2,345 research outputs found
Plasmonic absorber based on nano-scale dielectric resonator antennas
No full textNano-scale dielectric resonator antennas (DRAs) have shown potential for various optical applications. In this paper, the use of DRAs to couple free-space waves to surface plasmon polaritons (SPPs) is discussed. As an example, a design of DRA-based perfect absorber is proposed and demonstrated through simulation. The predicted ab sorption of > 99:9% of the incident power confirms the DRAs as a building block for efficient SPP couplers and promises applications in integrated optics and field enhancement.Chengjun Zou, Withawat Withayachumnankul, Longfang Zou, Christophe Fumeau
Resonance breakdown of dielectric resonator antennas on ground plane at visible frequencies
No full textNanoscale dielectric resonator antennas (DRAs) are promising elements for constructing the next generation of efficient and compact optical devices. Their efficient light manipulation capability underpinned by electric and magnetic resonances at visible frequencies is appealing for optical metasurfaces with various functions such as anomalous re ection, polarization conversion and surface plasmon coupling. To realize these functions, the resonance properties of the individual DRA elements are of critical importance. In this paper, we study the resonance breakdown of nanoscale cylindrical DRAs on metallic substrates. By gradually increasing the relative permittivity of DRAs on a metallic ground plane from low to high values, we observe two types of resonance breakdown and on that basis we can define a permittivity range for efficient resonance. More specifically, the resonance breakdown occuring at low DRA permittivities is a result of weak confinement and excessive radiation loss. The resonance breakdown at high DRA permittivities is a result of an elevated plasmonic loss at the metal- dielectric interface when the negative permittivity of the metal and the positive permittivity of the dielectric material have matched in their absolute values. The latter breakdown can be avoided by inserting a thin dielectric spacer with a low permittivity between the metal and dielectric. This study suggests important considerations for designing dielectric resonator metasurfaces at the visible frequencies.Chengjun Zou, Withawat Withayachumnankul, Longfang Zou, Christophe Fumeau
Terahertz and optical Dielectric Resonator Antennas: potential and challenges for efficient designs
No full textThe unique characteristics of Dielectric Resonator Antennas (DRAs) make them suitable for various niche applications throughout the spectrum, from microwave frequencies to the optical regime. One of the striking features of DRAs is their high efficiency when the resonator is realized in low-loss high-permittivity dielectric material. This interesting property arises from their radiation mechanism being mostly based on displacement currents, and opens the door to efficient device realizations towards higher frequencies where conductor losses degrade the performance of metallic resonators. This paper will highlight some of the distinctive properties of the DRAs and review their potential applications in various frequency regimes. It will in particular consider the latest developments at THz and optical frequencies, with highefficiency realizations of reflect-arrays and magnetic mirrors.Christophe Fumeaux, Chengjun Zou, Daniel Headland, Shruti Nirantar, Philipp Gutruf, Longfang Zou, Madhu Bhaskaran, Sharath Sriram, Withawat Withayachumnanku
Nanoscale TiO(2) dielectric resonator absorbers
No full textWe demonstrate a narrow-band plasmonic absorber based on a uniform array of nanoscale cylindrical dielectric resonators (DRs) on a metallic substrate at visible frequencies. Under a normally incident plane-wave excitation, the DRs resonate in their horizontal magnetic dipolar mode, which can be seen as localized plasmonic hot spots. Such a localized resonance also couples incident waves into surface plasmon polaritons (SPPs) bidirectionally, and perfect absorption is achieved by creating SPP standing waves. The simulation shows perfect absorption at 633 nm and 1.8% relative bandwidth with >90%absorption, while the measurement demonstrates maximum absorption of 90% at 636 nm. Both simulation and measurement results are analyzed with coupled mode theory. An additional numerical study elaborates on the dependence of absorption on the resonator size, period, and incidence angle.Chengjun Zou, Philipp Gutruf, Withawat Withayachumnankul, Longfang Zou, Madhu Bhaskaran, Sharath Sriram and Christophe Fumeau
Mutual coupling reduction in a multi-mode multi-function dielectric resonator antenna
No full textIn a rectangular dielectric resonator, the mutual coupling between TE111 and Quasi-TM111 mode is in theory zero due to the orthogonal field distributions. In practice, some coupling is observed in a two ports dielectric resonator antenna (DRA) design based on those two modes. The mutual coupling can be explained by the asymmetric field distribution resulting from asymmetric feeding methods. Through analysis of the field distribution, two different methods are proposed to reduce mutual coupling to less than -15 dB. The first method considers an asymmetric resonator, whereas the second one symmetrizes the feeding. Designs with both methods are presented and their advantages and weaknesses are discussed.Longfang Zou and Christophe Fumeau
Horizontally polarized omnidirectional dielectric resonator antenna
No full textThis paper presents the concept of using cylindrical dielectric resonator antenna (DRA) as horizontally polarized omnidirectional antenna. The design is achieved through the excitation of the TE 01δ mode in the dielectric cylinder, a mode traditionally exploited in the filtering operation of dielectric resonators. As the mode is intrinsically narrow band, an air gap is introduced in the design and a dual point feeding network is optimized to achieve a wider impedance bandwidth with radially symmetric radiation patterns. The experimental results show a good agreement with simulation and demonstrate omnidirectional operation with horizontal polarization over a bandwidth of 5.6% around the center frequency of 3.9 GHz. © 2011 Engineers Australia.L. Zou and C. Fumeauxhttp://www.apmc2011.com
Skin-Stiffener Separation in T-Stiffened Composite Specimens in Postbuckling Condition
No full textAn experimental and numerical investigation was conducted to study the skin-stiffener separation of single T-shape stiffener specimens in postbuckling condition. Three specimens were manufactured with a centrally located Teflon insert, and were loaded in compression until collapse. Deformation patterns and separation evolution were monitored during the tests. To measure the full-field displacements and the strain distributions of the specimens, a digital image correlation (DIC) system was used. Skin-stiffener separation was observed and measured with an ultrasound system. Finite-element (FE) analyses were conducted to capture interlaminar damage mechanism based on the virtual crack closure technique. The numerical analysis accurately predicted the postbuckling deformation and the skin-stiffener separation behavior. The close correlation between the experimental and numerical results allows for further exploitation of the strength reserve in the postbuckling region and wider design options for the next generation of composite aircraft designs.</p
Dielectric resonator antennas : from multifunction microwave devices to optical nano-antennas.
No full textSince a cylindrical dielectric resonator antenna (DRA) was firstly proposed by Long et al. in the 1980s, extensive research has been carried out on analyzing DRA shapes, characterizing the resonant modes, improving their radiation characteristics with various excitation schemes. Compared with conventional conductor-based antennas, DRAs have attractive features such as small size, high radiation efficiency and versatility in their shape and feeding mechanism. Importantly, various orthogonal modes with diverse radiation characteristics can be excited within a single DRA element. These modes can be utilized for various requirements, which makes the DRA a suitable potential candidate for multifunction applications. Based on this principle, this thesis presents different multifunction designs: Firstly a cross-shaped DRA with separately fed broadside circularly polarized (CP) and omnidirectional linearly polarized (LP) radiation patterns and, secondly, a multifunction annular cylindrical DRA realizing simultaneously omnidirectional horizontally and vertically polarized radiation patterns with low cross-coupling. The evolution, design process and experimental validation of these two antennas are described in details in the thesis. The second part of the thesis dramatically scales down DRA to shorter wavelengths. Inspired by the fact that DRA still exhibits high radiation efficiency (>90%) in the millimetre wave range, while the efficiency of conventional metallic antenna degrades rapidly with frequencies, this thesis proposes the concept of nanometer-scale DRA operated in their fundamental mode as optical antennas. To validate the concept, optical DRA reflectarrays have been designed and fabricated. Although the zeroth-order spatial harmonic reflection is observed in the measurement due to the imperfect nanofabrication, the power ratio of deflected beam to the specular component of reflection amounts to 4.42, demonstrating the expected operation of the reflectarray. The results strongly support the concept of optical DRA and proposes design methods and strategies for their realization. This proof of concept is an essential step for future research on nano-DRA as building block of emerging nano-structured optical components.Thesis (Ph.D.)--University of Adelaide, School of Electrical & Electronic Engineering, 2013
A cross-shaped dielectric resonator antenna for multifunction and polarization diversity applications
No full textThis letter proposes a multifunction cross-shaped dielectric resonator antenna (DRA) with separately fed broadside circularly polarized (CP) and omnidirectional linearly polarized (LP) radiation patterns. These distinct radiation patterns are achieved in overlapping frequency bands by exciting two different modes in a single dielectric resonator (DR) volume. This letter also investigates the effect of the feeding geometry on the mutual coupling between the modes and concludes that an asymmetric feeding degrades the orthogonality of the modes and thus increases the interport coupling coefficient. By using a symmetric feeding, the coupling coefficient can be significantly reduced to below - 30 dB in the frequency band common to both operation modes. The experimental results show a good agreement with simulation and demonstrate a broadside CP operation over a bandwidth of 6.8%, which overlaps with the omnidirectional LP impedance bandwidth of 38.5%. The proposed antenna could be used not only as multifunction, but also as polarization diversity antenna due to the overlapping dual-feed CP and LP operation.Longfang Zou and Christophe Fumeau
Finite Element Methods and Their Convergence for Elliptic and Parabolic Interface Problems
No full textIn this paper, we consider the finite element methods for solving second order elliptic and parabolic interface problems in two-dimensional convex polygonal domains. Nearly the same optimal L 2 -norm and energy-norm error estimates as for regular problems are obtained when the interfaces are of arbitrary shape but are smooth, though the regularities of the solutions are low on the whole domain. The assumptions on the finite element triangulation are reasonable and practical. Mathematics Subject Classification (1991): 65N30, 65F10. A running title: Finite element methods for interface problems. Correspondence to: Dr. Jun Zou Email: [email protected] Fax: (852) 2603 5154 1 Institute of Mathematics, Academia Sinica, Beijing 100080, P.R. China. Email: [email protected]. The work of this author was partially supported by China National Natural Science Foundation. 2 Department of Mathematics, the Chinese University of Hong Kong, Shatin, N.T., Hong Kong. E-mail: [email protected]...
- …
