 The major distinguishing feature of a SDD is the transversal field generated by a series of ring electrodes that causes charge carriers to 'drift' to a small collection electrode.The 'drift' concept of the SDD (which was imported from particle physics) allows significantly higher count rates coupled with a very low capacitance of the detector.In older detector designs, the collection electrode is centrally located with an external FET (field effect transistor) to convert the current into a voltage and thus represents the first stage of amplification.