Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Maier, William B. ; Crooker, Peter P. "December 2009." Description based on title screen as viewed on January 29, 2010. Author(s) subject terms: Railgun, Railgun recoil, Lorentz force, eutectic. Includes bibliographical references (p. 49-51). Also available in print.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on September 16, 2009). Thesis advisor: Dr. Thomas G. Engel. Includes bibliographical references.

The use of electrodynamic tethers for propulsion and power generation is attractive for missions to the outer planets, which are traditionally handicapped by large propellant requirements, large times of flight, and a scarcity of power available. The proposed electrodynamic tether propulsion scheme is shown to be capable at reducing or eliminating these mission constraints. In this work, the orbital dynamics of a spacecraft using electrodynamic tether propulsion during the mission phases of capture, apojove pump-down and perijove pump-up in the Jovian system are investigated. The main result is the mapped design space involving mission duration, tether length and minimum perijove radius. Phase-free flyby sequences and bang-bang control laws are also included, which provide performance upper bounds for a given mission architecture. It is found to be advantageous to utilize in-bound only flybys of the Galilean moons during capture, and few, if any, out-bound only flybys during apojove pump-down. The electrodynamic tether system is also shown to be capable of lowering the spacecraft’s orbit to a Europa-Ganymede Hohmann orbit with a total flight time after entering Jupiter’s sphere of influence of just under two years. The benefits of leveraging solar third body perturbations, ballistic flyby tours, and adding a secondary propulsion system are also considered. / text

Lorentz forces provide a unique method for the control and mixing of gas flows without the physical intrusion of objects into the flow. Lorentz forces arise when an electric current is passed through a volume in the presence of a magnetic field. The interaction between the electric current and the electric and magnetic fields produces a body force which affects the flow. These forces have been investigated experimentally by other researchers and show promise as a way to accelerate combustion in diffusion flames by increasing the mixing rate of fuel and oxidant streams. Theoretical and numerical models were developed to gain insight into this process. Alkali metal seeding raises the electrical conductivity of a flame by two to three orders of magnitude. This has two significant effects: the Lorentz force becomes stronger for the same applied electric current and magnetic field, and the alkali seed concentration becomes a dominant factor in determining electrical conductivity of seeded gases. This makes electrical conductivity much easier to predict, and so the Lorentz body force produced is easier to determine. A theoretical basis for numerical modeling of reactive flows with variable body forces has been developed. Many issues are important in simulating gas flows. Conservation of chemical species must be carefully maintained. Mass transport by gaseous diffusion, which limits combustion rates in a diffusion flame, must be appropriately modeled. Viscous action is also important, since it promotes mixing of the fuel and oxidant streams. Convective, conductive, and diffusive transport of energy must be carefully treated since energy transport directly affects the fluid flow. A numerical model of an incompressible gas flow affected by Lorentz forces was written and tested. Although assumptions made in the model, such as isothermal conditions and uniform density, are not found in diffusion flames, the numerical model predicts velocity vector patterns similar to those observed in actual Lorentz force tests on diffusion flames. A simulation code for compressible, reactive gas flows which include Lorentz forces has also been written. Several parts of the model have been validated, and the approach used appears likely to produce successful simulations. Further validation studies will be required, however, before complete modeling of the diffusion flame can proceed. / Graduation date: 1995

Die vorliegende Arbeit widmet sich der, vorwiegend experimentellen, Untersuchung der Wirkung wandparalleler Lorentzkräfte in Strömungsrichtung auf Grenzschichtprofile und Körperumströmungen. Die Themen - Beeinflussung der Grenzschicht an ebenen Platten mit stationären Lorentzkräften - Kontrolle von Strömungsablösungen an Zylindern und symmetrischen Profilen mit stationären Lorentzkräften - Beeinflussung von Zylindernachläufen und abgelösten Tragflügelumströmungen mit zeitlich periodischen Lorentzkräften werden behandelt.

Die vorliegende Arbeit widmet sich der, vorwiegend experimentellen, Untersuchung der Wirkung wandparalleler Lorentzkräfte in Strömungsrichtung auf Grenzschichtprofile und Körperumströmungen. Die Themen - Beeinflussung der Grenzschicht an ebenen Platten mit stationären Lorentzkräften - Kontrolle von Strömungsablösungen an Zylindern und symmetrischen Profilen mit stationären Lorentzkräften - Beeinflussung von Zylindernachläufen und abgelösten Tragflügelumströmungen mit zeitlich periodischen Lorentzkräften werden behandelt.

The use of high-powered electrical energy systems requires an efficient and capable means to move electrical energy from one location to another while reducing energy losses. This paper describes the design and construction process of a high-powered busbar system that is to be implemented in pulsed-power applications. In order to obtain a robust system capable of handling in excess of 25kJ, both mechanical and electrical analyses were performed to verify a capable design. The following methodology describes how the Lorentz force was balanced with mechanical forces during the design process and then validated after construction was completed using the fundamental Maxwell equations and computer simulations. Main focuses include handling of EMF, high current density concentrations, and overall mechanical stability of the system and how these effects determine the physical design and implementation. In the end, a repeatable methodology is presented in the form of a design process that can be implemented in any system given the design criteria. / Master of Science

We present a novel two-dimensional (2D) MAET scanner, with a rotating object of interest and two fixed pairs of electrodes. Such an acquisition scheme, with our novel reconstruction techniques, recovers the boundaries of the regions of constant conductivity uniformly well, regardless of their orientation. We also present a general image reconstruction algorithm for the 2D MAET in a circular chamber with point-like electrodes immersed into the saline surrounding the object. An alternative linearized reconstruction procedure is developed, suitable for recovering the material interfaces (boundaries) when a non-ideal piezoelectric transducer is used for acoustic excitation. The work of the scanner and the linearized reconstruction algorithm is demonstrated using several phantoms made of high-contrast materials and a biological sample.

Micromirrors and diffraction gratings were developed for spectroscopy and magnetic field sensor in this thesis. MEMS blazed gratings were successfully fabricated in different grating periodicities to cover a wide infrared wavelength range. Lorentz force actuated micromirrors were investigated, and two types of mirrors were fabricated: rotating and pop-up micromirrors. The deflection angle of the mirrors was controllable by altering the driving current on the mirror. Deflection angle vs. driving current was studied for different mirror types and different spring dimensions. A Lorentz force based magnetic field sensor is also demonstrated. The sensor employs the rotating micromirror as a resonator. With an AC current flowing around the micromirror, a periodic Lorentz force is generated which drives the resonator. The rotational amplitude of the micromirror is measured with an optical positioning system and external circuits. The highest resolution of the magnetic field sensor is 0.4 nT at 50 mArms, and 53 mHz filter bandwidth. With appropriate current level, this sensor can measure a wide range of magnetic field, from nT to T. / October 2016

The use of electrostatic transduction has enabled high-Q miniaturized mechanical resonators made of non-piezoelectric material that vibrate at high and ultra high frequencies. However, this transduction technique suffers from large values of motional resistance associated with the technique, limiting its use for interfacing to standard 50 RF circuits. Piezoelectric transduction has advantages over the electrostatic method because of its comparable to 50 motional resistance. However, the technique requires use of thin film piezoelectric materials with the demonstrated Qs that are much lower than their corresponding non-piezoelectric resonators. This research proposes use of electrodynamic transduction, reports analytic and experimental studies on electrodynamic transduction for RF application, highlights the method’s advantages, and lists the contributions. The use of Lorentz-force transduction for RF micromechanical filters proposed in this work is pursued by experimentally evaluating the transduction technique implemented for microfabricated designs. By fabricating single and coupled microresonators in a few different fabrication technologies, including CMOS35, the performance of the Lorentz-force driven microresonators is studied. Using a laser vibrometer, the actual performance, including the displacement and velocity of the moving points of the microstructures’ surfaces, are measured. The mode shapes and resonance specifications of the microstructures in air and vacuum derived by laser vibrometer provide data for characterizing the employed Lorentz-force transduction technique. Furthermore, the results from the electrical measurements are compared to the micromechanical resonators’ frequency response obtained from the mechanical measurements by laser vibrometer. The significantly low values of motional resistance computed for the differently fabricated designs demonstrate the advantage of Lorentz-force transduction for RF filter applications. Should a device similar in size be driven electrostatically, the motional resistance would be multiple orders of magnitude higher. This research reports the experimental results obtained by examining a Lorentz- force transduction application for developing RF micromechanical filters. The results demonstrate the Lorentz-force transduction’s advantages over other transduction methods used for RF μ-mechanical filters. Compared to electrostatic transduction, the Lorentz-force method provides greater electromechanical coupling, multiple orders of magnitude lower motional resistance, the independence of the filter center frequency from the bias voltage, higher power handling, and no requirement for bias lines, which decreases the work in microfabrication. Unlike piezoelectric transduction, the electrodynamic technique requires no piezoelectric material. Use of non-piezoelectric materials provides more flexibility for resonator material in the IC-compatible fabrications. Power handling in electrodynamic transduction has fewer limitations than other transduction techniques because the higher power needed in electrostatic or piezoelectric methods requires a higher voltage, which is limited by the breakdown voltage. The higher power in Lorentz-force-based transduction demands a larger current. The larger current produces heat that is removable by applying an appropriate cooling technique.