Thermal switching of the scattering coefficients of terahertz surface plasmon polaritons impinging on a finite array of subwavelength grooves on semiconductor surfaces

8 págs.; 8 figs.; 1 tab. ; PACS number s : 73.20.Mf, 78.68. m, 65.40. b, 41.20.JbWe present a theoretical framework that allows us to investigate the scattering of terahertz surface plasmon polaritons (SPP's) by arrays of subwavelength grooves and ridges on semiconductors. The formulation is based on the reduced Rayleigh equation resulting upon imposing an impedance boundary condition. Guided by approximate estimations of the broadening with temperature of the first gap in the SPP dispersion relation in the case of indium antimonide samples with rectangular grooves, numerical calculations are carried out to determine the spectral dependence of all the SPP scattering channels (reflection, transmission, and radiation) in the immediate vicinity of that gap. The thermally induced switching of the SPP reflection and transmission nearby the lower SPP band edge is investigated as a function of groove parameters (size and number); near-field intensity maps are also presented. We thus shed light on the SPP scattering and switching physical mechanisms, thereby providing the most suitable experimental configurations. © 2006 The American Physical Society.This work was supported in part by the Spanish “Ministerio de Educación y Ciencia” Grant Nos. BFM2003-0427 and FIS2004-0108 and “Comunidad de Madrid” Grant MICROSERES and by the European Union Grant HPRN-CT- 2002-00206. The work of J.G.R. was supported by the “Stichting voor Fundamenteel Onderzoek der Materie” FOM, which is financially supported by the “Nederlandse Organisatie voor Wetenschappelijk Onderzoek” NWO.Peer Reviewe

Approximate impedance models for point-to-point sound propagation over acoustically-hard ground containing rectangular grooves

A modal model for diffraction by a contiguous array of rectangular grooves in an acoustically-hard plane is extended to predict the free space acoustic field from a point source above such a structure. Subsequently, an approximate effective impedance model for grooved surfaces is presented. Measurements have shown that these ground surfaces can be used for outdoor noise reduction but accurate modelling has required the use of computationally expensive numerical methods. The extended modal model and approximate impedance model inspired by it yield equivalent results in a fraction of the time taken by the boundary element method, for example, and could be used when designing grooved surfaces to reduce noise from road traffic

Modelling Of Sound Attenuation By Periodic, Rectangular Structures

The problem of noise reduction in outdoor environments is the subject of significant research effort because of the wide reaching impact it has on the population, especially those in urban areas. From existing outdoor and laboratory data it has already been established that periodic structures embedded into the ground may be tuned to significantly reduce transported noise at nuisance frequencies. Such structures possessing rectangular section are of particular interest due to the relative ease with which they can be implemented. While significant data is available, it has traditionally been a time consuming task to model and simulate such structures due to the need to apply complex numerical methods to do so. Finding simplified modelling methods is the aim of this research. Modelling of these structures will be considered in detail, culminating in the presentation of a novel analytic model with application in practical acoustic engineering and environmental planning. Existing general methods are explored before moving on to consider simpler techniques which may be employed by applying the simplifying assumption that all cavities within the periodic structure are rectangular in nature. By considering the structure as an effective impedance a novel analytic model is presented to conclude the thesis

An Investigation of the Sound Field Above a Surface With Periodically-Spaced Roughness

Outdoor audio-frequency acoustic signals can be amplified passively at selected frequencies by exploiting the interaction of incident sound with surfaces composed of periodically-spaced rectangular strips on an acoustically-hard base. When sound is incident near grazing on acoustically-rigid ground with roughness composed from elements with periodic sub-wavelength spacing, air-borne acoustic surface waves are generated due to a high imaginary-component to the surface impedance as well as the formation and coupling of quarter-wavelength resonances in the gaps. This allows for passive amplification of acoustic signals at the surface wave frequency. This thesis provides a detailed, systematic study into the total sound field generated above surfaces with periodic roughness and how the topography and geometry affect the generation of air-borne acoustic surface waves. Surfaces with a high number of scattering edges per wavelength result in strong surface wave generation due to high reactive component to the impedance. As the gap is increased thereby reducing the number of edges per wavelength, the gap resonances couple less strongly and the surface behaves as a rough surface. As the number of edges per wavelength approaches one, the signal enhancement is provided by Bragg diffraction. Through measurements and predictions, it is found that surface wave enhancement is not detected by a collocated geophone in sand via acoustic-seismic coupling since the sand is sufficiently absorbing so that no surface wave is detected. This systematic study provides a detailed insight into the formation of audio-frequency surface waves generated over periodically-rough surfaces

An investigation of the sound field above a surface with periodic roughness

When audio-frequency sound is incident near grazing on acoustically-hard surfaces with periodic sub-wavelength roughness air-borne acoustic surface waves are generated which could be used to amplify acoustic signals and, therefore, improve detection ranges of, perimeter security systems. Experimental and numerical studies using the Boundary Element Method (BEM) of the sound field generated over periodically-spaced rectangular strips also show several enhancements as a result of complex interactions between the sound field and the rough surface. Surface waves result in excess attenuation spectra with anomalous maxima greater than the 6.02 dB that would be expected from constructive interference above a smooth acoustically rigid surface. The enhancements are found to depend on the roughness spacing and can be attributed to effects due to the finite width and periodicity of the array, quarter-wavelength resonances in the gaps between elements and Bragg diffraction. Pressure maps of the total sound field over rough surfaces show the details of the sound field at the frequencies of interest. As well as being useful for amplifying frequencies arriving at a sensor array, detailed study of the enhancements provides understanding of the evolution of the sound field over rough surfaces

Optical resonances on sub-wavelength silver lamellar gratings

Copyright © 2008 Optical Society of America. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/abstract.cfm?URI=oe-16-26-22003 Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.The optical response of sub-wavelength silver lamellar gratings has been theoretically investigated. Two distinct types of resonance have been predicted for incident radiation with E-field perpendicular to the long axis of the wires. The first resonance has been identified as a cavity mode resonance that is associated with transmission enhancement. The second resonance has been identified as an entirely new horizontal plasmon resonance on the incident (and transmission) surfaces of the wires of the grating. Normal surface plasmon modes are investigated on discontinuous gratings, and their relation to those found on continuous gratings is highlighted by focusing on the perturbation effect of the discontinuities. It is shown that the new horizontal plasmon mode is in no way related to the well known diffractively coupled surface plasmon, and is shown to have a particle plasmon-like nature. It is therefore termed a horizontal particle plasmon, and may be either an uncoupled horizontal particle plasmon resonance (a 1-dimensional particle plasmon) or a coupled horizontal particle plasmon resonance (a 2-dimensional particle plasmon) depending on the height of the grating. It is shown that this resonance may result in a reflection efficiency that is very high, even when the grating would be optically thin if it were a homogeneous film, therefore, it behaves as an inverse wire grid polariser as it reflects more TM than TE incident radiation

Designing and optimizing gratings for soft X-ray diffraction efficiency

The diffraction efficiency is critical to the speed and sensitivity of grating-based spectroscopy instruments. This becomes particularly important for soft x-ray instruments, used on material science beamlines at synchrotrons around the world, where the low reflectivity of materials makes it challenging to create efficient optics. The efficiency of soft x-ray gratings is examined from a rigorous electromagnetic approach using the differential method, adapted for deep gratings using the S-matrix propagation algorithm. New software is written to provide an open-source implementation with fast performance on cluster computing resources. Trends in diffraction efficiency are examined as a function of grating materials, coatings, groove geometry, and incidence conditions; these trends are used to provide recommendations for instrument design, including the identification of a new principle of optimal incidence angle. Efficiency calculations and optimizations are applied to the design of a high-performance soft x-ray emission spectrometer for the REIXS beamline at the Canadian Light Source. The process produces an innovative design that exploits an efficiency peak in the third diffraction order to offer higher resolution than would otherwise be possible given the space constraints of the machine. Finally, the spectrometer's actual gratings are measured for diffraction efficiency as a function of wavelength. Although the real-world efficiencies differ substantially from the nominal calculations, the differences are explained by incorporating real-world effects: geometry errors, groove variation, oxidation, and surface roughness. A fitting process is proposed to match the calculated to the measured efficiency spectra. The geometry parameters predicted by the fitting process are found to agree exactly with atomic force microscopy (AFM) measurements for all the gratings studied. Because each grating parameter affects the shape of the efficiency spectrum in a different way, the spectrum can be considered as a unique "fingerprint" or "hash"; we conclude that this might be extended to use efficiency measurements and fitting calculations to characterize grating parameters that are difficult or impossible to measure directly

New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits

Research interest: In recent years we have seen the emergence of commercial applications at high frequencies, such as the top part of the microwave band and the millimeter and sub-millimeter bands, and it is expected a big increase in the coming years. This growing demand requires a rapid development of low-cost technology with good performance at these frequencies, where common technologies, such as microstrip and standard waveguides, have some shortcomings. In particular, existing solutions for high-gain planar scanning antennas at these frequencies su er from the disadvantages of these technologies giving rise to high-cost products not suitable for high volume production. Objectives: The main objective of this thesis is to study the feasibility of a new proposal to improve existing solutions to date for low-cost high-gain planar scanning antennas at high frequencies. This overall objective has resulted in another central objective of this thesis, which is the research of new quasi-TEM waveguides that are more appropriate than current technologies for the realization of circuits and components at these frequency bands. These guided solutions make use of periodic or arti cial surfaces in order to con- ne and channel the elds within these waveguides. Methodology: The work follows a logical sequence of speci c tasks aimed at achieving the main objective of this thesis. Chapter 2 presents the proposed guiding solution and shows its performance numerical and experimentally. The optimized design of high-gain antennas based on waveguide slot arrays requires the development of e cient ad-hoc codes. The implementation and validation of this code is presented in Chapter 3, where a new method for the analysis of corrugated surfaces is proposed, and in Chapter 4, which extends this code to the analysis of waveguide slot arrays. The process design and optimization of a two-dimensional array is described in Chapter 5, where a preliminary experimental validation is also described. Moreover, the proposed guiding solution has inspired the development of a new guiding technology of wider bandwidth and more versatile for the realization of circuits and components at high frequencies. Chapter 6 presents the contributions to the study of this technology and its application to the design of circuits.Alfonso Alós, E. (2011). New quasi-TEM waveguides using artificial surfaces and their application to antennas and circuits [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/11073Palanci