• Journal of Sensor Science and Technology
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• v.25 no.2
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• pp.124-130
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• 2016

NDIR $CO_2$ gas sensor was built with ASIC implemented thermopile sensor which included temperature sensor and unique elliptical waveguide structures in this paper. The temperature dependency of dual infrared sensor module ($CO_2$ and reference IR sensors) has been characterized and its output voltage characteristics according to the temperature and gas concentration were proposed for the first time. NDIR $CO_2$ gas and reference IR sensors showed linear output voltages according to the variation of ambient temperatures from 243 K to 333 K and their slopes were 14.2 mV/K and 8.8 mV/K, respectively. The output voltages of temperature sensor also presented a linear dependency according to the ambient temperature and could be described with V(T)=-3.191+0.0148T(V). The output voltage ratio between $CO_2$ and reference IR sensors revealed irrelevant to the changes of ambient temperatures and gave a constant value around 1.6255 with standard deviation 0.008 at 0 ppm. The output voltage of $CO_2$ gas sensor at zero ppm $CO_2$ gas consisted of two components; one is caused by the HPB (half pass-band) of IR filter and the other is attributed to the part of $CO_2$ absorption wavelength. The characteristics of output voltages of $CO_2$ gas sensor could be accurately modeled with three parameters which are dependent upon the ambient temperatures and represented small average error less than 1.5% with 5% standard deviation.

• Journal of IKEEE
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• v.18 no.4
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• pp.586-592
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• 2014

In this paper, high efficiency power management IC(PMIC) with DT-CMOS(Dynamic threshold voltage Complementary MOSFET) switching device is presented. PMIC is controlled PWM control method in order to have high power efficiency at high current level. The DT-CMOS switch with low on-resistance is designed to decrease conduction loss. The control parts in Buck converter, that is, PWM control circuit consist of a saw-tooth generator, a band-gap reference(BGR) circuit, an error amplifier, comparator circuit, compensation circuit, and control block. The saw-tooth generator is made to have 1.2MHz oscillation frequency and full range of output swing from supply voltage(3.3V) to ground. The comparator is designed with two stage OP amplifier. And the error amplifier has 70dB DC gain and $64^{\circ}$ phase margin. DC-DC converter, based on current mode PWM control circuits and low on-resistance switching device, achieved the high efficiency nearly 96% at 100mA output current. And Buck converter is designed along LDO in standby mode which fewer than 1mA for high efficiency. Also, this paper proposes two protection circuit in order to ensure the reliability.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.7
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• pp.675-678
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• 2015

In this paper, we proposed a multi-function conversion block for microwave receiver. The proposed multi-function conversion block is composed of a broadband voltage controlled oscillator and a dual-mode mixer. Depending on whether the bias voltage is supplied, the first IF(Intermediate Frequency) output frequency(4,595 MHz/6,045 MHz) needed in microwave receiver is converted to 720 MHz and the another IF output frequency(720 MHz) for receiving Ku-band has the multi-functional operations of the dual mode that are bypass and attenuation without frequency conversion. Implementation and measurement results show that each intermediate frequency has conversion loss characteristic according to the LO power. The LO power conversion loss of 4,595 MHz at the LO levels from 2 dBm to 4 dBm is 13 dB, another of 6,035 MHz is 12 dB and the other of 720 MHz is 7.0 dB.

• Smart Structures and Systems
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• v.26 no.4
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• pp.481-493
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• 2020

The negative stiffness spring and inerter are both characterized by the negative stiffness effect in the force-displacement relationship, potentially yielding an amplifying mechanism for dashpot deformation by being incorporated with a series tuning spring. However, resisting forces of the two mechanical elements are dominant in different frequency domains, thus leading to necessary complementarity in terms of vibration control and the amplifying benefit. Inspired by this, this study proposes a Negative Stiffness Inerter System (NSIS) as an earthquake protection system and developed analytical design formulae by fully utilizing its advantageous features. The NSIS is composed of a sub-configuration of a negative stiffness spring and an inerter in parallel, connected to a tuning spring in series. First, closed-form displacement responses are derived for the NSIS structure, and a stability analysis is conducted to limit the feasible domains of NSIS parameters. Then, the dual advantageous features of displacement reduction and the dashpot deformation amplification effect are revealed and clarified in a parametric analysis, stimulating the establishment of a displacement-based optimal design framework, correspondingly yielding the design formulae in analytical form. Finally, a series of examples are illustrated to validate the derived formulae. In this study, it is confirmed that the synergistic incorporation of the negative stiffness spring and the inerter has significant energy dissipation efficiency in a wide frequency band and an enhanced control effect in terms of the displacement and shear force responses. The developed displacement-based design strategy is suitable to utilize the dual benefits of the NSIS, which can be accurately implemented by the analytical design formulae to satisfy the target vibration control with increased energy dissipation efficiency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.830-838
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• 2003

In this paper, TX/RX dual operation microstrip single antenna for satellite communication is designed, analyzed, fabricated and measured. TX/RX frequency ranges are 14.0∼l4.5 GHz, 11.7∼12.75 GHz in respectively and vertical and horizontal polarizations are used for TX and RX. This antenna uses microstrip direct feeding for RX and aperture coupled strip-line feeding for TX and accommodates stacked elements for a high directivity and wide impedance bandwidth. In an analysis of single element, FDTD and MOM was compared and FDTD analysis was more accurate because of the consideration of finite structure and imperfect two ground planes. The proposed structure facilitates generally to an extension of two dimensional array and lower an unwanted radiation by strip-line feed in TX. TX/RX 8${\times}$4 array has a return loss below -10 dB, -14 dB in TX, RX respectively and a gain ranging from 19.1∼20.7 dB in TX, 21.2∼21.8 dB in RX which has a radiation efficiency of 43∼5l %, 52∼57 %.

• Journal of Korea Water Resources Association
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• v.53 no.6
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• pp.417-425
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• 2020

In order to predict and prevent hydrological disasters such as flood, it is necessary to accurately estimate rainfall. In this paper, an areal average rainfall estimation method using multiple elevation observation data of an electromagnetic wave rain gauge is presented. The small electromagnetic rain gauge system is a very small precipitation radar that operates at K-band with dual-polarization technology for very short distance observation. The areal average rainfall estimation method is based on the assumption that the variation in rainfall over the observation range is small because the observation distance and time are very short. The proposed method has been evaluated by comparing with ground instruments such as tipping-bucket rain gauges and a Parsivel. The evaluation results show that the methodology works fairly well for the rainfall events which are shown here.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.75-76
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• 2016

Even if ICS(Interference Cancellation System) repeater is used in wireless communication system, it has the disadvantage that it must have enough distance between Donor and Service antenna to be isolated. In this paper, new ICS repeater integrated antenna with high insolation characteristics is designed. The proposed antenna is fabricated for 800MHz and measured. Bandwidth and gain are optimized by changing the stub lengths near main patch and power divider, and also by changing the size of parasitic patch. This antenna has a return loss less than -13 dB, a gain over 3 dBi, and an isolation between the donor and the server antennas less than -56 dB from 824~894 MHz for CDMA mobile communication. Therefore, the proposed antenna structure can be applied to eliminate the shadow area and to expand the coverage area for any other wireless communication bands.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.3C
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• pp.239-247
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• 2003

This paper presents a dual-rate (2.4/4.0 kbps) Improved Harmonic-CELP(IHC) speech coder based on the EHC(Efficient Harmonic-CELP) which was presented by the authors. The proposed IHC employs the harmonic coding for voiced and the CELP for unvoiced segments. In the IHC, an initial voiced/unvoiced estimate is obtained by the pitch gain and energy. Then, the final V/UV mode is decided by using the frame energy contour. A new harmonic estimation combining peak picking and delta adjustment provides a more reliable harmonic estimation than that in the EHC. In addition, a noise mixing scheme in conjunction with an improved band voicing measurement provides the naturalness of the synthesized speech. To demonstrate the performance of the proposed IHC coder, the coder has been implemented and compared with the 2.0/4.0 kbps HVXC(Harmonic excitation Vector Coding) standardized by MPEG-4. Results of subjective evaluation showed that the proposed IHC coder and produce better speech quality than the HVXC, with only 40% complexity of the HVXC.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.10
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• pp.1050-1060
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• 2009

In this paper, a X-Band T/R-module for SAR(Synthetic Aperture Radar) systems based on active phased array antennas is designed and fabricated. The T/R modules have a and width of more than 800 MHz centered at X-Band and support dual, switched polarizations. The output power of the module is 7 watts over a wide bandwidth. The noise figure is as low as 3.9 dB. Phase and amplitude are controlled by a 6-bit phase shifter and a 6-bit digital attenuator, respectively. Further the fabricated T/R module has est and calibration port with directional coupler and power divider. Highly integrated T/R module is achieved by using LTCC(Low Temperature Co-fired Ceramic) multiple layer substrate. RMS gain error is less than 0.8 dB max. in Rx mode, and RMS phase error is less than $4^{\circ}$ max. in Rx/Tx phase under all operating frequency band, or the T/R module meet the required electrical performance m test. This structure an be applied to active phase array SAR Antennas.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.1040-1049
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• 2014

In this paper, a quad-band antenna for DCS1800, PCS1900, WCDMA, WLAN and Mobile WiMAX application is proposed. The proposed antenna is a printed monopole structure, and consists of two rectangular ring-shaped radiating patches on the front side and two different size of L-shaped slots on the back side(ground plane). Two rectangular ring radiation patches are respectively resonant at 2 GHz and 3.5 GHz bands, and additional resonance is occurred at 5.3 GHz by the coupling effect between two ring patches. In addition, the optimized matching characteristic is obtained by controlling the gaps. Also, by adding two L-slots on the ground plane, additional resonant frequency band of 5.6 GHz is occurred. Finally the measured bandwidths of the proposed antenna below -10 dB return loss are 1,200 MHz(1.6~2.8 GHz), 800 MHz(3.2~4.0 GHz), 300 MHz(5.14~5.44 GHz), and 690 MHz(5.56~6.25 GHz). The radiation patterns have the omni-directional characteristic, and the measured antenna average gains at resonant bands are 0.86~4.07 dBi.