Giedrius Janusas

High-Frequency Excitation for Thermal Imprint of Microstructures Into a Polymer

The main objective of this paper was to propose a novel method for the formation of microstructures using high-frequency excitation during the thermal imprint process. High-frequency excitation of replica during the thermal embossing process helps to fill gaps of the stamp by the polymer. This external factor can provide a possibility to increase the quality and accuracy of the replica. Furthermore, this method does not require expensive or complex developments of the experimental setup and could be applied in most equipments of thermal imprint.

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.

Periodical Microstructures Based on Novel Piezoelectric Material for Biomedical Applications.

A novel cantilever type piezoelectric sensing element was developed. Cost-effective and simple fabrication design allows the use of this element for various applications in the areas of biomedicine, pharmacy, environmental analysis and biosensing. This paper proposes a novel piezoelectric composite material whose basic element is PZT and a sensing platform where this material was integrated. Results showed that a designed novel cantilever-type element is able to generate a voltage of up to 80 µV at 50 Hz frequency. To use this element for sensing purposes, a four micron periodical microstructure was imprinted. Silver nanoparticles were precipitated on the grating to increase the sensitivity of the designed element, i.e., Surface Plasmon Resonance (SPR) effect appears in the element. To tackle some issues (a lack of sensitivity, signal delays) the element must have certain electronic and optical properties. One possible solution, proposed in this paper, is a combination of piezoelectricity and SPR in a single element.

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.

Polycarbonate as an Elasto-Plastic Material Model for Simulation of the Microstructure Hot Imprint Process

The thermal imprint process of polymer micro-patterning is widely applied in areas such as manufacturing of optical parts, solar energy, bio-mechanical devices and chemical chips. Polycarbonate (PC), as an amorphous polymer, is often used in thermoforming processes because of its good replication characteristics. In order to obtain replicas of the best quality, the imprint parameters (e.g., pressure, temperature, time, etc.) must be determined. Therefore finite element model of the hot imprint process of lamellar periodical microstructure into PC has been created using COMSOL Multiphysics. The mathematical model of the hot imprint process includes three steps: heating, imprinting and demolding. The material properties of amorphous PC strongly depend on the imprint temperature and loading pressure. Polycarbonate was modelled as an elasto-plastic material, since it was analyzed below the glass transition temperature. The hot imprint model was solved using the heat transfer and the solid stress-strain application modes with thermal contact problem between the mold and polycarbonate. It was used for the evaluation of temperature and stress distributions in the polycarbonate during the hot imprint process. The quality of the replica, by means of lands filling ratio, was determined as well.

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.

Influence of PZT Coating Thickness and Electrical Pole Alignment on Microresonator Properties

With increasing technical requirements in the design of microresonators, the development of new techniques for lightweight, simple, and inexpensive components becomes relevant. Lead zirconate titanate (PZT) is a powerful tool in the formation of these components, allowing a self-actuation or self-sensing capability. Different fabrication methods lead to the variation of the properties of the device itself. This research paper covers the fabrication of a novel PZT film and the investigations of its chemical, surface, and dynamic properties when film thickness is varied. A screen-printing technique was used for the formation of smooth films of 60 µm, 68 µm, and 25 µm thickness. A custom-made poling technique was applied to enhance the piezoelectric properties of the designed films. However, poling did not change any compositional or surface characteristics of the films; changes were only seen in the electrical ones. The results showed that a thinner poled PZT film having a chemical composition with the highest amount of copper and zirconium led to better electrical characteristics (generated voltage of 3.5 mV).

Analysis dynamics of piezoelectric optical scanner with periodical microstructure

Piezoelectric optical scanner is developed for multi-coordinate control of optical laser beam by excitation of microstructures. The manufactured microstructure is the grating which implemented in piezoelectric optical scanner. Such type of opto-micro-mechanical systems can be used for accurate angular or linear deflection of optical elements in various optomechanical and optoelectronic systems. The operating principle of these devices is based on piezoelectric effect and on conversion of high-frequency multi-dimensional mechanical oscillations of piezoelectric vibration transducers into directional multi-coordinate motion of the optical elements in the measurement chain. The main distinctive feature of such optical piezoelectric scanners is the combination of high micrometer range resolution with a wide range of angular deflections of the scanning elements. The manufacturing process and visualization of the microstructure were presented. The device consists of piezoelectric cylinder and a scanning element with three degrees of freedom. The control model of this device was derived using simulation of the working regimes of optical scanner by COMSOL Multiphysics software. Optical holography system was used to validate the result of simulation of piezoelectric optical scanner and to test the functionality of piezoelectric optical scanner with implemented microstructures.

Investigation of periodical microstructures using coherent radiation

Low-cost effective characterization methodology was developed that allows indirect evaluation of mechanical, geometrical and optical parameters of periodical microstructures in the cases when traditional measurement techniques are not suitable. Proposed methods are applicable for optimization and control of technological processes. Laser diffractometer is used in the experimental works for measurement of optical parameters of periodical microstructure and estimation of geometrical parameters with an error of less than 5% by comparing theoretical and experimental values of diffraction efficiencies of periodical microstructures. This method is suitable for geometry control of periodical microstructures during all technological process. Also an efficient method was developed that is capable to estimate with an error of 5% the depth of periodical microstructures, which have characteristic depths that are larger than the wavelength of coherent light used in the experiment. Quality of periodical microstructures is sensitive to thermal conditions during replication process. Therefore an experimental setup based on Michelson interferometer was developed for the investigation of induced thermal deformation. The radius and stress kinetics could be analyzed for different thickness of coated polymer. These are the problems that are considered in this paper.

Image encryption scheme based on computer generated holography and time-averaged moiré

A technique of computational image encryption and optical decryption based on computer generated holography and time-averaged moir´e is investigated in this paper. Dynamic visual cryptography (a visual cryptography scheme based on time-averaging geometric moir´e), Gerchberg–Saxton algorithm and 3D microstructure manufacturing techniques are used to construct the optical scheme. The secret is embedded into a cover image by using a stochastic moir´e grating and can be visually decoded by a naked eye. The secret is revealed if the amplitude of harmonic oscillations in the Fourier plane corresponds to an accurately preselected value. The process of the production of 3D microstructure is described in details. Computer generated holography is used in the design step and electron beam lithography is exploited for physical 3D patterning. The phase data of a complex 3D microstructure is obtained by Gerchberg-Saxton algorithm and is used to produce a computer generated hologram. Physical implementation of microstructure is performed by using a single layer polymethyl methacrylate as a basis for 3D microstructure. Numerical simulations demonstrate efficient applicability of this technique.