K. B. Pfeifer

Sandia National Laboratories, Albuquerque, New Mexico, United States

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Publications (17)12.72 Total impact

  • K.B. Pfeifer, W.G. Yelton, D.R. Kerr
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    ABSTRACT: We have developed a tool we call Two-Dimensional Péclet analysis to help in determining optimum operational parameters for analytical systems that require automated analysis of large numbers of analyte data peaks. In this paper, we derive the technique from moment analysis of the peaks and single-dimensional Péclet theory. Two-Dimensional Péclet analysis allows automated comparison of response peaks with differing shapes and amplitudes to be compared simultaneously in multicomponent mixtures. In addition to peak resolution and fidelity, individual two-dimensional moment components can provide feedback to total mass (zero moment), centroid location in time space (first moment), and two-dimensional spread of data (second moment).
    IEEE Sensors Journal 01/2011; 11(9):2108-2110. · 1.48 Impact Factor
  • K.B. Pfeifer, S.M. Thornberg
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    ABSTRACT: Fiber-optic gas phase surface plasmon resonance (SPR) detection of several contaminant gases of interest to state-of-health monitoring in high-consequence sealed systems has been demonstrated. These contaminant gases include H<sub>2</sub>, H<sub>2</sub>S, and moisture using a single-ended optical fiber mode. Data demonstrate that results can be obtained and sensitivity is adequate in a dosimetric mode that allows periodic monitoring of system atmospheres. Modeling studies were performed to direct the design of the sensor probe for optimized dimensions and to allow simultaneous monitoring of several constituents with a single sensor fiber. Testing of the system demonstrates the ability to detect 9 Pa partial pressures of H<sub>2</sub> using this technique, <; 0.04 Pa partial pressures of H<sub>2</sub>S, and increases in H<sub>2</sub>O concentration from - 70°C frost point. In addition, a multiple sensor fiber has been demonstrated that allows a single fiber to measure H<sub>2</sub>, H<sub>2</sub>S, and H<sub>2</sub>O without changing the fiber or the analytical system.
    IEEE Sensors Journal 09/2010; · 1.48 Impact Factor
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    ABSTRACT: This paper describes a mass-sensitive microfabricated preconcentrator for use in chemical detection microsystems. The device combines mass sensing and preconcentration to create a smart preconcentrator (SPC) that determines when it has collected sufficient analyte for analysis by a downstream chemical microsystem. The SPC is constructed from a Lorentz-force-actuated pivot-plate resonator with an integrated heater. Subsequent to microfabrication, the SPC is coated with an adsorbent for collection of chemical analytes. The frequency of operation varies inversely with the mass of collected analyte. Such shifts can be measured by a back-EMF in the SPC's drive/transducer line. By using a calibrated vapor system, the limit of detection of the SPC was determined to be less than 50 ppb for dimethyl-methyl-phosphonate (DMMP) (actual limits of detection are omitted due to export control limitations). At 1 ppm of DMMP, 1-s collection was sufficient to trigger analysis in a downstream microsystem; other micropreconcentrators would require an arbitrary collection time, normally set at 1 min or longer. This paper describes the theory of operation, design, fabrication, coating, vapor system testing, and integration of the SPC into microanalytical systems. The theory of operation, which is applicable to other torsional oscillators, is used to predict a shear modulus of silicon (100) of G = 57.0 GPa plusmn2.2 GPa.
    Journal of Microelectromechanical Systems 01/2009; · 2.13 Impact Factor
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    ABSTRACT: The mass-sensitive smart preconcentrator (SPC) consists of a Lorentz-Force-actuated MEMS resonator with an integral heater and surface coating for the collection of chemical analytes. Control circuitry is used to drive the SPC to resonance and measure its oscillation frequency. The frequency shift produced by adsorption of analyte on the SPC surface is inversely proportional to the mass of analyte collected. Thus, the SPC can measure when it has collected sufficient analyte for a downstream detection system. The limit of detection (LOD) of the SPC is less than 50 ppb for DMMP (dimethyl-methyl-phosphonate). At 1 ppm, less than 1 second collection of DMMP is sufficient to trigger analysis. An analytical model of operation of the SPC is used to predict the motion of the paddle and the shear modulus of silicon.
    ECS Transactions 10/2008; 16(11).
  • K.B. Pfeifer, S.B. Rohde
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    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; · 1.48 Impact Factor
  • W. G. Yelton, K. B. Pfeifer, A. W. Staton
    Journal of The Electrochemical Society - J ELECTROCHEM SOC. 01/2002; 149(1).
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    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.
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    ABSTRACT: Solid Polymer Electrolytes (SPE) 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 SPE films used as chemical sensors. The authors 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. They present impedance spectroscopy of PEO films in the frequency range 0.0001 Hz to 1 MHz for different concentrations of VOCs and relative humidity. They find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and the parasitic capacitance.
    The Electrochemical Society. 07/2000;
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    ABSTRACT: The authors have demonstrated a sensor based on an interdigitated electrode platform coated with a conductive viologen polymer that has excellent moisture sensitivity, response time, and low power consumption. Work has been done to explain the limits of sensitivity and characterize the response of the sensor in low-humidity environments and also characterize the response of the device to various organic interferents such as alcohols and organophosphonates. Using lumped-circuit models, the nature of the response is explained and design parameters are isolated that will allow future performance improvements. In addition, the temperature dependence of moisture sensitivity is presented.
    Journal of The Electrochemical Society 01/1999; 146(2):794-799. · 2.59 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Solid Polymer Electrolytes (SPE) 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 work on using these films as chemical sensors. We have found that thin films of polymers like polyethyleneoxide (PEO) are very sensitive to low concentrations of volatile organic compounds (VOCS) like common solvents. We will present impedance spectroscopy of PEO films in the frequency range 0.01 Hz to 1 MHz for different concentrations of VOCS. We find that the measurement frequency is important for distinguishing ionic conductivity from the double layer capacitance and parasitic capacitances.
    01/1999;
  • K. B. Pfeifer, S. J. Martin, A. J. Ricco
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    ABSTRACT: The measurement of VOC concentrations in harsh chemical and physical environments is a formidable task. A surface acoustic wave (SAW) sensor has been designed for this purpose and its construction and testing are described in this paper. Included is a detailed description of the design elements specific to operation in 300 C steam and HCl environments including temperature control, gas handling, and signal processing component descriptions. In addition, laboratory temperature stability was studied and a minimum detection limit was defined for operation in industrial environments. Finally, a description of field tests performed on steam reforming equipment at Synthetica Technologies Inc. of Richmond, CA is given including a report on destruction efficiency of CCl4 in the Synthetica moving bed evaporator. Design improvements based on the field tests are proposed.
    06/1993;
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    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. · 1.89 Impact Factor
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    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 velocity responses
    Ultrasonics Symposium, 1991. Proceedings., IEEE 1991; 01/1992
  • M A Butler, K B Pfeifer, S J Martin
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    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. · 1.69 Impact Factor
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    W G Yelton, K B Pfeifer, A W Staton
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    ABSTRACT: Recent efforts have focused on the chemical and physical diversity of interface materials for Surface Acoustic Wave (SAW) technology[1]; however, the issues of wide dynamic range and high sensitivity must also be addressed for sensor arrays to compete in applications requiring low detection limits. Because SAW devices respond in proportion to change in mass per nominal unit area of the device surface, sensitivity is enhanced by surface modification with high-area, thin-film coating materials: a greater mass of analyte is adsorbed at a given ambient concentration. Material studies of high-surface area (submicron) metal/oxide films developed to improve SAW sensitivity, reveal common factors can also diminish sensitivity. These factors include the density of the material, rigidity of the microstructure, and the thickness of the coating. Films deposited from high-density metals e.g., Pt, Pd, or Au, yield higher dendritic order of nano geometries, but result in greater insertion losses. Because of its low density, microstructure rigidity, ordered porosity, and controllable pore-volume, anodized aluminum formed from evaporated deposits of aluminum provides promising films for enhanced sensor sensitivity. During evaporative deposition, the dominant influence on the final microstructure of the coating is the surface mobility of the adatoms, which is affected by the substrate temperature and deposition rate. The microstructure of evaporative films is viewed in terms of the Movchan-Demchishin model [2]. Coatings are based on three crystal-structure zones. In zone 1, film growth is more agglomerated with "islands" of crystalline structures separated by columnar voids. Because of low thermal energy, due in part to the relatively low substrate temperature as compared to the melting point of the material, T m , the surface mobility of adatoms is limited. Where upon sulfuric acid (0.5M) anodization, under fixed anodic potential, the crystal morphology of the Al 2 O 3 in Figure 1 is characterized by disorder alumina microstructures with low effective surface area. However, from TEM analysis, these agglomerated oxides reveal tortuous pore openings on the same order as films developed under zone 2 conditions.
  • K. B. Pfeifer, G. C. Frye, T. W. Schneider
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    ABSTRACT: Moisture corrosive gas stream is measured as a function of the difference in resonant frequencies between two acoustic wave (AW) devices, each with a film which accepts at least one of the components of the gas stream. One AW is located in the gas stream while the other is located outside the gas stream but in the same thermal environment. In one embodiment, the film is a hydrophilic material such as SiOâ. In another embodiment, the SiOâ is covered with another film which is impermeable to the corrosive gas, such that the AW device in the gas stream measures only the water vapor. In yet another embodiment, the film comprises polyethylene oxide which is hydrophobic and measures only the partial pressure of the corrosive gas. Other embodiments allow for compensation of drift in the system. 8 figs.
  • K. B. Pfeifer, M. A. Butler
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    ABSTRACT: A fiber optic weight monitor is described that utilizes single-mode optical fiber technology at 1300 nm. The sensor, based on a Michelson interferometer, provides a pulse train output with the frequency reflecting the rate of change of the loading on the sensor. The characteristic time signature of footfalls on the sensor has been determined and the total number of counts per footfall is shown to be a measure of the individuals' weight. The response of the sensor to acoustic noise and temperature variations has also been determined. 3 refs., 8 figs.