Active Microwave Thermography for Nondestructive Evaluation of Surface Cracks in Metal Structures


Detection of covered surface cracks in metal structures is an important issue in numerous industries. Various nondestructive testing (NDT) and evaluation techniques have been applied for this goal with varying levels of success. Recently, a technique based on the integration of microwave and thermographic NDT, herein referred to as active microwave thermography (AMT), has been considered for various applications. In AMT, electromagnetic energy is utilized for the thermal excitation, and the subsequent surface thermal profile of the structure/material under test is measured with a thermal camera. Utilizing electromagnetic energy allows the inspection to be tailored to the application through choice of frequency, polarization, and power level. It is shown that for metal with a dielectric-filled crack irradiated with an electric field (E-field) polarized perpendicular to the crack length, a propagating mode (TE10) is generated inside the crack, which causes dielectric heating to occur in the (filled) crack. In the particular case of study in this paper, based on the excitation power and the thermal camera sensitivity, the crack can be detected via an AMT inspection as long as the angle between the crack length and incident E-field is between 0⁰ (perpendicular polarization) and ~ 65⁰. In addition, from the measured thermal contrast and signal-to-noise ratio, the optimum heating time is ~ 5-30 s for successful detection.


Electrical and Computer Engineering

Keywords and Phrases

Active Microwave Thermography (AMT); Corrosion; Covered Crack; Crack Detection; Crack Under Coating; Nondestructive Testing And Evaluation (NDT&E)

International Standard Serial Number (ISSN)

0018-9456; 1557-9662

Document Type

Article - Journal

Document Version


File Type





© 2018 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Feb 2019