Transfer Function Characteristics Research Articles

Transfer function characterization for HFCTs used in partial discharge detection

High frequency current transformers (HFCTs) are widely employed to detect partial discharge (PD) induced currents in high voltage equipment. This paper describes measurements of the wideband transfer functions of HFCTs so that their influence on the detected pulse shape in advanced PD measurement applications can be characterized. The time-domain method based on the pulse response is a useful way to represent HFCT transfer functions as it allows numerical determination of the forward and reverse transfer functions of the sensor. However, while the method is accurate at high frequencies it can have limited resolution at low frequencies. In this paper, a composite time-domain method is presented to allow accurate characterization of the HFCT transfer functions at both low and high frequencies. The composite method was tested on two different HFCTs and the results indicate that the method can characterize their transfer functions ranging from several kHz to tens of MHz. Results are found to be in good agreement with frequency-domain measurements up to 50 MHz. Measurement procedures for using the method are summarized to facilitate further applications.

Research on modulation transfer function of the linear-array CCD for hyperspectral imager

As an image-spectrum merging technology, hyperspectral imaging has been used in battlefield reconnaissance rapidly．Based on response of CCD to the sine input signal, the period and extremal positions of output signal were analyzed and simulated. According to the definition of MTF based on contrast, three expressions of the average MTF of line-array CCD were presented and compared with those based on Fourier transform method. Finally, the average MTF of line-array CCD is confirmed. Accordingly, the characteristics of modulation transfer function of line-array CCD are studied. The simulation results indicate that the frequency increase, while at Nuquist frequency, the effect of the initial position, which becomes much stronger with frequency increase, while at other frequency, the effet of the initial position is weak. In the frequency range of |ζ |>0.1%, the effect of the initial position on MTF can be ignored.

面阵光纤传像束与面阵CCD的像元耦合调制传递函数特性

面阵光纤传像束与面阵CCD的像元耦合调制传递函数特性

Possibilities of the Additional Damping of Unidirectional Fiber Composites by Implementation of Viscoelastic Neoprene and Rubber Layers

The aim of the presented work is to assess modal, transmission, and damping characteristics of layered carbon plates. The base is to carry experimental analysis verified by FEM model, which evaluates the vibration transfer of tested composites and describes possibilities of additional damping by implementation of viscoelastic layers. Preimpregnated carbon fibers known as prepreg were used for creation of the samples composed of four (2 constant and 2 variable) layers. The task was to assess impact of changing the fiber orientation on the transfer function and individual modal characteristics. As another option, testing of some additional damping materials was included. Neoprene and thin rubber coat were added as an outside damping element when the neoprene ply was inserted also among the layers. Expected dependence of the plies orientation onto the shape of the transfer function and even swapping of some of MOD characters (bending, torsion, and their combinations) have been found. The use of the additional damping materials is also possible but the right combination of the individual plies layout and stacking sequence is the most significant part. The results had been statistically analyzed and showed that the created layered shell FE models could be used to describe the behavior.

Characterization of transfer function, resolution and depth of field of a soft X-ray microscope applied to tomography enhancement by Wiener deconvolution.

Full field soft X-ray microscopy is becoming a powerful imaging technique to analyze whole cells preserved under cryo conditions. Images obtained in these X-ray microscopes can be combined by tomographic reconstruction to quantitatively estimate the three-dimensional (3D) distribution of absorption coefficients inside the cell. The impulse response of an imaging system is one of the factors that limits the quality of the X-ray microscope reconstructions. The main goal of this work is to experimentally measure the 3D impulse response and to assess the optical resolution and depth of field of the Mistral microscope at ALBA synchrotron (Barcelona, Spain). To this end we measure the microscope apparent transfer function (ATF) and we use it to design a deblurring Wiener filter, obtaining an increase in the image quality when applied to experimental datasets collected at ALBA.

Solution of signal uncertainty problem at analytical design of consecutive compensator in piezo actuator control

Subject of Research.We present research results for the signal uncertainty problem that naturally arises for the developers of servomechanisms, including analytical design of serial compensators, delivering the required quality indexes for servomechanisms. Method. The problem was solved with the use of Besekerskiy engineering approach, formulated in 1958. This gave the possibility to reduce requirements for input signal composition of servomechanisms by using only two of their quantitative characteristics, such as maximum speed and acceleration. Information about input signal maximum speed and acceleration allows entering into consideration the equivalent harmonic input signal with calculated amplitude and frequency. In combination with requirements for maximum tracking error, the amplitude and frequency of the equivalent harmonic effects make it possible to estimate analytically the value of the amplitude characteristics of the system by error and then convert it to amplitude characteristic of open-loop system transfer function. While previously Besekerskiy approach was mainly used in relation to the apparatus of logarithmic characteristics, we use this approach for analytical synthesis of consecutive compensators. Main Results. Proposed technique is used to create analytical representation of "input–output" and "error–output" polynomial dynamic models of the designed system. In turn, the desired model of the designed system in the "error–output" form of analytical representation of transfer functions is the basis for the design of consecutive compensator, that delivers the desired placement of state matrix eigenvalues and, consequently, the necessary set of dynamic indexes for the designed system. The given procedure of consecutive compensator analytical design on the basis of Besekerskiy engineering approach under conditions of signal uncertainty is illustrated by an example. Practical Relevance. The obtained theoretical results are used in the task of developing precise positioning systems with piezoelectric actuation mechanism. Proposed procedure for analytical synthesis of consecutive compensator is also believed to be usable for design of servo mechanisms of arbitrary application.

Firing-rate resonances in the peripheral auditory system of the cricket, Gryllus bimaculatus.

In many communication systems, information is encoded in the temporal pattern of signals. For rhythmic signals that carry information in specific frequency bands, a neuronal system may profit from tuning its inherent filtering properties towards a peak sensitivity in the respective frequency range. The cricket Gryllus bimaculatus evaluates acoustic communication signals of both conspecifics and predators. The song signals of conspecifics exhibit a characteristic pulse pattern that contains only a narrow range of modulation frequencies. We examined individual neurons (AN1, AN2, ON1) in the peripheral auditory system of the cricket for tuning towards specific modulation frequencies by assessing their firing-rate resonance. Acoustic stimuli with a swept-frequency envelope allowed an efficient characterization of the cells' modulation transfer functions. Some of the examined cells exhibited tuned band-pass properties. Using simple computational models, we demonstrate how different, cell-intrinsic or network-based mechanisms such as subthreshold resonances, spike-triggered adaptation, as well as an interplay of excitation and inhibition can account for the experimentally observed firing-rate resonances. Therefore, basic neuronal mechanisms that share negative feedback as a common theme may contribute to selectivity in the peripheral auditory pathway of crickets that is designed towards mate recognition and predator avoidance.

Modeling of Response Amplitude Operator for Coupled Sway, Roll and Yaw Motions of a Floating Body in Sinusoidal Waves Using Frequency Based Analysis

The paper investigates the characteristics of response amplitude operators (RAO) or transfer function of a floating body in frequency domain for coupled sway, roll and yaw motions in sinusoidal waves. The floating body is considered to be initially at rest and waves act as beam to the floating body with varying frequency (ω) between 0.3 rad/s and 1.2 rad/s. The hydrodynamic coefficients (HC) are computed using strip theory formulation and the general expression of RAO is derived. The behavior of RAO under coupled conditions is examined by considering two asymptotic cases, corresponding to ω→0 and ω→∞. For the intermediate frequency range, analytical expression for system frequency is derived. The effects of viscous damping for uncoupled and coupled transfers have been compared with the result of nonviscous case. A mathematical analogy with respect to Mathieu and Hill equations has been established using frequency based classifications of governing equations. This modeling approach can provide useful guidelines to determine RAO for coupled motions and computing of wave loads and sensitivity analysis with respect to initial conditions of a floating body for the wide range of frequencies.

Experimental Control and Design of Low-Frequency Bias Networks for Dynamically Biased Amplifiers

To reach the video bandwidth requirements on the supply paths, power amplifiers with dynamic bias schemes are constrained to reduce the values of the low-frequency (LF) decoupling capacitors on their bias lines. This can entail a decrease of the LF stability margins, among other negative effects. In this work, a methodology is proposed to experimentally monitor and control the dominant poles that govern the LF dynamics of both gate and drain bias lines from dc to high compression power. A specific topology for the bias observation accesses allows a consistent characterization in large-signal regimes. An automatic procedure to trace root contours versus four control parameters is also developed. The complete approach can be used to optimize the design of the bias lines in terms of video bandwidth, relative stability margins, and bias voltage transfer function characteristics. Moreover, the design can account for the effect of the large-signal RF drive on these LF performances. The methodology is exemplified and validated in a demonstrator prototype specifically built for that purpose.

A Synchronous Approach for Numerical Simulation of Machine Tools

In this paper, a synchronous approach for dynamic simulation of machine tools is described. Computer Aided Engineering (CAE) method models and analyzes a dynamical parameter prototype of machine tools. In which, the flexible structure, interactive movement, non-linear factor effects as well as characteristics of resonance frequencies and mechanical transfer function are considered. The integrating Finite Element Method (FEM), Multi-Body Dynamics (MBD) and control carries out a solution of machine tools simulation for predicting dynamic machine behaviors. The static analysis and modal analysis of components are presented with sample examples. Cybernetic characteristics like Bode diagram and such a controller are implemented for movement tailors. The synchronous approach deduces a practically technical method for machines tools.

Effect of reverberation on instrumental vibrato tones

Musical vibrato is the process by which a performer subtly varies the frequency and amplitude of a note for expressive effect. Previous work has suggested that the vibrato modulation may not be uniform across all overtones, causing the individual frequency trajectories to become decorrelated. In this study, we investigate the effect of reverberation on instrumental tones performed with vibrato. This is accomplished by performing a detailed time-frequency analysis to extract the instantaneous frequencies of many overtones. In order to accurately track the low amplitudes of the upper harmonics, we present an algorithm tailored for optimal tracking in as little as 10 dB SNR. For tones recorded in an anechoic environment, the instantaneous frequency modulations of all the overtones are found to be highly correlated. However, tones recorded in a reverberant space, as well as anechoic recordings processed with a synthetic reverberation are found to have significantly lower correlations between the overtones. In addition to providing insight into musical timbre variations, these results could be useful for characterization of acoustic transfer functions or applications where overtone correlation is assumed, such as audio source separation.

Vibration Reduction Method Using Transfer Function Characteristics of Operational TPA

Vibration Reduction Method Using Transfer Function Characteristics of Operational TPA

Intelligent Image Rendition

The traditional image rendition process assumes an ideal output imaging system where each image pixel will be perfectly reproduced regardless of different image formation processes. In reality, each individual imaging system can be approximated as a linear system with its own unique transfer function characteristics, which could exhibit spatial and/or temporal variations. Consequently, it will produce inconsistent tone scale reproduction curves during the print production run. The objective of this paper is to investigate the tone reproduction curve variations caused primarily by the interaction of neighboring imaging pixels. An intelligent image rendition algorithm is presented to compensate for this macroscopic imaging process deficiency. Experimental results will be demonstrated to show the effectiveness of the proposed algorithm, which has been deployed commercially on a digital printing press.

A bottom-up characterization of transfer functions for synthetic biology designs: lessons from enzymology.

Within the field of synthetic biology, a rational design of genetic parts should include a causal understanding of their input-output responses—the so-called transfer function—and how to tune them. However, a commonly adopted strategy is to fit data to Hill-shaped curves without considering the underlying molecular mechanisms. Here we provide a novel mathematical formalization that allows prediction of the global behavior of a synthetic device by considering the actual information from the involved biological parts. This is achieved by adopting an enzymology-like framework, where transfer functions are described in terms of their input affinity constant and maximal response. As a proof of concept, we characterize a set of Lux homoserine-lactone-inducible genetic devices with different levels of Lux receptor and signal molecule. Our model fits the experimental results and predicts the impact of the receptor's ribosome-binding site strength, as a tunable parameter that affects gene expression. The evolutionary implications are outlined.

Non-stationary nonparametric inference of river-to-groundwater travel-time distributions

The travel-time distribution between rivers and groundwater observation points and the mixing of freshly infiltrated river water with groundwater of other origin is of high relevance in riverbank filtration. These characteristics usually are inferred from the analysis of natural-tracer time series, typically relying on a stationary input–output relationship. However, non-stationarity is a significant feature of the riparian zone causing time-varying river-to-groundwater transfer functions. We present a non-stationary extension of nonparametric deconvolution by performing stationary deconvolution with windowed time series, enforcing smoothness of the determined transfer function in time and travel time. The nonparametric approach facilitates the identification of unconventional features in travel-time distributions, such as broad peaks, and the sliding-window approach is an easy way to accommodate the method to dynamic changes of the system under consideration. By this, we obtain time-varying signal-recovery rates and travel-time distributions, from which we derive the mean travel time and the spread of the distribution as function of time. We apply our method to electric-conductivity data collected at River Thur, Switzerland, and adjacent piezometers. The non-stationary approach reproduces the groundwater observations significantly better than the stationary one, both in terms of overall metrics and in matching individual peaks. We compare characteristics of the transient transfer function to base flow which indicates shorter travel times at higher river stages.

Comparison of resonant current regulators for DFIG during grid voltage distortion

We investigate two different kinds of resonant current regulators for a doubly fed induction generator (DFIG) under distorted grid voltage conditions: proportional integral resonant (PIR) regulator with traditional resonant part and vector proportional integral (VPI) regulator with VPI resonant part. Based on the mathematical model of DFIG under distorted grid voltage, the transfer function and frequency response characteristics of the two current regulators are analyzed and compared. The superiority of the VPI current regulator over the PIR regulator is pointed out, and the influence of discretization methods on the performance of the resonant current regulator is studied. All the results are validated by MATLAB simulation and experiments.

An Sample Analysis of Heavy Metal Pollution to Urban Surface Soil Based on Transfer Function Theory

The degree of heavy-metal pollution of different district in city area is discussed by improved Nemerow model and further topographic maps are drawn .From the improved Nemerow model, the Nemerow integrated pollution index is determined . The main reason of pollution is found according to weight, then the corresponding heavy-metal pollution things portion in the overall district is computed by using the model . The element that corresponds the maximum weight is found .And it proves that the heavy-metal pollution element Hg is the main pollution reason .The pollution source is determined by heavy metal spreading features using transfer function theory. Thinking of the main pollution elements as the researched object ,the spreading features are analized using transfer function characteristics. And the spreading process is described using flow chart.

Optimization of cascaded regenerative links based on phase sensitive amplifiers

We develop an analytical method for optimizing phase sensitive amplifiers for regeneration in multilevel phase encoded transmission systems. The model accurately predicts the optimum transfer function characteristics and identifies operating tolerances for different signal constellations and transmission scenarios. The results demonstrate the scalability of the scheme and show the significance of having simultaneous optimization of the transfer function and the signal alphabet. The model is general and can be applied to any regenerative system.

The application of an innovative inverse model for understanding and predicting landslide movements (Salazie cirque landslides, Reunion Island)

The prediction of landslide movement acceleration is a complex problem, among others identified for deep-seated landslides, and represents a crucial step for risk assessment. Within the scope of this problem, the objective of this paper is to explore a modelling method that enables the study of landslide function and facilitates displacement predictions based on a limited data set. An inverse modelling approach is proposed for predicting the temporal evolution of landslide movement based on rainfall and displacement velocities. Initially, the hydrogeology of the studied landslides was conceptualised based on correlative analyses. Subsequently, we applied an inverse model with a Gaussian-exponential transfer function to reproduce the displacements. This method was tested on the Grand Ilet (GI) and Mare-a-Poule-d’Eau (HB) landslides on Reunion Island in the Indian Ocean. We show that the behaviour of landslides can be modelled by inverse models with a bimodal transfer function using a Gaussian-exponential impulse response. The cumulative displacements over 7 years of modelling (2 years of calibration period for GI, and 4 years for HB) were reproduced with an RMSE above 0.9. The characteristics of the bimodal transfer function are directly related to the hydrogeological functioning demonstrated by the correlative analyses: the rapid reaction of a landslide can be associated with the effect of a preferential flow path on groundwater level variations. Thus, this study shows that the inverse model using a Gaussian-exponential transfer function is a powerful tool for predicting deep-seated landslide movements and for studying how they function. Beyond modelling displacements, our approach effectively demonstrates its ability to contribute relevant data for conceptualising the sliding mechanisms and hydrogeology of landslides.

Integrated photonic filters based on SiC multilayer structures

Combined tunable WDM converters based on SiC multilayer photonic active filters are analyzed. The operation combines the properties of active long-pass and short-pass wavelength filter sections into a capacitive active band-pass filter.The sensor element is a multilayered heterostructure produced by PE-CVD. The configuration includes two stacked SiC p–i–n structures sandwiched between two transparent contacts. Transfer function characteristics are studied both theoretically and experimentally.Results show that optical bias activated photonic device combines the demultiplexing operation with the simultaneous photodetection and self amplification of an optical signal acting the device as an integrated photonic filter in the visible range. Depending on the wavelength of the external background and irradiation side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. The output waveform presents a nonlinear amplitude-dependent response to the wavelengths of the input channels. A numerical simulation and a two building-blocks active circuit are presented and give insight into the physics of the device.