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A linear ultrasonic motor was designed by a combination of the longitudinal and bending mode. linear ultrasonic motors are based on an elliptical motion on the surface of elastic body, such as bar or plates. The corresponding eigen-mode of one resonance frequency can be excited twice at the same time with a phase shift of 90 degrees in space and time. That is excite symmetric and anti-symmetric modes. Then it determines the thrust and speed of the motor. Linear ultrasonic motors are investigated experimentally in according to be fabricated a general classification to motor structure and material characteristic. There was the first to simulate as use of finite element analysis ANSYS 9.0. The AL-T2W8-ARM14-LEG18-ANGLE80 motor has a maxim efficiency 18 % under the speed 0.14 m/s, thrust 345 gf and preload 280 gf, operating frequency is 57.6 kHz.
A cantilever-type piezoelectric generator has advantages of simple structure, ease of fabrication and large displacement by transverse vibration of a beam. It is easy to control the natural frequency, and also possible to increase the output power by changing the length, width, and thickness of the generator. In particular, the length increases, the natural frequency sharply decreases, and vice versa. Hence, the natural frequency can widely be controlled by using change in the length of elastic body. In this paper, the generator was designed and fabricated to change natural frequency using the slides of the case. In addition, the generating characteristics were confirmed through finite element analyses and vibration experiment. As a result, the maximum output characteristics could be generated due to resonance phenomenon although any frequency of external force was applied.
The acoustical characteristics of a windscreen which has been used to reduce unwanted wind noise have been measured and analyzed by varying the wind speed in a wind tunnel and a reverberation room. The results show that the wind tunnel method is rarely applicable because of the many duct resonance modes whereas the reverberation room method is stable. The effects of wind noise are mainly observed in the low frequency range( i.e, <1000 Hz) rather than in the high frequency range. A windscreen having a diameter of 9 cm was shown to effectively reduce the wind noise for a wind speeds up to 6.6 m/s. 소음 측정에 있어 바람이 부는 경우는 마이크로폰에 방풍망을 설치하여 풍잡음을 최소화하는 것이 필요하다. 하지만 풍속 변화에 따른 방풍망의 효과에 대한 연구 결과가 발표된 것은 거의 없는 실정이다. 따라서 본 연구에서는 풍동과 잔향실에서 풍속변화에 따른 방풍망의 풍잡음 제어 효과를 살펴보았다. 측정결과 풍동실험에서는 덕트의 음향 공명 모드가 많이 발생되기때문에 방풍망의 특성을 평가하기 힘들었으나 잔향실에서는 안정된 결과를 얻을 수 있었다. 바람은 상대적으로 저주파 대역에 더 큰 영향을 미쳤으며, 직경 9 cm의 방풍망의 경우 풍속 6.6 m/s까지는 바람으로 인한 풍잡음을 효과적으로 제거할 수 있음을 확인하였다.
정성수,So-Yeon Lee,Jisun Yoon,Hyun-Ju Cho,Young-Ho Kim,Dong In Suh,Song-I Yang,Ji-Won Kwon,Gwang Cheon Jang,Yong Han Sun,Sung-Il Woo,You-Sook Youn,Kang-Seo Park,Eun Lee,Hwa Jin Cho,Myung-Hee Kook,Hye Ryo 대한천식알레르기학회 2020 Allergy, Asthma & Immunology Research Vol.12 No.1
Purpose: Data are lacking on the association between the allergic rhinitis (AR) phenotype and sensitization to specific allergens or bronchial hyperresponsiveness (BHR) in children. We here investigated risk factors and comorbidities, including sensitization to specific allergens and BHR, for the AR phenotype by AR and its Impact on Asthma (ARIA) classification in a general population-based birth cohort study. Methods: We enrolled 606 children aged 7 years from the Panel Study of Korean Children. The AR phenotype was assigned in accordance with the ARIA classification in children. Skin prick tests and Provocholine provocation test were performed. Risk factors and comorbidities for AR phenotypes were then analyzed.Results: The prevalence of mild and moderate to severe AR in our study cohort was 37.2% and 8.8%, respectively. Recent use of analgesics or antipyretics and current cat ownership were associated with the risk of mild persistent AR. Sensitizations to Dermatophagoides Pteronyssinus (Der p), Japanese hop and cat were associated with moderate to severe persistent AR. Children with moderate to severe AR had a higher risk of current asthma and BHR compared to mild AR cases (adjusted odds ratio [aOR], 5.26; 95% confidence interval [CI], 1.77–15.62). Moderate to severe AR with allergic sensitization was associated with the highest risk of BHR (aOR, 11.77; 95% CI, 3.40–40.74). Conclusions: Moderate to severe-persistent AR is more closely related to respiratory comorbidities and sensitizations than mild AR. Stratifying the AR phenotype by ARIA classification may assist in disease management.
Recently, energy harvesting technology is increasing due to the fossil fuel shortages. To compensate problem of low generating power than other energy harvesters, many researchers have studied about piezoelectric harvester for obtaining high output. In this paper, four kinds of unimorph based piezoelectric harvesters were proposed and its generating characteristics were studied. Each of the piezoelectric harvesters has three, four, and six unimorph arms, respectively, and the arms are symmetrically arranged from one central point. The centrosymmetric structure of the harvesters guarantees more stable and multiplied generation than a cantilever-type harvester since the arms of the harvester resonate at same frequency. Resonance frequency, output voltage, displacement, and stress characteristics of the generator were analyzed by using a FEM (finite element method) program. Harvesters were fabricated on the basis of analysis results. Experimental results were compared with simulated results.