Online monitoring of pore distribution in microporous membrane

The present investigation describes about the development of a cost effective system for real time monitoring of porosity of ion track etched membranes. The system uses a complementary metal oxide semiconductor (CMOS) image sensor to capture the image of the membranes from the optical microscope’s projector lens and a field-programmable gate array (FPGA) chip to process the captured image and transfer the pore distribution result to a LCD display. The porosity of the membrane is measured directly from the distribution of pores in the membrane. In the image processing by FPGA the pixels intensity greater than the threshold value is considered to be due to the presence of pores. This technique cannot be utilized in membranes with pore size less than 1 micron due to the limitation of magnification of the optical microscope. The porosities of three gamma ray irradiated thin track etched polycarbonate membranes of pore sizes 5, 8 and 10 mm are determined with the system and calculated to be in the range 8.1–10.5, 2.0–9.8 and 4.9–9.6% respectively. The system is designed at minimum cost and provides more detailed data at a faster rate. Evaluation of the performance characteristics of the setup indicates that its performance is comparable with much costlier systems.

The methodology presented here is capable of achieving real-time monitoring of porosity of membrane. The detection of pixel value more than the threshold value in the area where pores are presented indicates the existence of the pores which make the technique as acceptable for pore distribution investigation. The SOC design and integration of CMOS and FPGA technology to the optical microscope reduces operation time and makes the system faster for result analysis. This faster result analyzing ability is an added advantage of using this technique in comparison to other techniques. The low cost of the CMOS image sensor and use of FPGA chip reduces the cost of the experimental system quiet low in comparison to the system containing CCD camera. As the system processing core and the other required hardware are implemented on one board there is no need of computer processing unit (CPU) for experiment. Since it is a direct method, so porosity of the membranes can be computed more precisely and accurately with less time without damaging the surface microstructure. The same area can be viewed after several etching which is an added advantage of this non destructive real-time monitoring system.