Shant Arakelyan

Delaying control of non-homogeneous string forced vibrations under mixed boundary conditions

Optimal control problem on finite time-interval is considered for non-homogeneous wave equation with variable coefficients and mixed boundary conditions. It is assumed that control process is carried out by delaying impacts with arbitrary distribution. Functionals describing the summary momentum and total energy of control impacts in considered time-interval are taken as control process optimality criterias. Using Fourier generalized integral transformation the problem is firstly reduced to interpolation problem with respect to unknown function Fourier transform, and then to truncated system of moments problem with respect to required function. Solution of the problem is obtained explicitly by means of generalized functions. Necessary and sufficient conditions on existence of optimal control function in terms of space of measurable functions are obtained using existence theorems of general moments theory. Numerical calculations are done and optimal resolving control function is plotted for piecewise non-homogeneous string, consisting of two heterogeneous strings.

Temperature and microwave near field imaging by thermo-elastic optical indicator microscopy

A high resolution imaging of the temperature and microwave near field can be a powerful tool for the non-destructive testing of materials and devices. However, it is presently a very challenging issue due to the lack of a practical measurement pathway. In this work, we propose and demonstrate experimentally a practical method resolving the issue by using a conventional CCD-based optical indicator microscope system. The present method utilizes the heat caused by an interaction between the material and an electromagnetic wave, and visualizes the heat source distribution from the measured photoelastic images. By using a slide glass coated by a metal thin film as the indicator, we obtain optically resolved temperature, electric, and magnetic microwave near field images selectively with a comparable sensitivity, response time, and bandwidth of existing methods. The present method provides a practical way to characterize the thermal and electromagnetic properties of materials and devices under various environments.

Microwave Heating Visualization for Carbon Fibers Composite Material: Development of Tunable Microstrip Structures

The visualization of carbon fibers polyether ether ketone (PEEK) composite material heating for a grounded coplanar waveguide and a stepped impedance low-pass filter by the thermal camera is performed. The purpose of such visualization is to characterize electromagnetic field influence on the diagonally anisotropic composite material and find out its application opportunity. COMSOL Multiphysics simulation has been done in order to understand heating principles and origin. Experimental results were in a good agreement with simulations and they showed that the characteristics of the microstrip structures can be modulated/tuned by simple rotation of the composite material. Finally, a tunable application by the carbon/PEEK composite material for the microstrip low-pass filter was developed due to the microwave absorption selectivity dependence on the composite material orientation.