Facial Synthesized Co-doped SnO2@Multi-Walled Carbon Nanotubes as an Efficient Microwave Absorber in High Frequency Range

Zhenfeng Liu,Honglong Xing,Ling Lin,Xiaoli Ji,Ziyao Shen 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.10

Co-doped SnO2@multi-walled carbon nanotubes (MWCNTs) were fabricated by a one-pot hydrothermal process. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), high-resolution electron microscopy, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the morphology and structure of the composites. XRD, FT-IR, and XPS analyses demonstrated that Co was doped into SnO2 lattice, no other impure phases were detected. Co-doped SnO2, with a uniform size of 4–6 nm, is coated on MWCNTs but separated from the nanotubes with some aggregation. The microwave absorption properties of Co-doped SnO2@MWCNTs were investigated at room temperature within 2–18 GHz. Results indicated that Co-doping concentration plays an important role in the microwave absorption capability of Co-doped SnO2@MWCNTs. The maximum reflection loss (RL) is 22.8 dB at 14.1 GHz. The absorption bandwidth with RL less than 10 dB is 4.2 GHz (12.2–16.4) with coating thickness of only 1.5 mm; hence, Co-doping can enhance the microwave absorption performance of SnO2@MWCNTs. The excellent microwave absorption performance may be attributed to interfacial polarization, conductivity loss, and changes in electromagnetic parameters and lattice constant caused by Co-doping. Consequently, Co-doped SnO2@MWCNTs can be considered as efficient microwave absorbers in high-frequency range.

Facial Synthesis of Zn-Doped Fe3O4 with Enhanced Electromagnetic Wave Absorption Performance in S and C Bands

Zhenfeng Liu,Honglong Xing,Lei Wang,Dexin Tan,Ying Gan,Xiaoli Ji,Guocai Xu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.8

In this study, Zn-doped Fe3O4 nanoparticles were successfully synthesized by a facile solvothermal method in the presence of sodium dodecyl sulfate (SDS). The morphology, magnetic properties and electromagnetic wave absorbing properties of these materials were characterized. Results showed that Zn2+ played a significant role in the formation of Zn-doped Fe3O4. With the protection of SDS, highly dispersed Fe3O4 nanoparticles were obtained. The nanoparticle size decreased after Zn2+ doping, and the dispersity deteriorated with increasing Zn2+ doping concentration. Zndoped Fe3O4 exhibited excellent electromagnetic wave absorbing property, which resulted in magnetic loss and dielectric loss at an appropriate doping concentration. The minimum reflection loss (RL) was approximately -27.2 dB at 16.9 GHz. As the coating layer thickness increased to 4.0 mm, the bandwidth was approximately 5.0 GHz corresponding to RL below -10 dB, which nearly covered the entire S band (2–4 GHz) and C band (4–8 GHz). The peak frequency of RL and the number of peaks matched the quarter-wave thickness criteria. It was believed that the Zndoped Fe3O4 could be a potential electromagnetic wave absorbing material in S and C bands.

Novel Microwave Absorption Materials of Porous Flower-Like Nickel Oxide@Polyaniline in the X-Band

Ye Liu,Honglong Xing,Lei Wang,Zhenfeng Liu,Huan Wang,Hanxiao Jia 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.6

Porous flower nickel oxide@polyaniline (NiO@PANI) composites as excellent microwave absorption (MA) materials in the X-band were synthesized via a two-step strategy in this work. The porous NiO flower is uniformly dispersed and homogeneous in particle size after Ostwald ripening process. Coating conductive PANI on the surface of porous NiO microspheres could improve interfacial polarization and dielectric loss property that will lead to a great improvement of MA properties. Electromagnetic (EM) parameters of NiO@PANI composites with different NiO contents were investigated by a vector network analyzer and the reflection loss (RL) values with varied thickness were also calculated. The results showed that the effective absorption bandwidths (RL < -10 dB) of all NiO@PANI composites can cover the whole X-band. Especially, the NiO@PANI0.1 composite is able to attenuate microwave energy in the X-band with the thickness of 2.5mm. The NiO@PANI0.2 has a maximum RL of -32.8 dB at 10.1GHz and the effective absorption bandwidths cover 4.64GHz (11.12–15.76GHz) at 2.0mm. The excellent MA absorption performance may be ascribed to the polarization effect, dielectric loss and structure of porous flower-like NiO@PANI. Our work confirms that the synthesized NiO@PANI composite is an attractive candidate as a highly efficient MA material in the X-band.

Incremental Auto Regressive Prediction Models with External Variables of Greenhouse Air Temperature for Control Purposes

Zhenfeng Xu,Junjie Chen,Jingxia Zhang,Yuan Liu,Qiaowei Zhang 보안공학연구지원센터 2016 International Journal of Smart Home Vol.10 No.9

The impact of actuators should be considered in the prediction modeling of greenhouse air temperature. In this paper, the operating state of a greenhouse was divided into five sub-states based on the on-off characteristic of actuators. A group of novel incremental auto regressive models with external variables (IARX models) suitable for the five operat-ing sub-states were deduced from the mechanistic modeling of greenhouse air tempera-ture. The new IARX models have fewer coefficients than other known ARX models. In or-der to validate the IARX prediction models, the related environmental factors of a glass greenhouse were measured. The prediction results of the IARX models were compared with two typical ARX models. The maximum prediction errors and the mean square errors of the IARX models, under the three operating sub-states of passive state(all actuators are not working), mechanical ventilation and fan-pad cooling, are 0.1°C, 0.14°C, 0.7°C, and 0°C, 0.3°C, 0.4°C, respectively. The prediction results are much better than those of one compared model, while similar with the other.

Improved DV-Hop Localization Algorithm Based on Bat Algorithm in Wireless Sensor Networks

( Yuan Liu ),( Junjie Chen ),( Zhenfeng Xu ) 한국인터넷정보학회 2017 KSII Transactions on Internet and Information Syst Vol.11 No.1

Obtaining accurate location information is important in practical applications of wireless sensor networks (WSNs). The distance vector hop (DV-Hop) is a frequently-used range-free localization algorithm in WSNs, but it has low localization accuracy. Moreover, despite various improvements to DV-Hop-based localization algorithms, maintaining a balance between high localization accuracy and good stability and convergence is still a challenge. To overcome these shortcomings, we proposed an improved DV-Hop localization algorithm based on the bat algorithm (IBDV-Hop) for WSNs. The IBDV-Hop algorithm incorporates optimization methods that enhance the accuracy of the average hop distance and fitness function. We also introduce a nonlinear dynamic inertial weight strategy to extend the global search scope and increase the local search accuracy. Moreover, we develop an updated solutions strategy that avoids premature convergence by the IBDV-Hop algorithm. Both theoretical analysis and simulation results show that the IBDV-Hop algorithm achieves higher localization accuracy than the original DV-Hop algorithm and other improved algorithms. The IBDV-Hop algorithm also exhibits good stability, search capability and convergence, and it requires little additional time complexity and energy consumption.

Structure and Microwave Absorption Properties of Polyaniline/Zn Ferrite Composites

Honglong Xing,Ye Liu,Zhenfeng Liu,Huan Wang,Hanxiao Jia 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2018 NANO Vol.13 No.09

Polyaniline (PANI)/Zn ferrite composites were fabricated by simple two-step method. The crystal phase, particle size, morphology, thermal stability and conductivity were characterized. Electromagnetic parameters of PANI/Zn ferrite composites were measured at room temperature in the frequency of 2–18 GHz. The prepared composite had an amorphous fluffy structure, Zn ferrite nanoparticles with diameters ranging from 20 nm to 30 nm are encapsulated in PANI or on PANI surface, and the thermal stability of the composite is poor. But Zn ferrite content plays a key role in influencing this structure and regulating microwave attenuation capability. The PANI/Zn ferrite composites showed an enhanced microwave absorption performance in Ku band at thin coating thickness which corresponds to RL value below - 10 dB and the minimum reflection loss (RL) is - 54.4 dB at 17.6 GHz with the coating thickness of 1.4 mm.

Excellent Microwave Absorption Behaviors of Polyaniline Composites Containing CeO2 Nanorods in the X-Band

Honglong Xing,Qing Yin,Zhenfeng Liu,Lei Wang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.4

Conductive polyaniline/CeO2 nanocomposite powders (PANI/CeO2) were prepared by an in situ polymerization method. The effects of CeO2 content on the microwave absorption properties of composites were investigated. The phase composition, morphological characteristics, electromagnetic parameters and microwave absorption properties of the composites were characterized through X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and vector network analysis. Results show that CeO2 nanorods are coated with PANI to form a well-defined hierarchical structure. CeO2 is wellincorporated into the PANI matrix. CeO2/PANI exhibits excellent microwave absorption properties at 2–18 GHz. As the CeO2 content increases to 30 wt.%, an optimal reflection loss (RL) of -40 dB (99.99% of electromagnetic wave absorption) is observed at 8.8 GHz with a thickness of 3.0 mm. The frequency bandwidth corresponding to 90% of electromagnetic wave absorption crosses the X-band. Therefore, PANI/CeO2 can be used as an advantageous candidate for a new type of microwave absorptive material.

Synthesis and Excellent Microwave Absorption Properties of ZnO/Fe3O4/MWCNTs Composites

Lei Wang,Honglong Xing,Zhenfeng Liu,Ziyao Shen,Xiang Sun,Guocai Xu 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.12

ZnO nanocrystals were introduced into Fe3O4/MWCNTs composites to improve the impedance matching and electromagnetic (EM) wave attenuation of the system. The as-synthesized ZnO/ Fe3O4/MWCNTs composites were characterized by X-ray diffraction, vibrating sample magnetometer, field-emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy. SEM and TEM images showed that Fe3O4 microspheres 100–200 nm in size connected MWCNTs. Analysis of EM parameters revealed that the impedance matching of the ZnO/Fe3O4/MWCNTs composites was considerably improved after ZnO nanocrystals were introduced. The ZnO/Fe3O4/MWCNTs composites exhibited a highly efficient microwave absorption (MA) capacity within the tested frequency range of 2–18 GHz. The optimal reflection loss of EM waves was -38.2 dB at 6.08 GHz with an absorber thickness of 3.5 mm. The excellent MA properties of the composites could be attributed to the improved impedance matching, interfacial polarization, and combined effects of dielectric and magnetic losses.

Effects of Supplementing Different Levels of a Commercial Enzyme Complex on Performance, Nutrient Availability, Enzyme Activity and Gut Morphology of Broilers

Yuan, Jiu,Yao, Junhu,Yang, Fengxia,Yang, Xiaodan,Wan, Xinjie,Han, Jincheng,Wang, Yaojie,Chen, Xinke,Liu, Yurui,Zhou, Zhenfeng,Zhou, Ningbo,Feng, Xinyu Asian Australasian Association of Animal Productio 2008 Animal Bioscience Vol.21 No.5

A trial was conducted to study the influence of different levels of a commercial enzyme complex on performance, nutrient availability, blood parameters, digestive tract measurements, amylase and trypsin activity of the digestive tract and gut morphology in broilers fed the typical diets in north China. There were four treatments: the control diet and the other three enzyme complex supplemented diets which were 180 mg/kg, 360 mg/kg and 720 mg/kg enzyme complex supplemented to the control diet, respectively. The birds fed the diets supplemented with 180 mg/kg and 360 mg/kg enzyme complex had better performance and nutrient availability, the activities of amylase and trypsin in the digestive tract in the two treatments were improved, the villus height and surface area of villus in the small intestine increased and the crypt depth and epithelial thickness of small intestine decreased. Relative weights of pancreas and relative weights and lengths of small intestine decreased. However, the addition of 720 mg/kg enzyme complex had no effects on these parameters and increased crypt depth and epithelial thickness of the small intestine. The data suggested that suitable supplementation of enzyme complex was beneficial for the birds, while excess enzyme complex inhibited secretion of endogenous enzyme and destroyed the structure of the small intestine.