Sharif Digital Repository

This work utilizes the direct simulation Monte Carlo (DSMC) calculations and examines the influence of rarefication on the mixing length and effective diffusion coefficient in a two-species mixing problem. There have been efforts in past rarefied mixing flow studies to bridge between the mixing evolution rate and Knudsen number. A careful review of those efforts shows that the past derived relations did not determine the weights of Reynolds (or Peclet) number in the rarefaction influences. Although they indicated that an increase in Knudsen would decrease the mixing length, such reductions were primarily due to the Reynolds (or Peclet) reduction. Therefore, those studies could not explicitly... 

In this paper, a new formulation based on conversion matrix method is proposed to analyze near-the-carrier local ocillator (LO) noise down conversion to IF in microwave mixers. This method could be easily applied to analyze LO noise down conversion in any type of mixer. Practical results of this method have been compared with the envelope method and measurement results. It is shown that despite the conventional AM noise suppression in balanced mixers, the near-the-carrier LO noise suppression does not occur necessarily at the center frequency of hybrid in balanced mixers. AM noise suppression values are predicted precisely. © 2006 IEEE  

A terahertz modulator based on the Type-II superconductor flux flow oscillator has been proposed. Analytical calculations are presented and the effects of intrinsic and extrinsic parameters such as disorder strength of crystal, penetration depth, frequency, and amplitude of the modulated current on the radiation power spectrum have been studied. The proposed structure also exhibits a mixer-like behavior, in the sense that its output harmonics range from the washboard frequency up to the superconductor gap frequency, so the input signal is practically mixed with the washboard frequency and its harmonics. The modulation index for each harmonic of this modulator has also been investigated. This... 

In the case that phased array systems are not capable of attenuating interferences, Radio Frequency (RF) front-ends and Analog Digital Converters (ADCs) with a large dynamic range are required to avoid saturation of the receiver. This leads to a higher power consumption. In this paper, employing N-path circuits in Mixer-First receivers, a novel method is introduced in which spatial and frequency blockers are eliminated right before entering the system on the antennas input. In fact using this technique, adjustable spatial notch filter and band-pass frequency filter are implemented to suppress spatial and frequency interferences. The proposed method enhances the robustness and effectiveness... 

Micro-mixers are considered as vital components of Micro Total Analysis systems (μTAS). Major objective in the design of micro-mixers is achieving high mixing quality in short mixing times. In this paper, numerical simulation of some micro-mixer designs has been carried out to understand the detailed flow pattern and thereby to propose modifications for improving mixing efficiency. It is well known that inducing convection will provide turbulent like behavior with corresponding mixing enhancement. In micro systems to drive the flow, electro-osmotic force is usually used by introducing electrodes. In this work, mixing electrodes have been implemented to induce convection and eddies. This... 

In most of the microfluidic applications, it is necessary to have a mixed fluid from the beginning, but in microchannels, due to facing with low Reynolds flows, the fluids flow in the channel by the laminar regimes. Hence the mixing process is a challenging problem and researchers are trying to present fast and reliable micromixers. In this paper, using Ionic Polymer-Metal Composites (IPMCs), an active micromixer has been designed. To investigate the appropriateness of IPMC, using experimental and simulation tests, we show that the IPMC actuator is a potential candidate as an active element of microfluidic micromixers  

Nucleic acid amplification via polymerase chain reaction (PCR) is one of the essential and powerful methods used in a myriad of bio-assays in clinical laboratories. Application of microfluidic devices in biologically-related processes like PCR can result in the usage of less volume of reactant samples and reduce the processing time. By implementing PCR systems on centrifugal microfluidic platforms, automation and portability can be easily achieved. Although several methods have been developed, most of them are still dealing with challenges of the required high processing time. This study presents the numerical simulation of a fully automated PCR system with the goal of enhancing the mixing... 

Microfluidic-based concentration gradient generators (CGGs) have a number of applications in chemical, biological and pharmaceutical studies. Thus, precise design of the microfluidic system is crucial to maintaining the desired concentration gradient in microchannels. One of the design considerations is the length of microchannels in the structure of a CGG. A CGG with a short length fails to provide the complete diffusive mixing, while the size of the microchip would unfavorably increase by incorporating a long CGG. Considering a CGG as a tree-like structure consisting of T-shaped micromixers, the mixing process of the species at a straight microchannel has been solved analytically. Herein,... 

Electroactive-Polymers (EAPs) are one of the best soft $mu $ -actuators with great biomedical applications. Ionic ones (i-EAPs) have more promising features and have adequate potential for using in the active microfluidic devices. Here, as a case study, we have designed and fabricated a microfluidic micromixer using an i-EAP named Ionic Polymer-Metal Composite (IPMC). In microfluidics, active devices have more functionality but due to their required facilities are less effective for Point of Care Tests (POCTs). In the direction of solving this paradox, we should use some active components that they need minimum facilities. IPMC can be one of these components, hence by integrating the IPMC... 

In this paper, a low power receiver for medical implant communication service (MICS) is presented. Low power design is vital in the MICS applications since the implanted chip has to work for a long time without the need to change its battery. As a result, a merged N-path low noise amplifier (LNA) and mixer block is proposed. In this structure, the LNA and down-conversion mixer share a transconductance to lower the overall power consumption. An N-path feedback is utilized around the shared transconductance not only to improve the LNA selectivity and relax the linearity requirements but also to downconvert the radio frequency (RF) component and create the intermediate frequency (IF) signal. In... 

The flow and mixing behavior of two miscible liquids has been studied in an innovative static mixer by using CFD, with Reynolds numbers ranging from 20 to 160. The performance of the new mixer is compared with those of Kenics, SMX, and Komax static mixers. The pressure drop ratio (Z-factor), coefficient of variation (CoV), and extensional efficiency (α) features have been used to evaluate power consumption, distributive mixing, and dispersive mixing performances, respectively, in all mixers. The model is firstly validated based on experimental data measured for the pressure drop ratio and the coefficient of variation. CFD results are consistent with measured data and those obtained by... 

The present study is concerned with the computational fluid dynamics (CFD) simulation of turbulent dispersion of immiscible liquids, namely, water–silicone oil and water–benzene through Kenics static mixers using the Eulerian–Eulerian and Eulerian–Lagrangian approaches of the ANSYS Fluent 16.0 software. To study the droplet size distribution (DSD), the Eulerian formulation incorporating a population balance model (PBM) was employed. For the Eulerian–Lagrangian approach, a discrete phase model (DPM) in conjunction with the Eulerian approach for continuous phase simulation was used to predict the residence time distribution (RTD) of droplets. In both approaches, a shear stress transport (SST)... 

Separation of circulating tumor cells (CTCs) from blood samples and subsequent DNA extraction from these cells play a crucial role in cancer research and drug discovery. Microfluidics is a versatile technology that has been applied to create niche solutions to biomedical applications, such as cell separation and mixing, droplet generation, bioprinting, and organs on a chip. Centrifugal microfluidic biochips created on compact disks show great potential in processing biological samples for point of care diagnostics. This study investigates the design and numerical simulation of an integrated microfluidic device, including a cell separation unit for isolating CTCs from a blood sample and a... 

Negative magnetophoresis is a novel and attractive method for continuous microparticle sorting inside a magnetic medium. In this method, diamagnetic particles are sorted based on their sizes using magnetic buoyancy force and without any labeling process. Although this method provides some attractive features, such as low-cost fabrication and ease of operation, there are some obstacles that adversely affect its performance, especially for biological applications. Most types of magnetic media, such as ferrofluids, are not biocompatible, and the time-consuming process of sample preparation can be threatening to the viability of the cells within the sample. Furthermore, in this method, both the... 

A compact low power circuit for implementation of a direct conversion OQPSK modulator is proposed. The circuit consists of a digital to analog converter, a low pass filter and an up-converter mixer. By embedding these three blocks, the circuit performance is enhanced and the total power consumption is reduced. The mixer is designed base on a Gilbert cell with on chip inductor loads. Instead of transconductance transistors of Gilbert cell, a fully deferential current mode DAC is used and proficiently a low pass filter is embedded between them and therefore the linearity of total system is improved. All of circuits are designed based on 0.18 μm CMOS technology with a single 1.8 volt power... 

This article presents the theory and implementation of a quadrature and differential RF front-end receiver. Combining balun, low-noise amplifier (LNA), mixer, and oscillator in a single stage, the proposed circuit, named the Blixator, is well suited for low-power applications. The baseband's transimpedance amplifier (TIA) also shares part of its dc current with the Blixator cell, resulting in sub-milliwatt power consumption. To avoid additional power and area by quadrature LO generation, the I/Q signals are generated at RF, employing the inductors already required for providing the dc current path of the LNA transistors. The expressions for gain, noise figure (NF), and phase noise of the... 

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics... 

Separation and lysis of RBCs play an important role in diagnosis of different diseases. Although they have been partially studied in several researches, a comprehensive study on integrating both separation and lysis units on a single chip has been seen rarely in the literature. Also, the factors related to the chemical lysis process have not been investigated in detail. In this study, we introduce a novel microfluidic channel design for sequential RBC's separation and lysis. For the separation part, an active method with an electric field was applied to the cells. Besides, a novel mixer was designed for mixing the cell solution and lysis reagent. In the lysis section, we used a mathematical...