Forward Transfer Function Research Articles

Accurate detection method of traveling wave shape based on EEMD and L1 norm regularization

Aiming at the problem of waveform distortion of the secondary traveling wave obtained from the primary traveling wave signal transmitted by the voltage traveling wave sensor, an accurate detection method of voltage traveling wave based on ensemble empirical mode decomposition (EEMD) and L1 norm least squares regularization is proposed in this paper. Firstly, the forward transfer function model of the specialized voltage traveling wave sensor is established, and the inversion model is derived to analyze the phase frequency and amplitude frequency characteristics of the secondary traveling wave after transmission. EEMD is used to decompose the secondary traveling wave into the intrinsic modal function (IMF) components of different frequency bands. The L1 norm least square regularization inversion algorithm was used to invert each IMF component. Finally, the IMF' components after inversion are synthesized to obtain the primary traveling wave. Simulation and experimental results demonstrate that the proposed method is not affected by noise, mode aliasing effect and regularization parameter accuracy, and the obtained waveform has high similarity to the simulated waveform, which enables precise identification of fault traveling wave.

Motion planning and control strategy of a cable-driven body weight support gait training robot

Abstract. In this paper, a cable-driven body weight support gait training robot (C-BWSGTR) that provides patients with partial body weight support as well as a kind of stable gait training driving force was designed; this device enabled those patients to walk again. Firstly, the overall configuration of the C-BWSGTR was determined, and the structural composition and working principle of the robot were established. Secondly, the vector algebra method was applied to carry out the kinematic analysis and establish the mathematical model of the C-BWSGTR. The displacement of each cable during the patient gait training was also calculated. Thirdly, the motion planning of the C-BWSGTR was carried out in stages, using the time–phase distribution relationship based on an S-shaped speed curve. Meanwhile, the displacement, speed, and acceleration of each cable during the patient gait training were calculated and corresponding change curves were generated. Finally, a position servo composite control strategy for the C-BWSGTR was designed by analyzing the robot's dynamic characteristics of the forward channel transfer function. The simulation analysis and prototype experiment in this paper verified that the designed composite position servo control strategy can meet the requirements of the system with respect to stability and a fast response of the system to the loading command.

Physical-virtual time reversing of nonlinear Lamb waves for fatigue crack detection and quantification

This article presents the investigation of a nonlinear Lamb wave time reversing technique for fatigue crack detection and quantification. A 2D analytical framework is initially presented, modeling Lamb wave generation, propagation, wave crack linear and nonlinear interaction, and reception. This study extends the Time Reversal (TR) techniques into the realm of nonlinear Lamb waves. Due to the structural transfer function variation between the forward and backward transmission process, the Virtual Time Reversal (VTR) algorithm reveals obvious deviation for predicting nonlinear Lamb waves, given that it replaces the backward TR procedure with the forward transfer function. However, this study demonstrates that the difference between the physical nonlinear TR method and the conventional VTR algorithm proves to be sensitive to detect and quantify fatigue cracks. Fatigue tests on a thin aluminum plate with a rivet hole are conducted to induce a fatigue crack. The experimental results further illuminate that the proposed physical-virtual nonlinear Lamb wave TR technique possesses remarkable sensitivity to the nucleation and growth of fatigue cracks. The paper finishes with discussion, concluding remarks, and suggestions for future work.

Fractional-order modelling and simulation of human ear

ABSTRACTConventional integer-order lumped element models cannot fully describe the memory-dependent viscoelastic behaviour of bio-tissues. We propose a tunable and more predictive lumped element modelling of fractional-order sense for human ear, which is better adapted to the physical nature of the bio-materials. We develop a computational–mathematical framework for human ear to account for the power-law characteristics of viscoelastic bio-tissues. On the experiment side, we obtain impedance data and distortion product otoacoustic emissions data from several participants, to estimate the round-trip outer-middle ear gain, for parameter fitting and validation of the proposed model. This modelling approach provides a sound basis for data-driven modelling and simulation of the viscoelastic tissues of the human ear.Abbreviations: DPOAE: distortion product otoacoustic emission; FTF: forward transfer function; OMEG: round-trip outer-middle ear gain; RTF: reverse transfer function; TM: tympanic membrane

Middle-ear function in the chinchilla: Circuit models and comparison with other mammalian species

The middle ear efficiently transmits sound from the ear canal into the inner ear through a broad range of frequencies. Thus, understanding middle-ear transmission characteristics is essential in the study of hearing mechanics. Two models of the chinchilla middle ear are presented. In the first model, the middle ear is modeled as a lumped parameter system with elements that represent the ossicular chain and the middle-ear cavity. Parameters of this model are fit using available experimental data of two-port transmission matrix parameters. In an effort to improve agreement between model simulations and the phase of published experimental measurements for the forward pressure transfer function at high frequencies, a second model in which a lossless transmission line model of the tympanic membrane is appended to the original model is proposed. Two-port transmission matrix parameter results from this second model were compared with results from previously developed models of the guinea pig, cat, and human middle ears. Model results and published experimental data for the two-port transmission matrix parameters are found to be qualitatively similar between species. Quantitative differences in the two-port transmission matrix parameters suggest that the ossicular chains of chinchillas, cats, and guinea pigs are less flexible than in humans.

Simultaneously Suppressing Low-Frequency and Relaxation Oscillation Intensity Noise in a DBR Single-Frequency Phosphate Fiber Laser**Supported by the National High-Technology Research and Development Program of China under Grant Nos 2013AA031502 and 2014AA041902, the National Natural Science Foundation of China under Grant Nos 11174085, 51132004, and 51302086, the Guangdong Natural Science Foundation under Grant Nos S2011030001349 and S20120011380, the China National Funds

Effective multiple optoelectronic feedback circuits for simultaneously suppressing low-frequency and relaxation oscillation intensity noise in a single-frequency phosphate fiber laser are demonstrated. The forward transfer function, which relates the laser output intensity to the pump modulations, is measured and analyzed. A custom two-path feedback system operating at different frequency bands is designed to adjust the pump current directly. The relative intensity noise is decreased by 20 dB from 0.2 to 5kHz and over 10 dB from 5 to 10 kHz. The relaxation oscillation peak is suppressed by 22 dB. In addition, a long term (24 h) laser instability of less than 0.05% is achieved.

On improving Popov's criterion for nonlinear feedback system stability

For the L2-stability of a nonlinear single-input–single-output (SISO) feedback system, described by an integral equation and with the forward block transfer function and a first- and third-quadrant non-monotone nonlinearity in the feedback path, we derive an interesting generalization of the celebrated criterion of Popov [(1962). Absolute stability of nonlinear systems of automatic control. Automation and Remote Control, 22(8), 857–875]: , where is a constant. The generalization entails the addition of a general causal+anticausal O'Shea–Zames–Falb multiplier function whose time-domain -norm is constrained by certain characteristic parameters (CPs) of the nonlinearity obtained from certain novel algebraic inequalities. If the nonlinearity is monotone or belongs to any prescribed subclass of , its CPs are reduced, thereby relaxing the time-domain constraint on the multiplier. An important special feature of the new stability results is a partial bridging of the significant gap between the Popov criterion and the stability results that appeared post-Popov in the form of considering monotone and other subclasses of nonlinearities in exchange for weakening the restrictions on the phase angle behaviour of . Extensions to time-varying nonlinearities more general than those in the literature are also presented. Numerical examples are given to illustrate the theorems and to demonstrate their superiority over the existing literature.

Parameter fitting of a lumped parameter middle ear model

Measurements of otoacoustic emissions in the ear canal are affected by the forward and reverse pressure transfer functions and the reverse middle ear impedance. Thus, a comprehensive middle ear model should reflect each of these measurements of middle ear function using a single set of parameters. A middle ear circuit model consisting of a lumped parameter representation of the ossicular chain coupled to a transmission line model of the eardrum was selected (O’Connor and Puria, JASA, 2008). In the original model, the parameters were fit solely to measurements of the magnitude and phase of the stapes velocity relative to the ear canal pressure in the forward direction. In this paper, the model parameters are optimized through a non-linear least square regression method so that the model’s forward pressure transfer function, reverse pressure transfer function, and reverse middle ear impedance agree with experimental data for the human middle ear from 0.1 to 10 kHz. This parameter fitting procedure is repeat...

Nyquist stability analysis of a VSC-HVDC system using a distributed parameter DC-cable model

In this paper a two terminal VSC-HVDC system embedded in a strong grid AC-environment is considered, emphasizing modeling, controllers design and small-signal stability analysis. Traditionally, DC cables are most often modeled by Π-sections, and when using them for higher frequencies or in case of transmission over long distances, approximation accuracy aspects must be considered. Here, a distributed parameter cable model, based on the damped wave equation, is used to overcome this limitation. It is shown that the VSC-HVDC system can be described by a forward transfer function cascaded with a feedback loop. The first transfer function will be different, due to which input and output variables that are considered but is in all realistic cases stable. The feedback loop, where the forward path is a rational function and the return path is a dissipative infinite dimensional system, remains the same in all cases. The stability is then analyzed, using the Nyquist criterion, in a straight forward manner. Numerical examples are given by MATLAB.

SGEMS-UQ: An uncertainty quantification toolkit for SGEMS

While algorithms and methodologies to study uncertainty in the Earth Sciences are constantly evolving, there is currently no free integrated software that allows the general practitioners access to these developments. This paper presents SGEMS-UQ, a plugin for the SGEMS platform, that is used to perform distance-based uncertainty analysis on geostatistical simulations, and the resulting forward transfer function responses used in subsurface modeling and engineering. A versatile XML-derived dialect is defined for communicating with external programs that reduces the need for ad-hoc linking of codes, and a relational database system is implemented to automate many of the steps in data mining the spatial and forward model parameters. Through a graphical user interface, one can map a set of realizations and forward transfer function responses into a multidimensional scaling (MDS) space where visualization utilities, and clustering techniques are available. Once mapped in the MDS space, the user can explore linkage between simulation parameters and forward transfer function responses using a module based on a SQL database. Consideration is given to the use of software engineering paradigms and design patterns to produce a code-base that is manageable, efficient, and extensible for future applications, while being scalable to work with large datasets. Finally, we illustrate the versatility of the code-base on an application of modeling uncertainty in reservoir forecasts for an oil reservoir in the West Coast of Africa.

Forward and reverse transfer functions of the middle ear based on pressure and velocity DPOAEs with implications for differential hearing diagnosis

Recently it was shown that distortion product otoacoustic emissions (DPOAEs) can be measured as vibration of the human tympanic membrane in vivo, and proposed to use these vibration DPOAEs to support a differential diagnosis of middle-ear and cochlear pathologies. Here, we investigate how the reverse transfer function (r-TF), defined as the ratio of DPOAE-velocity of the umbo to DPOAE-pressure in the ear canal, can be used to diagnose the state of the middle ear. Anaesthetized guinea pigs served as the experimental animal. Sound was delivered free-field and the vibration of the umbo measured with a laser Doppler vibrometer (LDV). Sound pressure was measured 2–3 mm from the tympanic membrane with a probe-tube microphone. The forward transfer function (f-TF) of umbo velocity relative to ear-canal pressure was obtained by stimulating with multi-tone pressure. The r-TF was assembled from DPOAE components generated in response to acoustic stimulation with two stimulus tones of frequencies f1 and f2; f2/f1 was constant at 1.2. The r-TF was plotted as function of DPOAE frequencies; they ranged from 1.7 kHz to 23 kHz. The r-TF showed a characteristic shape with an anti-resonance around 8 kHz as its most salient feature. The data were interpreted with the aid of a middle-ear transmission-line model taken from the literature for the cat and adapted to the guinea pig. Parameters were estimated with a three-step fitting algorithm. Importantly, the r-TF is governed by only half of the 15 independent, free parameters of the model. The parameters estimated from the r-TF were used to estimate the other half of the parameters from the f-TF. The use of r-TF data – in addition to f-TF data – allowed robust estimates of the middle-ear parameters to be obtained. The results highlight the potential of using vibration DPOAEs for ascertaining the functionality of the middle ear and, therefore, for supporting a differential diagnosis of middle-ear and cochlear pathologies.

Enabling Automation of Friction Stir Welding: The Modulation of Weld Seam Input Energy by Traverse Speed Force Control

Friction stir welding (FSW) joins materials by plunging a rotating tool into the work piece. The tool consists of a shoulder and a pin that plastically deforms the parent materials and then forges them together under the applied pressure. To create the pressure needed for forging, a rather large axial force must be maintained on the tool. Maintaining this axial force is challenging for robots due to their limited load capacity and compliant nature. To address this problem, force control has been used, and historically, the force has been controlled by adjusting the plunge depth of the tool into the work piece. This paper develops the use of tool traverse speed as the controlling variable instead of plunge depth. To perform this investigation, a FSW force controller was designed and implemented on a retrofitted Milwaukee Model K milling machine. The closed loop proportional, integral plus derivative (PID) control architecture was tuned using the Ziegler–Nichols method. Results show that the control of axial force via traverse speed is feasible and predictable. The resulting system is more robust and stable when compared with a force controller that uses plunge depth as the controlling variable. A standard deviation of 41.5 N was obtained. This variation is much less when compared with a standard deviation of 129.4 N obtained when using plunge depth. Using various combinations of PID control, the system’s response to step inputs was analyzed. From this analysis, a feed forward transfer function was modeled that describes the machinery and welding environment. From these results, a technique is presented regarding weld seam input energy modulation as a by product of force control via traverse speed. A relative indication of thermal energy in the welding environment is obtained with the feedback of axial force. It is hypothesized that, while under force control, the controller modulates weld seam input energy according to the control signal. The result is constant thermomechanical conditions in the welding environment. It is concluded that the key enablers for force control are the unidirectional behavior and load dynamics of the traverse motor. Larger bandwidths and more stable weld conditions emerge when using traverse speed instead of plunge depth to control the force. Force control of FSW via traverse speed has importance in creating efficient automatic manufacturing operations. The intelligence of the controller naturally selects the most efficient traverse speed.

Simultaneous measurement of middle-ear input impedance and forward/reverse transmission in cat

Reported here is a technique for measuring forward and reverse middle-ear transmission that exploits distortion-product otoacoustic emissions (DPOAEs) to drive the middle ear "in reverse" without opening the inner ear. The technique allows measurement of DPOAEs, middle-ear input impedance, and forward and reverse middle-ear transfer functions in the same animal. Intermodulation distortion in the cochlea generates a DPOAE at frequency 2f1-f2 measurable in both ear-canal pressure and the velocity of the stapes. The forward transfer function is computed from stapes velocities and corresponding ear-canal pressures measured at the two primary frequencies; the reverse transfer function is computed from velocity and pressure measurements at the DPOAE frequency. Middle-ear input impedance is computed from ear-canal pressure measurements and the measured Thévenin equivalent of the sound-delivery system. The technique was applied to measure middle-ear characteristics in anesthetized cats with widely opened middle-ear cavities (0.2-10 kHz). Stapes velocity was measured at the incudo-stapedial joint. Results on five animals are reported and compared with a published middle-ear model. The measured forward transfer functions and input impedances generally agree with previous measurements, and all measurements agree qualitatively with model predictions. The reverse transfer function is shown to depend on the acoustic load in the ear canal, and the measurements are used to compute the round-trip middle-ear gain and delay. Finally, the measurements are used to estimate the parameters of a two-port transfer-matrix description of the cat middle ear.

RF channel performance assessment for a multiple carrier millimeter-wave communication system *

Abstract Channel capacity, system versatility and ease of maintenance are factors of prime concern in future generations of wireless communication systems. As a result, millimeter-wave can offer considerable advantages in providing broadband interface. Nonlinearity and noise effects, including parametric fluctuations, are two significant causes for signal degradation in broadband communication systems. Two methods to assess the performance of an RF channel in a multi-carrier system are described. By measuring the forward transfer function from transmitter IF to receiver IF as the frequency is swept across the channel bandwidth, characteristics such as gain flatness, channel dispersion, and saturation effects are revealed. To evaluate the ability of the communication link in preserving the synchronization between two carriers, their heterodyned spectrum at the receiver IF output is studied. Both measurement methods employ standard equipment and have been found to be effective when applied to a multi-carrier millimeter-wave system with over 1 GHz instantaneous bandwidth.

Otoacoustic emissions from residual oscillations of the cochlear basilar membrane in a human ear model.

Sounds originating from within the inner ear, known as otoacoustic emissions (OAEs), are widely exploited in clinical practice but the mechanisms underlying their generation are not entirely clear. Here we present simulation results and theoretical considerations based on a hydrodynamic model of the human inner ear. Simulations show that, if the cochlear amplifier (CA) gain is a smooth function of position within the active cochlea, filtering performed by a middle ear with an irregular, i.e., nonsmooth, forward transfer function suffices to produce irregular and long-lasting residual oscillations of cochlear basilar membrane (BM) at selected frequencies. Feeding back to the middle ear through hydrodynamic coupling afforded by the cochlear fluid, these oscillations are detected as transient evoked OAEs in the ear canal. If, in addition, the CA gain profile is affected by irregularities, residual BM oscillations are even more irregular and tend to evolve towards self-sustaining oscillations at the loci of gain irregularities. Correspondingly, the spectrum of transient evoked OAEs exhibits sharp peaks. If both the CA gain and the middle-ear forward transfer function are smooth, residual BM oscillations have regular waveforms and extinguish rapidly. In this case no emissions are produced. Finally, and paradoxically albeit consistent with observations, simulating localized damage to the CA results in self-sustaining BM oscillations at the characteristic frequencies (CFs) of the sites adjacent to the damage region, accompanied by generation of spontaneous OAEs. Under these conditions, stimulus-frequency OAEs, with typical modulation patterns, are also observed for inputs near hearing threshold. This approach can be exploited to provide novel diagnostic tools and a better understanding of key phenomena relevant for hearing science.

Optoelectronic feedback control for intensity noisesuppression in a codoped erbium-ytterbium glass laser

An effective optoelectronic feedback circuit for the suppression of relaxation oscillations in a codoped erbium-ytterbium laser is designed and demonstrated. The presence of an additional dominant pole in the forward transfer function, due to the energy transfer process inside the active material requires a feedback control which introduces a suitable phase shift and provides high gain at the relaxation oscillation frequency. A 30 dB reduction in the relaxation oscillation noise peak has been achieved.

An adaptive neural processing node

The design and test results for two analog adaptive VLSI processing chips are described. These chips use pulse coded signals for communication between processing nodes and analog weights for information storage. The weight modification rule, implemented on chip, uses concepts developed by E. Oja (1982) and later extended by T. Leen et al. (1989) and T. Sanger (1989). Experimental results demonstrate that the network produces linearly separable outputs that correspond to dominant features of the inputs. Such representations allow for efficient additional neural processing. Part of the adaptation rule also includes a small number of fixed inputs and a variable lateral inhibition mechanism. Experimental results from the first chip show the operation of function blocks that make a single processing node. These function blocks include forward transfer function, weight modification, and inhibition. Experimental results from the second chip show the ability of an array of processing elements to extract important features from the input data.

Pharmacokinetics from a dynamical systems point of view

The pharmacological action of many drugs depends on several variables at the same time and therefore will be dominated by an attractor of a dimension greater than zero. The pharmacokinetic behavior is likely to be dominated by a zero dimensional point attractor so that it is highly predictable. Pharmacokinetics is discussed from a dynamical systems point of view, whereby the transport of drugs in the tissues and organs is considered a stochastic process characterized by density functions of transit times and blood flows. In the body, the tissues and organs are arranged in parallel, in series, and in a feedback-loop fashion. Consequently, the single-pass transport of drugs through the body is again a stochastic process characterized by the density function of total body transit times, the cardiac output, and the total body extraction. The drug molecules, however, may pass through the body several times before ultimately leaving the system by metabolism or excretion. As a result, the body may be regarded as a positive feedback system with the pulmonary circulation (and its tissues) as the forward transfer function and the systemic circulation (with all its tissues) as the feedback transfer function. Consequently, the total body transport function (closed loop) is again a stochastic process characterized by a density function of total body residence times. The relationship between the body transit time distribution and the body residence distribution is determined by the feedback-loop arrangement, the cardiac output, and the extraction ratio which can easily be written in the Laplace domain. The pharmacokinetic parameters logically follow from the systems approach. They are the cardiac output, the mean transit time, the extraction ratio, the clearance, the volume of distribution in steady state, the mean residence time, and the average number of recirculations. The dynamic systems approach in pharmacokinetics has been illustrated with some examples notably with caffeine.

Modeling a vented push‐pull hearing‐aid fitting in situ as a feedback control system

For the investigation of acoustic feedback encountered with push‐pull amplification for in‐the‐ear hearing aids, a simulated fitting was considered a feedback control system to include the acoustic leakage from the hearing‐aid receiver traveling back to the microphone. A Gennum WS531 amplifier was connected to an earmold shell made for the right ear of KEMAR. This shell contained a Knowles EK 3024 microphone, a Knowles BK1613 receiver, and a 0.09‐in.‐diam by 0.8‐in.‐long vent hole. Transfer function magnitude and phase were obtained for the microphone, amplifier, receiver, for the open loop while breaking the signal path between microphone and amplifier, and for the closed loop, all with maximum gain before onset of oscillation. The acoustic feedback transfer function was determined by subtracting the forward loop transfer function from the closed loop transfer function. A circuit synthesis program was used to fit the transfer function measurement data into mathematical transfer function expressions. Comp...

A study of the closed-loop structure of multivariable feedback control systems

A method of analysis for feedback systems with multiple inputs and outputs is presented, based on the transfer-function matrix representation. It allows the direct computation of any transfer function tij relating the ith input to the jth output, given the forward and feedback transfer function matrices G (s) and H (s), and sets out clearly the relationship between the numerator and denominator of such a transfer function. The derivation of the method from first principles, starting with the system connection matrix, is felt to impart a certain insight into the behaviour of such complex structures.