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    A thz metamaterial absorber with multiple polarization: Insensitive, sensitive, and tunable
    (2021-01-01)
    Mohanty, Ayesha
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    Acharya, Om Prakash
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    Appasani, Bhargav
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    Sooksood, Kriangkrai
    ;
    Mohapatra, Sushanta Kumar
    Terahertz (THz) absorbers are gaining interest in many applications. In this paper, we present the design and simulation of a multiband metama-terial absorber (MMA) with combined polarization properties and prominent absorption at 2.2 THz and 3.9 THz. The MMA comprises two square split-ring resonators and one square ring resonator placed on top of a polyimide dielectric spacer, offering multiband absorption characteristics with maximum absorptivity of 93.18% and 96.09%, respectively. The most protruding feature of this design is that it displays multiple polarization characteristics, including insensitivity, sensitivity, and tunability, even though the structure is similar to those of conventional absorbers. Firstly, the distinctly visible absorption spectra at 1.8 THz, gradually diminishes with an increase in polarization angle and then completely vanishes for TM polarization. Secondly, the prominent band at 2.2 THz is insensitive to changes in polarization of the incident wave, whereas, at 3.9 THz, the absorption band displays polarization tunability characteristics. Due to the multiple characteristics displayed by the structure, this MMA can be simultaneously used for several applications in the terahertz frequency regime such as imaging, terahertz spectroscopy, sensing, and stealth technology.
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    A review on thin-film sensing with terahertz waves
    (2012-03-01)
    O'Hara, John F.
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    Withayachumnankul, Withawat
    ;
    Al-Naib, Ibraheem
    In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thinfilm sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy. © Springer Science+Business Media, LLC 2012.
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    Survey of terahertz metamaterial devices
    (2008-12-01)
    Withayachumnankul, Withawat
    ;
    Abbott, Derek
    Metamaterials have arisen in an attempt to engineer the electromagnetic properties of natural substances. It has been acknowledged that the emergence of metamaterials has implications to nearly all branches of science and engineering exploiting the electromagnetic radiation. This paper reviews seminal work of metamaterials from the vision to the realisation of subwavelength elements that contribute to varieties of electric and magnetic responses. Emphasis is given to the significance and opportunity of this new class of material augmenting terahertz technology. Although now there remain major milestones that scientists and engineers need to conquer, the future of this cutting-edge material technology is very bright. © 2008 SPIE.
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    Numerical removal of water vapour effects from terahertz time-domain spectroscopy measurements
    (2008-09-08)
    Withayachumnankul, Withawat
    ;
    Fischer, Bernd M.
    ;
    Abbott, Derek
    The use of T-rays, or terahertz radiation, to identify substances by their spectroscopic fingerprints is a rapidly moving field. The dominant approach is presently terahertz time-domain spectroscopy. However, a key problem is that ambient water vapour is ubiquitous and the consequent water absorption distorts the T-ray pulses. Water molecules in the gas phase selectively absorb incident T-rays at discrete frequencies corresponding to their molecular rotational transitions. When T-rays propagate through an atmosphere, this results in prominent resonances spread over the T-ray spectrum; furthermore, in the time domain, fluctuations after the main pulse are observed in the T-ray signal. These effects are generally undesired, since they may mask critical spectroscopic data. So, ambient water vapour is commonly removed from the T-ray path by using a closed chamber during the measurement. Yet, in some applications, a closed chamber is not always feasible. This situation, therefore, motivates the need for an optional alternative method for reducing these unwanted artefacts. This paper represents a study on a computational means that is a step towards addressing the problem arising from water vapour absorption over a moderate propagation distance. Initially, the complex frequency response of water vapour is modelled from a spectroscopic catalogue. Using a deconvolution technique, together with fine tuning of the strength of each resonance, parts of the water vapour response are removed from a measured T-ray signal, with minimal signal distortion, thus providing experimental validation of the technique. © 2008 The Royal Society.
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    Quarter-wavelength multilayer interference filter for terahertz waves
    (2008-05-01)
    Withayachumnankul, Withawat
    ;
    Fischer, Bernd M.
    ;
    Abbott, Derek
    This work presents a multilayer interference filter, suitable for operation with terahertz waves (T-rays). An analysis of the effect of the number of layers on the spectral response is given, with full measurement data including time-resolved signals, transmittances, and phase spectra. The silicon-air structure with a submillimeter thickness shows a stop-band between 0.2 and 0.5 THz, and the attenuation inside the stop-band increases in proportion to the number of layers in the structure. The measurement of the fabricated structure is in agreement with a characteristic matrix analysis. © 2008 Elsevier B.V. All rights reserved.
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    T-rays in biomedicine and security
    (2005-12-01)
    Rainsford, T.
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    Png, G. M.
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    Withayachumnankul, W.
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    Ferguson, B.
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    Mickan, S. P.
    With a number of commercial systems becoming increasingly available, and improved generation and detection techniques T-ray systems are increasingly finding new applications. One of the main technical challenges is to make systems low cost, compact and easy to use. In this paper we suggest some novel solutions for parameter extraction, image enhancement, improved signal-to-noise ratio and classification schemes. These tools are useful in a number of biomedical and security applications. © 2005 IEEE.