Larry Epp

Bio: Larry Epp is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Carbon nanotube & Resonator. The author has an hindex of 14, co-authored 36 publications receiving 1002 citations. Previous affiliations of Larry Epp include Jet Propulsion Laboratory.

A TE/TM modal solution for rectangular hard waveguides

Abstract: A TE/TM modal solution for a longitudinally corrugated rectangular waveguide is developed. These longitudinal corrugations can be used to excite a quasi-TEM wave and form a hard waveguide by correctly choosing the impedance at the guide wall. The correctly chosen impedance is referred to as the hard boundary condition. The modal solution developed here solves the problem of longitudinal corrugations filled with a dielectric material by first finding and solving the characteristic equation for a complete TE/TM modal set. It is shown that this TE/TM mode solution can be used to achieve the hard boundary condition resulting in the quasi-TEM wave in a hard waveguide for discrete values of corrugation depth. Beyond each of these depths, a mode becomes a surface wave. The theoretical mode set is amenable to the solution of problems using the mode-matching method. A combination of the mode-matching method and the TE/TM modal solution will allow the solution of larger problems.

Scattering from ferrite bodies of revolution using a hybrid approach

Abstract: The scattered fields from axisymmetric problems containing anisotropic media are found by a hybrid finite element method. In particular a symmetric formulation for bodies of revolution that incorporates a finite element formulation for axially magnetized ferrite materials is presented. The method is applied to a ferrite cylinder with quartz matching layers. A Gaussian beam input is used to predict the Faraday rotation through the ferrite cylinder and display it visually. >

Interrogating vertically oriented carbon nanofibers with nanomanipulation for nanoelectromechanical switching applications

Abstract: We have demonstrated electrostatic switching in vertically oriented carbon nanofibers synthesized on refractory metallic nitride substrates, where pull-in voltages Vpi ranged from 10 to 40 V. A nanoprobe was used as the actuating electrode inside a scanning-electron microscope and van der Waals interactions at these length scales appeared significant, suggesting such structures are promising for nonvolatile memory applications. A finite element model was also developed to determine a theoretical Vpi and results were compared to experiment. Nanomanipulation tests also revealed tubes synthesized directly on Si by dc plasma-enhanced chemical-vapor deposition with ammonia and acetylene were electrically unsuitable for dc nanoelectromechanical switching applications.

MAVEN relay operations

Abstract: The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission launched in late 2013 and began commissioning operations in September 2014 following a 10 month cruise to Mars. The Mission will study the upper atmosphere of the planet. In addition to the science instruments, the MAVEN spacecraft is equipped with an Electra UHF transceiver to support relay communication with landed assets. This paper describes how the UHF relay service was developed and validated through assembly test and launch operations (ATLO) as well as during cruise to, and transition into, Mars orbit. The discussion includes a description of the various functional and thread tests conducted during ATLO, a description of checkout activities during Cruise, a ground-based operational readiness test to simulate a future contact with the Mars Science Laboratory (MSL) rover, and a description of an actual overflight with MSL during the Transition phase.

Applications and methods of operating a three-dimensional nano-electro-mechanical resonator and related devices

Abstract: Carbon nanofiber resonator devices, methods for use, and applications of said devices are disclosed. Carbon nanofiber resonator devices can be utilized in or as high Q resonators. Resonant frequency of these devices is a function of configuration of various conducting components within these devices. Such devices can find use, for example, in filtering and chemical detection.

Intrinsic Piezoelectricity in Two-Dimensional Materials

Abstract: We discovered that many of the commonly studied two-dimensional monolayer transition metal dichalcogenide (TMDC) nanoscale materials are piezoelectric, unlike their bulk parent crystals. On the macroscopic scale, piezoelectricity is widely used to achieve robust electromechanical coupling in a rich variety of sensors and actuators. Remarkably, our density-functional theory calculations of the piezoelectric coefficients of monolayer BN, MoS2, MoSe2, MoTe2, WS2, WSe2, and WTe2 reveal that some of these materials exhibit stronger piezoelectric coupling than traditionally employed bulk wurtzite structures. We find that the piezoelectric coefficients span more than 1 order of magnitude, and exhibit monotonic periodic trends. The discovery of this property in many two-dimensional materials enables active sensing, actuating, and new electronic components for nanoscale devices based on the familiar piezoelectric effect.

Harvesting Wireless Power: Survey of Energy-Harvester Conversion Efficiency in Far-Field, Wireless Power Transfer Systems

Abstract: The idea of wireless power transfer (WPT) has been around since the inception of electricity. In the late 19th century, Nikola Tesla described the freedom to transfer energy between two points without the need for a physical connection to a power source as an ?all-surpassing importance to man? [1]. A truly wireless device, capable of being remotely powered, not only allows the obvious freedom of movement but also enables devices to be more compact by removing the necessity of a large battery. Applications could leverage this reduction in size and weight to increase the feasibility of concepts such as paper-thin, flexible displays [2], contact-lens-based augmented reality [3], and smart dust [4], among traditional point-to-point power transfer applications. While several methods of wireless power have been introduced since Tesla?s work, including near-field magnetic resonance and inductive coupling, laser-based optical power transmission, and far-field RF/microwave energy transmission, only RF/microwave and laser-based systems are truly long-range methods. While optical power transmission certainly has merit, its mechanisms are outside of the scope of this article and will not be discussed.

Recycling ambient microwave energy with broad-band rectenna arrays

Abstract: This paper presents a study of reception and rectification of broad-band statistically time-varying low-power-density microwave radiation. The applications are in wireless powering of industrial sensors and recycling of ambient RF energy. A 64-element dual-circularly-polarized spiral rectenna array is designed and characterized over a frequency range of 2-18 GHz with single-tone and multitone incident waves. The integrated design of the antenna and rectifier, using a combination of full-wave electromagnetic field analysis and harmonic balance nonlinear circuit analysis, eliminates matching and filtering circuits, allowing for a compact element design. The rectified dc power and efficiency is characterized as a function of dc load and dc circuit topology, RF frequency, polarization, and incidence angle for power densities between 10/sup -5/-10/sup -1/ mW/cm/sup 2/. In addition, the increase in rectenna efficiency for multitone input waves is presented.

Nanoscale wires and related devices

Abstract: The present invention relates generally to sub-microelectronic circuitry, and more particularly to nanometer-scale articles, including nanoscale wires which can be selectively doped at various locations and at various levels. In some cases, the articles may be single crystals. The nanoscale wires can be doped, for example, differentially along their length, or radially, and either in terms of identity of dopant, concentration of dopant, or both. This may be used to provide both n-type and p-type conductivity in a single item, or in different items in close proximity to each other, such as in a crossbar array. The fabrication and growth of such articles is described, and the arrangement of such articles to fabricate electronic, optoelectronic, or spintronic devices and components. For example, semiconductor materials can be doped to form n-type and p-type semiconductor regions for making a variety of devices such as field effect transistors, bipolar transistors, complementary inverters, tunnel diodes, light emitting diodes, sensors, and the like.