Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs

Nanowire and Fiber Composite Electromechanical Sensor

Fiber or nanowire composites offer many benefits for piezoelectric sensor and actuator applications. Piezoelectric composite is comprised of piezoelectric ceramics lain in polymer matrix. The composite with the piezoelectric ceramics connected in one direction and the polymer in three directions is named as 1-3 composite. 1-3 composites are most ordinary used and the anisotropic alignment of PZT in the composite may substantially lower lateral piezoelectric coupling and increases the sensitivity of the transducer mechanically. Piezoelectric fiber composites are suitable for sensor applications, medical diagnostics and nondestructive testing. Single crystal zinc-oxide nanowires were synthesized through a simple hydrothermal route and subsequently mixed with polyimide matrix to form ZnO nanocomposites. Superimposed a.c. and d.c. electric fields were applied to microscopically tailor the alignment of ZnO nanowires in polyimide matrix to form anisotropic nanocomposites. Piezoresistive property of ZnO nanocomposite was investigated for strain sensor application. A large gauge factor was obtained from the monotonic uniaxial stress-strain experiment for this nanocomposite and it is much higher than that of ordinary metal strain sensor. A low frequency fiber composite vibration sensor was fabricated and experimentally studied. The global parameters of the composite were substituted into lumped and distributed element constituent equations for piezoelectric unimorph to theoretically predict the sensitivity and effective frequency response range of the vibration sensor. An experiment was carried out to validate the result from the theoretical model. The output voltage per unit input displacement keeps stable in a wide frequency range with a suitable damping ratio. This PZT fiber composite sensor was also applied for soft material strain measurement and soft biomaterial surface morphology and elastic modulus characterization. From the theoretical evaluation and experiment result, this strain sensor is suitable for strain measurement with high sensitivity and high softness. A rectangular breathing sensor and an annular breathing sensor were fabricated for breathing rate and depth monitoring. Both sensors were tested under different physiological conditions and measurement results could be utilized for precaution and monitoring of breathing diseases. Both of them are excellent for monitoring breathing rate and depth and be nice choices for daily use and diagnose purpose

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

Design, development and characterisation of piezoresistive and capacitive polymeric pressure sensors for use in compression hosiery

The work in this thesis was focused in developing a flexible and cost-effective pressure sensor capable of detecting pressure variations within the low working range (0-6kPa) of compression hosiery. For this cause, both piezoresistive and capacitive pressure sensors were developed and characterised, utilising conductive and non-conductive polymeric elements to sense compressive loads. In the first case, the developed piezoresistive sensor is composed of a conductive filler - polymer composite, with a force-dependent conductivity, encapsulated in between a structured and unstructured configuration of electrodes. Initially, as the sensing element of the sensor a multi-walled carbon nanotubes-polydimethylsiloxane (MWCNT-PDMS) composite was tested. A fabrication process is also proposed for developing the MWCNT-PDMS composite which involves a series of successive direct ultrasonications and shear mixing in order to disperse the two constituents of the composite, with the use of an organic solvent. Developing the composite over a range of different filler concentrations revealed a sharp step-like conductivity behaviour, typical amongst percolating composites. The MWCNT-PDMS sensor exhibited a positive piezoresistive response when subjected to compression, which was substantially enhanced when structured electrode layers were utilised. A Quantum Tunnelling Composite (QTC) material was also tested as the sensing material, which displays a large negative piezoresistive response when deformed. The QTC pressure sensor exhibited an improved performance, which was similarly significantly increased when a structured electrode was employed. In the second case, a parallel-plate capacitive pressure sensor was developed and characterised, which successfully provided a pressure sensitivity within the working range of compression hosiery. The sensor employs an ultra-thin PDMS blend film, with tuneable Young’s modulus, as the dielectric medium of the capacitor, bonded in between two rigid copper-coated glass layers. A casting process is also presented, involving the use of a sacrificial mould, in order to pattern the polymeric film with a micro-pillar structure to assist the deformation of the medium under compressive loads. The performance of the sensor with regards to the polymeric film thickness, structure and mechanical softness was explored. Overall, the combination of an ultra-thin dielectric medium with a very low Young’s modulus and a microstructured surface resulted in a capacitive pressure sensor with a good performance within the desired pressure regime

Laser-assisted processing of multilayer films for inexpensive and flexible biomedical microsystems

Flexible/stretchable electronics offer ideal properties for emerging health monitoring devices that can seamlessly integrate with the soft, curvilinear, and dynamic surfaces of the human body. The resulting capabilities have allowed novel devices for monitoring physiological parameters, improving surgical procedures, and human-machine interfaces. While the attractiveness of these devices are indubitable, their fabrication by conventional cleanroom techniques makes them expensive and incompatible with rapid large-scale (e.g., roll-to-roll) production. The purpose of this research is to develop inexpensive fabrication technologies using low-cost commercial films such as polyimide, paper, and metalized paper that can be utilized for developing various flexible/stretchable physical and chemical sensors for wearable and lab-on-chip applications. The demonstrated techniques focus on an array of laser assisted surfaces modification and micromachining strategies with the two commonly used CO2 and Nd: YAG laser systems. The first section of this dissertation demonstrates the use of localized pulsed CO2 laser irradiation to selectively convert thermoset polymer films (e.g., polyimide) into electrically conductive highly porous carbon micro/nanostructures.Thisprocessprovidesauniqueandfacileapproachfordirect writing of carbonized conductive patterns on flexible polyimide sheets in ambient conditions, eliminating complexities of current methods such as expensive CVD processes and complicated formulation/preparation of conductive carbon based inks used in ink jet printing. The highly porous laser carbonized layer can be transferred to stretchable elastomer or further functionalized with various chemical substances such as ionic solutions, nanoparticles, and chemically conductive polymers to create different mechanical and chemical sensors. The second section of this dissertation describes the use of laser ablation for selective removal of material from multilayer films such as ITO-coated PET, parchment paper, and metalized paper to create disposable diagnostic platforms and in-vitro models for lab-on-chip based studies. The ablated areas were analyzed using electrical, mechanical, and surface analysis tools to understand change in physical structure and chemical properties of the laser ablated films. As proof-of-concept demonstrations of these technologies, four different devices are presented here: mechanical, electrochemical, and environmental sensors along with an in-vitro cell culture platform. All four devices are designed, fabricated, and characterized to highlight the capability of commercial laser processing systems in the production of the next generation, low-cost and flexible biomedical devices

Lab-on-a-chip nucleic-acid analysis towards point-of-care applications

Recent infectious disease outbreaks, such as Ebola in 2013, highlight the need for fast and accurate diagnostic tools to combat the global spread of the disease. Detection and identification of the disease-causing viruses and bacteria at the genetic level is required for accurate diagnosis of the disease. Nucleic acid analysis systems have shown promise in identifying diseases such as HIV, anthrax, and Ebola in the past. Conventional nucleic acid analysis systems are still time consuming, and are not suitable for point-ofcare applications. Miniaturized nucleic acid systems has shown great promise for rapid analysis, but they have not been commercialized due to several factors such as footprint, complexity, portability, and power consumption. This dissertation presents the development of technologies and methods for a labon-a-chip nucleic acid analysis towards point-of-care applications. An oscillatory-flow PCR methodology in a thermal gradient is developed which provides real-time analysis of nucleic-acid samples. Oscillating flow PCR was performed in the microfluidic device under thermal gradient in 40 minutes. Reverse transcription PCR (RT-PCR) was achieved in the system without an additional heating element for incubation to perform reverse transcription step. A novel method is developed for the simultaneous pattering and bonding of all-glass microfluidic devices in a microwave oven. Glass microfluidic devices were fabricated in less than 4 minutes. Towards an integrated system for the detection of amplified products, a thermal sensing method is studied for the optimization of the sensor output. Calorimetric sensing method is characterized to identify design considerations and optimal parameters such as placement of the sensor, steady state response, and flow velocity for improved performance. An understanding of these developed technologies and methods will facilitate the development of lab-on-a-chip systems for point-of-care analysis

Seedless hydrothermal growth of ZnO nanorods as a promising route for flexible tactile sensors

Hydrothermal growth of ZnO nanorods has been widely used for the development of tactile sensors, with the aid of ZnO seed layers, favoring the growth of dense and vertically aligned nanorods. However, seed layers represent an additional fabrication step in the sensor design. In this study, a seedless hydrothermal growth of ZnO nanorods was carried out on Au-coated Si and polyimide substrates. The effects of both the Au morphology and the growth temperature on the characteristics of the nanorods were investigated, finding that smaller Au grains produced tilted rods, while larger grains provided vertical rods. Highly dense and high-aspect-ratio nanorods with hexagonal prismatic shape were obtained at 75 °C and 85 °C, while pyramid-like rods were grown when the temperature was set to 95 °C. Finite-element simulations demonstrated that prismatic rods produce higher voltage responses than the pyramid-shaped ones. A tactile sensor, with an active area of 1 cm2, was fabricated on flexible polyimide substrate and embedding the nanorods forest in a polydimethylsiloxane matrix as a separation layer between the bottom and the top Au electrodes. The prototype showed clear responses upon applied loads of 2–4 N and vibrations over frequencies in the range of 20–800 Hz

Analysis of systems hardware flown on LDEF. Results of the systems special investigation group

The Long Duration Exposure Facility (LDEF) was retrieved after spending 69 months in low Earth orbit (LEO). LDEF carried a remarkable variety of mechanical, electrical, thermal, and optical systems, subsystems, and components. The Systems Special Investigation Group (Systems SIG) was formed to investigate the effects of the long duration exposure to LEO on systems related hardware and to coordinate and collate all systems analysis of LDEF hardware. Discussed here is the status of the LDEF Systems SIG investigation through the end of 1991

Research and technology highlights of the Lewis Research Center

Highlights of research accomplishments of the Lewis Research Center for fiscal year 1984 are presented. The report is divided into four major sections covering aeronautics, space communications, space technology, and materials and structures. Six articles on energy are included in the space technology section