Thickness reduction arising due to corrosion or in any other way can cause severe damages to structures. As a result, the frequent structural examination is critical in many industries. The minimal thickness remaining is one of the parameters used to determine whether or not a structure should be replaced. We introduce a novel ultrasonic method that precisely evaluates the minimum remnant thickness of structures. This method utilizes the cut-off property of guided wave modes. This seminar presentation discusses the numerical and experimental investigation of defect quantification for various applications.