198,092 research outputs found
Effect of magnetostatic interactions on the hysteresis parameters of single-domain and psuedo-single domain grains
No full textFrom experiments it is known that magnetostatic interactions between grains strongly affect the magnetic behavior of samples. However, because of the difficulty in predicting the nonlinear behavior, the effect of interactions has been largely ignored from theoretical models. Instead models are often based on noninteracting assemblages. This approximation is valid for certain natural systems, but there are many cases where interactions are known to be important, for example, bacterial magnetosomes found in sedimentary rocks. Using a three-dimensional micromagnetic model, we have conducted a detailed study of the role of magnetostatic interactions on the magnetic properties of assemblages of ideal single domain (SD) grains and cubic grains between 30–250 nm in size. We quantify the contribution of interactions to hysteresis parameters and the Day plot. We show that interactions can strongly affect the magnetic characteristics of a grain assemblage. For example, assemblages of interacting SD grains can plot in the traditional multidomain (MD) area of the Day plot. For grains >100 nm in size, interactions can have the opposite effect, and can cause the hysteresis parameters to shift toward the SD region of the Day plot. In addition to varying grain size, we have also considered various anisotropies, e.g., uniaxial and cubic, and the importance of the alignment configuration of the particle assemblages, i.e., randomly distributed or aligned. It is shown that for assemblages of aligned magnetite particles, that as the interaction spacing is decreased, the SD/MD transition size increases, which may explain why some magnetotatic bacteria possess aligned grains of magnetite above the traditional transition size value of 70 nm. By aligning the anisotropies, the grains become stable SD, and having larger crystals will increase the magnetic signal
Compact Single-Layer Traveling-Wave Antenna DesignUsing Metamaterial Transmission Lines
No full textThis paper presents a single-layer traveling-wave antenna (TWA) that is based on composite right/left-handed (CRLH)-metamaterial (MTM) transmission line (TL) structure, which is implemented by using a combination of interdigital capacitors and dual-spiral inductive slots. By embedding dual-spiral inductive slots inside the CRLH MTM-TL results in a compact TWA. Dimensions of the proposed CRLH MTM-TL TWA is 21.5 x 30.0 mm(2) or 0.372 lambda(0) x 0.520 lambda(0) at 5.2 GHz (center frequency). The fabricated TWA operates over 1.8-8.6 GHz with a fractional bandwidth greater than 120%, and it exhibits a peak gain and radiation efficiency of 4.2 dBi and 81%, respectively, at 5 GHz. By avoiding the use of lumped components, via-holes or defected ground structures, the proposed TWA design is economic for mass production as well as easy to integrate with wireless communication systems
Wideband planar array antenna based on SCRLH-TL for airborne synthetic aperture radar application
No full textThis paper presents empirical results of a novel planar microstrip array antenna based on a simplified composite right/left-handed transmission line (SCRLH-TL) for application in circularly polarized synthetic aperture radar (CP-SAR) systems operated in UHF, L, S, and C-Bands. The array antenna consists of 6x6 matrix of spiral-shaped radiating elements that are excited through proximity-coupled, single feed-line. Pattern synthesis technique is used to determine the excitation coefficients (amplitude and phase) to apply to the individual array elements to achieve the required pattern shape. The array antenna has dimensions of 111.5x96.06mm(2). The measured impedance bandwidth of the antenna is 3.85GHz for S-11<-10dB from 300MHz to 4.15GHz, corresponding to a fractional bandwidth of 173%. Maximum gain and radiation efficiency measured are 4.8 dBi and 79.5%, respectively, at 2.40GHz. The antenna has a 3-dB axial-ratio bandwidth of 3.94GHz from 144MHz to 4.66GHz. The antenna's beamwidth in azimuth and elevation planes vary between 60 degrees and 120 degrees across its operational frequency range from 300MHz to 4.15GHz. The antenna design fulfills the challenging electrical and physical specifications required for CP-SAR employed onboard unmanned aerial vehicle (UAV)
A Technique to Suppress Mutual Coupling in Densely Packed Antenna Arrays Using Metamaterial Supersubstrate
No full textA simple and practical technique for reducing the mutual coupling between neighbouring antennas is presented for application in densely packed antenna arrays. This is achieved by locating between the radiation elements a smaller patch with metamaterial decoupling structure (MTM-DS). In this case the radiating elements are circular patches and the MTM-DS is constructed from a hexagonal slit resonator. The consequence of implementing the MTM-DS patch is significant reduction in mutual coupling between adjacent radiating patches by 60%, improvement in impedance match by 200% and substantial increase in the antenna's fractional bandwidth by 369%. Since the ground plane is unaltered the front-to-back ratio is unaffected too. The proposed technique is easily realizable and can be used effectively in beam scanning applications
Study on isolation and radiation behaviours of a 34×34 array-antennas based on SIW and metasurface properties for applications in terahertz band over 125–300 GHz
No full textThis paper describes the feasibility of conceptual design of a 34 x 34 array antenna for operation at Terahertz over a frequency range of 125-300 GHz for S-11 <= -10dB, which corresponds a fractional bandwidth of 82.35%. Each radiation element constituting the array consists of a square patch of dimensions of 2 x 2 mm(2) that are excited by a matched microstrip line. Each patch is isolated from each other with metallic via-holes, which are implemented based on the substrate integrated waveguide (SIW) technique. This technique is shown to effectively reduce mutual coupling between adjacent radiation elements that can otherwise undermine the arrays radiation gain and pattern. Periphery of each patch is embedded with circular dielectric slots, which are created based on the metasurface concept to enhance the radiation gain and efficiency performances. With the proposed approaches (1) the mutual coupling is suppressed on average by 25dB over its operating frequency range, and (2) the effective aperture area of the array antenna is extended without increase in the array's physical dimensions. Radiation gain and efficiency of the proposed array antenna over its operating range vary from 7.51 dBi to 40.08 dBi, and from 70.51% to 90.11%, respectively. Improvement in gain and efficiency of approximately 60% and 30%, respectively, is achieved with the inclusion of the metasurafce slots. The proposed 34 x 34 array antenna is proper candidate for applications in Terahertz wireless communication systems
Triple-band planar dipole antenna for omnidirectional radiation
No full textThis Letter presents a compact triple-band dipole antenna that radiates omnidirectionally. The antenna is a T-shaped structure that is excited through a vertical feedline. Located under the horizontal rectangular patch are two λ/2 long meander-line stubs symmetrically interfaced to the feedline. On the bottom side of the substrate is a trident shaped ground-plane structure located under the T-shaped radiator. The proposed configuration is essentially composed of three radiating elements, which has a small footprint of 19×16 mm2 on a 0.8 mm thick substrate. Regions of enhanced impedance matching are realized between 0.5 – 2.69 GHz, 3.2 – 4.44 GHz and 4.82 – 6.6 GHz covering major portions of L, S and C-bands. It is shown by reducing the gap between the meander lines stub and rectangular patch reduces results in increased gain performance. Measured results confirm the antenna exhibits omnidirectional radiation with enhanced impedance match at 1.5, 4 and 5.4 GHz with corresponding average gain of 1.6 dBi, 3.4 dBi and 3 dBi, respectively
Broadband 3-D shared aperture high isolation nine-element antenna array for on-demand millimeter-wave 5G applications
No full textUniversidad Carlos III de Madrid, European Union-Horizon 2020 [801538]; Ministerio de Ciencia, innovación y Universidades, Gobierno de España (MCIU/AEI/FEDER, UE) [RTI2018-095499-B-C31]Alibakhshikenari, M., Virdee, B.S., Vadalà, V., Dalarsson, M., de Cos Gómez, M.E., Alharbi, A.G., Burokur, S.N., Aïssa, S., Dayoub, I., Falcone, F., Limiti, E
CMS General Brochure
No full textThe CMS General Brochure developed in 2006 (EN, FR, IT updated in 2009). Available in multiple languages: English (updated in Sept 2015) - D. Barney, J. Virdee French (updated in Sept 2015) - C. Pralavorio, P. Bloch, M.Della-Negra Italian (updated in Sept 2015) - F. Cavallari et al German (updated in Sept 2015) - C. Wulz et al Dutch (2006) - F. Blekman, B. Van Konigsveld Greek (2006) - P. Vichoudis, E. Petrakou, E. Symeonidou, N. Tracas Spanish (2006) - J. Puerta-Pelayo, P. Garcia Finnish (2006) - J. Tuominiemi, K. Aspola Polish (2006) - M. Lapka, G.Wrochna Portuguese (2006) - C. Lourenco Serbian (2006) - D. Lazic, P. Milenovic, D. Maletic, A. Vitlic Turkish (2006) - Erhan Gulmez et a
Extended Aperture Miniature Antenna Based on CRLH Metamaterials for Wireless Communication Systems Operating Over UHF to C-Band
No full textThis paper presents a simple technique to extend the aperture of planar composite right/left-handed (CRLH) metamaterial antennas with minimal impact on the antenna’s dimensions. Unlike most CRLH antenna structures the proposed antenna is via-free. The proposed antenna is shown to operate over a wideband from UHF to C-band with good radiation characteristics. The antenna configuration consists of a vertically stacked CRLH unit-cells comprising of a patch and meandered lines, where the patch is engraved with an S-shaped slot. The design uses minimal ground plane area. The meander line inductance is grounded using CPW ground which eliminates conventional CRLH TL metallic via into ground plane. The antenna is feed through a coplanar waveguide (CPW) match stub that is electromagnetically coupled to the unit cells. Antenna dimensions are 17.5×32.15×1.6 mm3, which corresponds to 0.204λ_0×0.375λ_0×0.018λ_0 where free-space wavelength (λ_0) is 3.5GHz. Parametric study enabled the optimization of the antenna performance in terms of impedance bandwidth, radiation gain and radiation efficiency. Measured results confirm the antenna can operate from 850 MHz to 7.90 GHz, which is equivalent to a fractional bandwidth of 161.14%. The antenna has a maximum gain and radiation efficiency of 5.12 dBi and ~80%, respectively, at 3.5GHz
Miniaturised planar-patch antenna based on metamaterial L-shaped unit-cells for broadband portable microwave devices and multiband wireless communication systems
No full textThis study describes the design of a metamaterial planar antenna for multi-octave band operation. The metamaterial unit-cell comprises L-shaped slit which is etched inside a rectangular patch with a grounded inductive spiral. The slit essentially behaves as a series left-handed capacitance and the spiral as a shunt left-handed inductance. The antenna was modelled and optimised for impedance bandwidth, gain and efficiency performance using commercial three-dimensional full-wave electromagnetic simulation tools. The antenna has a measured impedance bandwidth of 6.02GHz for S-11<-10dB. This corresponds to a fractional bandwidth of 172.49%, which is higher than multiband planar antennas reported to date. The antenna has a maximum gain and efficiency performance of 3.7dBi and 73%, respectively, at 3.25GHz. The physical footprint of the antenna is comparable to other wideband planar antennas reported to date. The overall size of the antenna is 0.037(0)x0.027(0)x0.002(0) and 0.25(0)x0.18(0)x0.017(0), where (0) is free-space wavelength at 0.48 and 3.25GHz, respectively
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