Microwave Imaging of Subsurface Defects in Coated Metallic Structures Using Small Ring Resonators

Microwave testing has the advantage of detecting surface and sub-surface flaws and anomalies under coatings, paint or dirt. Thus, major application of microwave sensors is imaging to determine the shape, size, and location of buried flaws using scattered field measurements. A typical microwave system consists of transmitting and receiving antennas and requires that both sides of the material under test to be accessible. Therefore, one-sided sensors are desirable in certain applications. Electrically small ring resonators etched on printed circuit boards are good candidates as they can provide the benefit of one-sided small footprint sensors that operate at low frequencies with high lateral resolution. This work investigates a simulation study that validates the use of these resonators for imaging subsurface flaws in coated metallic structures in the S band. The results are promising.