Structured light illumination for pressure-sensitive paint measurement under ambient light.

We propose a pressure-sensitive paint (PSP) method under ambient light based on structured light illumination. In the PSP method, pressure is obtained by measuring the variation of the emission light intensity from a PSP coating when it is illuminated by a light source. Since the extraction of the emission light from ambient light is difficult in the conventional PSP method, the existence of ambient light induces a noticeable measurement error. While spatially uniform light is used as illumination light in the conventional PSP method, structured light, the spatial intensity of which is actively controlled, is used in the proposed method. By measuring the PSP emission by varying the spatial pattern of the structured light illumination, one can eliminate ambient light, which is not synchronized with the structured light and can measure pressure without the effect of ambient light. In this study, we demonstrate the pressure measurement under ambient light using structured light with a sinusoidal wave generated by a digital mirror device. The measured pressure agrees well with the pressure measured by a pressure transducer connected to a pressure tap. The proposed method is promising under ambient light conditions.