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(a) A schematic of the multibeam x-ray source with a field emission cathode that contains five emitting pixels and a molybdenum target at pressure. The pixels were evenly spaced with a center-to-center spacing of . Each pixel is capable of emitting current. The anode voltage is set at . The gate voltage varies depending on the flux required. Switching the x-ray beam from each pixel is controlled by sweeping a dc pulse through the MOSFET. (b) Each emitting pixel is comprised of diameter CNT film coated on a metal disk, a thick dielectric spacer, an extraction gate, and a focusing electrode.
(a) Experimentally measured cathode current from the five pixels recorded over a period under the constant current mode using 100% duty cycle. The set cathode current was and the anode voltage was . (b) Pin-hole measurement showed five evenly spaced focal spots on the target. (c) The focal spot size was determined based on the European Standard EN 12543-5 (Ref. 20). All of the five focal spots are in the range between in diameter under same focusing voltge .
Five projection images of the same blade-metal rod phantom from different viewing angles were taken by the MBFEX. The digital 2D x-ray image sensor (Hamamatsu C7921) has a photodiode array with size. It was operated at (fps) with binning. The imaging conditions are: , cathode current, and exposure time. The source to object distance is and the blade is placed close to the x-ray detector.
(a) The projection image of a circuit board which is a superimposed image of several overlapped circuit planes. (b) and (c) Two tomosynthesis images showed different layers of the circuit board. It is very clear that the original thick wire on the top layer of the circuit board was removed in (c). Limited axial resolution is due to the fact that there are only five scanning beams providing limited viewing angle.
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