Paulius Palevicius

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.

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.

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.

Design, Analysis and Application of Dynamic Visual Cryptography for Visual Inspection of Biomedical Systems

Health care industry has a growing need for advanced tools that enables the discovery the existence or concentration of biological analytes. In this article a concept of novel cantilever-type microsystem platform in the field of biomechanics using optical technique of image encryption and communication scheme based on computer generated holography is proposed. An image hiding technique based on computer generated holography and dynamic visual cryptography is employed. Dynamic visual cryptography is a visual cryptography scheme based on time-averaging geometric moire. It is used together with Gerchberg–Saxton algorithm and 3D microstructure manufacturing techniques to design the optical scheme. Stochastic moire grating is used to embed the secret image into a cover image. The image can 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 phase information of computer generated hologram is then formed on a piezoelectric cantilever-type microsystem platform using electron beam lithography. It serves as an optical element for visual inspections of dynamical changes in investigated biological environment.

Development of complex 3D microstructures based on computer generated holography and their usage for biomedical applications

The main focus of the paper is the development of technological route of the production of complex 3D microstructure, from designing it by the method of computer generated holography till its physical 3D patterning by exploiting the process of electron beam lithography and thermal replication which is used for biomedical application. A phase data of a complex 3D microstructure was generated by using Gerchberg-Saxton algorithm which later was used to produce a computer generated hologram. Physical implementation of microstructure was done using a single layer polymethyl methacrylate (PMMA) as a basis for 3D microstructure, which was exposed using e-beam lithography system e-Line and replicated, using high frequency vibration. Manufactured 3D microstructure is used for designing micro sensor for biomedical applications.

Vibration Based Microstructure Replication and Analysis

The main focus of the paper is the development of technological process for the production of complex 3D microstructure, from designing it by using computer generated holography to its physical 3D patterning by exploiting the process of electron beam lithography. The logo image was chosen for numerical generation, which was performed by using Gerchberg–Saxton algorithm for computer generated hologram design. Physical implementation of microstructure was performed by using a single layer polymethyl methacrylate (PMMA) as a basis for 3D microstructure, which was exposed by using e-beam lithography system e-LINEplus. After production, verification of 3D microstructure is performed by exposing it under the laser beam and qualitative analysis is performed by using atomic force microscope. Finally, improvement of mass production of complex microstructures, designed by using computer generated holography, is presented.

Applicability of Time-Averaged Holography for Reliability Assessment of Chemical Sensors

This paper investigates applicability of time-averaged holography for reliability assessment of chemical sensors operating in dynamic mode. Time-averaged holography, which is an experimental method for quantitative registration of surface oscillations, is applied for computational results of a paradigmatic cantilever chemical sensor model for various excitation parameters. It is shown that even a harmonic excitation of a non-linear microsystem may result into an unpredictable chaotic motion. The results show that a straightforward interpretation of time-averaged holographic interferograms of chemical sensors can be misguiding.

A technique for the reconstruction of a map of continuous curves from interference fringes

The well-known phase-shifting approach for three-dimensional surface measurement uses multiple fringe patterns along with the phase-shifting algorithm to obtain 3-D profiles with high accuracy though this approach is not applicable for dynamic object measurement techniques such as time-averaged holography and in cases when only a single interference fringe pattern is available. In this case the fringe tracing method can be used that is based on localization of centers of interference fringes. We propose a technique for the reconstruction of the contour map from fringe patterns which comprises standard image processing techniques and a scheme for reconstruction of the map of continuous curves from the binary matrix of pixels representing fringe centers. The approach of image division into grid cells is taken and such problems as derivation of approximate line equations in each cell using Hough transformation, grouping contacting cells into curves and interpolation between curves with fractures are solved. The functionality of this approach is demonstrated for a demanding optical image containing fractures and noise.