• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.5 no.2
• /
• pp.83-89
• /
• 1996

The objective of this study is to find experimentally the characteristics of the noise generated by the impinging jet on the normal plate, and also to compare the noise characteristics of the impinging jet with those of the free jet. The experiment is performed for the measurement of the noise specturm, the noise power, and the directivity for the free and impinging jets. From the experiment. it is found that the power of noises generated by the free jet as well as the impinging jet is proportional to the eighth power of the jet velocity through the circular converging nozzle, and that the noise power of the impinging jet is 15dB as high as one of the free jet when the plate distance is about within one to three times the nozzle diameter at the pressure ratio 1.39. The sound pressure level of the impinging jet depends upon the jet pressure and the plate distance. The plate distance with the maximum overall sound pressure level is increased with the jet pressure. The directivities with 1/3 octave band frequency for both the free jet and the impinging jet are greatly influenced by the convection effect.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.7
• /
• pp.612-619
• /
• 2016

In this paper, a dual band electrical beam tilting array antenna with bi-directional directivity is designed. Radiating element operates at dual-resonance frequencies and is designed as planar dipole using PCB. In order to tilt the main beam, the phase delay line is designed by use of only the phase shifting line of a $50\Omega$ microstrip line for broadband. The designed antenna has tilting angle of $0^{\circ}$ to ${\pm}8^{\circ}$. For validation of the designed antenna specification, the array antenna is fabricated and the performances are measured. Comparison between theory and experiment shows good agreement.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.5 no.2
• /
• pp.171-179
• /
• 2010

Effective monitoring and maintenance operation of towers, power lines and other defects to ensure high quality and reliability of electric power supplied to customers is becoming one of the most important tasks of today's power industry. One specific technology that has the potential to automate the entire surveillance process is unmanned aerial vehicles. In this paper, we propose a new power line extraction method using the directivity of a power line and Hough transform to detect efficiently power lines from thermal aerial images. In simulation results for several aerial images, the proposed method shows good performance in extracting power line detection.

• Transactions on Electrical and Electronic Materials
• /
• v.9 no.3
• /
• pp.128-133
• /
• 2008

In this paper, in order to analyze property of frequency response in microphone using optical sensor, acousto-optic sensor system has been implemented. The capacitance microphone and fiber-optic transmission path type fiber-optic microphone (FOM) have weaknesses in directivity, size, weight, and price. However suggested optical microphone can be constituted by cheap devices, so it has many benefits like small size, light weight, high directivity, etc. Head part of optical microphone which is suggested in this paper is movable back and forth by sound pressure with the attached reflection plate. Operating point has also been determined by measuring the response characteristics. The choosing the point, which has maximum linearity and sensitivity has changing the distance between optical head and vibrating plate. We measured the output of the O/E transformed signal of the optical microphone while frequency of sound signal is changed using sound measurement /analysis program, "Smaart Live" and "USBPre", which are based on PC, and compared the result from an existing capacitance microphone. The measured optical microphone showed almost similar output characteristics as those of the compared condenser microphone, and its bandwidth performance was about 4 kHz at up to 3 dB.

• ETRI Journal
• /
• v.40 no.1
• /
• pp.26-38
• /
• 2018

To overcome considerable path loss in millimeter-wave propagation, high-gain directional beamforming is considered to be a key enabling technology for outdoor 5G mobile networks. Associated with beamforming, this paper investigates propagation power loss characteristics in two aspects. The first is beamwidth effects. Owing to the multipath receiving nature of mobile environments, it is expected that a narrower beamwidth antenna will capture fewer multipath signals, while increasing directivity gain. If we normalize the directivity gain, this narrow-beamwidth reception incurs an additional power loss compared to omnidirectional-antenna power reception. With measurement data collected in an urban area at 28 GHz and 38 GHz, we illustrate the amount of these additional propagation losses as a function of the half-power beamwidth. Secondly, we investigate power losses due to steering beam misalignment, as well as the measurement data. The results show that a small angle misalignment can cause a large power loss. Considering that most standard documents provide omnidirectional antenna path loss characteristics, these results are expected to contribute to mmWave mobile system designs.

• Composites Research
• /
• v.37 no.1
• /
• pp.53-57
• /
• 2024

Numerous studies have explored structural antennas for integrating advanced wireless systems into aircraft without altering their external form. However, much of the research on structural antennas has focused on patch antennas, which are characterized by limitations such as narrow frequency bands and low directivity. In contrast, the Vivaldi antenna, widely utilized in wireless applications, offers the advantages of a wide frequency band and high directivity. Nevertheless, its application to aircraft has been challenging due to radiation direction constraints. In this study, we endeavor to address this issue by proposing the application of the antenna patch onto the honeycomb wall, thus enabling the use of the Vivaldi antenna on aircraft. The impact of the honeycomb structure on antenna radiation performance was analyzed, and the potential of the honeycomb Vivaldi antenna was validated through simulation.

• The Journal of the Acoustical Society of Korea
• /
• v.23 no.2
• /
• pp.146-161
• /
• 2004

There have been always some difficulties in target setting and conditioning of acoustic performances of the Korean traditional music hall due mainly to the lack of the information on the sound radiation characteristics of Korean musical sources. In this study, the radiation characteristics of four typical Korean traditional musical sources were investigated in precision and their usage was demonstrated: The selected musical sources were Gayageum (string), Daegeum (woodwind), Jango (drum), and Pansori Chang (vocal performance). Each sound source was located at the center of a semi-anechoic chamber and the directivity was determined by the measured sound pressure levels in every 10° angular position, for both vertical and horizontal directions. The directivity pattern of Gayageum varies from a uniform to a complex pattern having many side lobes with the increase of frequency. The main radiation of Daegeum is toward the upward direction. The directivity pattern of Jango is clearly a side-oriented one and the left direction intensity is sharper than its right side at low frequencies. For the Chang, the directivity pattern change from a uniform pattern to a frontally directed one as the frequency goes high. Measured directional and spectral characteristics of traditional Korean music sources were implemented into the computation of architectural acoustic measures for the Busan National Korean Traditional Music Hall which is under construction. Parameters such as RT, SPL, C80, IE, STI were calculated at two receiver positions by using a ray tracing technique. Significant differences in the acoustic measures at receiver positions were observed between the results in using the omni-directional source and the directional one. It is thought that the suggested source data and design method can be used as a basic reference in the future acoustic design of performance halls for the Korean traditional music.

• Proceedings of the Optical Society of Korea Conference
• /
• 2003.02a
• /
• pp.318-319
• /
• 2003

이동통신 시스템에서 데이터, 음성, 영상신호를 효율적으로 전송하기 위해 위상 배열 안테나(Phased-Array Antenna： PAA)에 관한 연구가 최근 국내외적으로 활발히 진행되고 있다. 광통신 기술을 이용한 PAA용 실시간 지연선로 (True Time-Delay： TTD)는 넓은 대역폭, 저 손실, 전자파 간섭에 무관, 소형화, 특히 ‘beam squintr´ 현상이 없는 장점이 있기 때문에 각광을 받고 있다. 특히, 신호의 간섭을 줄이기 위해 안테나 방사 패턴의 부엽 (side lobe)의 크기를 감소시킬 수 있는 안테나 설계기술이 필요하다. (중략)

• Journal of Biomedical Engineering Research
• /
• v.13 no.3
• /
• pp.201-208
• /
• 1992

In the indirect optical bio-telemetry, high frequency response and low minimum detectable optical power can be achieved by using photodiode with small light receiving area which minimizes junction capacitance. But, on the other hand, S/N ratio becomes low because the optical signal current is small. To solve such a problem, we attach plato-convex lens in front of photo diode, The results of comput- er simulation and experiments suggest promotion of light receiving efficiency and possibility of multi- telemetry system through directivity of convex lens in one room.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2001.10a
• /
• pp.218-221
• /
• 2001

이 논문에서는 800MHz 대역에서의 interdigital 커패시터를 이용한 높은 지향성의 방향성 결합기를 설계하였다. 본 논문에서는 20dB 방향성 결합기 설계에 있어 interdigital 커패시터의 파라미터 W, G, Ge, Lo, Wt에 따른 결합도와 격리도의 변화를 분석하여 최적화 함으로써 30dB이상의 지향성을 얻도록 설계하는 것을 목적으로 하였다.