Sharif Digital Repository

In this paper, implosion of a micron-sized air bubble was studied numerically using OpenFoam software package. Then a parametric investigation on the flow physics of the problem was performed. The results show that as the initial pressure of the liquid increases, the pressure and the temperature inside the bubble increases such that in some cases, the temperature is as high as the one required for luminescence. Also, increasing the density and the temperature of the liquid solely, decreases the intensity of the collapse. © 2018  

The analysis and design of a tunable low noise active inductor is presented. The noise performance of the proposed gyrator-based active inductor is improved without either degrading its quality factor or consuming more power using a linear Feed Forward Path (FFP). The proposed low noise active inductor has been designed and fabricated using standard 0.18-μm CMOS technology. The measurements show a 3 fold improvement in the input noise current compared to that of conventional active inductors. The active inductor was tuned and measured at the resonance frequency of 2.5 GHz, which could be extended as high as 5.5 GHz, with a quality factor of 30. The circuit draws 4.8 mA from a 1.8 V supply  

In this paper, an area-efficient LNA with on-chip input matching circuit utilizing an active inductor is presented. The active inductor is implemented based on the gyrator structure and its noise is improved by employing a feed-forward path (FFP). The overall low-noise performance of the LNA is achieved by cancelling the inductor noise through an additional FFP. It is shown that the proposed LNA circuit is capable of achieving low-noise performance with wideband tuning at the input in a small die area. A 0.32- to 1-GHz LNA has been designed and fabricated in a standard 0.18-μm CMOS technology. The LNA occupies a die area of less than 0.1 mm 2. The measured results show noise figure of... 

The effects of resonator topology on the phase noise of LC oscillators are studied in this paper. It is shown that there is a neglected factor that can considerably influence the phase noise behavior of the oscillator. We designate this factor as the Inductance Energy Factor (IEF), which directly depends on the topology of the resonator. It is shown that through proper design of the resonator for a better IEF, the oscillator phase noise can be improved. It is also shown that by modifying the resonator structure to improve IEF, the phase noise does not have to be constrained by the minimum realizable inductance and its maximum quality factor. Therefore, the power-phase noise trade-off remains... 

Liquid-liquid two-phase flow is capable of boosting heat transfer in microdevices compared to the single-phase and gas-liquid flows. A thorough investigation is performed here to characterize the heat transfer in water-oil flow in a microtube. Finite element method along with the level-set model is employed for numerical simulation. A main part of this paper is devoted to studying the effect of wettability on the heat transfer performance. Four contact angles of 0°, 30°, 150°, and 180° are investigated, which revealed that the contact angle of 150° produces the highest Nusselt number (Nu). Triple points form at this contact angle, and the slugs slide on the wall, which results in more... 

Liquid–liquid two-phase flow in microchannels is capable of boosting the heat removal rate in cooling processes. Formation of different two-phase flow patterns which affect the heat transfer rate is numerically investigated here in a T-junction containing water-oil flow. For this purpose, the finite element method (FEM)is applied to solve the unsteady two-phase Navier–Stokes equations along with the level set (LS)equation in order to capture the interface between phases. It is shown that the two-phase flow pattern in microchannels depends on the flow initial condition which causes hysteresis effect in two-phase flow. In this study, the hysteresis is observed in flow pattern and consequently... 

In this paper, we propose a two dimensional optimal linear detector (2-D OLD) for slowly fluctuating target in Gaussian interference. We assume that the samples of received signal in the range and in the successive pulsation times are collected in a two dimensional array. In conventional detectors, each column of this matrix (the Samples of the same pulsation time) is detected separately and the binary results may be integrated for successive pulsation times in order to improve the detection performance. In fact, by applying binary integration, we ignore the considerable correlation among 2-D data in the azimuth direction. In the proposed 2-D OLD detector, this correlation is considered,... 

The design of a Gm-C filter for High-Frequency applications is described in this paper. A low-pass, sixth-order elliptic Gm-C filter based on the new biquadratic architecture in 0.18 um CMOS process is designed with the proper dynamic rang. A simple structure of the high Q biquadratic filter is used to enhance the linearity and tunability of the filter. The cut off frequency of this filter is 33 MHz. It has a THD of -45 dB for 0.2 Vpp, 8 MHz signal. The complete filter including on-chip tuning circuit consumes only 0.8mA with 1.8 V single supply voltage. ©2006 IEEE  

Dissimilar Al/Cu joints were produced through simple cold compression technique. The influence of different reductions (40, 53 and 66 %) on the joint strength was studied. Also, the effect of heat treatment on the joints’ mechanical characteristics was investigated using a modified miniature shear test. Microscopical examinations by means of optical and scanning electron microscopes were conducted and results confirmed that acceptable joints produced through 53 and 66 % deformations. According to the shear test results, it was revealed that post-weld heat treatment influenced the joint’s strength and caused strength enhancement in the samples which were not subjected to annealing prior to... 

An X-band core chip is designed and fabricated in 0.18-μm CMOS technology, which can significantly reduce the monolithic microwave integrated circuit count required for realizing an active beam-former T/R module. The core chip consists of two RX/TX paths, each of which includes a 6-b phase shifter, a 6-b attenuator, along with two input and output amplifiers. A new architecture for realizing such a core chip system and a low loss circuit for 5.625° phase shift block are proposed. The overall rms phase and gain errors are better than 2° and 0.25 dB, respectively, in both RX/TX paths. The gain of each path is around 12 dB, while the output 1-dB compression point is higher than 10 dBm over the... 

Surface tension driven passive micro-pumping relies mainly on the surface tension properties. To have control over surface tension driven passive micro-pumps (STD-PMPs), it is essential to understand the physical background of the fluid flow in these pumps. Hence, the purpose of this work is to give an exploration of the flow physics of a STD-PMP. In this regard, computer simulation is used to give detailed information about the flow pattern and physical phenomena at different conditions. To this end, a droplet of water, with a specified diameter, is placed onto an entry port connected to another droplet at the exit port via a microchannel. The results indicate that the pumping process, in...