Sharif Digital Repository

A simple and straight forward method for acoustic impedance measurement is presented and evaluated. In this method a speaker is used as the signal source. The relationship between the electrical impedance of the speaker and its acoustical load is developed and studied. It is shown that the electrical current and voltage of the speaker relate to the acoustical pressure and volume velocity. The mechanical and acoustical impedances are therefore easily derived by measuring the electrical current and voltage of the circuit. The proposed method yield itself to the automatic computer measurement and can be used for the field and in situ measurements. Comparison of the measurement data with those... 

Nickel modified NiOOH electrodes were used for the electrocatalytic oxidation of ethanol in alkaline solutions. The electro-oxidation of ethanol in a 1 mol/L NaOH solution at different concentrations of ethanol was studied by ac impedance spectroscopy. Electrooxidation of ethanol on Ni shows negative resistance on impedance plots. The impedance shows different patterns at different applied anodic potential. The influence of the electrode potential on impedance was studied and a quantitative explanation for the impedance of ethanol oxidation was given by means of a proposed mathematical model. At potentials higher than 0.52 V(vs. Ag/AgCl), a pseudoinductive behavior was observed, but at those... 

In this article, impedance control of a two link flexible link manipulators is addressed. The concept of impedance control of flexible link robots is rather new and is being addressed for the first time. Impedance Control provides a universal approach to the control of flexible robots - in both constrained and unconstrained maneuvers. The initial part of the paper concerns the use Hamilton's principle to derive the mathematical equations governing the dynamics of joint angles, vibration of the flexible links and the constraining forces. The approximate elastic deformations are then derived by means of the Assumed-Mode-Method (AMM). Using the singular perturbation method, the dynamic of the... 

A novel electrode structure is introduced for micro-electrical impedance tomography. The composite electrode structure is made up of gold nanoparticles (AuNPs) and carbon nanotube (CNT) which are deposited on the surface. The nanostructure-based composition of electrodes improved the effective surface area, increased the double-layer capacitance of electrodes, and enhanced the electron transfer on the electrode–analyte interface. The proposed electrodes exhibit lower frequency-dependent electrical properties in impedance measurement. © 2020, Springer Science+Business Media, LLC, part of Springer Nature  

Aluminum electrocrystallization is studied by means of electrochemical impedance spectroscopy (EIS). A model based on random birth and deterministic growth of monolayers is proposed, in which the edges are assumed to follow a propagation law. The high frequency impedance data show charge transfer reaction of AlCl4- reduction while the low frequency features signifies the growth mode of deposits. The inductive response observed in the course of polycrystalline deposition reflects the activation of electrode area while a capacitive loop appears in regular growth. Parameters of impedance model in this system can be calculated from the fitting of experimental data to the Faradaic impedance... 

At least four source impedances are required to characterize the noise parameters of a two-port network. The accuracy of the noise parameters depends on the configuration of the employed source impedances (pattern). The configuration of a specified pattern, generated generally by an impedance tuner, changes with frequency, and as such, the accuracy is usually degraded in a wideband characterization. To realize a low-error wideband noise characterization, the present article thoroughly investigates the method of choosing a four-source impedance pattern. A Monte Carlo simulation-based approach is proposed to obtain the desired impedance patterns. The measurement and simulation results show... 

In this research, solar cells sensitized with CdS and PbS Nanocrystalline metal sulfides, chemically grown by SILAR, were fabricated and characterized. PV experiments including I-V test in the presence of light and dark,Vocdecay, and Electrochemical impedance spectroscopy were performed on the Cells made through this method in the presence of light and dark and in the time period of 2, 3, 6 and 10 days. From these experiments, the changes in indicators including fill factor, efficiency, open-circuit voltage, short-circuit current, lifetime of electrons in nanostructured anode electrode, recombination resistance and capacitance of the anode electrode-electrolyte interface were observed. Also,... 

The present study provides an inverse solution and analysis on a new approach for Electrical Impedance Tomography (EIT) process as block method in EIT. In this method, it is assumed that all of the panicles of each block have the same electrical properties (electrical conductivities). This technique is used to enhance image resolution and also to improve reconstruction algorithm. Although this method has been developed for 3D objects, in this study it is assumed that the subject has a (two-dimensional) rectangular shape and is made of fixed size blocks. By considering the previous conditions and computing relationship among currents, voltages and electrical impedances of blocks, the required... 

In this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e., for the wavelength varying from 478 to 3278 nm that yields an ultra-wide band with the width of 2800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin layer of Mn, the absorption bandwidth is reduced to 274 nm. Therefore, adding only... 

In this paper we investigate the active impedance of Time Modulated Array (TMA) as a low-cost and simple beamforming architecture. Since the antenna elements in TMA are periodically turned on and off, the active impedance of this structure has less variation compared to a phased array architecture. In this paper, we have compared the active impedance of a TMA structure and that of the phased array for different cases. The active reflection coefficient of the TMA is always below-10 dB, while the impedance of the phased array becomes unmatched for certain scan angles  

The transfer of pyridinium ion across the water/nitrobenzene interface has been studied by the methods of cyclic voltammetry and ac-impedance measurements. The diffusion coefficients of these species in both media, Dw,pyH+ = 4.4 × 10-5 and DNB,pyH+ = 2.16 × 10-5 cm2 s-1, as well as the diffusion coefficient of pyridine in the organic phase, DNB,py, 3.05 × 10-7 cm2 s-1, have been calculated. The standard potential of pyridinium ion transfer, and the corresponding free energy change and its distribution coefficient between the two phases, have been reported by means of cyclic voltammetry. Impedance measurements resulted in an arc in Nyquist diagrams representing the transfer of pyridinium ion... 

A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide.The proposed structure has a return loss of <-10 dB over a broad bandwidth of 0.5-5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are investigated through various simulations. A case of the proposed antenna is fabricated, and measurement results are presented including return loss, gain, and radiation patterns  

This paper deals with realization of fractional-order impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. The necessary and sufficient conditions for the existence of such a realization are found in a general case. Also for impedance functions described by a class of fractional-order transfer functions, the realizability conditions are stated as some algebraic conditions on the parameters of the transfer function. Moreover, a procedure is proposed for implementation of such impedance functions by passive electrical networks composed of a fractional capacitor and some RLC components. Numerical examples are presented to show the... 

A highly linear X-band low-noise amplifier (LNA) is proposed and implemented in a standard 0.18-μm CMOS technology. The LNA features both high and low-gain operation modes. In its normal high-gain mode, the LNA shows a small-signal gain of 13.6 dB with an IIP3 of +9.5 dBm and a noise figure of 4.7 dB. The two-stage amplifier draws 90 mA from the 3.3V power supply to achieve +14.8 dBm output P1dB (+2.2 dBm input P1dB). In the low-gain mode, the gain is reduced by about 10 dB to further enhance the linearity and to accommodate very large blockers. Accordingly, the input P1dB is enhanced to +13.7 dBm while the noise figure is increased by 8.1 dB. A technique is also introduced to maintain the... 

Human–robot interaction is an important issue in robotic researches which is the key in many rehabilitation and robot-assisted therapy applications. Impedance control can properly handle soft interaction of robots with the environment. Optimal target impedance selection can increase the performance of the overall system and guarantee the stability. The target impedance cannot be selected without proper knowledge about the stiffness and inertia parameters of the human. In this paper, a systematic analysis is done to introduce a method to estimate the human stiffness and consequently adjust the robot target stiffness. Then, particle swarm optimization is used to find the damping and inertia... 

In this paper, conditions for checking the realizability of fractional-order impedance functions by passive networks composed of a fractional element (either a fractional capacitor or a fractional inductor) and some RLC components are derived. To this end, at first the newly obtained conditions for realizability of fractional-order impedance functions by a passive network composed of a fractional capacitor and some RLC components are extended to include the case that the polynomials involving in the impedance function can have roots on the imaginary axis. Then, the necessary and sufficient conditions are found on a fractional-order impedance function to be realized by a passive network... 

A compact printed monopole antenna for broadband application is presented. The proposed antenna, having a total physical size of 21 × 6.5 mm consists of a patch fed by a coaxial line and an SMA connector as partial finite ground plane. The modified patch plane with a slot in its feed point helps to increase the impedance bandwidth of the proposed antenna. The optimal design may offer an ultra-wide impedance bandwidth from 2.56 GHz to 20 GHz. A prototype is fabricated and tested. The agreement between the simulated and measured results is quite good  

Ni/SiC nanocomposite coatings were electrodeposited using Watts type bath and different SiC particle size. The electrodeposition behavior of Ni/SiC nanoelectrocomposites was studied using electrochemical techniques such as impedance spectroscopy (EIS) and voltammetry. In this study it was shown that SiC particles modify the EIS diagram and voltammograms as well as surface morphology of electrodeposited layers. Experimental results showed that SiC particles not only affect the formation of intermediate species and decrease charge transfer resistance but also increase the nucleation sites for nickel electrodeposition and thus affect the microstructure of electrodeposited Ni/SiC nanocomposites.... 

Nanostructured molybdenum oxide was potentiodynamically deposited onto a stainless steel surface from an aqueous bath by cycling the potential between 0 and -0.75 V vs. Ag/AgCl. The deposit consisted of particulates in the range of 30 to 80 nm. Electrochemical studies under galvanostatic charge/discharge and also impedance spectroscopy revealed capacitive behavior in the potential range of -0.3 to -0.55 V vs. Ag/AgCl with the value of 477 F g-1 at 0.1 mA/cm2. An equivalent circuit comprising of three parallel branches consisting of double-layer capacitance, Warburg impedance, and a constant phase element signifying pseudo-capacitance each coupled with their corresponding resistances was... 

A stable robust adaptive impedance control strategy is introduced here as a model-based low-level control scheme for active ankle prostheses. The effects of amputee-prosthesis and prosthesis-environment interactions are included in the controller design. An interesting feature of the proposed controller is that only shank and ankle angles and angular velocities, and ground reaction forces are required to implement the control law. In other words, no feedback from amputee-prosthesis interaction forces and moment, global or local positions, and accelerations of amputated place is required. Using a Lyapunov analysis, exponential convergence characteristics of the proposed controller are proven....