Near Field Subsurface Microwave Imaging Using the Substrate Integrated Waveguide Based Planar Sensor

Abstract

In this work, a new subsurface microwave imaging methodology based on the near field resonance measurement to detect various objects hidden behind thin coating or paint layer is presented. The proposed methodology employs a novel substrate integrated waveguide (SIW) resonant sensor with a metamaterial unit cell etched on the ground plane, which is designed at 6.5 GHz to facilitate the near field imaging. The underlying principle behind the imaging procedure is that any variation in the electrical characteristics of the object placed beneath the sensor shifts the resonance frequency of the sensor, which can be mapped spatially to image the overall specimen. The imaging technique under this kind of situation requires the sensor to possess a high sensitivity, which is achieved in the present situation by the newly designed SIW sensor having a shift in the resonance frequency of about 210 MHz for a change in dielectric constant of 0.5. The proposed imaging methodology is validated by carrying out the scanning of a customized non-homogeneous specimen prepared using a 3D-printer with two different materials. The newly designed SIW sensor can potentially be used for subsurface microwave imaging under various situations such as the detection of concealed metallic objects, detection of subsurface flaws in metallic, wooden or some other dielectric structure, etc.