PSI - Issue 17

Pedro J. Sousa et al. / Procedia Structural Integrity 17 (2019) 828–834 Sousa et. al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 2. LED control circuit prototype

Fig. 3 . CXM32’s response to an input pulse, as seen through a photodetector

Additionally, the current flow was analysed using a small resistor placed between the LED and the MOSFET. Unlike [3], where the resistor is placed between the MOSFET and ground, this positioning has the advantage of a more accurate measurement, i.e. the gate current does not go through this resistor, but the disadvantage of requiring differential measurement. The obtained results are promising for its application to the intended application of digital image correlation with rotating targets. 3. Optical Design The next step of development involved the optical optimizat ion of the LED’s light output, in order to concentrate it in a disk of approximately 200 mm diameter. Additionally, it was interesting to obtain either a collimated beam or a very slightly diverging beam. The chosen approach for this was to design a parabolic mirror that is capable of concentrating the light output into a smaller region. Ray-tracing simulations were performed with a receiver at a distance of one meter from the LED, and for a set of focus distances, diameters and focus offsets. By analyzing the effects of each parameter individually and as a group, it was possible to define the shape of the reflector. Fig. 4 shows the ray-trace result of one of the performed simulations; the LED is in the origin plane and a parabolic mirror is aligned with the Z-axis (blue).