• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.9
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• pp.31-39
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• 2011

In this paper, we propose a signal readout system with small area and low power consumption for CNT sensor arrays. The proposed system consists of signal readout circuitry, a digital controller, and UART I/O. The key components of the signal readout circuitry are 64 transimpedance amplifiers (TIA) and SAR-ADC with 11-bit resolution. The TIA adopts an active input current mirror (AICM) for voltage biasing and current amplification of a sensor. The proposed architecture can reduce area and power without sampling rate degradation because the 64 TIAs share a variable gain amplifier (VGA) which needs large area and high power due to resistive feedback. In addition, the SAR-ADC is designed for low power with modified algorithm where the operation of the lower bits can be skipped according to an input voltage level. The operation of ADC is controlled by a digital controller based on UART protocol. The data of ADC can be monitored on a computer terminal. The signal readout circuitry was designed with 0.13${\mu}m$ CMOS technology. It occupies the area of 0.173 $mm^2$ and consumes 77.06${\mu}W$ at the conversion rate of 640 samples/s. According to measurement, the linearity error is under 5.3% in the input sensing current range of 10nA - 10${\mu}A$. The UART I/O and the digital controller were designed with 0.18${\mu}m$ CMOS technology and their area is 0.251 $mm^2$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.4
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• pp.743-748
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• 2010

Boron nitride (BN) and carbon nitride (CN) films, which have relatively low work functions and commonly exhibit negative electron affinity behaviors, were coated on carbon nanotubes (CNTs) by magnetron sputtering. The CNTs were directly grown on metal-tip (tungsten, approximately 500nm in diameter at the summit part) substrates by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The variations in the morphology and microstructure of CNTs due to coating of the BN and CN films were analyzed by field-emission scanning electron microscopy (FE-SEM). The energy dispersive x-ray (EDX) spectroscopy and Raman spectroscopy were used to identify the existence of the coated layers (CN and BN) on CNTs. The electron-emission properties of the BN-coated and CN-coated CNT-emitters were characterized using a high-vacuum field emission measurement system, in terms of their maximum emission currents ($I_{max}$) at 1kV and turn-on voltage ($V_{on}$) for approaching $1{\mu}A$. The results showed that the $I_{max}$ current was significantly increased and the $V_{on}$ voltage were remarkably reduced by the coating of CN or BN films. The measured values of $I_{max}-V_{on}$ were as follows; $176{\mu}A$-500V for the 5nm CN-coated emitter and $289{\mu}A$-540V for the 2nm BN-coated emitter, respectively, while the $I_{max}-V_{on}$ of the as-grown (i.e., uncoated) emitter was $134{\mu}A$-620V. In addition, the CNT emitters coated with thin CN or BN films also showed much better long-term (up to 25h) stability behaviors in electron emission, as compared with the conventional CNT emitter.

• Wind and Structures
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• v.25 no.2
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• pp.131-156
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• 2017

This paper deals with the dynamic stability of embedded functionally graded (FG)-carbon nanotubes (CNTs)-reinforced micro cylindrical shells. The structure is subjected to harmonic non-uniform temperature distribution and 2D magnetic field. The CNT reinforcement is either uniformly distributed or FG along the thickness direction where the effective properties of nano-composite structure are estimated through Mixture low. The viscoelastic properties of structure are captured based on the Kelvin-Voigt theory. The surrounding viscoelastic medium is considered nonhomogeneous with the spring, orthotropic shear and damper constants. The material properties of cylindrical shell and the viscoelastic medium constants are assumed temperature-dependent. The first order shear deformation theory (FSDT) or Mindlin theory in conjunction with Hamilton's principle is utilized for deriving the motion equations where the size effects are considered based on Eringen's nonlocal theory. Based on differential quadrature (DQ) and Bolotin methods, the dynamic instability region (DIR) of structure is obtained for different boundary conditions. The effects of different parameters such as volume percent and distribution type of CNTs, mode number, viscoelastic medium type, temperature, boundary conditions, magnetic field, nonlocal parameter and structural damping constant are shown on the DIR of system. Numerical results indicate that the FGX distribution of CNTs is better than other considered cases. In addition, considering structural damping of system reduces the resonance frequency.

• Composites Research
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• v.34 no.1
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• pp.47-50
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• 2021

In this paper, the Curing process for Epoxy Molding Compound (EMC) Package was developed by comparing the performance of the EMC/Cu Bi-layer package manufactured by the conventional Hot Press process system and Carbon Nanotubes (CNT) Heater process system of the surface heating system. The viscosity of EMC was measured by using a rheometer for the curing cycle of the CNT Heater. In the EMC/Cu Bi-layer Package manufactured through the two process methods by mentioned above, the voids inside the EMC was analyzed using an optical microscope. In addition, the interfacial void and warpage of the EMC/Cu Bi-layer Package were analyzed through C-Scanning Acoustic Microscope and 3D-Digital Image Correlation. According to these experimental results, it was confirmed that there was neither void in the EMC interior nor difference in the warpage at room temperature, the zero-warpage temperature and the change in warpage.

• Steel and Composite Structures
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• v.38 no.5
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• pp.533-545
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• 2021

What is desirable in engineering is to bring the engineering model as close to reality as possible while the simplicity of model is also considered. In recent years, several studies have been performed on nanocomposites but some of these studies are somewhat far from reality. For example, in many of these studies, the carbon nanotubes (CNTs) are assumed completely straight, flawless and uniformly distributed throughout the matrix but by studying nanocomposites, we find that this is not the case. In this paper, three steps have been taken to bring the presented models for nanocomposites closer to reality. One is that assuming the straightness of nanotubes is removed and the waviness is considered. Also, the nanotubes are not considered to be pristine and the influence of defect is included in accordance with reality. In addition, the approximation of uniform distribution of nanotubes is ignored and according to experimental observations, the effect of nanotube aggregation is considered. As far as we know, this is the first study on these three topics together in an article. Moreover, we also include the size effects in our models for nanocomposites. To show the accuracy of our models, our results are calibrated with experimental results and compared with theoretical model. For numerical examples, we present the buckling behaviors of nanocomposites including the size effects using nonlocal theory and compare the results of our models with the results of models with above-mentioned approximations.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.4
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• pp.739-744
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• 2007

In this paper, we have investigated mechanical and chemical properties by changing the content of carbon nanotube, which is component part of semiconductive shield in underground power transmission cable. Specimens were made of sheet with the eight of those for measurement. The condition of specimens was a solid sheet. Chemical properties of specimens was measured by FT-ATR (Fourier Transform Attenuated Total Reflectance). Stress-strain of specimens was measured by TENSOMETER 2000. A speed of measurement was 200[mm/min], ranges of stress and strain were 400[Kgf/Cm] and 600[%]. We could observe (unctional group (C=O, carbonyl group) of specimens through FT-ATR. From these experimental result, the concentration of functional group [C=O] was high accor야ng to increasing the content of carbon nanotube. We could know CNT/EEA was excellent more than other specimens from above experimental results. In Addition, the elongation ratio was decreased, and yield strength was increased according to increasing the content of carbon nanotube. Also, from these experimental result, we could know that a small amount of CNT/EEA has a excellent mechanical and chemical properties.

• Journal of Powder Materials
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• v.20 no.4
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• pp.291-296
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• 2013

SKD11 (ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. The CNTs was good additives to improve the mechanical properties of metal. In this study, 1, 3 vol% CNTs was dispersed in SKD11 matrix by mechanical alloying. The SKD11+ CNT hybrid nanocomposites were investigated by FE-SEM, particle size distribution, hardness and wear resistance. The CNT was well dispersed in the SKD11 matrix and the mechanical properties of the composite were improved by CNTs addition. It shows good feasibility as cold work die tool.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.3
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• pp.275-283
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• 2007

An experimental study was conducted to investigate the effect of the morphology of CNT (Carbon Nanotube) on the thermal conductivity of suspensions. The effective thermal conductivities of the samples were measured using a steady-state cut bar apparatus method. Enhancements based on the thermal conductivity of the base fluid are presented as functions of both the volume fraction and the temperature. Although functionalized SWNT (Single-Walled Carbon Nanotube) produced more stable and homogeneous suspensions, the addition of small amounts of surfactant to suspensions of 'as produced' SWNT demonstrated a greater increase in effective thermal conductivity than functionalized SWNT alone. The effective thermal conductivity enhancement corresponding to 1.0% by volume approached 10%, which was observed to be lower than expected, but more than twice the values, 3.5%, obtained for similar tests conducted using aluminum oxide suspensions. However, for suspensions of MWNT (Multi-Walled Carbon Nanotube), the degree of enhancement was measured to be approximately 37%. It was postulated that the effect of clustering, resulting from the multiple heat-flow passages constituted by interconnecting neighboring CNT clusters, played an important role in significant enhancement of effective thermal conductivity.

• Journal of Information Display
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• v.4 no.2
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• pp.35-42
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• 2003

The field emission and luminescent properties of carbon nanotubes (CNTs) that were straightened by argon ion irradiation were investigated. Argon ion irradiation permanently straightened both as-grown and screen-printed CNTs (SP-CNTs) in the presence of a strong electric field. The straightening process enhanced the emission properties of as-grown CNT films by showing a decrease in turn-on field, an increase in total emission current, and a stable emission. Recurring problems associated with SP-CNTs, such as bent or/and buried CNTs and the degradation in binder-residue-induced emission, were improved by the permanent straightening of CNTs and protruding CNTs from binders by the irradiation treatment, in addition to its surface cleaning effect. Furthermore, we confirmed that the number of emission sites increases by observing the luminescent properties of CNT films after the straightening. These findings here suggest that ion irradiation treatment is an effective method for achieving uniform field emission and to reduce the electrical aging time.

• Journal of Sensor Science and Technology
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• v.22 no.5
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• pp.315-320
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• 2013

In this paper, the properties of strain sensors made of spin-capable multi-walled carbon nanotubes (MWCNTs) were characterized and their sensing mechanisms analyzed. The key contribution of this paper is a new fabrication technique that introduces a simpler transfer method compared to spin-coating or dispersion CNT. Resistance of the MWCNT sheet strain sensor increased linearly with higher strain. To investigate the effect of CNT concentration on sensitivity, two strain sensors with different layer numbers of MWCNT sheets (one and three layers) were fabricated. According to the results, the sensor with a three-layer sheet showed higher sensitivity than that with one layer. In addition, experiments were conducted to examine the effects of environmental factors, temperature, and gas on sensor sensitivity. An increase in temperature resulted in a reduction in sensor sensitivity. It was also observed that ambient gas influenced the properties of the MWCNT sheet due to charge transfer. Experimental results showed that there was a linear change in resistance in response to strain, and the resistance of the sensor fully recovered to its unstressed state and exhibited stable electromechanical properties.