David Schurig

Bio: David Schurig is an academic researcher from University of Utah. The author has contributed to research in topics: Metamaterial & Lens (optics). The author has an hindex of 33, co-authored 107 publications receiving 22899 citations. Previous affiliations of David Schurig include Duke University & University of California, San Diego.

Spatial imaging using a communication system's channel state information

Abstract: We investigate the use of a communication system's channel state information (CSI) for spatial imaging. The CSI provides the the magnitude and phase of the link between pairs of (transmit and receive) antennas in sub-bands operating in the overall system bandwidth. Since these links are sensitive to the system's electromagnetic environment, information regarding physical objects in that environment are, to some extent, encoded in the CSI. In particular, the time history of objects (such as people) in the environment is partly encoded in the time history of the CSI. Combined with suitable prior information, useful facts regarding the dynamics of moving objects may be extracted using the methods of computational sparse imaging. Prior information can include a detailed characterization of the static electromagnetic environment (or boundary conditions) and the electromagnetic signature of the objects that are to be tracked. Specifically, we perform experiments using an 802.11n Wifi system operating at 2.4GHz, and which has been modified to allow acquisition of the CSI. Experimental results are compared with computational results (using CST Microwave Studio) for comparable electromagnetic environments. Image reconstructions are attempted, both experimentally and computational, to correctly locate a human sized reflective object.

Performance Analysis of a Helmet-Based Radar System for Impact Prediction

Abstract: We analyze the performance of a helmet-based frequency modulated continuous wave (FMCW) radar system for use in impact prediction in contact sports, or other risky environments. It has been shown that the head trauma and concussions can have significant detrimental effects on the health and quality life of contact sport athletes, from the high school to professional level. Impact prediction capability could be an important part of a comprehensive, helmet-based system for mitigating the neurological damage caused by impacts. Mitigation strategies include using imminent impact information in an audible warning system, or dynamic preloading and control of an active helmet suspension. Our analysis centers on the prediction of an impact offset parameter (and its uncertainty) in a representative player interaction scenario. We consider realistic radar measurement specifications consistent with our player interaction scenario, and COTS radar hardware, including oscillator phase noise, operation frequency, sweep frequency, bandwidth, range, target scattering cross-section, and antenna gain.

Optical device with interchangeable corrective elements

Abstract: Exemplary embodiments enable an enhanced direct-viewing optical device to include customized adjustments that accommodate various optical aberrations of a current user. Customized optical elements associated with an authorized current user are incorporated with the direct-viewing optical device to produce a specified change in optical wavefront at an exit pupil. Possible replacement optical elements may have refractive and/or reflective and/or diffractive and/or transmissive characteristics based on current performance viewing factors for a given field of view of the direct-viewing optical device. Some embodiments enable dynamic repositioning and/or transformation of replaceable corrective optical elements responsive to a detected shift of a tracked gaze direction of a current user. Replaceable interchangeable corrective optical elements may be fabricated for current usage or retained in inventory for possible future usage in designated direct-viewing optical devices.

Customized user options for optical device

Abstract: Exemplary methods, systems and components enable an enhanced direct-viewing optical device to include customized adjustments that accommodate various optical aberrations of a current user. A real-time adjustment of transformable optical elements is sometimes based on predetermined corrective optical parameters associated with a current user. Customized optical elements are incorporated with the direct-viewing optical device to produce a specified change in optical wavefront at an exit pupil. Possible transformable or replacement optical elements may have refractive and/or reflective and/or diffractive and/or transmissive characteristics that are selected based on current performance viewing factors for a given field of view of the direct-viewing device. Some embodiments enable dynamic repositioning and/or transformation of corrective optical elements responsive to a detected shift of a tracked gaze direction of a current user. Replacement corrective optical elements may be fabricated for current usage or retained in inventory for possible future usage in the direct-viewing device.

Computationally fast EM field propagation through axi-symmetric media using cylindrical harmonic decomposition

Abstract: We describe and provide a systematic procedure for computationally fast propagation of arbitrary vector electromagnetic (EM) fields through an axially symmetric medium. A cylindrical harmonic field propagator is chosen for this purpose and in most cases, this is the best and the obvious choice. Firstly, we describe the cylindrical harmonic decomposition technique in terms of both scalar and vector basis for a given input excitation field. Then we formulate a generalized discrete Fourier-Hankel transform to achieve efficient vector basis decomposition. We allow a slower, pre-computation step, that finds a representation of the axi-symmetric medium as a transfer matrix in a discrete, cylindrical-harmonic basis. We find this matrix from a series of axi-symmetric (2D) finite element simulations (also known as the 2.5D technique). This transfer matrix approach significantly reduces the computational load when the transverse size or range exceeds about 30 wavelengths. This matrix is independent of the input excitation field for a given space-bandwidth product and hence makes it reusable for different excitation fields. We numerically validate the above approaches for different axi-symmetric EM scattering media which include a hemispherical gradient-index Maxwell’s fish-eye lens, a transformation optics designed spherical invisibility cloak, a thin aspheric lens, and a cylindrical perfect lens.

Controlling Electromagnetic Fields

Abstract: Using the freedom of design that metamaterials provide, we show how electromagnetic fields can be redirected at will and propose a design strategy. The conserved fields-electric displacement field D, magnetic induction field B, and Poynting vector B-are all displaced in a consistent manner. A simple illustration is given of the cloaking of a proscribed volume of space to exclude completely all electromagnetic fields. Our work has relevance to exotic lens design and to the cloaking of objects from electromagnetic fields.

Metamaterial Electromagnetic Cloak at Microwave Frequencies

Abstract: A recently published theory has suggested that a cloak of invisibility is in principle possible, at least over a narrow frequency band. We describe here the first practical realization of such a cloak; in our demonstration, a copper cylinder was "hidden" inside a cloak constructed according to the previous theoretical prescription. The cloak was constructed with the use of artificially structured metamaterials, designed for operation over a band of microwave frequencies. The cloak decreased scattering from the hidden object while at the same time reducing its shadow, so that the cloak and object combined began to resemble empty space.

Light Propagation with Phase Discontinuities: Generalized Laws of Reflection and Refraction

Abstract: Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

Perfect metamaterial absorber.

Abstract: We present the design for an absorbing metamaterial (MM) with near unity absorbance A(omega). Our structure consists of two MM resonators that couple separately to electric and magnetic fields so as to absorb all incident radiation within a single unit cell layer. We fabricate, characterize, and analyze a MM absorber with a slightly lower predicted A(omega) of 96%. Unlike conventional absorbers, our MM consists solely of metallic elements. The substrate can therefore be optimized for other parameters of interest. We experimentally demonstrate a peak A(omega) greater than 88% at 11.5 GHz.

Flat Optics With Designer Metasurfaces

Abstract: Metamaterials are artificially fabricated materials that allow for the control of light and acoustic waves in a manner that is not possible in nature. This Review covers the recent developments in the study of so-called metasurfaces, which offer the possibility of controlling light with ultrathin, planar optical components. Conventional optical components such as lenses, waveplates and holograms rely on light propagation over distances much larger than the wavelength to shape wavefronts. In this way substantial changes of the amplitude, phase or polarization of light waves are gradually accumulated along the optical path. This Review focuses on recent developments on flat, ultrathin optical components dubbed 'metasurfaces' that produce abrupt changes over the scale of the free-space wavelength in the phase, amplitude and/or polarization of a light beam. Metasurfaces are generally created by assembling arrays of miniature, anisotropic light scatterers (that is, resonators such as optical antennas). The spacing between antennas and their dimensions are much smaller than the wavelength. As a result the metasurfaces, on account of Huygens principle, are able to mould optical wavefronts into arbitrary shapes with subwavelength resolution by introducing spatial variations in the optical response of the light scatterers. Such gradient metasurfaces go beyond the well-established technology of frequency selective surfaces made of periodic structures and are extending to new spectral regions the functionalities of conventional microwave and millimetre-wave transmit-arrays and reflect-arrays. Metasurfaces can also be created by using ultrathin films of materials with large optical losses. By using the controllable abrupt phase shifts associated with reflection or transmission of light waves at the interface between lossy materials, such metasurfaces operate like optically thin cavities that strongly modify the light spectrum. Technology opportunities in various spectral regions and their potential advantages in replacing existing optical components are discussed.