Accéléromètre

Résumé

vignette|Un accéléromètre MEMS. vignette|alt=|Un accéléromètre piézoélectrique. Un accéléromètre est un capteur qui, fixé à un mobile ou tout autre objet, permet de mesurer l'accélération non gravitationnelle linéaire de ce dernier. On parle d'accéléromètre même lorsqu'il s'agit en fait de qui calculent les accélérations linéaires selon orthogonaux. Par contre, lorsqu'on cherche à détecter une rotation ou vitesse angulaire, on parle de gyromètre. Plus généralement on parle de centrale à inertie lorsqu'on cherche à mesurer l'ensemble des . Bien que l'accélération linéaire soit définie en m/s (SI), la majorité des documentations sur ces capteurs exprime en g () l'accélération (comme celle causée par la gravitation terrestre). Le capteur Approche intuitive thumb|Schéma d'un système masse-ressort. Un accéléromètre peut être schématisé par un système masse-ressort. Considérons ce schéma ci-contre : à l'équilibre, la position x de la masse m sera la référence, donc

Source officielle

https://fr.wikipedia.org/wiki/Acc%C3%A9l%C3%A9rom%C3%A8tre

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Measurement and comparison of graphene-based resonant accelerometers

Driss Belkass

An accelerometer is a device used to measure acceleration. Acceleration is the rate of change of an object’s velocity, measured in square meters per second [m/s2] or g force. This type of device is used to detect vibrations or the orientation of certain systems. We can find accelerometers in many fields like engineering or industry. Today accelerometers are very much expected in the fields of biology and biomechanics, that said for these fields the devices must become smaller and smaller to be able to respond to the problem encountered in this sector, for example to equip micro-ships that could be used in the human body and thus help in their navigation. In this project we will try to test accelerometers that could address this important issue. These accelerometers are developed at KTH[1] Royal Institute of Technology, they are the smallest accelerometer today, they have been designed with a graphene membrane that supports a silicone proof mass. They belong to the category of Nano-Electro-Mechanical Systems (NEMS). We studied different types of masses (different shapes and sizes) and under different conditions. Firstly to see if we could verify some form of repeatability in the devices and if we were close to the theoretical results. And secondly to see if one configuration was better than the others. The results show that the circles masses were way more effective and that the sizes did not really affect the results. And we also showed that the annealing and the clamping had a important effect on the devices.

2021

Chargement

Modelling, Simulations and Characterization of NEMS accelerometers based on graphene

Daniel Moreno Garcia

Accelerometers are widely used in industrial applications and consumer electronics. We can find them in automotive crash detection or fitness trackers. The majority are based on piezoresistive or capacitive effect which are limited by their large size. This negatively influences their utility in emerging applications such as Internet of Things and biomedical applications. NEMS (Nanoelectromechanical systems) are presented as a possible solution for this problem. The accelerometers used in this project are made of a suspended graphene membrane and an attached silicon proof mass. They were fabricated by KTH researchers. We study the possibility of measuring accelerations by monitoring the changes in the device resonant frequency. If proven, to the best of our knowledge, they would be the first ultra-miniaturized and sensitive resonant accelerometer. To do so, we built a functioning model of the accelerometers by combining a theoretical framework and finite element simulations. The chip was placed on a piezo-shaker and measurements were conducted using a Laser Doppler Vibrometer. To complement the study, further measures were taken with an Atomic Force Microscope and a Digital Holographic Microscope. The results show a good match between theory and simulations. However, the acceleration measurements in the device show higher signals not related with accelerations. We proved they were related to displacements and theorized that they were caused by internal chip forces. Horizontal forces on the accelerometer frame could eclipse the effect of the accelerations on the resonant frequency. We suggest the use of a more rigid chip frame as a potential solution.

2020

Chargement

In this master thesis, the use of MEMS technology to miniaturize existing accelerometers used for vibration sensing is demonstrated. An updated process flow was established and carried out in the cleanrooms. MEMS piezoelectric accelerometers were fabricated and known fabrication issues were successfully avoided. A first characterization of the fabricated devices was done, and results show a strong agreement with the FEM simulations done during and before this project. FEM simulations were done for alternative designs and showed a possibility to almost double the charge generation of the accelerometers.

2020

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