ABSTRACT: Ion mobility spectroscopy (IMS) is a technology that is ideally suited for the detection of very low levels of analyte due to its extreme sensitivity and ability to speciate. Detection of common military and industrial explosives using IMS is an ideal application, since IMS can be tailored to be sensitive to compounds that form negative ions such as nitrate-laden explosives. However, realization of a miniaturized IMS-based detection system for explosives has been hampered by limitations in resolution of miniaturized IMS tubes and by the need to preconcentrate explosive samples and then rapidly desorb them creating a transient chemical concentration. We have demonstrated a new gating and data processing technique that takes advantage of pulse compression approaches developed for modern radar systems for decreasing granularity in target identification. We will show that closely spaced peaks can be isolated by adding discriminating codes to the gating signal. We will then employ matched filtering for the received ion current signal greatly improving instrument performance. This scheme is most advantageous to small geometry IMS drift cells that suffer from lack of resolution due to their small size but would improve sensitivity and peak location uncertainty in any geometry IMS tube. Specifically, we have demonstrated a 13 fold increase in signal-to-noise ratio and have effectively decreased the uncertainty in the location of the signal peak by a factor of 4.4 using a 13-bit Barker coding pattern to operate our IMS gating.
IEEE Sensors Journal 09/2007; · 1.52 Impact Factor
ABSTRACT: Solid polymer electrolytes are widely used in batteries and fuel cells because of the high ionic conductivity that can be
achieved at room temperature. The ions are usually Li or protons, although other ions can be shown to conduct in these polymer
films. There has been very little published work on solid polymer electrolyte films used as chemical sensors. We have found
that thin films of polymers like polyethylene oxide (PEO) are very sensitive to low concentrations of volatile organic compounds
(VOCs) such as common solvents. Evidence of a new sensing mechanism involving the percolation of ions through narrow channels
of amorphous polymer is presented. We will present impedance spectroscopy of PEO films in the frequency range 0.0001 Hz to
1 MHz for different concentrations of VOCs and relative humidity. We find that the measurement frequency is important for
distinguishing ionic conductivity from the double layer capacitance and the parasitic capacitance. © 2001 The Electrochemical
Society. All rights reserved.
Journal of The Electrochemical Society. 03/2001; 148(4):H37-H44.
ABSTRACT: There is a need for sensitive detection of organophosphonates by inexpensive, portable instruments. Two kinds of chemical
sensors, based on surface acoustic wave (SAW) devices and fiberoptic micromirrors, show promise for such sensing systems.
Chemically sensitive coatings are required for detection, and data for thin films of the polymer polysiloxane are reported
for both kinds of physical transducers. Both kinds of sensors are shown to be capable of detecting concentrations of diisopropylmethylphosphonate
(DIMP) down to 1 ppm.
Applied Biochemistry and Biotechnology 03/1993; 41(1):77-85. · 1.94 Impact Factor
ABSTRACT: A portable acoustic wave chemical sensor system that has the
unique advantage of providing two independent responses, doubling the
amount of information provided by the sensor, is described. These
sensors utilize surface acoustic wave (SAW) devices coated with
viscoelastic polymers that absorb a wide variety of volatile organic
species, including chlorinated hydrocarbons (CHCs). A comparison of the
relative magnitudes of these two responses, specifically the wave
velocity and the wave attenuation can be used to discriminate between
different isolated chemical species. This allows species identification
and quantification using a single SAW sensor. Tests of this portable
acoustic wave sensor (PAWS) system using polymer-coated SAW devices show
rapid, reversible detection of gas phase species, rapid reestablishment
of sensor baseline using an activated carbon scrubber, and
discrimination of species based on a comparison of the attenuation and
Ultrasonics Symposium, 1991. Proceedings., IEEE 1991; 01/1992
ABSTRACT: Two-dimensional patterns that have properties suited for optical alignment have been constructed from one-dimensional binary Barker codes. Applications include automated alignment of masks with patterns in photolithography.
Applied Optics 11/1991; 30(32):4600-1. · 1.41 Impact Factor