Investigation of the Pulsing Characteristic of a Carbon Nanotube Emitter.

Helin Zhu,Gyuwan Im,Kyung-Seo Kim,Jehwang Ryu,Jejin Jang,Hyungsoo Mok

doi:10.3390/nano12030522

Helin Zhu, Gyuwan Im + Show 4 more

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https://doi.org/10.3390/nano12030522

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Abstract

The carbon nanotube (CNT) field emitter is suitable for the high frequency pulsing of X-ray. Pulsing reduces 49% of the dose in grid-controlled fluoroscopy and improves the image of moving objects. Various structures and manufacturing processes are being studied. However, more studies on the dynamic characteristic of a pulsing CNT and its application are needed. In this study, the combined dynamics including the field emission, MOSFET, and modified gate driver for MOSFET have been analyzed. In this configuration, between the cathode of the tube and ground, there is a MOSFET switch that turns the tube current on/off and a shunt resistor that measures the tube current. Due to the high impedance of the vacuum between the gate and cathode of the tube, about 85% of the gate voltage is still exerted between the Gate and cathode of the tube during the off-state of the MOSFET. Therefore, space charges are built during the off-state and then released at the beginning of the on-state of the MOSFET. The modified gate driver structure for MOSFET that we propose in this paper can limit the amount of current flow through the cathode. Tube current (boosted current) can be accurately controlled through a modified gate driver structure. Combining the boosted current and pulse control of MOSFET, the dynamic current performance of a CNT tube can be enhanced and the average tube current or dose can be accurately controlled. Experiments, simulation, and analysis have been conducted to study the combined dynamics and its applications.

Highlights

Research on CNT-based X-ray tubes has mainly focused on the microscopic structures of carbon nanotubes and their effects on performance, or how their manufacturing process associates with stability, longevity, and robustness [16]
Research on CNT-based X-ray tubes has mainly focused on microscopic structures of carbon nanotubes and their effects on performance, or how their manufacturing process associates with stability, longevity, and robustness
We studied the combined dynamics of X-ray pulsing using CNT-based tubes

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Since Roentgen discovered X-ray with vacuum tubes, this spectrum of electromagnetic wave has been widely used in health care, industry, science, and many other fields [1,2,3,4]. The classical way of generating X-ray is to accelerate free electrons which are generated by the heating tungsten filament inside a vacuum tube by exerting high voltage [5,6,7]. The accelerated electrons collide with anode to convert its tiny (typically about 1%) portion of kinetic energy to X-ray by bremsstrahlung [8]

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