The complex permittivity and impedance of undoped and unpoled single crystal strontium barium niobate (SBN) were measured with a computer interfaced impedance analyzer over a frequency range from 100 millihertz to 10 kilohertz using small AC signals with millivolt amplitudes. The thin (%7e2 mm) planar crystal sample was placed between the plates of a modified parallel plate capacitor and illuminated on the side with linearly polarized argon-ion laser light operating at select wavelengths in the blue-green with photon energies that are slightly below the bandgap energy of SBN. Impedance spectra were obtained in the dark between room temperature and 70°C and compared with impedance spectra obtained with laser illumination and no heating except that produced by absorption of the laser light. Dark measurements at all temperatures are consistent with studies in the literature that suggest electron hopping as the predominant charge transfer mechanism. Illumination markedly changed the conductivity of the crystal and the charge transfer mechanism by elevating significant numbers of charge carriers into the conduction band. This was found to be independent of the polarization of the light and slightly dependent on its wavelength over our wavelength range of 458 nm to 515 nm. The dielectric constant of the crystal under illumination changed less than twenty percent and is probably due to the slight heating of the crystal induced by the laser.
Associate Professor Steven R. Montgomery
Assistant Professor Charles A. Edmondson
The Navy, in an effort to reduce costs and operate within the budgetary constraints of the near future, is planning to reduce the manning on combat ships. To accomplish this without reducing the readiness or capability of these ships, the remaining personnel must work more efficiently. To support this required increase in efficiency, several wireless technologies are being considered, including wireless LANs and a wireless sensor system augmented by a computer-controlled log keeping system.
The internal volume of a combat ship is a generally un-studied wireless environment. While a preliminary study demonstrated that radio energy can be radiated and received from compartment to compartment (room to room) within a ship, a detailed analysis of this environment has not been done.
In this project, data was collected aboard decommissioned and active ships to characterize the wireless channel on combat ships and to attempt to determine the effect of bulkheads (walls) and hatches (doors) in the information path. Both narrowband and ultra-wideband techniques were used to demonstrate and measure transmissions through the shipboard environment. Each bulkhead attenuated the test signal roughly 20dB.
Computer modeling of the bulkhead supported the hypothesis that the radio energy is propagating through the non-conductive structures within the bulkhead – hatch seals, for example – rather than through the steel.
Professor Antal A. Sarkady
CDR Thaddeus B. Welch, III, USN
Electrical Engineering Department
High strength aluminum alloys are used in a variety of different applications due to their favorable properties. These properties include a high strength to weight ratio, ease of formability, and relatively low density. The 7075 aluminum alloy, when used in aerospace applications, is typically aged to the T6, or the peak aged temper. The problem with the alloy in this temper is that it exhibits a poor resistance to stress corrosion cracking (SCC). The susceptibility of this temper to SCC is alleviated through the use of the T73 temper, or overaged temper. The T73 temper exhibits significantly better SCC resistance, but at a 10-15% strength loss compared to the T6 temper.
In 1974, Cina and Ranish patented a new heat treatment known as retrogression and reaging (RRA). RRA consists of a two-step heat treatment applied to a material already in the T6 condition. Experimental test results indicate that RRA eliminates the traditional trade-off between T6 strength and T73 SCC corrosion resistance. However, one of the problems with the RRA heat treatment is that the process is limited to thin sheets of material.
The objective of this research was to investigate variations of the RRA heat treatment process that would be more applicable for industrial use, compare properties of the different heat treatments, and investigate the kinetics of the RRA treatment in high-strength aluminum alloys. An overview of the experimental procedure is as follows. Retrogression and reaging treatments were carried out on aluminum alloy 7075 T6 samples. Following these heat treatments, the aluminum 7075 was available for testing in the T6, T73, and various RRA tempers. The testing included fatigue, hardness, tensile, and conductivity measurements. Double-cantilever beam tests and alternate immersion tests were performed in order to investigate the corrosion properties of the material.
Associate Professor Angela L. Moran
Assistant Professor Michelle G. Koul
Mechanical Engineering Department
An understanding of the formation of larger molecules in the outer solar system, by radiation induced processing of more primitive constituents, has implications relating to the evolution of the solar system. Organic residues formed by cosmic ray irradiation on cosmic ices may also have some exobiological significance, directly relating to the process from which life began on Earth. Since Pluto is one of the most primitive and well-preserved bodies in the solar system, its surface chemistry is of particular relevance. This project was an attempt to correlate recent astronomical data with a radiation model for compound formation.
Spectroscopic observations of Pluto suggest the presence of ethane, presumably caused by cosmic ray irradiation of methane trapped in solid nitrogen at the surface. This project used near-infrared (NIR) spectroscopy to examine this process in laboratory analogs. Samples of nitrogen doped to appropriate low concentrations with methane and/or carbon monoxide were deposited at 50 K or below, and the resulting films irradiated with varied doses of 1 MeV protons. The formation of ethane, and other products, was observed at radiation dosages consistent with levels experienced at the planet’s surface. However, neither the intensity nor bandwidths of the spectroscopic signals compared very well with the NIR telescope data. These facts lend some support to a model suggesting two different terrains on the planet, one with low methane concentration, and another with much higher levels. Irradiation of the latter might account for ethane signals observable from earth. The laboratory irradiation experiments also resulted in the formation of a residue, stable at high temperatures, consistent with models of organic polymer formation on icy bodies in the outer solar system. Some attempts at determining the composition of the residue were also performed.
Professor Robert F. Ferrante
A capillary pumped loop (CPL) is an advanced, passive heat transfer device that transports energy through the latent heat of vaporization of a working fluid. Energy applied to the evaporator vaporizes the working fluid, which is transported to a condenser region where energy is removed to a heat sink. Capillary forces return the condensed working fluid to the evaporator. The evaporator is the heat acquisition unit and provides the capillary force necessary to drive the system. Much literature exists on the theory and operation of a cylindrical evaporator for a CPL system but little is known about flat plate evaporators. This project focused on the design, fabrication, and evaluation of a flat plate CPL evaporator.
A flat plate evaporator is particularly attractive for thermophotovoltaic (TPV) energy conversion or any system requiring a uniform, low temperature (140° F) heat sink. The geometry of a flat plate evaporator allows for higher heat fluxes and more uniform surface temperatures than cylindrical evaporators can provide.
A computer-based model of the CPL provided a design tool for maximizing system operation. Particular attention was paid to fluid flow through the system and temperature gradients in the evaporator. A flat plate evaporator was designed, fabricated, and tested in a CPL that utilized a conventional shipboard (shell and tube) condenser. These tests evaluated the performance of the CPL in a shipboard setting. Strip heaters attached to the evaporator surface simulated the heat flux generated by an infrared heat source and a temperature regulated water bath provided the condensing fluid that simulated a seawater heat sink. Tests demonstrated the performance of the flat plate evaporator under transient condenser temperatures and power loads. A computer-based data acquisition system monitored system parameters and provided precise data. Results indicated a proof of theory and areas for future development.
Associate Professor Mark J. Harper
Associate Professor Martin R. Cerza
Mechanical Engineering Department
A simple, accurate, and autonomous method of finding a position on the surface of Mars currently does not exist. The same method of celestial navigation used on the Earth will work equally well on Mars. The goal of this project was to develop a celestial navigation process that will fix a position on Mars with better than 100 meter accuracy. This process required knowing the position of the stars and planets referenced to the martian surface with one arcsecond accuracy. This information was contained in an ephemeris known as the Arenautical Almanac (from Ares, the god of War). The Naval Observatory Vector Astrometry Subroutines (NOVAS) formed the basis of the code used to generate the almanac. Planetary position data came from the JPL DE405 planetary ephemeris. The accuracy of the almanac was determined using the physical ephemerides of Mars contained in the Astronomical Almanac. A preliminary design of a celestial navigation system able to fix a position on the martian surface was developed, and recommendations how to integrate celestial navigation into NASA’s current Mars exploration program were also considered as part of this project. This project proved to be more than just an interesting study; it is a useful and much-needed tool that will help open a new world to human exploration on the surface of Mars.
Visiting Professor Richard P. Fahey
Aerospace Engineering Department
The non-destructive characterization of materials is of great interest to not only the Navy, but also to engineering and medical organizations throughout society. For the Navy and other such organizations with an abundance of mechanical equipment, non-destructive testing (NDT) can mean a large savings in maintenance costs. For the medical community, NDT has the potential to provide a means by which diseased tissue can be detected and analyzed.
While ultrasonic NDT has been implemented with varying success to characterize materials, current methods fail when applied to materials with complex microstructures. This is due to the inherent inhomogeneity of the material involved, and due to the fact that almost all ultrasonic NDT methods rely on the propagation of a coherent ultrasonic signal. What is needed to successfully employ ultrasonics in materials with complex microstructures is a system model that takes multiple scattering into account. A multiple scattering model for ultrasonics termed the ultrasonic radiative transfer equation (URTE) was recently developed.
This research project extended the application of remote sensing techniques to the characterization of multiple scattering materials. More specifically, an inverse ultrasonic radiative transfer technique was developed. In its most general form the URTE is a vector valued integro-differential equation describing the propagation of multiply scattered wave energy in a randomly disordered medium supporting several wave types. Ultimately, parameters of the URTE were inversely determined to gain insight into the microstructure of the material. The test materials were ultrasonic phantoms generated at the U.S. Naval Academy. The URTE parameters of these phantoms were determined theoretically. Subsequently, these were compared with the URTE parameters determined experimentally and they were then used to assess the effectiveness of the inverse ultrasonic radiative transfer technique.
Assistant Professor John A. Burkhardt
Mechanical Engineering Department
For the new millennium, the U.S. Navy has made a fundamental commitment to considerable crew size reductions. Automated systems can help support this commitment by significantly improving the efficiency and effectiveness of a ship and its sailors. This automation must be continuously available and dependable under all conditions, especially during battle damage. To continue to work during the worst casualty conditions, the command and control networks must automatically reconfigure around battle damage.
Network fragment healing dramatically improves distributed control system survivability by autonomously routing data around damaged components in an intelligent manner. Dynamic reconfiguration, using network fragment healing, can provide the continuity of communications service that is required aboard a U.S. Naval vessel during combat operations.
To achieve survivable distributed communication an industry proven networking standard, ANSI-709.1-A Lon-Works, was extended to military applications as the focus of this Trident Scholar project. Specifically, the topology of a semi-mesh connection of rings was investigated through availability analysis. Furthermore, enhanced network fragment healing algorithms were derived to route message traffic around damaged network components in a more efficient manner. These routing algorithms were subsequently evaluated through network simulation, and validated with data obtained from network fragment healing tests performed aboard YP679, an Office of Naval Research test craft that is representative of a small scale combatant.
Assistant Professor Edwin L. Zivi
CDR Bradley D. Taylor, USNR
Weapons & Systems Engineering Department
The objective of this project was to develop an algorithm to accurately determine atmospheric density via simulated GPS data. This algorithm was designed to support a future United States Naval Academy (USNA) Small Satellite mission.
Atmospheric density is the most variable factor in orbit propagation. Thus, the uncertainty in density generates the most error when predicting a satellite’s future position. Numerous models have been developed to account for the variations, but more accurate models are needed.
The USNA Small Satellite Program is planning to place a USNA-designed satellite in low-Earth orbit with a GPS receiver onboard. The primary mission of the satellite will be a determination of the density in the upper atmosphere. By following specific design requirements presented in this Trident Scholar project, it will be possible to calculate the density of the atmosphere in the satellite’s orbit.
In developing the algorithm in this Trident Scholar project, the orbit propagation software, Satellite Tool Kit (STK) was used to generate data using one of several atmospheric models. By measuring the changes in the satellite’s orbit due to atmospheric drag, the density was calculated. To validate the algorithm, the density output was compared to that of the actual model used in STK.
Once the USNA satellite is on orbit, the algorithm can be used to create a database of densities. Other small satellite programs will launch similar satellites to generate sufficient data. With the new atmospheric density data, scientists can create an improved atmospheric model.
Professor Daryl G. Boden
Aerospace Engineering Department