Tuesday, 25 June 2019

A Stretchable Terahertz Parabolic‐Shaped Metamaterial

Xu, Zefeng, and Yu‐Sheng Lin. "A Stretchable Terahertz Parabolic‐Shaped Metamaterial." Advanced Optical Materials(2019): 1900379.

Abstract
A stretchable parabolic‐shaped metamaterial (PSM) coated onto polydimethylsiloxane (PDMS) is proposed and demonstrated for operation in the terahertz (THz) frequency range. By stretching the PDMS‐based PSM device along different directions, ultranarrowband, polarization dependent, switchable optical characteristics are obtained. By stretching the PSM width and length in the transverse electric (TE) and transverse magnetic (TM) modes, resonant tuning ranges of 0.55 and 0.32 THz, respectively, are demonstrated for the PSM device. In these deformation ranges, the Q‐factors of the PSM device for different widths and lengths are quite stable and maintained in the range of 9 to 14 for the TE mode, with a high Q‐factor of 50 obtained at resonance for the TM mode. The integration of the PSM on a mechanically deformable PDMS substrate provides potential for use in flexible electronics applications. Furthermore, the PSM device exhibits single‐/dual‐band switching and polarization switching characteristics. These multifunctional states for the PSM device can be determined by mechanical inputs to represent binary digits that can then be used to perform logic operations. Such a stretchable PSM device offers an effective approach for the realization of programmable metamaterials with enhanced optical‐mechanical performance due to its high flexibility, applicability, and cost‐effectiveness.
… This measurement system was filled with nitrogen gas to eliminate water vapor in the testing chamber. The transmittance of the PSM device was measured by using a commercial THz time-domain spectroscopy system (Teraview 3000) … 

Influence of annealing on the optical properties of monoclinic vanadium oxide VO2 prepared in nanoscale by hydrothermal technique

Afify, H. H., S. A. Hassan, M. Obaida, and A. Abouelsayed. "Influence of annealing on the optical properties of monoclinic vanadium oxide VO2 prepared in nanoscale by hydrothermal technique." Physica E: Low-dimensional Systems and Nanostructures (2019): 113610.

Abstract
Terahertz and infrared reflectivity measurements were carried out on monoclinic vanadium oxide VO2 prepared directly in nanoscale by hydrothermal technique. The product was annealed in argon atmosphere at pressure 100 Pa for 6 h at temperatures 350 °C, 450 °C and 550 °C. The as-grown and annealed samples were investigated by XRD, HRTEM, VSM, DSC, THz, and FTIR techniques to explore the effect of annealing on the optical and electronic properties. The obtained results reveal the existence of monoclinic M-B-VO2 phase for the as-grown sample, while the annealed samples include two other oxidation phases V6O13 and V2O5 together with the monoclinic VO2 phase. This observation is supported by the data obtained from XRD, VSM, and DSC measurements. Both THz transmittance and infrared reflectivity measurements performed at room temperature show insulating behavior for the as-grown monoclinic VO2 sample whereas subtle modifications of monoclinic VO2 phase by annealing induces a metallic behavior via enhancement of surface area to volume ratio and increasing the grain boundaries as a result of embedded and distributed of two other phases V6O13 and V2O5 within the monoclinic VO2 matrix. Fitting of the optical conductivity deduced from both THz and infrared measurements clearly shows Drude-like behavior for the annealed sample while this behavior was not observed in case of the as-grown sample.

… The ATR unit-350) with silicon crystal and under Nitrogen gas N 2 purging in the frequency range between 60 GHz and 3 THz (2 cm −1 - 100 cm −1 ) and the number of scans 1800 scan/sec with spectral resolution 1.2 cm …from TeraView





Tuesday, 18 June 2019

Measuring bulk density variations in a moving powder bed via terahertz in-line sensing



    Stranzinger, Sandra, Eva Faulhammer, Jingyi Li, Runqiao Dong, Johannes G. Khinast, J. Axel Zeitler, and Daniel Markl. "Measuring bulk density variations in a moving powder bed via terahertz in-line sensing." Powder Technology 344 (2019): 152-160.
    Abstract
    Monitoring the relative density of static or moving powder inside a process line is essential for manufacturing high-quality products. The aim of this study was to predict density variations in a moving powder bed using terahertz reflection technology. We systematically investigated three grades (varying true density and particle size) of two materials: lactose and silicified microcrystalline cellulose (SMCC). These six powders specifically differ in their compressibility, which can be applied to assess the sensitivity and applicability of our method. The powders were filled into a round container, and terahertz reflection measurements were acquired continuously during the container’s rotation. The setup allowed to adjust the relative density by compacting the powders into specific powder bed heights. Each powder was compacted to various relative densities (compression pressures up to 100 kPa). We calculated the surface refractive index based on the in-line terahertz measurements acquired during rotation, which has a linear dependence on the relative density of the powder. This was confirmed by correlating the refractive index values with the theoretical relative densities based on the bulk and true densities of the powder. The coefficient of determination (R2) was larger than 0.962 (Lactohale 100) for all six powders, with the highest coefficients for Lactohale 220 (R2 = 0.996) and SMCC 50 LD (R2 = 0.995). The results suggest that the proposed method can resolve relative densities averaged across the powder bed that are as small as 0.3% (Lactohale 100). The high acquisition rate of the terahertz system (15 Hz) made it possible to determine the powder density in 230 positions uniformly distributed throughout the container, facilitating the investigation of the relative density uniformity in the container as a function of the powder bed height. It was observed that SMCC powders undergo a smaller change in the relative density variations upon compaction than the lactose powders. Moreover, the relative density maps clearly indicate local density differences in the powder bed for all powders. The relative density variations that were introduced by packing of the container prevailed throughout the compaction process for all samples with the exception of Lactohale 220. The presented approach allows a precise resolution of the spatial distribution of relative density, which facilitates an in-depth analysis of powder behavior upon compaction.
    … In order to use THz-TDS to quantify the porosity and relative density of powders and porous media,
    pulses of terahertz radiation are propagated through the material of … A commercial time-domain
    terahertz spectrometer (TeraPulse 4000TeraView Ltd., Cambridge …

    Millimeter Wave Radiation Activates Leech Nociceptors via TRPV1-Like Receptor Sensitization

    Romanenko, Sergii, Alan R. Harvey, Livia Hool, Shuting Fan, and Vincent P. Wallace. "Millimeter Wave Radiation Activates Leech Nociceptors via TRPV1-Like Receptor Sensitization." Biophysical journal (2019).

    Abstract

    There is evidence that millimeter waves (MMWs) can have an impact on cellular function, including neurons. Earlier in vitro studies have shown that exposure levels well below the recommended safe limit of 1 mW/cm2 cause changes in the action potential (AP) firing rate, resting potential, and AP pulse shape of sensory neurons in leech preparations as well as alter neuronal properties in rat cortical brain slices; these effects differ from changes induced by direct heating. In this article, we compare the responses of thermosensitive primary nociceptors of the medicinal leech under thermal heating and MMW irradiation (80–170 mW/cm2 at 60 GHz). The results show that MMW exposure causes an almost twofold decrease in the threshold for activation of the AP compared with thermal heating (3.9 ± 0.4 vs. 8.3 ± 0.4 mV, respectively). Our analysis suggests that MMWs-mediated threshold alterations are not caused by the enhancement of voltage-gated sodium and potassium conductance. We propose that the reduction in AP threshold can be attributed to the sensitization of the transient receptor potential vanilloid 1-like receptor in the leech nociceptor. In silico modeling supported our experimental findings. Our results provide evidence that MMW exposure stimulates specific receptor responses that differ from direct thermal heating, fostering the need for additional studies.

    … Values for the leech saline solution, the paraffin, and the polystyrene Petri dish were measured
    using a commercial THz time-domain spectroscopy system (TeraPulse 4000TeraViewCambridge, UK) over the temperature range used in the experiments (24–45°C). At ambient …

    Thursday, 25 April 2019

    Optimization of THz diffractive optical elements thickness

    Surma, Mateusz, Izabela Ducin, Maciej Sypek, Przemyslaw Zagrajek, and Agnieszka Siemion. "Optimization of THz diffractive optical elements thickness." Photonics Letters of Poland 10, no. 4 (2018): 115-117.

    Abstract


    Diffractive optical elements (DOEs) are strictly related to the design wavelength due to the fact that they must introduce particular phase delay of the wavefront propagating through the structure. Mostly the attenuation of the material is not taken into account. In this article we propose to optimize thickness of the DOE by reducing introduced phase retardation but also attenuation. The efficiency of DOEs is determined by the method of coding phase distribution and can be easily measured by using diffraction orders of corresponding diffraction grating. Here, we analyze binary phase diffraction gratings with assumed attenuation. 


    … The designed gratings were manufactured in a 3D printing technique in paper using an MCor Iris printer [15]. Prior to the design process was the determination of the material optical properties. Time Domain Spectroscopy (TDS ‒ TeraView) was used for this task …