Estimating motion, size and material properties of moving non-line-of-sight objects in cluttered environments

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 111-117).The thesis presents a framework for Non-Line-of-Sight Computer Vision techniques using wave fronts. Using short-pulse illumination and a high speed time-of-flight camera, we propose algorithms that use multi path light transport analysis to explore the environments beyond line of sight. What is moving around the corner interests everyone including a driver taking a turn, a surgeon performing laparoscopy and a soldier entering enemy base. State of the art techniques that do range imaging are limited by (i) inability to handle multiple diffused bounces [LIDAR] (ii) Wavelength dependent resolution limits [RADAR] and (iii) inability to map real life objects [Diffused Optical Tomography]. This work presents a framework for (a) Imaging the changing Space-time-impulse-responses of moving objects to pulsed illumination (b) Tracking motion along with absolute positions of these hidden objects and (c) recognizing their default properties like material and size and reflectance. We capture gated space-time impulse responses of the scene and their time differentials allow us to gauge absolute positions of moving objects with knowledge of only relative times of arrival (as absolute times are hard to synchronize at femto second intervals). Since we record responses at very short time intervals we collect multiple readings from different points of illumination and thus capturing multi-perspective responses allowing us to estimate reflectance properties. Using this, we categorize and give parametric models of the materials around corner. We hope this work inspires further exploration of NLOS computer vision techniques.by Rohit Pandharkar.S.M

ULTRAFAST OPTICAL RESPONSE AND TRANSPORT PROPERTIES OF STRONTIUM TITANATE-BASED COMPLEX OXIDE NANOSTRUCTURES

As the silicon-based semiconductor integrated circuits led by Moore's Law approaching their physical limits, the search for a new generation of nanoelectronic and nanophotonic devices is becoming a hot topic in this post-Moore era. The strontium titanate-based complex oxide heterostructure appears to be a promising alternative due to its diverse emergent properties. Being able to control the metal-insulator transition at the polar/nonpolar LaAlO3/SrTiO3 interface using conductive atomic force microscopy (c-AFM) lithography has made LaAlO3/SrTiO3, in particular, an attractive platform. Expanding the class of heterostructures which can be controlled at nanoscale dimensions is important for alternative oxide-based nanodevices. In this dissertation, the writing and erasing of nanostructures at the nonpolar/nonpolar oxide interface of CaZrO3/SrTiO3 using c-AFM lithography is investigated. Conducting nanostructures as narrow as 1.2 nm at room temperature is achieved. Low-temperature transport measurements based on these nanostructures provide insight into the electronic structure of the CaZrO3/SrTiO3 interface. Such extreme nanoscale control, with dimensions comparable to most single-walled carbon nanotubes, holds great promise for oxide-based nanoelectronic devices. Nanophotonic devices operating at terahertz frequencies, on the other hand, offer unique information for many applications. In this dissertation, broadband nanoscale terahertz generators based on c-AFM lithography defined LaAlO3/SrTiO3 nanojunctions are proved to be able to detect the plasmonic response of a single gold nanorod. By femtosecond pulse shaping using a home-built pulse shaper, over 100 THz bandwidth selective difference frequency generation at LaAlO3/SrTiO3 nanojunctions is also demonstrated, which has great potential in both studying fundamental light-matter interaction and realizing selective control of rotational or vibrational resonances in nanoparticles. With this unprecedented control of THz field, the two-dimensional (2D) material graphene and its coupling with the quasi-2D LaAlO3/SrTiO3 interface are also under investigation. The preliminary data shows evidence for graphene response up to 60 THz. These results help to fill the terahertz gap as well as offer new opportunities for oxide-based nanophotonic devices or even hybrid optoelectronic integrated circuits

Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays

Massive MIMO (multiple-input multiple-output) is no longer a "wild" or "promising" concept for future cellular networks - in 2018 it became a reality. Base stations (BSs) with 64 fully digital transceiver chains were commercially deployed in several countries, the key ingredients of Massive MIMO have made it into the 5G standard, the signal processing methods required to achieve unprecedented spectral efficiency have been developed, and the limitation due to pilot contamination has been resolved. Even the development of fully digital Massive MIMO arrays for mmWave frequencies - once viewed prohibitively complicated and costly - is well underway. In a few years, Massive MIMO with fully digital transceivers will be a mainstream feature at both sub-6 GHz and mmWave frequencies. In this paper, we explain how the first chapter of the Massive MIMO research saga has come to an end, while the story has just begun. The coming wide-scale deployment of BSs with massive antenna arrays opens the door to a brand new world where spatial processing capabilities are omnipresent. In addition to mobile broadband services, the antennas can be used for other communication applications, such as low-power machine-type or ultra-reliable communications, as well as non-communication applications such as radar, sensing and positioning. We outline five new Massive MIMO related research directions: Extremely large aperture arrays, Holographic Massive MIMO, Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin

Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications

Orbital angular momentum (OAM) has aroused a widespread interest in many fields, especially in telecommunications due to its potential for unleashing new capacity in the severely congested spectrum of commercial communication systems. Beams carrying OAM have a helical phase front and a field strength with a singularity along the axial center, which can be used for information transmission, imaging and particle manipulation. The number of orthogonal OAM modes in a single beam is theoretically infinite and each mode is an element of a complete orthogonal basis that can be employed for multiplexing different signals, thus greatly improving the spectrum efficiency. In this paper, we comprehensively summarize and compare the methods for generation and detection of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications and technical challenges of OAM in communications, including free-space optical communications, optical fiber communications, radio communications and acoustic communications. To complete our survey, we also discuss the state of art of particle manipulation and target imaging with OAM beams

Small business innovation research. Abstracts of completed 1987 phase 1 projects

Non-proprietary summaries of Phase 1 Small Business Innovation Research (SBIR) projects supported by NASA in the 1987 program year are given. Work in the areas of aeronautical propulsion, aerodynamics, acoustics, aircraft systems, materials and structures, teleoperators and robotics, computer sciences, information systems, spacecraft systems, spacecraft power supplies, spacecraft propulsion, bioastronautics, satellite communication, and space processing are covered