Local sound field synthesis

This thesis investigates the physical and perceptual properties of selected methods for (Local) Sound Field Synthesis ((L)SFS). In agreement with numerical sound field simulations, a specifically developed geometric model shows an increase of synthesis accuracy for LSFS compared to conventional SFS approaches. Different (L)SFS approaches are assessed within listening experiments, where LSFS performs at least as good as conventional methods for azimuthal sound source localisation and achieves a significant increase of timbral fidelity for distinct parametrisations.Die Arbeit untersucht die physikalischen und perzeptiven Eigenschaften von ausgewählten Verfahren zur (lokalen) Schallfeldsynthese ((L)SFS). Zusammen mit numerischen Simulationen zeigt ein eigens entwickeltes geometrisches Modell, dass LSFS gegenüber konventioneller SFS zu einer genauere Synthese führt. Die Verfahren werden in Hörversuchen evaluiert, wobei LSFS bei der horizontalen Lokalisierung von Schallquellen eine Genauigkeit erreicht, welche mindestens gleich der von konventionellen Methoden ist. Für bestimmte Parametrierung wird eine signifikant verbesserte klangliche Treue erreicht

Wave Field Synthesis in a listening room

This thesis investigates the influence of the listening room on sound fields synthesised by Wave Field Synthesis. Methods are developed that allow for investigation of the spatial and timbral perception of Wave Field Synthesis in a reverberant environment using listening experiments based on simulation by binaural synthesis and room acoustical simulation. The results can serve as guidelines for the design of listening rooms for Wave Field Synthesis.Diese Dissertation untersucht den Einfluss des Wiedergaberaums auf Schallfelder, die mit Wellenfeldsynthese synthetisiert werden. Es werden Methoden zur Untersuchung von räumlicher und klangfarblicher Wahrnehmung von Wellenfeldsynthese in einer reflektierenden Umgebung mittels Hörversuchen entwickelt, die auf Simulation mit Binauralsynthese und raumakustischer Simulation beruhen. Die Ergebnisse können als Richtlinien zur Gestaltung von Wiedergaberäumen für Wellenfeldsynthese dienen

Nanodevices for Microwave and Millimeter Wave Applications

The microwave and millimeter wave frequency range is nowadays widely exploited in a large variety of fields including (wireless) communications, security, radar, spectroscopy, but also astronomy and biomedical, to name a few. This Special Issue focuses on the interaction between the nanoscale dimensions and centimeter to millimeter wavelengths. This interaction has been proven to be efficient for the design and fabrication of devices showing enhanced performance. Novel contributions are welcome in the field of devices based on nanoscaled geometries and materials. Applications cover, but not are limited to, electronics, sensors, signal processing, imaging and metrology, all exploiting nanoscale/nanotechnology at microwave and millimeter waves. Contributions can take the form of short communications, regular or review papers

Computer Generation of Integral Images using Interpolative Shading Techniques

Research to produce artificial 3D images that duplicates the human stereovision has been ongoing for hundreds of years. What has taken millions of years to evolve in humans is proving elusive even for present day technological advancements. The difficulties are compounded when real-time generation is contemplated. The problem is one of depth. When perceiving the world around us it has been shown that the sense of depth is the result of many different factors. These can be described as monocular and binocular. Monocular depth cues include overlapping or occlusion, shading and shadows, texture etc. Another monocular cue is accommodation (and binocular to some extent) where the focal length of the crystalline lens is adjusted to view an image. The important binocular cues are convergence and parallax. Convergence allows the observer to judge distance by the difference in angle between the viewing axes of left and right eyes when both are focussing on a point. Parallax relates to the fact that each eye sees a slightly shifted view of the image. If a system can be produced that requires the observer to use all of these cues, as when viewing the real world, then the transition to and from viewing a 3D display will be seamless. However, for many 3D imaging techniques, which current work is primarily directed towards, this is not the case and raises a serious issue of viewer comfort. Researchers worldwide, in university and industry, are pursuing their approaches in the development of 3D systems, and physiological disturbances that can cause nausea in some observers will not be acceptable. The ideal 3D system would require, as minimum, accurate depth reproduction, multiviewer capability, and all-round seamless viewing. The necessity not to wear stereoscopic or polarising glasses would be ideal and lack of viewer fatigue essential. Finally, for whatever the use of the system, be it CAD, medical, scientific visualisation, remote inspection etc on the one hand, or consumer markets such as 3D video games and 3DTV on the other, the system has to be relatively inexpensive. Integral photography is a ‘real camera’ system that attempts to comply with this ideal; it was invented in 1908 but due to technological reasons was not capable of being a useful autostereoscopic system. However, more recently, along with advances in technology, it is becoming a more attractive proposition for those interested in developing a suitable system for 3DTV. The fast computer generation of integral images is the subject of this thesis; the adjective ‘fast’ being used to distinguish it from the much slower technique of ray tracing integral images. These two techniques are the standard in monoscopic computer graphics whereby ray tracing generates photo-realistic images and the fast forward geometric approach that uses interpolative shading techniques is the method used for real-time generation. Before this present work began it was not known if it was possible to create volumetric integral images using a similar fast approach as that employed by standard computer graphics, but it soon became apparent that it would be successful and hence a valuable contribution in this area. Presented herein is a full description of the development of two derived methods for producing rendered integral image animations using interpolative shading. The main body of the work is the development of code to put these methods into practice along with many observations and discoveries that the author came across during this task.The Defence and Research Agency (DERA), a contract (LAIRD) under the European Link/EPSRC photonics initiative, and DTI/EPSRC sponsorship within the PROMETHEUS project

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium