نشریه الکترومغناطیس کاربردی
سال یازدهم شماره 2 (پیاپی 27، پاییز و زمستان 1402)

An optical spectrometer is a tool used to separate an electromagnetic radiation into its wavelength components and has a variety of applications in science and industry. In this paper, an optical spectrometer in the UV-A spectral region, which has not been investigated before, is designed. For this design, a holographic diffraction grating with a groove density of 3600 lines/mm and a number of lenses with different materials suitable for the ultraviolet region are used. To achieve high contrast and resolution, the beams of each wavelength scattered by the grating must be carefully focused on the detector screen. For this purpose, eight lenses made of silica and fused silica, which have a high transfer coefficient in the ultraviolet region, were used. Then, after the initial calculations and determining the estimated radius of curvature of the surfaces, in order to achieve the desired results, the lenses were placed at a distance of 1 mm from each other and by using appropriate operands defined in the merit function editor of Zemax software, the thickness of the surfaces and the radius of curvature of the lenses was optimized in several stages . After optimization, at the central wavelength, all points of the spot diagram were located inside the Airy disk and the resolution of approximately 30 pm was obtained, which is a very good result compared to the previous works of researchers in other areas of the electromagnetic spectrum.

Today, a wide variety of methods have been proposed to measure temperature and strain at the same time with the help of FBG sensors, all of which can be divided into two general categories. Methods that use two or more uniform or non-uniform FBGs for the measurement, and methods that use only one non-uniform FBG for this purpose. In this paper, unlike all the methods proposed so far, for the measurement of temperature and strain at the same time, the use of only one uniform FBG is proposed, which will occupy the least amount of spectral range of the broadband source. In this method, a mechanical tool called a cantilever is used to convert uniform strain to non-uniform strain during FBG. With this method, the peak power of reflection spectrum of the Bragg grating will be sensitive to changes in the applied strain to the grating while not reacting to temperature changes. As a result, the strain will be determined by changes in reflection peak power and temperature by changes in reflection Bragg wavelength. According to the simulation results, the sensitivity of this sensor to the temperature is 14.21 / pm/℃ and to the strain was 0.68136 pm/με.

This paper presents a Butler matrix in Ridge Gap Waveguide (RGW)technology. For this purpose, we first design the riblet coupler in the millimeter wave band. The riblet coupler is designed with a coupling coefficient of 3 dB and a phase difference of 90 degrees at the outputs. Also, the return loss of all ports of this coupler in the frequency range of 53-60 GHz is better than 10 dB. Then we design a crossover and 45-degree phase shifter in the mentioned frequency range. By integrating four ribelt couplers, two phase shifters and a crossover, the Butler matrix structure is formed. The designed Butler matrix has 4 input and 4 output ports. The simulasion results of the designed matrix obtained by HFSS software show that for excitation of each input port in the frequency range of 53-60 GHz, the power is divided approximately equal between 4 output ports with a ratio of about -6 dB. But there is a linear phase difference between the matrix output ports, which also the phase of output ports change as the excitation port changes to other port. The simulation results are valid due to the desired amplitude and phase distribution at the matrix outputs. Also, comparing the results with those obtained by CST software confirms the proper performance of the designed matrix..

In this article, a novel geometry for the multiple input multiple output (MIMO) array slot antenna with directive radiation patterns for WLAN (IEEE 802.11ac) & ITU applications is proposed. By using a two sub-element topology, a combined novel element is obtained. The proposed MIMO array slot antenna illustrates beneficences in terms of small size with physical dimensions of 8.5λh×8.5λh and relatively high front-to-back ratio without using reflectors and directors with approximately 20dB F/B. Therefore, a compact MIMO antenna array with high isolation among those the combined elements are obtained. The practicality of the proposed MIMO is validated by Simulated and measured results.

In this paper, the design, fabrication and testing of an integrated three-axis magnetic torque on the cube satellite driver range in accordance with the requirements of ISIS's external sample. Based on the specified mission requirements, magnetic torque generators generate a magnetic field around the satellite that interacts with the Earth's magnetic field and produces a torque on the satellite, so that the satellite's angular momentum can be changed and controlled. The use of these actuators in the status control system has advantages such as no need for fuel (such as thrusters), low power consumption, lack of moving parts and is especially popular in cubic satellites. The focus of the design space is on maximizing the magnetic dipole moment to find the response vector, including the number of turns, the length and radius of the core, and the number of turns and dimensions of the non-magnetic nucleus for the air core. The design of the windings based on the optimization method of sequential quadratic SQP programming under the constraints of inequality requirements such as mass, power, etc. has been done with the aim of achieving a magnetic dipole moment of 0.2 Am2. This three-axis integrated torques with their integrated drivers were calibrated by Honeywell's HMR2300 magnetometer sensor after measuring the generated magnetic field using a magnetic dipole moment relationship. The results show that the specifications of the designed sample are met.

The main purpose of this article is to use metasurfaces to make objects invisible. The process is that, after examining how to analyze the electromagnetic plan metasurface of the plate, a method for the analysis of cylindrical metasurfaces is presented. Then, inspired by the modeling of plan metasurfaces, a method based on the physical characterization of cylindrical metasurfaces in order to model and extract their tensor parameters is expressed. The methods presented in this paper for analyzing, modeling and extracting the parameters of cylindrical metasurfaces can be implemented for any desired type of linear metasurfaces in a wide frequency range consisting of radio and microwave waves to light waves. In the next step, the proposed formulation is used to reduce the scattering of electromagnetic waves from objects or so-called invisibility. The proposed method for invisibility makes it possible to provide different configurations of metasurfaces to achieve any type of invisibility according to the limitations of practical implementation. In addition, the formulation is effective in providing a physical understanding and description of invisibility. To test the results, the formulation of this paper was applied to a designed metasurface sample. Finally, with the help of full-wave simulations, the metasurface tensor parameters are extracted and the desired invisibility is realized.

In this paper, the simulation and analysis of the all-optical NOT logic gate using photonic crystal semiconductor optical amplifier (PC-SOA) based on Mach-Zehnder interferometer and nonlinear cross-phase modulation (XPM) mechanism is performed. The input light pulse sequence used in the design is RZ (Return to Zero). With 4fJ input pulse train energy and 1mA injection current, the most suitable mode for NOT logic gate with 80Gbps bit rate is obtained. The finite difference method (FDM) is used to solve the rate and propagation equations. Also, in this paper for proper performance and better efficiency of the all-optical NOT logic gate, pattern effect(PE) parameters, conversion efficiency (CE), extinction ratio (ER), contrast ratio(CR), quality factor(QF), and gain recovery are simultaneously examined. Another important parameter that plays a vital role in improving PC-SOA as well as the bit rate value is the carrier lifetime. In previous publications, this parameter has been considered as a constant value in PC-SOA equations. Therefore, it can increase the error of the results to some extent. But in this paper, the structure of each PC-SOA and the materials used in it are based on an experimental and valid model. As a result, the carrier lifetime calculations that depend on the carrier density changes are accurately calculated. Also, according to the obtained results, PC-SOA shows a better logical performance than conventional SOA, and due to its much shorter length than SOA, it can be a very suitable candidate for integrated optical circuits.

In this article, while analytically reviewing the Landau formalism for electrodynamic equations in the presence of a gravitational field, we show that the three-dimensional electromagnetic constitutive relations in this formalism can be expressed by two equivalent methods. Then we obtain the constitutive relations for the Galilean rotating observer with both methods and show its compatibility with the previous results. We also present the electromagnetic constitutive relations for an eccentric rotating observer. To solve some ambiguities, especially in the articles related to this topic in the field of electrical engineering, different representations of the three-dimensional form of constitutive relations in the Galilean rotating observer’s frame are expressed in full detail. Also, the connection between different representations of three-dimensional constitutive relations will be explained. In the end, considering the practical and experimental importance of the eccentric rotating observer, we will obtain the electromagnetic constitutive relations for this particular observer.

Light intensity filters are a new class of optical filters that are needed with the increasing use of lasers in various fields, including medicine and industry. The mechanism of these filters is such that if the light intensity increases beyond a permissible threshold, it is activated and prevents the passage of intense light, which cause casualties in devices and humans. In this report, a new type of these filters is designed based on the heat generated by plasmonic absorption of metal nanoparticles and the use of this heat to disrupt the order of liquid crystal molecules. In addition, the absorption spectra of different metal nanoparticles have been simulated to achieve the appropriate material at each wavelength. Also, the increase in temperature induced in the substrate due to the absorption of nanoparticles is simulated and based on the existing equations, it is ensured that this temperature increase can lead to the rotation of liquid crystal molecules and thus filter the intense incoming light. .

In this article the theoretical principles and design and simulation of high power phase shifter based on 90 degree hybrid coupler are given. One of the special features of this type of shifter is high power handling, linearity of phase changes with respect to frequency, provision of a full range of 360 degrees of phase change,, tow structure width, return loss greater than 25 dB and phase deviation less than 0.5 degrees in the bandwidth 400 MHz in 10.2GHz centeral frequency, which can be used in applications of high power antenna arrays with beam scanning capability. The basis for changing the phase of the designed phase shifter is based on changing the length of the electrical path of the signal, through the movement of pistons embedded inside the structure.Two types of 90 degree hybrid coupler structures, E and H plane, have been investigated and the results of the two structures have been compared. It is shown that the H plane coupler has a better efficiency than the E type coupler

Mechanical errors are one of the most common errors related to electric machines. Among them, eccentricities have the major share of mechanical errors. Resolvers, as an electric machine, can be affected by eccentricities or the electric motor connected to it. The existence of eccentricities in the resolvers, which can be caused by the rotation of the machine at critical speed, incorrect installation of the rotor and stator, core turning defects, and wear and corrosion of the bearings, leads to an increase in the position estimation error. The position estimation error will eventually increase the torque fluctuations, reduce the efficiency, lose the ideal control of the electric motor, and disrupt the automation process. Therefore, providing indicators to detect the occurrence of eccentricity in the resolver can be a preventive solution. Based on this, in this article, focusing on the inclined eccentricity, the equations describing air gap reluctance, magnetic flux density, and mutual inductance will be presented using the modified winding function method. By using the relationships describing the output voltage, the harmonic spectrum of the output voltage in the static and dynamic eccentricities will be compared with the healthy mode, and an index will be provided to identify static and dynamic mechanical error.

In this paper, design and fabrication of Fabry-Perot optical fiber sensors with a coating of polyurethane, Soft PVC and Rigid PVC with the same thickness of 300 μm and a cavity length of 0.1 mm was introduced for the pressure gas and the effect of these three polymeric materials on the sensitivity of gas pressure sensors was investigated. The above sensors have been tested at a constant laboratory temperature and have been compared with each other. To perform gas pressure tests, two gases of oxygen and nitrogen in the pressure range of 10 to 50mbar have been used. The sensitivity of the sensor with the coated polyurethane for oxygen and nitrogen gas is 0.438 and 0.392 nm/bar, respectively, the sensor coated with soft PVC has the sensitivity of 0.311 and 0.224 nm/bar, for oxygen and nitrogen gas respectively, and the sensors with rigid PVC coated for oxygen and nitrogen gas has the sensitivities of 0.298 and 0.186 nm/mm, respectively. The results show that the sensor made with polyurethane coating is more sensitive than the other sensors.