Calculation Of Frequency Characteristics Research Articles

Quadrupole resonator mode versus dipole one in photonic crystal ferrite circulators

We propose a photonic crystal circulator based on quadrupole resonance of a magnetized ferrite cylinder. This device consists of a T-junction composed by three waveguides in a two-dimensional photonic crystal with square lattice. The ferrite cylinder is placed in the center of the T-junction. The scattering matrix, analytical model and the numerically calculated frequency characteristics of the circulator for the central frequency 94.5 GHz are presented. This device is compared with the previously suggested T-type circulator based on the dipole resonance mode. In particular, we show that the use of the quadrupole resonance permits to reduce the necessary DC magnetic field in comparison with dipole mode case by six times and this is important at THz frequencies where the necessary field is excessively high. Besides, quadrupole resonance requires the higher diameter of the ferrite resonator. The ferrite cylinders are produced by a special technology, and higher dimensions lead to a better reproducibility of such elements. However, these advantages are achieved at the expense of higher insertion losses and lower bandwidth of the circulator.

Analysis of dynamic characteristics of the inverter operating on a complex load

A simulation model of a converter with soft switching of transistors has been created. New calculation methods and means of measuring the equivalent frequency characteristics of converting devices with negative feedback to the problems of stability analysis have been applied. A comparative analysis of the calculated frequency characteristics of the converter in the normal operation mode with the characteristics of its linear model is presented. The features of calculating the equivalent frequency characteristics of the loop amplification of key devices are considered. It is noted that it is the equivalent frequency characteristics of the loop amplification that describe the relationship of frequency properties with the dynamics of voltage converters with pulse-width modulation and make it possible to reliably determine the real stability margins, predict the generation modes and open up the possibility of obtaining maximum negative feedback in a given frequency band of key devices. The non-minimal phase properties of the converter significantly complicate the achievement of high-quality stabilization of the output current (stabilization coefficient) of pulse stabilizers using only the deflection control principle. A successful solution to the problem is provided by the use of the principle of combined control. Compensation of the disturbance effect (changes in the supply voltage) gives a much better result than countering it through the feedback loop. It is quite realistic to exclude the influence of the input voltage u ( t ) on the output current i 2 in a static mode ( u =const) and in the absence of a negative feedback loop, which provides for u =const in a steady state, and to provide better dynamic properties of the converter. The influence of the nonlinear properties of pulse width modulation on stability is manifested in the considered characteristics in the form of an additional phase shift and resonant bursts in the vicinity of the clock frequency subharmonics. Additional feedbacks introduced into the control loop make it possible to solve synthesis problems using the most simple technical means

On the Influence of the Electron Velocity Spread on the Passband Properties of Gyroklystrons

We present the results of studying the passband properties of gyroklystrons theoretically and experimentally and analyze the main causes of limitations in the bandwidth of the frequencies that they amplify. It is shown that in the range of low beam currents, where the electron velocity spread is rather low, the amplification bandwidth of a two-cavity gyroklystron is close to the bandwidth of the output cavity loaded with an electron beam. In the range of high currents, the amplification bandwidth depends only weakly on the parameters of the output cavity and is determined mainly by the spread in the times of electron passing through the drift space, which is caused by the difference in their translational velocities. Good qualitative agreement of the calculated and experimental dependences indicates that the proposed method can be applied to the calculation and interpretation of frequency characteristics of gyroklystrons. The possibility to expand the passband of operating frequencies in the high-current region by decreasing the influence of the electron velocity spread on beam bunching in the three-cavity gyroklystron operating in the maximum acceleration regime is demonstrated experimentally. Theoretically, the developed method for calculation of frequency characteristics can be expanded to the case of a three-cavity gyroamplifier with slight modifications.

Monoharmonic method for calculating the frequency characteristics of the dynamic stiffness of nonlinear dynamic objects

The paper comprises results of algorithm design for monoharmonic method for calculating the frequency characteristics of the dynamic stiffness of nonlinear dynamic objects with a specified computational error and for a minimum time. The proposed alternative method relates to auto-integration methods and is based on numerical integration of the nonlinear differential equation system for a mathematical model of a dynamic object with monoharmonic input actions at fixed frequencies, and analysis of responses to these actions by Fourier method. The integration process at each fixed frequency continues until the average values of Fourier coefficients of the investigated harmonic of dynamic stiffness of a nonlinear dynamic object on the input monoharmonic force or moment action for a passed number of periods of the input signal become sensibly constant. The efficiency of the developed method and algorithm is studied using the example of calculation of frequency characteristics of the dynamic stiffness of a hydraulic power cylinder with closed hydraulic lines. The obtained frequency characteristics of the dynamic stiffness can be used to evaluate the damping properties of nonlinear dynamic objects. Key words: frequency characteristics of dynamic stiffness; calculation method; nonlinear dynamic objects.

Method to calculate frequency characteristics of reconstruction filter kernel in X-ray computed tomography.

A computed tomography (CT) image is generally reconstructed by a filtered back projection (FBP) algorithm. In an FBP algorithm, the image quality primarily depends on a reconstruction filter kernel. Although the details of the filter kernel are not disclosed to users, the frequency response of the filter kernel can theoretically be calculated using the relational formula of the filter kernel and the modulation transfer function (MTF) of the reconstruction algorithm (MTFA). In this study, we proposed a method to determine the frequency response of a filter kernel and verify its validity. Two clinical CT scanners were used to derive the filter kernel. The MTF was obtained and subsequently separated to the MTF of the scanner system and MTFA. Using the relational formula of the filter kernel and MTFA, we calculated the frequency response of the filter kernel. To verify the calculated result, we measured the noise power spectrum (NPS). Additionally, the filter kernel was calculated using the relational formula of the filter kernel and NPS. In both CT scanners, the filter kernels calculated by the two methods showed good agreement, and we confirmed the validity of the results and the effectiveness of the proposed method. Furthermore, the inherent image quality performance of the CT scanner could be clarified by the reconstruction filter kernel.

Narrowing of the Emission Spectrum of a Gyrotron with External Reflections

The stabilizing influence of external reflections on gyrotron operation has been demonstrated in direct particle-in-cell modeling. A model with a temporal realization duration providing an opportunity to calculate frequency characteristics with a relative accuracy no worse than 2 × 10–6 has been used for the first time. An almost twofold reduction in the spectrum width of a 28-GHz gyrotron has been observed experimentally after the introduction of reflections of the output signal.

Уменьшение ширины спектра излучения гиротрона при использовании внешних отражений

AbstractThe stabilizing influence of external reflections on gyrotron operation has been demonstrated in direct particle-in-cell modeling. A model with a temporal realization duration providing an opportunity to calculate frequency characteristics with a relative accuracy no worse than 2 × 10^–6 has been used for the first time. An almost twofold reduction in the spectrum width of a 28-GHz gyrotron has been observed experimentally after the introduction of reflections of the output signal.

A method for the design of ultrasonic devices for scanning acoustic microscopy using impulsive signals

Scanning acoustic microscopy (SAM) using impulsive signals is useful for characterization of biological tissues and cells. The operating center frequency of an ultrasonic device strongly depends on the performance characteristics of the device if the measurement is conducted by using impulsive signals. In this paper, a method for the design of ultrasonic devices for SAM using impulsive signals was developed. A new plane-wave model was introduced to calculate frequency characteristics of loss of ultrasonic devices by taking into account the conversion loss at the ultrasonic transducer, the transmission loss at the acoustic anti-reflection coating, and the propagation loss in the couplant. Ultrasonic devices were fabricated with a ZnO ultrasonic transducer using two acoustic lenses with aperture radii of 1.0 mm and 0.5 mm, respectively. The frequencies at which measured losses became minima corresponded to the calculation results by the plane-wave model. This numerical calculation method is useful for designing ultrasonic devices for acoustic microscopy using impulsive signals.

On the resonance and antiresonance frequencies of a plate piezoceramic transducer

Problems related to applying the concepts of resonance and antiresonance frequencies of a plate piezotransducer have been studied. The case of a plate unilaterally loaded on an aqueous medium has been researched. It has been shown that the concept of the antiresonance frequency determined with the use of an elastic modulus c33 D can be applied only conditionally, still allowing one to calculate frequency characteristics for different values of a squared electromechanical-coupling coefficient. Notwithstanding the conditional nature of the term “antiresonance”, its practical use does not cause any difficulties.

Influence of resonance and nonlinear properties of soils on seismic hazard of construction areas

The article discusses the need to take into account the resonance and nonlinear phenomena in soils for the seismic micro zoning of building and operating sites. Resonance and nonlinear phenomena are closely related to each other and depend on the structure of the medium under the site, and the intensity of seismic effects. Examples of what these phenomena are a common cause of destruction and damage of earthquake-resistant structures during earthquakes are presented. The methods that allow at a modern level to count the frequency characteristics of soil models taking into account it’s non-linear and resonance properties are reviewed. The results of the comparative analysis of theoretical calculations of the frequency characteristics of soil layered models with different thickness and different seismic properties are supplied. It has been shown that appearance of the nonlinear properties of the soil depends on its physical properties and stress condition. A comparison of the calculated frequency characteristics of ground systems taking into account the rheological properties for a variety of construction sites in the Odessa area in Kiev town are provided. The influence of various factors on the spectral contents and the value of oscillation of the upper section of the geological environment at the construction site are analyzed. The conditions of occurrence in it of dangerous resonance phenomena are formulated.

Realization Method of Calculating the Logarithmic Decrement in Turning and Boring CNC Machines Technological Systems

The paper considers the processing technique for amplitude-frequency response of turning and boring CNC machine units. The technique developed by V.A. Kudinov is proposed as the basic one. The essence of the technique is that the use of the experimental or calculated frequency characteristics makes it possible to determine the values of the constants characterizing natural frequency of vibration, decrement factor, unit stiffness, or weight of the technological system elements. The logarithmic decrement is calculated from the resonance peak breadth by applying the formula of the vibration theory for the system with one-degree-of-freedom vibrations. The force of impulse action on the system units is determined by experiment based on measurements by accelerometer built in an impact hammer. The theoretical amplitude-response curve is plotted for the vibration displacement of the units and the logarithmic decrement is calculated in MathCAD.

Two-dimensional photonic-crystal-based double switch-divider

We propose and investigate a new multifunctional component, consisting of a T-junction of three waveguides in 2D photonic crystal with a square lattice. One waveguide is the input port, while the other two serve as output ports. This component can fulfil three functions: First, it can switch OFF the two output ports; second, our component can be used as a 3 dB divider of the input power; and third, it can switch ON any one of the two output ports. Changing the regime is achieved by a DC magnetic field that magnetizes a cylindrical ferrite resonator placed in the T-junction. We present an analysis of the scattering matrices of the component and calculated frequency characteristics in the low terahertz region. In the frequency band of about 1 GHz with a central frequency of f=98.46 GHz, the device has the following parameters: isolation of the output ports from the input port in the first regime is better than -30 dB, division of the input signal is about (-3.8±1.0) dB in the second regime, and isolation in the regime switch ON, where any one of the two output ports is higher than -15 dB and the insertion loss is lower than -2.0 dB.

Frequency Characteristics of the Input Impedance of Meander Slow-wave System with Additional Shields

A method for determination of input impedance of meander slow-wave system with additional shields is presented. It is based on a technique used for a calculation of frequency characteristics of helical slow-wave systems. The input impedance was determined at two ports: on the edge and in the centre of a system. S11 parameter is known as the input reflection coefficient, so system‘s input impedance in the lower frequencies can be determined by changing the signal source and load resistances until minimum value of S11 parameter is obtained. Using proposed method frequency characteristics of input impedance and S11 parameter of a meander slow-wave system with additional shields is analysed in Sonnet software. DOI: http://dx.doi.org/10.5755/j01.eee.20.3.6678

Calculation of frequency characteristics of electronic circuits via the method of limiting states

An effective method for the determination of analytical relations for frequency characteristics of linear circuits is suggested. In contrast with the known methods of symbol calculations of the functions of an electric circuit targeted to the improvement of final formulas, the calculation is carried out with the use of simplified schemes corresponding to limiting states of the linear circuit under study.

A complete small-signal equivalent circuit model of cooled butterfly-type 2.5 Gbps DFB laser modules and its application to improve high frequency characteristics

A small-signal equivalent circuit model of 2.5 Gbps DFB laser modules with butterfly-type dual-in-line packages has been proposed and verified using extracted parameters. Parameters related to the equivalent circuit have been extracted from measured S parameters using the modified two-port black box model. This model includes small-signal equivalent circuits of components used for 2.5 Gbps DFB laser modules such as DFB laser, coplanar waveguides, matching resistor, bonding wires, and thermoelectric cooler (TEC). From this equivalent circuit modeling, we show that calculated frequency characteristics of DFB lasers on submount and complete DFB laser modules are similar to their measured frequency characteristics, respectively. Based on this equivalent circuit model, we propose and demonstrate a method that can improve frequency characteristics of 2.5 Gbps DFB laser modules through both experiments and simulations.

An Analysis of Jumping and Dropping Phenomena of Piezoelectric Transducers using the Electrical Equivalent Circuit Constants at High Vibration Amplitude Levels

This paper presents an analysis of the jumping and dropping phenomena of piezoelectric transducers, using the electrical equivalent circuit constants at high vibration amplitude levels of resonance based on the electrical transient response technique. The calculated frequency characteristics well simulated the measured ones driven by a constant voltage source. It is clarified from the results that the jumping and dropping phenomena are caused mainly by the nonlinear behavior of the elastic constant at high vibration amplitude levels. The effects of the loss, the voltage and the driving method are also discussed.

The Response of a Centrifugal Pump to Fluctuating Rotational Speed

A theoretical and experimental study has been made on the dynamic characteristics of a centrifugal pump subject to sinusoidal changes in rotational speed. Time-dependent rotational speed, flow-rate, and total pressure rise are measured for a variety of amplitude and frequency of the fluctuating rotational speed. Measured flow-rate as well as total pressure rise is compared with the quasi-steady ones. Unsteady flow analysis is made for a two-dimensional circular cascade by use of the singularity method. The calculated frequency characteristics are compared with the corresponding experimental ones. The deviation of unsteady characteristics from quasi-steady ones is evident, and the numerical results agree qualitatively with the measured ones. It was found that with the increased frequency of rotational speed fluctuations the dynamic characteristics deviate remarkably from quasi-steady ones. Moreover, a criterion for the assumption of quasi-steady change is presented.

Reference ac resistance standards with calculated frequency characteristics

Reference ac resistance standards with calculated frequency characteristics

Determination of frequency characteristics of the pressure-detecting system

Evaluation of the pressure-detecting system should be given in terms of both static and dynamic accuracy. Stablility, lineality, sensitivity, and error of the system were discussed in relation to static accuracy. Frequency characteristics is most important in dynamic accuracy. Because of technical difficulty in determining frequency characteristics by steady-state movements in the high frequency area, a substitute method was developed theoretically. Modification of the method applied to the calculation of frequency response and phase lag of the system in damped oscillation was adequate to calculate frequency characteristics. The method applicable both in critically damped and slightly over-damped system was also mentioned.

Prediction of Traveling Wave Magnetron Frequency Characteristics: Frequency Pushing and Voltage Tuning

An approximate method has been developed for determining the shape and density of the spokes of electronic space charge when large RF potentials exist in the magnetron. With the estimation of space-charge configuration which this method makes possible, induced current theory and knowledge of the magnetron electrode geometry and external circuit can be applied to the calculation of frequency characteristics. These characteristics relate frequency to operating anode potential and anode current and are defined as frequency pushing or voltage tuning characteristics. Relatively simple equations for these characteristics are presented. Calculated characteristics for typical values of the variables of magnetron design are presented. The correspondence of the results of the theory with experimental data is discussed very briefly.