Comparison Between Damping Coefficients of Measured Perforated Micromechanical Test Structures and Compact Models

Measured damping coefficients of six different perforated micromechanical test structures are compared with damping coefficients given by published compact models. The motion of the perforated plates is almost translational, the surface shape is rectangular, and the perforation is uniform validating the assumptions made for compact models. In the structures, the perforation ratio varies from 24% - 59%. The study of the structure shows that the compressibility and inertia do not contribute to the damping at the frequencies used (130kHz - 220kHz). The damping coefficients given by all four compact models underestimate the measured damping coefficient by approximately 20%. The reasons for this underestimation are discussed by studying the various flow components in the models.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Mechanical Fatigue on Gold MEMS Devices: Experimental Results

The effect of mechanical fatigue on structural performances of gold devices is investigated. The pull-in voltage of special testing micro-systems is monitored during the cyclical load application. The mechanical collapse is identified as a dramatic loss of mechanical strength of the specimen. The fatigue limit is estimated through the stair-case method by means of the pull-in voltage measurements. Measurements are performed by means of the optical interferometric technique.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

A Geostatistical Approach to Define Guidelines for Radon Prone Area Identification

Radon is a natural radioactive gas known to be the main contributor to natural background radiation exposure and the major leading cause of lung cancer second to smoking. Indoor radon concentration levels of 200 and 400 Bq/m3 are reference values suggested by the 90/143/Euratom recommendation, above which mitigation measures should be taken in new and old buildings, respectively, to reduce exposure to radon. Despite this international recommendation, Italy still does not have mandatory regulations or guidelines to deal with radon in dwellings. Monitoring surveys have been undertaken in a number of western European countries in order to assess the exposure of people to this radioactive gas and to identify radon prone areas. However, such campaigns provide concentration values in each single dwelling included in the sample, while it is often necessary to provide measures of the pollutant concentration which refer to sub-areas of the region under study. This requires a realignment of the spatial data from the level at which they are collected (points) to the level at which they are necessary (areas). This is known as change of support problem. In this paper, we propose a methodology based on geostatistical simulations in order to solve this problem and to identify radon prone areas which may be suggested for national guidelines.Radon Prone Areas, kriging, geostatistical conditional simulation, change of support problem

3D numerical modeling and experimental validation of diamagnetic levitated suspension in the static field

Diamagnetic levitation principle opens to promising solutions for innovative powerless and low stiffness suspension applicable to many technological fields. The peculiarities of diamagnetic suspension make this design solution very attractive for some applications such as microdevices and energy harvesters. Low stiffness and powerless functioning are the most appreciable characteristics of this kind of suspension, despite their force-displacement curve is generally hard to predict and strongly nonlinear. The modeling complexity resides in the preliminary prediction of magnetic field distribution and in the calculation of diamagnetic forces as function of the levitation height. This work introduces a modeling approach for calculating the levitation height of a parameterized diamagnetic suspension composed of a ground of permanent magnets and a levitating mass made of pyrolytic graphite. The numerical discretization approach is used and the predicted values are compared with experiments providing good agreement between result

RF-MEMS beam components : FEM modelling and experimental identification of pull-in in presence of residual stress

In this paper an experimental validation of numerical approaches aimed to predict the coupled behaviour of microbeams for out-of-plane bending tests is performed. This work completes a previous investigation concerning in plane microbeams bending. Often out-of-plane microcantilevers and clamped-clamped microbeams suffer the presence of residual strain and stress, which affect the value of pull-in voltage. In case of microcantilever an accurate modelling includes the effect of the initial curvature due to microfabrication. In double clamped microbeams a preloading applied by tensile stress is considered. Geometrical onlinearity caused by mechanical coupling between axial and flexural behaviour is detected and modelled. Experimental results demonstrate a good agreement between FEM approaches proposed and tests. A fairly fast and accurate prediction of pull-in condition is performed, thus numerical models can be used to identify residual stress in microbridges by reverse analysis from the measured value of pull-in voltage.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

Association between EEG Paroxysmal Abnormalities and Levels of Plasma Amino Acids and Urinary Organic Acids in Children with Autism Spectrum Disorder

Abnormalities in the plasma amino acid and/or urinary organic acid profile have been reported in autism spectrum disorder (ASD). An imbalance between excitatory and inhibitory neuronal activity has been proposed as a mechanism to explain dysfunctional brain networks in ASD, as also suggested by the increased risk of epilepsy in this disorder. This study explored the possible association between presence of EEG paroxysmal abnormalities and the metabolic profile of plasma amino acids and urinary organic acids in children with ASD. In a sample of 55 children with ASD (81.8% male, mean age 53.67 months), EEGs were recorded, and 24 plasma amino acids and 56 urinary organic acids analyzed. EEG epileptiform discharges were found in 36 (65%) children. A LASSO regression, adjusted by age and sex, was applied to evaluate the association of plasma amino acids and urinary organic acids profiles with the presence of EEG epileptiform discharges. Plasma levels of threonine (THR) (coefficient = −0.02, p = 0.04) and urinary concentration of 3-Hydroxy-3-Methylglutaric acid (HMGA) (coefficient = 0.04, p = 0.02) were found to be associated with the presence of epileptiform discharges. These results suggest that altered redox mechanisms might be linked to epileptiform brain activity in ASD

Reliability Testing Procedure for MEMS IMUs Applied to Vibrating Environments

The diffusion of micro electro-mechanical systems (MEMS) technology applied to navigation systems is rapidly increasing, but currently, there is a lack of knowledge about the reliability of this typology of devices, representing a serious limitation to their use in aerospace vehicles and other fields with medium and high requirements. In this paper, a reliability testing procedure for inertial sensors and inertial measurement units (IMU) based on MEMS for applications in vibrating environments is presented. The sensing performances were evaluated in terms of signal accuracy, systematic errors, and accidental errors; the actual working conditions were simulated by means of an accelerated dynamic excitation. A commercial MEMS-based IMU was analyzed to validate the proposed procedure. The main weaknesses of the system have been localized by providing important information about the relationship between the reliability levels of the system and individual components

Energy harvesting from human motion with piezo fibers for the body monitoring by MEMS sensors

Piezoelectric fibers composite materials can be effectively used as electro-mechanical transducers to harvest power from human body motion thanks to high flexibility and improved reliability compared to traditional piezoceramic sheets. In this work, the motions of elbow and knee joints are replicated with test bench at variable amplitudes and angular velocities to characterize a piezo fiber composite with polymeric matrix. The output power is compared with the electrical specifications of a simple wearable system for sensing human body parameters composed of MEMS accelerometer and temperature sensor