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Dual output acoustic wave sensor for molecular identification

Description: The invention comprises a method for the identification and quantification of sorbed chemical species onto a coating of a device capable of generating and receiving an acoustic wave, by measuring the changes in the velocity of the acoustic wave resulting from the sorption of the chemical species into the coating as the wave travels through the coating and by measuring the changes in the attenuation of an acoustic wave resulting from the sorption of the chemical species into the coating as the wave travels through the coating. The inventive method further correlates the magnitudes of the changes of velocity with respect to changes of the attenuation of the acoustic wave to identify the sorbed chemical species. The absolute magnitudes of the velocity changes or the absolute magnitude of the attenuation changes are used to determine the concentration of the identified chemical species.
Date: October 3, 1990
Creator: Frye, G. C. & Martin, S. J.
Partner: UNT Libraries Government Documents Department

Evaluation of aqueous cleaners as alternatives to vapor degreasing

Description: As part of the preparation process during assembly of thermally activated batteries, the stainless steel piece parts are normally cleaned by vapor degreasing with trichloroethylene. Severe restrictions on the use of chlorinated and fluorinated hydrocarbons in recent years prompted the evaluation of a number of aqueous cleaners as a replacement technology for this application. A total of seven commercial aqueous degreasers was evaluated in this study at several dilution ratios and temperatures. One organic cleaner was also examined under ambient conditions. The effectiveness of the cleaner was determined by the use of x-ray photoelectron spectroscopy (XPS), which is a surface analytical technique that is very sensitive to low levels of surface contaminants. A quartz-crystal microbalance (QCM) that is immersed in the cleaning bath was evaluated as a tool for monitoring the bath cleanliness. The best overall cleaning results were obtained with Micro, Impro-Clean 3800, and Sonicor cleaners.
Date: May 1, 1996
Creator: Guidotti, R.A.; Schneider, T.W. & Frye, G.C.
Partner: UNT Libraries Government Documents Department

Metal-loaded polymer films for chemical sensing of ES&H-related pollutants

Description: This report summarizes the results of a Laboratory Directed Research and Development (LDRD) effort to study and model surface acoustic wave (SAW) devices for environmental applications. The response of polymer-coated SAW devices to temperature changes and polymer vapor absorption is examined. A perturbational approach is used to relate velocity and attenuation responses to film translational and strain modes generated by the SAW. Two distinct regimes of film behavior arise, causing different SAW responses. For glassy films, displacement is nearly uniform across the film thickness, varying only in the direction of propagation. A model developed to predict velocity and attenuation in this regime, reduces to the familiar Tiersten (Wohltjen) equation for purely elastic films. For elastomeric (rubbery) films, inertial effects cause a phase lag to occur across the film for shear displacements. A model to account for these cross-film displacement gradients predicts a characteristic resonant response when the film phase shift reaches np/2, where n is an odd integer. These model predictions are compared with measured responses from polyisobutylene-coated SAW devices as temperature is varied and during exposure to high vapor concentrations.
Date: March 1, 1997
Creator: Martin, S.J. & Frye, G.C.
Partner: UNT Libraries Government Documents Department

Gas sensing with acoustic devices

Description: A survey is made of acoustic devices that are suitable as gas and vapor sensors. This survey focuses on attributes such as operating frequency, mass sensitivity, quality factor (Q), and their ability to be fabricated on a semiconductor substrate to allow integration with electronic circuitry. The treatment of the device surface with chemically-sensitive films to detect species of interest is discussed. Strategies for improving discrimination are described, including sensor arrays and species concentration and separation schemes. The advantages and disadvantages of integrating sensors with microelectronics are considered, along with the effect on sensitivity of scaling acoustic gas sensors to smaller size.
Date: December 31, 1996
Creator: Martin, S.J.; Frye, G.C.; Spates, J.J. & Butler, M.A.
Partner: UNT Libraries Government Documents Department

Evaluation of aqueous cleaners as alternatives to vapor degreasing

Description: As part of the preparation process during assembly of thermally activated batteries, the stainless steel piece parts are normally cleaned by vapor degreasing with trichloroethylene. Severe restrictions on the use of chlorinated and fluorinated hydrocarbons in recent years prompted the evaluation of a number of aqueous cleaners as a replacement technology for this application. A total of seven commercial aqueous degreasers was evaluated in this study at several dilution ratios and temperatures. One organic cleaner was also examined under ambient conditions. The effectiveness of the cleaner was determined by the use of x-ray photoelectron spectroscopy (XPS), which is a surface analytical technique that is very sensitive to low levels of surface contaminants. A quartz-crystal microbalance (QCM) that is immersed in the cleaning bath was evaluated as a tool for monitoring the bath cleanliness. The best overall cleaning results were obtained with Micro, Impro-Clean 3800, and Sonicor cleaners.
Date: February 1, 1996
Creator: Guidotti, R.A.; Schneider, T.W. & Frye, G.C.
Partner: UNT Libraries Government Documents Department

Clustering-based pattern recognition applied to chemical recognition using SAW array signals

Description: We present a new patter recognition (PR) technique for chemical identification using arrays of microsensors. The technique relies on a new empirical approach to k-dimensional cluster analysis which incorporates measured human visual perceptions of difficult 2- dimensional clusters. The method can handle nonlinear SAW array data, detects both unexpected (outlier) and unreliable array responses, and has no user-adjustable parameters. We use this technique to guide the development of arrays of thin-film-coated SAW (Surface Acoustic Wave) devices that produce optimal PR performance for distinguishing a variety of volatile organic compounds, organophosphonates and water.
Date: May 1, 1994
Creator: Osbourn, G. C.; Bartholomew, J. W.; Frye, G. C. & Ricco, A. J.
Partner: UNT Libraries Government Documents Department

Optimizing surface acoustic wave sensors for trace chemical detection

Description: This paper describes several recent advances for fabricating coated surface acoustic wave (SAW) sensors for applications requiring trace chemical detection. Specifically, we have demonstrated that high surface area microporous oxides can provide 100-fold improvements in SAW sensor responses compared with more typical polymeric coatings. In addition, we fabricated GaAs SAW devices with frequencies up to 500 MHz to provide greater sensitivity and an ideal substrate for integration with high-frequency electronics.
Date: June 1, 1997
Creator: Frye, G.C.; Kottenstette, R.J. & Heller, E.J.
Partner: UNT Libraries Government Documents Department

Development and evaluation of on-line detection techniques for polar organics in ultrapure water

Description: An on-line monitor that can perform rapid, trace detection of polar organics such as acetone and isopropanol in ultrapure water (UPW) is necessary to efficiently recycle water in semiconductor manufacturing facilities. The detection of these analytes is problematic due to their high solubility in water, resulting in low partitioning into sensor coatings for direct water analysis or into the vapor phase for detection by vapor phase analyzers. After considering various options, we have evaluated two conventional laboratory techniques: gas chromatography and ion mobility spectroscopy. In addition, optimizations of sensor coating materials and sample preconditioning systems were performed with the goal of a low cost, chemical sensor system for this application. Results from these evaluations, including recommendations for meeting the needs of this application, are reported.
Date: March 1, 1996
Creator: Frye, G.C.; Blair, D.S.; Schneider, T.W.; Mowry, C.D.; Colburn, C.W. & Donovan, R.P.
Partner: UNT Libraries Government Documents Department

Development of a GaAs Monolithic Surface Acoustic Wave Integrated Circuit

Description: An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. The oscillator consists of a two-port SAW delay line in a feedback loop with a four-stage GaAs MESFET amplifier. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other RF applications.
Date: March 8, 1999
Creator: Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M. et al.
Partner: UNT Libraries Government Documents Department

Development of GaAs-Based Monolithic Surface Acoustic Wave Devices for Chemical Sensing and RF Filter Applications

Description: Since their invention in the mid-1960's, surface acoustic wave (SAW) devices have become popular for a wide variety of applications. SAW devices represent a low-cost and compact method of achieving a variety of electronic signal processing functions at high frequencies, such as RF filters for TV or mobile wireless communications [1]. SAW devices also provide a convenient platform in chemical sensing applications, achieving extremely high sensitivity to vapor phase analytes in part-per-billion concentrations [2]. Although the SAW acoustic mode can be created on virtually any crystalline substrate, the development of SAW technology has historically focused on the use of piezoelectric materials, such as various orientations of either quartz or lithium niobate, allowing the devices to be fabricated simply and inexpensively. However, the III-V compound semiconductors, and GaAs in particular, are also piezoelectric as a result of their partially covalent bonding and support the SAW acoustic mode, allowing for the convenient fabrication of SAW devices. In addition, GaAs microelectronics has, in the past decade, matured commercially in numerous RF wireless technologies. In fact, GaAs was recognized long ago as a potential candidate for the monolithic integration of SAW devices with microelectronics, to achieve compact RF signal processing functions [3]. The details of design and fabrication of SAW devices can be found in a variety of references [1].
Date: December 24, 1998
Creator: Baca, A.G.; Casalnuovo, S.A.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M. et al.
Partner: UNT Libraries Government Documents Department

Measuring liquid properties with smooth- and textured-surface resonators

Description: The sensitivity of quartz resonators to surface mass accumulation enables their use in a number of sensing applications. The linear change in resonant frequency that occurs with mass accumulation allows the device to function as a general-purpose gravimetric detector or ``microbalance.`` The device is easily instrumented as a sensor by incorporating it as the frequency-control element of an oscillator circuit. The response of thickness shear mode (TSM) resonators in liquids is examined. Smooth-surface devices, which viscously entrain a layer of contacting liquid, respond to the product of liquid density and viscosity. Textured-surface devices, which also trap liquid in surface features, exhibit an additional response that depends on liquid density alone. Combining smooth and textured resonators in a monolithic sensor allows simultaneous measurement of liquid density and viscosity.
Date: August 1, 1993
Creator: Martin, S.J.; Wessendorf, K.O.; Gebert, C.T.; Frye, G.C.; Cernosek, R.W.; Casaus, L. et al.
Partner: UNT Libraries Government Documents Department

Development of a GaAs-Based Monolithic Surface Acoustic Wave Integrated Chemical Microsensor

Description: An oscillator technology using surface acoustic wave delay lines integrated with GaAs MESFET electronics has been developed for GaAs-based integrated microsensor applications. Oscillators with frequencies of 470, 350, and 200 MHz have been designed and fabricated. These oscillators are also promising for other rf applications.
Date: October 28, 1998
Creator: Baca, A.G.; Casalnuovo, S.C.; Drummond, T.J.; Frye, G.C.; Heller, E.J.; Hietala, V.M. et al.
Partner: UNT Libraries Government Documents Department

Quartz crystal microbalance (QCM) arrays for solution analysis

Description: Quartz crystal microbalances (QCMs) are piezoelectric thickness-shear-mode resonators where the resonant frequency has long been known to vary linearly with the mass of rigid layers on the surface when the device is in contact with air. This reports summarizes the results from a Laboratory Directed Research and Development effort to use an array of QCMs to measure and identify volatile organic compounds (VOCs) in water solutions. A total of nine polymer-coated QCMs were tested with varying concentrations of twelve VOCs while frequency and damping voltage were measured. Results from these experiments were analyzed using a Sandia-developed pattern recognition technique called visually empirical region of influence (VERI) developed at Sandia. The VERI analyses of data with up to 16% and 50% sensitivity drifts were carried out on an array with six signals obtained from five sensors. The results indicate that better than 98% and 88% correct chemical recognition is maintained for the 16% and 50% drifts, respectively. These results indicate a good degree of robustness for these sensor films.
Date: January 1, 1997
Creator: Schneider, T.W.; Frye, G.C.; Martin, S.J.; Kottenstette, R.J.; Osbourn, G.C.; Bartholomew, J.W. et al.
Partner: UNT Libraries Government Documents Department