Fieldable Systems Research Articles

Note: Switch-mode hybrid current controllers for quantum cascade lasers

Chemical sensing in the mid-infrared has been revolutionized by the advent of quantum cascade lasers. Their higher current and voltage demands compared to laser diodes however, negatively impact size, weight, and power footprint for fieldable systems, particularly in hot environments. This Note presents a switch-mode/linear hybrid controller, furnishing drive currents up to 2 A at compliance voltages up to 15 V, with output noise near levels determined by shot and Johnson contributions from within the linear regulator, from frequencies below 100 Hz to the switching frequency. Current modulation from near 0 to 1.8 A is also demonstrated at frequencies up to a kilohertz.

Design and Characterization of Optofluidic Photonic Crystal Structures for the Detection of Fluorescent-Labeled Biomolecules

The combination of optics and microfluidics into optofluidic systems has provided a means of creating portable integrated platforms for performing fluorescence emission analyses in fieldable systems. We present here the design of a photonic crystal transducer for highly sensitive and selective fluorescence-based biomolecule detection using a reduced-size lattice nanocavity tuned for resonance at emission wavelengths. This novel approach to biosensing is based upon photonic crystal defect structures that are engineered to act as waveguides, optical resonant cavities, and nanofluidic flow channels. This paper will discuss modeling, design, and nanofabrication of optofluidic photonic crystal (PhC) transducers in silicon and GaN materials. First-order results of PhC optical property characterization will be provided. Preliminary simulations indicate that fluorescence emission intensity inside of a PhC resonant defect nanocavity is enhanced to a level 26 times greater than emission outside of a defect due to resonant optical confinement and the Purcell effect.

Computation and scaling of inductance gradients in electromagnetic launch systems

When a pulsed electric potential is applied to the terminals of a sliding electrical contact system, the armature translates under the influence of Lorentz forces caused by diffusing currents. The inductance gradient is conventionally used as a parameter to quantify the total Lorentz force acting on the armature and size the systems. The determination of the variation of the inductance gradient with system parameters such as the dimensions of the rails and armature, and the ramp rate of the applied potential is of interest in the design of sliding electrical contact systems with specified objectives. It is also useful in scaling results from laboratory to fieldable systems. The inductance gradient can be calculated with finite-element analyses using codes such as EMAP3D; this will be a time-consuming process. Semi-analytical formulations are possible for systems with simple and regular geometries such as rectangular sections. Solutions of the field diffusion equation can be expressed as a weighted sum of eigen functions characteristic of the geometry with imposed boundary conditions. A semi-analytical formulation based on eigen functions is presented here for computing and scaling inductance gradients of a sliding electrical contact system with rectangular rails and armatures. The effects of the dimensions of the rails and armatures, and the effect of the external ramp rate of the applied current on the inductance gradients are studied. The results are compared with available computational and experimental data.

Development of Fieldable Systems for Inspecting Aircraft Composite Structures

Development of Fieldable Systems for Inspecting Aircraft Composite Structures

Environmental and forensic applications of field-portable GC-MS: an overview

GC-MS can provide analytical information that is most reliable for many types of organic analyses. As field-portable GC-MS analytical systems evolve, the application scenarios have diversified as well. With the development of rugged fieldable systems, these instruments were demonstrated to be usable in the harsh environment of the jungle and in chemical demilitarization or military reconnaissance situations. Continuous unattended operations of a GC-MS for 12- or 24-hour monitoring applications in the field have been shown to be possible. A real-time algorithm strategy is proposed, which can be developed to aid in the advancement of field-portable mass spectrometry applied to chemical warfare agent analysis in military vehicles and can be used to raise the standard for field data quality. Each of these capabilities is discussed with the intent on reviewing analysis situations that can be expanded because of developments in field GC-MS instrumentation.

An evaluation of radioxenon detection techniques for use with a fluid-based concentration system

A portable monitoring system to measure the quantity of radioxenon (/sup 131m/Xe, /sup 133/Xe, /sup 133m/Xe, and /sup 135/Xe) in the atmosphere is being developed which incorporates a fluid-based concentration system with a detection system. To this end a number of radioxenon detection techniques have been evaluated to determine the best method of analyzing the output of the concentration system, which may contain significant amounts of radon in addition to concentrated xenon. Three detector configurations have been tested to measure the characteristic electron/photon coincidence radiation: gas proportional detector/NaI(Tl), plastic scintillator/NaI(Tl), and liquid scintillator/NaI(Tl). In addition to standard coincidence measurements, some additional gating criteria were also used: pulse height discrimination, pulse shape discrimination, and delayed coincidence. While the lowest relative minimum detectable activity was achieved using the liquid scintillator with delayed coincidence gating, the best performance for fieldable detection systems depends on the ratio of xenon to radon in the output of the concentration system. A high ratio favors the use of a gas proportional/NaI(Tl) detector using coincidence gating with pulse height discrimination. The use of a plastic scintillator/NaI(Tl) detector using coincidence gating with pulse shape discrimination is preferred when the ratio is low.

Implementation of real-time acoustic communications systems

Over the past several years, the field of underwater acoustic (UWA) communications has been focusing on bandwidth efficient phase coherent modulation techniques. In this application, practical communication algorithms, and thus their implementations, are still maturing. In addition to the computer-intensive algorithms used to track and decode these acoustic data, the systems may incorporate compression, coding, and error-detection schemes to provide usable communication links. Several programs are currently underway to utilize these developments in fieldable systems. In this paper, an overview of the signal processing requirements for UWA communications is provided, as well as some constraints placed on these systems by specific applications. The effect of these requirements on overall system design and implementation is outlined.