• 한국음향학회:학술대회논문집
• /
• 한국음향학회 2002년도 하계학술발표대회 논문집 제21권 1호
• /
• pp.373-376
• /
• 2002

Most previous studies using ultrasound for osteoporosis diagnosis have employed ultrasound in a frequency range of 0.2-1 MHz. In this study, acoustic properties of the 12 defatted bovine cancellous bone specimens were investigated in vitro. Speed of sound (SOS) and broadband ultrasonic attenuation (BUA) were measured using three matched pairs of transducers with the center frequencies of 1, 2.25, and 3.5 MHz, respectively, in order to cover a broad frequency range of 0.5-2 MHz. The relative orientation between ultrasonic beam and bone specimens was the mediolateral (ML) direction of the bovine tibia. SOS showed significant linear positive correlations with apparent density for all three pairs of transducers of 1 MHz, 2.25 MHz, and 3.5 MHz, respectively. BUA showed relatively weak correlations with apparent density for the pairs of transducers of 1 MHz and 2.25 MHz. Furthermore, in the measurement with the pair of 3.5 MHz transducers, BUA was independent of apparent density. SOS and BUA were only weakly correlated with each other. The linear combination of SOS and BUA showed significant correlations with apparent density. These results suggest that the frequency range up to 1.5 MHz may be also useful in the osteoporosis diagnosis.

• 한국통신학회논문지
• /
• 제16권12호
• /
• pp.1266-1273
• /
• 1991

장거리 국간 선로에 포설된 단일모드 광섬유의 샘플집단과 모집단의 손실특성을 측정하였고, 구간(중계)거리분포를 측정 분석하였다. 접속손실을 포함한 평균손실은 130nm와 155nm에서 각각 0.55 0.05dB/km, 0.59 0.11/km로써 1550nm대역의 손실이 크게 나타났다. OTDR에 의한 손실특성 조사결과 1550nm대역의 손실증가 주 요인은 접속지점의 부적절한 여장처리에 따른 것이었다. 그리고 국내 평균중계거리는 24 7 km로써 31km 이하의 구간거리가 전체의 약 90%를 차지하고 있었다.

• 한국전자통신학회논문지
• /
• 제3권3호
• /
• pp.153-157
• /
• 2008

MCS(Micro-coplanar strip) 선은 전부터 분석되어 왔었다. 등각 지도로 나타낸 방법은 이 MCD 선의 준정적인 효과적인 유전율 그리고 독특한 임피던스를 산출하기 위하여 이용되곤 했다. 현재 이용되는 모든 성과들은 상업적인 S/W, IE3D를 사용하여 얻어진 결과와 비교할 때 유리한 계약에 있기 위해서이다. 그리고 이 부분에서, 적합한 임피던스 저역 원반꼴 안테나 여과기는 주파수 응답 개량을 위한 MCS 선으로 디자인되고 날조되었다. LPF는 구조는 또한 디자인되고 정지하여 있는 예리한 묶음성 특성이 유지하기 위하여 끈을 실행할 수 있도록 하였다. 가장 끝과 측량 결과에서의 결과는 실행한 LPF로 확인할 수 있다.

• Journal of Electrical Engineering and Technology
• /
• 제13권1호
• /
• pp.521-531
• /
• 2018

This paper presents a procedure for field measurements which provides a generalized Narrowband Power Line Communications (NB-PLC) channel model for low voltage (LV) access network in order to deploy advanced metering infrastructure (AMI) within Lahore, Pakistan. The measurements of allocated sites were performed in the residential (urban and rural), industrial and commercial electricity consumers for the NB-PLC channel modeling of overhead transmission lines (TLs). On the basis of extensive field measurement results, the average attenuation profile and transfer functions are presented. The results obtained from field measurements are validated by comparing them with a proposed Simulink model. A close agreement in the measured and simulated transfer function (TF) results is observed. The proposed Simulink model is an effort to model the NB-PLC channels in an effective way, especially in South Asian countries.

• Transactions on Electrical and Electronic Materials
• /
• 제3권3호
• /
• pp.34-38
• /
• 2002

In this paper, efficiency estimation of toxicity fee fire resistance cable experiments was measured smoke density of toxicity free fire resistance polyolefin insulation material and electric field dependence of tree shape in low density polyethylene (LDPE). One of the most serious causes of failure in high-voltage cables, can be an electrical discharge across an internal gab or void in the insulating material. Treeing due to partial discharge is one of the main causes of breakdown in the insulating materials and reduction of the insulation life. Therefore the necessity for establishing a method to diagnose the aging of insulation materials and to predict the breakdown of insulation and research of the fire resistance character has become important. First, we have studied on electric field dependence of tree shape in LDPE about treeing phenomena occurring on the high electrical field. Second, the measurement method is the attenuation quantity of irradiation by smoke accumulating with in a closed chamber due to non-flaming heat decomposition and flaming combustion. A main cause of fire-growth and generating toxic gas when, it bums, should be dealt with great care in life. safety design. The fire gases were occurred carbon monoxide and decomposition than in polyolefin due to incomplete combustion of PVC, which has high content of carbon in chemical compound.

• 한국자동차공학회논문집
• /
• 제14권5호
• /
• pp.93-99
• /
• 2006

Flexible couplers are widely used for exhaust transmitted vibration reduction in vehicles. This paper describes an investigation into the acoustical characteristics of exhaust flexible coupler by the simulation and testing. Computational acoustic simulation is carrying out to investigate resonance frequency and transmission loss of decoupler using the boundary element method and transfer matrix approach. To confirm the acoustical simulation results of exhaust decoupler, we compare with measured experimental results by the test of transmission loss measurement system. In the comparison with simulation results and tests results, there is correctly fit the resonance frequency and the trend of transmission loss. Also, we show that the acoustical structure of decoupler is analogous to the expended tube or side branch resonator. The characteristics of exhaust decoupler have a marked increase in the acoustic attenuation at the specified frequency bend. Therefore the decoupler is applied to develop the exhaust system not only for the vibration isolator but also for the noise attenuator.

• Journal of Biosystems Engineering
• /
• 제32권4호
• /
• pp.237-246
• /
• 2007

In this study, the microwave free-space transmission technique was used to measure the dielectric property of powdered food at microwave frequencies. The sample holder was designed and fabricated to transmit the microwave signals ranging from 1 to 15GHz. From the microwave propagation theory the equation expressing the dielectric property of powdered food was derived and validated by standard dielectrics. The dielectric property of powdered food such as wheat flour, coffee powder and milk powder was measured and analyzed. In the uniform range of bulk density of material, the real parts of permittivity of the food samples increased with the increase of moisture content, bulk density and temperature of the samples. The propagation properties such as attenuation and phase shift increased linearly as the moisture density of the food samples increased. As a measuring frequency of the moisture content, the X-band was recommended.

• 한국안전학회지
• /
• 제24권1호
• /
• pp.60-68
• /
• 2009

The aim of this paper is to evaluate the compatibility of anti-vibration gloves, to predict the attenuation of vibration with different types of anti-vibration gloves, to estimate the spectra of the ISO 10819 standard, and to present an oscillating spectrum adequate for vibrating tools. This paper use two ISO standards for the measurement and evaluation of hand-arm vibration. Some anti-vibration gloves can attenuate vibration, but all the anti-vibration gloves in this study do not satisfy the ISO 10819 requirements. In case of equal vibration types, the outside materials are effective in order of leather, fabrics and rubber-coating. Anti-vibration gloves manufactured in the United State satisfy ISO 10819 criteria using United State subjects, but do not satisfy ISO 10819 using Japanese subjects. M-spectrum acceleration exists below 10Hz and H-spectrum exists above 500Hz. Generally vibrating tools have the peak of Z-axis, but generation of vibration differ from each vibrating tools.

• 전기학회논문지
• /
• 제56권8호
• /
• pp.1430-1435
• /
• 2007

We developed a 440MHz surface acoustic wave (SAW) microsensor integrated with pressure-temperature sensors and ID tag. Two piezoelectric substrates were bonded, in which ${\sim}150\;{\mu}m$ cavity was structured. Four sides were completely sealed by JSR photoresist (PR). Pressure sensor was placed on the top substrate, whereas ill tag and temperature sensor were placed on the bottom substrate. Using network analyzer, the developed microsensor was wirelessly tested. Sharp reflection peaks with high S/N ratio, small signal attenuation, and small spurious peaks were observed. All the reflection peaks were well matched with the coupling of mode (COM) simulation results. With a 10mW RF power from the network analyzer, a ${\sim}1$ meter readout distance was observed. Eight sharp ON reflection peaks were observed for ID tag. Temperature sensor was characterized from $20^{\circ}C$ to $200^{\circ}C$. A large phase shift per unit temperature change was observed. The evaluated sensitivity was ${\sim}10^{\circ}/^{\circ}C$.

• 터널과지하공간
• /
• 제18권4호
• /
• pp.280-288
• /
• 2008

발파진동은 암반 및 인근 구조물에 심각한 문제를 야기할 수 있기 때문에 시공 전 발파진동의 예측과 안전성 평가가 반드시 선행되어야 한다. 최근 발파진동 영향평가를 위하여 시추공이나 시험발파를 통해 획득한 실측진동파형을 이용한 동적수치해석이 증가하고 있다. 하지만 시추공 발파 진동파형은 실제 발파현장에서 측정된 진동파형과 진동수준이나 진동지속시간에서 다소 차이가 있으며 이는 단일공 파형과 유사한 특성을 가진다. 따라서 본 연구에서는 단일공 파형의 중첩모델링을 통해 발파조건 변화에 따른 진동파형을 획득하고 이 파형을 이용한 동적수치해석을 수행하였다.