Jae-Ho Rhee

Damage modeling on a radar affected by high power electromagnetic pulse

As the damage caused by high power electromagnetic (HPEM) is getting worse, it is necessary to analyze the damage and to study of shielding it. The coupling of HPEM to electronic devices is divided into two ways; (1) Front-door coupling and (2) Back-door coupling [1]. The former is inflow of HPEM pulse through an intended path and the latter is inflow through an unintended path. Since HPEM pulse flow in through an intended path in former case, HPEM pulse with higher power is induced and cause bigger damage to electronic devices. Because of these problems, it is necessary to study the damage and shield of RF systems affected by HPEM pulse. In this paper, damage modeling on the radar affected by HPEM pulse is shown. The damage of a radar falls into four types: (1) Deception, (2) Jamming, (3) Upset and (4) Burnout [2]. The process of damaged radar, which is sorted by each damage levels, is simulated by circuit elements. Particularly on this paper, it is examined the low noise amplifier (LNA) in a radar system. Because it operates in lower power level than HPEM pulse, LNA burns out even in the low input power circumstances. This circuit model is simulated by PSIM. Through the circuit models, which non-linear phenomena and damage of LNA, was expressed through the steps and it is expected to help studies which are to model the damage of a radar and to shield a radar affected by HPEM pulse.

In-line circuit modeling for damage analysis of RF front end system affected by high power electromagnetic pulse

Output of microwave have been increased with development of pulsed power system. The risk of RF front end system is dramatically increasing as the output of high power electromagnetic (HPEM) pulse increases. There are largely two ways of coupling HPEM pulse: (i) Front door coupling, which is through antennas and sensors to receive signals (ii) Back-door coupling, which is through unintended way such as punctures and slots. Compared to back-door coupling, front-door coupling is more risky and hazardous since it is coupled with intended parts. The simulation studies of this problem are conducted by numerical method. However it takes too many times in computation. In this paper, the in-line circuit modeling for damage analysis of the RF front end system affected by HPEM pulse is proposed. This integrated circuit modeling is simulated by the Electro Magnetic Transient Program (EMTP). It is simulated from the output of the HPEM system to the RF front end system. The target RF system of the study is the antenna. Passive circuit elements are used to model for antenna efficiency, propagation attenuation and etc.

Adjustable circuit model of vircator according to its characteristics

A virtual cathode oscillator (vircator) is one of the most important microwave generators, because it has advantages in simple structure, giga-watt level power and low impedance. Because of these advantages, it is widely used in high power electromagnetic (HPEM) pulse applications. The main disadvantage of the vircator is its low efficiency and it is complemented by simulation studies. Many of simulation studies are conducted by numerical method. Considering the connection to the pulse power part, a circuit modeling is needed. In this paper, the adjustable circuit model of the vircator according to its characteristics is proposed. Through the circuit model of the vircator, HPEM system can be handled as an integrated system, which contains a prime power part, a pulsed power part, a microwave source part, and others. This circuit analysis is simulated by the electromagnetic transient program (EMTP). Passive elements and switch are used to model for space-charge limitation, absorptions, oscillation and etc, which are derived from simulation condition (structure, input power). The vircator emission in the air is represented by the load. This study is helpful to efficiency researches because circuit elements are derived by the simulation conditions.

Optimization of a cathode configuration in gas insulated switchgear with a permittivity graded insulator

An application of a functionally graded material (FGM) to the solid spacer in gas insulated switchgears (GISs) can reduce the electric field intensity. Especially, the location of the high electric field concentration moves from the anode to the interface between the spacer and the gas, when the FGM spacer is used. However, the electric field stress near the triple junction of the cathode with a rounded shape, which remarkably affects the insulation capability of a GIS, increases reversely. Therefore, in order to prevent this, it is necessary to modify the cathode geometry in the common C-GIS. In this research, we dug a groove in the cathode near the triple junction, and performed the optimization of this cathode configuration by using the design of experiments (DOE). Additionally, the permittivity graded spacer with the permittivity variation of a reverse direction distribution unlike that of the existing unidirectional or bidirectional distribution was applied. Consequently, both the maximum electric field intensity generating near the inflection point of the spacer geometry and the electric field stress near the triple junction of the cathode can be efficiently reduced by using the FGM spacer and designing the optimal cathode shape.

Design for Compression Improvement of a Magnetic Pulse Compressor by Using a Multiwinding Magnetic Switch

In a magnetic pulse compressor (MPC), the saturation inductance of the magnetic switch (MS) determines the energy transfer time. Thus, in general, the number of windings on the MS is modulated to vary the saturation inductance. Changing the number of windings also changes the energy transfer time and the saturation time. In this paper, we propose and analyze an MS with multiwindings to modulate the pulse width without affecting the saturation time of the MS. The parallel structure of the multiwindings on the MS decreases the energy transfer time without affecting the saturation time. Through experiments, we show that the energy transfer time is decreased by 13% via a double winding MS. Therefore, an MS with multiwindings can be used to modulate the pulse width at the last stage of the MPC without affecting the saturation time of the MS.

A 25-F Electric Double-Layer Capacitor Bank and DC Power Supply for Portable High-Current Applications

A portable dc power supply based on electric double-layer capacitor (EDLC) bank was established for high-power applications. EDLC bank needs a dc–dc converter to maintain a constant output voltage and current. Especially, a low-impedance load makes the voltage of capacitors discharge faster, and their discharging time is determined by RC time constant. The proposed system is designed as a fundamental concept, and deals with some issues occurring in a large-scale system. Also, this paper provides detailed information and consideration for a real establishment. Last, we performed a full-scale experiment using basic techniques.

Experimental analysis on hazardness of RF front-end system damaged by high power electromagnetic pulse

The high power electromagnetic(HPEM) is one of the major issue on military area in several years. Contrary to other direct weapons, it is nonlethal weapon that destroy or deceive electronic device but minimize the harm to human1. Commonly, there are two coupling path of electronic device damaged by HPEM pulse. One is the front-door coupling and the other is the back-door coupling2. Due to the front-door coupling is induced a lot more power than the back-door coupling, it is difficult to protect perfectly. Thus it needs to study the damage prediction and the protection method of RF front-end system affected by HPEM pulse.

Design of magnetic switch reset circuit using circuit elements in MPC systems

Magnetic Pulse Compressor (MPC) is a pulse generator using magnetic switch (MS). MS uses characteristics of saturation and unsaturation of magnetic core to be on and to be off. It has been studied due to its high compression rate, high repetitive rate, and availability in high power circumstances. In this paper, it is studied that using circuital element to reset the MS without external sources. The resetting process is as in the following; 1) charging reset circuit during MPC operation, and 2) resetting MS after MPC operation by discharging of reset circuit to MS. This process is analyzed and verified using computer simulation. Because passive reset circuit is used, there is a limitation that it decreases the output of MPC. Although there is decrease in output, it helps reducing the size and cost of the system. This helps MPC being applicable to various applications.

Effects of electron beam focusing on virtual cathode formation in virtual cathode oscillator

As a high power microwave (HPM) source, virtual cathode oscillator has been studied due to its simplicity. A lot of experiments on virtual cathode oscillator has been conducted and reported to study the characteristics and to increase its efficiency. In order to increase its efficiency, ballistic focusing of an electron diode has been studied. And it is reported that the efficiency of virtual cathode oscillator is somewhat increased through the ballistic focusing.

PPC-2015: Analysis of magnetic switch core to improve reliability of magnetic pulse compressor system

Magnetic switch is a type of inductor with magnetic core. It has a property of operating like as a switch using saturation and non-saturation region in hysteresis loop of magnetic materials. The magnetic switch has an advantage in high repetition rate and being usable in the high power field compared to semiconductor switches such as IGBT, Thyristor, and etc. However, it also has a limitation in reliability of the operation compared to semiconductor switches. For this reason, a lot of researches have been made to improve the reliability. To improve the reliability, previous researches have been conducted focusing on altering the value of the residual flux of the magnetic materials. In this paper, the relationship between the operation of switch and the change of initial magnetic flux has been analyzed by altering the DC-bias of the reset circuit. It is conducted on various structures of MPC system. Thus the interrelation of MPC system and the switching operation is analyzed. Using the result of the study, it is expected to have more reliable and less lossy magnetic switch and to be applicable to various areas.