The Advanced Radars and Electro-Optical Sensors group at the University of Missouri is constructing a new all-optical analog-to-digital converter (ADC) platform. This integrated optics application especially suits the data acquisition and processing requirements of mobile sensor systems that have dramatically increased alongside the requirements for reductions in system mass, volume, and power consumption. The platform of the ADC is composed of a direct-modulated laser (DML) at λ = 1.55 μm with a 40 G bits/sec sampling optical pulse source; a prism LiTaO3 (lithium tantalate) electro-optical deflector; an integrated focusing unit; a three-dimensional binary-coded spatial filter array; and collection optics. Using discrete Fourier transform, we also investigate both the center frequency-shifting phenomenon of the optical pulse propagation, and the frequency response. The simulations are calculated by using the two-dimensional Finite Difference Time Domain (FDTD) method, the results of which are much more reliable than Beam Propagation Methods (BPM). The spatial filter array and collection optics will be fabricated by the separated implanted oxygen process (SIMOX), silicon on insulator (SOI). Also, a new design and simulation of LiTaO3 (lithium tantalate) electro-optical deflector to be integrated in the same substrate is proposed. This platform is to be tested for 50 Giga-samples/sec analog-to-digital conversion, and be the prototype of a 100 Giga-samples/sec ADC.
KEYWORDS: Magnetism, Radar, Inductance, Computer simulations, Microsoft Foundation Class Library, Land mines, High power radar, Electrical engineering, Antennas, Velocity measurements
Recent advances in the development of miniature high power radar sources are presented. The miniature radar sources convert mechanical energy into electrical energy by compressing either piezoelectric materials or magnetic flux. The results of experiments performed to reach 100 kW of converted power are presented and discussed. Estimates are also given indicating the maximum power that can be generated with such devices.
KEYWORDS: Magnetism, Radar, Computer simulations, Land mines, Antennas, Velocity measurements, Ground penetrating radar, Helium, High power radar, Signal detection
Research progress on the design, construction, and operation of a novel, airborne ground penetrating radar system to detect surface and subsurface landmines is presented. The landmine detection system is unique in that active, electronic projectiles are shot into the ground from an airborne platform to create high power, monopulse radar signals. Intimate contact between the projectile and the ground reduces the amount of reflected radar energy at the air-soil interface and ensures that maximum radar energy is propagated into the surrounding ground. The end result is that the reflected radar signal is of higher energy and possesses a higher signal-to- noise ratio allowing enhanced detectability. The high power, monopulse signal that is reflected off the landmine is received at the airborne platform via scanned antenna array. In comparison, conventional ground penetrating radar systems typically use chirped or long pulse signals and horn type antennas located close to the ground limiting their usefulness in this application. To generate electrical energy, two types of projectiles are used and are based on the principle of magnetic flux compression or by the principle of piezoelectric compression. The performance results of these two projectile types as well as the models used to predict their behavior are presented and discussed. To evaluate the overall performance of the system, a sub-scale radar test range was also constructed. The radar test range consists of a large dirt- filled tank containing a high power impulse source, several targets that simulate buried landmines, and a post scanned antenna array located above the dirt-filled tank. The high power impulse source simulates the radar signal generated when the projectiles impact the ground. The radar cross-sectional data generated in the test range is presented and discussed.
This paper discusses the generation of subnanosecond pulses in the kilovolt range using TRAPATT diodes as overvolted, subnanosecond switches in a Marx circuit using the traveling wave method of erection. The design, operation, and simulation of the solid state Marx generator is discussed including the design of the signal probes and inherent signal distortion. A transient circuit simulation code was used to assist in determining the true operation of the circuit and to assist in designing additional circuits.
A reconfigurable antenna whose size, shape, and polarization can be dynamically modified is a desirable component for today's communication and surveillance systems. To date most proposed reconfigurable antenna concepts have used a matrix of conducting elements connected by electronic/optoelectronic switches with the on-off pattern of the switches defining the size or shape of the antenna. An alternative approach for realizing this concept is to exploit the photoconductive effect in various semiconductor materials. This paper reviews the general theory of photoconductivity in semiconductors emphasizing the parameters relevant to this application. The experimental arrangement and the initial results for our proof- of-concept demonstration are then presented. In this experiment a bow-tie shaped transient carrier distribution was created in a 4 inch diameter, high resistivity (6 - 8 k(Omega) -cm) Si wafer through illumination with a pulsed Nd:Glass laser. The voltage amplitudes measured by the transient Si bow-ties (three different wafers) were 45 - 50% of those received in the same environment by an equivalent copper bow-tie antenna designed to operate from 1.4 - 2.1 GHz. Analysis of this initial data indicates that an optimized design incorporating improved semiconductor processing techniques, an optimized feed/balun, soldered interconnects, and impedance matching would significantly improve performance.
KEYWORDS: Switches, Gallium arsenide, Semiconductors, Monte Carlo methods, Switching, General applications engineering, Silicon, Visualization, Data modeling, Doping
A general microcomputer based engineering model for high voltage photoconductive switch operation in the linear mode (closure by high photon flux) and nonlinear mode (closure by low photon flux) has been devised and implemented. The engineering model has been used to predict nonlinear photoconductive switch closure times with reasonable accuracy. Using an interactive graphics 'shell' the model is being used to search for an improved switch design through the use of selective doping distributions. This paper presents an overview of the model and some simulated data results.
We report further investigations of the surface electric fields present between the contacts ofan optically controlled silicon switch. The Kerr electro-optic effect and a phase sensitive interferometric analyzer is used to measure the surface fields when a pulsed high voltage is applied across the contacts. The experimental arrangement has a temporal resolution of 100 nanoseconds and a spatial resolution of 50 microns. The experimental results show preferential field enhancement near the anode and the surface electric fields are nonuniform in space and time. The temporal non-uniformity is more pronounced at higher electric fields.
The continuing development of optically controlled bulk high power semiconductor switches with sub-ns closure times and sub-ns synchronization has made the direct generation of microwave energy feasible. The object of this paper are to 1) describe two transmission line approaches for generation of multiple cycles of high power microwave energy using optically controlled switches 2) describe the optically controlled switch requirements for each approach 3) compare the point design performance of the above types of direct high power microwave generators and 4) draw several conclusions from this system study. I.
We report our investigations of the surface electric fields present between the contacts of an optically controlled semiconductor switch. The experimental arrangement uses the Kerr electrooptic effect to measure the surface fields when a pulsed voltage is applied across a gap between two electrodes on planar samples fabricated on a silicon wafer. The system arrangement measurement technique and preliminary experimental data is presented for deposited aluminium contacts.
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