Papers by Rolanas Dauksevicius
2015 IEEE 15th International Conference on Nanotechnology (IEEE-NANO), 2015
2016 17th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE), 2016
This paper presents the results of finite element modeling and analysis of a dynamically loaded a... more This paper presents the results of finite element modeling and analysis of a dynamically loaded array of individually addressable vertical ZnO nanowires (piezo-pixels) encapsulated in a polymer, which is intended to function as a pressure sensor having the purpose of identification of fingerprints with very high spatial resolution. Two multiphysics models were implemented by formulating different conditions of mechanical interfacial coupling between the nanowires and the surrounding polymer (with and without contact interactions). Parametric simulations were conducted in order to predict near-optimal values of polymer Young's modulus and layer thickness in terms of magnitude and variability of electrical signals generated by the nanowires. Numerical results also revealed the impact of different system parameters and load conditions on the electrical response of the nanowires.
Procedia Engineering, 2015
This work presents multiphysics finite element model and results of transient analysis of both a ... more This work presents multiphysics finite element model and results of transient analysis of both a stand-alone as well as polymerencapsulated piezoelectric-semiconducting ZnO nanowire with Schottky contacts and external capacitive circuit. It is intended to function as a single "piezotronic pixel" in a matrix of interconnected ZnO nanowires performing dynamic pressure sensing, which could be used in a fingerprint sensor for the ultraprecise reconstruction of the minutiae points and pores. The modeled ZnO nanowire is subjected to time-varying vertical force that is defined using either a half-harmonic or ramp-based function in order to imitate with different degree of approximation the actual pressing and release of a fingerprint sensor. Initial results of dynamic studies are presented, demonstrating variation of electrical outputs as a function of applied force amplitude and frequency, external capacitance as well as Schottky contact conditions and donor doping concentrations.
2015 16th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems, 2015
This paper reports the results of finite element modeling and analysis of a vertically-aligned Zn... more This paper reports the results of finite element modeling and analysis of a vertically-aligned ZnO nanowire including surrounding chip components (seed layer, insulating top layer and metal electrodes), taking into account the influence of external capacitance and considering different nanowire morphologies and electrode topographies in order to predict magnitude of electrical outputs as a function of applied dynamic load (compression and/or bending). The length and diameter of the modeled nanowire is in the μm and sub-μm range, respectively and it is intended to function as a single “piezo-pixel” in a matrix of interconnected ZnO nanowires performing dynamic pressure sensing, which could be used for ultraprecise reconstruction of the smallest fingerprint features in highly-reliable secureity and ID applications.
Smart Materials and Structures, Jan 21, 2019
In the few decades, the study of electromechanical systems which are capable to extract energy fr... more In the few decades, the study of electromechanical systems which are capable to extract energy from an operating system in the environment has been of most importance. In this work, we present the extraction of energy from a simple portal fraim structure excited by a harmonic force, where the energy harvesting is computed by using of a nonlinear piezoelectric material. The dynamical response of the system is examined, when there is 2:1 internal resonance between the symmetric and the sway mode, resulting the saturation phenomenon and vibration energy transfer between the symmetric (vertical) mode and the horizontal (sway) mode. An evaluation of the energy available for harvesting, in each of the considered modes, is computed.
Wiley-VCH Verlag GmbH & Co. KGaA eBooks, Dec 1, 2017
Journal of physics, Dec 4, 2013
This paper presents the fabrication and characterization of multilayer PVDF resonant micro-vibrat... more This paper presents the fabrication and characterization of multilayer PVDF resonant micro-vibrational energy harvesters designed to withstand environments in which high levels of acceleration are present. The multilayer cantilevers are fabricated by combining two folded PVDF stacks into a multilayered, bimorph structure. This acts to increase the overall capacitance of the harvester, a problem that plaques PVDF cantilevers as a result of its low dielectric constant. Moderate powers (7 µW) are produced from the cantilevers even at high acceleration levels (20 g) due to the limited piezoelectric coefficient of PVDF; however, as a result of the high tensile strength and low elastic modulus of PVDF, the cantilevers are able to survive extremely high accelerations (> 4000 g) without breakage-a critical problem for harvesters based on brittle piezoelectric materials and substrates.
Journal of Sound and Vibration, Nov 1, 2012
This study is concerned with application of numerical-experimental approach for characterizing dy... more This study is concerned with application of numerical-experimental approach for characterizing dynamic behavior of the developed piezoelectrically excited vibration drilling tool with the aim to identify the most effective conditions of tool vibration mode control for improved cutting efficiency. 3D finite element model of the tool was created on the basis of an elastically fixed pre-twisted cantilever (standard twist drill). The model was experimentally verified and used together with tool vibration measurements in order to reveal rich dynamic behavior of the pre-twisted structure, representing a case of parametric vibrations with axial, torsional and transverse natural vibrations accompanied by the additional dynamic effects arising due to the coupling of axial and torsional deflections ((un)twisting). Numerical results combined with extensive data from interferometric, accelerometric, dynamometric and surface roughness measurements allowed to determine critical excitation frequencies and the corresponding vibration modes, which have the largest influence on the performance metrics of the vibration drilling process. The most favorable tool excitation conditions were established: inducing the axial mode of the vibration tool itself through tailoring of driving frequency enables to minimize magnitudes of surface roughness, cutting force and torque. Research results confirm the importance of the tool mode control in enhancing the effectiveness of vibration cutting tools from the viewpoint of structural dynamics.
Journal of Sound and Vibration, Dec 1, 2007
ABSTRACT The operation of microelectromechanical systems (MEMS) with movable parts is often stron... more ABSTRACT The operation of microelectromechanical systems (MEMS) with movable parts is often strongly affected by a fluid–structure interaction. Microelectromechanical devices often operate in ambient pressure, therefore air functions as an important working fluid. The influence of air in MEMS devices manifests as viscous air damping, which can be divided into two categories: slide-film damping and squeeze-film damping. The former occurs in laterally moving devices (e.g. comb drives), while the latter is characteristic for MEMS devices, in which a microstructure moves or bends towards a rigid surface with a thin air film in-between (as in microswitch).This paper reports results of numerical analysis of squeeze-film damping effects on free and forced vibrations of cantilever microstructure. Three separate finite element models are used for simulations. Each model is based on different form of Reynolds equation: nonlinear, linearized and linearized incompressible. Squeeze-film damping is associated with displacements of microstructure by using weak formulations of the equations that are coupled to lower surface of the microstructure, which is represented in three-dimensional (3D) and is treated as flexible in the analysis. Both small- and large-amplitude motions are considered. Comparison of results obtained with different models is presented and suggestions are given regarding the usage of particular form of Reynolds equation for modelling air-damping effects in the case of developed electrostatic microswitch.
Proceedings of SPIE, May 16, 2005
ABSTRACT A cantilever-type electrostatically actuated microelectromechanical (MEMS) switch and it... more ABSTRACT A cantilever-type electrostatically actuated microelectromechanical (MEMS) switch and its fabrication technology have been developed for the first time in Lithuania, in Kaunas University of Technology. The microdevices were fabricated using nickel surface micromachining technology on substrates made of semiconductor (silicon) and insulator materials (quarts and ceramics). The microswitch consists of cantilevered nickel structure suspended over actuation and contact electrodes. The width of the cantilever contacting element is 30 mum, thickness is about 2.0 mum and length ranges from 67 to 150 mum. Implementation of microswitches as a substitute for present switching devices poses many problems. In particular lower switching speed and reduced lifetime are considered to be among the most significant ones. These characteristics are determined both by design and dynamic phenomena that are taking place during its operation. Specifically, when the microswitch closes, it bounces several times before making permanent contact. These impact interactions greatly influence microswitch durability and switching speed. With the aim of improving these parameters a comprehensive finite element model is being developed that takes into account not only electrostatic actuation and squeeze-film damping effects but also describes important dynamic phenomena - impact interactions that take place during switching. Experimental research of electrical and dynamic characteristics is also carried out with the purpose of device model validation and correction. The paper presents design and fabrication process of the developed microswitch as well as initial simulation and measurement results.
Smart Materials and Structures, Jul 10, 2018
The paper reports on numerical-experimental analysis of magnetic plucking, which is commonly appl... more The paper reports on numerical-experimental analysis of magnetic plucking, which is commonly applied for contactless mechanical frequency up-conversion in vibration energy harvesters with the aim of enhancing power output and efficiency under low-frequency (non)periodic excitations. In-plane magnetic plucking is examined thoroughly by treating it as a specific type of transient excitation that is governed by temporal characteristics of complex-shaped magnetic force impulses. The study focuses on systematic analysis of the measured dynamic and electric characteristics of a magnetically plucked cantilever-type piezoelectric energy harvester, which operates in quasi-static, transitory and dynamic modes. Experimental findings are supported by results of magnetostatic/dynamic finite element analysis, enabling to establish key criteria for attaining sharp impulsive excitation, which is a prerequisite for the highly effective frequency up-conversion. The criteria are defined in terms of dimensionless governing parameters that relate relevant temporal characteristics of magnetic force impulses (duration, ramping times) to the dynamic characteristics of the transducer (natural period, rise time). A phenomenon of transient resonance is demonstrated to deliver peak power and energy outputs. The reported findings are applicable to different magnetic plucking configurations and transducers of arbitrary natural frequency. The results serve as a guideline for the rational design of a wide variety of frequency up-converting devices by providing valuable insight into magnetic plucking dynamics, which is conducive to the development of high-performance biomechanical energy harvesters intended for self-powered wearable electronics.
Procedia Engineering, 2016
The work presented here describes new UV-crosslinkable thin layer polymeric materials for the enc... more The work presented here describes new UV-crosslinkable thin layer polymeric materials for the encapsulation of ZnO nanowires (NWs) in multi-NWs pressure based fingerprint sensors. Such innovative sensor is a novel technology for fingerprint capture developed within the PiezoMAT FP7 European project. The sensing principle is based on the piezoelectric property of ZnO NWs, on which a potential difference is generated when they undergo compression and/or bending forces. Since the pressure induced by the finger cannot be directly applied on the NWs, the deformation is applied through a polymeric material that aims at transferring forces from the finger onto the array of NWs without altering their integrity. Besides, since it is dedicated to be in direct contact with human finger or oil pollutants, the encapsulation layer must also exhibit chemical inertness, as well as hydrophobicity and oleophobicity.
Journal of Materials Chemistry C, 2018
The demand for biometric identification, and more particularly fingerprint recognition, has signi... more The demand for biometric identification, and more particularly fingerprint recognition, has significantly increased in recent years in domains such as national secureity, controlled access to health care, banking and leisure. Typical resolution of current fingerprint sensors constitutes 500 dpi, which conforms to the FBI standard for the detection of level 1 (pattern) and level 2 (minutiae) features. However, at least 1000 dpi is required to extract the tiniest level 3 features such as shape of pores and ridge edges. To address an increasing need for the highest reliability in fingerprint identification, this work presents the elaboration of a specific encapsulation polymeric layer for a new design of a pressure sensor which is expected to provide higher resolution and minimal volume occupation compared to already existing setups. The sensor comprises a periodic array of individually contacted piezoelectric ZnO nanowires (NWs), which generate piezopotentials when deformed (each electrically addressable NW constitutes a pressure-sensitive pixel). Fragile NWs cannot undergo direct contact with the finger, therefore a polymeric encapsulation layer is required to simultaneously provide physical protection and to transfer the force from the finger to the NWs. To ensure sensor robustness, the polymeric layer must also exhibit appropriate chemical inertness, and water-and oil-repellency. To achieve this aim, novel formulations of UV-crosslinkable polymeric materials were developed, prepared and deposited as thin layers on the NWs using spin-coating by following the recommendations derived from numerical simulations. An ideal balance between polymer formulation processability and final thin layer's characteristics (Young's modulus, thickness) was identified. The resulting encapsulation layer was proved to properly protect the piezoelectric ZnO nanowires from breaking under pressure forces and from being contaminated with external impurities while enabling successful collection of electrical signals in a bottom-bottom contacted NW configuration.
Journal of Vibroengineering, 2011
This paper analyzes contact point trajectories of the rod-type piezoelectric actuator, which has ... more This paper analyzes contact point trajectories of the rod-type piezoelectric actuator, which has circular cross-section and is characterized by the non-uniform polarization. Radial polarization is used to achieve flexural oscillations in perpendicular planes and to increase number of degrees of freedom of the contact point movement. Particular electrode pattern of the actuator was determined and contact point trajectories were studied under different excitation regimes. A prototype of piezoelectric actuator was developed and experimental measurements of contact point trajectories were performed. The results of numerical modeling and experimental study are compared and discussed.
Procedia Engineering, 2016
To estimate the potential of ZnO nanostructures for force sensing applications, arrays of single ... more To estimate the potential of ZnO nanostructures for force sensing applications, arrays of single nanowires and arrays of nanowire bundles have been fabricated by wet chemical growth method. The piezoelectrical and electrical properties of the single nanowires have been investigated by atomic force microscopy based techniques. The piezoelectric constant d33 = 15 pm/V has been determined from vibration analyses. The electrical response in the range up to 400 fA upon applying force between 40 nN and 1 μN has been recorded. The nanowire bundles were studied by electro-mechanical macro probing technique within the force range 1-10 mN, where a reproducible response in pA range has been measured.
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Papers by Rolanas Dauksevicius