Dongpyo Hong

Effects on electronics exposed to high-power microwaves on the basis of a relativistic backward-wave oscillator operating on the X-band

Abstract An analysis of the effects of electromagnetic pulses from a high-power microwave (HPM) radiation technique is conducted using a relativistic backward-wave oscillator (RBWO) which uses relativistic electron beams in vacuum circuits. The application described here is based on a relativistic electron device and uses relativistic electron beams to generate high-power electromagnetic radiation. The RBWO was fabricated to operate in a relativistic region with a gamma factor (γ) of 2 at an acceleration voltage of 500 kV. A mode-converted relativistic back-wave oscillator with an antenna that converts TM01 to TE11 was designed and fabricated because the electric field of the center in the RBWO circuit is null. The effects on electronic devices by HPM radiation and exposure were assessed. The effects on electronic devices exposed to HPMs, the failure of information equipment, and modulation of and interference with the received signal through a theoretical model of the threshold power relative to the influence on the target were confirmed in a high-output microwave exposure environment. Particularly, information devices containing semiconductors can undergo serious failures and breakdowns due to the thermal secondary breakdown caused by the high-output transient electromagnetic waves, and it is a theoretical consideration that reverse voltage occurs due to the generation of surge current when caught in the PN-junction region. Finally, the range of power regarding the effectiveness of the electromagnetic coupling of electronics exposed to HPM radiation was estimated.

Origin of Sideband and Spurious Noises in Microwave Oven Magnetron

The 3-D particle-in-cell (PIC) simulations are performed to determine the origin of sideband and spurious noises generated in a cooker magnetron. A novel simulation technique is used, which introduces cathode emission current nonuniformities. These nonuniformities are due to nonuniform distributions of electric field on a thermionic emission surface, which result from cathode geometry. It is shown that cathode end-caps shape and magnetic pole-piece geometries are the causes of sideband and spurious noises in conventional microwave ovens. The 3-D simulation results are in satisfactory agreement with the spectrum of a typical cooker magnetron.

Transient pulse analysis of ionized electronics exposed to γ-radiation generated from a relativistic electron beam

When a semiconductor element is irradiated with radiation in the form of a transient pulse emitted from a nuclear explosion, a large amount of charge is generated in a short time in the device. A photocurrent amplified in a certain direction by these types of charges cause the device to break down and malfunction or in extreme cases causes them to burn out. In this study, a pulse-type γ-ray generator based on a relativistic electron beam accelerator (γ=2.2, β=0.89) which functions by means of tungsten impingement was constructed and tested in an effort to investigate the process and effects of the photocurrent formed by electron hole pairs (EHP) generated in a pMOSFET device when a transient radiation pulse is incident in the device. The pulse-type γ-ray irradiating device used here to generate the electron beam current in a short time was devised to allow an increase in the irradiation dose. A precise signal processing circuit was constructed to measure the photocurrent of the small signal generated by t...

Miniaturized two-stack Blumlein pulser with a variable repetition-rate for non-thermal irreversible-electroporation experiments

Non-thermal irreversible electroporation (NTIRE) to avoid thermal damage to cells during intense DC ns pulsed electric fields (nsPEFs) is a recent modality for medical applications. This mechanism, related to bioelectrical dynamics of the cell, is linked to the effect of a DC electric field and a threshold effect with an electrically stimulated membrane for the charge distribution in the cell. To create the NTIRE condition, the pulse width of the nsPEF should be shorter than the charging time constant of the membrane related to the cell radius, membrane capacitance, cytoplasm resistivity, and medium resistivity. It is necessary to design and fabricate a very intense nanosecond DC electric field pulser that is capable of producing voltages up to the level of 100 kV/cm with an artificial pulse width (∼ns) with controllable repetition rates. Many devices to generate intense DC nsPEF using various pulse-forming line technologies have been introduced thus far. However, the previous Blumlein pulse-generating devices are clearly inefficient due to the energy loss between the input voltage and the output voltage. An improved two-stage stacked Blumlein pulse-forming line can overcome this limitation and decrease the energy loss from a DC power supply. A metal oxide silicon field-effect transistor switch with a fast rise and fall time would enable a high repetition rate (max. 100 kHz) and good endurance against very high voltages (DC ∼ 30 kV). The load is designed to match the sample for exposure to cell suspensions consisting of a 200 Ω resistor matched with a Blumlein circuit and two electrodes without the characteristic RC time effect of the circuit (capacitance =0.174 pF).

Uniform high current and current density field emission from the chiseled edge of a vertically aligned graphene-based thin film

Abstract The field emission properties of the controlled emission edge of a vertically aligned graphene-based thin film are presented. A current and current density of above 7 mA and 200 A/cm2, respectively, with uniform electron emission, are achieved. Uniform high current and current density emissions can be realized by the pre-mechanical shaping and post electrical conditioning of reduced graphene oxide (rGO) film emission, owing to the robustness, thinness (<1 μm), and well-defined uniform film thickness. Field emission luminance demonstrates uniform emission over the entire emission area with a high aspect ratio. Along with a high current emission, the rGO film exhibits excellent emission stability, long-term. This offers prospects for various applications in field emission displays, electron microscopy, and particularly for the realization of miniaturized terahertz vacuum electronic devices, which require electron sources with uniform high currents and current densities, such as long-lifetime cold cathodes.