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Metamaterial-based microfluidic sensor for dielectric characterization
(2013-01-01)
Withayachumnankul, Withawat
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Jaruwongrungsee, Kata
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Tuantranont, Adisorn
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Fumeaux, Christophe
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Abbott, Derek
A microfluidic sensor is implemented from a single split-ring resonator (SRR), a fundamental building block of electromagnetic metamaterials. At resonance, an SRR establishes an intense electric field confined within a deeply subwavelength region. Liquid flowing in a micro-channel laid on this region can alter the local field distribution and hence affect the SRR resonance behavior. Specifically, the resonance frequency and bandwidth are influenced by the complex dielectric permittivity of the liquid sample. The empirical relation between the sensor resonance and the sample permittivity can be established, and from this relation, the complex permittivity of liquid samples can be estimated. The technique is capable of sensing liquid flowing in the channel with a cross-sectional area as small as (0.001λ<inf>0</inf>)<sup>2</sup>, where λ<inf>0</inf> denotes the free-space wavelength of the wave excitation. This work motivates the use of SRR-based microfluidic sensors for identification, classification, and characterization of chemical and biochemical analytes. © 2012 Elsevier B.V.
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Metamaterial-inspired microfluidic-based sensor for chemical discrimination
(2012-12-01)
Jaruwongrungsee, Kata
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Withayachumnankul, Withawat
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Wisitsoraat, Anurat
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Abbott, Derek
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Fumeaux, Christophe
This work proposes a metamaterial-inspired microfluidic-based chemical sensor. The sensor comprises a microwave split-ring resonator (SRR), an important building block of metamaterials, integrated with a disposable flow-channel made of a transparency film. The electromagnetic response of the sensor is observed in the presence of various analytes including glycerol, ethanol, and phosphate buffered saline. It is found that the resonance frequency in the transmission amplitude and the zero crossing in the reflection phase of the sensor are good features for discrimination of these analytes and for determining their concentrations. The developed metamaterial-inspired microfluidic-based chemical sensor has a potential for advanced chemical sensing applications. © 2012 IEEE.
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Metamaterial-inspired multichannel thin-film sensor
(2012-04-24)
Withayachumnankul, Withawat
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Jaruwongrungsee, Kata
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Fumeaux, Christophe
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Abbott, Derek
A multichannel thin-film sensor is implemented from a set of microstrip-coupled split-ring resonators (SRRs) with different dimensions. Each SRR exhibits a unique high-Q resonance that is sensitive to the presence of a sample in a particular area. Hence, this SRR-based sensor can function (i) to detect different samples simultaneously to increase the throughput or (ii) to characterise nominally identical samples at multiple frequencies to increase the sensor selectivity. In addition, the sensitivity of this SRR-based sensor is optimized through strategic design of the resonator shape to produce a strong confined electric field at each sensing region. The design principle is validated with simulation and measurement. Owing to the optimized design, sensing a low-permittivity film with a thickness as small as one thousandth of the operating wavelength is achievable. © 2012 IEEE.
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Sub-diffraction thin-film sensing with planar terahertz metamaterials
(2012-01-30)
Withayachumnankul, Withawat
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Lin, Hungyen
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Serita, Kazunori
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Shah, Charan M.
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Sriram, Sharath
Planar metamaterials consisting of subwavelength resonators have been recently proposed for thin dielectric film sensing in the terahertz frequency range. Although the thickness of the dielectric film can be very small compared with the wavelength, the required area of sensed material is still determined by the diffraction-limited spot size of the terahertz beam excitation. In this article, terahertz near-field sensing is utilized to reduce the spot size. By positioning the metamaterial sensing platform close to the sub-diffraction terahertz source, the number of excited resonators, and hence minimal film area, are significantly reduced. As an additional advantage, a reduction in the number of excited resonators decreases the inter-cell coupling strength, and consequently the resonance Q factor is remarkably increased. The experimental results show that the resonance Q factor is improved by more than a factor of two compared to the far-field measurement. Moreover, for a film with a thickness of λ/375 the minimal area can be as small as 0.2λ× 0.2λ. The success of this work provides a platform for future metamaterial-based sensors for biomolecular detection. © 2012 Optical Society of America.
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Metamaterial-based strain sensors
(2011-12-01)
Li, Jining
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Withayachumnankul, Withawat
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Chang, Shengjiang
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Abbott, Derek
In this paper, two metamaterial-based strain sensors at terahertz frequencies are introduced and simulated using CST Microwave Studio. They exhibit a large shift in the resonance frequency upon stretching or compression. They are very well suitable to monitoring and detecting mechanical deformation of a target structure remotely. © 2011 IEEE.
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Planar array of electric-LC resonators with broadband tunability
(2011-07-04)
Withayachumnankul, Withawat
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Fumeaux, Christophe
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Abbott, Derek
A planar array of microwave electric-LC (ELC) resonators with broadband tunability of the resonance frequency is presented in this letter. An ELC resonator is typically composed of inductive loops and a capacitive gap, resonant at a wavelength much larger than its physical dimension. Here, the original resonator is modified to accommodate a varactor and its accompanying dc bias enabling resonance tunability. The wideband operation can be achieved through strategic placement of the varactor. The robustness of the response for a large array containing hundreds of the varactor-loaded resonators is considered via a sensitivity analysis. The numerical and experimental results show that the fabricated array possesses a wide tuning range of nearly 32% with no significant resonance broadening, despite the tolerance in varactor characteristics. © 2011 IEEE.
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Compact electric-LC resonators for metamaterials
(2010-12-06)
Withayachumnankul, Withawat
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Fumeaux, Christophe
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Abbott, Derek
Alternative designs to an electric-LC (ELC) resonator, which is a type of metamaterial inclusion, are presented in this article. Fitting the resonator with an interdigital capacitor (IDC) helps to increase the total capacitance of the structure. In effect, its resonance frequency is shifted downwards. This implies a decreased overall resonator size with respect to its operating wavelength. As a result, the metamaterial, composed of an array of IDC-loaded ELC resonators with their collective electromagnetic response possesses improved homogeneity and hence is less influenced by diffraction effects of individual cells. The impact of incorporating an IDC into ELC resonators in terms of the electrical size at resonance and other relevant properties are investigated through both simulation and experiment in the microwave regime. The proposed structures can be applied to the terahertz regime via appropriate lithographic scaling. © 2010 Optical Society of America.
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Modeling terahertz heating effects on water
(2010-03-01)
Kristensen, Torben T.L.
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Withayachumnankul, Withawat
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Jepsen, Peter Uhd
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Abbott, Derek
We apply Kirchhoff's heat equation to model the influence of a CW terahertz beam on a sample of water, which is assumed to be static. We develop a generalized model, which easily can be applied to other liquids and solids by changing the material constants. If the terahertz light source is focused down to a spot with a diameter of 0.5 mm, we find that the steadystate temperature increase per milliwatt of transmitted power is 1.8°C/mW. A quantum cascade laser can produce a CW beam in the order of several milliwatts and this motivates the need to estimate the effect of beam power on the sample temperature. For THz time domain systems, we indicate how to use our model as a worst-case approximation based on the beam average power. It turns out that THz pulses created from photoconductive antennas give a negligible increase in temperature. As biotissue contains a high water content, this leads to a discussion of worst-case predictions for THz heating of the human body in order to motivate future detailed study. An open source Matlab implementation of our model is freely available for use at www.eleceng.adelaide.edu.au/thz. © 2010 Optical Society of America.
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A systemized view of superluminal wave propagation
(2010-01-01)
Withayachumnankul, Withawat
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Fischer, Bernd M.
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Ferguson, Bradley
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Davis, Bruce R.
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Abbott, Derek
This paper reviews earlier studies on superluminal wave propagation in anomalously dispersive media that have been carried out in the electronic, microwave, and optical regimes. Those studies are relevant to observation of modulated Gaussian pulses transmitted through various media at speeds apparently faster than $c$ without distortion. This paper also presents the condition for superluminal propagation that is established based on the magnitudephase relation of a causal and minimum-phase filter. Since the condition is modeled on the basis of filter theory, it is applicable to all types of media. A terahertz experiment with a periodic bandgap structure is also included to illustrate superluminal propagation. © 2006 IEEE.
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Measurement of linearity in THz-TDS
(2009-12-31)
Withayachumnankul, Withawat
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Ung, Benjamin S.Y.
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Fischer, Bernd M.
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Abbott, Derek
This article presents an approach to the measurement of the amplitude linearity in terahertz time-domain spectroscopy (THz-TDS) systems. The approach exploits a single wafer of high-purity float-zone silicon to produce multiple Fabry-Pérot reflections, which are stepwise attenuated and delayed. Comparison between the theoretical and experimental results can indicate a deviation in linearity. © 2009 IEEE.

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