Showing papers by "David Schurig published in 2016"

Compact Low-Frequency Metamaterial Design for Wireless Power Transfer Efficiency Enhancement

Abstract: An extremely compact and low-frequency metamaterial design is presented in the following work. A ferrite loaded solenoid with a size on the order of 1/10000 of the wavelength of operation is used as the unit cell of the proposed metamaterial. This unit cell allows for the construction of a 77 unit-cell sample with dimensions of ${\text {6 cm}}\times {\text {6 cm}}\times {\text {2 cm}}$ and operating at a working frequency of 5.57 MHz. Measurements show that using this metamaterial sample in a wireless power transfer (WPT) system results in an efficiency enhancement of 10% at a working distance of 4.5 cm, which is twice the efficiency of the original system at the same distance. Alternatively, for a target efficiency of 10%, the range of the system can be extended from 4.5 to 8.8 cm by using the proposed metamaterial, a 4.3-cm, or 95%, extension over the original system range. The proposed metamaterial design, characterized by compactness, low frequency of operation, and large efficiency enhancement, is useful in a number of applications, such as biomedical telemetry systems and wireless charging.

Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

Abstract: Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators, we cover almost five octaves in resonance frequency within a single setup. The measurements with a common π-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.

Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

Abstract: Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common pi-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.

W-band sparse synthetic aperture for computational imaging.

Abstract: We present a sparse synthetic-aperture, active imaging system at W-band (75 - 110 GHz), which uses sub-harmonic mixer modules. The system employs mechanical scanning of the receiver module position, and a fixed transmitter module. A vector network analyzer provides the back end detection. A full-wave forward model allows accurate construction of the image transfer matrix. We solve the inverse problem to reconstruct scenes using the least squares technique. We demonstrate far-field, diffraction limited imaging of 2D and 3D objects and achieve a cross-range resolution of 3 mm and a depth-range resolution of 4 mm, respectively. Furthermore, we develop an information-based metric to evaluate the performance of a given image transfer matrix for noise-limited, computational imaging systems. We use this metric to find the optimal gain of the radiating element for a given range, both theoretically and experimentally in our system.

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.

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.

Terahertz waveguide with a negative effective index of refraction measured using time domain techniques

Abstract: We present the first experimental realization of a terahertz (THz) waveguide that exhibits a negative effective index of refraction. To demonstrate this, we designed fabricated and characterized a linear array of three-dimensional structures that consist of split ring resonators and posts. THz radiation is launched and guided in the form of surface plasmon polaritons (SPPs) along the 3D metallic structures. Using THz time-domain spectroscopy, we measure the temporal evolution of the propagating THz SPP, which yields the evidence of a negative refractive index.

Systems and methods of sensing and/or heating using nanostructures

Abstract: Various methods for sensing and/or heating that utilize nanostructures or carbon structures, such as nanotubes, nanotube meshes, or graphene sheets, are disclosed. In some methods, at least a pair of contacts are electrically coupled with a given nanostructure or carbon structure to sense a change or to pass a current for heating.