Hyojin Jeon

A high-performance carbon nanotube-based field emission x-ray tube for commercial dental imaging

We developed a fully vacuum-sealed carbon nanotube (CNT)-based field emission x-ray tube with commercial-level performance for dental imaging application. The CNT x-ray tube was designed in a triode configuration with the focus-functional gate and had a compact size, much smaller than the conventional hot-cathode tubes. The small size of CNT x-ray tubes along with no cathode heating enables us to make a very compact portable dental imaging system. We have obtained a quite good x-ray image of a human tooth phantom by operating the CNT x-ray tube in an anode voltage of 65 kV, an emission current of 3 m A, and a pulse duration of 0.5 s, which is comparable to that of the conventional commercial hot-cathode tube.

A fully vacuum-sealed miniature x-ray tube with carbon nanotube field emitters for compact portable dental x-ray system

There have been many efforts to develop x-ray sources using field electron emitters instead of conventional thermionic cathodes for digital controlling of x-rays in medical imaging. Specially, portable x-ray systems need a miniature x-ray tube with less-power consumption, easy insulation of high voltage and light shielding of x-rays. Carbon nanotube (CNT) has attracted much attention as the most promising field emitter due to its geometric high aspect ratio, high physical and chemical inertness. To date, however, CNT field emitters have not been satisfactorily incorporated into a fully vacuum-sealed x-ray tube due to their instability and/or unreliability. We successfully developed a fully vacuum-sealed, miniature x-ray tube with CNT emitters for portable dental x-ray systems. The x-ray tube was designed in a triode configuration with a self-electron focusing gate and reliable CNT emitters, and was fully vacuum-sealed within a miniaturized volume of 15 mm in diagonal and 65 mm in length, very tiny and small as compared with conventional thermionic one. The nominal focal spot size of the x-ray tube is 0.4 mm with an operational tube voltage of 65 kV and a current of 3 mA, which offers quite good x-ray images of a human tooth phantom. No heating the miniature x-ray tube for electron emission leads to easy insulation of high tube voltage and light shielding of x-rays, giving a compact and light portable x-ray system. Furthermore, digital operation of the x-ray tube through an active-current control could provide a commercial lifetime along with pretty good stability.

A field emission nano-focus x-ray source with effective electron beam focusing module

We developed a field emission nano-focus x-ray source using carbon nanotube (CNT) emitters and electron beam (E-beam) focusing modules, which could be used in the applications requiring the high-resolution x-ray images. For the nano-size focusing of E-beam from CNT emitters, we designed special focusing modules consisting of electrostatic and magnetic lenses. The geometries and operating conditions of focusing modules were optimized to give the desired demagnification characteristics by performing the electron optics simulations of the designed x-ray source under external electric and magnetic fields. We constructed and operated an open-type nano-focus x-ray system using the focusing modules under a high-voltage condition to attain the high-resolution x-ray images. The results showed a possibility of field emission nano-focus x-ray sources with a relatively high current and controllable magnification through the effective focusing modules.

Aging process of carbon nanotube-based field emission X-ray tubes for their stable and reliable operation

We have optimized the aging process of fully vacuum-sealed carbon nanotube (CNT) X-ray tubes in terms of an anode voltage, a cathode current and pulse on-time. Degradation and electrical arcing have been monitored and severely suppressed during the aging process. The completely aged CNT X-ray tube with an outer diameter of 15 mm and a length of 60 mm shows a cathode current of 3 mA at an anode voltage of 65 kV, applicable to X-ray imaging like dental examination.

Fast active-current control with a push-up voltage source for carbon nanotube field-emission X-ray tubes

The advanced active-current control with a push-up voltage source is proposed for the fast operation of a carbon nanotube (CNT) field-emission X-ray tube while maintaining the advantages of improved stability and reliability. The push-up voltage source, composed of a resistor and a voltage supply, was found to reduce the response time of CNT X-ray tubes down to sub-microsecond.

Brightness of electron beam from a small carbon nanotube emitter fabricated using the probe contact method

A novel method for fabricating a small-sized carbon nanotube (CNT) emitter was developed. The emitter was fabricated by contacting the tungsten probe covered with CNT paste to the surface of Kovar rod, and then the brightness of electron beam generated from the CNT paste emitter was measured. We obtained the virtual source size of 1.13 × 10^-10 m² and the brightness of 1.2 × 10⁷ A m^-2sr^-1 at an applied voltage of 3,100 V.