MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Integrated polysilicon thermistors for microfluidic sensing

This thesis documents results related to the design, fabrication, and testing of integrated polysilicon thermistors for microfluidic sensing in experimental investigations of micro impinging jet cooling and microchannel flow. Such experimental study has yielded fundamental understanding and practical design guidelines of these two microfluidic applications. Novel MEMS devices fabricated include temperature imagers, MEMS nozzles and nozzle arrays, and micro fluidic couplers. A technology for suspended microchannels with integrated polysilicon thermistors has been developed and used for microchannel flow study and flow-rate sensing. Theoretical models have been developed to analyze such micro thermal and fluidic phenomena. In the micro impinging jet cooling study, a MEMS-based heat transfer measurement paradigm has been successfully developed for the first time. This includes technology for MEMS device fabrication, an experimental setup well suited for microscale thermal study, and accurate and efficient data processing techniques. Sensing and heating are integrated into a single thermal imager chip, which allows temperature measurement over a large area at very high spatial resolution. The heat transfer data demonstrate the excellent promise of micro-impinging-jet heat transfer, and provide useful rules for designing impinging-jet-based micro heat exchangers for IC packages. In the investigation of micro channel flow, suspended microchannels with integrated thermistors have successfully been designed and fabricated to study the basic science of micro-scale channel flow. Considerable discrepancies between existing theory and experimental data have been observed, and an improved flow model that accounts for the effects of compressibility, boundary slip, fluid acceleration, non-parabolic fluid velocity profile and channel-wall bulging has been proposed to address such discrepancies. In addition, micro fluidic couplers have been designed and fabricated as the fluidic interface connection between micro fluidic systems and the external macro environment. The experiments show that MEMS couplers are capable of handling pressures as high as 1200 psig. Finally, this thesis presents the development of liquid flow sensors. Resolution of 0.4 nL/min and a capability of bubble detecting have been demonstrated. A numerical model is developed to understand device operation and to guide the design process. Excellent agreement has been found between numerical and experimental results

Development of MEMS Piezoelectric Vibration Energy Harvesters with Wafer-Level Integrated Tungsten Proof-Mass for Ultra Low Power Autonomous Wireless Sensors

La génération d’énergie localisée et à petite échelle, par transformation de l’énergie vibratoire disponible dans l’environnement, est une solution attrayante pour améliorer l’autonomie de certains noeuds de capteurs sans-fil pour l’Internet des objets (IoT). Grâce à des microdispositifs inertiels résonants piézoélectriques, il est possible de transformer l’énergie mécanique en électricité. Cette thèse présente une étude exhaustive de cette technologie et propose un procédé pour fabriquer des microgénérateurs MEMS offrant des performances surpassant l’état de l’art. On présente d’abord une revue complète des limites physiques et technologiques pour identifier le meilleur chemin d’amélioration. En évaluant les approches proposées dans la littérature (géométrie, architecture, matériaux, circuits, etc.), nous suggérons des métriques pour comparer l’état de l’art. Ces analyses démontrent que la limite fondamentale est l’énergie absorbée par le dispositif, car plusieurs des solutions existantes répondent déjà aux autres limites. Pour un générateur linéaire résonant, l’absorption d’énergie dépend donc des vibrations disponibles, mais aussi de la masse du dispositif et de son facteur de qualité. Pour orienter la conception de prototypes, nous avons réalisé une étude sur le potentiel des capteurs autonomes dans une automobile. Nous avons évalué une liste des capteurs présents sur un véhicule pour leur compatibilité avec cette technologie. Nos mesures de vibrations sur un véhicule en marche aux emplacements retenus révèlent que l’énergie disponible pour un dispositif linéaire résonant MEMS se situe entre 30 à 150 Hz. Celui-ci pourrait produire autour de 1 à 10 μW par gramme. Pour limiter la taille d’un générateur MEMS pouvant produire 10 μW, il faut une densité supérieure à celle du silicium, ce qui motive l’intégration du tungstène. L’effet du tungstène sur la sensibilité du dispositif est évident, mais nous démontrons également que l’usage de ce matériau permet de réduire l’impact de l’amortissement fluidique sur le facteur de qualité mécanique Qm. En fait, lorsque l’amortissement fluidique domine, ce changement peut améliorer Qm d’un ordre de grandeur, passant de 103 à 104 dans l’air ambiant. Par conséquent, le rendement du dispositif est amélioré sans utiliser un boîtier sous vide. Nous proposons ensuite un procédé de fabrication qui intègre au niveau de la tranche des masses de tungstène de 500 μm d’épais. Ce procédé utilise des approches de collage de tranches et de gravure humide du métal en deux étapes. Nous présentons chaque bloc de fabrication réalisé pour démontrer la faisabilité du procédé, lequel a permis de fabriquer plusieurs prototypes. Ces dispositifs ont été testés en laboratoire, certains démontrant des performances records en terme de densité de puissance normalisée. Notre meilleur design se démarque par une métrique de 2.5 mW-s-1/(mm3(m/s2)2), soit le meilleur résultat répertorié dans l’état de l’art. Avec un volume de 3.5 mm3, il opère à 552.7 Hz et produit 2.7 μW à 1.6 V RMS à partir d’une accélération de 1 m/s2. Ces résultats démontrent que l’intégration du tungstène dans les microgénérateurs MEMS est très avantageuse et permet de s’approcher davantage des requis des applications réelles.Small scale and localized power generation, using vibration energy harvesting, is considered as an attractive solution to enhance the autonomy of some wireless sensor nodes used in the Internet of Things (IoT). Conversion of the ambient mechanical energy into electricity is most often done through inertial resonant piezoelectric microdevices. This thesis presents an extensive study of this technology and proposes a process to fabricate MEMS microgenerators with record performances compared to the state of the art. We first present a complete review of the physical and technological limits of this technology to asses the best path of improvement. Reported approaches (geometries, architectures, materials, circuits) are evaluated and figures of merit are proposed to compare the state of the art. These analyses show that the fundamental limit is the absorbed energy, as most proposals to date partially address the other limits. The absorbed energy depends on the level of vibrations available, but also on the mass of the device and its quality factor for a linear resonant generator. To guide design of prototypes, we conducted a study on the potential of autonomous sensors in vehicles. A survey of sensors present on a car was realized to estimate their compatibility with energy harvesting technologies. Vibration measurements done on a running vehicle at relevant locations showed that the energy available for MEMS devices is mostly located in a frequency range of 30 to 150 Hz and could generate power in the range of 1-10 μW per gram from a linear resonator. To limit the size of a MEMS generator capable of producing 10 μW, a higher mass density compared to silicon is needed, which motivates the development of a process that incorporates tungsten. Although the effect of tungsten on the device sensitivity is well known, we also demonstrate that it reduces the impact of the fluidic damping on the mechanical quality factor Qm. If fluidic damping is dominant, switching to tungsten can improve Qm by an order of magnitude, going from 103 to 104 in ambient air. As a result, the device efficiency is improved despite the lack of a vacuum package. We then propose a fabrication process flow to integrate 500 μm thick tungsten masses at the wafer level. This process combines wafer bonding with a 2-step wet metal etching approach. We present each of the fabrication nodes realized to demonstrate the feasibility of the process, which led to the fabrication of several prototypes. These devices are tested in the lab, with some designs demonstrating record breaking performances in term of normalized power density. Our best design is noteworthy for its figure of merit that is around 2.5 mW-s-1/(mm3(m/s2)2), which is the best reported in the state of the art. With a volume of 3.5 mm3, it operates at 552.7 Hz and produces 2.7 μW at 1.6 V RMS from an acceleration of 1 m/s2. These results therefore show that tungsten integration in MEMS microgenerators is very advantageous, allowing to reduce the gap with needs of current applications

Thick film electronic ceramic sensors for civil structures health monitoring

Buildings, roads, bridges and structures in general suffer many kinds of damages due to overstress caused by settlements of foundations, high winds, dynamic forces, passing traffic, vibration and unexpected external loads beyond the safe design forces. The damages manifest itself by cracks, falling of plaster and render uneven roads and some time complete collapse. The cost of maintaining and fixing damages caused by the above is quite high for the building and construction industry. The same phenomenon is common to many other structures like airplanes, wind turbine and machinery in general.Structural Health Monitoring (SHM) is the engineering branch, which aims to give, at every moment during the life of a structure, a diagnosis of the "state" of the constituent materials, of the different parts of a structure. The state of the structure must remain in the domain specified in the design, although this can be altered due to usage or due to normal aging by the action of the environment, and by accidental events. By using special electronic sensors to monitor the unexpected high concentration of stresses or changes of these stresses throughout the life of the structure and pavement, reduces the cost of maintenance and repair. Historic buildings would also benefit from using such sensors to monitor the overstress in the old and frugally stones and bricks. The sensors can be embedded in the lime mortar joints and an electronic meter is used periodically to check for any unusual overstress during the life of the building.The main aim of the proposed research project is to investigate the possibility of using thick-film technology stress sensors in masonry, concrete and building materials in general to monitor overstress and instability throughout the life of the structures. The sensors could be used in brick, block, stone, and concrete and they could be mounted on the surface or embedded in the materials.There are many research studies on strain gauge devices in structural monitoring; Thick Film (TF) piezo-resistive sensors are proposed as a direct alternative to the widely used metal Foil Strain Gauges (FSG). Due to the low cost of TF sensors, their ease of use, suitability to integrate electronics on board, and to have different geometrical shapes, they could be deployed at different locations in a building, road or be distributed in arrays. This offers the continuous monitoring of stresses at any time by using a data logger on two points on the surface or by using wireless electronic transmission.In this research, new thick film screen-printed ceramic piezo-resistive sensor has been developed and characterized as discrete device for deployment on surface of a structure and embedded into the structure during building material curing or after structure erection. The sensor response on different building materials has been experimented and compared. Mechanical and electronic simulation tools were used to characterise the sensor and to choose an adequate interface electronic circuit.The experimental results of the simulated sensor and circuitry, showed the suitability of the sensor to be embedded in building materials during curing period and on erected structures. Materials used were wood, concrete, brick and plaster. In addition, the overall linearity of response of the sensors applied on building material surface was asserted which makes the technology a candidate for a more wide deployment in SHM field

First International Symposium on Strain Gauge Balances

The first International Symposium on Strain Gauge Balances was sponsored and held at NASA Langley Research Center during October 22-25, 1996. The symposium provided an open international forum for presentation, discussion, and exchange of technical information among wind tunnel test technique specialists and strain gauge balance designers. The Symposium also served to initiate organized professional activities among the participating and relevant international technical communities. Over 130 delegates from 15 countries were in attendance. The program opened with a panel discussion, followed by technical paper sessions, and guided tours of the National Transonic Facility (NTF) wind tunnel, a local commercial balance fabrication facility, and the LaRC balance calibration laboratory. The opening panel discussion addressed "Future Trends in Balance Development and Applications." Forty-six technical papers were presented in 11 technical sessions covering the following areas: calibration, automatic calibration, data reduction, facility reports, design, accuracy and uncertainty analysis, strain gauges, instrumentation, balance design, thermal effects, finite element analysis, applications, and special balances. At the conclusion of the Symposium, a steering committee representing most of the nations and several U.S. organizations attending the Symposium was established to initiate planning for a second international balance symposium, to be held in 1999 in the UK

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 05)

For abstract, see N75-13677

Nevada Test Site-Directed Research and Development, FY 2007 Report

The Nevada Test Site-Directed Research and Development (SDRD) program completed a very successful year of research and development activities in FY 2007. Twenty-nine new projects were selected for funding this year, and eight projects started in FY 2006 were brought to conclusion. The total funds expended by the SDRD program were $5.67 million, for an average per-project cost of$153 thousand. An external audit conducted in September 2007 verified that appropriate accounting practices were applied to the SDRD program. Highlights for the year included: programmatic adoption of 8 SDRD-developed technologies; the filing of 9 invention disclosures for innovation evolving from SDRD projects; participation in the tri-Lab Laboratory Directed Research and Development (LDRD) and SDRD Symposium that was broadly attended by Nevada Test Site (NTS), National Nuclear Security Administration (NNSA), LDRD, U.S. Department of Homeland Security (DHS), and U.S. Department of Defense (DoD) representatives; peer reviews of all FY 2007 projects; and the successful completion of 37 R&D projects, as presented in this report. In response to a company-wide call, authors throughout the NTS complex submitted 182 proposals for FY 2007 SDRD projects. The SDRD program has seen a dramatic increase in the yearly total of submitted proposals--from 69 in FY 2002 to 182 this year--while the number of projects funded has actually decreased from a program high of 57 in FY 2004. The overall effect of this trend has helped ensure an increasingly competitive program that benefited from a broader set of innovative ideas, making project selection both challenging and rewarding. Proposals were evaluated for technical merit, including such factors as innovation, probability of success, potential benefit, and mission applicability. Authors and reviewers benefited from the use of a shortfalls list entitled the 'NTS Technology Needs Assessment' that was compiled from NTS, National Weapons Laboratory (NWL), and NNSA sources. This tool continues to be of considerable value in aligning the SDRD program with mission priorities, and was expanded in FY 2007 to include technology development needs from the DHS and other agencies with missions closely aligned to that of the NTS