• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.4
• /
• pp.2770-2776
• /
• 2015

The development of efficient wearable antennas is required to implement short range body-centric wireless communication links for various internet of thing applications. We present simulation and measurement results of conductive-fiber-based wearable antennas which can comfortably fabricated directly on usual clothing materials. The proposed antenna is a form of a rectangular patch antenna designed by weaving conductive fibers on a felt substrate. A full-wave electromagnetic simulation tool is used to investigate the antenna performance such as antenna impedance, resonant frequency, and radiation efficiency. Parametric studies show that the radiation efficiency increases from 67.5% to 70.4% by widening the gap between conductive fibers from 0.25mm to 3mm. This implies a wearable antenna with good radiation efficiency can be designed despite of less portion of conductive fibers on the antenna. The simulation results are also verified by measured results with fabricated antennas.

• Journal of Sensor Science and Technology
• /
• v.11 no.3
• /
• pp.132-137
• /
• 2002

The single crystal of $LiTaO_3$ ($x-112^{\circ}$ y) has very stable thermal characteristics in a piezoelectric transformer. In this paper, a piezoelectric transformer made of the crystal is newly designed and its operating characteristics are analyzed. The length of the transformer is determined as twice as its width for Lame'-mode because the single crystal of $LiTaO_3$ has low electro-acoustic efficiency. The electric and vibrational characteristics of the transformer is simulated by the PSpice program, and its results are compared to experimental ones. As the results, the ratio of output voltage to input shows large than 10 at 290.83[kHz], which is the frequency coupled the 2nd harmonic for length and the fundamental for width of the Lame'-mode transformer.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.7
• /
• pp.985-997
• /
• 1999

In this paper, the detection of 1 g and 10 g averaged SAR on human head caused by PCS handheld phones is analyzed and discussed. Conventional monopole antenna and planar structured PIFA are used in the computational model to apply to the antennas mounted on handheld phone. These antennas are designed to operate in the near of frequency 1.8 GHz, human head model is sampled to have cell size 1.5 mm and sloped to front direction by 30$^{\circ}$. It is found that, when monopole antenna is applied, 1 g averaged SAR is 1.4 W/kg, 10 g averaged SAR is 0.7 W/kg, when PIFA is applied, for each case, SARs are 1.143 W/kg, 0.4866 W/kg. While the radiation pattern of the monopole antenna is symmetrical, that of planar structured antenna is asymmetrical and SAR caused by PIFA is less than SAR by the monopole antenna. The radiation efficiency of PIFA is 62.6%, which is higher than that of monopole, 53%.

• Journal of the Korean Society for Railway
• /
• v.19 no.4
• /
• pp.489-497
• /
• 2016

The rail fastening system, which provides a structural connection between the rail and the sleepers, is a main track component that plays an important role in retaining the rail gauge within acceptable tolerances, as well as in passing the train load to the roadbed through the sleepers. In this paper, a modal test was first performed to evaluate the dynamic characteristics (e.g., natural frequency) of the clips of the railway fastening system under the condition of rail corrugation in urban railway operation. The corrugation-induced passing frequency was then compared with the natural frequency of the clips to investigate any resonance effect during train passage. Furthermore, a field test under train passage was conducted to measure the accelerations on the rail and the rail fastening clips as well as the strains on the rail fastening clips in the rail corrugation condition. The field measurements indicated that the accelerations on the rail and the rail fastening clips have a close relationship with the rail corrugation, but they had a minimal effect on the strains of the rail fastening clips.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.43 no.4
• /
• pp.459-468
• /
• 2023

Power plant is a kind of basic industrial facility and might cause fatal industrial and human damage. In this study, the characteristics and effect of blast-induced vibration for tunnelling which underpass ○○ power plant in operation were evaluated. Previous blasting cases adjacent to industrial facilities were intensively reviewed, then allowable vibration criteria were suggested. 3 dimensional dynamic numerical analysis based on finite element method was performed to investigate particle velocity and resonance was examined by calculating the predominant frequencies. As a result, particle velocity at pump foundation which is nearest to the source was approached to the allowable criteria, therefore, the modified blasting pattern was newly suggested and confirmed the attenuation effect based on the test blasting. Consequently, appropriated decision-support procedure was established in case of adjacent blasting to industrial facilities.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.24 no.1
• /
• pp.41-56
• /
• 2008

The methods of surface modification of commercial implants were various according to the manufacturer. Surface modification of implant may produce diverse physical and chemical surface characteristics resulted from the treatment method and treatment condition. As a result, the bone response might be different. Even though surface modified implants have been used clinically, most researches are focusing on the bone response of surface modified implants comparing to machined implants rather than surface modified commercial implants. This study compare and analyze bone responses of 4 surface modified commercial implants with different shapes and surfaces. Eighty surface modified commercial implants with 4 different surface characteristics were installed in the tibia of white Newzealand rabbits. Biomechanical stability tests and histomorphometric evaluation were done. The results were as follows: 1. Surface modified commercial implants showed stable osseointegration at 6 weeks after installation. 2. Histomorphometric evaluation showed that there was no significant differences in bone to implant contact among 4 different commercial titanium implants. In comparing the implants with different shape the measurement of bone growth in subcortical area would be more reliable than entire bone to implant contact length. 3. Resonance Frequency Analysis showed that there was no significant differences among 4 types of implants, even though they were significantly different in installation. 4. There was significant differences in interfacial shear strength among 4 type of implants. 5. It is difficult to observe accurate bone to implant interface using Micro-CT. However, it is possible to measure the entire contact length of the implant to the bone.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.49 no.2
• /
• pp.1-8
• /
• 2012

This paper presents the accelerometer which is a key component of TPMS(Tire Pressure Monitoring System). Generally a piezoresistive accelerometer has characteristics of lower cost, better linearity and better immunity about the environmnet noise than a capacitive one. Three types of piezoresistive accelerometers are degined and simulated using ANSYS program. The best one is a piezoresistive sensor which is supported by four beams located at the center of the edge of the mass after comparing the characteristics of resonant frequency of the three types. Considering the sensor size and a simulated maximum stress and maximum displacement, the length of beams is set as $200{\mu}m$. The size of a piezoresistive accelerometer is $3.0mm{\times}3.0mm{\times}0.4mm$. The sensor output is characterized by measuring the output characteristic depending on angle. As a result the offset voltage of the accelerometer is 43.2 mV and its sensitivity is $42.5{\mu}V/V/g$. The temperature bias drift is measured. The shock durability of the sensor is 1500g and the measuring range is 0 ~ 60 g.

• Journal of the Korean Ceramic Society
• /
• v.38 no.2
• /
• pp.117-121
• /
• 2001

본 연구에서는 Zr $O_2$첨가가 Ba(Zn$_{1}$3/Ta$_{2}$3/) $O_3$(BZT)세라믹의 구조와 고주파 유전특성에 미치는 영향을 조사하였다. 모든 시료에서 $Ba_{5}$Ta$_4$ $O_{15}$ 이차상이 발견되었으며 Zr $O_2$의 첨가량이 증가하면 $Ba_{5}$Ta$_4$ $O_{15}$ 상의 양은 감소하였다. 반면에 Zr $O_2$의 첨가량이 1.5 mol% 이상인 시료에서는 $Ba_{0.5}$Ta $O_3$상이 발견되었다. BZT의 입자 크기는 약 1$mu extrm{m}$ 정도였지만, Zr $O_2$를 첨가하면 입자 크기가 증가하였다. SEM 및 TEM 분석에 의하여 Zr $O_2$가 첨가되면 액상이 존재하는 것을 알 수 있었으며, 이로 인하여 입자가 성장되는 것이 발견되었다. 시편의 밀도는 소량의 Zr $O_2$를 첨가하면 증가하지만 Zr $O_2$첨가량이 증가하면 감소하였다. 유전율은 모든 시료가 27에서 30 사이의 값을 가지고 있었다. 공진주파수 온도계수는 소량의 Zr $O_2$을 첨가하였을 때는 변화하지 않았지만 첨가량이 2.5 mol% 이상에서는 증가하였다. Q$\times$f 값은 Zr $O_2$을 첨가하면 증가하였고, 입자 성장이 완료되는 조성에서 최대 값을 보였다. 본 연구에서는 Zr $O_2$를 2.0 mol% 첨가하고 15$50^{\circ}C$에서 10시간 소결한 시료에서 최대의 Q$\times$f 값(164,000)을 얻을 수 있었다.다.다.

• Journal of IKEEE
• /
• v.23 no.1
• /
• pp.14-21
• /
• 2019

In this paper, we implemented an on-board miniaturization antenna operating 2.4 GHz using MZR(Mu Zero Resonator). It is must be operating under the constraint that the size of the small terminal PCB should be $78{\times}38{\times}0.8mm^3$ and the size of the system should be $63{\times}38{\times}0.8mm^3$ and the size of the radiating part should be $15{\times}38{\times}0.8mm^3$. The feeding structure uses a CPW structure for stable feeding and a feeding point at the upper left of the system board. A magnetic field coupling structure is used for coupling the feeding part and the antenna. The resonance frequency of the MZR is determined by the series inductance and capacitance of the cell, so the gap between the cells, the length of the cell, the length of the interdigital capacitor, and the spacing between the radiation part and the ground plane are analyzed. The antenna was designed and fabricated using the results. The total size of the antenna including the feed structure is $20.8{\times}9.0{\times}0.8mm^3$, and the electrical length is $0.1664{\lambda}_0{\times}0.072{\lambda}_0{\times}0.0064{\lambda}_0$. The measurement result for 10 dB bandwidth, gain and directivity are 440 MHz(18.3%), 0.4405 dB, and 2.722 dB respectively. It is confirmed that the radiation pattern has omnidirectional characteristics and it can be applied to ultra small terminal antenna.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.4
• /
• pp.56-64
• /
• 2021

Leakage due to deterioration and damage is one of the major causes of volume change by freezing and thawing, and it leads micro-cracking and surface scaling in concrete structures. The deterioration of damaged concrete accelerates with the chloride attack. Thus, in the detailed guidelines for facility performance evaluation (2020), the quality of cover concrete and the freeze-thaw (FT) repetition cycle were newly suggested for concrete durability assessment. The quality of cover concrete should be evaluated by the rebound hammer test and the FT repetition cycle should be also considered in the deterioration environmental assessment. This study suggested the application of fast dynamic based nonlinear ultrasound method to monitor initial micro-scale damage under freezing and thawing environment. Concrete specimens were fabricated with different water-cement ratios (40%, 60%) and air contents (1.5% and 3.0%). The compressive strength, rebound number, relative dynamic modulus, and nonlinear ultrasound were measured with different FT cycles. The scanning electron microscopy was also performed to investigate the micro-scale FT damage. As a result, both the rebound number and the relative dynamic modulus had difficulty to detect early damage but the proposed method showed a potential to detect initial micro-scale damage and predict the FT resistance performance of concrete.