In order to solve the problem of poor damage resistance of foam, limited thickness of ordinary spacer fabric and complex preparation process of composite, a high-distance spacer fabric/foam composite ...(HFFC) was designed via a simple and rapid method without molds. The HFFC was composed of two polyvinyl chloride (PVC) faces and a foam-filled high-distance spacer fabric core. Nine kinds of high-distance spacer fabric/foam composites (HFFCs) were prepared by changing the density of the core layer and spacer yarns. The microstructure, compression, bending, thermal insulation, sound absorption and low-velocity impact resistance properties of HFFCs were characterized. Remarkably, the HFFCs with lower foam density have better thermal insulation, sound absorption and low-velocity impact resistance properties while reducing weight. The HFFCs with higher density of spacer yarns exhibit more outstanding compression and thermal insulation properties. In addition, the thermal conductivities of the nine kinds of HFFCs are lower than 0.05 w/(m*K), belonging to high-efficiency thermal insulation material. The developed HFFCs show great potential in many practical applications in packaging, construction and other fields.
High-distance woven spacer fabrics have been developed into a variety of special textile products for a wide range of applications. As a type of sandwich structure, their applications are heavily ...dependent on their compressive properties. In this study, the compressive properties of high-distance woven spacer flexible inflatable composites (HDWSFICs) have been evaluated by varying the indenter diameter, initial inflation pressure, and spacer yarn density. The experimental results showed that the compression process can be divided into three stages, including the Contact Stage, the Stress Transition Stage and the Densification Stage. In the Stress Transition Stage, the HDWSFICs can transform compressive load into tension stress, and especially local stress into integral stress, which can be considered a “Stress Transformer”. The existence of the spacer yarns allows the inflatable composites to bear more than three times the compressive load of the inflatable membrane material itself. The compressive modulus increases with spacer yarn density and initial inflation pressure, thus the stiffness of HDWSFICs can be designed. The findings of this study may provide ideas for the design of a “Stress Transformer” and theoretical references for the development of high-distance woven spacer inflatable composites with excellent mechanical properties.
The power fluctuation problem has been a key issue in dynamic wireless power transfer (WPT) systems. In the past research studies, the power fluctuation problem at low-transmission distance has been ...solved, but existing solutions often involve complex control strategies and cannot realise power stabilisation for dynamic WPT systems under high-transmission distance. As a remedy, the spatial rotating coil design scheme is proposed based on magnetic field aggregation to solve the power fluctuation problem without control strategy for high distance dynamic WPT system. Firstly, the crucial parameters affecting power fluctuations are analysed. Then the relative optimisation backgrounds are introduced. Afterwards, the mechanism of power sag is analysed based on magnetic field analysis. Subsequently, the spatial rotating double D (DD) coil design is proposed inspired by omnidirectional WPT coil, and various different DD coil schemes are optimised utilising magnetic field aggregation method to acquire the optimal scheme. Compared with the original coil scheme, the proposed design scheme improves fluctuation of system mutual inductance without complicated control strategies according to simulation results. Finally, a physical coil system consistent with the simulation system is constructed, which verifies the improvement effect of the proposed scheme and effectively confirm feasibility of the optimal scheme.
This paper mainly introduces a high-distance warp-knitted spacer flexible composite material which is a special material consisting of high-distance warp-knitted spacer fabric and some coating ...materials. It introduces the designing process as well as the preparation of high-distance warp-knitted flexible composite material. In order to comprehend the influence of internal pressure on the material, the mechanical properties under 100 %, 80 % and 60 % gas pressure have been explored. A compression test under these three kinds of gas pressure was carried out and the related force displacement diagram, the stress-strain curve and the energy strain curve which directly reflects the variation of the mechanical properties of the composites material under the different gas pressure were obtained and presented. A deep investigation and analysis was conducted into knowing the compressive properties of the material and how they are affected by the gas pressure. The experimental results obtained shows that the compressive properties of the high-distance warp-knitted space flexible material is dependent on the amount of gas inserted. Again the compressive strength of the material keeps growing stronger with an increase in the intensity of the gas pressure.
The wireless power transfer (WPT) technology is an effective way to solve the underwater equipment charging problem to achieve long-term continuous work. However, the presence of eddy current loss ...leads to a significant decrease in the efficiency of long-distance WPT in a seawater environment. Focusing on the efficiency problem of the seawater WPT system, this paper analyzes the principle of eddy-current loss first. Then, a 50 cm×50 cm coupler is simulated using HFSS finite element analysis software, with a distance of 50 cm. The relationship among eddy current loss, magnetic core, frequency, and coupler parameters is analyzed. At last, the total loss and efficiency of the system are derived based on the S-S compensation topology. At a frequency of 15kHz and transmitting 500W of power, the system efficiency is 87.365%, significantly improving the transmission efficiency under HDDR conditions in SWPT systems.
The performance of the chirp stepped signal (CSS) is investigated in this paper. Based on the ambiguity function theory, a 60GHz radar system performance with CSS, such as, distance, speed and angle ...detection are firstly analyzed and then simulated and experimental verified. Finally, using our designed CSS, a higher signal-to-noise ratio (SNR) and improved range detection capability are obtained under the condition of low instantaneous bandwidth when compared with the FMCW signal. Our results show that the CSS has a good potential for 60GHz millimeter radar applications.
The traditional microwave power transmission is based on S-band and C-band microwave, and its frequency is generally lower than 8 GHz. Therefore, the power transmission system is bulky. In this ...paper, a space millimeter wave wireless energy transmission system is proposed, which uses Ka band millimeter wave for wireless energy transmission. Compared with the traditional microwave power transmission system, the frequency is up to 35GHz. The antenna array has the advantages of small volume, long transmission distance and high aspect ratio energy transmission.
A remark on Plotkin's bound de Launey, W.; Gordon, D.M.
IEEE transactions on information theory,
2001-Jan., 2001-01-00, 20010101, Volume:
47, Issue:
1
Journal Article
Peer reviewed
Let A(n,d) denote the greatest number of codewords possible in a binary block code of length n and distance d. Plotkin gave a simple counting argument which leads to an upper bound B(n,d) for A(n,d) ...when d>n/2. Levenshtein (1964) proved that if Hadamard's conjecture is true then Plotkin's bound is sharp. Though Hadamard's conjecture is probably true, its resolution remains a difficult open question. So it is natural to ask what one can prove about the ratio R(n,d)=A(n,d)/B(n,d). This note presents an efficient heuristic for constructing, for any d/spl ges/n/2, a binary code which has at least 0.495B(n,d) codewords. A computer calculation confirms that R(n,d)>0.495 for d up to one trillion.
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