• Title/Summary/Keyword: coaxial

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NO Gas Sensing Properties of ZnO-Carbon Nanotube Composites (산화아연-탄소나노튜브 복합체의 일산화질소 가스 감지 특성)

  • Park, Seong-Yong;Jung, Hoon-Chul;Ahn, Eun-Seong;Nguyen, Le Hung;Kang, Youn-Jin;Kim, Hyo-Jin;Kim, Do-Jin
    • Korean Journal of Materials Research
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    • v.18 no.12
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    • pp.655-659
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    • 2008
  • The NO gas sensing properties of ZnO-carbon nanotube (ZnO-CNT) composites fabricated by the coaxial coating of single-walled CNTs with ZnO were investigated using pulsed laser deposition. Upon examination, the morphology and crystallinity of the ZnO-CNT composites showed that CNTs were uniformly coated with polycrystalline ZnO with a grain size as small as 5-10 nm. Gas sensing measurements clearly indicated a remarkable enhancement of the sensitivity of ZnO-CNT composites for NO gas compared to that of ZnO films while maintaining the strong sensing stability of the composites, properties that CNT-based sensing materials do not have. The enhanced gas sensing properties of the ZnO-CNT composites are attributed to an increase in the surface adsorption area of the ZnO layer via the coating by CNTs of a high surface-to-volume ratio structure. These results suggest that the ZnO-CNT composite is a promising template for novel solid-state semiconducting gas sensors.

Development of an Improved Point Load Apparatus (개량형 점하중강도시험기의 개발)

  • Kim, Yong-Phil;Um, Jeong-Gi
    • Tunnel and Underground Space
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    • v.19 no.6
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    • pp.473-478
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    • 2009
  • The accuracy of point load apparatus is depend on point to point coaxial fitting. Also, the estimation of applied point load using the pressure gauge frequently lead to erroneous results. An improved point load apparatus has been developed in this study by mounting linear bearing on polished support rod, and eccentric error of point to point axis has been sustained less than 0.1 mm even under series of extreme work load conditions. Two digital displacement gauges are attached to measure the distance from point to point with sample specimen. A load cell mounted at the end of upper conical platen measure the applied net load on sample instead of preassure gauge. Total of 107 point load tests has been achieved to assure the quality and performance of developed apparatus. This exercise turned out to be successful.

Design and Fabrication of Dual-Band Patch Antenna with Bridge for WLAN Applications (WLAN용 이중대역 브리지 패치 안테나설계 및 제작)

  • Kim, Kab-Ki
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.14 no.3
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    • pp.547-551
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    • 2010
  • In this paper, Double rectangular patch with 4-bridges is investigated for solution of IEEE 802.11b/g(2.4GHz) and 802.11a(5.7GHz). Rectangular patch for 5.7GHz frequency band is printed on the PCB substrate and connected to another rectangular patch for 2.4GHz frequency band with 4-bridges to obtain dual band operation in a antenna element. The proposed antenna has a low profile and is fed by $50{\Omega}$ coaxial line. The dielectric constant of the designed antenna substrate is 3.27. Two rectangular patches have each resonance frequencies that are 2.4GHz and 5.7GHz. A dual-band characteristic is shown as connecting two rectangular patch using four bridges. Also, the proposed antenna is shown input return loss that is below -10dB at 2.4GHz and 5.7GHz of WLAN(Wireless LAN).

Compact Rectenna System Design Using a Direct Impedance Matching Method (임피던스 직접 정합 방법에 의한 Rectenna 시스템 소형화 설계)

  • Choi, Taemin;Han, Sang-Min
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.24 no.3
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    • pp.286-291
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    • 2013
  • In this paper, a compact rectenna system is designed using a circular sector antenna with harmonic-rejecting characteristics and a direct impedance matching method. The system is designed with bandpass filtering performed by the harmonic-rejection of the circular sector antenna and without impedance matching circuit for the diodes by the direct impedance matching technique. Therefore, while the rectifying circuit of the proposed system can be implemented without a bandpass filter and a impedance matching circuit, it is integrated on the back side of the antenna using precise fabrication techniques for coaxial feedings without degrading the system performances corresponding to the feeding points. From the experimental results, the optimized rectenna system has presented excellent performances of a conversion efficiency of more than 52 % and a conversion voltages of more than 1.5 V at 2.5 GHz.

Effects of Atmospheric Pressure Microwave Plasma on Surface of SUS304 Stainless Steel

  • Shin, H.K.;Kwon, H.C.;Kang, S.K.;Kim, H.Y.;Lee, J.K.
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.268-268
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    • 2012
  • Atmospheric pressure microwave induced plasmas are used to excite and ionize chemical species for elemental analysis, for plasma reforming, and for plasma surface treatment. Microwave plasma differs significantly from other plasmas and has several interesting properties. For example, the electron density is higher in microwave plasma than in radio-frequency (RF) or direct current (DC) plasma. Several types of radical species with high density are generated under high electron density, so the reactivity of microwave plasma is expected to be very high [1]. Therefore, useful applications of atmospheric pressure microwave plasmas are expected. The surface characteristics of SUS304 stainless steel are investigated before and after surface modification by microwave plasma under atmospheric pressure conditions. The plasma device was operated by power sources with microwave frequency. We used a device based on a coaxial transmission line resonator (CTLR). The atmospheric pressure plasma jet (APPJ) in the case of microwave frequency (880 MHz) used Ar as plasma gas [2]. Typical microwave Pw was 3-10 W. To determine the optimal processing conditions, the surface treatment experiments were performed using various values of Pw (3-10 W), treatment time (5-120 s), and ratios of mixture gas (hydrogen peroxide). Torch-to-sample distance was fixed at the plasma edge point. Plasma treatment of a stainless steel plate significantly affected the wettability, contact angle (CA), and free energy (mJ/$m^2$) of the SUS304 surface. CA and ${\gamma}$ were analyzed. The optimal surface modification parameters to modify were a power of 10 W, a treatment time of 45 s, and a hydrogen peroxide content of 0.6 wt% [3]. Under these processing conditions, a CA of just $9.8^{\circ}$ was obtained. As CA decreased, wettability increased; i.e. the surface changed from hydrophobic to hydrophilic. From these results, 10 W power and 45 s treatment time are the best values to minimize CA and maximize ${\gamma}$.

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Compact Dual-band Slot Antenna With Bent Slots (접힌 슬롯이 추가된 소형 이중 대역 슬롯 안테나)

  • Baek, Woon-Seok
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.20 no.6
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    • pp.1049-1056
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    • 2016
  • In this paper, a design method for a compact dual-band slot antenna with bent slot is studied. Bent slots are added on the rectangular slot of the proposed antenna for dual-band operation. The rectangular slot is fed by a coaxial cable by placing a rectangular feeding patch inside the slot. When the bent slots are added onto the both corner of the upper side of the rectangular slot symmetrically, a new resonant frequency is created in low frequency because of the increasement of the slot length. A prototype of the proposed dual-band slot antenna operating at 2.45 GHz WLAN band and 4.50-8.30 GHz band including 5GHz WLAN band is fabricated on an FR4 substrate with a dimension of 30 mm by 30 mm. Experiment results show that the antenna has a desired impedance characteristic with a frequency band of 2.40-2.49 GHz and 4.33-9.85 GHz for an input reflection coefficient < -10 dB.

Relationships between dielectric properties and characteristics of impregnated and activated samples of potassium carbonate-and sodium hydroxide-modified palm kernel shell for microwave- assisted activation

  • Alias, Norulaina;Zaini, Muhammad Abbas Ahmad;Kamaruddin, Mohd Johari
    • Carbon letters
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    • v.24
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    • pp.62-72
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    • 2017
  • The aim of this work was to evaluate the dielectric properties of impregnated and activated palm kernel shells (PKSs) samples using two activating agents, potassium carbonate ($K_2CO_3$) and sodium hydroxide (NaOH), at three impregnation ratios. The materials were characterized by moisture content, carbon content, ash content, thermal profile and functional groups. The dielectric properties were examined using an open-ended coaxial probe method at various microwave frequencies (1-6 GHz) and temperatures (25, 35, and $45^{\circ}C$). The results show that the dielectric properties varied with frequency, temperature, moisture content, carbon content and mass ratio of the ionic solids. PKSK1.75 (PKS impregnated with $K_2CO_3$ at a mass ratio of 1.75) and PKSN1.5 (PKS impregnated with NaOH at a mass ratio of 1.5) exhibited a high loss tangent ($tan{\delta}$) indicating the effectiveness of these materials to be heated by microwaves. $K_2CO_3$ and NaOH can act as a microwave absorber to enhance the efficiency of microwave heating for low loss PKSs. Materials with a high moisture content exhibit a high loss tangent but low penetration depth. The interplay of multiple operating frequencies is suggested to promote better microwave heating by considering the changes in the materials characteristics.

A CMOS Wide-Bandwidth Serial-Data Transmitter for Video Data Transmission (영상신호 전송용 CMOS 광대역 시리얼 데이터 송신기)

  • Lee, Kyungmin;Park, Sung Min
    • Journal of the Institute of Electronics and Information Engineers
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    • v.54 no.4
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    • pp.25-31
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    • 2017
  • This paper presents a 270/540/750/1500-Mb/s serial-data transmitter realized in a $0.13-{\mu}m$ CMOS technology for the applications of video data transmission. A low-cost RG-58 copper cable(5C-HFBT-RG6T) is exploited as a transmission medium connected to a single BNC connector, which shows cable loss 45 dB in maximum at 1.5 GHz. RLGC modeling provides an equivalent circuit for SPICE simulations of which characteristics are very similar to the measured cable loss. The loss can be compensated by pre-emphasis at transmitter and equalization at receiver if needed. Measurements of the proposed transmitter chip demonstrate the operations of 270-Mb/s, 540-Mb/s, 750-Mb/s and 1.5-Gb/s, and provide the output voltage levels of $370mV_{pp}$ at 1.5 Gb/s even with the pre-emphasis turned-off. The total power consumption is 104 mW from 1.2/3.3-V supplies and the chip occupies the area of $1.65{\times}0.9mm^2$.

Combustion Experiments of a High Pressure Liquid Propellant Thrust Chamber (고압 실물형 연소기의 저압 및 설계점 연소시험)

  • Seo Seonghyeon;Han Yeoung-Min;Moon Il-Yoon;Lee Kwang-Jin;Song Joo-Young;Choi Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • v.y2005m4
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    • pp.269-273
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    • 2005
  • A practical, 30-tonf-class fullscale thrust chamber has been combustion tested using real propellants for the first time in the domestic technology scene. The very first combustion test was conducted at a low mass flow rate condition for the preliminary assessment of any problems associated with its function and performance while reducing risks from a high chamber pressure never achieved before. A test for the design condition achieved through a low-pressure stage shows stable characteristics of all the static pressures and thrust. Dynamic pressures measured in the manifolds and the chamber did not reveal any distinct wave coupled to a specific frequency and their intensities reside in the allowable range. Moreover, it is encouraging to find no physical failures with a thrust chamber hardware.

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NO Gas Sensing Characteristics of Layered Composites of Carbon Nanotubes Coated with Al-Doped ZnO (탄소나노튜브를 알루미늄이 첨가된 산화아연으로 코팅한 층상 복합체의 일산화질소 가스 감지 특성)

  • Ahn, Eun-Seong;Jung, Hoon-Chul;Nguyen, Nguyen Le;Oh, Dong-Hoon;Kim, Hyo-Jin;Kim, Do-Jin
    • Korean Journal of Materials Research
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    • v.19 no.11
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    • pp.631-636
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    • 2009
  • We investigated the NO gas sensing characteristics of ZnO-carbon nanotube (ZnO-CNT) layered composites fabricated by coaxial coating of single-walled CNTs with a thin layer of 1 wt% Al-doped ZnO using rf magnetron sputtering deposition. Morphological studies clearly revealed that the ZnO appeared to form beadshaped crystalline nanoparticles with an average diameter as small as 30 nm, attaching to the surface of the nanotubes. It was found that the NO gas sensing properties of the ZnO-CNT layered composites were dramatically improved over Al-doped ZnO thin films. It is reasoned from these observations that an increase in the surface-to-volume ratio associated with the numerous ZnO “nanobeads” on the surface of the CNTs results in the enhancement of the NO gas sensing properties. The ZnO-CNT layered composite sensors exhibited a maximum sensitivity of 13.7 to 2 ppm NO gas at a temperature of 200${^{\circ}C}$ and a low NO gas detection limit of 0.2 ppm in dry air.