• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.30-35
• /
• 2007

Various acoustic tests were carried out to investigate the acoustic performance of diesel engine exhaust silencers. In order to consider flow effects, test equipment composed of fan, duct and silencer was set up. Using the test equipment, insertion loss tests were carried out to improve the performance in the low-frequency ranges. Through a series of tests, the fact that array resonators may be effective in the low-frequency noise has been verified. Consequently, the hybrid-type silencer which is the combination of reflective silencer with array resonators and conventional absorptive silencer were proposed and its high acoustic performance in the low-frequency range has also been verified.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2013년도 추계학술대회 논문집
• /
• pp.257-258
• /
• 2013

• ETRI Journal
• /
• 제32권1호
• /
• pp.112-119
• /
• 2010

We present a useful design for a free access mat which supports two frequency bands of 2.4 GHz and 5 GHz. The free access mat is a sheet-shaped waveguide which consists of a tightly coupled double-layered microstrip resonator array. It provides easy access for devices in short-range wireless communications. Interference is a common problem with conventional applications which use free space transmission. Our proposed wireless access system uses a subsidiary waveguide, the free access mat. Wireless devices are proximately coupled to the free access mat through which the coupled electromagnetic (EM) wave transmits. The arrival domain of the EM wave of an application is therefore limited to an area close to the free access mat. Wireless devices can be coupled to the free access mat at an arbitrary position without contact. We previously presented a free access mat for a single frequency band. This paper presents a free access mat for the two frequency bands of 2.4 GHz and 5 GHz. The free access mat uses a ring patch resonator array which is easily excited by typical antennas and is resistant to interference. These characteristics are demonstrated by numerical simulation and confirmed by experiment.

• Advances in Computational Design
• /
• 제8권4호
• /
• pp.273-293
• /
• 2023

This study evaluated the acoustic performance of two configurations of serial HR arrays and lined HR arrays in the presence of grazing flow using a 3D numerical simulation. The dual, triple, and quad HR arrays were compared to the conventional HR array. The simulation results showed that the number of resonant frequencies increased with the number of serial HR arrays. The C_TL did not significantly change with the number of serial HR arrays. The acoustic performance of the two, three, and four-lined HR arrays was compared to the conventional HR array. The results showed that the resonant frequency and TLmax increased with the number of lined HR arrays. The C_TL also increased with the number of lined HR arrays. The effect of the grazing flow Mach number (M_a) was investigated on the four-lined HR array configuration and compared to the conventional HR configuration. TLmax and C_TL decreased for both configurations with increasing M_a. The four-lined HR array configuration had significantly better acoustic performance than the conventional HR configuration. The TLmax and C_TL increased by more than 300% when the configuration was changed from the conventional HR to the four-lined HR array at M_a = 0.The increment percentage decreased with increasing M_a.

• 한국소음진동공학회논문집
• /
• 제23권2호
• /
• pp.167-175
• /
• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2009년도 정기 학술대회
• /
• pp.135-138
• /
• 2009

Most of the studies use model order reduction for low frequency (LF) response analysis due to their high computational efficiency. In LF response analysis, one of model order reduction, algebraic substructuring (AS) retains all LF modes when using the modal superposition. However, in mid-frequency (MF) response analysis, the LF modes make very little contribution and also increase the number of retained modes, which leads to loss of computational efficiency. Therefore, MF response analysis should consider low truncated modes to improve the computational efficiency. The current work is focused on improving the computational efficiency using a AS and a frequency sweep algorithm. Finite element simulation for a MEMS resonator array showed that the performance of the presented method is superior to a conventional method.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.234-237
• /
• 2007

To protect a satellite and electronic equipment from the acoustic load generated by rocket propulsion system, many launch vehicle use acoustic blanket. Acoustic load is main source of random vibration working on the payload. Most high frequency region of the acoustic loads is reduced by payload fairing skins and acoustic blanket, but low frequency region is not. In order to reduce acoustic load of low frequency region, we designed array resonator panel which was made of composite materials. Insertion loss capacity of the payload fairing with acoustic blanket was verified from PLF acoustic test in the acoustic chamber.

• Journal of electromagnetic engineering and science
• /
• 제14권3호
• /
• pp.306-313
• /
• 2014

A Fabry-Perot resonator cavity antenna for Ku-band application is presented in this paper. The Fabry-Perot cavity is formed by a ground plane and a frequency selective surface (FSS) made of a circular hole array. The cavity resonance is excited by a single-feed microstrip patch located inside the cavity. The measured results show that the proposed antenna has an impedance bandwidth of approximately 13% ($VSWR{\leq}2$) and a 3-dB gain bandwidth of approximately 7%. The antenna produces a maximum gain of 18.5 dBi and good radiation patterns over the entire 3-dB gain bandwidth. The antenna's very thin profile, high directivity, and single excitation feed make it promising for use in wireless and satellite communication applications in a Ku-band frequency.

• 대한전자공학회논문지TC
• /
• 제46권7호
• /
• pp.52-60
• /
• 2009

본 논문에서는 십자형 슬롯 급전방식을 이용한 다층 CP-DRA(Circularly Polarized Dielectric Resonator Antenna)의 이득 및 축비대역폭 증대에 관하여 연구한다. CP-DRA의 이득 및 축비대역폭 증대를 위하여 단층 CP-DRA에 대하여 분석하고, 이를 바탕으로 다층 CP-DRA의 구조를 제안하여 동작특성을 연구한다. 또한, 안테나의 이득 증대를 위하여 다층 CP-DRA 사이의 간격을 0.7$\lambda_0$ 및 1.2$\lambda_0$로 2$\times$2 평면 배열한 안테나의 방사특성을 CST사의 MWS을 이용하여 시뮬레이션을 통해 검토한다. 제안한 다층 CP-DRA를 제작하여 측정한 결과, 이득 및 대역폭이 단층 CP-DRA에 비하여 약 2배 개선됨을 알 수 있다. 그리고, 다층 CP-DRA를 1.2$\lambda_0$ 간격으로 배열한 안테나에서 일반적인 배열안테나와 달리 grating lobe가 크게 감소하며, 이득은 13.4dBi, 축비대역폭은 0.8GHz으로 증가하였다.

• 산업기술연구
• /
• 제29권B호
• /
• pp.139-144
• /
• 2009

A Doppler radar is a radar using the doppler effect of the returned echoes from targets to measure their radial velocity. To be more specific the microwave signal sent by the radar antenna's directional beam is reflected toward the radar and compared in frequency, up or down from the original signal, allowing for the direct and highly accurate measurement of target velocity component in the direction of the beam. In this paper, we designed the doppler radar composed of 10.5 GHz band DROs(Dielectric Resonator Oscillator), $90^{\circ}C$ branch line coupler, single balanced mixer and $4{\times}4$ array antenna of high gain, high directivity, for non-contact type hydrometer. Fabricated Doppler radar can detect slow moving objects.