166 research outputs found

    MEMS Inertial Sensor to Measure the Gravity Gradient Torque in Orbit

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    Since the dawn of the Space Age, over six thousand satellites have been launched into Earth orbit. The function of determining the orientation of a satellite in orbit, so that it can point its antennas and instruments in the required direction is known as attitude determination. Depending on the nature of the mission, this important function is typically performed by means of optical instruments that determine the orientation of the satellite with respect to known bodies such as the Earth, the sun, and bright stars. Conventional Earth sensors use cameras and telescopes to locate the position of the Earth's horizon and hence to calculate the orientation of the satellite. In the event that a satellite starts to tumble, existing Earth sensors that use optical sensing are severely limited in their ability to reacquire the attitude due to the limited field of view of the instruments. Also, due to this limited field of view, multiple Earth sensor units need to be placed on all faces of the satellite to ensure 4π steradian coverage. Because of the optical sensing principle of existing Earth sensors, constraints are imposed on the positioning of solar panels and antennas so that they do not block the field of view of optical sensors. This thesis describes a novel inertial sensor that uses the Earth's gravity gradient as a reference for attitude determination on-board a satellite in low Earth orbit. Using the gravity gradient for attitude determination makes it possible to realise a single, compact Earth sensor instrument which can be positioned flexibly within the satellite. Due to its 4π steradian field of view, such an instrument can offer added capability as a backup sensor, or act as the main Earth sensor. By using Micro-Electro-Mechanical System (MEMS) technology for the inertial sensor, a target mass of 1 kg and target volume of 1 dm3 can be realised for the entire gravity gradient Earth sensor system. The gravitational force decreases as the square of the distance from the center of the Earth. An elongated object in orbit around the Earth will have slightly different values of gravity acting over the different points in its volume. This gives rise to a small torque, the Gravity Gradient Torque (GGT), on the object. A compact micromachined inertial sensor was designed with an elongated proof mass and compliant spring to measure the GGT, so that the orientation of the proof mass with respect to the normal from the Earth's surface can be determined. Such a sensor on-board a satellite can act as an Earth sensor, and provide information about the satellite attitude with respect to the normal to the Earth's surface. An inertial sensor to measure GGT, which with readout electronics fits within a 1 dm3 volume, has to measure a torque of magnitude 10-15 N.m. Currently, no inertial sensor is capable of such a fine measurement. In addition to the required performance in microgravity, the inertial sensor must be robust enough to be tested on Earth with no special handling, and must survive the vibration and shock of a launch, to be used in space. The readout scheme to measure the displacement due to GGT must also be simple and robust. The designs of two generations of a novel inertial sensor to measure the GGT are presented in the thesis. To be able to measure the GGT with the required accuracy a sensor is designed that has a proof mass 5 cm long, suspended by springs which have widths less than ten microns. The sensor resonant frequency of the inertial sensor is on the order of 1 Hz. A new fabrication process is developed for the sensor, which incorporates hard stops to limit the motion of the proof mass along all the axes, thus making it robust enough for testing without any special precautions. The sensor survives low magnitude vibration tests. A digital electronic readout based on capacitive sensing of the displacement due to GGT, is developed based on commercially available ICs, and allows easy interfacing of the inertial sensor output to a PC or microcontroller. To test the sensor on Earth, a dedicated test setup is developed to replicate the nm-scale motion of the proof mass expected in orbit. The electronic readout is capable of measuring the sub-nm displacements due to GGT. The 2nd generation sensor design with capacitive displacement sensing is the first demonstration of an inertial sensor capable of measuring the GGT in low Earth orbit, and an important step towards realization of a 1 kg, 1 dm3 Earth sensor that uses the gravity gradient of the Earth for attitude determination

    MME2010 21st Micromechanics and Micro systems Europe Workshop : Abstracts

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    A microgripper for single cell manipulation

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    This thesis presents the development of an electrothermally actuated microgripper for the manipulation of cells and other biological particles. The microgripper has been fabricated using a combination of surface and bulk micromachining techniques in a three mask process. All of the fabrication details have been chosen to enable a tri-layer, polymer (SU8) - metal (Au) - polymer (SU8), membrane to be released from the substrate stress free and without the need for sacrificial layers. An actuator design, which completely eliminates the parasitic resistance of the cold arm, is presented. When compared to standard U-shaped actuators, it improves the thermal efficiency threefold. This enables larger displacements at lower voltages and temperatures. The microgripper is demonstrated in three different configurations: normally open mode, normally closed mode, and normally open/closed mode. It has-been modelled using two coupled analytical models - electrothermal and thermomechanical - which have been custom developed for this application. Unlike previously reported models, the electrothermal model presented here includes the heat exchange between hot and cold arms of the actuators that are separated by a small air gap. A detailed electrothermomechanical characterisation of selected devices has permitted the validation of the models (also performed using finite element analysis) and the assessment of device performance. The device testing includes electrical, deflection, and temperature measurements using infrared (IR) thermography, its use in polymeric actuators reported here for the first time. Successful manipulation experiments have been conducted in both air and liquid environments. Manipulation of live cells (mice oocytes) in a standard biomanipulation station has validated the microgripper as a complementary and unique tool for the single cell experiments that are to be conducted by future generations of biologists in the areas of human reproduction and stem cell research

    Towards new hermeticity test methods for MEMS

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    Hermeticity is a measure of how well a package can maintain its intended ambient cavity environment over the device lifetime. Since many Micro-Electro-Mechanical Systems (MEMS) sensors, actuators and microelectronic devices require a known cavity environment for optimum operational performance, it is important to know the leak rate of the package for lifetime prediction purposes. In this field, limitations in the traditional leak detection methods and standards used originally for integrated circuits and semiconductors have been blindly and often incorrectly applied to MEMS and microelectronic packages. The aim of this project is to define accurately the limitations of the existing hermeticity test methods and standards when applied to low cavity volume MEMS and microelectronic packages and to demonstrate novel test methods, which are applicable to such packages. For the first time, the use of the Lambert-W function has been demonstrated to provide a closed form expression of the maximum true leak rate achievable for the most commonly used existing hermeticity test method, the helium fine leak test. This expression along with the minimum detectable leak rate expression is shown to provide practical guidelines for the accurate testing of hermeticity for ultra-low volume packages. The three leak types which MEMS and microelectronic packages are subject to: molecular leaks, permeation and outgassing, are explained in detail and it is found that the helium leak test is capable of quantifying only molecular leak in packages with cavity volumes exceeding 2.6 mm3. With many MEMS and microelectronic package containing cavities with lower volumes, new hermeticity test methods are required to fill this gap and to measure the increasingly lower leak rates which adversely affect such packages. Fourier Transform Infra-Red (FTIR) spectroscopy and Raman spectroscopy are investigated as methods of detecting gas pressure within MEMS and microelectronics packages. Measured over time, FTIR can be used to determine the molecular and permeation leak rates of packages containing infra-red transparent cap materials. Future work is required to achieve an adequate signal to noise ratio to enable Raman spectroscopy to be a quantitative method to determine molecular leaks, permeation leaks and potentially outgassing. The design, fabrication and calibration procedure for three in-situ test structures intended to monitor the hermeticity of packages electrically are also presented. The calibration results of a piezoresistive cap deflection test structure show the structure can be used to detect leak ii rates of any type down to 6.94×10-12 atm.cm3.s-1. A portfolio of hermeticity test methods is also presented outlining the limitations and advantages of each method. This portfolio is intended to be a living document and should be updated as new research is undertaken and new test methods developed

    Morphing wing : experimental boundary layer transition determination and wing vibrations measurements and analysis

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    This Master’s thesis is written within the framework of the multidisciplinary international research project CRIAQ MDO-505. This global project consists of the design, manufacture and testing of a morphing wing box capable of changing the shape of the flexible upper skin of a wing using an actuator system installed inside the wing. This changing of the shape generates a delay in the occurrence of the laminar to turbulent transition area, which results in an improvement of the aerodynamic performances of the morphed wing. This thesis is focused on the technologies used to gather the pressure data during the Wind tunnel tests, as well as on the post-processing methodologies used to characterize the wing airflow. The vibration measurements of the wing and their real-time graphical representation are also presented. The vibration data acquisition system is detailed, and the vibration data analysis confirms the predictions of the flutter analysis performed on the wing prior to Wind tunnel testing at the IAR-NRC. The pressure data was collected using 32 highly-sensitive piezoelectric sensors for sensing the pressure fluctuations up to 10 KHz. These sensors were installed along two wing chords, and were further connected to a National Instrument PXI real-time acquisition system. The acquired pressure data was high-pass filtered, analyzed and visualized using Fast Fourier Transform (FFT) and Standard Deviation (SD) approaches to quantify the pressure fluctuations in the wing airflow, as these allow the detection of the laminar to turbulent transition area. Around 30% of the cases tested in the IAR-NRC wind tunnel were optimized for drag reduction by the morphing wing procedure. The obtained pressure measurements results were compared with results obtained by infrared thermography visualization, and were used to validate the numerical simulations. Two analog accelerometers able to sense dynamic accelerations up to ±16g were installed in both the wing and the aileron boxes to obtain the vibration sensing measurements. The measured accelerations were acquired by an NI real-time acquisition system using LABVIEW software for a real-time graphical visualization. The recorded data were then analyzed and the analysis indicated that no aeroelastic phenomenon occurred on the model during the wind tunnel tests, at speeds of 50 m/s and 80m/s

    Real-Time Biosensing and Energy Harvesting on Human Body

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    This thesis covers two technologies that can be applied to the human body for real-time applicable usages: biosensors and energy harvesters. The first part of the thesis describes optical biosensing techniques based on surface-enhanced Raman spectroscopy (SERS). Our large-scale spatially uniform Raman enhancing substrates allow low-level bio molecule detection due to their strong plasmonic enhancement of the 3D Au-NP clusters. This method also enables low-level insulin sensing as well as insulin concentration analysis in islet secretion. These results can lead to developing simple and easy biosensing methods allowing real-time biosensing applications including convenient monitoring of health, early disease detection, and diabetes-related clinical measurements. The second part of the thesis suggests an energy harvesting method using vocal vibrations. The vocal folds produce mechanical vibrations that can serve as an energy source with consistent amplitude and frequency. The vibration hotspots exist at various locations on the human upper body. The energy harvesting system consisting of piezoelectric devices and energy harvesting circuits generates 3.99 mW of electrical power. The amount of energy generated from vocal vibrations is sufficient to charge a Li-Po battery which can drive an LCD display or charge Bluetooth headphones. This method demonstrating a relatively high power generation and convenience of practical use can provide a real-time complementary charging technique for wearable electronics like wireless headphones and smart glasses as well as medical implantable devices such as deep brain stimulators, cochlear implants and pacemakers.</p

    Single-Chip Scanning Probe Microscopes

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    Scanning probe microscopes (SPMs) are the highest resolution imaging instruments available today and are among the most important tools in nanoscience. Conventional SPMs suffer from several drawbacks owing to their large and bulky construction and to the use of piezoelectric materials. Large scanners have low resonant frequencies that limit their achievable imaging bandwidth and render them susceptible to disturbance from ambient vibrations. Array approaches have been used to alleviate the bandwidth bottleneck; however as arrays are scaled upwards, the scanning speed must decline to accommodate larger payloads. In addition, the long mechanical path from the tip to the sample contributes thermal drift. Furthermore, intrinsic properties of piezoelectric materials result in creep and hysteresis, which contribute to image distortion. The tip-sample interaction signals are often measured with optical configurations that require large free-space paths, are cumbersome to align, and add to the high cost of state-of-the-art SPM systems. These shortcomings have stifled the widespread adoption of SPMs by the nanometrology community. Tiny, inexpensive, fast, stable and independent SPMs that do not incur bandwidth penalties upon array scaling would therefore be most welcome. The present research demonstrates, for the first time, that all of the mechanical and electrical components that are required for the SPM to capture an image can be scaled and integrated onto a single CMOS chip. Principles of microsystem design are applied to produce single-chip instruments that acquire images of underlying samples on their own, without the need for off-chip scanners or sensors. Furthermore, it is shown that the instruments enjoy a multitude of performance benefits that stem from CMOS-MEMS integration and volumetric scaling of scanners by a factor of 1 million. This dissertation details the design, fabrication and imaging results of the first single-chip contact-mode AFMs, with integrated piezoresistive strain sensing cantilevers and scanning in three degrees-of-freedom (DOFs). Static AFMs and quasi-static AFMs are both reported. This work also includes the development, fabrication and imaging results of the first single-chip dynamic AFMs, with integrated flexural resonant cantilevers and 3 DOF scanning. Single-chip Amplitude Modulation AFMs (AM-AFMs) and Frequency Modulation AFMs (FM-AFMs) are both shown to be capable of imaging samples without the need for any off-chip sensors or actuators. A method to increase the quality factor (Q-factor) of flexural resonators is introduced. The method relies on an internal energy pumping mechanism that is based on the interplay between electrical, mechanical, and thermal effects. To the best of the author’s knowledge, the devices that are designed to harness these effects possess the highest electromechanical Qs reported for flexural resonators operating in air; electrically measured Q is enhanced from ~50 to ~50,000 in one exemplary device. A physical explanation for the underlying mechanism is proposed. The design, fabrication, imaging, and tip-based lithographic patterning with the first single-chip Scanning Thermal Microscopes (SThMs) are also presented. In addition to 3 DOF scanning, these devices possess integrated, thermally isolated temperature sensors to detect heat transfer in the tip-sample region. Imaging is reported with thermocouple-based devices and patterning is reported with resistive heater/sensors. An “isothermal electrothermal scanner” is designed and fabricated, and a method to operate it is detailed. The mechanism, based on electrothermal actuation, maintains a constant temperature in a central location while positioning a payload over a range of >35μm, thereby suppressing the deleterious thermal crosstalk effects that have thus far plagued thermally actuated devices with integrated sensors. In the thesis, models are developed to guide the design of single-chip SPMs and to provide an interpretation of experimental results. The modelling efforts include lumped element model development for each component of single-chip SPMs in the electrical, thermal and mechanical domains. In addition, noise models are developed for various components of the instruments, including temperature-based position sensors, piezoresistive cantilevers, and digitally controlled positioning devices

    Development and evaluation of a calibration free exhaustive coulometric detection system for remote sensing.

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    Most quantitative analytical measurement techniques require calibration to correlate signal with the quantity of analyte. The purpose of this study was to employ exhaustive coulometry, an implementation of coulometric analysis in a stopped-flow, fixed-volume, thin-layer cell, to attain calibration-free measurements that would directly benefit intervention-free analysis systems designed for remote deployment. This technique capitalizes on the short diffusion lengths (\u3c 100 µm) to dramatically reduce the time for analysis (\u3c 30 sec). For this work, a thin-layer fluidic cell was designed in software, fabricated via CNC machining, and evaluated using Ferri/Ferrocyanide {Fe(CN)63-/4-} as a model analyte. The 2 µL fixed volume incorporated an oval, 8mm by 4 mm, thin-film gold electrode sensor with an integrated Ag|AgCl pseudo-reference electrode. The flow cell area matched the shape of the sensor, with a volume set by the thickness of a laser-cut silicone rubber gasket (~80 µm). A semi-permeable membrane isolated the working electrode and counter electrode chambers to prevent analyte diffusion. A miniaturized custom potentiostat was designed and built to measure reaction currents ranging from 10 mA to 0.1 nA. Software was developed to perform step voltammetry as well as cyclic voltammetry analysis for verifying electrode condition and optimal redox potential levels. Experimentally determined oxidation/reduction potentials of -100 mV and 400 mV, respectively, were applied to the working electrode for sample concentrations ranging from 50 µM to 10,000 µM. The current generated during the reactions was recorded and the total charge captured at each concentration was obtained by integrating the amperograms. When compared to the expected charge for a 2 µL sample, the total charge vs. concentration plots displayed a near perfect linearity over the full concentration range, and the expected charge (100 % converted) was reached within 20 seconds. The reaction currents ideally should have decayed to background levels, but exhibited constant offset values slightly larger than the background signal, a phenomenon assumed to be lingering residual flow from sample injection. After adding rigid tubing and external valves, the thin-layer cell was shown to remain within 6% of the theoretical charge after 200 seconds. Continued development of this system will offer the possibility of remote, calibration-free determinations of real-world analytes such mercury and lead

    Power-Scavenging MEMS Robots

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    This thesis includes the design, modeling, and testing of novel, power-scavenging, biologically inspired MEMS microrobots. Over one hundred 500-μm and 990-μm microrobots with two, four, and eight wings were designed, fabricated, characterized. These microrobots constitute the smallest documented attempt at powered flight. Each microrobot wing is comprised of downward-deflecting, laser-powered thermal actuators made of gold and polysilicon; the microrobots were fabricated in PolyMUMPs® (Polysilicon Multi-User MEMS Processes). Characterization results of the microrobots illustrate how wing-tip deflection can be maximized by optimizing the gold-topolysilicon ratio as well as the dimensions of the actuator-wings. From these results, an optimum actuator-wing configuration was identified. It also was determined that the actuator-wing configuration with maximum deflection and surface area yet minimum mass had the greatest lift-to-weight ratio. Powered testing results showed that the microrobots successfully scavenged power from a remote 660-nm laser. These microrobots also demonstrated rapid downward flapping, but none achieved flight. The results show that the microrobots were too heavy and lacked sufficient wing surface area. It was determined that a successfully flying microrobot can be achieved by adding a robust, light-weight material to the optimum actuator-wing configuration—similar to insect wings. The ultimate objective of the flying microrobot project is an autonomous, fully maneuverable flying microrobot that is capable of sensing and acting upon a target. Such a microrobot would be capable of precise lethality, accurate battle-damage assessment, and successful penetration of otherwise inaccessible targets

    Micro-manufactured Rogowski coils for fault detection of aircraft electrical wiring and interconnect systems (EWIS)

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    Aircraft wiring failures have increased over the last few years resulting in arc faults and high-energy flashover on the wiring bundle, which can propagate down through aircraft Electrical Wiring and Interconnect Systems (EWIS). It is considered cost prohibitive to completely rewire a plane in terms of man hours and operational time lost to do this, and most faults are only detectable whilst the aircraft is in flight. Temperature, humidity and vibration all accelerate ageing and failure effects on EWIS. This research investigates methods of in-situ non-invasive testing of aircraft wiring during fight. Failure Mode Effects and Analysis (FMEA) was performed on legacy aircraft EWIS using data obtained from RAF Brize Norton. Micro-Electro-mechanical- Systems (MEMS) were evaluated for use in a wire monitoring system that measures the environmental parameters responsible for ageing and failure of EWIS. Such MEMS can be developed into a Health and Usage Monitoring MicroSystem (HUMMS) by incorporating advanced signal processing and prognostic software. Current and humidity sensors were chosen for further investigation in this thesis. These sensors can be positioned inside and outside cable connectors of EWIS so that arc faults can be reliably detected and located. This thesis presents the design, manufacture and test of micro-manufactured Rogowski sensors. The manufactured sensors were benchmarked against commercial high frequency current transformers (HFCT), as these devices can also detect high frequency current signature due to wire insulation failure. Results indicate that these sensors possess superior voltage output compared to the HFCT. The design, manufacture and test of a polymer capacitive humidity sensor is also presented. Two different types of polymer were reviewed as part of the evaluation. A feature of the sensor design is recovery from exposure to chemicals found on wiring bundles. Current and humidity sensors were demonstrated to be suitable for integrating onto a common substrate with accelerometers, temperature sensors and pressure sensors for health monitoring and prognostics of aircraft EWIS
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