Microelectromechanically tunable multiband metamaterial with preserved isotropy

Abstract

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-of-plane movable cantilevers preserves the symmetry at different configurations of the metamaterial. The metamaterial is shown to provide polarization independent response for both electrical inductive-capacitive (eLC) resonance and dipolar resonance at all states of actuation. The proposed metamaterial has a switching range of 0.16 THz and 0.37 THz and a transmission intensity change of more than 0.2 and 0.7 for the eLC and dipolar resonances, respectively for both TE and TM modes. Further optimization of the metal layer thickness, provides an improvement of up to 80% modulation at 0.57 THz. The simultaneously tunable dual band isotropic metamaterial will enable the realization of high performance electro-optic devices that would facilitate numerous terahertz applications such as compressive terahertz imaging, miniaturized terahertz spectroscopy and next generation high speed wireless communication possible in the near future.

All THz transmission spectra measured in this paper were acquired using TeraView's TPS Spectra 3000.

http://www.nature.com/srep/2015/150626/srep11678/full/srep11678.html

Electrothermally actuated microelectromechanical systems based omega-ring terahertz metamaterial with polarization dependent characteristics

Chong Pei Ho, Prakash Pitchappa, Yu-Sheng Lin, Chia-Yi Huang, Piotr Kropelnicki and Chengkuo Lee

Abstract

We present the design, simulation, fabrication, and characterization of a continuously tunable Omega-ring terahertz metamaterial. The tunability of metamaterial is obtained by integratingmicroactuators into the metamaterial unit cell. Electrothermal actuation mechanism is used to provide higher tuning range, larger stroke, and enhanced repeatability. The maximum achieved tuning range for the resonant frequency is around 0.30 THz for the input power of 500 mW. This shows the potential of using electrothermally actuated microactuators based tunablemetamaterial design for application such as filters, absorbers, sensors, and spectral imagers.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://scitation.aip.org/content/aip/journal/apl/104/16/10.1063/1.4871999

Frequency Dependent Optical and Dielectric Properties of Zinc Sulfide in Terahertz Regime

Abstract

Frequency dependent optical and dielectric properties for several grades of chemical vapor deposited (CVD) zinc sulfide (standard, elemental, and multi-spectral) was performed using a terahertz time-domain spectroscopy (THz-TDS) system in the frequency range from 0.15 THz to 2.5 THz. Zinc sulfide exhibits low frequency vibrational modes characterized by the THz-TDS. Two low-frequency phonon resonance lines were revealed at 0.78, and 2.20 THz. These samples were also characterized in the GHz range using a backward wave oscillator (BWO) source quasi-optical spectrometer, and the data obtained by both approaches were compared. Experimental data were also compared with an undamped harmonic oscillator model. These results compare well with the literature values obtained using other methods.

This study was performed using TeraView's TPS spectra 3000 system. (TeraView, Cambridge, UK)

Full Article: http://www.sciencedirect.com/science/article/pii/S1350449514000541

A THz spectroscopy method for quantifying the degree of crystallinity in freeze-dried gelatin/amino acid mixtures: An application for the development of rapidly disintegrating tablets

• J. Darkwah, 
• G. Smith, 
• I. Ermolina

• Leicester School of Pharmacy, De Montfort University, Leicester, UK

Abstract

Objective

In rapidly disintegrating tablets (RDTs) manufactured by freeze-drying processes, the % crystallinity of the freeze-dried matrix underpins the physical properties such as mechanical strength and dissolution profile. This study examines the feasibility of using terahertz pulsed spectroscopy (TPS) as an off-line tool (in the first instance) for assessing the degree of crystallinity in co-freeze dried amino-acid/gelatine mixtures.

Materials and method: Three amino acids (L- alanine, serine and proline) were studied by TPS (in the wave number range of 3 to 100 cm⁻¹) both in the pure crystalline form and in the form of a co-freeze-dried matrix with gelatin (in weight fractions of 10:90, 30:70, 50:50, and 70:30).

Results

In co-freeze dried proline/gelatin matrix no crystallinity was observed using TPS, whereas ∼62% ± 1% (n = 3) and 72% ± 0.5% (n = 3) crystallinity was observed in the co-freeze dried alanine/gelatin matrix (50%w/w and 70%w/w respectively). Similarly, ∼41% ± 0.5% (n = 3) and ∼80% ± 0.5% (n = 3) crystallinity was observed in the serine/gelatin matrix (30% w/w and 50% w/w respectively).

Conclusion

The potential for using TPS as a quantitative in-line tool for determining the degree of crystallinity in a range of complex systems such as RDTs, conventional tablets, sprayed dried micro particles, is suggested from these results

For more information, follow this link

... of the resultant 9 measurements (n = 3 samples x 3 points).95 2.3 Terahertz spectroscopy The
experimental setup and principles of terahertz pulsed spectroscopy ... A TPS spectra 3000 (TeraView Limited, UK) in transmission mode was used to obtain THz absorption spectra ...

Characterization of T-ray Penetration to Composite Materials

Kwang-Hee Im, David K. Hsu, Chien-Ping Chiou, Daniel J. Barnard and In-Young Yang

Department of Auto. Eng., Woosuk University 490, Samrae-up, Wanju-kun, Chonbuk, 565-701, Korea

Center for Nondestructive Evaluation, Iowa State University, Ames, Iowa 50011, USA

School of Mechanical Eng., Chosun University, 375 Seosuk-dong, Dong-gu, Kwangju 501-759, Korea

Abstract

Using T-ray (Terahertz waves) characterization of the non-destructive evaluation was made on the penetration on composite materials. The modalities of the T-ray radiation used were time domain spectroscopy (TDS) and continuous wave (CW) for composites. The composite materials investigated include both non-conducting polymeric composites and carbon fiber composites. T-ray signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, T-ray pulse can detect a crack hidden behind a larger crack (shadow effect). Thick GFRP laminates containing double saw cuts was tested. Also, in carbon composites the penetration of T-ray waves was investigated in order to detect flawsis strongly affected by the angle between the electric field vector of the terahertz waves and the intervening fiber directions. The T-ray effect was intensively studied between the carbon fiber direction and the electric field of T-ray. Other composites tested in this study include both solid laminates and honeycomb sandwiches. The defects and anomalies investigated by T-ray were foreign material inclusions, simulated disbond and delamination, mechanical impact damage, and water or hydraulic fluid ingression. The intensive characterization of T-ray for the NDE of composites is being discussed.

... 2. T-ray system 2.1 T-ray scanner The terahertz instrumentation systems used in this research
were provided by TeraView Limited. The instrumentation includes a time domain spectroscopy
(TDS) pulsed system and a frequency domain continuous wave (CW) system. ...

Keywords: T-ray, Time domain spectroscopy, Composite materials, Penetration.

Full paper

Terahertz Spectroscopy and Imaging - New Book

Series: Springer Series in Optical Sciences, Vol. 171,2013, XXXI, 641 p.

Authors: Peiponen, Kai-Erik; Zeitler, Axel; Kuwata-Gonokami, Makoto (Eds.

+SpringerMaterials
More details at: http://www.springer.com/physics/optics+%26+lasers/book/978-3-642-29563-8

• Presents the state-of-the-art of Terahertz spectroscopy
• Gives a concise presentation of the basics of THz spectroscopy
• Describes important applications of THz technology

"This book presents the current state of knowledge in the field of terahertz spectroscopy, providing a comprehensive source of information for beginners and experienced researchers alike whose interests lie in this area. The book aims to explain the fundamental physics that underpins terahertz technology and to describe its key applications. Highlights of scientific research in the field of terahertz science are also outlined in some chapters, providing an overview as well as giving an insight into future directions for research.

Over the past decade terahertz spectroscopy has developed into one of the most rapidly growing areas of its kind, gaining an important impact across a wide range of scientific disciplines. Due to substantial advances in femtosecond laser technology, terahertz time-domain spectroscopy (THz-TDS) has established itself as the dominant spectroscopic technique for experimental scientists interested in measurements at this frequency range. In solids and liquids THz radiation is in resonance with both phonon modes and hydrogen bonding modes, which makes it an ideal tool to study the interaction between molecules in a unique way; thus opening a wealth of opportunities for research in physics, chemistry, biology, materials science and pharmaceuticals.

This book provides easy access to scientists, engineers and students who want to understand the theory and applications of modern THz spectroscopy."

Chapter: Industrial Applications of Terahertz Imaging

This chapter gives a concise overview of potential industrial applications for terahertz imaging that have been reported over the past decade with a discussion of the major advantages and limitations of each approach. In the second half of the chapter we discuss in more detail how terahertz imaging can be used to investigate the microstructure of pharmaceutical dosage forms. A particular focus in this context is the nondestructive measurement of the coating thickness of polymer coated tablets, both by means of high resolution offline imaging in research and development as well as for in-line quality control during production.


... Defect in copper trace (a) (b) Fig. 18.3 Electro Optical Terahertz Pulse Reflectometry (EOTPR) for semiconductor fault testing. a Optical images of the two failed devices showing the cut in the copper traces. b Results obtained with EOTPR (source: TeraView Ltd.) ...

More on applications of terahertz technology http://www.teraview.com/applications/index.html