1,721,040 research outputs found
MEMS Inclinometer with Tunable-Sensitivity and Segmented Overlapping Allan Variance Analysis
No full textAn electrostatic-capacitive Micro Electro-Mechanical System (MEMS) inclinometer based on a position-feedback mechanism and data analysis with Segmented Overlapping Allan VARiance (S-OAVAR) are presented in this paper. A closed-loop mechanism allows to keep the position of the movable proof mass of the MEMS sensor fixed while is acted upon by gravity, and to electrically tune the angle sensitivity and measurement range of the sensor independently from the working position. To investigate the evolution of noise contributions affecting the sensor over specific time frames of the day, a 15-hour data set of acquired measurements has been divided in one-hour segments each, and have been analysed with the OAVAR, thus leading to a S-OAVAR. Experimental results have shown that the angle sensitivity can be tuned from 9.41 mV/deg up to 33.1 mV/deg. The S-OAVAR analysis has highlighted the presence of distinctive noise contributions over time introduced by different environmental conditions such as mechanical vibrations induced by foot and vehicular traffics
Double-actuator position-feedback mechanism for adjustable sensitivity in electrostatic-capacitive MEMS force sensors
No full textThis paper presents a novel double-actuator position-feedback mechanism for micro electro-mechanical electrostatic-capacitive force sensors. Compared to a single-actuator position-feedback operation, the innovative use of two independent electrostatic actuators allows to obtain electrically adjustable force sensitivity and measurement range independently from the working position and the stiffness of the internal mechanical movable structure of the device. Additionally, the proposed configuration allows to electrically set and keep fixed the working position of the force probe tip thanks to the position-feedback loop, thus ideally offering an infinite input mechanical impedance, irrespectively from the force measurement range and sensitivity adjusted to the desired values. The proposed mechanism has been experimentally validated on an electrostatic-capacitive MEMS device that includes a capacitive position sensor and a pair of electrostatic actuators, employing the gravity force to provide accurate and repeatable values for the external applied force. The obtained experimental results are in good agreement with both theoretical predictions and parametric numerical analyses. The proposed mechanism allows to adjust the sensitivity in the range from 2.34 up to 8.43 V/μN with a corresponding force measurement range, defined at a maximum nonlinearity error of 1% referred to the full scale, from [-217, 226] down to [-20.5, 21.4] nN, respectively. The measurement repeatability, which sets the resolution of the MEMS force sensor, has been estimated at one standard deviation σ resulting in 345 pN
Rietveld refinement of the zorite structure of the ETS-4 molecular sieves
No full textThe crystal structure of ETS-4 titanosilicate [Na9Si12Ti5O38(OH). 12H(2)O] was refined using synchrotron X-ray powder diffraction and the Rietveld method (R-P=0.050; R-wP=0.063; R-B=0.169). Our diffraction data provide direct evidence that ETS-4 has the same structure as the zorite mineral. The framework of zorite can be described as nenadkevichite-like chains, laterally connected by 4[SiO4]/[TiO6] units, corresponding to two different chemical environments for Si. Similar to previous observations, a discrepancy was found between the population ratio of Si positions as calculated by the occupancy refinement of atomic sites related to these two environments, and that inferred from Si-29 MAS NMR. This is tentatively explained here on the basis of the large amounts of protons in the proximity of the Si2 site as indicated by Si-29 CP/MAS NMR. The low thermal stability of the zorite/ETS-4 structure is explained in terms of relevance of the hydrogen bonding between extra framework water molecules and framework oxygens
Submicron machining and biomolecule immobilization on porous silicon by electron beam
No full textThree-dimensional submicrometric structures and biomolecular patterns have been fabricated on a porous silicon film by an electron beam-based functionalization method. The immobilized proteins act as a passivation layer against material corrosion in aqueous solutions. The effects' dependence on the main parameters of the process (i.e., the electron beam dose, the biomolecule concentration, and the incubation time) has been demonstrated
Laboratory and synchrotron X-ray powder diffraction study of synthetic levynes: comparison with natural levynes
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