Broadband, slow sound on a glide-symmetric meander-channel surface

This is the final version. Available from Acoustical Society of America via the DOI in this record.All data created during this research are openly available from the University of Exeter’s institutional repository at https://ore.exeter.ac.uk/.The acoustic surface waves supported by hard surfaces patterned with repeat-period, meandering grooves are explored. The single, continuous groove forms a glide-symmetric surface, inhibiting the formation of a bandgap at the first Brillouin-zone boundary. Consequently, the acoustic surface waves exhibit an almost constant, sub-speed-of-sound, group velocity over a broad frequency band. Such slow, broadband modes may have applications in controlling the flow of noise over surfaces.QinetiQ LtdEngineering and Physical Sciences Research Council (EPSRC)QinetiQ Lt

A Framework for Symmetric Part Detection in Cluttered Scenes

The role of symmetry in computer vision has waxed and waned in importance during the evolution of the field from its earliest days. At first figuring prominently in support of bottom-up indexing, it fell out of favor as shape gave way to appearance and recognition gave way to detection. With a strong prior in the form of a target object, the role of the weaker priors offered by perceptual grouping was greatly diminished. However, as the field returns to the problem of recognition from a large database, the bottom-up recovery of the parts that make up the objects in a cluttered scene is critical for their recognition. The medial axis community has long exploited the ubiquitous regularity of symmetry as a basis for the decomposition of a closed contour into medial parts. However, today's recognition systems are faced with cluttered scenes, and the assumption that a closed contour exists, i.e. that figure-ground segmentation has been solved, renders much of the medial axis community's work inapplicable. In this article, we review a computational framework, previously reported in Lee et al. (2013), Levinshtein et al. (2009, 2013), that bridges the representation power of the medial axis and the need to recover and group an object's parts in a cluttered scene. Our framework is rooted in the idea that a maximally inscribed disc, the building block of a medial axis, can be modeled as a compact superpixel in the image. We evaluate the method on images of cluttered scenes.Comment: 10 pages, 8 figure

Measuring Glide Reflection Symmetry in Human Movements

abstract: Many studies on human walking pattern assume that adult gait is characterized by bilateral symmetrical behavior. It is well understood that maintaining symmetry in walking patterns increases energetic eciency. We present a framework to provide a quantitative assessment of human walking patterns, especially assessments related to symmetric and asymmetric gait patterns purely based on glide reflection. A Gliding symmetry score is calculated from the data obtained from Motion Capture(MoCap) system. Six primary joints (Shoulder, Elbow, Palm, Hip, Knee, Foot) are considered for this study. Two dierent abnormalities were chosen and studied carefully. All the two gaits were mimicked in controlled environment. The framework proposed clearly showed that it could distinguish the abnormal gaits from the ordinary walking patterns. This framework can be widely used by the doctors and physical therapists for kinematics analysis, bio-mechanics, motion capture research, sports medicine and physical therapy, including human gait analysis and injury rehabilitation.Dissertation/ThesisMasters Thesis Electrical Engineering 201

Water drop lens antenna for sub-THz imaging

La banda de frecuencias de ondas milimétricas (MMW), caracterizada por una elevada atenuación atmosférica y un gran ancho de banda disponible, se ha convertido de gran interés para aplicaciones de imágenes de radar de alta precisión. El desarrollo continuo de la tecnología de circuitos de microondas monolíticos integrados (MMIC) da lugar a la aparición de diferentes transceptores de radar comerciales (COTS) en esta banda de frecuencia, donde las antenas están totalmente integradas en el chip para evitar pérdidas en el sustrato. Las lentes se utilizan para corregir el frente de fase de estos chips mejorando la directividad y, por tanto, el rango de funcionamiento. Las lentes geodésicas, que pueden ser construidas utilizando sólo metales, ofrecen las propiedades atractivas de las lentes dieléctricas comunes sin sus pérdidas en el metarial. En este trabajo de fin de máster se ha diseñado una antena del tipo lente geodésica específica con propiedades de enfoque para mejorar las capacidades de imagen de radar del transceptor TRA-120-002 que trabaja en la banda ISM de 120 GHz. Se ha hecho un estudio de diferentes transiciones para los puntos singulares de la antena, minimizando reflexiones sin aumentar las aberraciones en la lente. En el trabajo se muestra un diseño optimizado de la apertura de la antena donde se utilizan corrugacions para mejorar el diagrama de radiación. Se ha diseñado también una pequeña antena de apertura con una metasuperfície de pines periódicos para maximizar la transmisión de energía entre el transceptor COTS y la lente. Finalmente, se ha añadido una metasuperfície basada en agujeros con simetría deslizada para evitar fugas entre las placas de la antena debido a posibles limitaciones en su fabricación. Los resultados muestran que se puede conseguir una antena de tipo lente de 5l de radio totalmente metálica con directividad superior a 19,5 dB y niveles de lóbulos secundários (SLL) entre -10,5 dB y -9,2 dB dentro de la banda de 119 GHz - 125,5 GHz mientras que la antena focaliza a 30 cm.La banda de freqüències d'ones mil·limètriques (mmW), caracteritzada per una elevada atenuació atmosfèrica i un gran ample de banda disponible, ha esdevingut de gran interès per a aplicacions d'imatges de radar d'alta precisió. El desenvolupament continu de la tecnologia de circuits de microones monolítics integrats (MMIC) dona lloc a l'aparició de diferents transceptors de radar comercials (COTS) en aquesta banda de freqüència, on les antenes estan totalment integrades al xip per evitar pèrdues en el substrat. Les lents s'utilitzen per corregir el front de fase d'aquests xips millorant la directivitat i, per tant, el rang de funcionament. Les lents geodèsiques, que poden ser construïdes utilitzant només metalls, ofereixen les propietats atractives de les lents dielèctriques comuns sense les seves pèrdues en el material. En aquest treball de fi de màster s'ha dissenyat una antena del tipus lent geodèsica específica amb propietats d'enfocament per millorar les capacitats d'imatge de radar del transceptor TRA-120-002 que treballa a la banda ISM de 120 GHz. S'ha fet un estudi de diferents transicions per als punts singulars de l'antena, minimitzant reflexions sense augmentar les aberracions a la lent. En el treball es mostra un disseny optimitzat de l'obertura de la antena on s'utilitzen corrugacions per millorar el diagrama de radiació. S'ha dissenyat també una petita antena d'obertura amb una metasuperfície de pins periòdics per maximitzar la transmissió d'energia entre el transceptor COTS i la lent. Finalment, s'ha afegit una metasuperfície basada en forats amb simetria lliscada per evitar pèrdues entre les plaques de l'antena a causa de possibles limitacions en la seva fabricació. Els resultats mostren que es pot aconseguir una antena de tipus lent de 5l de radi totalment metàl·lica amb directivitat superior a 19,5 dB i nivells de lòbuls secundaris (SLL) entre -10,5 dB i -9,2 dB dins de la banda de 119 GHz - 125,5 GHz mentre que l'antena focalitza a 30 cm.The Millimiter Wave (mmW) frequency band, characterized by a high atmospheric attenuation and wide available bandwidth has become of big interest for high accuracy radar imaging applications. The continuous development of the Monolithic Microwave Integrated Circuit (MMIC) technology yields to the appearance of different commercial-off-the-shelf (COTS) radar transceivers at that frequency band, where the antennas are fully integrated into the chip. Lenses are being used to correct the phase front of those MMIC improving the directivity and therefore the operating range. Fully metallic geodesic lenses offer the attractive properties of common dielectric lenses without their material losses. In this master thesis, a specific water-drop geodesic lens antenna with focusing properties has been designed to enhance the radar imaging capabilities of the theTRA-120-002 transceiver working at the 120 GHz Industrial, Scientific and Medical (ISM) band. Different transitions for the antenna singular points have been studied to minimize reflections without increasing aberrations in the lens. An optimized design of a radiating flare is shown where corrugations are used to improve the antenna radiation pattern. A small feeding horn antenna with a bed-of-nails Electromagnetic Band-Gap (EBG) metasurface has been designed to maximize the energy transmission between the COTS transceiver and the lens. Finally, a glide-symmetric holey metasurface has been added to prevent leakage between the antenna plates due to manufacturing limitations. The results show that a fully metallic folded lens antenna with 5l radius can achieve directivities higher than 19.5 dB and side-lobe levels (SLL) between -10.5 dB and -9.2dB within the 119 GHz - 125.5 GHz band while having an image point located at 30cm from the antenna

Polarization entangled state measurement on a chip

The emerging strategy to overcome the limitations of bulk quantum optics consists of taking advantage of the robustness and compactness achievable by the integrated waveguide technology. Here we report the realization of a directional coupler, fabricated by femtosecond laser waveguide writing, acting as an integrated beam splitter able to support polarization encoded qubits. This maskless and single step technique allows to realize circular transverse waveguide profiles able to support the propagation of Gaussian modes with any polarization state. Using this device, we demonstrate the quantum interference with polarization entangled states and singlet state projection.Comment: Revtex, 5+2 pages (with supplementary information), 4+1 figure