Coded Source Imaging: Initial investigations with visible light and thermal neutrons
Daniel S. Hussey, David L. Jacobson and Muhammad Arif
Ionizing Radiation Division, Physics Laboratory, NIST
Fuel cell developers have gained tremendous insight into the water management of proton exchange membrane fuel cells (PEMFC) through traditional neutron radiography. Of particular importance has been the identification of the factors that influence anode flooding, the bottlenecks in removing product water from the cathode flow channels and extraction of gas diffusion layer water permeability. However, as PEMFC developers fine tune their designs, their diagnostic needs become more demanding. In order to improve the performance of the PEMFC, being able to identify the region in which product water is forming from 3 -dimensional depth profiles with high temporal resolution (1-15 Hz) is crucial. A factor limiting the lifetime of PEMFC is the formation of cracks and pinholes in the membrane. Also, delamination of the membrane electrode assembly reduces the maximum performance. The temporal and/or spatial resolution required to investigate these aspects of the fuel cell are beyond the current capabilities of traditional neutron radiography. We are investigating an imaging method with the specific imaging goals of obtaining real-time (1-15 Hz) depth profiles of the water density and phase imaging of defect formation in the proton exchange membrane and delamination of the membrane electrode assembly with exposure times less than one minute.
To achieve the imaging objectives for fuel cell research, we are developing coded source imaging. A coded source is an array of pinholes with a mathematically described pattern. The pattern is chosen such that correlation with a decoding array results in an ideal (delta-function like) point spread function. With several thousand pin-holes, these arrays would reduce the exposure time required for neutron phase imaging, which would enable the study of defect formation and delamination in PEMFC. Also, the arrays can be used to recreate 3-dimensional laminographs from a single 2-dimensional projection image. The first such arrays were proposed by Mertz and Young for observational astronomy and have been used extensively for emission radiography in astronomy and medical imaging. Despite the similar nature of emission and transmission imaging, there has been relatively little effort on applying coded mask imaging in the transmission case, in fact we know of only one previous attempt. We will present our first coded source images taken with thermal neutrons and visible light and discuss future possibilities.
Author: Daniel S. Hussey
Mentor: Muhammad Arif
Division: Ionizing Radiation
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