Anode current efficiency simulation with grid mesh perforation rate in cold cathode X-Ray device

Recently, cold cathode emitters have been applied to many fields, such as field emission displays (FEDs), nano-bio-sensors in medical devices, transparent electrodes of various devices, and so on. Specially, CNT (Carbon Nano Tube) has the spotlight with its own unusual properties and merits. For the purpose of applying it to diagnostic systems, we have fabricated a triode type of X-ray device (i.e., anode, cathode, grid, and electrostatic lens), and investigated its electron beam behavior using computer simulation. On the basis of the simulation results, we calculated anode efficiency, which is the ratio of anode current with respect to the total emission current of CNT emitter. Although as the perforation rate of grid mesh increases the anode efficiency of X-ray device is enhanced correspondingly, however, it decreased the emissive total current. This is obviously attributed due to the lack of electric field around the CNT emitter. On the other hand, when the perforation rate of grid mesh is decreased, the total emissive current increases with sacrificing the anode efficiency. Consequently, anode current has the highest value when the perforation rate of grid mesh is about 60%. Some preliminary X-ray images were obtained and discussed with anode tube current and voltage of ≑1 mA and 40kV, respectively with 0.5, 1.0 and 2.0 sec of exposure time.