• Korean Journal of Environmental Agriculture
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• v.35 no.1
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• pp.55-61
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• 2016

BACKGROUND: This study was carried out to survey the levels of heavy metals in perennial root vegetables and to assess dietary exposure and risk to the Korean population health.METHODS AND RESULTS: Perennial root vegetables (n=214) including Panax ginseng C.A mayer, Woodcultivated ginseng, Codonopsis lanceolata, and Platycodon granditloum were collected from markets or harvested from farmhouse in Korea. Lead(Pb), cadmium(Cd) and arsenic (As) analysis were performed with microwave device and inductively coupled plasma mass spectrometer. Limit of detection for heavy metals were 0.010~0.050 μg/kg, while limit of quantitation were 0.035~0.175 μg/kg. The recovery results were in the range of 76~102%. The average contents of heavy metals in perennial root vegetables were in the range of Pb 0.013(Panax ginseng C.A Mayer)~0.070 (Wood-cultivated ginseng) mg/kg, Cd 0.009(Panax ginseng C.A Mayer)~0.034(Codonopsis lanceolata) mg/kg, and As 0.002(Panax ginseng C.A Mayer)~0.004(Plafycodon grandiflorum) mg/kg, respectively. For risk assessment, daily intakes of heave metals were estimated and risk indices were calculated in comparison with reference dose. The dietary exposures of heavy metals through usual intake were Pb 0.070 μg/day, Cd 0.041 μg/day and As 0.008 μg/day, taking 0.03%, 0.08% and 0.0003% as risk indices, respectively.CONCLUSION: The risk level for Korean population exposed to heavy metals through intake of perennial root vegetables was far low, indicating of little possibility of concern.

• Journal of the Korean Vacuum Society
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• v.14 no.4
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• pp.207-214
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• 2005

This paper presents a channel structure for promising high performance pseudomorphic high electron mobility transistor(pHEMT) switching device for design and fabricating of microwave control circuits, such as switches, phase shifters, attenuators, limiters, for application in personal mobile communication systems. Using the designed epitaxial channel layer structure and ETRI's $0.5\mu$m pHEMT switch process, single pole double throw (SPDT) Tx/Rx monolithic microwave integrated circuit (MMIC) switch was fabricated for 2.4 GHz and 5 GHz band wireless local area network (WLAN) systems. The SPDT switch exhibits a low insertion loss of 0.849 dB, high isolation of 32.638 dB, return loss of 11.006 dB, power transfer capability of 25dBm, and 3rd order intercept point of 42dBm at frequency of 5.8GHz and control voltage of 0/-3V These performances are enough for an application to 5 GHz band WLAN systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.2
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• pp.397-401
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• 2005

In this paper, we have developed a frequency mixer which can be used as a microwave phase conjugator in the retrodirective array antenna. The retrodirective array, which can reflect the incident wave retrodirertively back to the source direction without any priori information, requires phase conjugators to achieve the phase change of 180 degrees for the incoming signal. frequency mixers can efficiently serve as phase conjugators. The circuit topology is of the 2-port structure to avoid the complexity of LO and Rf signal combination and matching circuits, using a pseudomorphic HEU device. The operating frequencies are 4.0 CHz, 2.01 CHz, and 1.99 CHz for LO, RF, and If signals, respectively. Conversion loss is measured to be -ldB and 1-dB compression point -l5 dBm at the LO power of -10 dBm.

• Journal of Advanced Navigation Technology
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• v.24 no.2
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• pp.107-114
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• 2020

A power amplifier of 2.4 GHz ISM band is designed to implement a transmitter system. High efficiency amplifiers can be implemented as class E or class F amplifiers. This study has designed a 20 W high efficiency class E amplifier that has simple circuit structure in order to utilize for the ISM band application. The impedance matching circuit was designed by class E design theory and circuit simulation. The designed amplifier has the output power of 44.2 dBm and the power added efficiency of 69% at 2.45 GHz. In order to apply 30 dBm input power to the designed power amplifier, voltage controlled oscillator (VCO) and driving amplifier have been fabricated for the input feeding circuit. The measurement of the power amplifier shows 43.2 dBm output and 65% power added efficiency. This study can be applied to the design of power amplifiers for various wireless communication systems such as wireless power transfer, radio jamming device and high power transmitter.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.1
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• pp.8-14
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• 1999

The active devices used at microwave frequency have the different phase shift according to input power. Especially, The difference of the phase shift is large in the saturation region of the amplifier. In this paper, we disigned the phase control system for fixing the different phase shift at device. With the high frequency nonlinear amplifier, we fabricated such system that the phase shift to be fixed automatically using the varible phase shifter. The variable phase shifter fixed total phase variation of the circuit using the information that was obtained from the comparison of imputsignal phase with output signal phase. Even though the input signal is 2-tone or FM type, we could estimate and also fix the phase variation on DUT Dynamic range is about 10dB. It has been experimented at 1960MHz using Teflon (H=31mil, ${\varepsilon}r$=3.2)

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.498-505
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• 1999

The ferrite device that has nonreciprocal characteristics has been used as various microwave components. In this paper, the spectral-domain method was used to analyze the characteristics of structure(strip line on multilayer structure with ferrite material) for which no paper has been published yet. It is assumed that an external dc magnetic field is applied perpendicular to the ground conductor. The propagation constant is calculated for each parameter and frequency. Also we considered convergence by increasing the number of basis functions and verified the numerical analysis results. From the results, we could confirm that as the thicknesses of YIG is increased, the cutoff region is widened and the propagation constant is decreased at the frequency of upper cutoff region. For a larger applied dc magnetic field, the frequency of cutoff region is found to be increased. Also the simulation results for strip line show that the cutoff region is widened and the propagation constant is larger than that of microstrip line.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.11
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• pp.2479-2485
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• 2013

In this paper, we present a design for solid-state radar SSPA with sequential bias. We apply to variable extension pulse generator to eliminate signal distortion which is caused by bias rising/falling delay of power amplifier. There is an optimum impedance matching circuit to have high efficiency of GaN-power device by measuring microwave characteristics through load-pull method. The designed SSPA is consisted of pre-amplifier, drive-amplifier and main-amplifier as a three stages to apply for X-Band solid-state radar. Thereby we made a 200W SSPA which has output pulse maximum power shows 53.67dBm and its average power is 52.85dBm. The optimum design of transceiver module for solid-state pulse compression radar which is presented in this dissertation, it can be available to miniaturize and to improve the radar performances through additional research for digital radar from now on.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.154-160
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• 2005

Microwave Otters are essential device in modem wireless systems. A compact dimension BPF(Band-pass Filter) for IEEE 802.11a WLAN service is realized using LTCC multi-layer process. To extrude 2-stage band-pass equivalent circuit, band-pass and J-inverter transform applied to Chebyshev low-pass prototype filter. Because parallel L-C resonator is complicate and hard to control the inductor characteristics in high frequency, the shorted $\lambda/4$ stripline is selected for the resonator structure. The passive element is located in the different layers connected by conventional via structure and isolated by inner GND. The dimension of fabricated stacked band-pass filter which is composed of six layers, is $2.51\times2.27\times1.02\;mm^3$. The measured filter characteristics show the insertion loss of -2.25 dB, half-power bandwidth of 220 MHz, attenuation at 5.7 GHz of -32.25 dB and group delay of 0.9 ns at 5.25 GHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.7
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• pp.761-770
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• 2008

Impedance or admittance inverter is a conceptual 2-port device frequently used in microwave filter design. In this paper, the equivalent circuit using inverter for general loss less 2-port circuit is presented. Our equivalent circuit can be directly and easily represented with z- or y-parameters compared with the conventional methods. Based on the representation, the derived results for various coupled lines such as parallel coupled line and anti-parallel coupled lines are compared ours. In addition, the results of other workers for improvement of the distortion in frequency response of microstrip coupled line filter are derived using our representation and compared. The proposed equivalent circuit shows the difference with conventional equivalent circuit so the conventional design method can not be applied to parallel coupled line filter with our representation. So in this paper the novel design method is proposed and we showed the method yields more accurate design results.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.5
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• pp.787-794
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• 2001

In this paper, the development of large-signal model extractor for GaAs FET device through the Monolithic Microwave integrated Circuit(MMIC) is presented. The measurement program controlled by personal computer is developed for the processing of an amount of measured data, and the de-embedding algorithm is added to the program for voltage dropping as attached series resistance on measurement system. The small-signal model parameters are typically consisted of 7 elements that are considered as complexity of large-signal model and its the accuracy of the small-signal model is verified through comparing with measured data as varied bias point. The fitting function model, one of the empirical model, is used for quick simulation. In the process of large-signal model parameter extraction, one-dimensional optimization method is proposed and optimized parameters are extracted. This study can reduce the modeling and measuring time and can secure a suitable model for circuit.