Sharif Digital Repository

In this paper, for the first time, current distribution inside multiwall carbon nanotube (MWCNT) bundles is studied in the high frequency range in which resistance becomes saturated. It is shown that current distribution of MWCNT bundles in this range is not strictly decreasing vs. distance from surface as in Cu wires  

A divide-by-3 frequency divider for Inphase and Quadrature (I/Q) LO signal generation in a multi-band frequency synthesizer is presented. Using divisor numbers other than powers of 2 (2n) for quadrature signal generation, reduces the required frequency range of the VCO in multi-band frequency synthesizers. The divide-by-3 circuit is designed in a 0.18um CMOS technology. © 2008 IEEE  

Squeak and rattle (S&R) noises are important in-cabin sources of annoyance for occupants. Originally, S&R is generated as a result of colliding and slamming of car's trim and body structure which in turn occurs because of the dynamic displacements of components excited by road and power-train. Squeak noise is interpreted as periodic stick and slip phenomena in the contact boundary of two neighbor surfaces. While rattle noise is the emitted noise when adjacent surfaces collide and impact. Squeak noise takes place at low frequency while rattle phenomenon happens in high-frequency range, even though the excitation sources (road and power-train line) works in low frequency range. In practice,... 

These days, the pace of utilizing CAE tools is increasing with an eye to the vehicle development time and cost considerations. This paper deals with the NVH virtual analyses performed for a trimmed body of a B-segment sedan car. Since the main source of annoyance in low frequency range is the booming noise, the NVH diagnoses are performed by FEM tools. Firstly, the finite element model of the car is generated and this is followed by the modal analysis simulations for the car and cavity models in order to investigate the frequency attributes of the car and identify the NVH characteristics of body structure and acoustic cavity. Afterwards, noise transfer function (NTF) analyses are performed... 

Integrated on-chip inductors with high quality factors are demonstrated using a low loss artificial conductor technology. This concept is based on an artificial layered meta-material comprising a bi-layered Ni 80Fe 20/Cu superlattice. By properly tailoring the thickness ratio between the non-magnetic and magnetic metallic layers, the skin effects can be effectively suppressed within a wide frequency range, and can be tuned to a minimum at the frequency of interest up to 67 GHz. The quality factor has been increased by 41% of a 2nH inductor at 14.5GHz. The bandwidth of skin effect suppression is obtained between 10-18 GHz  

I propose a novel method for designing a broadband THz absorber by using periodic arrays of graphene ribbons on a Salisbury-screen-like structure. The recently proposed analytical circuit model of graphene arrays is used for obtaining analytical expressions for the input admittance of the proposed device. The input admittance is then adjusted to be closely matched to the free space in a wide frequency range. Consequently, it is demonstrated that a bandwidth of 90% absorption can be extended up to 100% of the central frequency with only one layer of patterned graphene  

When illuminated by TM polarized waves, periodic arrays of graphene ribbons are known to exhibit plasmonic resonances due to their dual inductive-capacitive nature. It is demonstrated here that even in TE polarization, resonances can be observed in these structure. These resonances, which are of nonplasmonic origin, are explained by means of a circuit model. It is shown that, for a certain frequency range, arrays of graphene ribbons have both capacitive and inductive properties, which lead to an ultra-sharp inductor-capacitor resonance. The banw idth of this resonance can be as narrow as ∼0.0002 nm at a wavelength of 630 nm. The resonance can also be viewed as the grating excitation of a TE... 

A compact planar wideband microstrip antenna is introduced. The antenna is a log-periodic antenna with 7 dipole elements. The antenna is designed to function in the frequency range of 500 to 700 MHz. It has a dimension of 268 mm by 145 mm by 3 mm. The matching is better than -10 dB in the working bandwidth. The proposed antenna generates linear polarization. Its maximum gain is 4.5 dB at the central frequency. It provides a low-cost alternative to the conventional Yagi-Uda TV antennas. © 2007 IEEE  

Out-of-time-order correlators (OTOCs) progressively play an important role in different fields of physics, particularly in the nonequilibrium quantum many-body systems. In this paper, we show that OTOCs can be used to probe the Floquet dynamical quantum phase transitions (FDQPTs). We investigate the OTOCs of two exactly solvable Floquet spin models, namely, Floquet XY chain and synchronized Floquet XY model. We show that the border of driving frequency range, over which the Floquet XY model shows FDQPT, is signaled by the global minimum of the infinite-temperature time averaged OTOC. Moreover, our results manifest that OTOCs decay algebraically in the long time, for which the decay exponent... 

The factors affecting the quality of material identification by simulating a simple THz spectroscopy system in the frequency range of 0.5–1 THz, have been investigated. Two methods, using the Kramers-Kronig relation and the derivative of the reflection coefficient, are applied to identify the C-4 material. Also, the optimal incident angle to minimize the sensitivity of the reflectance to the incident angle has been obtained theoretically. To improve the THz spectroscopy of rough objects, two methods are proposed including transmitter displacement and rotation. Using the relations between the scattered waves and the spatial frequencies, the proposed methods are theoretically analyzed and... 

A method to design a tunable low noise amplifier (LNA) for multiband receivers is proposed. This paper also presents a single-ended to differential conversion (S2DC) topology which improves the LNA linearity without degrading its noise performance. Combining input tuning with S2DC in a single stage reduces power consumption of the LNA and decreases effects of supply noise. An LNA has been designed based on the proposed method for 2.3-4.8 GHz in a 0.18 μm CMOS technology. Simulations show an IIP3 of -3.2 dBm, a less than 3.7 dB noise figure (NF), a voltage gain of 24 dB in the whole frequency range. The LNA draws 13.1 mW from a 1.8 V supply. The results indicate that the proposed tuning... 

In this study electrical properties of different water liquids at frequency range of 100-2000 Hz are investigated by using the short invasive and non-invasive cylindrical capacitive sensors (CCSs). Operation of the capacitance measurement module for such probes is based on the auto balancing bridge method. Comparison of the measured capacitances and measured resistances for different water liquids shows decrease by increasing the frequency. In another study the dielectric constant of distilled water, mineral water, tap water and salt water are measured. The effects of the frequency on the resistivity, permittivity and conductance of the different water liquids are also investigated  

Design of an Ultra-Wideband 3-dB quadrature (90°) Hybrid using ADS and HFSS softwares plus Measurement report are presented. Simultaneous Use of these two softwares lead to fast and accurate design procedure. The coupler is realized in broadside stripline and with the connection of coupled regions in tandem structure. The measured data agrees well with the expected values from simulations, and shows a good ultra wide bandwidth response over the frequency range of 1-10 GHz. Measurements showed an amplitude unbalance of ±1.5 dB, a phase unbalance of 90°±7° , and an isolation and a return loss characteristics of more than 14 dB over the frequency of 1 to 10 GHz  

In this paper, a new technique based on nonlinear resonance of microbubbles is investigated in order to estimate the amplitude of an ultrasound wave pressure field. First, the existing theoretical model is reviewed. Then, an experimental setup consisting of a bubble generator and transmitting/receiving ultrasound transducers operating in the 1 MHz frequency range is described. The effect of background noise is also taken into account. Results show that the second harmonic oscillations are detectable, paving the way to develop a quantitative method for in vivo calibration of ultrasound waves  

Closed cell aluminum foams are fabricated by using the casting method. The electromagnetic interference (EMI) shielding effectiveness of foams are investigated in the frequency range of 1.44–5 and 8–12 GHz (X band).The shielding materials are made of Al foam with the addition of different concentrations of SiC (5, 10, 15 wt%). Results show that the Al/SiC composite foams have good shielding effectiveness. EMI shielding effectiveness of samples generally increased with increasing porosity and with the increasing of SiC content. The sample with 15 wt% SiC had shielding effectiveness values of up to 150 dB  

A wind turbine transformer internal resonance, excited by high frequency transients i.e.; under its energization through a short length of cable, is considered to obtain a proper transformer design method. A multi-objective optimum design method (using TOC and inrush current energy factor as objective functions) is employed and the optimal Pareto solutions for this design are derived. Selected design from the Pareto optimal solutions are then modeled using the lumped RLC ladder network, valid over a wide frequency range. The obtained frequency responses are then compared with each other to investigate the effect of multi-objective design on different aspects of the transformer winding... 

In this paper, a reconfigurable receiver front-end for the frequency range of 800 MHz to 2.5 GHz is presented. The radio frequency front-end is realized in wideband form with reconfigurable baseband filter. The proposed front-end targets the GSM, WLAN, WCDMA, and GPS standards residing in the aimed frequency range. The necessary specifications for each individual standard have been revisited and recalculated. The interaction of the different standards and their interoperability has been thoroughly investigated and extra specifications derived for the multistandard receiver. The multistandard receiver has been designed, layouted, and simulated in RFCMOS 0.18-μm process. Copyright © 2018 John... 

One of the shortcomings of photoconductive (PC) antennas in terahertz (THz) generation is low effective radiated power in the desirable direction. In this paper, we propose a defective photonic crystal (DPC) substrate consisting of a customized 2D array of air holes drilled into a solid substrate in order to improve the radiation characteristics of THz PC antennas. The effect of the proposed structure on the performance of a conventional THz PC antenna has been examined from several aspects including radiation efficiency, directivity, and field distribution. By comparing the radiation performance of the THz antenna on the proposed DPC substrate to that of the conventional solid substrate, it...