Final report of LDRD project: Electromagnetic impulse radar for detection of underground structures

Abstract

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.Approved for public release; further dissemination unlimited. @ Sandia National LaboratoriesIssued by Sandia National Laboratories, operated for the United States Department of Energy by Sandia Corporation. NOTICE:This report was prepared a s an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government, any agency thereof, or any of their contractors or subcontractors. The views and opinions expressed herein do not necessarily state or reflect those of the United States Government, any agency thereof, or any of their contractors.Printed in the United States of America. This report has been reproduced directly from the best available copy. This report provides a summary of the LDRD project titled: Electromagnetic impulse radar for the detection of underground structures. The project met all its milestones even with a tight two year schedule and total funding of $400 k. The goal of the LDRD was to develop and demonstrate a ground penetrating radar (GPR) that is based on high peak power, high repetition rate, and low center frequency impulses. The idea of this LDRD is that a high peak power, high average power radar based on the transmission of short impulses can be utilized effect can be utilized for ground penetrating radar. This direct time-domain system we are building seeks to increase penetration depth over conventional systems by using: 1) high peak power, high repetition rate operation that gives high average power, 2) low center frequencies that better penetrate the ground, and 3) short duration impulses that allow for the use of downward looking, low flying platforms that increase the power on target relative to a high flying platform. Specifically, chirped pulses that are a microsecond in duration require (because it is difficult to receive during transmit) platforms above 150 m (and typically 1 km) while this system, theoretically could be at 10 m above the ground. The power on target decays with distance squared so the ability to use low flying platforms is crucial to high penetration. Clutter is minimized by time gating the surface clutter return. Short impulses also allow gating (out) the coupling of the transmit and receive antennas.

Device Technology Investigation: Subsystems Packaging Study: Feasibility of PCSS - Based Pulser for Highly Portable Platforms

“…The fact that the degradation is confined to regions near the contacts suggests that developing better contacts that allow for higher current density can make substantial increases in switch lifetime. When this project started, high-gain PCSS would last for ~10 4 pulses under a specific set of test conditions (0.5 MW). During the course of this project, the lifetime has been improved to 100´10 6 .…”

“…This would not only offer a size and complexity advantage, but also increase the potential repetition rate of the system. PCSS have been triggered at MHz repetition rates in burst mode [4]. The limit in this system would be due to heating in the PCSS due to lock-on and resistive losses.…”

“…Switch jitter was a major issue in reliable and consistent production of a bipolar pulse. This line was used for the initial GPR work reported in [4]. As PFL output was increased to produce higher levels of radiated electric fields, PCSS size increased, and so did jitter in the triggering of the two switches.…”

Photoconductive, semiconductor switch technology for short pulse electromagnetics and lasers

“…[2,9] Precision gas switch triggers (figure 1) make use of low jitter, timing agility, optical isolation, and high voltage that is available with PCSS.…”

“…This paper will provide a brief discussion of PCSS switching properties and general applications, and then focus on optical pulse generation and control with PCSS technology. Specific electromagnetic pulse applications have been demonstrated and documented in internal reports [2,3].…”