فهرست مطالب alireza erfanian

Graphene transfer from a metal substrate to the dielectric one is often the first step in graphene device fabrication. in order to achieve the proper performance of these devices surface cleanliness and maximum coverage of transferred graphene are crucial. In this paper wet transfer method and the effects of each stage of the process on transferred graphene quality have been investigated and also the reasons of tear formation and contamination during transfer process have been studied. In this research scanning electron microscopy images has been employed because of graphene surface morphology observation. by applying van der pauw method and measuring electrical resistance which itself depends on coverage percentage and contamination area , the quality of transferred graphene has been evaluated. The results are confirmed by raman spectroscopy in which spectra peaks display crystalline network defects and doping concentration. Finally an optimal process with 95% coverage level and 700 ± 50 ohm electrical resistance has been presented.

In this paper, a quasi-optical millimeter wave imaging antenna at central frequency of 94 GHz in W-band is designed. The designed imaging system requires resolution less than 30 mm at distance of 5 meters to recognize metal objects. This passive system consists of a combination of a dielectric lens (primary optics) to focus the radiation and a pyramidal horn (secondary optics) with open metal walls to properly direct and couple the focal radiation to the detector. The general parameters of this system are calculated using the geometrical optics method. Then the combination of Gaussian beam method and ABCD ray transfer matrix is used to analyze the lens antenna to find the location and size of the feeding horn. The powerful optical design software ZEMAX was used to design the lens and to verify the design results based on ray tracing. The designed dielectric lens is made of High Density Polyethylene (HDPE) with a diameter of 650 mm. Then, an optimized pyramidal horn with gain of 18.9 dB at center frequency of 94 GHz is designed. The simulation of the horn and investigation of its results performed using the FEKO and CST commercial softwares. The simulation results of the pyramid horn antenna indicate that its combination with dielectric lens is appropriate and the hybrid method (geometrical optics, Gaussian beam and ABCD matrix) to design the quasi-optical system, including the lens and the horn antenna for imaging with considered requirements, is accurate, simple and efficient.

In this paper, a radiometer system include Low Noise Amplifier (LNA), mixer and local oscillator, Ku band detector, different frequency band filters, acquisition and processing system are designed for achievement maximum gain and minimum noise. The goal of this design is fabrication a discrete radiometer system for detect very low power in Millimeter Wave (MMW) band, and Another contribution of this design is achieve to the minimum Noise Equivalent Temperature Difference (NETD) with regularize and analyze parameter. For this purpose and due to the available equipment, intended systems are designed and in return for one degree temperature difference in system input, we have 2.51 microvolt changes in output voltage, and leading to fabricate optimum operational PMMW systems. In the following, in order to evaluate the designed system, the output image from the designed system is made up. After the formation of the image, due to the inherent blurring of the PMMW image, the processes of improving and improving the visual quality of the image are executed on the image. In the image processing section, new proposals for super resolution, fusion and their sequence of actions, are presented. The above mentioned methods have been applied to output simulated images and resulted in improved output images.

he Josephson Fluxonic Diode is a long Josephson Junction that uses oppositely directed magnetic flux quanta, associated with current votrices and antivortices, as its basis operation. the movement of the vortices creates a changing phase. this in turn creates a voltage drop. in this paper, discrete JJ is proposed instead of continues JJ in JFD. Also, by numerical calculation of the discrete sine- Gordon equation, the manner of the carriers is discussed in discrete JJ. Numerically study of the dynamics of JFD based on discrete JJ shows a rectification. Because of it is easy to adjust the value of the junction parammeters, and it is possible to have single flux quantum stuffed in a small area by adjusting the discreetness parameter, it is expected that the useful and practical Josephson fluxonic devices can be made by discrete JJs.