Ultrawideband (UWB) systems that radiate very high-level transient waveforms and exhibit operating bandwidths of over two decades are now in demand for a number of applications. Such systems are known to radiate impulse-like waveforms with rise times around 100 ps and peak electric field values of tens of kilovolts per meter. Such waveforms, if properly radiated, will exhibit an operating spectrum of over two decades, making them ideal for applications such as concealed object detection, countermine, transient radar, and communications. In this paper, we describe a large, high-voltage transient system built at the Air Force Research Laboratory, Kirtland AFB, NM, from 1997 to 1999. The pulsed power system centers around a very compact resonant transformer capable of generating over 1 MV at a pulse-repetition frequency of /spl sim/ 600 Hz. This is switched, via an integrated transfer capacitor and an oil peaking switch onto an 85-/spl Omega/ half-impulse radiating antenna. This unique system will deliver a far radiated field with a full-width at half-maximum on the order of 100 ps, and a field-range product (rE/sub far/) of /spl sim/ 5.3 MV, exceeding all previously reported results by a factor of several.

We consider the detection of subsurface unexploded ordnance via magnetometer and electromagnetic-induction (EMI) sensors. Detection performance is presented, using model-based signal processing algorithms. We first develop and validate the parametric models, using both numerical and measured data. These models are then applied in the context of feature extraction, and the features are processed via two signal-processing algorithms. The detection algorithms are discussed in detail, with comparisons made based on performance with measured magnetometer and EMI data.

A simple and accurate model is presented for computation of the electromagnetic induction (EMI) resonant frequencies of canonical conducting and ferrous targets, in particular, finite-length cylinders and rings. The imaginary resonant frequencies correspond to the well known exponential decay constants of interest for time-domain EMI interaction with conducting and ferrous targets. The results of the simple model are compared to data computed numerically, via method-of-moments (MoM) and finite-element models. Moreover, the simple model is used to fit measured wideband EMI data from ferrous cylindrical targets (in terms of a small number of parameters). It is also demonstrated that the general model for the magnetic-dipole magnetization, in terms of a frequency-dependent diagonal dyadic, is applicable to general rotationally symmetric targets (not just cylinders and rings).

The low-frequency natural response of conducting, permeable targets is investigated. The authors demonstrate that the source-free response is characterized by a sum of nearly purely damped exponentials, with the damping constants strongly dependent on the target shape, conductivity, and permeability, thereby representing a potential tool for pulsed electromagnetic induction (EMI) identification (discrimination) of conducting and permeable targets. This general concept is then specialized to the particular case of a body of revolution (BOR), for which the method-of-moments (MoM)-computed natural damping constants from several targets are compared with measurements. Moreover, theoretical natural (equivalent) surface currents and damping coefficients are shown for other targets of interest. Finally, the authors investigate the practical use of such natural signatures in the context of identification, wherein Cramer-Rao bound (CRB) studies address signal-to-noise ratio (SNR) considerations.

If the fields incident on a buried body of revolution are polarized vertically or horizontally (relative to the ground), the backscattered fields are exclusively copolarized (i.e., there are no cross-polarized backscattered fields). After substantiating this theoretically, measured ultrawideband (UWB) synthetic aperture radar (SAR) data are used for corroboration, considering real, buried landmines that approximate bodies of revolution.

Since the 1960s significant effort has gone into developing requisite technology for the nuclear electromagnetic pulse (EMP). In the late 1970s several important summary documents were published. The author updates this information to the present. It is noted that EMP has affected a set of related areas which can be collectively referred to as high-power electromagnetics (HPE). This includes direct-strike lightning, high-power microwaves (HPM), and some aspects of transient radar.>

The singularity expansion method (SEM) for quantifying the transient electromagnetic (EM) scattering from targets illuminated by pulsed EM radiation is reviewed. SEM representations for both induced currents and scattered fields are presented. Natural-resonance-based target identification schemes, based upon the SEM, are described. Various techniques for the extraction of natural-resonance modes from measured transient response waveforms are reviewed. Particular attention is given to the aspect-independent (extinction) E-pulse and (single-mode) S-pulse discriminant waveforms which, when convolved with the late-time pulse response of a matched target, produce null or mono-mode responses, respectively, through natural-mode annihilation. Extensive experiment results for practical target models are included to validate the E-pulse target discrimination technique. Finally, anticipated future extensions and areas requiring additional research are identified.>