Vytautas Ostasevicius

Numerical Analysis of Dynamic Effects of a Nonlinear Vibro-Impact Process for Enhancing the Reliability of Contact-Type MEMS Devices.

This paper reports on numerical modeling and simulation of a generalized contact-type MEMS device having large potential in various micro-sensor/actuator applications, which are currently limited because of detrimental effects of the contact bounce phenomenon that is still not fully explained and requires comprehensive treatment. The proposed 2-D finite element model encompasses cantilever microstructures operating in a vacuum and impacting on a viscoelastic support. The presented numerical analysis focuses on the first three flexural vibration modes and their influence on dynamic characteristics. Simulation results demonstrate the possibility to use higher modes and their particular points for enhancing MEMS performance and reliability through reduction of vibro-impact process duration.

Segmentation of a Vibro-Shock Cantilever-Type Piezoelectric Energy Harvester Operating in Higher Transverse Vibration Modes

The piezoelectric transduction mechanism is a common vibration-to-electric energy harvesting approach. Piezoelectric energy harvesters are typically mounted on a vibrating host structure, whereby alternating voltage output is generated by a dynamic strain field. A design target in this case is to match the natural frequency of the harvester to the ambient excitation frequency for the device to operate in resonance mode, thus significantly increasing vibration amplitudes and, as a result, energy output. Other fundamental vibration modes have strain nodes, where the dynamic strain field changes sign in the direction of the cantilever length. The paper reports on a dimensionless numerical transient analysis of a cantilever of a constant cross-section and an optimally-shaped cantilever with the objective to accurately predict the position of a strain node. Total effective strain produced by both cantilevers segmented at the strain node is calculated via transient analysis and compared to the strain output produced by the cantilevers segmented at strain nodes obtained from modal analysis, demonstrating a 7% increase in energy output. Theoretical results were experimentally verified by using open-circuit voltage values measured for the cantilevers segmented at optimal and suboptimal segmentation lines.

Validation of Noninvasive MOEMS-Assisted Measurement System Based on CCD Sensor for Radial Pulse Analysis

Examination of wrist radial pulse is a noninvasive diagnostic method, which occupies a very important position in Traditional Chinese Medicine. It is based on manual palpation and therefore relies largely on the practitioner′s subjective technical skills and judgment. Consequently, it lacks reliability and consistency, which limits practical applications in clinical medicine. Thus, quantifiable characterization of the wrist pulse diagnosis method is a prerequisite for its further development and widespread use. This paper reports application of a noninvasive CCD sensor-based hybrid measurement system for radial pulse signal analysis. First, artery wall deformations caused by the blood flow are calibrated with a laser triangulation displacement sensor, following by the measurement of the deformations with projection moiré method. Different input pressures and fluids of various viscosities are used in the assembled artificial blood flow system in order to test the performance of laser triangulation technique with detection sensitivity enhancement through microfabricated retroreflective optical element placed on a synthetic vascular graft. Subsequently, the applicability of double-exposure whole-field projection moiré technique for registration of blood flow pulses is considered: a computational model and representative example are provided, followed by in vitro experiment performed on a vascular graft with artificial skin atop, which validates the suitability of the technique for characterization of skin surface deformations caused by the radial pulsation.

Identification of Capacitive MEMS Accelerometer Structure Parameters for Human Body Dynamics Measurements

Due to their small size, low weight, low cost and low energy consumption, MEMS accelerometers have achieved great commercial success in recent decades. The aim of this research work is to identify a MEMS accelerometer structure for human body dynamics measurements. Photogrammetry was used in order to measure possible maximum accelerations of human body parts and the bandwidth of the digital acceleration signal. As the primary structure the capacitive accelerometer configuration is chosen in such a way that sensing part measures on all three axes as it is 3D accelerometer and sensitivity on each axis is equal. Hill climbing optimization was used to find the structure parameters. Proof-mass displacements were simulated for all the acceleration range that was given by the optimization problem constraints. The final model was constructed in Comsol Multiphysics. Eigenfrequencies were calculated and models response was found, when vibration stand displacement data was fed into the model as the base excitation law. Model output comparison with experimental data was conducted for all excitation frequencies used during the experiments.

Holographic imaging technique for characterization of MEMS switch dynamics

An innovative holographic imaging technique is applied in characterization of MEMS switch non-linear dynamics. The Duffings non-linear oscillator based phenomenological model was adopted to study MEMS switch non-linear response due to the complicated contact phenomena and corresponding boundary conditions. An experimental contact measurement result of MEMS cantilever response that matches theoretical trends is provided. Non-destructive contact measurements were performed by means of quantitative nanomechnical test instruments. Non-contact holographic characterization method yielded results comparable with phenomenological model and contact measurements. The proposed holographic characterization method consists of digitized holographic measurements enhanced by the FEM eigenvector problem solution. Two cases were analyzed for simple and perturbated sinusoidal excitations that correspond to the free and contact boundary conditions, respectively.

Peculiarities of the Third Natural Frequency Vibrations of a Cantilever for the Improvement of Energy Harvesting

This paper focuses on several aspects extending the dynamical efficiency of a cantilever beam vibrating in the third mode. A few ways of producing this mode stimulation, namely vibro-impact or forced excitation, as well as its application for energy harvesting devices are proposed. The paper presents numerical and experimental analyses of novel structural dynamics effects along with an optimal configuration of the cantilever beam. The peculiarities of a cantilever beam vibrating in the third mode are related to the significant increase of the level of deformations capable of extracting significant additional amounts of energy compared to the conventional harvester vibrating in the first mode. Two types of a piezoelectric vibrating energy harvester (PVEH) prototype are analysed in this paper: the first one without electrode segmentation, while the second is segmented using electrode segmentation at the strain nodes of the third vibration mode to achieve effective operation at the third resonant frequency. The results of this research revealed that the voltage generated by any segment of the segmented PVEH prototype excited at the third resonant frequency demonstrated a 3.4–4.8-fold increase in comparison with the non-segmented prototype. Simultaneously, the efficiency of the energy harvester prototype also increased at lower resonant frequencies from 16% to 90%. The insights presented in the paper may serve for the development and fabrication of advanced piezoelectric energy harvesters which would be able to generate a considerably increased amount of electrical energy independently of the frequency of kinematical excitation.

Optical characterization of diffractive optical elements replicated in polymers

Due to relative ease and cost effectiveness with which planar polymeric structures can be fabricated, diffractive optical elements replication in polymeric substrates are receiving global attention for a myriad of planar photonic and optoelectronic applications including optical interconnects. In this work we present an optical laser control method to control replication of microperiodic profile structures in polymers. Diffraction efficiency of diffraction gratings (originally produced in silicon, quartz glass and in replicated polymer substrates) was measured experimentally and estimated using linear dimensions of gratings or replica defined by atomic force microscopy (AFM). Diffraction efficiency of periodic structure was used to control the surface relief formation during the combined ion etching of crystalline Si (100) and replication of this structure using UV light hardening and hot embossing. The main experimental results are compared with the computer simulations where the standard programme (PCGrate-SX6.0) was employed.

Applicability of Time-Averaged Holography for Micro-Electro-Mechanical System Performing Non-Linear Oscillations

Optical investigation of movable microsystem components using time-averaged holography is investigated in this paper. It is shown that even a harmonic excitation of a non-linear microsystem may result in an unpredictable chaotic motion. Analytical results between parameters of the chaotic oscillations and the formation of time-averaged fringes provide a deeper insight into computational and experimental interpretation of time-averaged MEMS holograms.

Applicability of holographic technique for analysis of nonlinear dynamics of MEMS switch

Recent technological advances have enabled the fabrication of mechanical resonators down to micrometer and even nanometer scales, with super high frequencies. One particularly interesting aspect of the physical behavior of microelectromechanical systems (MEMS) is their nonlinear mechanical response at relatively small deviations from equilibrium which is caused by nonlinear electromagnetic forces, nonlinear stiffness, heat transfer porperties. It is important to understand the nonlinear behavior of MEMS in order to improve their future designs. Hybrid numerical - experimental optical techniques are applied for holographic imaging and characterization of non-linearity in micro-mechanical relays, in particular their cantilevers. The apparent simplicity of the problem is misguiding due to non-linear interaction between the cantilever and the bottom electrode. Therefore the results of optical measurements of the cantilever dynamics are inaccurate due to the shift of the fringes in time average laser holographic interferograms. Numerical modeling helps to solve non-uniqueness of the inverse problem and to validate the interpretation of the pattern of fringes.

Numerical investigation of microstructures using principles of holographic interferometry

Numerical methodology for the investigation of structures in the virtual reality is developed. This methodology is based on the principles oftime averaging laser holographic interferometry. Ability to vary the parameters ofthe virtual optical experiment enables smooth transfer to the smaller dimensions and levels of amplitudes up to the nanoscale investigations. Such type of analysis can be successfully used for different applications, starting from biological investigations of cells, up to the design of microelectronics components.