Detection of a Conductive Object Embedded in an Optically Opaque Dielectric Medium by the Thermo-Elastic Optical Indicator Microscopy

We present a new method for the subsurface imaging of a conductive object embedded in a dielectric medium based on microwave imaging by thermo-elastic optical indicator microscopy. The present method is based on the imaging of the microwave near field distribution generated by a conductive object embedded in a dielectric medium. When the thickness of the dielectric medium is small so that the microwave near field generated by the conductive object can emerge from the dielectric medium, one can find the presence of the object by visualizing the microwave distribution appearing on the surface of the medium. By using the present method, we visualized the microwave field distribution appearing on a surface of a dielectric medium containing a conductive object with an irradiating microwave. We observed that strong microwave near fields that were present around the conductive object appeared on the surface of the dielectric medium, and their intensities were dependent on the frequency and polarization direction of the irradiated microwave. By visualizing various conductive lines having different lengths of 4~10 mm with a width of 1 mm, and buried depths of 1~5 mm, we showed that the present method can be a practical nondestructive and noncontact way for the detection of conductive lines and structures embedded in an optically opaque dielectric medium.