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http://hdl.handle.net/2440/292
2016-12-08T22:05:08ZTerahertz signal classification based on geometric algebra
http://hdl.handle.net/2440/103005
Title: Terahertz signal classification based on geometric algebra
Author: Zhou, S.; Valchev, D.G.; Dinovitser, A.; Chappell, J.M.; Iqbal, A.; Ng, B.W.H.; Kee, T.W.; Abbott, D.
Abstract: This paper presents an approach to classification of substances based on their terahertz spectra. We use geometric algebra to provide a concise mathematical means for attacking the classification problem in a coordinate-free form. For the first time, this allows us to perform classification independently of dispersion and, hence, independently of the transmission path length through the sample. Finally, we validate the approach with experimental data. In principle, the coordinate-free transformation can be extended to all types of pulsed signals, such as pulsed microwaves or even acoustic signals in the field of seismology. Our source code for classification based on geometric algebra is publicly available at: https://github.com/swuzhousl/Shengling-zhou/blob/geometric-algebra- classifier/GAclassifier/.2016-01-01T00:00:00ZTime as a geometric property of space
http://hdl.handle.net/2440/102998
Title: Time as a geometric property of space
Author: Chappell, J.M.; Hartnett, J.G.; Iannella, N.; Iqbal, A.; Abbott, D.
Abstract: The proper description of time remains a key unsolved problem in science. Newton conceived of time as absolute and universal which “flows equably without relation to anything external.” In the nineteenth century, the four-dimensional algebraic structure of the quaternions developed by Hamilton, inspired him to suggest that he could provide a unified representation of space and time. With the publishing of Einstein's theory of special relativity these ideas then lead to the generally accepted Minkowski spacetime formulation of 1908. Minkowski, though, rejected the formalism of quaternions suggested by Hamilton and adopted an approach using four-vectors. The Minkowski framework is indeed found to provide a versatile formalism for describing the relationship between space and time in accordance with Einstein's relativistic principles, but nevertheless fails to provide more fundamental insights into the nature of time itself. In order to answer this question we begin by exploring the geometric properties of three-dimensional space that we model using Clifford geometric algebra, which is found to contain sufficient complexity to provide a natural description of spacetime. This description using Clifford algebra is found to provide a natural alternative to the Minkowski formulation as well as providing new insights into the nature of time. Our main result is that time is the scalar component of a Clifford space and can be viewed as an intrinsic geometric property of three-dimensional space without the need for the specific addition of a fourth dimension.2016-01-01T00:00:00ZReconfigurable and tunable S-shaped split-ring resonators and application in band-notched UWB antennas
http://hdl.handle.net/2440/102910
Title: Reconfigurable and tunable S-shaped split-ring resonators and application in band-notched UWB antennas
Author: Horestani, A.K.; Shaterian, Z.; Naqui, J.; Martin, F.; Fumeaux, C.
Abstract: This paper proposes a compact reconfigurable (bandstop/bandpass) and frequency-tunable structure based on S-shaped split-ring resonators (S-SRRs). It is known that an S-SRR coupled to a coplanar waveguide (CPW) provides a stopband in the transmission characteristic of the line. It is shown here that this behavior of the S-SRR can be switched between fundamental resonance and second harmonic response by introduction of a p-i-n diode in the center segment of the S-SRR. Alternatively, if the S-SRR is loaded with a varactor diode instead of a switch, the frequency of the stopband can be continuously tuned from the S-SRRs fundamental resonance frequency to its second harmonic. Furthermore, it is shown that if a pair of shunt p-i-n diodes are introduced across the slots of the host CPW, the structure can be reconfigured from a bandstop to a bandpass structure. Thus, the proposed resonator structure can be used as the building block of reconfigurable (bandstop/bandpass) filters with tunable operating frequency. Finally, to demonstrate a practical application of the proposed structure, an ultrawideband antenna with a tunable band notch is designed and experimentally validated.2016-01-01T00:00:00ZNanoscale TiO₂ dielectric resonator absorbers
http://hdl.handle.net/2440/102572
Title: Nanoscale TiO₂ dielectric resonator absorbers
Author: Zou, C.; Gutruf, P.; Withayachumnankul, W.; Zou, L.; Bhaskaran, M.; Sriram, S.; Fumeaux, C.
Abstract: We 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.2016-01-01T00:00:00Z