• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.68-72
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• 1993

A method to measure the distortions of the loudspeaker at low frequencies without an anechoic chamber is proposed. This method utilizes the fact that the n-th harmonic distortion outside the enclosure is boosted by 40log n dB compared to that inside the enclosure. By compensating for the effect of standing waves occuring inside the enclosure, it is possible to predict the distortions for wide frequency ranges below the first break-up frequency of the diaphragm. The method is applicable to the intermodulation distortion as well.

• Proceedings of the IEEK Conference
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• 2001.06b
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• pp.173-176
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• 2001

A new EMI estimation technique concerned with a PDP system is presented. A physical circuit model is developed which can fairly well describe the AC-PDP system. Then EMIs are determined by exploiting Hertzian dipole antenna model. The simulation results are experimentally verified with the test panel. The AC PDP system was measured in the frequency range of 30MHz ~ 300MHz in a semi-anechoic chamber, according to CISPR 13 code. Thereby, it is shown that the proposed technique can be usefully employed for EMI reduction.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.704-707
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• 2000

In this experimental study, noise level measurements were conducted on physical LBB(Linear Ball Bush) samples in a semi-anechoic chamber. Evaluation of the measured data demonstrates that LBB's noise level is proportional to the logarithmic of its speed multiplied by the ball diameter. Furthermore details of implementations and process for measuring noise level and operating speed of LBB are also presented.

• 전기의세계
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• v.25 no.2
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• pp.40-45
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• 1976

유도전동기의 고주파진동토오크의 산정법에 대하여는 Morrill, Chang, Puchstein Kimball 및 Veinott씨 등에 의한 불평형공간자속분포의 대칭좌표법 또는 2회전자계법해석으로 많은 연구가 거듭되어 기계정수가 고주파토오크에 미치는 영향의 관계를 풀이하고 있다. 또한 Jordan과 Lax씨에 의하여 편심 및 기계적진동에 따른 전자력파의 분포력 mode수 및 그 주파수를 개발함으로서 소음방지대책에 많은 진전을 보았다. 소음진동측정방법으로는 원래 진동측정이 정밀한 장치에 의존하여야 하며 그 방법 또한 어려운 점이 많아 method of 1-point measurement of electromagnetic-force waves로 처리되어 왔으나 요즈음에는 anechoic chamber와 같은 장치에서의 특별한 조작에 의하여 method of resultant measurement of accoustic noise powers에 의하여 보다 합리적인 소음측정 및 해석이 가능하게 되었다.

• The Journal of the Acoustical Society of Korea
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• v.19 no.3E
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• pp.19-24
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• 2000

The present research examined the contribution of sounds′ familiarity to auditory distance perception, while attempting to control the influences of unavoidable physical characteristics among sounds. Different vocal "styles" ("shouts", "whispers" and "a normal conversation") of man and woman were recorded digitally and presented from a stationary loudspeaker to blindfolded listeners in a semi anechoic chamber. Playback levels were adjusted to remove extraneous sound level cues. The results showed that the shouting voice was judged as appearing farthest, the whispering voice closest, and the conversational voice was intermediate. The findings suggested that the perception of auditory distance may be affected by past experience (or familiarity).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.484-488
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• 2007

In this paper, the measurement system using the microphone array developed for analyzing cabin noise of the vehicle and its applications are discussed. The sensor is a three dimensional microphone array, the microphones and cameras are equipped on the rigid sphere. The cameras are used for acoustic visualization. As applications, the experiments in both reverberation chamber and anechoic chamber are discussed. These results show that this system is very useful to evaluate or improve the vehicle sound insulation performance.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.84-90
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• 2012

Since the major cellular data service providers in U.S, Japan as well as in Korea started the LTE (Long Term Evolution) service, there has been more strong need for the methods that can accurately measure the MIMO (Multi Input-Multi Outout) OTA (Over The Air) performance of LTE handsets because the performance of the MIMO antenna determines the packet data rates in the downlink and therefore the higher system throughput of the network. In this regard, there has been a lot discussions in 3GPP on the candidate MIMO OTA test solutions. In this paper, a faire comparison has been done for the conventional method, the Envelop Correlation Coefficient (ECC) measurements, and the anechoic chamber based MIMO OTA test solution, one of the candidate system being discussed in 3GPP. The evaluations and the comparisons are conducted by numerically and experimentally.

• Journal of the Korean Institute of Navigation
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• v.23 no.1
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• pp.23-28
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• 1999

With a rapid progress in electronic industry we enjoy various conveniences of life. As many kinds of information equipments are supplied even to most of individuals as to be called an information society, we are exchanging much information with one another surprisingly. Consequently the occupation density of microwave frequency band is highly increased, and electromagnetic environment is getting more seriously bad. It often gives fatal blow to even human life and thus becomes serious social problems. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve it the alone requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the useful frequency bandwidth by the way of forming air layer(practically use urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. Accordingly, in this paper, a broadened electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 6,000 MHz in the bandwidth. Then we achieved the goal by design the inserting square Ferrite Cylinders with the thickness less than 17.5 mm on existing grid type Ferrite absorber. The purpose of this research is on the development of very wide-band electromagnetic absorber for a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell, wall material for preventing TV ghost, etc.

• Journal of Advanced Navigation Technology
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• v.21 no.6
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• pp.593-600
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• 2017

This paper analyzes the performances of direction finding, interference cancellation, and beamforming performance by array antenna pattern measurement distance between the center of array antenna and reference emitter. Array antenna is widely adopted for example as wireless communications, radar, and sonar. In order to use array antenna, array antenna pattern must be known and it can be measured in anechoic chamber. However, the size of anechoic chamber is generally limited. So measurement error of array antenna can be occurred and this could effect performance decrease of direction finding, interference cancellation, and beamforming. It is verified by computer simulation that the performances of direction finding, interference cancellation, and beamforming by array antenna pattern measurement distance.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.343-343
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• 2001

최근 전자산업과 전파통신산업의 발달에 따라 불요전자파에 의한 전자파장해가 심각한 수 준에 이르게 되었다. 그 결과 국 . 내외 전자파환경은 나날이 악화되고 있으며, 이로 인한 사 회적 문제가 점차 증가되고 있는 실정이다. 이에 대한 대책으로 CISPR(Comite Internationale S Special des Perturbations Radioelectrique), FCC (Federal Communications Commissions) A ANSI(Amercian National Standards Institute) 둥이 주축이 되어 국제 규정이 제정되어 각종 전자기기들에 대해 방사(EMI) 및 내성(EMS)의 규제가 강화되고 있다. 그러나 국제규정이 요구하는(30 MHz - 18 GHz) 주파수 범위에서의 EMIjEMS 측정을 하기 위해 광대역(Broad-band) 전파무향실(Anechoic Chamber)이 필요하지만1 기존의 Ferrite T Tile 또는 그리드형 전파홉수체는 20 dB 이상 전파를 홉수할 수 잇는 주파수 대역이 30 M MHz - 400 MHz 또는 780 MHz에 불과하기 때문에 상기의 조건을 만족하는 전파무향실 을 구성하기에는 곤란한 실정이다. 본 논문에서는 국제 규격을 만족하는 전파무향실을 위한 광대역 전파홉수체를 개발하기 위해, 다충형으로 구성하고, 전파흡수체의 형상을 변화시켜 등가재료정수법을 사용하여 설계하고 그 특성을 평가함을 그 목적으로 하였다. 따라서 본 논문에서는 본 연구실에서 기폰에 제안한바 있는, 금속판 위에 타일형 페라이 트 충, 그 위에 원추절단형 페라이트 층과 원통형 페라이트 층을 적층시칸 형상의 전파홉수 체는 30 MHz - 6 GHz 정도까지 커버할 수 있으나, 1 GHz 부근의 주파수 대에서 16 dB 정도의 홉수능 밖에 가지지 못하였다. 이를 개선하기 위해, 금속판 위에 타일형 페라이트 층 을 형성하고 그 위에 원통형 페라이트 충, 원추절단형 페라이트 충I 원통형 페라이트 충, 타 원형 페라이트 충을 형성한 새로운 형태의 전파홉수체를 제안하였다. 본 논문에 제안한 새로운 형태의 전파흡수체의 시물레이션 결과 30 MHz - 20 GHz의 주파수 범위에서 전반적으로 25 dB이상의 전파흡수능을 가짐을 확인하였으며/ 특히 기폰에 제안한 전파홉수체와 비교하면,1GHz 부끈에서의 전파홉수능을 10 dB 이상 개선하였다. 나아가서/ 실재로 제작한 전파흡수체의 측정된 주파수특성이 시율레이션에 의한 이론치와 3 30 MHz - 6 GHz의 범위에서 잘 일치함을 확인하였다. 또한y 전파 홉수체의 전체 높이는 2 27 mm 밖에 되지 않으므로 본 연구에서 제안한 전파 홉수체를 사용할 경우 전파무향실의 유 효공간 확보에 매우 유리한 이점을 가진다