MEMS accelerometer: proof of concept for geotechnical engineering testing

Geotechnical engineering materials are inherently variable, which leads to many simplifications when trying to model their behavior. The materials must always be characterized prior to any design work so that the engineer knows which direction he must progress to have a reliable design. Although subsurface characterization techniques and geotechnical design steadily improve, they are by no means infallible. The combination of geotechnical subsurface characterization along with geophysical techniques for improved design and construction monitoring has begun to surface as a viable alternative to the standard techniques in geotechnical engineering. This is important because there is a lack of Quality Control/Quality Assurance during the construction stage of a project, which further compounds the problems inherent from the complexity of the subsurface. Geophysical techniques based on elastic wave propagation provide an excellent combination of characterization and monitoring for the observation of geotechnical engineering projects. Elastic wave propagation provides coverage between traditional boreholes and it helps infer changes in the state of stresses. Unfortunately, sensors for this type of monitoring have typically been expensive, and the use of elastic wave propagation for characterization and monitoring has just begun to become to be implemented. The application of elastic wave tomography needs an inexpensive set of sensors to help justify its inclusion in the broad area of construction monitoring and characterization systems. This set of inexpensive sensors has arrived on the market developed from Miniature Electro-Mechanical Systems (MEMs) technology. This research developed the Analog Devices’ ADXL250 MEMS accelerometer to determine its limitations and its range of applications. In addition, a packaging system developed to allow for a broader range of applications in geotechnical engineering. Once the sensor was fully calibrated, a long-term goal for the research was to utilize the instrument in a laboratory experiment to obtain a tomographic image of the state of stress within a model. While the sensor was utilized in a model in this study, the final reasoning for its use within the model was simply to show its capabilities and areas of application. Simple velocity distributions are given as well as inferences made about the driving factors for these behaviors

Inertial MEMS: readout, test and application

This thesis moves towards the investigation of Micro Electro-Mechanical Systems (MEMS) intertial sensors from different perspectives and points of view: readout, test and application. Chapter 1 deals with the state-of-the-art for the interfaces usually employed for 3- axes micromachined gyroscopes. Several architecture based on multiplexing schemes in order to extremely simplify the analog front-end which can be based on a single charge amplifier are analysed and compared. A novel solution that experiments an innovative readout technique based on a special analog-Code Division Multiplexing Access (CDMA) is presented; this architecture can reach a considerable reduction of the Analog Front-End (AFE) with reference to other multiplexing schemes. Many family codes have been considered in order to find the best trade-off between performance and complexity. System-level simulations prove the effectiveness of this technique in processing all the required signals. A case study is also analysed: a comparison with the SD740 micro-machined integrated inertial module with tri-axial gyroscope by SensorDynamics AG is provided. MEMS accelerometers are widely used in the automotive and aeronautics fields and are becoming extremely popular in a wide range of consumer electronics products. The cost of testing is a major one within the manufacturing process, because MEMS accelerometer characterization requires a series of tests that include physical stimuli. The calibration and the functional testing are the most challenging and a wide selection of Automatic Test Equipments (ATEs) is available on the market for this purpose; those equipments provide a full characterization of the Device Under Test (DUT), from low-g to high-g levels, even over temperature. Chapter 2 presents a novel solution that experiments an innovative procedure to perform a characterization at medium-g levels. The presented approach can be applied to low-cost ATEs obtaining challenging results. The procedure is deeply investigated and an experimental setup is described. A case study is also analysed: some already trimmed Three Degrees of Freedom (3DoF)-Inertial Measurement Unit (IMU) modules (three-axes accelerometer integrated with a mixed signal ASIC), from SensorDynamics AG are tested with the experimental setup and analysed, for the first time, at medium-g levels. Standard preprocessing techniques for removing the ground response from vehicle- mounted Ground Penetrating Radar (GPR) data may fail when used on rough terrain. In Chapter 3, a Laser Imaging Detection and Ranging (LIDAR) system and a Global Positioning System (GPS)/IMU is integrated into a prototype system with the GPR and provided high-resolution measurements of the ground surface. Two modifications to preprocessing were proposed for mitigating the ground bounce based on the available LIDAR data. An experiment is carried out on a set of GPR/LIDAR data collected with the integrated prototype vehicle over lanes with artificially rough terrain, consisting of targets buried under or near mounds, ruts and potholes. A stabilization technique for multi-element vehicle-mounted GPR is also presented

National MEMS Technology Roadmap - Markets, Applications and Devices

MEMS teknologiaa on jo pitkään käytetty lukuisien eri laitteiden valmistamiseen. Osa näistä laitteista on ollut markkinoilla jo useita vuosia, kun taas osa on vasta kehitysvaiheessa. Jotta tutkimus ja kehitystyötä osattaisiin jatkossa kohdistaa oikeille painopistealueille, on tärkeää tietää mihin suuntaan kehitys on menossa. Tämä työ on osa kansallista MEMS teknologioiden tiekartta -projektia ja sen tavoitteena oli selvittää MEMS laitteiden kehityksen suuntaa. Työ toteutettiin laajana kirjallisuustutkimuksena. Lisäksi tulosten tueksi haastateltiin asiantuntijoita Suomen MEMS teollisuudesta. Työssä tarkasteltiin lukuisia jo markkinoilta löytyviä ja vasta kehitteillä olevia MEMS laitteita ja analysoitiin niitä sekä teknisestä että kaupallisesta näkökulmasta. Tutkimuksen perusteella kävi ilmi, että MEMS markkinat ovat pitkään muodostuneet vakiintuneista laitteista kuten mustesuihkupäistä, kiihtyvyysantureista, paineantureista sekä RF suotimista. Lisäksi mikrofonit, gyroskoopit ja optiset laitteet ovat olleet kaupallisesti saatavilla jo pitkään. Markkinat ovat hiljattain alkaneet tehdä tilaa myös uusille MEMS laitteille, joita tulee ulos nopeaa vauhtia. Viimeisimpänä markkinoille tulleita laitteita ovat erilaiset mikrofluidistiikka laitteet, mikrobolometrit sekä yhdistelmäanturit. Pian kaupallisesti saatavia laitteita ovat magnetometrit, automaattitarkennuslaitteet sekä MEMS oskillaattorit. Näiden laitteiden lisäksi kehitteillä on monia uusia MEMS laitteita, jotka saattavat tarjota merkittäviä mahdollisuuksia tulevaisuudessa. Kehitteillä olevia laitteita ovat erilaiset lääketieteelliset laitteet, atomikellot, mikrojäähdyttimet, mikrokaiuttimet, energiantuottolaitteet sekä RFID-laitteet. Kaikki kehitteillä olevista laitteista eivät välttämättä tule menestymään kaupallisesti, mutta jatkuva tutkimustyö osoittaa, että monilla MEMS laitteilla on potentiaalia useissa eri sovelluksissa. Markkinanäkökulmasta tarkasteltuna suurin potentiaali piilee kuluttajaelektroniikka markkinoilla. Muita tulevaisuuden kannalta potentiaalisia markkinoita ovat lääketieteelliset ja teollisuusmarkkinat. Tutkimus osoitti että MEMS laitteiden tutkimukseen ja kehitykseen liittyy monia potentiaalisia painopistealueita tulevaisuudessa. Käyttömahdollisuuksien parantamiseksi monet jo vakiintuneet laitteet kaipaavat vielä parannuksia. Toisaalta, jo olemassa olevia laitteita voidaan hyödyntää uusissa sovelluksissa. Lisäksi monet uusista ja kehitteillä olevista MEMS laitteista vaativat vielä kehitystyötä.MEMS technology has long been applied to the fabrication of various devices from which some have already been in use for several years, whereas others are still under development. In order to find future focus areas in research and development activities in the industry, it is important to know where the development is going. This thesis was conducted as a part of National MEMS technology roadmap, and it aimed for determining the evolution of MEMS devices. The work was conducted as an extensive literature review. In addition, experts from the Finnish MEMS industry were interviewed in order obtain a broader insight to the results. In this thesis various existing and emerging MEMS devices were reviewed and analyzed from technological and commercial perspectives. The study showed that the MEMS market has long been composed of established devices, such as inkjet print-heads, pressure sensors, accelerometers and RF filters. Also gyroscopes, microphones and optical MEMS devices have already been on the market for a long time. Lately, many new devices have started to find their place in the markets. The most recently introduced commercial devices include microfluidic devices, micro bolometers, and combo sensors. There are also a few devices including magnetometers, MEMS oscillators, and auto-focus devices that are currently crossing the gap from R&D to commercialization. In addition to the already available devices, many new MEMS devices are under development, and might offer significant opportunities in the future. These emerging devices include various bioMEMS devices, atomic clocks, micro-coolers, micro speakers, power MEMS devices, and RFID devices. All of the emerging devices might not find commercial success, but the constant stream shows, that there are numerous applications, where MEMS devices could be applied in. From a market point of view, the greatest potential in the future lies in consumer electronics market. Other highly potential markets include medical and industrial markets. The results of the thesis indicate that there are many potential focus areas in the future related to MEMS devices, including improvements of the existing devices in order to gain better utilization, application of the existing devices in new areas, and development work among the emerging devices

Design of electronic systems for automotive sensor conditioning

This thesis deals with the development of sensor systems for automotive, mainly targeting the exploitation of the new generation of Micro Electro-Mechanical Sensors (MEMS), which achieve a dramatic reduction of area and power consumption but at the same time require more complexity in the sensor conditioning interface. Several issues concerning the development of automotive ASICs are presented, together with an overview of automotive electronics market and its main sensor applications. The state of the art for sensor interfaces design (the generic sensor interface concept), consists in sharing the same electronics among similar sensor applications, thus saving cost and time-to-market but also implementing a sub-optimal system with area and power overheads. A Platform Based Design methodology is proposed to overcome the limitations of generic sensor interfaces, by keeping the platform generality at the highest design layers and pursuing the maximum optimization and performances in the platform customization for a specific sensor. A complete design flow is presented (up to the ASIC implementation for gyro sensor conditioning), together with examples regarding IP development for reuse and low power optimization of third party designs. A further evolution of Platform Based Design has been achieved by means of implementation into silicon of the ISIF (Intelligent Sensor InterFace) platform. ISIF is a highly programmable mixed-signal chip which allows a substantial reduction of design space exploration time, as it can implement in a short time a wide class of sensor conditioning architectures. Thus it lets the designers evaluate directly on silicon the impact of different architectural choices, as well as perform feasibility studies, sensor evaluations and accurate estimation of the resulting dedicated ASIC performances. Several case studies regarding fast prototyping possibilities with ISIF are presented: a magneto-resistive position sensor, a biosensor (which produces pA currents in presence of surface chemical reactions) and two capacitive inertial sensors, a gyro and a low-g YZ accelerometer. The accelerometer interface has also been implemented in miniboards of about 3 cm2 (with ISIF and sensor dies bonded together) and a series of automatic trimming and characterization procedures have been developed in order to evaluate sensor and interface behaviour over the automotive temperature range, providing a valuable feedback for the implementation of a dedicated accelerometer interface

Microsystems technology: objectives

This contribution focuses on the objectives of microsystems technology (MST). The reason for this is two fold. First of all, it should explain what MST actually is. This question is often posed and a simple answer is lacking, as a consequence of the diversity of subjects that are perceived as MST. The second reason is that a map of the somewhat chaotic field of MST is needed to identify sub-territories, for which standardization in terms of system modules an interconnections is feasible. To define the objectives a pragmatic approach has been followed. From the literature a selection of topics has been chosen and collected that are perceived as belonging to the field of MST by a large community of workers in the field (more than 250 references). In this way an overview has been created with `applications¿ and `generic issues¿ as the main characteristics

Advanced Integration of GNSS and External Sensors for Autonomous Mobility Applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

Fabrication of a MEMS micromirror based on bulk silicon micromachining combined with grayscale lithography

A 1D MEMS (Micro-Electro-Mechanical Systems) mirror for LiDAR applications, based on vertically asymmetric comb-drive electrostatic actuators, is presented in this work employing a novel fabrication process. This novel micromachining process combines typical SOI-based bulk micromachining and grayscale lithography, enabling the fabrication of combs actuators with asymmetric heights using a single lithography step in the active layer. With this technique, the fabrication process is simplified, and the overall costs are reduced since the number of required lithography steps decrease. The fabricated mirrors present self-aligned electrodes with a 2.8 mu m gap and asymmetric heights of the movable and the fixed electrodes of 20 mu m and 50 mu m, respectively. These asymmetric actuators are an essential feature for the operation mode of this device, enabling both in resonant and static mode operation. A mirror field of view (FOV) of 54 degrees at 838 Hz was achieved under low-pressure, when resonantly operated, and a FOV of 0.8 degrees in the static mode.This work was supported by the European Structural and Investment Funds in the FEDER Component through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) under Project 037902 (POCI-01-0247-FEDER-037902). The work of Carlos Ferreira was supported by the Fundacao para a Ciencia e Tecnologia (FCT) under Grant PD/BDE/135102/2017. Subject Editor M. Rais-Zadeh

Structural health monitoring of offshore wind turbines: A review through the Statistical Pattern Recognition Paradigm

Offshore Wind has become the most profitable renewable energy source due to the remarkable development it has experienced in Europe over the last decade. In this paper, a review of Structural Health Monitoring Systems (SHMS) for offshore wind turbines (OWT) has been carried out considering the topic as a Statistical Pattern Recognition problem. Therefore, each one of the stages of this paradigm has been reviewed focusing on OWT application. These stages are: Operational Evaluation; Data Acquisition, Normalization and Cleansing; Feature Extraction and Information Condensation; and Statistical Model Development. It is expected that optimizing each stage, SHMS can contribute to the development of efficient Condition-Based Maintenance Strategies. Optimizing this strategy will help reduce labor costs of OWTs׳ inspection, avoid unnecessary maintenance, identify design weaknesses before failure, improve the availability of power production while preventing wind turbines׳ overloading, therefore, maximizing the investments׳ return. In the forthcoming years, a growing interest in SHM technologies for OWT is expected, enhancing the potential of offshore wind farm deployments further offshore. Increasing efficiency in operational management will contribute towards achieving UK׳s 2020 and 2050 targets, through ultimately reducing the Levelised Cost of Energy (LCOE)

Micro-g MEMS accelerometer based on time measurement

Programa Doutoral em Engenharia Electrónica e de ComputadoresThe MEMS sensor market has experienced an amazing growth on the last decades, with accelerometers being one of the pioneers pushing the technology into widespread use with its applications on automotive industry. Since then, accelerometers have been gradually replacing conventional sensors due mainly to its lower cost. As the performance of MEMS accelerometers improves, the applications range where they replace conventional accelerometers increases. Nowadays, there is still a large range of applications for which suitable MEMS accelerometers are yet to be developed. This work focuses on the development of a high performance accelerometer taking advantage of the high sensitivity of a non-linear phenomenon that occurs in electrostatically actuated movable capacitive microdevices: electrostatic pull-in. Although the pull-in effect has been known for more than 40 years, it is usually avoided when dealing with movable microstructures as it leads to a region of instability, where the position of movable parts cannot be fully controlled. In the last decade, the pull-in displacement profile of 1-DOF parallel-plates devices has been the subject of research that revealed the presence of a so-called meta-stability. This meta-stability occurs in specific damping and voltage actuation conditions and translates as a non-linear displacement profile, rather than simple time-of-flight. This feature makes the pull-in time duration significantly longer, and it happens to be extremely sensitive to intervenient forces, such as external acceleration. Basically, measuring the pull-in time of specifically designed microstructures (while maintaining the other parameters constant) allows the measurement of the external acceleration that acts on the system. Using a pull-in time measurement rather than direct capacitance/displacement/acceleration transduction presents several advantages. The most important is the fact that time can be measured very accurately with technology readily available. For instance, if one uses a 100MHz clock on the time counting mechanism, which corresponds to a time measurement resolution of 100 ns, given the 0.26 μs/μg sensitivity of the accelerometer developed in this work, an acceleration resolution of 0.38 μg could be achieved. One of the main challenges of the time based accelerometer development is the damper design, as damping is of outmost importance in defining the accelerometer performance parameters, namely sensitivity and noise. A new squeeze-film damper geometry design has been presented and studied. It consists of flow channels implemented on the parallel-plates that relieve the squeeze-film damping pressures generated when the device is moving. This geometry has proved to be very effective in increasing the capacitance/damping ratio in parallel-plates, which was up to now a great challenge of in-plane parallel-plates design. This work reports the development of an open-loop accelerometer with 0.26 μs/μg sensitivity and 2.7 μg /√Hz noise performance. The MEMS structures used for its experimental implementation were fabricated using a commercially available SOI micromachining process. The main drawbacks of this accelerometer were the low system bandwidth and non-linearity. Closed-loop approaches using electrostatic feedback were explored in this work in order to overcome these limitations, and the dynamic range was successfully extended to 109 dB along with improvements on the linearity. From the thorough damping study performed in this work, a new application for the pullin time using the same microstructures was developed. It consists of a gas viscosity sensing application. At the low frequencies operated, damping is directly proportional to the viscosity of the gas medium. The experimental results obtained with gases with viscosities ranging from 8 μP to 18 μP have shown a sensitivity of 2 ms/μP, making the pull-in time viscosity sensor a very promising approach.Nas últimas décadas assistiu-se a um imenso crescimento no mercado de sensors MEMS, tendo os acelerómetros sido uma das maiores forças impulsionadoras desse crescimento devido às suas aplicações na indústria automóvel. Desde então, a gama de aplicações destes sensores expandiu-se multidirecionalmente, novas aplicações emergiram e acelerómetros convencionais em aplicações já existentes foram substituídos por acelerómetros MEMS. Isto deve-se essencialmente ao seu baixo custo e pequenas dimensões. Há no entanto, aplicações para as quais o desempenho dos acelerómetros MEMS ainda não é suficiente. O objectivo deste trabalho é desenvolver um acelerómetro de elevado desempenho tirando partido da elevada sensibilidade do efeito de pull-in a forças externas tais como a aceleração. O efeito de pull-in, descrito pela primeira vez há mais de 40 anos, ocorre em dispositivos capacitivos com partes móveis. Este é um efeito não-linear geralmente evitado/indesejado, uma vez que se traduz numa instabilidade que dificulta o controlo da posição das partes móveis. Na última década foi dedicada alguma investigaçao científica a este fenómeno, tendo sido descoberta a existência de um perfil de deslocamento particular, denominado meta-estabilidade, em determinadas condições de amortecimento e de actuação electrostática. Esta característica do pull-in torna a sua duração extremamente sensível a variações nas forças intervenientes, incluindo aceleração externa. Assim sendo, a medição do tempo de pull-in de micro-estruturas especificamente concebidas para o efeito pode ser utilizada para medir aceleração. Esta abordagem apresenta vantagens significativas em comparação com a transdução direta de capacidade para aceleração (caso da generalidade dos acelerómetros capacitivos). Nomeadamente, a variável tempo pode ser medida com elevada precisão com relativa facilidade e sem necessidade de desenvolvimentos tecnológicos (o que não é o caso da medição de capacidade). Por exemplo, o uso de uma frequência de relógio de 100 MHz no mecanismo de contagem de tempo permite uma resolução de 100 ns na medição de tempo, o que corresponde, considerando a sensibilidade de 0.26 μs/μg do acelerómetro desenvolvido neste trabalho, a uma resolução na medição de acceleração de 0.38μg. Um dos maiores desafios do desenvolvimento de um acelerómetro baseado no tempo de pull-in é o desenho do amortecedor, pois a sensibilidade e o ruído/resolução do sensor final dependem do nível de amortecimento. Uma nova geometria para o amortecedor (estabelecido por um mecanismo de squeeze-film) é apresentada e estudada neste trabalho. Esta consiste em abrir canais nas placas paralelas facilitando assim o fluxo de ar quando as placas se movem. Ficou provado que esta geometria é eficaz na redução da razão capacidade/amortecimento, o que constituía um problema recorrente no desenho de dispositivos de placas paralelas in-plane. Neste trabalho é descrito o desenvolvimento de um acelerómetro em malha aberta com uma sensibilidade de 0.26 μs/μg e 2.7 μg /√Hz de ruído. As estruturas MEMS utilizadas na sua implementação foram fabricadas num processo de microfabrico SOI comercial. As principais desvantagens desta abordagem são pequena gama dinâmica devido à não-linearidade da resposta. Neste trabalho foram exploradas abordagens em malha fechada, usando feedback electrostático, de modo a ultrapassar estas limitações, tendo sido alcançado um aumento da gama dinâmica para 109 dB, com grandes melhoria na linearidade. Uma nova aplicação para o tempo de pull-in foi também desenvolvida: medição de viscosidade de gases. Uma vez que as microstruturas utilizadas são operadas a baixas frequências, o amortecimento é proporcional à viscosidade. O estudo efectuado mostra que o tempo de pull-in é muito sensível ao amortecimento e portanto a variações de viscosidade. Os resultados experimentais obtidos com gases e misturas de gases com viscosidades entre 8 μP e 18 μP mostraram uma sensibilidade de 2 ms/μP, confirmando o potencial da utilização de tempo de pull-in na medição de viscosidade.The author, Rosana Maria Alves Dias, was supported by Portuguese Foundation for Science and Technology (SFRH/BD/46030/2008)