حسین شاهمیرزایی

Due to the good propagation of sound waves in the ocean, sound energy is used to reveal the subsurface of the sea. In order to take advantage of the different characteristics of the environment in which sound is emitted, modeling and simulation of sound waves should be used. For this purpose, the environmental factors should be investigated and the way of sound rays propagation and the efficiency of sonar should be simulated in different conditions and in different times and places. This research is designed with the aim of investigating the effects of topographical shape on the propagation of ultrasound rays. In this research, firstly, the environmental data of the study area, which includes salinity, temperature and depth data in the northern Indian Ocean, has been extracted from international databases (such as HYCOM, GEBCO, WOA, etc.). Then, using the beam method, the propagation of ultrasonic waves in the presence of roughness of the seabed has been simulated. First, changes in hydrophysical parameters were analyzed using temperature and salinity data in the Indian Ocean and with the help of graphic models. Then, using Mackenzie's formula, the speed of sound in these sections was calculated and analyzed. With the help of the existing acoustic model, pressure changes were first checked and then this output was used to calculate the amount of return signal from a hypothetical underwater target. The results of different simulation scenarios of ultrasonic beam propagation show that when the source is placed under the thermocline layer, the acoustic beams are deflected downwards. As the frequency increases, the transmission loss increases and the intensity of the acoustic pressure decreases. Because the amount of absorption of sound waves increases with increasing frequency.

Technologies related to underwater acoustics are used for underwater communication, determining the location and discovering unknown targets under the sea, depth finding, seabed mapping, shipping, navigation, etc. Estimating the effectiveness and efficiency of underwater acoustic equipment requires underwater acoustic modeling. In this research, in order to implement different scenarios of acoustic wave propagation modeling in the waters of the Gulf of Oman, different methods of solving acoustic equations and, accordingly, several acoustic models have been used. In the following, the results of these scenarios are examined and compared. The results show that the acoustic pressure obtained from the acoustic models are related to water depth, independent issues with frequency (low and high) and dependent on range (short or long).

investigate the effect of the size of metal nanoparticles of gold, silver and copper on the nonlinear optical properties of glass. In this way, spherical nanoparticles with a volume fraction less than 0.1 (in order to ignore the interaction between them) are distributed in the glass, and using the T-matrix method, their effective dielectric coefficient is determined as a function of size ( radius) of nanoparticles and their volume fraction are obtained at different wavelengths. At the end, the relevant diagrams are drawn

In this article new micro-scale hydrophone sensor has been introduced, designed and modeled. Proposed structure is absolutely feasible by current MEMS technology. Mechanical structure consists of two micro-scale arms which together hang a plat. In length of each arms embedded Mosfet transistor placed which on its’ gate plate very thin layer of piezoelectric material, PZT-5A, has been placed. Incident acoustic wave cause mechanical stress which induce surface charge on the interface of piezoelectric and gate layer. These charges will modulate transistor’s channel resistance and finally with employing electronic circuit electric current variation transfers to voltage variation. Simulation results indicated sensitivity of -160 dB in frequencies well below first resonance. In this article new micro-scale hydrophone sensor has been introduced, designed and modeled. Proposed structure is absolutely feasible by current MEMS technology. Mechanical structure consists of two micro-scale arms which together hang a plat. In length of each arms embedded Mosfet transistor placed which on its’ gate plate very thin layer of piezoelectric material, PZT-5A, has been placed. Incident acoustic wave cause mechanical stress which induce surface charge on the interface of piezoelectric and gate layer. These charges will modulate transistor’s channel resistance and finally with employing electronic circuit electric current variation transfers to voltage variation. Simulation results indicated sensitivity of -160 dB in frequencies well below first resonance.

In this paper, a complete study has been done in the field of optical crystal logic gates. Also, several gates have been designed and simulated in the ultraviolet and infrared wavelengths (wavelength range of 1500 nm). In all cases, the boundary conditions of the complete absorber are considered. First, the method of constructing a waveguide is presented, which is used to construct a divider. Then, with the help of this waveguide, an amplifier loop is designed. In this simulation, an attempt has been made to reduce the gate operator time. For this purpose, we have used dividers as a combination of wave generators in the center of the gate. These gates respond in a very short time, about 0.3 femtoseconds, to incoming light. In the telecommunication area, silicon has been used to build gates. Also, in the center of the gate, the Mach Zander interferometer is used instead of the power combiner, which increases the response time; In this range, the dispersion of silicon material is considered. Another advantage of these gates is the input and output on one side, which can be used in integrated circuits. Powerful RSOFT software has been used to simulate the gate and to observe and analyze the results. Also, the band gap calculations of the PWE flat wave expansion method have been performed with the same software, and in the gate output wavelength calculations, the time domain finite difference method of FDTD has been used.

In this paper, a new hydrophone sensor in low frequency is designed and simulated. The transducer mechanism is based on variation of gate source capacitor in MOSFET transistor, while the transistor gate is suspended using two beams. In response to incoming acoustic wave, gate goes under deformation and causes variation of gate-source capacitor. As a result, acoustic wave alters the drain source current of the MOSFET transistor. In contrast to previous studies, instead of using uniform rectangular gate, the comb-drive gate is used so as to increase the gate-source capacitor. First, structures and parameters such as pressure, stress and thickness of the gate are carried out. Finally, for different materials the sensitivity is calculated and compared with previous studies. By employing the finite-element-method simulation software, sensitivity and bandwidth are calculated. Simulation results indicate high sensitivity around  in low frequencies. The proposed hydrophone shows flat frequency response in rang of 10-11400 Hz.

In this paper a new hydrophone sensor in low frequency has been designed and simulated. Transducer mechanism is based on variation of gate source capacitor in MOSFET transistor. Gate of transistor is suspended using two beams. In response to incoming acoustic wave, gate will go under deformation and cause variation of gate-source capacitor. As a result, acoustic wave will alter drain source current of MOSFET transistor. In contrast to privies studies, instead of using uniform rectangular gate, comb-drive gate is proposed so as to increase the gate-source capacitor. At beginning, structure and parameters such as pressure, stress and thickness of gate carried out. Finally, for different material the sensitivity is calculated and compared with previous studies. By employing finite-element-method simulation software sensitivity and bandwidth has been calculated. Simulation results indicate high sensitivity around -165dB (ref: 1V/1µPa) in low frequencies. Proposed hydrophone shows flat frequency response in rang of 10-11400 Hz.

In this paper, the contribution of Sr and Hf atoms in piezoelectric properties of tetragonal SrHfO3 with P4mm space group, were investigated by using first principle calculations based on density functional perturbation theory. Lattice constants, Born effective charges, piezoelectric constant and Sr and Hf contributions in total polarization and piezoelectric coefficient were calculated. Our results show that tetragonal SrHfO3 has piezoelectric property and its polarization and piezoelectricity mainly come from Hf atoms. The effect of lattice constant changes on polarization and piezoelectric constant were also studied. It was found that polarization and piezoelectric constant enhance by increasing lattice parameter and at c=4.5 Å, Sr atom contributes 50% of the total piezoelectric constant. This behavior assigns to significant covalent bonding between Sr and surrounding O atoms.

In this paper sound generation by laser pulse irradiated on a solid block is investigated. After an introduction to known mechanisms and main equation of laser acoustics, the laser pulse profile of NdYAG laser by straight radiation on a photo-resistor was recorded and the profile was substituted as an optoacoustic source in related equation of sound evolution. Finally the solution of numerically solved equation and measured generated sound were compared. Results show that there exists direct relationship between generated sound pulse width and laser pulse width. Furthermore there exists reverse relationship between generated sound pulse width and solid block thickness. In addition, results of simulation and experimental data measured by laser microphone with photo-resistor detector are compared by obtained sound spectrum from Spectrogram which confirm previous theoretical and experimental data. Finally general rule of the similarity of sound pulse profile and sound generator laser pulse profile are observed in this experiment.

Porous materials have good acoustic damping characteristics over a wide frequency range. As for sound waves, many small-scale pores in the coating materials can convert underwater-coating to rough surfaces. The main property of porous absorbents is their resistance against incident sound wave that leads to damping effect. From a physical point of view, damping occurs due to friction between fluid molecules inside the cavity and absorbent structure. In this study, the acoustic properties of porous absorbents with different porosity levels have been evaluated using different mathematical models. These models use one or more parameters of materials for calculating acoustic characteristics. In all of these models, materials are considered as equivalent fluid and reactionary characteristics have not been into account.

In the present article a novel structure is proposed to design and fabricate a high sensitivity wide bandwidth hydrophone. A MOSFET transistor with suspended gate has been used. Directed incident acoustic waves will cause deflection on suspended gate, which will turn into changes in gate-source capacitance and as a result leads to drain-source current variation. Here, acoustic waves will be detected by analysis of drain-source current obtained from changes in distance of gate and channel. In order to calculate sensitivity of proposed hydrophone, first by using finite element method displacement of gate as a response to acoustic wave is determined, then the current variation is determined in another simulation. Results indicate that sensitivity of -170db in low frequency which are in competition to other traditional works improved considerably. One noticeable point regarding this work is that higher sensitivity did not come at the cost of scarification of bandwidth, which was the case in many other works. Usable frequency of proposed hydrophone is from very low frequency up to 13.5 kHz and in contrast to piezoelectric based hydrophone there is no need for charge amplifier in vicinity of hydrophone. In addition, the dimensions of the proposed structure are smaller than conventional structures.

Detecting by the means of the marine magnetic anomaly maps is one of the detection and passive controlling methods for the surface and subsurface equipments including the submarines. Considering the point that nowadays, that submarines are made very silent in an acoustic view, detection and recognition of them by using acoustic detector in the sea has become hard and almost impossible. Thus, using magnetic anomaly methods seems to be necessary. By using this method, the fluctuation in the earth's magnetic field due to a ferromagnetic object is detected and by the help of computer processing, the magnetic map of the area is prepared. In this study, by processing and analyzing magnetometric data, a magnetic anomaly map was created in the region of the Persian Gulf near the Genaveh coast, after necessary corrections. Magnetic anomalies were first used to highlight superficial anomaly using the first-order derivative filter. The maps are further processed using Euler de-convolution method to determine the depth of anomalies. Both methods show surface abnormalities with low depth in the north and south in the lower and middle regions of the study area.

The basic principles of calculations in the framework of density functional theory and density functional perturbation theory were used to investigate the elastic and piezoelectric properties of hypothetical SrHfO3 compound in tetragonal structure with P4mm space group. Polarization and Born effective charges tensor were calculated to investigate the nature of ferro-electricity of this system in an atomic scale. Our results show that Born effective charges of both Hf and O atoms are much larger than their anticipated nominal charges which show a strong bonding between Hf and O atoms. Formation energy calculation revealed that the compound will be stable, if it is synthesized and would not decompose to its ingredients. Non-vanishing and significant calculated piezoelectric constants imply system piezoelectricity. The effect of uniaxial stress along the c-axis on polarization, Born effective charges and piezoelectric stress and strain coefficients were also investigated. We found that the polarization increases as the uniaxial stress goes from negative to positive. These changes suggest that the uniaxial tensile stress could raise the ferro-electricity, while the uniaxial compressive stress would cancel it. We also found that the piezoelectricity of this system could be improved by applying stress. These results could be significant in the field of lead free piezoelectric materials.

The main goal of this paper is to calculate the reflectivity index and scattering index of incident acoustic plate waves from a sound absorbent tile. The simulations are performed using Comsol software and obtained results are plotted as a function of the frequency of incident wave. It should be noted that the acoustic absorbent tile consists of an array of close-packed cones which are placed on a simple plate. Additionally, the acoustic absorbent tile is made of metal loaded butyl rubber. The butyl rubber is loaded with aluminum and lead. By comparing obtained results with analytical and experimental reported results one can deduce that performed simulations with Comsol software are as reliable as expected. Moreover, it is shown that the absolute values of the scattering index and reflectivity index of tile which is made of aluminum loaded butyl rubber are larger and hence this tile should be applied in experimental fabrication.

There is a kind of composite materials made up of noble metal nanoparticles (such as gold، silver، copper) and a dielectric material (such as silica) with unique properties. In this paper، using Strong Permittivity Fluctuation Theory (SPFT) method، the coefficient of effective permittivity and the effective susceptibility coefficient are calculated for combining glass with metal nanoparticles، assuming that the nanoparticles are spherical. Coefficient of effective permittivity and the effective susceptibility index are estimated for the sample of homogeneous composite materials. And the results of this study are compared with experimental results and other models. It is observed that the data obtained for the zero-order estimate do not match the experimental results. By appropriate correlation length for the second- and third-order، specially for the second-order estimate of SPFT method، conformity between results can be established. Therefore، it can be concluded that SPFT method is betler than other models for calculating and improving the properties of the non-linear model.