Algimantas Bubulis

Design, fabrication, and simulation of cantilever-type electrostatic micromechanical switch

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 μm, thickness is about 2.0 μm and length ranges from 67 to 150 μm. 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.

Development and operational optimization of microspray system

Construction of a novel liquid material micro dosing and spraying apparatus and its design optimization is presented in the paper. Its functionality is based on the influence of high frequency vibrations generated by cylindrical piezo-actuator to the flow of liquid substances in a micro tube. New models of the micro dosing elements are presented. Such spray systems provide high accuracy of micro dosing and are applicable in a variety of applications from avionics to medicine. Hybrid experimental-numerical analysis techniques are used for investigation of micro spray systems. Experimental analysis of the investigated systems is based on laser holographic interferometry which is used for the identification and optimization of working regimes of the system.

System Analysis of Automatic Balancing (Self-Balancing) Machine Rotors with Liquid Working Bodies

This article deals with automatic balancing (self-equalizing) of rotors with vertical axis of rotation by means of liquid. There used to be a statement claiming that automatic balancing was possible only after first critical (above resonance) rotation zone of rotors. However in 1995 the phenomenon of automatic balancing with liquid in both below resonance zone of rotor rotation and in the resonance itself was registered using the method of high speed video shooting. The paper suggests theoretical explanation of the phenomenon stated by means of carried out experiments.

Generalized Abel transform for the analysis of fluid vibration in a tube

Fluid vibrations in axisymmetric geometry according to the first harmonic in the circumferential direction are analyzed. This problem has a practical application in the analysis of transverse vibrations of fluid in an axisymmetric pipe. The numerical model is developed using finite-element techniques in axisymmetric geometry. Irrotational motions of ideal compressible fluid are analyzed. The finite-element model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the circumferential variation of the volumetric strain is calculated, exploiting conjugate approximation techniques. Obtained volumetric strains are used for the numerical construction of the interference pattern of the vibrating fluid. For this purpose the Abel transform, which is usually exploited in axisymmetric problems, is generalized for problems with circumferential variation of displacements. The obtained interference patterns are used in hybrid experimental–numerical procedures and help to interpret experimental results.

Simulation of Vibration Resistance and the Ways for Its Improvement on Designing Multistage Constructions

The paper considers the possibility of a theoretical definition of the natural frequencies of vibrations of thermoelectric coolers with a different number of stages and different configurations in the design phase. Determination of natural frequencies of vibrations in parallel was carried out for products, taking into account the damping produced by a number of structural elements as well - without taking into account the damping capacity of the solder layers at the ends of thermocouples. The analysis and comparison of the theoretical results were carried out. The results of the calculation determining the natural vibration frequencies of thermoelectric coolers (TEC) through a system of Lagrange equations of the 2nd kind were compared with the calculated values obtained by using the method of electrodynamic analogies.

Investigation of Dynamics of Laser Shutter System

In this paper, the investigation of piezoelectric unimorph laser shutting system transient vibrations damping is presented. A magnetic force technique and magneto-rheological fluid (MRF) is used for the damping of transient vibrations of the piezoelectric unimorph shutter. A methodology is presented for the analysis and design optimization of piezoelectric unimorph actuator used for laser beam shutting systems. The magnetically coupled piezoelectric unimorph cantilever and disc type piezoelectric unimorph motions are analyzed using a one-dimensional forced harmonic oscillator with a non-linear magnetic spring and MRF damper setting. Using a magneto-rheological effect for damping of transient vibrations the piezoelectric unimorph shutter has been experimentally determined.

The Mechanism of Defects Formation in Silicon Substrates

Components of navigating devices can be affected by acoustic emission and vibration. Therefore prototype samples and electronic components must be tested in such conditions. Heterostructures, which destructed under the action of external physical factors and kinetics of formations of porous defects in silicon substrates, were analyzed.

Experimental investigation of waveguide dynamics for the medical invasion treatment

The aim of the article is to introduce into usage of waveguide for the medical invasion treatment and to provide methods that allow investigating the vibrations of the stainless steel waveguide by combining non-contact techniques with the state-of-the-art multiphysics software. The vibrations of the waveguide, used in surgery are examined by the aids of the hybrid numerical-experimental techniques, acoustic emission method, holographic interferometry technique and vibrometer based on Doppler shift of backscattered laser light. The virtual modeling of the waveguide is used by the Comsol Multiphysics software.

Investigation of Electrostatic Cantilever-Type Micromechanical Actuator

Electrostatic microswitch and its fabrication technology have been developed for the first time in Lithuania, at Kaunas University of Technology (KTU). The microdevices were produced by using a nickel surface micromachining process. The microswitch consists of a cantilevered nickel structure suspended over the bottom electrodes. The width of the structure is 30 μm, thickness - 2 μm and length ranges from 67 to 150 μm. Implementation of microswitches as a substitute for the present solid-state switching devices poses many problems. In particular higher actuation voltages, lower switching speed and a reduced lifetime are considered to be among the most significant ones. With the aim of improving these parameters a finite element model is currently developed that takes into account not only microscale-specific electrostatic actuation and air damping effects but also includes the bouncing phenomena. Experimental studies of electrical and dynamic characteristics were also carried out with the purpose of model validation and correction. The paper presents initial results of theoretical modal and air damping analysis as well it shows the first attempts to measure vibration modes of the cantilever structure of the microswitch using Laser Doppler vibrometer.

Generalised Abel transform for the analysis of fluid vibrations

Development of hybrid numerical-experimental techniques is an important method of analysis used for interpretation and validation of experimental results. Laser holography is a powerful experimental technique for analysis of high frequency vibrations of the fluid, especially when the amplitudes of those vibrations are relatively small. It is assumed that the angular frequency of excitation coincides with the eigenfrequency of the appropriate eigenmode and thus the eigenproblem is solved. The problem of fluid eigen-vibrations in axi-symmetric geometry according to the first harmonic in the circumferential direction is analyzed. This problem has a practical application in the analysis of transverse vibrations of the fluid in an axi-symmetric pipe. The numerical model is developed on the basis of the finite element model of the fluid and the method of analysis of the problems with axi-symmetric geometry. The irrotational motions of the ideal compressible fluid are analyzed. The numerical model of the system is based on the approximation of nodal displacements via the shape functions. Thus the field of the amplitudes of the circumferential variation of the volumetric strain is calculated using the procedure of conjugate approximation. By using the procedure of conjugate approximation the amplitudes of circumferential variation of nodal volumetric strains for the eigenmodes are determined. The obtained field of volumetric strain is used in the numerical procedure for the construction of the digital holographic image. Thus the calculation of the amplitudes of circumferential variation of nodal volumetric strains consists of two stages: 1) calculations using the displacement formulation for the first harmonic in the circumferential direction by the method of finite elements; 2) determination of the field of the amplitudes of the circumferential variation of the volumetric strain by using the procedure of conjugate approximation. The obtained nodal values of the amplitudes of the circumferential variation of the volumetric strain are used in the construction of the digital holographic images. For this purpose the Abel transform which is usually used in axi-symmetric problems is generalized for the problems with axi-symmetric geometry with the variation of displacements according to the first harmonic in the circumferential direction. On the basis of the generalized Abel transform the digital holographic images are constructed. The obtained digital holographic images are used in the hybrid experimental-numerical procedure for the determination of the correlation with the experimental holographic images.