The increased use of fiber-reinforced polyester composites in an outdoor environment has led to questions concerning the environmental durability of these materials, particularly as related to ultraviolet (UV) exposure. In this research the effects of UV radiation on mechanical properties of glass/polyester composites were studied. Since the photo degradation is a surface mechanism and is restricted to degradation of mechanical properties of resin (fiber is not degraded), this research is focused on resin properties. For this reason, test samples made of polyester resin were prepared and treated in a UV chamber through accelerated tests. Three types of specimen were manufactured. The tensile testing samples were prepared based on ASTM D638 standard with a nominal thickness of 1 mm. Also, Arcan specimens for shear tests and ASTM D3410 for compression tests were manufactured. To obtain time dependent mechanical properties of polyester resin under UV radiation, samples were radiated in three different time intervals, equivalent to 3, 6 and 12 months, using an artificial UV exposure chamber. Test specimens were tested under tension load and showed a decrease of up to 15% in average failure strain, a decrease of up to 30% in ultimate strength, and 18% decrease in tensile modulus after 100 h exposure. Also, significant changes were considered in shear modulus and strength of polyester. The effect of ultraviolet absorbers (UVA) on preventing polyester mechanical properties degradation is also studied. The results showed that the samples which have UVA additives were not degraded after UV exposure. After obtaining matrix properties due to exposure, mechanical properties of unidirectional laminate of glass/polyester composites under UV radiation were simulated using micromechanics theories. The results of simulation were validated with tensile testing of ASTM D3039 specimens of [0/90]s glass/polyester laminated composites. The results show that shear modulus of this laminate decreased about 20% due to UV exposure.
Physical principals and the relations between Surface Plasmon Resonance (SPR) spectra and geometrical properties of metal nanostructures specially silver and gold were reported. Applying SPR technique enable us to investigate the accuracy of some simple equations for investigating geometrical properties of metal nanostructures based on their plasmonic spectrum. Geometrical properties, shape and size polydispersity of particles as well as particles' embedding medium refractive index are the crucial ignored parameters, effective in the accuracy of those equations. The restrictions of these relations in terms of shape, size distribution and refractive index of particles' embedding medium are also investigated and compared with other published reports. Furthermore, the equations of spherical particles have been extended to non-spherical ones and their accuracy has been investigated. It was found that the modified forms of the equations may lead to more exact results for non-spherical metal particles.
The next generation of wireless networks (5G) employs directional transmission at millimeter wave (mmW) frequencies to provide higher bandwidth and faster data rates. This is achieved by applying antenna arrays with proper beam steering capabilities. Rotman lens has long been used as a lens-based beamformer in electronically scanned arrays and its efficient design is important in the overall performance of the array. Minimizing the phase error on the aperture of the antenna array is an important design criterion in the lens. In this paper, a 7 × 8 wideband Rotman lens is designed. Particle swarm optimization is applied to minimize the path length error and thereby the phase error. The optimized lens operates from 25 to 31 GHz, which covers the frequency bands proposed by the Federal Communications Commission for 5G communications. The proposed optimized lens shows a maximum phase error of <0.1°. The proposed Rotman lens is a good candidate to be integrated with wideband microstrip patch antenna arrays that are suitable for 5G mmW applications.
In this article, a metamaterial‐based broadband low‐profile antenna is presented. The proposed antenna employed an array of uniplanar quasi‐composite right/left‐hand (CRLH) metamaterial cells. This structure contributes to exciting the operating modes in lower frequencies. The antenna has an overall electrical size of 0.75 × 0.60 × 0.07 λ03 (λ0 is the center operating wavelength in free space) and provides a 25% measured bandwidth with the center frequency of 5.1 GHz and maximum gain of 6.6 dB. The proposed antenna is an appropriate candidate for WLAN, WiMAX, and other wireless communication applications.
In this paper, a miniaturized CPW-fed tapered slot antenna (TSA) with a modified CPW to slot-line transition structure was introduced. An air-bridge and tapered slot edge (TSE) structure was also employed to broaden the transition bandwidth. Through these applied modifications, negative features of the original TSA (limitation of transition) and antipodal Vivaldi antenna (bad cross-polarization) are both removed, while all the positive features remained. Results showed that the proposed structure offered a broad bandwidth of 2.6–20 GHz and also exhibited an appropriate current distribution with high radiation efficiency. The radiation pattern was stable in the working frequency band with good directivity, gain, and low cross-polarization. The proposed antenna structure also presented satisfactory time-domain characteristics. In this study, we confirmed the simulation results through data measurements.
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