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

Abstract

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.

Visualization of microwave near-field distribution in sodium chloride and glucose aqueous solutions by a thermo-elastic optical indicator microscope

“…The ITO layer of OI heats up by an applied microwave signal, and the thermal energy from the conductive layer diffuses to the glass. The circularly polarized incident light changes its state to elliptically polarized due to the photo-elastic effect of the glass substrate during the reflection depending on the material characteristics of the medium and orientation of the mechanical stress axis 51 . For image processing two images were measured, both of which were used to calculate the final result by using a custom computer program.…”

“…We detected the linear birefringent (LB) distribution images with two different analyzer orientation 0° and 45°. These two images, β 1 and β 2 are related to the normal and shear stress distributions of the OI, respectively 51,52 . The initial heat distribution, causing those thermal deformations, was calculated by the following Eq.…”

Electrical Defect Imaging of ITO Coated Glass by Optical Microscope With Microwave Heating

“…For a sufficiently large ITO-glass, the surface current distribution will be identical to that of magnetic field of the incident microwave. In this case, because the ITO-glass is heated by the surface current through the Joule heating process, the heating distribution, surface current distribution, and the excitation magnetic field structure will be identical to each other [17].…”

“…The increase of the local temperature causes a thermal stress around the electrical defect due to a non-uniform thermal expansion of the glass substrate. In this case, one can find heat source distribution from the thermal stress distribution by solving plane thermal equation [17]. This can be done by measuring the linear birefringence (LB) distribution of the ITO-glass through the polarized light microscope system.…”

“…When a circularly polarized light is passed through a stressed glass, the LB changes the circularly polarized light to an elliptically polarized one. The LB depends on the strength and direction of the stress as shown in equations (1-2), and it can be analyzed by measuring the intensity change of a probing light passing through a linear polarizer (analyzer) by the following equation [17]:…”