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排序方式： 共有478条查询结果，搜索用时 0 毫秒
91.
Muammer Omran;Changiz Ghobadi;Javad Nourinia;Majid Shokri; 《国际射频与微波计算机辅助工程杂志》2024,2024(1):2742806
A small antenna is critical in wireless communication and monitoring of vital signs using data collected by implantable devices. Numerous studies address antenna miniaturization and reliability challenges while maintaining performance efficiency in this field. A reliable small-sized circularly polarized antenna of dimension (4.152 π × 1.28) mm3 developed for medical implants operating at the 1.4-GHz Wireless Medical Telemetry Service (WMTS) narrow band is presented in this work. The shorting pin, variable arc slots, and substrate and superstrate of high dielectric constant techniques were used. The proposed antenna underwent testing in a three-layer biological simulation environment that includes the skin, fat, and muscle. Subsequently, the antenna was fabricated, and measurements were performed by placing the antenna in beef biological tissues. The measurement results confirmed the simulated results. The antenna achieves an impedance bandwidth of 98 MHz (1.367~1.465 GHz, 7%). The effective axial ratio bandwidth (AR <3 dB) is 55.2 MHz (1.3668~1.422 GHz, 3.94%), which covers the CP operating frequency range. The simulation results attain a peak realized gain of −19.2 dBic. The communication link budget and the specific absorption rate (SAR) were analyzed. The results indicate that the radiation of the proposed antenna aligns with the safety limit of IEEE C95.1-1999 standards. The antenna exhibits excellent performance and reliability compared to other works operating within the 1.4-GHz WMTS band. 相似文献
92.
93.
Mohammad A. Obeid;Lina Akil;Alaa A Aljabali;Ibrahim Khadra; 《大分子材料与工程》2024,309(4):2300376
Electrospun drug-loaded polymers are used to make formulations that slowly release medication. This study creates ciprofloxacin (Cip)-loaded fiber mats by melt electrospinning using polycaprolactone (PCL) and PEG4000 for controlled release of Cip. The increase in Cip concentration and PEG4000 percentages increases the mat thickness resulting in uniform morphology. The tensile strength of the PCL mat is significantly improved by adding higher concentrations of Cip while PEG inclusion reduced the tensile strength significantly. Differential Scanning Calorimetry (DSC) curves of PCL and PEG 4000 either as free components of after melt electrospinning are identical and both components shows a single endothermic peak at 63 and 61 °C respectively. Fourier transform infrared spectroscopy confirms the chemical stability of the raw materials, while X-ray diffraction shows the conversion of PEG and Cip from crystalline to amorphous structure following melt electrospinning. Cip is released gradually over 72 h, and the release is increased in the presence of PEG with a maximum Cip release ≈25% after 72 h. The study provides new insights into the development of controlled release fiber mats loaded with antibacterial agents. This can help to develop formulations for wound dressings that improve the clinical outcomes. 相似文献
94.
Amged Saeed El-Wakeel Abou El-Eyoun Kamel Mohamed Ellissy Alaa Mohamed Abdel-hamed 《电力部件与系统》2015,43(3):309-319
Abstract—The proportional-integral-derivative controllers were the most popular controllers of this century because of their remarkable effectiveness, and simplicity of implementation. However, proportional-integral-derivative controllers are usually poorly tuned in practice. This article presents a hybrid particle swarm optimization and bacterial foraging techniques for determining the optimal parameters of a proportional-integral-derivative controller for speed control of a permanent magnet brushless DC motor. The first part of the article deals with the system modeling and its verification where a model of modest accuracy cannot be expected to give a fair comparison of different controllers. The remaining parts of the article present the application of different optimization techniques to tune the proportional-integral-derivative controller as applied to the motor model. The particle swarm optimization, bacterial foraging, and bacterial foraging-particle swarm optimization algorithms are implemented in MATLAB while the GA Toolbox is used. The performance of the tuned controllers is simulated and experimentally verified to evaluate the main characteristics of each one. It is found that the proposed hybrid bacterial foraging-particle swarm optimization technique is more efficient in improving the step response characteristics and achieving the desired performance indices. 相似文献
95.
Measurements of surface temperature and mass loss of decomposing construction materials during rapid pyrolysis are presented. Experiments have been performed with samples of low‐density fiberboard, medium‐density fiberboard, particleboard and poly(methyl methacrylate) in a single particle reactor at temperatures between 300° and 600°C. Ultraviolet laser light was used to excite micrometer‐sized thermographic phosphor particles that were deposited on the investigated materials, and the temperature was obtained from temporally resolved measurements of the laser‐induced emission. The wood‐based materials show a similar behavior, with small differences being attributed to differences in material properties. The surface temperature rapidly increases to about 400°C when a particle is introduced to the hot reactor. The initial phase is followed by rapid decomposition during which the surface temperature is 380°–540°C. The heating rate is slowed down during the rapid pyrolysis, and again increases as the remaining char is heated to the reactor temperature. The poly (methyl methacrylate), however, melts and at high temperatures can be characterized as a liquid with a boiling point of about 400°C. Thermographic phosphors are concluded to be suitable for high precision remote measurements of the surface temperature of decomposing construction materials, and possibilities for further studies and developments of the technique are discussed. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
96.
Alaa M. Rashad 《Materials Science & Technology》2013,29(17):2043-2056
In the recent years, grinding technology has been brought a new product with prospective properties. If quartz sand is ground, a new product is obtained with superior properties than its original. The literature contains some studies focused on employing quartz powder (QP) in traditional cementitious materials and geopolymers as additives to obtain modified matrices. This article presents a brief of the past studies fixated on adding QP into different matrices. Fresh and hardened properties have been briefed.This review was submitted as part of the 2018 Materials Literature Review Prize of the Institute of Materials, Minerals and Mining run by the Editorial Board of MST. Sponsorship of the prize by TWI Ltd is gratefully acknowledged. 相似文献
97.
This article describes the study of induced temperature and stress fields in an elastic half-space in the context of classical coupled thermoelasticity (Biot) and generalized thermoelasticity (Lord–Shulman, Green–Lindsay and Green–Naghdi) in a unified system of equations. The medium is considered to be made of an isotropic homogeneous thermoelastic half-space. The bounding plane of the surface is heated by a non-Gaussian laser beam with pulse duration of 2 ps. An exact solution of the problem is first obtained in Laplace transform space. Because the response is of more interest in the transient state, the inversion of Laplace transforms were carried out numerically. The derived expressions were computed numerically for copper, and the results are presented in graphical form. 相似文献
98.
99.
Engineering with Computers - Due to the increasing usage of nanostructures in nanotechnology and nanodevice, the following article aims to investigate the free vibration and buckling behaviours of... 相似文献
100.
Zouaneb C. Dahmane F. Seddik T. Khenata R. Bouhemadou A. Khalid Shah Meradji H. Srivastava V. Azam Sikander Bin Omran S. 《Journal of Superconductivity and Novel Magnetism》2022,35(1):141-153
Journal of Superconductivity and Novel Magnetism - The first-principle calculations of density functional theory were used to study the structural, electronic, magnetic, mechanic, and half-metallic... 相似文献