A limited opening faraday cup (LOFC) was designed to determine the absorbed dose in different materials of incident proton with energy below 20 MeV.Compared with the traditional FC
the main difference is on the suppressor electrode
which is composed of the outer cup and the tight circle.The distribution of electric field is influenced by the tight circle that could suppress the ejection of secondary electrons effectively
without affecting the ion beam.And this improves the accuracy of FC.