Showing papers on "Frequency response published in 2000"

Modes of vortex formation and frequency response of a freely vibrating cylinder

Abstract: In this paper, we study the transverse vortex-induced vibrations of an elastically mounted rigid cylinder in a fluid flow. We use simultaneous force, displacement and vorticity measurements (using DPIV) for the first time in free vibrations. There exist two distinct types of response in such systems, depending on whether one has a high or low combined mass–damping parameter (m*ζ). In the classical high-(m*ζ) case, an ‘initial’ and ‘lower’ amplitude branch are separated by a discontinuous mode transition, whereas in the case of low (m*ζ), a further higher-amplitude ‘upper’ branch of response appears, and there exist two mode transitions.To understand the existence of more than one mode transition for low (m*ζ), we employ two distinct formulations of the equation of motion, one of which uses the ‘total force’, while the other uses the ‘vortex force’, which is related only to the dynamics of vorticity. The first mode transition involves a jump in ‘vortex phase’ (between vortex force and displacement), ϕvortex, at which point the frequency of oscillation (f) passes through the natural frequency of the system in the fluid, f ∼ fNwater. This transition is associated with a jump between 2S [harr ] 2P vortex wake modes, and a corresponding switch in vortex shedding timing. Across the second mode transition, there is a jump in ‘total phase’, phis;total , at which point f ∼ fNvacuum. In this case, there is no jump in ϕvortex, since both branches are associated with the 2P mode, and there is therefore no switch in timing of shedding, contrary to previous assumptions. Interestingly, for the high-(m*ζ) case, the vibration frequency jumps across both fNwater and fNvacuum, corresponding to the simultaneous jumps in ϕvortex and ϕtotal. This causes a switch in the timing of shedding, coincident with the ‘total phase’ jump, in agreement with previous assumptions.For large mass ratios, m* = O(100), the vibration frequency for synchronization lies close to the natural frequency (f* = f/fN ≈ 1.0), but as mass is reduced to m* = O(1), f* can reach remarkably large values. We deduce an expression for the frequency of the lower-branch vibration, as follows:formula herewhich agrees very well with a wide set of experimental data. This frequency equation uncovers the existence of a critical mass ratio, where the frequency f* becomes large: m*crit = 0.54. When m* < m*crit, the lower branch can never be reached and it ceases to exist. The upper-branch large-amplitude vibrations persist for all velocities, no matter how high, and the frequency increases indefinitely with flow velocity. Experiments at m* < m*crit show that the upper-branch vibrations continue to the limits (in flow speed) of our facility.

Detection of bridge tap using frequency domain analysis

Abstract: A method for detecting the presence of a bridge tap and other types of fault in a transmission line. Initially, test signals of predetermined frequencies are transmitted into a transmitting end of the transmission line. The test signals are received at a receiving end of the transmission line and the amplitudes of the received signal are measured. A frequency response of the transmission line is computed based on the measured amplitudes. The frequency response is then analyzed for the presence of a frequency-domain signature that corresponds to one of the detectable types of fault. The presence of a bridge tap or another type of fault is identified based on the detected frequency-domain signature. The frequency-domain signature associated with a bridge tap can comprise a set of one or more attenuation dips in the frequency response, with each attenuation dip corresponding to a local minima in the frequency response. The length of the bridge tap can be estimated based on a fundamental frequency of the set of harmonically related attenuation dips. Also, the location of the bridge tap in the transmission line can be estimated by performing a time domain reflectometer (TDR) test.

An Integrated Health Monitoring Technique Using Structural Impedance Sensors

Abstract: This paper presents an integrated methodology to detect and locate structural damage. Two different damage detection schemes are combined in this methodology, which involves utilizing the electromechanical coupling property of piezoelectric materials and tracking the changes in the frequency response function data, respectively. Physical changes in the structure cause changes in mechanical impedance. Due to the electromechanical coupling in piezoelectric materials, this change in structural mechanical impedance causes a change in the electrical impedance of the piezoelectric sensor. Hence, by monitoring the electrical impedance one can qualitatively determine when structural damage has occurred or is imminent. Based on the fact that damage produces local dynamic changes, this technique utilizes a high frequency structural excitation (typically greater than 30 kHz) through the surface-bonded piezoelectric sensor/actuators. As a second step, a newly developed model-based technique, using a wave propagation ...

A Frequency and Curvature Based Experimental Method for Locating Damage in Structures

Abstract: This paper presents a method for locating structural damage using experimental vibration data. The method uses measured frequency response functions to obtain displacement as a function of frequency. The displacement functions are converted to curvature functions, which are further processed to yield a damage index, displayed on a plot of position versus frequency. The method can be applied when there is no a priori knowledge about the undamaged structure, and it is suitable for automation. This paper details the theory of the broadband method, and the results of an experimental demonstration in which a steel beam was damaged with a narrow slot. It is shown that this proposed damage detection method is highly sensitive, and can locate a very small amount of damage. For example, the narrow slot was correctly located when there was only a 0.8 percent reduction in thickness in the beam. Traditionally, damage causes a change in natural frequencies, but at this small level of damage the frequency changes were within experimental error. Other published methods failed to locate the slot until it was significantly deeper.

Method and device for multi-user channel estimation

Abstract: The invention computes frequency-domain channel gains by compiling a set of estimated channel gains as a function of pilot sequences, a set of analytical channel gains variables, and a set of weighting coefficients variables. A plurality of weighting coefficients are computed as a function of time and frequency correlation functions, a noise correlation matrix, and pilot sequences. A weighting matrix is computed from the weighting coefficients. After receiving a training sequence from at least one transmitter, a received data matrix is computed from the training sequence. The weighting matrix and the received data matrix are used to compute the frequency-domain channel gains. The invention also provides a method for reducing the computational complexity of estimating the time and frequency response of at least one desired signal received by at least one antenna. Also, the time and frequency response of at least one desired signal received by at least one antenna can be both interpolated and predicted with the present invention.

Modeling and transient simulation of planes in electronic packages

Abstract: This paper presents a modeling and simulation approach for ground/power planes in high speed packages. A plane pair structure is first characterized in terms of its impedance (Z) matrix at arbitrary port locations in the frequency domain. This solution is then extended for multiple plane pairs under the assumption that skin effect is prominent at higher frequencies causing isolation between the layers. Since the solutions are in analytical form, the frequency and transient response can be computed efficiently requiring small computational time. To develop spice models, equivalent circuits are constructed using resonator models with passive elements using model order reduction methods. This paper also discusses a method for incorporating decoupling capacitors into the plane models. The simulation results show good correlation with measured data.

Monolithically integrated resonator microoptic gyro on silica planar lightwave circuit

Abstract: We report a novel configuration of resonator microoptic gyro (MOG), which is monolithically integrated on silica planar lightwave circuit (PLC) with countermeasures for noise factors. Optical ring-resonator gyros suffer mainly from polarization fluctuation induced noise and backscattering induced noise. We discuss eigenstate of polarization in the waveguide to clarify behavior of the former and propose a countermeasure with control of the waveguide birefringence. As for the latter, binary phase shift keying (B-PSK) with a special signal processing is proposed. Thermooptic (TO) phase modulation is the only one scheme to apply B-PSK in the silica waveguide, whose bandwidth is limited to /spl sim/1 KHz. To utilize the narrow bandwidth of the TO modulator effectively, we propose an electrical signal processing scheme and a modulation waveform to compensate the frequency response. By constructing an experimental setup, suppression of the backscattering induced noise is demonstrated, and the gyro output is observed with applying an equivalent rotation.

Biomedical Signal Processing and Signal Modeling

Abstract: The Nature of Biomedical Signals. Memory and Correlation. The Impulse Response. Frequency Response. Modeling Continuous-Time Signals as Sums of Sine Waves. Responses of Linear Continuous-Time Filters to Arbitrary Inputs. Modeling Signals as Sums of Discrete-Time Sine Waves. Noise Removal and Signal Compensation. Modeling Stochastic Signals as Filtered White Noise. Scaling and Long-Term Memory. Nonlinear Models of Signals. Assessing Stationarity and Reproducibility. Appendix.

Filter structures for integrated circuit interfaces

Abstract: A method of optimizing the frequency response of an interconnect system of the type which conveys high frequency signals between bond pads of separate integrated circuits (ICs) mounted on a printed circuit board (PCB) through inductive conductors, such as bond wires and package legs, and a trace on the surface of the PCB. To improve the interconnect system, capacitance is added to the trace and inductance is added to the conductors, with the added trace capacitance and conductor inductance being appropriately sized relative to one another and to various other interconnect system impedances to optimize the interconnect system impedance matching frequency response.

Evaluation of an algorithm for the assessment of the MTF using an edge method.

Abstract: An algorithm to calculate the presampling modulation transfer function (MTF) of an imaging system from an angled edge image has its own inherent transfer function. Factors such as the angle of the sampling aperture to the edge, registration of edge function profiles using the determined edge angle, differentiation, smoothing, and folding all combine to produce the frequency response of the algorithm. In this work, the profile registration transfer function accounting for an error in the determined edge angle has been derived. This has been incorporated with other, previously reported, algorithm component transfer functions to fully characterize the MTF calculation algorithm. When registering profiles, small errors in the edge angle determination were found to result in large errors in the MTF, as the misalignment errors increase with the number of profiles. For example, registering 50 profiles a 0.07 degree error in a 7 degree edge angle (1% error) produces a 36% error in the MTF at the system cutoff frequency f=f(c) when profiles are oversampled at a frequency f(s)=8f(c)(f(c) is defined as the maximum frequency reproducible without aliasing when sampling at the limiting system Nyquist frequency f(s) = 2f(c)). These results highlight the importance of quantifying the transfer function of the algorithm used to determine an imaging system modulation transfer function. The MTF calculation algorithm and the transfer function analysis have been incorporated into a Windows-based software program to be made available for general use.

High bandwidth passive integrated circuit tester probe card assembly

Abstract: Described herein is a probe card assembly providing signal paths for conveying high frequency signals between bond pads of an integrated circuit (IC) and an IC tester. The frequency response of the probe card assembly is optimized by appropriately distributing, adjusting and impedance matching resistive, capacitive and inductive impedance values along the signal paths so that the interconnect system behaves as an appropriately tuned Butterworth or Chebyshev filter.

High-performance microwave transversal filter using fiber Bragg grating arrays

Abstract: Measured results from a microwave photonic traversal filter exploiting fiber Bragg grating (FBG) arrays and achieving a high-performance tunable bandpass microwave response are presented. Tuning is affected by changing the optical carrier wavelength to select the operating gratings, and the high-quality frequency response is obtained by weighting the reflections of the gratings. This experiment demonstrates that sophisticated passive signal processing functionality can be achieved practically using FBGs.

Characteristics of the Vold-Kalman order tracking filter

Abstract: The filter characteristics of the Vold-Kalman (1993, 1960, 1961) order tracking filter are presented. Both the frequency response as well as the time response and their time-frequency relationship have been investigated for different filter types and guidelines for optimum choice of filter parameters are presented. The Vold-Kalman filter allows for the high performance simultaneous tracking of orders in systems with multiple independent shafts. With this new filter and using multiple tacho references, waveforms, as well as amplitude and phase may be extracted without the beating interactions that are associated with conventional methods. Orders extracted as waveforms have no phase bias, and may hence be used for playback, synthesis and tailoring.

Wideband, minimum-rating filters and multicouplers for power amplifiers

Abstract: A method and a circuit for power amplification over a wide frequency range based upon the use of minimum-rating filters or matching networks, negative-component signal processing, and single or multiple amplifiers. The filters and matching networks are preferably designed to minimize the required ratings of the amplifier(s) driving them. The signal processor or generator preferably uses negative components to produces a driving signal that is compensated for the ripple in the filter, matching network, and load. The outputs of multiple amplifiers optimized for different frequency ranges can be combined into a single load with flat frequency response, resistive loads presented to the amplifiers, and no inherent power loss in the combining network.

On the performance of HTS microstrip quasi-elliptic function filters for mobile communications application

Abstract: The low-loss and high-selective high-temperature superconducting (HTS) bandpass filters can enhance performance of mobile communications systems. In this paper, we summarize a recent progress of novel HTS preselect bandpass filters that have been developed for a European research project. The objective of the project is to construct an HTS-based transceiver for mast-mounted DCS1800 base stations. The HTS preselect receive filters have been designed to have a quasi-elliptic function response in order to provide low insertion loss and very steep rolloff at the filter band edges. The filters cover a 15-MHz sub-band of a receive band, which ranges from 1710 to 1785 MHz. The filters have been fabricated using double-sided YBCO thin films on 03-mm-thick MgO or 0.5-mm-thick LAO substrates. The latest experimental results of the filters, including those encapsulated with a low-noise amplifier in an RF module are presented, showing very promising performance. The issues associated with asymmetric frequency response are investigated to improve the filter performance.

A linearized electrohydraulic servovalve model for valve dynamics sensitivity analysis and control system design

Abstract: This paper presents the derivation of a linearized model for flapper-nozzle type two-stage electrohydraulic servovalves from the nonlinear state equations The coefficients of the linearized model are derived in terms of the valve physical parameters and fluid properties explicitly, and are useful for valve design and sensitivity analysis When using this model structure to fit experimental frequency response data, the results render closer agreement than when using existing low order linear models This model also suggests important servovalve dynamic properties such as the nonminimum phase zero and the transfer function relative degree, and how they relate to the valve component arrangement Because of the small modeling errors over a wide frequency range, a high bandwidth control system can be designed A robust performance controller is designed and implemented to demonstrate the utility of the model

Classical feedback control with MATLAB

Abstract: Feedback and sensitivity feedforward, multiloop and MIMO systems frequency response methods shaping the loop frequency response compensator design analog controller implementation linear links and system simulation introduction to alternative methods of controller design adaptive systems provision of global stability describing functions process instability multi-window compensators appendices - feedback control, elementary treatment, frequency responses, causal systems, passive systems and positive real functions, derivation of bode integrals, programme for phase calculation, generic single-loop feedback system, effect of feedback on mobility, derivation, dependence of a function on a parameter, balanced bridge feedback, phase-gain relation for describing functions, discussions, design sequence, examples, bode step toolbox.

A computationally efficient frequency-domain LMS algorithm with constraints on the adaptive filter

Abstract: The frequency domain implementation of the LMS algorithm is attractive due to both the reduced computational complexity and the potential of faster convergence compared with the time domain implementation. Another advantage is the potential of using frequency-domain constraints on the adaptive filter, such as limiting its magnitude response or limiting the power of its output signal. This paper presents a computationally efficient algorithm that allows the incorporation of various frequency domain constraints into the LMS algorithm. A penalty function formulation is used with a steepest descent search to adapt the filter so that it converges to the new constrained minimum. The formulation of the algorithm is derived first, after which the use of some practical constraints with this algorithm and a simulation example for adaptive blind equalization are described.

The frequency response of magnetoelastic sensors to stress and atmospheric pressure

Abstract: Earlier work demonstrated that the characteristic resonant frequency of magnetoelastic thick-film sensors shifts linearly downwards in response to increasing atmospheric pressure. In this paper, the response mechanism is detailed and shown to be a function of both pressure and the way that the sensor is mechanically stressed. Stressing the sensor, in either the elastic or plastic regime, induces out-of-plane vibrations that act as a pressure-dependent damping force to the longitudinal sensor oscillations excited by the interrogation field. This damping force, in turn, acts to shift the resonant frequency of the magnetoelastic sensor lower in response to increasing pressure.

A discrete multitone power line communications system

Abstract: In-building power lines have been considered as a medium for high speed data transmission for applications like home networking and Internet access. Frequency selectivity and time variation of this medium in addition to the high level of narrow-band and impulsive interference makes multi-carrier modulation, and especially its popular variant discrete multitone (DMT), an attractive modulation candidate for this application. This paper presents the results of our measurements of the high frequency characteristics of ordinary in-building power lines, as well as simulation results of a DMT transceiver system in an in-building power line environment.

Magnetic and acoustic tapping mode microscopy of liquid phase phospholipid bilayers and DNA molecules

Abstract: We have constructed a fluid cell for an atomic force microscope that operates in tapping mode using either an oscillating piezo or magnetic drive. This fluid cell allows direct comparison of the image quality using the two drive mechanisms over identical areas of a sample without fluid or cantilever exchange. We found that the magnetically driven cantilever’s tuning curve was very similar to the thermal noise power spectrum, allowing an accurate determination of the cantilever resonance frequency. This is in contrast to the piezo driven tuning curve, which contained a number of peaks that appeared to be a convolution of the true cantilever resonance with the complicated acoustic spectrum of the fluid cell. We imaged two biologically relevant samples: DNA molecules and liquid phase phospholipid bilayers. For both samples, we found that the image quality, as measured by feature height, lateral resolution, and image stability, was independent of the drive method. This suggests that, despite the apparent differences in the frequency response, the physical motion of the cantilever tip, when it is driven near its resonance frequency, is the same for both driving mechanisms.

Computer-aided small-signal analysis based on impulse response of DC/DC switching power converters

Abstract: The paper describes a method for automated small-signal frequency response analysis based on transient response obtained using a general-purpose simulation tool such as simulation program with integrated circuit emphasis (SPICE). The method is based on using the simulation tool to evaluate the converter impulse response. The main advantage of the proposed method as a design verification tool is that frequency responses can be generated efficiently for any converter configuration and any model complexity supported by the general-purpose simulator. Application examples are included to demonstrate very good correlation between the generated responses and experimental data, and to compare the results with predictions of approximate analytical methods. In particular, the method is applied to investigate high-frequency dynamics of pulse width modulation (PWM) converters operating in discontinuous conduction mode, and the results are used to compare and validate several existing analytical modeling approaches.