Sharif Digital Repository

In this paper, implementing a guard-ring electrode in a capacitive transducer system is described. The performance of the transducers with and without a guard-ring in terms of output linearity and dynamic range is investigated and deviations from the expected theoretical results are reported. The two-terminal capacitors perform well only for a small gap distance in the range of 2-3 mm while the three-terminal sensor (50 mm diameter) demonstrates a very good performance for a wide range of 0.5-5 mm. For a gap distance of 3 mm, the slope deviation for the sensors without a guard-ring is in the range of 15%-29%, whereas for the system with a guard-ring is only 6%, which clearly shows the range... 

In this paper, application of a capacitive sensor system in recording small displacements is discussed. Through using a simple transducer and a monitoring circuit, change in capacitance has been detected as a function of the capacitor air-gap distance. There is a linear relation between gap distance and output of a sensor for a wide gap range of 0.5 to 5 mm. The reported system provides means for measuring displacements up to 5 mm with a resolution better than 250 nm. By decreasing the dynamic range of the transducer to 250 μm, a small displacement of the order of 100 nm is detectable. With the present system, a minimum displacement of about 200 nm (200 ppm) for the gap distance of 1 mm is... 

Determination of the time lag caused by utilization of different tubes to measure pressure on the surface of a wind tunnel model is an important problem in the field of aerodynamic especially for unsteady measurements where the pressure signature changes continuously with time. In this investigation the time required for the applied pressure at one end of different tubes to reach its original value (applied pressure) at the other end has been measured. Three plastic tubes and two polyethylene tubes with different lengths and different inner diameters; L=2, 5 and 10 m, d=1, 2 and 4 mm, were used to study the time lag. Experimental data show that the response time in a pressure measuring... 

In this paper, we divide the imaging geometry of a photoacoustic computed tomography (PACT) structure that have a circular geometry and have focused transducers of positive or negative focus, into different zones of varying resolution. With using the presented analysis, it is possible to find the maximum range in which the system resolution is at its best value, according to the device specifications. The following equations are used to find the blind spot angles of the system for each source point inside the chamber. These are important for two reasons: the first is that the user can calculate the range in which the imaging system has the best quality by entering the specifications of his... 

In recent years, there has been a growing interest in the simulation and analysis of piezoelectric transducers with the he help of equivalent electrical circuit simulations (EECS). This paper has been devoted to study of such approach for two designed and fabricated ultrasonic sandwich transducers. By using analytical analysis, the dimensions of components of the two piezoelectric transducers were determined for the assumed resonance frequencies of 30 kHz and 40 kHz. Then, by using a two dimensional finite element model, and regarding two different modeling techniques for the transducers and by application of a current source which was connected directly to the piezoelectric pieces of the... 

This paper discusses the design of a high frequency wide bandwidth ultrasound transducer with the center frequency of 50 MHz and an aperture diameter of 3 mm for medical ultrasonic imaging. The piezoelectric material used in this design is Lithium Niobate. The design is verified by both KLM equivalent circuit and spatial impulse response method as used in FIELD II software and the theoretical imaging resolution has been calculated as 50 um axially and 80 um laterally. The possible applications of this probe are skin layer imaging, tumor detection and superficial blood flow measurement  

A unified and robust method has been introduced to compute magnetostatic and electrostatic fields for nonperiodic excitations in periodically corrugated anisotropic structures. The method extends a previously published concept of modified phased-periodic Green's functions for solving flat-surface problems. Convergent results have been obtained for corrugations with aspect ratios exceeding 15. Novel elemental field distributions are presented as examples  

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  

Designing efficient acoustic stack and elements for high-frequency (HF) medical ultrasound (US) transducers involves various interrelated parameters. So far, optimizing spatial resolution and acoustic field intensity simultaneously has been a daunting task in the area of HF medical US imaging. Here, we introduce optimized design for a 50-MHz US probe for skin tissue imaging. We have developed an efficient design and simulation approach using Krimholtz, Leedom and Matthaei (KLM) equivalent circuit model and spatial impulse response method by means of Field II software. These KLM model and Field II software are integrated, and a GA algorithm is used to optimize the design of the US transducer... 

An optical apta-nanosensor was designed and developed based on reduced graphene quantum dots (rGQDs) and multi-walled carbon nanotubes (MWCNTs) and applied for the selective detection of diazinon as one of the most widely used organophosphorus pesticides. Considering the GQDs and rGQDs high fluorescence emission and optical stability, efficient optical transducers could be designed and precise detection methods could be developed based on such transducers. Herein, by using rGQDs, diazinon specific aptamer, and MWCNTs, a simple economical fluorescence method has been introduced to detect and measure diazinon with the detection limit of 0.4 nM (0.1 μg/L) in the range of 4-31 nM, meeting the... 

In this paper, the relationship between the position of ultrasound transducers from the photoacoustic source and the reconstructed image is investigated. Our studies have shown that the distance of the transducer and its location from the photoacoustic source specifically affects and is closely related to the quality of the reconstructed image of the source. Also, we introduce a concept called blind angle for photoacoustic computed tomography (PACT) that have planar or circular limited-view geometry. Complete and accurate equations of this relationship are presented in this paper for all different 2D photoacoustic geometries. The main source of these equations is the spherically of the... 

Experimental acoustic cell separation methods have been widely used to perform separation for different types of blood cells. However, numerical simulation of acoustic cell separation has not gained enough attention and needs further investigation since by using numerical methods, it is possible to optimize different parameters involved in the design of an acoustic device and calculate particle trajectories in a simple and low cost manner before spending time and effort for fabricating these devices. In this study, we present a comprehensive finite element-based simulation of acoustic separation of platelets, red blood cells and white blood cells, using standing surface acoustic waves... 

In recent years, new Structural Health Monitoring (SHM) methodologies with a concept of "instantaneous baseline damage detection" are being developed by many researchers. In this context, this paper uses a new method to identify multiple damage in the aluminum plate. For this goal use from spars PZWS sensor network to generate and received guided waves. Ultrasonic waves are generated and measured from all possible different pairs of excitation and sensing transducers. For feature extraction of received signals used from continues wavelet transform. A probabilistic damage diagnostic algorithm based on correlation analysis was investigated to locate single or multiple damages. In this study,... 

Nowadays, the importance of the blood particles separation is undeniable in medical fields and there are different sorts of separation methods accordingly. Acoustic cell separation is chosen in this paper. Also, numerical methods have been used to study the effect of geometrical factors on the separation of the particles before spending time and expenses in a trial and error manner experimentally. We have implemented a plenary finite-element-based simulation of separatingblood particles such as white blood cells and platelets in an acoustic field using standing surface acoustic waves. In this paper, unlike previous works in which the channel is rectangular; the channel is trapezoidal in... 

Signal Transducer and Activator of Transcription (STAT) pathway is functionally located downstream of Janus kinases proteins and can integrate signals from diverse pathways, thus regulating several aspects of immune responses. Although contribution of STAT proteins in the pathogenesis of several inflammatory conditions has been confirmed, their role in the development of periodontitis has been less appraised. Thus, we assessed levels of STAT transcripts in the periodontal tissues and circulation of affected individuals compared with the corresponding controls. Expression of STAT1 was remarkably lower in tissues samples of patients compared with control tissues (Ratio of mean expression (RME)... 

Pipelines are one of the most important and efficient ways for transporting energy like water, gas, oil and etc. between different places all across the world. As these pipelines are located in different conditions and situations, they are all sensitive to a wide variety of damages like vibration, so monitoring their structural behavior is an essential task. Monitoring pipeline vibration caused by cavitation through an orifice by a piezoelectric sensor is presented in this paper  

In Minimally Invasive Surgery (MIS) the operation is performed through introducing surgery instruments, graspers, scissor into the body. In the present work, a novel smart grasper is presented in which the surgeon can virtually acquire a feeling of force/momentum experienced by the organ/tissue. The smart grasper uses piezoelectric sensors bonded at desired locations to detect the applied force/momentum by surgeon and to measure the transmitted response to the tissue/organ. © 2009 IEEE  

The study of air-water, two-phase flows in hydraulic structures such as pressurized flow tunnels, culverts, sewer pipes, junctions, and similar conduits is of great importance for design purposes. Air can be provided by vortices at water intakes, pumping stations, aerators, steep channels, etc. Under certain conditions, air may also be introduced into pressurized intake systems, which may form large bubbles in portions of the pipe. The bubbles may, in turn, cause an unstable slug flow, or other flow patterns, that leads to sever periodic transient pressure. In this paper, an experimental model (a circular and transparent pipeline, 90 mm in ID and 10 m in length) is used to predict pressure...