Patent ID: 7553070

Claim:
A method of non-destructive inspection (NDI) of a structure, the method comprising: identifying an irregularity on a surface of the structure; determining a null value representing a difference between respective response functions of a first non-imaging thermal sensor and a second non-imaging thermal sensor; measuring the temperature of a first portion of a surface of a structure proximate the irregularity with the first non-imaging thermal sensor; measuring the temperature of a second portion of the surface of the structure proximate the irregularity with the second non-imaging thermal sensor, wherein measuring the temperatures of the first and second portions each comprise halting measurement of the temperature of the respective portion once the temperature that is measured has fallen by a predefined decrement; determining a normalized difference signal by determining a difference signal representing any difference in temperature between the first and second portions as measured by the first and second non-imaging thermal sensors, respectively, and defining the normalized difference signal to represent any departure of the difference signal from the null value; repeatedly measuring different first and second portions of the surface of the structure proximate the irregularity and repeatedly determining the normalized difference signal for each of the different first and second portions of the surface of the structure that are measured; and emitting an alert signal based upon the normalized difference signal if the temperature of the first portion is different from the temperature of the second portion by at least a temperature difference threshold for any of the different first and second portions of the surface of the structure that are measured.