This paper reports on a system using a Digital Micromirror Device (DMD) to modulate a near-infrared laser source spatially and temporally. The DMD can produce an arbitrary heat source varying both spatially and temporally over the target. When the thermal response of the target surface is recorded using a thermal imager, this provides new possibilities in subsurface defect detection, partially with regard to features whose orientation does not allow them to be resolved using conventional thermographic inspection techniques. In this respect it is similar to conventional focused spot detection approaches; however, the DMD allows the signal to be frequency/phase multiplexed which provides for simultaneous interrogation over a large area. The parallel nature of the process permits a longer inspection time at each point which has signal-to-noise benefits. Preliminary experiments demonstrating the multiplexing approach are presented using a low-cost thermal imager. A NIR laser is spatially and temporary modulated to generated multiple thermal line sources on the surface of a composite circuit board. The infrared response is demodulated point-by-point at each drive frequency. This permits the thermal response from each line source to be resolved individually. Beyond damage detection the approach also has applications to system identification. Initial limitations due to the test setup are discussed along with future system improvements.
J. D. Pribe et al., "Toward DMD Illuminated Spatial-Temporal Modulated Thermography," Proceedings of the SPIE Defense + Commercial Sensing (DCS) (2016, Baltimore, MD), vol. 9861, SPIE, May 2016.
The definitive version is available at https://doi.org/10.1117/12.2223859
SPIE Defense + Commercial Sensing (DCS) (2016: Apr. 18-21, Baltimore, MD)
Mechanical and Aerospace Engineering
Keywords and Phrases
Defects; Infrared Devices; Infrared Lasers; Infrared Radiation; Nondestructive Examination; Signal Detection; Signal to Noise Ratio; Surface Defects; Thermography (Imaging), Active Thermography; Defect Detection; Digital Micro-Mirror Device; Laser Modulation; Non Destructive Evaluation; Damage Detection
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Article - Conference proceedings
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