes." Carbon (2021).

for more information click here 

for full paper see https://www.sciencedirect.com/science/article/abs/pii/S0008622321009477

Abstract

We present transmission measurements on chirality enriched semiconducting (12,1) and (13,2) single-walled carbon nanotubes (CE-s-SWCNTs) and CE-s-SWCNTs doped with iodine (I2@CE-s-SWCNTs) and bromine (Br2@CE-s-SWCNTs) in wide frequency range from 0.1 to 40 THz. The real part of the optical conductivity σreal(ω) was fitted using Drude-Lorentz model. The Drude (D) term in the CE-s-SWCNTs was attributed to the presence of metallic tubes traces in the sample. The D/scattering rate(γD) ratio was increased by a factor of 1.13 and 2.35 with iodine and bromine p-doping, respectively. This increase was compensated by large increase in D term leading to an increase in the optical conductivity at the DC limit (σDC), growing from 186 Ω−1cm−1 for the CE-s-SWCNTs to 203 and 426 Ω−1cm−1 for the I2@CE-s-SWCNTs and Br2@CE-s-SWCNTs, respectively. In addition, the plasmon peak was shifted to higher frequencies and gains more spectral weight with doping. The calculated optical parameters determine that iodine and bromine create acceptor levels above the top of the CE-s-SWCNTs valence band by 0.04 and 0.08 eV, respectively, shifting the Fermi level. The high σDC value of the Br2@CE-s-SWCNTs is due to the higher electronegativity of bromine which enables removal of more electrons from the valence band of CE-s-SWCNTs to bromine acceptor levels.

Passively Tunable Terahertz Filters Using Liquid Crystal Cells Coated with Metamaterials

Chiang, Wei-Fan, Yu-Yun Lu, Yin-Pei Chen, Xin-Yu Lin, Tsong-Shin Lim, Jih-Hsin Liu, Chia-Rong Lee, and Chia-Yi Huang. "Passively tunable terahertz filters using liquid crystal cells coated with metamaterials." Coatings 11, no. 4 (2021): 381.

for full paper see https://www.mdpi.com/2079-6412/11/4/381/pdf

for more information click here

Abstract

Liquid crystal (LC) cells that are coated with metamaterials are fabricated in this work. The LC directors in the cells are aligned by rubbed polyimide layers, and make angles θ of 0◦ , 45◦ , and 90◦ with respect to the gaps of the split-ring resonators (SRRs) of the metamaterials. Experimental results display that the resonance frequencies of the metamaterials in these cells increase with an increase in θ, and the cells have a maximum frequency shifting region of 18 GHz. Simulated results reveal that the increase in the resonance frequencies arises from the birefringence of the LC, and the LC has a birefringence of 0.15 in the terahertz region. The resonance frequencies of the metamaterials are shifted by the rubbing directions of the polyimide layers, so the LC cells coated with the metamaterials are passively tunable terahertz filters. The passively tunable terahertz filters exhibit promising applications on terahertz communication, terahertz sensing, and terahertz imaging.


Experimental

.......Figure 2 displays the experimental terahertz spectra of three metamaterials that are coated with the PI layers. These spectra are obtained using a commercial terahertz spectrometer (TPS 3000, TeraView, Cambridge, UK) in transmission mode, and the chamber in the spectrometer is filled with nitrogen gas to prevent terahertz waves from absorbing moisture. The polarization of incident terahertz waves is set parallel to the x axis of Figure 1a. The PI-coated metamaterials have transmission peaks in their terahertz spectra due to the absorption of the electromagnetic resonance of the metamaterials. The transmission peaks are at an identical frequency of 0.588 THz, and the two PI-coated metamaterials .........

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