Thursday, 16 November 2017

Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial

Liu, Mingkai, Mohamad Susli, Dilusha Silva, Gino Putrino, Hemendra Kala, Shuting Fan, Michael Cole et al. "Ultrathin tunable terahertz absorber based on MEMS-driven metamaterial." Microsystems & Nanoengineering 3 (2017): 17033.

Abstact

The realization of high-performance tunable absorbers for terahertz frequencies is crucial for advancing applications such as single-pixel imaging and spectroscopy. Based on the strong position sensitivity of metamaterials’ electromagnetic response, we combine meta-atoms that support strongly localized modes with suspended flat membranes that can be driven electrostatically. This design maximizes the tunability range for small mechanical displacements of the membranes. We employ a micro-electromechanical system technology and successfully fabricate the devices. Our prototype devices are among the best-performing tunable THz absorbers demonstrated to date, with an ultrathin device thickness (~1/50 of the working wavelength), absorption varying between 60% and 80% in the initial state when the membranes remain suspended, and fast switching speed (~27 μs). The absorption is tuned by an applied voltage, with the most marked results achieved when the structure reaches the snap-down state. In this case, the resonance shifts by 4200% of the linewidth (14% of the initial resonance frequency), and the absolute absorption modulation measured at the initial resonance can reach 65%. The demonstrated approach can be further optimized and extended to benefit numerous applications in THz technology.

.....To quantify the absorption properties of the samples, we measured the reflection spectra with a commercial THz time-domain spectrometer (TeraPulse4000, Teraview Ltd, Cambridge, UK). The incident angle of the THz beam in the spectrometer is 30°, and the polarization is dominated by the TE component........



For full paper see


https://search.proquest.com/openview/6132b105e4dc0c6b0ea0e3959df2112e/1?pq-origsite=gscholar&cbl=2041946

Tuesday, 14 November 2017

Qualitative identification of food materials by complex refractive index mapping in the terahertz range

Shin, Hee Jun, Sung-Wook Choi, and Gyeongsik Ok. "Qualitative identification of food materials by complex refractive index mapping in the terahertz range." Food Chemistry (2017).

Abstract

We investigated the feasibility of qualitative food analysis using complex refractive index mapping of food materials in the terahertz (THz) frequency range. We studied optical properties such as the refractive index and absorption coefficient of food materials, including insects as foreign substances, from 0.2–1.3 THz. Although some food materials had a complex composition, their refractive indices were approximated with effective medium values, and therefore, they could be discriminated on the complex refractive index map. To demonstrate food quality inspection with THz imaging, we obtained THz reflective images and time-of-flight imaging of hidden defects in a sugar and milk powder matrix by using time domain THz pulses. Our results indicate that foreign substances can be clearly classified and detected according to the optical parameters of the foods and insects by using THz pulses.
... 2.4. Reflective THz imaging setup. A reflective-mode THz-TDS was used in our experiment. The THz images of samples were obtained by using a two-dimensional scanning module on the THz-TDS (TPS-3000, Teraview, UK) (see Fig. S3(a) of the supplementary material). ...


For full paper see
http://www.sciencedirect.com/science/article/pii/S0308814617316874

Sunday, 12 November 2017

A non-destructive method for quality control of the pellet distribution within a MUPS tablet by terahertz pulsed imaging

Novikova, Anna, Daniel Markl, J. Axel Zeitler, Thomas Rades, and Claudia S. Leopold. "A non-destructive method for quality control of the pellet distribution within a MUPS tablet by terahertz pulsed imaging." European Journal of Pharmaceutical Sciences (2017).
Abstract
Image 1
Terahertz pulsed imaging (TPI) was applied to analyse the inner structure of multiple unit pellet system (MUPS) tablets. MUPS tablets containing different amounts of theophylline pellets coated with Eudragit® NE 30 D and with microcrystalline cellulose (MCC) as cushioning agent were analysed. The tablets were imaged by TPI and the results were compared to X-ray microtomography. The terahertz pulse beam propagates through the tablets and is back-reflected at the interface between the MCC matrix and the coated pellets within the tablet causing a peak in the terahertz waveform. Cross-section images of the tablets were extracted at different depths and parallel to the tablet faces from 3D terahertz data to visualize the surface-near structure of the MUPS tablets. The images of the surface-near structure of the MUPS tablets were compared to X-ray microtomography images at the same depths. The surface-near structure could be clearly resolved by TPI at depths between 24 and 152 μm below the tablet surface. An increasing amount of pellets within the MUPS tablets appears to slightly decrease the detectability of the pellets within the tablets by TPI. TPI was shown to be a non-destructive method for the detection of pellets within the tablets and could resolve structures thicker than 30 μm. In conclusion, a proof-of-concept was provided for TPI as a method of quality control for MUPS tablets.

... 2.2.2. Terahertz Pulsed Imaging. Five MUPS tablets, one from each batch, were imaged with a commercial TPI system (TPI™ imaga 2000, TeraView, Cambridge, UK) which represents an automated tablet scanner. As shown in Fig. ...
For full paper see 
http://www.sciencedirect.com/science/article/pii/S0928098717305845


Wednesday, 8 November 2017

Terahertz electrodynamics and superconducting energy gap of NbN

Sim, Kyung Ik, Young Chan Jo, Taewoo Ha, Jong Hyeon Kim, Jae Hoon Kim, and Hirotake Yamamori. "Terahertz electrodynamics and superconducting energy gap of NbN." Journal of the Korean Physical Society 71, no. 9 (2017): 571-574.

We have measured the transmission spectra of the conventional Bardeen-Cooper-Schrieffer (BCS) superconductor niobium nitride (NbN) thin films (Tc = 11 K) using terahertz time-domain spectroscopy (THz-TDS) over the spectral range of 10 - 110 cm −1 and the temperature range of 3.9 - 295 K. We extracted both the real part, σ1, and the imaginary part, σ2, of the optical conductivity, σ̃ = σ1 + iσ2, independently and simultaneously, without a Kramers-Kronig analysis. The superconducting gap Δ(T) was observed in the real part of the conductivity, σ1, below Tc = 11 K with a maximum value of 2Δ(0) = 30 cm −1 and the gap ratio 2Δ(0)/kBTc = 3.92.

... Terahertz transmission spectroscopy was performed with TeraView TPS-3000 Pulse Spectrometer over the frequency range of 2 - 120 cm −1 . The reliable spectral ...



For full paper see

https://link.springer.com/article/10.3938/jkps.71.571

Tuesday, 7 November 2017

Biomedical Applications of Terahertz Imaging and Spectroscopy

Feature issue in Biomedical Optics Express

Biomedical Applications of Terahertz Imaging and Spectroscopy

Submission Opens: 1 September 2017
Submission Deadline: 15 November 2017

Biomedical Optics Express will publish a feature issue covering topics in biomedical applications of terahertz imaging and spectroscopy. The scope of the issue encompasses fundamental research, technology development, biomedical studies and clinical applications. The focus will be on:
  • THz imaging and spectroscopy of tissues (ex vivo, in vivo, skin, breast, burns)
  • Effects of high THz fields on biomedical samples
  • Novel THz near-field imaging and spectroscopy
  • THz combined with other techniques
  • Molecular imaging and therapies
  • Microfluidic THz devices
  • Ophthalmology
  • Gas sensing e.g. exhaled breath analysis
  • Protein Spectroscopy
  • Pharmaceutical Science e.g. dry dissolution testing
All papers need to present original, previously unpublished work and will be subject to the normal standards and peer-review processes of the journals. Submissions are encouraged from all areas of THz imaging and spectroscopy, but the main novelty is expected to be in biomedical applications. The standard Biomedical Optics Express publication charges will apply to all published articles.
Authors are encouraged to include acceptable supplementary materials (visualizations, tabular data, data sets, design files, or code). Please see OSA's guidelines on supplemental material.
To be eligible for publication, submissions that are based on a conference paper must add substantial and/or significant new information to the original conference summary, in accordance with OSA's Policy on Conference Papers.
Manuscripts must be prepared according to the usual standards for submission to Biomedical Optics Express and must be uploaded through OSA's electronic submission system, specifying from the drop-down menu that the manuscript is for the Feature Issue on Biomedical Applications of Terahertz Imaging and Spectroscopy.
Feature Issue Editors
Vincent Wallace, University of Western Australia, Australia (Lead Editor)
Emma Pickwell-MacPherson, The Chinese University of Hong Kong, China
Zachary Taylor, University of California Los Angeles, USA