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Jang Jongmoon,Hwang Geon-Tae,민유호,Kim Jong-Woo,안철우,최종진,Hahn Byung-Dong,Choi Joon-Hwan,박동수,Jung Yongsuk,Yoon Woon-Ha 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.6
In the energy harvester, the fatigue caused by cyclic vibration is an important challenge aff ecting the lifetime of the device. The aim of this study is to evaluate the fatigue behavior of the cantilever-type piezoelectric energy harvester (PEH) based on a single crystal macro-fi ber composite (SFC), and propose a method for improving durability. The initial output of the fabricated PEH shows 6 mW root mean square power at 0.5 gravitational acceleration at resonance frequency (23 Hz). In fatigue test under cyclic vibration, the dramatic power decrease and waveform distortion caused by the mechanical crack at the top electrode line were identifi ed after 5 × 10 6 cycles. To improve the issue, the stress distribution on the top electrode line was analyzed by fi nite element analysis and the reinforced structure was proposed by attaching a 50 μm-thick polyimide fi lm. The reinforced PEH shows the durable output power until 10 7 fatigue cycles without a signifi cant output power loss. These study potentially can be applied to the development of reliable SFC-based PEH with long-term lifetime.
Jang, Jongmoon,Jang, Jeong Hun,Choi, Hongsoo IOP 2017 JOURNAL OF MICROMECHANICS AND MICROENGINEERING - Vol.27 No.7
<P>In this paper, we present a flexible artificial basilar membrane (FABM) that mimics the passive mechanical frequency selectivity of the basilar membrane. The FABM is composed of a cantilever array made of piezoelectric aluminum nitride (AlN) on an SU-8 substrate. We analyzed the orientations of the AlN crystals using scanning electron microscopy and x-ray diffraction. The AIN crystals are oriented in the <I>c</I>-axis (0 0 2) plane and effective piezoelectric coefficient was measured as 3.52 pm V<SUP>−1</SUP>. To characterize the frequency selectivity of the FABM, mechanical displacements were measured using a scanning laser Doppler vibrometer. When electrical and acoustic stimuli were applied, the measured resonance frequencies were in the ranges of 663.0–2369 Hz and 659.4–2375 Hz, respectively. These results demonstrate that the mechanical frequency selectivity of this piezoelectric FABM is close to the human communication frequency range (300–3000 Hz), which is a vital feature of potential auditory prostheses.</P>
Kim, Jongmoon,Jin, Jang Yong,Kim, Sung Shin The Korean Pediatric Society 2015 Clinical and Experimental Pediatrics (CEP) Vol.58 No.2
Purpose: This study aimed to investigate the relative weight gain at 2-week intervals up to 6 weeks after birth to predict retinopathy of prematurity (ROP) requiring treatment among very low birth weight infants. Methods: A total of 211 preterm infants with birth weights <1,500 g and gestational age <32 weeks were retrospectively reviewed. The main outcome was the development of ROP requiring treatment. Body weight measurements were recorded daily. Relative weight gains (g/kg/day) were calculated at the second, fourth, and sixth week after birth. Results: Of the 211 infants, 89 developed ROP, of which 41 spontaneously regressed and 48 with early treatment of ROP type I required laser treatment. The relative weight gain at 2, 4, and 6 weeks postnatal age was significantly lower in infants with ROP requiring treatment than in infants without ROP or those with spontaneous regression (P<0.001, P=0.005, and P=0.004, respectively). On logistic regression, poor relative weight gain in the first 2 weeks was found to be related to ROP requiring treatment (adjusted odds ratio, 0.809; 95% confidence interval, 0.695-0.941; P=0.006). Relative weight gain at 2 weeks postnatal age was significantly lower in infants with ROP requiring treatment compared to that in ROP requiring no treatment (P=0.012). Conclusion: Poor postnatal weight gain in the first 2 weeks of life is an important and independent risk factor for ROP requiring treatment. Postnatal weight gain can predict the development of severe ROP requiring treatment.
송원준,Jongmoon Jang,김상원,최홍수 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.5
We report an experimental assessment of the electrical performance of two piezoelectric beam arrays for artificial basilar membranes (ABMs): a continuous beam array (CBA) and a narrow-supports beam array (NSBA). Both arrays consist of piezoelectric beams of sequentially varying lengths that mimic the frequency selectivity of mammalian cochleae. The narrow supports of the NSBA resulted in lateral deformation of the beams, whereas the CBA beams were flat. The displacement and piezoelectric output of each beam were measured at the resonance frequency of each beam using a scanning laser-Doppler vibrometer (SLDV). Both ABM prototypes showed mechanical frequency selectivity that depended on the beam length. The CBA generated a piezoelectric output in the range 6.6 - 23.2 μV and exhibited electrical frequency separability, whereas the NSBA failed to generate sufficient electrical potential due to the lateral deformation of the piezoelectric beams. The CBA was found to be more effective as an ABM, with potential for use in cochlear implants.
Hyejin Jeon,Jongmoon Jang,Sangwon Kim,최홍수 대한금속·재료학회 2018 ELECTRONIC MATERIALS LETTERS Vol.14 No.2
In this study, we present a piezoelectric artificial basilar membrane (ABM) composed of a 10-channel aluminum nitridebeam array. Each beam varies in length from 1306 to 3194 μm for mimicking the frequency selectivity of the cochlea. Tocharacterize the frequency selectivity of the ABM, we measured the mechanical displacement and piezoelectric outputwhile applying acoustic stimulus at 100 dB sound pressure level in the range of 500 Hz–40 kHz. The resonance frequenciesmeasured by mechanical displacement and piezoelectric output were in the range of 10.56–36.5 and 10.9–37.0 kHz,respectively. In addition, the electrical stimulus was applied to the ABMs to compare the mechanical responses in air andfluid. The measured resonance frequencies were in the range of 11.1–47.7 kHz in the air and 3.10–11.9 kHz in the fluid. Understanding the characteristics of the ABM is important for its potential use as a key technology for auditory prostheses.