Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from creep. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material.
The analysis of the mechanical properties of cells is a field of great interest both in medicine and biology because it becomes fundamental each time it is necessary to recognize and prevent some diseases causing alterations in cellular behaviour and resistance. Biological Micro Electro-Mechanical Systems (Bio-MEMS) allow the application of extremely small and precise forces increasing, as a consequence, the number of results possible per experiment and the number of experiments that can be performed simultaneously. The aim of our work is to present a microgripper for single-cell manipulation and to detect the best structure design for keeping the cell and the integrated strategy for its actuation. Specifications and targets impose several limitations and difficulties in micro manipulators design and these obstacles are even more important when the target of microgripping are biological particles (e.g. living cells). The main parameters that have to be taken into account while designing a cell micromanipulator are, aside from its actuation principle, its kinematics, its fingertips shape, its releasing strategy and its material biocompatibility. Both thermal and piezoelectric actuation strategies are investigated in order to understand their main advantages and limitations related, for example, to motion range, hysteresis, thermal stability and insulation, high temperature and high voltage; all these parameters have to be considered to ensure the cell’s integrity during its micromanipulation.
The reduction of power consumption of sensors allows the local power supply or wireless sensor networks. This paper
introduces the results of design and experiments on devices for harvesting energy from vibrations of machines. The main
contribution of this research is the empirical evaluation of different technical solutions able to improve harvester
performances and sensing system duty cycle. Satisfactory results have been achieved in lowering of resonance by
levitating suspensions and in increasing of Q-factor by studying the air flows. Output power values of 10mW (5.7Hz,
1.4g) and 115mW (3.2Hz, 0.2g) were obtained for piezoelectric and inductive harvesters respectively.
The study of damping in MEMS (micro electro-mechanical systems) is crucial for dynamic response prediction and
functional parameters estimation as switch and release time, resonance and quality factor. Geometrical features (borders,
perforations, anchors, etc.) complicate the airflow and impose to validate the results calculated or simulated with models.
Fluid damping is the dominant dissipation source, accompanied by structural dissipations, thermo-elastic damping,
anchor losses, surface effects and electric losses.
In literature, the damping coefficient of MEMS is generally derived from the peaks of the structural frequency response
function (FRF) by the half power method. Despite the wide usage of this approach, it is affected by two main drawbacks:
highly precise and automated detection instruments are needed, and it is applicable only in resonance conditions.
The method presented here is based on the measurement of damping from the hysteresis cycle of the actuation force; it
applies in the time domain and works at any frequency and vibration amplitude. The effectiveness of this methodology
on MEMS is proved by comparing the damping results with those provided at resonance conditions by the half power
method. The samples, designed by the authors, are gold microplates with square holes and elastic springs. The
measurements are conducted by the laser vibrometer Polytech MSA500. The comparison shows very good agreement
with the damping coefficients calculated with the traditional approach (differences within 2% at resonance).
The aim of this work is that of analyzing how the discretization of a coupled electro-mechanical system has to be approached to have accurate results from a Finite Element Method (FEM) simulation. Main aspect concerns the definition of the finite element mesh at the interface between the two domains. From this point of view a hybrid approach is proposed, where a fixed mesh is used for the mechanical structure and for the electrostatic area, whereas a morphing approach is followed for the volume that surrounds the most deformable part of the structure. Other aspects related to the electrical domain discretization, as open boundary modelling, pole positioning of infinite mapped element dimension of the electrostatic area were also considered. Numerical tests were carried out in the simple case of a cantilever, following an explicit coupled solution based on an iterative scheme elaborated in ANSYSTM parametric design language (APDL).
KEYWORDS: 3D modeling, Chemical elements, Finite element methods, Beam analyzers, Microactuators, Instrument modeling, Distortion, Data modeling, Iterative methods, Mathematical modeling
The aim of this work is that of evaluating the relative contribution of the different non-linearities in the simple case of slender cantilever beams and plates under electrostatic loads. This case not allows analytical solution to be achieved and therefore a numerical approach must be followed. Multipurpose commercial software do not feature simultaneous solution of electrostatic and structural problems. In this work a solution algorithm for the coupled electro-mechanical system to be implemented in a finite element commercial software is prosed. The solution follows a Newton iterative method in which the solution of the linear system is obtained through the biconjugate gradient stabilized method. This approach is compared with the already proposed relaxation scheme. The 2D case was firstly considered taking into account the contribution of the fringing field on the tip of the beam. In order of evaluate the accuracy of such a model a 3D model has also been developed taking into account the fringing field on the lateral surface, the anticlastic curvature of the beam and the lateral effect of the constraint. The result obtained emphasizes the coupling between electrical and mechanical solution as an error around 30 percent is obtained if the mechanical solution is calculated on the base of the undeformed electric field On the other hand the 2D mode gives a suitable model of the structure as an error of the order of 2.5 percent with respect to the 3D case has been obtained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.