Calculation Of Transfer Function Research Articles

Measuring vibration-induced variations in pressures between the human body and a seat

When measuring total dynamic forces between the human body and seats during vibration, variations in force over the buttocks and the thighs have previously been ignored. In this study, sensors in a pressure mat were calibrated by applying static and dynamic pressures through foam and calculating transfer functions between the applied pressures and the outputs of the sensors. This provided static calibration of individual pressure sensors and dynamic calibration of groups of pressure sensors. Measurements of dynamic pressures were used to calculate the vertical forces over the ischial tuberosities, middle thighs, and front thighs and compare with similar measurements obtained by another method. Dynamic calibration of the pressure mat reduced errors in the total dynamic force to 10% at frequencies less than 5 Hz and less than 30% at frequencies between 5 and 15 Hz. Recommendations are offered for measuring dynamic pressures between the human body and seats in vibration environments.Relevance to industry: Dynamic pressure distributions at seat interfaces influence sitting comfort during whole-body vibration. Understanding of the dynamic performance of pressure sensors and recommendations on calibrating and using pressure sensors in vibration environments can assist seat design and other situations where dynamic pressure measurements are of interest.

Multilevel microvibration test for performance predictions of a space optical load platform.

This paper presents a framework for the multilevel microvibration analysis and test of a space optical load platform. The test framework is conducted on three levels, including instrument, subsystem, and system level. Disturbance source experimental investigations are performed to evaluate the vibration amplitude and study vibration mechanism. Transfer characteristics of space camera are validated by a subsystem test, which allows the calculation of transfer functions from various disturbance sources to optical performance outputs. In order to identify the influence of the source on the spacecraft performance, a system level microvibration measurement test has been performed on the ground. From the time domain analysis and spectrum analysis of multilevel microvibration tests, we concluded that the disturbance source has a significant effect on its installation position. After transmitted through mechanical links, the residual vibration reduces to a background noise level. In addition, the angular microvibration of the platform jitter is mainly concentrated in the rotation of y-axes. This work is applied to a real practical application involving the high resolution satellite camera system.

Calculation of undamped noise transfer functions

Mühendislik yapılarında gürültü iletimi yapısal yolla, hava yoluyla veya ikisinin birleşimi şeklinde gerçekleşmektedir. Gürültü iletiminin tanılanmasında deneysel metot kullanımı yaygındır. Deneysel çalışmalarda tercih edilen başlıca metot ise kaynak–iletim yolu–alıcı yaklaşımıdır. Gürültü transfer fonksiyonları bu metot ile ölçülmektedir. Yapısal yolla gürültü iletimi, bir binanın duvarındaki, bir köprünün tabliyesindeki veya bir aracın tabanındaki titreşimlerle oluşabilir. Verilen örneklerdeki yapısal titreşimlerin hiç birinin sönümlemeden azade olmadığı açıktır. Dolayısıyla, ölçülen gürültü transfer fonksiyonları sönümleme bilgisini de içermektedir. Bu çalışmada, gürültü transfer fonksiyonlarından sönümleme bilgisinin ayrıştırılması için analitik bir çözüm önerilmektedir. Sönümleme verisi ekseriyetle mevcut olmadığından, gürültünün modellenmesi ve azaltılmasına dönük bilgisayar benzetimi çalışmalarında sönümsüz hesaplamalı modeller kullanılmaktadır. Hesaplamalı ve deneysel modellerin ikisinin de sönümsüz olması, yüksek ilgileşim katsayılarına erişilmesine olanak sağlamaktadır.

Analysis of multistage amplifiers with hybrid cascode feedforward compensation using a modified model for load impedance

Hybrid cascode feedforward compensation (HCFC) is an effective technique to stabilize nano-scale three-stage amplifiers driving ultra-large load capacitors. It divides the compensation capacitance and shares it between two high-speed local feedback loops embedded within the amplifier core. In this article, a systematic approach to analyze the transfer function and to evaluate the pole expressions of nano-scale HCFC amplifiers is presented. For the first time, the equivalent output impedance is successfully modeled to approximate the complicated transfer function of the HCFC amplifier without the need for lengthy pencil-and-paper calculations. An HCFC amplifier is designed and simulated in 90-nm CMOS technology, to verify the effectiveness of the new analytic approach. The simulated transfer function of the amplifier is almost identical to a calculated transfer function derived based on the new model.

Effect of noise on MTF calculations using different phantoms.

In this work, the effect of noise on the precision in the modulation transfer function (MTF) calculation using different phantoms is investigated. Three different techniques are studied, based on three different phantoms: edge, bar, and star bar. For each technique, theoretical expressions for the standard deviation and the signal to noise ratio (SNR) of the MTF are derived. In addition, Monte Carlo simulations are carried out to study the accuracy and precision of all the three techniques. Using the analytic expressions for the MTF calculation, statistical fluctuations of noise in the phantom images are propagated to MTF values. Then, for each frequency the standard deviation and the SNR of the MTF are calculated. Monte Carlo simulations are carried out for each phantom image and for different noise level. Images are artificially generated following a procedure that simulates sampling, blurring, and noise present in a real phantom image and takes into account the attenuation of each phantom. Then, oversampling procedures are applied to these images to obtain presampled MTFs. In all three techniques the standard deviation of the MTF is proportional to that of the noise in the image. For the edge image, the standard deviation is proportional to the frequency f, whereas for the bar and star bar techniques it is proportional to the square root of f. Regarding the precision, theoretical expressions and simulations results agree that the bar technique shows the best precision for all the frequencies and all the noise levels analyzed in this study. In addition, simulation results show how, for large levels of noise, the edge technique gives rise to large bias errors at high and medium frequencies. Finally, the precision of the star bar technique is similar to that of the bar technique for isotropic systems, but worse for nonisotropic ones. The uncertainties in the MTF calculation with the edge technique are larger than with the bar technique, and the differences increase with the frequency. On the one hand, the stronger dependency on the frequency shown by the standard deviation of the MTF makes the precision gets worse faster in the edge technique. On the other hand, in the case of the edge and for high levels of noise, differentiation produces line spread functions (LSF) with a poor SNR, increasing erroneously the MTF and worsening accuracy.

Holographic Lenses in an Environment-Friendly Photopolymer.

In this paper, we theoretically and experimentally evaluated the quality of volume phase transmission lenses stored in an environmentally friendly photopolymer. Holographic lenses (HLs) were obtained using symmetrical and asymmetrical experimental setups with the same positive and negative focal length and pupil diameter. The image quality was evaluated from the calculation of the modulation transfer function (MTF) by capturing the point spread function (PSF) with a charge-coupled device (CCD). A maximum frequency of 14 L/mm, reaching an MTF value of 0.1, was obtained for a negative asymmetrically recorded HL, evaluated at 473 nm wavelength. A theoretical study of aberrations was carried out to qualitatively evaluate the experimental results obtained.

Calculation of Admittance Transfer Functions Using Manual Symbolic Suspendance Analysis

This paper introduces a new manual symbolic analysis for the calculation of admittance transfer functions. Suspendance terms are expressed in terms of circuit admittances and transadmittances. The admittance transfer function at each node of a circuit is equal to the ratio of the suspendance obtained when the node is open to the suspendance obtained when the node is shorted. To calculate the suspendance for each case, every passive circuit component is shorted one at a time and its admittance is multiplied by the suspendance of the remaining circuit. Admittances of previously shorted components are set to zero in succeeding calculations. The overall suspendance is calculated by summing all individual results obtained from each step. In comparison with all existing circuit analysis methods, suspendance calculation is easier, faster, and more practical.

Calculation of Transfer Functions of Multilayer Biotissues in the Problems of Correction of Their Fluorescence Spectra

A method for rapid calculation of a flux of stimulated fluorescence of a multilayer optically dense medium with inhomogeneous distribution of the fluorophore has been developed. The light field in the medium at the excitation wavelength of fluorescence is represented by a superposition of incident collimated, incident diffuse, and reflected diffuse fluxes. A two-stream approximation is used to describe the light field in the medium at the wavelength of emission of the fluorescence. Fluxes in adjacent elementary layers of the medium and on its surface are connected by simple matrix operators that are obtained using a combination of engineering approaches of radiation-transfer theory and single-scattering approximation. The calculations of fluorescence fluxes of a four-layer biotissue that are excited and recorded at 400–800 nm are compared with their Monte Carlo simulation with a discrepancy of 1%. The effect of the propagation medium on the fluorescence spectra of 5-ALA-induced protoporphyrin IX that are recorded from human skin was studied, and a technique for their correction that is based on measurements and quantitative analysis of the diffuse reflectance spectrum of skin was proposed.

Assessment of GIC Based On Transfer Function Analysis

AbstractTransfer functions are calculated for periods between 2 and 1,000 min between geomagnetically induced currents (GIC) measured at three transformers in the South Island of New Zealand and variations in the horizontal components of the geomagnetic field measured at the Eyrewell Observatory near Christchurch. Using an inverse Fourier transform, the transfer functions allow the GIC expected in these transformers to be estimated for any variation of the inducing magnetic field. Comparison of the predicted GIC with measured GIC for individual geomagnetic storms shows remarkable agreement, although the lack of high‐frequency measurements of GIC and the need for interpolation of the measurements lead to a degree of underestimation of the peak GIC magnitude. An approximate correction for this is suggested. Calculation of the GIC for a magnetic storm in November 2001 that led to the failure of a transformer in Dunedin suggests that peak GIC were as large as about 80 A. Use of spectral scaling to estimate the likely GIC associated with a geomagnetic storm of the magnitude of the 1859 Carrington Event indicates that GIC of at least 10 times this magnitude may occur at some locations. Although the impact of changes to the transmission network on calculated transfer functions remains to be explored, it is suggested that the use of this technique may provide a useful check on estimates of GIC produced by other methods such as thin sheet modeling.

MODELING SYSTEM OF AUTOMATIC SPEED REGULATION OF CONVEYOR MACHINES ROASTING TRUCKS

Context. Resolves an an actual task of developing advanced mathematical models to study regulation of the roasting trucks speed of the conveyor machine that allows to maintain a predetermined level of height pellet layer and provides optimal process for firing pellets and maximum performance Objective is a presentation of the mathematical model development results for the regulation roasting trucks speed of the conveyor machine with implementation modern SCADA-system for controlling the conveyor machine performance by regulating its moving speed roasting trucks, which leads to a change of height of the pellet layer on the trucks. Method. To evaluate the dynamic characteristics of the drive system and the simulation control the speed of movement of the roastingtrucks conveyor machine uses a powerful and universal method of research – graphical environment Simulink simulation modeling, which is a supplement to the package MATLAB for numerical analysis. When using Simulink simulation uses the principle of visual programming, in accordance with which the user on the screen of the library of standard blocks and creates a device model performs calculations. Results. The proposed mathematical model used baseline data of conveyor machines OK-306 and LURGI-278. To construct a mathematical model of the automated speed control system for moving the roasting trucks conveyor machines have calculated transfer functions of elements included in the system. As a result of simulation obtained transients when adjusting the height of the pellet layer on the roasting carts and determine their impact on the performance of the conveyor machine. For the feasibility of improving the control system pelletizing plant by the use of a mathematical model for the regulation of the speed of roasting trucks designed modern model interface SCADA-system that works in real time, and enables operational dispatch management. As the SCADA TRACE MODE 6, the height of the pellet layer control system should be developed using SCADA TRACE MODE 6 pelletizing plant systems leading automated management tool using the system. Conclusions. On the basis of the use of the output of the technological process of roasting of the pellets on the conveyor of the burning car and the calculations in a graphical environment Simulink MATLAB built a mathematical model of the system for controlling the speed of the roasting trucks conveyor machine in accordance with technological process allows to investigate influence on pellet burning process by controlling the height of the pellet layer and the performance of the conveyor machine. The proposed model of a modern SCADA-system interface that works in real time and enables operational dispatch management, can be used in real industrial environments.

Examining the Spatial Frequency Components of a Digital Dental Detector

Digital X-ray detectors are widely used in dental radiography. The scope of this work is the examination of the spatial frequency component of a dedicated dental CMOS detector. A commercially available SCHICK CDR CMOS detector was irradiated at a Del Medical Eureka X-ray system at 60kVp and 70kVp. The irradiation setup included images of an edge, for Modulation Transfer Function (MTF) calculation. The air-KERMA was measured with an RTI PIRANHA X-ray multimeter. The images were evaluated in ‘for presentation’ format with the use of ImageJ software. The linear range of the detector was found in the range 13μGy-183μGy at 60 kVp and 18μGy-180μGy at 70 kVp. By inspecting the MTF curves it was found that MTF(6lp/mm)60kVp=0.29 and MTF(6lp/mm)70kVp=0.25. The inspection of the Normalized Noise Power Spetrum (NNPS) showed similar low noise components. Our results indicate that this detector presents comparable performance at both kVp, although its X-ray response (pixel value vs air KERMA) was not equal to previously published results, for the same detector type.

An Approximate Transfer Function Model of Two Serially Connected Heterogeneous Transmission Lines

This brief presents an approximate transfer function model of two heterogeneous transmission lines connected in series. The proposed model is simple, intuitive, and can accurately describe the frequency response of various serially connected heterogeneous interconnects which satisfy a validity condition. The exact error of the proposed model is also provided. According to our analysis, the validity condition can be clearly interpreted by the propagation and the reflection waves. The accuracy of the proposed model is verified by comparing the calculated transfer function of LC-dominant off-chip and RC-dominant on-chip examples against SPICE simulation results. In these verifications, the maximum errors between calculation and simulation are, respectively, 2.58% and 3.32% for off-chip and on-chip examples. The computation time is also reduced about 29.76 and 289.07 times compared with a single-channel model and the SPICE ${w}$ -element model. With the proposed model, designers can easily understand the channel responses of diverse serially connected heterogeneous interconnects.

Numerical computation of aeroacoustic transfer functions for realistic airfoils

Based on Amiet's theory formalism, we propose a numerical framework to compute the aeroacoustic transfer function of realistic airfoil geometries. The aeroacoustic transfer function relates the amplitude and phase of an incoming periodic gust to the respective unsteady lift response permitting, therefore, the application of Curle's analogy to compute the radiated noise. The methodology is focused on the airfoil leading-edge noise problem being able to also consider the trailing-edge back-scattering and, consequently, airfoil compactness effects. The approach is valid for compressible subsonic flows and the airfoil blade is assumed of large aspect ratio subjected to three-dimensional periodic gusts with supersonic velocity trace at the airfoil leading edge (i.e. supercritical gusts). This work proposes the iterative application of the boundary element method to numerically solve the boundary value problem prescribed by the linearized airfoil theory. Details of the numerical implementation are discussed and include the application of boundary conditions in different steps of the iterative procedure, treatment of derivatives in the implementation of the Kutta condition and accurate representation of singularities present at the leading- and trailing-edges. This study validates the numerical approach by comparing results with Amiet's theory obtained analytically. Subsequently, effects of realistic airfoil geometries on the leading-edge airfoil radiated noise are presented.

Control-Relevant Design of System Identification Experiments to Improve Behavioral Interventions

This paper presents the design of system identification experiments for physical activity behavioral interventions, utilizing a control-relevant identification test monitoring approach. The goal is to find, in real-time, the shortest possible experiment with sufficient information for identification meeting robust performance conditions. The procedure considers multisinusoidal periodic inputs, and allows modifications on the amplitude and harmonic related frequency content of input signals after each periodic evaluation cycle. The local polynomial method (LPM) is utilized for the computation of transfer function and estimation uncertainties. An improved stopping criterion is formulated relying on robust performance metrics. The procedure is tested through a simulation study relying on a hypothetical system based on a real behavioral intervention.

Fast computation of the electrolyte-concentration transfer function of a lithium-ion cell model

One approach to creating physics-based reduced-order models (ROMs) of battery-cell dynamics requires first generating linearized Laplace-domain transfer functions of all cell internal electrochemical variables of interest. Then, the resulting infinite-dimensional transfer functions can be reduced by various means in order to find an approximate low-dimensional model. These methods include Padé approximation or the Discrete-Time Realization algorithm.In a previous article, Lee and colleagues developed a transfer function of the electrolyte concentration for a porous-electrode pseudo-two-dimensional lithium-ion cell model. Their approach used separation of variables and Sturm–Liouville theory to compute an infinite-series solution to the transfer function, which they then truncated to a finite number of terms for reasons of practicality. Here, we instead use a variation-of-parameters approach to arrive at a different representation of the identical solution that does not require a series expansion. The primary benefits of the new approach are speed of computation of the transfer function and the removal of the requirement to approximate the transfer function by truncating the number of terms evaluated. Results show that the speedup of the new method can be more than 3800.

Development of a flexible variable-view angioscopy system using face-angled GRIN lenses to enhance field of vision

A novel flexible variable-view angioscopy (VVA) system developed in a very simple way to enhance field of vision, using two face-angled graded-index (GRIN) lenses, a coherent image guide, and a complementary metal–oxide–semiconductor camera module. The two face-angled GRIN lenses are arranged in a line to change the visual field, thus enhancing the field of vision. In addition, this flexible angioscope can be miniaturized and inserted in a confined space such as a blood vessel. In order to evaluate the performance of this VVA system, we obtain optical images using a USAF 1951 target according to the variation of the visual field by simply rotating one GRIN lens without moving the distal end. From the images, we also measure the spatial resolutions of this system for each group and element of the USAF 1951 target and through calculation of the modulation transfer functions. Although the spatial resolution decreases slightly as the difference in rotation angle increases, we can enhance the field of vision by ∼23.2% using this VVA system.

Simulation of intra-ciliary diffusion suggests a novel role of primary cilia as a cell-signaling enhancer.

Besides the role to generate a fluid flow in the surrounding medium, eukaryotic cilia have a crucial function in sensing external signals such as chemical or mechanical stimuli. A large body of work has shown that cilia are frequently found in various types of sensory cells and are closely related to many regulatory mechanisms in differentiation and development. However, we do not yet have a definitive answer to the fundamental question, "why cilia?" It has been a long-standing mystery why cells use cilia for sensing external signals. To shed light on this, we sought to describe the kinetics of signaling with theoretical approaches. Based on the results, here we propose a new role of cilia as a cell-signaling enhancer. The enhancing effect comes from restricted volume for the free intra-ciliary diffusion of molecules due to the cylindrical shape of cilia, which can facilitate quick accumulation of intracellular signaling molecules. Our simulations demonstrate that both the rate and amplitude of response in signal transduction depend on where the membrane receptors or channels are located along the ciliary shaft. In addition, the calculated transfer function of cilia regarded as a transmitter of external signals also suggests the properties of cilia as a signal enhancer. Since such unique composition of receptors and channels in cilia is found in various types of eukaryotic cells, signal enhancing is presumably one of the most essential and conserved roles of cilia.

Real-time modelling of wavepackets in turbulent jets

Three methods are considered for estimating the downstream evolution of wavepackets in turbulent jets based on upstream measurements. The parabolised stability equations are used to compute a transfer function between axially and radially separated points in the flow, and the performance of this theoretical model is compared with that of two empirical approaches, direct transfer function calculation and autoregressive moving-average exogenous system identification, both of which require unsteady experimental data. The three approaches, which perform equally well, prove suitable for estimation of the downstream evolution of wavepackets using pressure data measured in the near-nozzle region. Over distances of the order of a couple of jet diameters, correlations of up to 80 % are observed between estimation and measurement. The performance deteriorates as axial separation between input and output is increased. While the two empirical approaches are limited in terms of both the number of input–output pairs and the number of flow variables that can be reasonably considered, the parabolised stability equations-based approach has no such limitation and can be used to perform full-field estimates comprising all of the dependent variables; in this it constitutes a potentially formidable means by which to perform single-input–multiple-output estimation. It has the further advantage of not requiring unsteady data for its construction, the only necessary ingredients being the mean flow and the linearised equations of motion.

Power line communication transfer function computation in real network configurations for performance analysis applications

Despite power line communication is considered a cost-effective solution to communicate electronic devices across the power system, the performance of this technology is highly affected by physical channel factors such as the presence of noise and signal attenuation. Such phenomena are mainly determined by the characteristics of the electrical infrastructure as well as by the network topology. This study presents an analytical approach to systematically compute the signal attenuation between any pair of nodes in real electric power distribution network topologies based on transmission-line theory and graph theory. The proposed methodology has been applied to obtain the attenuation matrix of two representative networks for low and medium voltage. In addition, the results have been used to analyse the communication performance of these networks, where the low voltage network shows better results due to the reduced number of nodes and network length. The conclusions of this study motivate the application of this methodology to power line communication networks planning.

STRUCTURAL SYNTHESIS OF A STABILIZING ROBUST CONTROLLER OF THE ROTOR FLUX LINKAGE

Purpose. The aim is to structural synthesis of robust stabilizing control of the rotor flux vector control system of induction motor. Methodology. Synthesis controller structure was carried out in two stages. The first stage constructed a mathematical model of the channel of the rotor flux with parametric uncertainty and calculated transfer function of H ∞ -suboptimal controller by method of the mixed sensitivity. The second stage was carried out the expansion of the transfer function of the continued fraction for the Euclidean algorithm. This fraction was used to construct the controller structural scheme. Results. Computer modeling of the transfer function of H ∞ -suboptimal controller. Achieved decomposition found the transfer function of the continued fraction. The flow diagram of suboptimal H ∞ -controller with a proportional and integrating links and a few summers. The curves of transient rotor flux linkage in packages Robust Control Toolbox and Simulink. They coincide in the steady state, but differ among themselves in the transition. Originality. We developed the method of structural synthesis of robust stabilizing controller of the flux linkage rotor, H ∞ -suboptimal structural scheme of which is presented in the form of simple compounds integrating and proportional elements of the same order as the controller with the strictly correct transfer function, and takes into account the parametric uncertainty of control object. The results of the simulation of transient processes in a variety of packages MATLAB applications confirms the adequacy and small sensitivity of the system to parametric perturbation. Practical value . The resulting structure of the controller makes it possible to carry out the modernization of electric control systems, in use, with minimal financial costs.