Block principle of constructing and estimating the rcs reduction of nonabsorbing broadband 2 bit anisotropic digital meta-coatings.

The block principle of constructing of coding matrices for non-absorbing flat digital anisotropic meta-coatings (MC) used to reduce monostatic RCS of objects is considered. The essence of this principle consists in 2-bit coding of the tilt angles of the anisotropy axes of the MC modules so that four arbitrary adjacent modules of the MC form two pairs of antiphase modules. The use of the block principle in the development of a MC provides a reduction of monostatic RCSs on cross polarization due to cancellation of interference waves. The reduction of the monostatic RCS of a MC at matched polarization (co-RCS) is due to the twist-effect. Simultaneously with cancellation and twist-effect, diffuse wave scattering is implemented in the developed digital MCs. The proposed 2-bit anisotropic MCs make it possible to achieve a more effective reduction of monostatic co-RCS (in relation to the traditionally accepted level of minus 10 dB) in a wide frequency band, for different polarization planes of the incident wave. The impedance and full-wave models of the two main blocks of digital anisotropic MCs are developed. An asymptotic representation of the polarization scattering matrix is obtained for the impedance model of the MC block using the method of physical optics. The algorithm for calculating the frequency characteristics (FC) of monostatic co-RCS of impedance models of MC blocks is implemented in the Octave program. Full-wave models of MC blocks are built using the HFSS program. Layouts of two main MC blocks were made. Monostatic co-RCSs of the blocks are measured in the 7÷17.5 GHz frequency band for different polarizations of the incident wave. It is shown that the calculated and measured frequency characteristics of monostatic RCS of the models and layouts of blocks of 2-bit anisotropic MCs are in good agreement. The calculated and measured levels of monostatic RCS reduction of the main blocks are at least 12.5 - 13.5 dB at different co-polarizations in the band from 10.2 to 17.5 GHz and higher (based on the results of calculations).

Numerical simulation of flow field in the twisting chamber of Murata vortex spinning based on the hollow spindle with different structures

The novel hollow spindle with spiral guide grooves is introduced into the manufacture of Murata vortex spun yarn for the sake of enhancing the vortex yarn’s strength. By means of numerical simulation, the airflow characteristics in the conventional twisting chamber and novel twisting chamber of Murata vortex spinning are obtained and compared in order to explain yarn formation for adoption of the novel hollow spindle. The airflow distribution near the spiral guide grooves is analyzed, and the influence of airflow changes caused by the groove structure on the movement of the free end fibers and the yarn strength is analyzed. The results show that the spiral guide grooves will influence the pressure and velocity distribution in the twisting chamber, especially near the areas of the guide grooves. The guide grooves can guide the swirling airflow moving down the conical cavity of the twisting chamber, resulting in increases of the tangential, axial, and radial velocities of airflow in the conical cavity. And it is expected to produce fiber migration in the yarn cross-section and the self-twist effect of wrapped fibers. These phenomena will strengthen the wrapping and twisting effect of the free end fibers and inter-fiber cohesive force of vortex spun yarn in the process of yarn formation, and finally improve the strength of vortex spun yarn due to adopting the novel hollow spindle.

Effects of Kevlar® 29 yarn twist on tensile and tribological properties of self-lubricating fabric liner

Yarn twist in textile technology is an important characteristic since it considerably affects the properties of knitted or woven fabrics. Many researchers have investigated the effect of staple-spun yarn twist on the properties of the yarns and fabrics. However, the effects of twist level of Kevlar® 29 filament yarn on the properties of yarn and its resin-impregnated self-lubricating fabric liner are not fully known yet. In this study, we have investigated the effects of Kevlar® 29 twist level on the tensile and tribological properties of the fabric liner (Kevlar® 29/polytetrafluoroethylene fabric-resin composite). Two unexpected findings about the effect of yarn twist have been observed, namely (1) asynchronous twist effect on the yarn’s and the liner’s tensile strength and (2) dissimilar yarn twist effect on the liner’s performance. These findings are mainly attributed to the synergic contributions of the yarn twist and strength and the interaction of the resin with the yarn orientation in the woven fabric structure of the liner.