Evaluation of 8-Channel Radiative Antenna Arrays for Human Head Imaging at 10.5 Tesla

For human head magnetic resonance imaging at 10.5 tesla (T), we built an 8-channel transceiver dipole antenna array and evaluated the influence of coaxial feed cables. The influence of coaxial feed cables was evaluated in simulation and compared against a physically constructed array in terms of transmit magnetic field (B1+) and specific absorption rate (SAR) efficiency. A substantial drop (23.1% in simulation and 20.7% in experiment) in B1+ efficiency was observed with a tight coaxial feed cable setup. For the investigation of the feed location, the center-fed dipole antenna array was compared to two 8-channel end-fed arrays: monopole and sleeve antenna arrays. The simulation results with a phantom indicate that these arrays achieved ~24% higher SAR efficiency compared to the dipole antenna array. For a human head model, we observed 30.8% lower SAR efficiency with the 8-channel monopole antenna array compared to the phantom. Importantly, our simulation with the human model indicates that the sleeve antenna arrays can achieve 23.8% and 21% higher SAR efficiency compared to the dipole and monopole antenna arrays, respectively. Finally, we obtained high-resolution human cadaver images at 10.5 T with the 8-channel sleeve antenna array.

A Multiband Antenna Stacked with Novel Metamaterial SCSRR and CSSRR for WiMAX/WLAN Applications

This paper presents an innovative method for the design of a triple band meta-mode antenna. This unique design of antenna finds application in a particular frequency band of WLAN and WiMAX. This antenna comprises of a square complimentary split ring resonator (SCSRR), a coaxial feed, and two symmetrical comb shaped split ring resonators (CSSRR). The metamaterial unit cell SCSRR independently gains control in the band range 3.15–3.25 GHz (WiMAX), whereas two symmetrical CSSRR unit cell controls the band in the ranges 3.91–4.01 GHz and 5.79–5.94 GHz (WLAN). This design methodology and the study of the suggested unit cells structure are reviewed in classical waveguide medium theory. The antenna has a miniaturized size of only 0.213λ0 × 0.192λ0 × 0.0271λ0 (20 × 18 × 2.54 mm3, where λ0 is the free space wavelength at 3.2 GHz). The detailed dimension analysis of the proposed antenna and its radiation efficiency are also presented in this paper. All the necessary simulations are carried out in High Frequency Structure Simulator (HFSS) 13.0 tool.

Selection of modes for laser cladding of PR-08Kh17N8S6G powder

A brief analysis of powders used in the industry for surfacing on the work surfaces of critical parts is given in order to increase their wear resistance. The results of experimental studies on the choice of parameters of gas-powder cladding modes are presented. The cladding process was carried out by a laser robotic complex with a coaxial feed of powder to the surfacing zone. The substrate used steel grade 08H18N10T, which was applied to the melt of wear-resistant powder grade PR-08H17N8S6G. The use of ytterbium fiber laser allowed to reduce the heat supply to the surfaces, which significantly reduced the residual stresses in the workpiece. Variable parameters of the laser cladding process were the output power of laser radiation, processing speed, and powder mass flow rate. During visual inspection, the absence of pores and cracks were used as the estimated indicators of the cladding. The study of macro geometry single clad track was conducted on cross section of the clad. During measurements, the quality of a single clad track was determined by its geometric dimensions: clad height, clad width, contact angle between the tangent to the cladding surface and the substrate plane, as well the depth of the mixing layer of the surfaced and substrate materials. According to the results of experimental studies of the selected optimal mode, providing a cladding track with a clad height above 1 mm; clad width 2.5 mm; the depth of the mixing layer – 0.2 mm; contact angle between the tangent to the clad surface and the substrate more than 50º. This work was financially supported by the Ministry of Science and Higher Education of the Russian Federation. Agreement on the provision of subsidies No. 075-15-2019-1833 dated December 03, 2019. Unique identifier PNI RFMEFI60419Kh0245.

SEMI-AUTOMATED DESIGN OF MICROSTRIP DUAL BAND COAXIAL FEED ANTENNA USING DIFFERENTIAL EVOLUTION ALGORITHM FOR WLAN APPLICATIONS

Traditional antenna design uses discrete steps manually to create and optimize the antenna structure. This approach costs both time and effort, especially when a complex antenna structure is on demand. The evolutionary algorithm emerges as a potential alternative method to formulate the antenna model as well as to optimize the structure so as to comply with the design requirements. In this paper, we propose a method for determining the surrogate model and dimensions of an ultra-wideband patch antenna using a differential evolution algorithm. This antenna is desired to work at the frequency range of 2.45GHz to 5.8GHz for WLAN applications. Through the evaluation of reflectivity and investigation of the algorithm,the surrogate model is obtained faster with optimized dimensions. The algorithm is investigated with different strategies to detect the best strategy when an object is a differential evolution applied.