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NASA NTRS2018

Carbon Nanomaterials for Biosensing Applications

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here, we report two studies using vertically aligned CNF nanoelectrodes for biomedical applications. CNF arrays are investigated as neural stimulation and neurotransmitter recording electrodes for application in deep brain stimulation (DBS). Polypyrrole coated CNF nanoelectrodes have shown great promise as stimulating electrodes due to their large surface area, low impedance, biocompatibility and capacity for highly localized stimulation. CNFs embedded in SiO2 have been used as sensing electrodes for neurotransmitter detection. Our approach combines a multiplexed CNF electrode chip, developed at NASA Ames Research Center, with the Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS) system, developed at the Mayo Clinic. Preliminary results indicate that the CNF nanoelectrode arrays are easily integrated with WINCS for neurotransmitter detection in a multiplexed array format. In the future, combining CNF based stimulating and recording electrodes with WINCS may lay the foundation for an implantable “smart” therapeutic system that utilizes neurochemical feedback control while likely resulting in increased DBS application in various neuropsychiatric disorders. In total, our goal is to take advantage of the nanostructure of CNF arrays for biosensing studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.

Carbon Nanomaterials for Biosensing Applications↗

NASA NTRS2014

Carbon Nanofiber Nanoelectrode Arrays for Neural Implant Devices

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here, we report two studies using vertically aligned CNF nanoelectrodes for biomedical applications. CNF arrays are investigated as neural stimulation and neurotransmitter recording electrodes for application in deep brain stimulation (DBS). Polypyrrole coated CNF nanoelectrodes have shown great promise as stimulating electrodes due to their large surface area, low impedance, biocompatibility and capacity for highly localized stimulation. CNFs embedded in SiO2 have been used as sensing electrodes for neurotransmitter detection. Our approach combines a multiplexed CNF electrode chip, developed at NASA Ames Research Center, with the Wireless Instantaneous Neurotransmitter Concentration Sensor (WINCS) system, developed at the Mayo Clinic. Preliminary results indicate that the CNF nanoelectrode arrays are easily integrated with WINCS for neurotransmitter detection in a multiplexed array format. In the future, combining CNF based stimulating and recording electrodes with WINCS may lay the foundation for an implantable smart therapeutic system that utilizes neurochemical feedback control while likely resulting in increased DBS application in various neuropsychiatric disorders. In total, our goal is to take advantage of the nanostructure of CNF arrays for biosensing studies requiring ultrahigh sensitivity, high-degree of miniaturization, and selective biofunctionalization.

carbon nanotubes↗

NASA NTRS1988

An electrochemical study of corrosion protection by primer-topcoat systems on 4130 steel with ac impedance and dc methods

To investigate metal surface corrosion and the breakdown of metal protective coatings, the ac impedance method is applied to six systems of primer coated and primer topcoated 4130 steel. Two primers were used: a zinc-rich epoxy primer and a red lead oxide epoxy primer. The epoxy-polyamine topcoat was used in four of the systems. The EG and G-PARC Model 368 ac impedance measurement system, along with dc measurements with the same system using the polarization resistance method, were used to monitor changing properties of coated 4230 steel disks immersed in 3.5 percent NaCl solutions buffered at pH 5.4 over periods of 40 to 60 days. The corrosion system can be represented by an electronic analog called an equivalent circuit consisting of resistors and capacitors in specific arrangements. This equivalent circuit parallels the impedance behavior of the corrosion system during a frequency scan. Values for the resistors and capacitors, that can be assigned in the equivalent circuit following a least-squares analysis of the data, describe changes that occur on the corroding metal surface and in the protective coatings. Two equivalent circuits have been determined that predict the correct Bode phase and magnitude of the experimental sample at different immersion times. The dc corrosion current density data are related to equivalent circuit element parameters. Methods for determining corrosion rate with ac impedance parameters are verified by the dc method.

Mendrek, M. J.↗

NASA NTRS2006

Aerogels for Thermal Insulation of Thermoelectric Devices

Silica aerogels have been shown to be attractive for use as thermal-insulation materials for thermoelectric devices. It is desirable to thermally insulate the legs of thermoelectric devices to suppress lateral heat leaks that degrade thermal efficiency. Aerogels offer not only high thermal- insulation effectiveness, but also a combination of other properties that are especially advantageous in thermoelectric- device applications. Aerogels are synthesized by means of sol-gel chemistry, which is ideal for casting insulation into place. As the scale of the devices to be insulated decreases, the castability from liquid solutions becomes increasingly advantageous: By virtue of castability, aerogel insulation can be made to encapsulate devices having any size from macroscopic down to nanoscopic and possibly having complex, three-dimensional shapes. Castable aerogels can permeate voids having characteristic dimensions as small as nanometers. Hence, practically all the void space surrounding the legs of thermoelectric devices could be filled with aerogel insulation, making the insulation highly effective. Because aerogels have the lowest densities of any known solid materials, they would add very little mass to the encapsulated devices. The thermal-conductivity values of aerogels are among the lowest reported for any material, even after taking account of the contributions of convection and radiation (in addition to true thermal conduction) to overall effective thermal conductivities. Even in ambient air, the contribution of convection to effective overall thermal conductivity of an aerogel is extremely low because of the highly tortuous nature of the flow paths through the porous aerogel structure. For applications that involve operating temperatures high enough to give rise to significant amounts of infrared radiation, opacifiers could be added to aerogels to reduce the radiative contributions to overall effective thermal conductivities. One example of an opacifier is carbon black, which absorbs infrared radiation. Another example of an opacifier is micron- sized metal flakes, which reflect infrared radiation. Encapsulation in cast aerogel insulation also can help prolong the operational lifetimes of thermoelectric devices that must operate in vacuum and that contain SiGe or such advanced skutterudite thermoelectric materials as CoSb3 and CeFe3.5Co0.5Sb12. The primary cause of deterioration of most thermoelectric materials is thermal decomposition or sublimation (e.g., sublimation of Sb from CoSb3) at typical high operating temperatures. Aerogel present near the surface of CoSb3 can impede the outward transport of Sb vapor by establishing a highly localized, equilibrium Sb vapor atmosphere at the surface of the CoSb3.

Sakamoto, Jeffrey↗

NASA NTRS2018

Impedance Eduction in a Duct Using the Linearized Euler Equations

An impedance eduction technique that is based upon a numerical solution to the linearized Euler equations coupled with the minimization of an objective function is presented. The linearized Euler equations are solved numerically using a cubic finite element method and the minimum of the objective function is obtained via a gradient based optimizer. The mean flow is allowed to have a gradient in two coordinate directions and the impedance of the liner may vary arbitrarily over the liner surface. A new regularized wall impedance boundary condition presented by Rienstra which contains the effects of the mean boundary layer thickness is implemented. Impedances are educed for a perforate over honeycomb liner using test data acquired in the Langley Grazing Flow Impedance Tube. The impedance of the liner is educed both with an upstream source and a downstream source. The method is validated by comparing the educed impedance to a benchmark method. The primary conclusion of the study is that the impedances educed for upstream and downstream sources are not well matched and that the primary effect of the boundary thickness is to reduce the resistance of the liner.

Watson, Willie R.↗

NASA NTRS1968

Electron beam selectively seals porous metal filters

Electron beam welding selectively seals the outer surfaces of porous metal filters and impedances used in fluid flow systems. The outer surface can be sealed by melting a thin outer layer of the porous material with an electron beam so that the melted material fills all surface pores.

Snyder, J. A.↗

NASA NTRS2003

Effect of Resonator Axis Skew on Normal Incidence Impedance

High by-pass turbofan engines have fewer fan blades and lower rotation speeds than their predecessors. Consequently, the noise suppression at the low frequency end of the noise spectra has become an increasing concern. This has led to a renewed emphasis on improving noise suppression efficiency of passive, duct liner treatments at the lower frequencies. For a variety of reasons, passive liners are comprised of locally-reacting, resonant absorbers. One reason for this design choice is to satisfy operational and economic requirements. The simplest liner design consists of a single layer of honeycomb core sandwiched between a porous facesheet and an impervious backing plate. These resonant absorbing structures are integrated into the nacelle wall and are very ef- ficient over a limited bandwidth centered on their resonance frequency. Increased noise suppression bandwidth and greater suppression at lower frequencies is typically achieved for conventional liners by increasing the liner depth and incorporating thin porous septa into the honeycomb core. However, constraints on liner depth in modern high by-pass engine nacelles severely limit the suppression bandwidth extension to lower frequencies. Also, current honeycomb core liners may not be suitable for irregular geometric volumes heretofore not considered. It is of interest, therefore, to find ways to circumvent liner depth restrictions and resonator cavity shape constraints. One way to increase effective liner depth is to skew the honeycomb core axis relative to the porous facesheet surface. Other possibilities are to alter resonator cavity shape, e.g. high aspect ratio, narrow channels that possibly include right angle bends, 180. channel fold-backs, and splayed channel walls to conform to irregular geometric constraints. These possibilities constitute the practical motivation for expanding impedance modeling capability to include unconventional resonator orientations and shapes. The work reported in this paper is in the nature of a progress report and is limited to examining the implications of resonator axis skew on the composite normal incidence impedance of an array of resonator channels. Specifically, experimental results are compared with a modified impedance prediction model for highaspect- ratio, rectangular, resonator channels with varying amounts of skew relative to the incident particle velocity. It is shown that for resonator channel widths of 1 to 2 mm, aspect ratios of 25 to 50, and skew angles of zero to sixty degrees, the surface impedance of test models can be predicted with good accuracy. Predicted resistances and reactances are particularly well correlated through the first resonance and first anti-resonance for all six test models investigated. Beyond the first anti-resonance, the impedance prediction model loses the ability to predict details of resistance and reactance but still predicts the mean trends very well.

Parrott, Tony L.↗

NASA NTRS1991

Diffraction by a multilayer slab recessed in a ground plane via generalized impedance boundary conditions

The diffraction problem associated with a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the generalized scattering matrix formulation in conjunction with the dual integral equation approach. The multilayer slab is replaced by a surface obeying a generalized impedance boundary condition to facilitate the computation of the pertinent Wiener Hopf split functions and their zeros. Both Ez and Hz polarizations are considered, and a number of scattering patterns are presented, some of which are compared to exact results available for a homogeneous recessed slab.

Ricoy, M. A.↗

NASA NTRS1989

A new technique for simulating composite material. Task 2: Analytical solutions with Generalized Impedance Boundary Conditions (GIBCs)

The diffraction problem associated with a multilayer material slab recessed in a perfectly conducting ground plane is formulated and solved via the Generalized Scattering Matrix Formulation (GSMF) in conjunction with the dual integral equation approach. The multilayer slab is replaced by a surface obeying a generalized impedance boundary condition (GIBC) to facilitate the computation of the pertinent Wiener Hopf split functions and their zeros. Both E(sub z) and H(sub z) polarizations are considered and a number of scattering patterns are presented, some of which are compared to exact results available for a homogeneous recessed slab.

Ricoy, M. A.↗

NASA NTRS1989

Electrochemical Studies Of Aluminum Coated With Primer

Technical paper describes experiments using ac-impedance method of analyzing corrosion of metal surfaces and breakdown of protective coatings. Alternating-current-impedance scans provide more detailed information, indicating changes in corrosion rates, progressive deterioration of coatings, changes in metal surfaces, and reaction mechanisms. Changes in conditions of coatings detected by ac method before dc methods show increase in metal-corrosion current. Measurements of impedance as function of frequency provides sufficient data to enable resistances and capacitances to be determined by performing least-squares fit. Knowledge of dependence of these values on time leads to more detailed understanding of corrosion process.

Danford, Merlin D.↗

NASA NTRS1991

Transition operators in acoustic-wave diffraction theory. I - General theory. II - Short-wavelength behavior, dominant singularities of Zk0 and Zk0 exp -1

A formal theory of the scattering of time-harmonic acoustic scalar waves from impenetrable, immobile obstacles is established. The time-independent formal scattering theory of nonrelativistic quantum mechanics, in particular the theory of the complete Green's function and the transition (T) operator, provides the model. The quantum-mechanical approach is modified to allow the treatment of acoustic-wave scattering with imposed boundary conditions of impedance type on the surface (delta-Omega) of an impenetrable obstacle. With k0 as the free-space wavenumber of the signal, a simplified expression is obtained for the k0-dependent T operator for a general case of homogeneous impedance boundary conditions for the acoustic wave on delta-Omega. All the nonelementary operators entering the expression for the T operator are formally simple rational algebraic functions of a certain invertible linear radiation impedance operator which maps any sufficiently well-behaved complex-valued function on delta-Omega into another such function on delta-Omega. In the subsequent study, the short-wavelength and the long-wavelength behavior of the radiation impedance operator and its inverse (the 'radiation admittance' operator) as two-point kernels on a smooth delta-Omega are studied for pairs of points that are close together.

Hahne, G. E.↗

NASA NTRS1995

An equivalent body surface charge model representing three-dimensional bioelectrical activity

A new surface-source model has been developed to account for the bioelectrical potential on the body surface. A single-layer surface-charge model on the body surface has been developed to equivalently represent bioelectrical sources inside the body. The boundary conditions on the body surface are discussed in relation to the surface-charge in a half-space conductive medium. The equivalent body surface-charge is shown to be proportional to the normal component of the electric field on the body surface just outside the body. The spatial resolution of the equivalent surface-charge distribution appears intermediate between those of the body surface potential distribution and the body surface Laplacian distribution. An analytic relationship between the equivalent surface-charge and the surface Laplacian of the potential was found for a half-space conductive medium. The effects of finite spatial sampling and noise on the reconstruction of the equivalent surface-charge were evaluated by computer simulations. It was found through computer simulations that the reconstruction of the equivalent body surface-charge from the body surface Laplacian distribution is very stable against noise and finite spatial sampling. The present results suggest that the equivalent body surface-charge model may provide an additional insight to our understanding of bioelectric phenomena.

NASA Discipline Regulatory Physiology↗

NASA NTRS1979

Phase 2: Array automated assembly task low cost silicon solar array project

Several microwave systems for use in solar cell fabrication were developed and experimentally tested. The first system used a standing wave rectangular waveguide horn applicator. Satisfactory results were achieved with this system for impedance matching and wafer surface heating uniformity. The second system utilized a resonant TM sub 011 mode cylindrical cavity but could not be employed due to its poor energy coupling efficiency. The third and fourth microwave systems utilized a circular waveguide operating in the TM sub 01 and TM sub 11 but had problems with impedance matching, efficiency, and field uniformity.

Jones, G. T.↗

NASA NTRS1972

Phased array antenna matching: Simulation and optimization of a planar phased array of circular waveguide elements

A computerized simulation of a planar phased array of circular waveguide elements is reported using mutual coupling and wide angle impedance matching in phased arrays. Special emphasis is given to circular polarization. The aforementioned computer program has as variable inputs: frequency, polarization, grid geometry, element size, dielectric waveguide fill, dielectric plugs in the waveguide for impedance matching, and dielectric sheets covering the array surface for the purpose of wide angle impedance matching. Parameter combinations are found which produce reflection peaks interior to grating lobes, while dielectric cover sheets are successfully employed to extend the usable scan range of a phased array. The most exciting results came from the application of computer aided optimization techniques to the design of this type of array.

Dudgeon, J. E.↗

NASA NTRS1985

Determination of the Si-conducting polymer interfacial properties using A-C impedance techniques

A study was made of the interfacial properties of poly(pyrrole) (PP) deposited electrochemically onto single crystal p-Si surfaces. The interfacial properties are dependent upon the counterions. The formation of 'quasi-ohmic' and 'nonohmic' contacts, respectively, of PP(ClO4) and PP films doped with other counterions (BF4 and para-toluene sulfonate) with p-Si, are explained in terms of the conductivity of these films and the flat band potential, V(fb), of PP relative to that of p-Si. The PP film seems to passivate or block intrinsic surface states present on the p-Si surface. The differences in the impedance behavior of para-toluene sulfonate doped and ClO4 doped PP are compared.

Nagasubramanian, G.↗

NASA NTRS1976

Propagation of aircraft noise

The major tasks undertaken were (1) analytical and laboratory experiments on the propagation of sound from sources near a flat surface of finite acoustic impedance; (2) laboratory experiments dealing with the reflection of sound from finite sized plane patches; and (3) the diffraction of sound by wedge-and trapezoidal-shape barriers. In addition, a series of measurements were made of the background noise levels for various jet flow conditions in the Anechoic Noise Facility of the Langley Research Center's Acoustic and Noise Reduction Laboratory.

Pierce, A. D.↗

NASA NTRS2008

Hand-Held Units for Short-Range Wireless Biotelemetry

Special-purpose hand-held radiotransceiver units have been proposed as means of short-range radio powering and interrogation of surgically implanted microelectromechanical sensors and actuators. These units are based partly on the same principles as those of the units described in "Printed Multi- Turn Loop Antennas for RF Biotelemetry" (LEW-17879-1), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 48. Like the previously reported units, these units would make it unnecessary to have wire connections between the implanted devices and the external equipment used to activate and interrogate them. Like a unit of the previously reported type, a unit of the type now proposed would include a printed-circuit antenna on a dielectric substrate. The antenna circuitry would include integrated surface-mount inductors for impedance tuning. Circuits for processing the signals transmitted and received by the antenna would be included on the substrate. During operation, the unit would be positioned near (but not in electrical contact with) a human subject, in proximity to a microelectromechanical sensor or actuator that has been surgically implanted in the subject. It has been demonstrated that significant electromagnetic coupling with an implanted device could be established at a distance of as much as 4 in. (.10 cm). During operation in the interrogation mode, the antenna of the unit would receive a radio telemetry signal transmitted by the surgically implanted device. The antenna substrate would have dimensions of approximately 3.25 by 3.75 inches (approximately 8.3 by 9.5 cm). The substrate would have a thickness of the order of 30 mils (of the order of a somewhat less than a millimeter). The substrate would be made of low-radiofrequency- loss dielectric material that could be, for example, fused quartz, alumina, or any of a number of commercially available radio-frequency dielectric composite materials. The antenna conductors would typically be made of copper or a combination of chromium and gold. The choice of metal and the thickness of the metal layer(s) would depend on the choice of substrate material. For example, on a quartz or alumina substrate, one would typically use a layer of chromium 150 A thick and a layer of gold 2 m thick. The proposed units and the implanted devices that they would interrogate or activate would be inherently safe to use. They would operate at low radiated-power levels for short interrogation times (typically, milliseconds). Hence, there would be little local heating of tissues surrounding the implanted devices and little absorption of radio energy by such sensitive body parts as the eyes and the brain. Because the implanted devices would not depend on battery power and would be activated only during short interrogation intervals and would otherwise be in the goff h state most of the time, the useful lifetimes of the implanted devices would be greater than those of comparable battery-powered implanted devices. The compactness of the hand-held transceiver units would facilitate transport and storage and would facilitate self-diagnosis by patients able to handle the units while away from medical facilities.

Miranda, Felix A.↗

NASA NTRS2024

Designing Payload and Spaceflight Operations for Plants From Extreme 1 Terrestrial Environments

Terrestrial plants from the edges of the limits of life are likely to harbor genes that confer an advantage in deep space environments. These plants are seemingly capable of performing mission critical functions under prevailing deep space conditions while informing directed gene manipulation in target plant species. However, their adaptations to physiologically extreme habitats may hinder efficacy of routine laboratory techniques established for model plants. Here we present the development of Antarctic moss Ceratodon purpureus payload and flight operations for the ARTEMOSS experiment to the ISS astute of limited physical space and crew time. We demonstrate that the hydrophobic surface of Antarctic moss impedes chemical tissue fixation and precludes usage of RNAlater coupled with payload hardware deployed in standard plant spaceflight experiments. We show that deep-freezing the moss tissue on Petri plates provides adequate tissue fixation and allows for extraction of high-quality RNA suitable for gene expression profiling. We replaced hardware with stacks of Petri plates housing Antarctic moss and chemical fixation with deep-freeze in cryogenic GLACIER freezer. Our design can be translated to other plant species, expanding current techniques of experimentation with plants from extreme terrestrial environments aimed toward advancing human space exploration.

Agata K Zupanska↗