Optical Lock-in Thermography for Structural Health Monitoring – A Study into Infrared Detector Performance

Abstract

This paper reports on a study comparing the noise performance of two relatively low-cost microbolometers to a high-grade photon detector as applied to optical lock-in thermography, a well-established broad area non-destructive inspection technique. The photon detector is shown to significantly outperform both microbolometers by margins inconsistent with their noise equivalent temperature detectivity specifications. It is demonstrated that this performance gap can be overcome by increasing observation time or optical illumination intensity. For practical situations in which such steps are plausible microbolometers may provide a viable alternative to photon detectors for optical lock-in thermography. This raises the prospect of applying this method to structural health monitoring, where the generally small size and low capital cost of microbolometers would be advantageous.