The Development of High-Performance Cold Cathode X-ray Tube Technology
– Professor Cheol Jin Lee in School of Electrical Engineering
)In 1895 Wilhelm Röntgen, the first ever Nobel prize winner, discovered by heating tungsten an electromagnetic wave that had never been identified before. After realizing that it had such enormous energy that it could penetrate most materials, including human flesh and bones, he named the unknown electromagnetic wave the “X-ray.” In 2019, over 120 years after his discovery, a new technology has been developed that will lead to a paradigm shift in the generation of X-rays. This is the achievement of Professor Cheol Jin Lee, who has studied carbon nanotubes and electron emitters for two decades with perseverance and patience, and with the attitude of ‘slow and steady wins the race.’
People often say that technology develops in the twinkling of an eye. However, there are still those who slowly and steadily push forward through their research in order to create a paradigm shift. One of them is Professor Cheol Jin Lee at the School of Electrical Engineering in KU, who has worked for 21 years to develop a new technology that can replace the filament-based hot-cathode X-ray tube that has been used for 120 years.
Carbon nanotube, a novel nanomaterial discovered in 1991, has attracted much attention, but researchers have struggled with it for years because the process of inducing electron emission from the material has not been as efficient as expected. In 1988, Professor Lee, who had previously studied new semiconductor materials and devices, began researching carbon nanotube synthesis and field emission characteristics in order to develop a new technology that could be useful to humankind. Of course, it was not Professor Lee’s group alone that was attempting to develop a carbon nanotube-based electron emitter. However, believing that he could never obtain productive results unless he left research into traditional methods behind, he devoted himself to the pursuit of this goal, animated by an original and creative idea. “While most researchers were structuring a carbon nanotube-based field emitter by using carbon nanotube paste, I was searching for a unique structuring and preparation method. Eventually, I hit on a method of vertically aligning carbon nanotubes at a high density in order to maximize the electron beam density. This method enables one to form a high-density carbon nanotube structure without incorporating an organic substance into the preparation of an electron emitter, and thus enables the manufacture of a high-efficiency electron emitter with excellent characteristics.”
▲Schematic diagram of nanomaterial-based cold cathode X-ray tube.
Besides the carbon nanotube-based emitter, Professor Lee also developed a type of gate electrode technology that had never been attempted before by using graphene, which is another new nanomaterial. He continued his R&D work on the carbon nanotube-based emitter, the graphene gate electrode, an electron beam focus lens, and an anode, and sealed the individual components in a glass vacuum tube, the completed technology designed to enable the production of a high-performance cold cathode X-ray tube. He presented his new technology at the 32nd International Vacuum Nanoelectronics Conference (IVNC 2019) held in Cincinnati, Ohio, on July 22-26, in a paper entitled “Nanomaterial-Based High-Performance Cold Cathode X-ray Tube Technology.” This new technology enables a novel method of generating high-quality X-rays by using carbon nanotube and graphene, and the cold cathode X-ray tube based on it is the first of its type in the world. In the course of Professor Lee’s research over the last two decades, he has published 202 articles in international SCI journals, had 12,770 citations in international SCI journals (h-index 63, i10-index 143), given 220 presentations at international conferences, been granted 18 international patents and 60 Korean patents, and applied additionally for two international patents and one Korean patent.
▲Schematic diagram of nanomaterial-based cold cathode X-ray tube.
Professor Lee explains the impetus behind his current work. “The conventional X-ray apparatus for medical imaging devices has several problems. First of all, since a filament must be heated to a temperature of over 2000℃ to enable it to emit an electron beam, it takes a long time to prepare it for its normal operation. In addition, only 5% of the input energy is used in the emission of the electron beam, and the rest is lost as thermal energy. In other words, the energy efficiency of the conventional apparatus is very low. Moreover, as the electrons are emitted by means of heat, the X-ray dose is difficult to control. In practice, the dose should be adjusted to a variety of levels to obtain clear X-ray images of different body parts with the varying bone structures, thicknesses and densities of a range of men and women, young and old. The difficulties involved in the dosage control of the conventional X-ray apparatus make it challenging to acquire high-resolution images. Another problem is that patients may be exposed to an excessive dose of X-ray.
In addition, because the existing hot cathode X-ray apparatus is large and has a single X-ray source, it has limitations in terms of providing three-dimensional X-ray images.”
Conversely, the nanomaterial-based cold cathode X-ray tube developed by Professor Lee is capable of efficiently emitting high-density electron beams by applying an electric field to carbon nanotube and graphene. Amazingly, its energy efficiency is almost 95%.
With Conviction in 'Geogyeonggungri, Beobgo changshin and Wubocheonli'
Professor Lee emphasizes that researchers who take the hard path of always seeking a new direction must hold fast to some core tenets. For his own part, he seeks to embody the attitude of Geogyeonggungri (居敬窮理, Seek the laws of things with a holy heart), the manner of Beobgochangshin (法古昌新, Find new things from old wisdom), and the spirit of Wubocheonli (牛步千里, Press forward to the end with patience). He emphasizes that a person who has an ultimate goal should not pay heed to the temporary trends or judgements of the world but instead steadily advance toward the new, even if it may not draw applause from others.
▲Schematic diagram of the method of fabricating the point-type and line-type carbon nanotube electron emitters and the graphene gate electrode for the nanomaterial-based cold cathode X-ray tube.
He says, “I anticipate that the nanomaterial-based cold cathode X-ray tube technology will soon replace the conventional hot cathode X-ray tube, and be applied to not only medical imaging devices but also to various other areas, including non-destructive inspection devices, security check devices and sterilization devices. “Realistically, it is difficult to follow up on the work of the leading researchers in Korea and other countries in the field of hot cathode X-ray tube technologies that have already been commercialized. However, the nanomaterial-based cold cathode X-ray tube technology that we recently developed provides a precious opportunity to secure comparative advantage over developed countries in various application technologies, including medical imaging devices. The driving force that has motivated me to walk the long and difficult path until I produced good results has been my resolution to create a technology that can be helpful to human life. My wish is that our technology will take the lead in the development of low-dose, high-quality X-ray apparatuses and the miniaturization of X-ray application devices to be applied to various fields.”
▲Nanomaterial-based cold cathode X-ray tube and its essential components.
Professor Lee has the twin goals of securing international technological competitiveness with his newly developed nanomaterial-based cold cathode X-ray technology and of being successful in a new, high value-added market in this area. He also hopes that he can establish his technology as a global standard that can enable a paradigm shift from the conventional X-ray tube and application technologies, so that it will be extensively used to further the welfare and health of humankind. Currently, Professor Lee is about to commence his slow-but-steady progress through the second stage of his research, which is the commercialization of the technology. He expresses his desire to engage in the R&D work required to commercialize the next-generation cold cathode X-ray tube through close cooperation with various enterprises in Korea and other countries.