Synchronized electronic shutter system and method for thermal nondestructive evaluation

#This invention pertains to a method and apparatus of thermal, non-destructive inspection of the surface of a material.

#Thermal, non-destructive inspection systems are an inspection tool for both manufacture and in-service applications. These inspection systems are based on the application of heat onto the surface of the structure to be inspected. Typical heat sources used are flash lamps. The short duration intense light is absorbed by the surface to be inspected and a temperature rise above 0 ambient temperature is produced. A device such as in an infrared detector is used to measure small differences in the surface temperature as the sample cools down. The temperature time history is recorded and stored for analysis using theoretical models. Model based thermal inspections are possible when extraneous factors are minimized so that the theoretical models best fit the data.

#Thermal inspection of a sample material can be achieved by single-sided inspection or by through-transmission inspection. Single-sided inspection means that the flash lamps that heat the sample under test are on the same side of the sample as the infrared detector that thermally inspects the temperature of various points on the sample versus time as the sample cools down after being heated. Through-transmission inspection requires that the infrared detector be on a side of the sample under test opposite to the flash heat lamps used to heat the sample. Through-transmission measurements can utilize either one or more flash heat lamps for thermal inspection, depending on the size of the sample.

#A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:

#FIG. 1 shows a single-side thermal inspection system setup using two flash heat lamps to heat a sample under test;

#FIG. 2 illustrates a temperature image taken by the system of FIG. 1 illustrating saturation of detectors;

#Referring now to the drawings, FIG. 1 illustrates a thermal inspection system 10 for single-side inspection, in accordance with the related art. The thermal inspection system in FIG. 1 has a thin sample 11 having two surfaces 12a and 12b opposite to each other, a first flash heat lamp 13a and a second flash heat lamp 13b, each having reflectors that point towards surface 12a of sample 11. Two flash lamps are generally used in same side thermal inspection systems to provide more even heating across the surface 12a of sample 11 and to provide a larger temperature rise of sample 11 than if just one flash lamp were used. First flash heat lamp 13a has a reflector 13x that is pointed at surface 12a of sample 11. Similarly, second flash heat lamp 13 b has a reflector 13y that is also pointed at surface 12a of sample 11. An infrared detector 15 having a lens 16 is pointed towards surface 12a of sample 11 to acquire thermal data as a function of elapsed time as sample 11 cools down after being heated by firing flash lamps 13a and 13b. Image processor 17 serves to process raw temperature data acquired by infrared detector 15 to form a processed image used in thermal inspections. Computer 18 having a central processing unit 19 works with image processor 17 to store raw temperature data captured by infrared detector 15 over time and then forms a processed image therefrom.

#The single-sided thermal inspection system of FIG. 1 is problematic for several reasons. In particular, the effect of the flash lamps on the infrared detector is a cause of major concern. For example, the system of FIG. 1 has a tendency to expose the detectors of the detector to a high intensity flash caused by the reflection of infrared photons off the sample under test. This reflection causes distorted temperature measurements of the sample under test. This distortion is illustrated in FIG. 2 which is a temperature image 20 having a reflected flash 21 that results in saturated pixels 22. The saturated pixels 22 are caused by the surface emissivity of the sample 11 not being a perfect absorber of all the incident infrared photons. The light intensity must be high in order to heat the structure sufficiently. Because of the high amount of infrared photons, some are reflected back into the infrared camera's detectors and saturate the temperature image.

#For cooled quantum detectors (infrared energy is detected by counting the number of photons absorbed), this saturation appears not to be as much of a problem because the saturated state of the detectors is temporary for one image cycle. Some newer infrared imagers use detectors that are based on thermal detector technology where the infrared energy is detected by the photons causing a temperature change on the detector element. Saturation of these detectors could result in residual thermal effects on the detectors thus potentially effecting the measurement over a number of image data cycles. This saturation would introduce unknown and uncorrectable errors when comparing the data to a model. By shielding the detector during the flash, the camera is not exposed to the high intensity photons but rather only the surface temperature of the sample under test.