JOURNAL OF IRANIAN ASSOCIATION OF ELECTRICAL AND ELECTRONICS ENGINEERS
Year:2019 | Volume:16 | Issue:2 |Papers Count:15

In this research, Zinc oxide (ZnO) nanostructures were synthesized by low cost hydrothermal method. The grown ZnO nanostructures had a dispersed distribution with nanowire morphology and the specific surface area of about 7 m2. gr-1 which they have crystalized in hexagonal wurtzite structure. ZnO nanowires/polyvinyl alcohol network (ZP) on the epoxy glass substrate with cu-interdigited electrods coated and it used as a solid state sensor of carbon dioxide gas (CO2) at environmental conditions. The gas sensing properties of ZP sensor were examined toward different CO2 concentrations (0. 037-0. 15 vol%) and also various relative humidity at room temperature. The highest response and lowest response time were reached 2. 2 and 58. 5 sec toward 0. 15 vol% CO2 concentrations at 30% and 90% relative humidity, respectively. The effect of relative humidity investigated on the sensor response and it displayed that ZP sensor response has been decreased with increasing relative humidity at room temperature. Moreover, the study of the functionalized sensor's selectivity toward air components has shown our hand made sensor has a appropriate CO2 selectivity than other gases.

In this paper, design and simulation of a new highly sensitive gas sensor based on a hybrid photonic crystal (PC) structure, containing negative and positive refractive index sections, is presented. It has been shown that using a PC with negative refraction in the first section, the transmitted power is concentrated on the entrance of the sensing channel, and the transmission of the proposed sensor will be increased. Based on the two dimensional finite-difference time-domain (2D FDTD) simulation results, the sensitivity and the transmission of the proposed sensor are measured as 876 nm/RIU and 0. 7, respectively. The modified structure, which is applicable for the gas sensing, is made using the creation of a single cavity in the center of the sensing channel. In modified structure, the sensitivity, the transmission and quality factor are measured as 880 nm/RIU, 0. 6 and 3920, respectively. The simulation results show that the modified structure could well be used in the gas sensing applications.

In this paper an ultraviolet (UV) photodetector has been fabricated using ZnO nanostructures. The cheap fabrication process, high-quality nanostructures and the desired results for the photodetector are the most important characteristics of the proposed method. ZnO nanostructures have been grown using sol-gel method. In order to increase the sensitivity, calcium impurities have been added to nanostructures. XRD results show that the obtained nanostructures are free from any unwanted impurities and phases. SEM images show that by adding Ca impurities the dimensions of the nanostructures have been reduced. EDS spectra illustrates that the Ca element exists in the nanostructures. In order to study the optical properties of the grown nanostructures, photoluminescence (PL) spectroscopy has been performed. PL results show that by increasing the impurity the bandgap has been slightly decreased. Raman spectroscopy and the XRD results depict that by increasing the impurity concentration the crystallization of the nanostructures would be reduced. The results for the UV sensor transient photocurrent measurement show that when exposed to light the current is much larger than the dark current, the sensor has a good sensitivity and adding Ca impurities increases the sensitivity considerably.

This manuscript reports the synthesis of V2O5 nanostructures using reflux method, without using additives such as surface reactants. The influence of reaction parameters like temperature and concentration on the growth of nanostructures have been investigated. It has been observed that the nanostructures are formed with a hexagonal nano-plate morphology, grown from a common core. The diameter of hexagonal nanostructures is around 5 um, and the thickness of nano-plates is less than 250 nm. XRD analysis shows the formation of ammonium vanadates in the reflux step. Calcinating these hydrated ammonium vanadates in 400oC results in formation of microstructures of V2O5. This structures are electrochemically active as the cathode material of Lithium ion battery, with an anodic and a cathodic peak, and can perform reversible reaction.

In this paper, a procedure for analyzing and designing of tunable wideband band-pass and band-stop graphene based filters in the terahertz band is proposed. These planar wideband plasmonic filters are unique in their kind. With this procedure, it is possible to design filters with the desired functional characteristics in the form of the similar quarter-wavelength resonance stubs. The discontinuity of the open stub used for this type of filter is investigated and the required length of compensation is obtained. Also, in order to analyze the designed filters, Transfer Matrix method is used based on transmission line model of structure. An example of wideband band-pass and band-stop filters are designed and analyzed according to the mentioned process. The obtained frequency response for bandpass and bandstop filters shows fractional bandwidth of 30% and 32% respectively including desired band-edge transition, attenuation level and group delay. The results of full-wave simulation also confirm analytical results. These types of filters due to the compact structure and simple design are suitable candidate for using in all-integrated wideband planar circuits of terahertz systems.

In this paper, we have presented an X band high power amplifier based on MMIC (Monolithic Microwave Integrated Circuit) technology for satellite remote sensing systems. We have used GaN HEMT process with 500 nm gate length technology with VD= 40 V and VG=-2 V in class E structure. The proposed two-stage power amplifier provides 25 dB power gain with maximum output power of 49. 3 dBm at 10 GHz. Bandwidth of proposed high power amplifier is 2 MHz and we have achieved 49% Power Added Efficiency (PAE). We have designed a band pass filter for decreasing of memory effects in output. The active on chip area of layout obtained 35 mm2 (8. 2 mm × 4. 3 mm). We have obtained AM/PM and AM/AM,-3. 8deg and 1 dB respectively in the worst case. The proposed power amplifier is unconditionally stable at the satisfied frequency range.

This paper presents a new variable gain low noise amplifier (VG-LNA) for ultra-wideband (UWB) applications. The proposed VG-LNA uses a common-source (CS) with a shunt-shunt active feedback as an input stage to realize input matching and partial noise cancelling. An output stage consists of a gain-boosted CS cascode and a gain control circuit that moves the high resonant frequency to higher frequencies and provides flatness gain. The direct power gain (S21) is continuously controlled without significant degradation in the input return loss (S11) and noise figure. The proposed VG-LNA is designed and simulated using RF-TSMC 0. 18 μ m CMOS technology by Advanced Design System (ADS). Simulation results show a maximum flat power gain (S21) of 14 dB with a noise figure (NF) lower than 3. 6 dB and an input impedance matching (S11) less than – 10 dB over the wide bandwidth of 3. 5 to 13. 5 GHz. Its power consumption is 12 mW with low power supply of 0. 9 V. In addition, the power gain ranges from 7 to 14 dB at the center frequency of 8. 5 GHz.

In this paper, for the first time, an analytical equation for threshold voltage computations in silicon-on-diamond MOSFET with an additional insulation layer is presented; In this structure, the first insulating layer is diamond which covered the silicon substrate and second insulating layer is SiO2 which is on the diamond and it is limited to the source and drain on both sides. Analytical solution was used to determine the threshold voltage by computations of capacitors in buried insulators. Simulation and Analytical results of threshold voltage in silicon-on-diamond and silicon-on-insulator with the same dimensions and channel length were compared. Theeffect of device parameters like gate oxide thickness, silicon body thickness, length and thickness of oxide on threshold voltage of the silicon-on-diamond MOSFET were investigated and the analytical results were compared against device simulation findings.

In this paper, to understand the concept of coupling, molecule density of states that coupled to the metal electrodes will be explained then, based on this concept, a weak and strong coupling for the molecules attached to the metal electrodes will be described. Capacitance model is used to explore the connection of addition energy with the Electron affinity and the ionization energy of the molecules. Also it will be showed that to calculate the single-electron current of a molecular single-electron transistor (SET), utilize of quantum-coulomb blockage (QCB) regime is necessary. The tunneling rate in the Quantum Colombian Blockade regimen will be obtained by replacing a Lorentzian function (as the tunneling transmission probability) at the tunneling rate in orthodox theory. Finally, based on the tunneling rate obtained for the QCB regime and using SIMON software, the current (or Coulomb oscillations) of the molecular SETs is calculated. Benzene and Carbon 60 are the two considering molecules for studying.

In this paper, using Thevenin’ s theorem and also nonlinear Lambert W function, a novel two-diode model of photovoltaic cells is presented in mathematical explicit manner. In comparison with existing explicit models in the literature which are valid exclusively for n2=n1 and n2=2n1, this model includes a wide range of silicon-based cells with arbitrary diodes ideality factors. Acquiring regulating parameter (a) of the proposed model, its suitability to conform the real data is verified at standard test condition with maximum error of 10-5. Moreover, recreating the changes in weather condition, the proposed model performance is validated for irradiations between 50 up to 1100 Watt/m2. Finally, with series and parallel configuration of the PV cells and analytic derivation of maximum power point, the two-diode model for PV modules is simulated in SimPowerSystems of MATLAB software for research and engineering applications.

In this work, we used the Atlas Tcad Silvaco software to investigate the effect of adding an additional BSF layer on the performance of InGap / GaAs dual junction solar cells with a hetero tunnel Al0. 7Ga0. 3As-In0. 49Ga0. 51P junction. These analyzes indicate that, the addition of a BSF layer to the bottom cell the increase in the thickness of the BSF top cell would reduce the recombination and increase the short circuit current and the efficiency. The thickness and optimal concentration of the BSF layer adds the highest cell efficiency to 56. 53%. In the next step, to obtain a higher open circuit voltage, we examined the high band gap semiconductors from the ш ѵ group and we selected the In 0. 5 (Al 0. 7Ga 0. 3) 0. 5P semiconductor to form a hetro junction with GaAs in the bottom cell of a InGap / GaAs dual Junction solar cell. The results show photogeneration and spectral response, the InAlGap-GaAs hetero junction, transmits most of the electrons and holes produced in the top cell and low recombination in the bottom cell. For this structure, under (1sun) AM1. 5, the optimal values of Voc= 2. 44 V, JSC = 28. 5 mA/cm2, FF =87. 25 % and η = 60. 89 % and finally the cell provided with other models compared.

In this paper we have presented a new design of fault tolerant comparator with a fault free hot spare. The aim of this design is to achieve a low overhead of time and area in fault tolerant comparators. We have used hot standby technique to normal operation of the system without interrupting and dynamic recovery method in fault detection and correction. The circuit is divided to smaller modules for ease of testing and one hot spare is used for reconfiguration. Complexity, time and area overhead of designed fault tolerant comparator are more effective in compared recent methods.

A new structure is presented for digital delta-sigma modulator (DDSM). Novel architecture decreases hardware consumption, output quantization noise and spurs in Comparison to previous architectures. In order to reduce the delay, power consumption and increase maximum working frequency, the pipelining technique and the carry skip adder are used. Simulation proposed architecture shows that the quantization noise is declined as 15dB compared to 13-bit conventional third-order modulator. Furthermore, the results of digital implementation report significant reduction in the hardware consumption, the power consumption and increase 3 times in the maximum working frequency.

In this paper, α and β parameters and gating variables equations of Hodgkin-Huxley neuron cell have been studied. Gating variables show opening and closing rate of ion flow of calcium and potassium in neuron cell. Variable functions α and β , are exponential functions in terms of u potential that have been obtained by Hodgkin and Huxley experimentally to adjust the equations of neural cells. In this study, using FGMOS transistors to model these equations has been reduced cost, complexity, voltage and power. The transistors work in the sub threshold region, hence the proposed circuit consumes less power. Hspice simulation software with 0. 18 μ technology has been carried out and silicon area for the designed circuit of gating variables is 115μ m×60μ m.