Showing papers on "Frequency response published in 1986"

Frequency response corrections for eddy correlation systems

Abstract: Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's ‘Hydra’ eddy correlation system. The results show that flux loss from such a system is typically 5 to 10% for sensible and latent heat flux, but can be much larger for momentum flux and variance measurements in certain conditions. A microcomputer program is included which, with little modification, can be used for estimating flux loss from other eddy correlation systems with different or additional sensors.

Adaptive microphone-array system for noise reduction

Abstract: This paper introduces a new adaptive microphone-array system for noise reduction (AMNOR system). It is first shown that there exists a tradeoff relationship between reducing the output noise power and reducing the frequency response degradation of a microphone-array to a desired signal. It is then shown that this tradeoff can be controlled by the introduction of a fictitious desired signal. A new optimization criterion is presented which minimizes the output noise power while maintaining the frequency response degradation below some pre-determined value (AMNOR criterion). AMNOR determines an optimal noise reduction filter based on this criterion by controlling the tradeoff utilizing the fictitious desired signal. Experiments on noise reduction processing were carried out in a room with a 0.4-s reverberation time. The superiority of the AMNOR criterion over conventional LMS and constrained LMS criteria for reducing noise in speech signals was confirmed in subjective preference tests. The AMNOR system improved the SNR by more than 15 dB in the 300-3200 Hz range.

Fast Maximnurm Likelihood Joint Estimation of Frequency and Frequency Rate

Abstract: A fast maximum likelihood algorithm is presented that jointly estimates the frequency and frequency rate of a sinusoid corrupted by additive Gaussian white noise It consists of a coarse search and a fine search First the two-dimensional frequency-frequency rate plane is subdivided into parallelograms whose size depends on the region of convergence of Newton's method used in maximizing the log-likelihood function (LLF) The size of the parallelogram is explicitly computed and is optimal for the method used The coarse search consists of maximizing the LLF over the vertices of the parallelograms Then starting at the vertex where the LLF attained its maximum, a two-dimensional Newton's method to find the absolute maximum of the LLF is implemented This last step consists of the fine search The rate of convergence of Newton's method is cubic, and is extremely fast Furthermore Newton's method will converge after two iterations when the starting point used in the method lies within 75 percent of the distances defined by the parallelogram of convergence whose center coincides with the true values of frequency and frequency rate In this case, the root mean square error (RMSEs) for frequency and frequency rate are practically equal to the Cramer-Rao bound at all signal-to-noise ratio (SNR)?15 dB The frequency-frequency rate ambiguity function is shown to be even and its periodicities are extracted

Feedback Control Systems

Abstract: Introduction and Linearized Dynamic Models Transfer Function Models of Physical Systems Modeling of Feedback Systems and Controllers The Performance of Feedback Systems Introduction to Feedback System Design The Root Locus Method Frequency Response Analysis Frequency Response Design Digital Control Systems Digital Control System Analysis and Design State-Space Analysis Introduction to State-Space Design Multivariable Systems in the Frequency Domain Nonlinear Control Systems Appendix A: Vectors, Matrices, and Determinants Appendix B: Computer Aids for Analysis and Design References Index

Efficient Eigenvalue and Frequency Response Methods Applied to Power System Small-Signal Stability Studies

Abstract: Frequency response and eigenvalue techniques are fundamental tools in the analysis of small signal stability of multimachine power systems. This paper describes two highly efficient algorithms which are expected to enhance the practical application of these techniques. One algorithm calculates exact eigenvalues and eigenvectors for a large power system, while the other produces the frequency response of the transfer functions between any two variables in the system. This paper also presents alternative computing procedures for the AESOPS eigenvalue estimation algorithm which are simpler and at least as efficient as those described in [1].

A high-frequency CMOS linear transconductance element

Abstract: A simple four-transistor, linear, tunable, high-frequency transconductance element is described. By using a pair of composite n -channel- p -channel devices, the circuit achieves its linearity by current differencing without undue matching requirements. It is shown that linearity and frequency response can be optimized simultaneously by appropriate choice of device dimensions. The performance is verified by SPICE simulations, and an operational transconductance amplifier (OTA) is used as one example for the many applications of the proposed element.

C. W. laser wavemeter/frequency locking technique

Abstract: A wavemeter/frequency locking technique suitable for indirectly locking an optical frequency f 0 to a radio frequency f 1 or for locking the radio frequency to the optical frequency. A beam of optical frequency f 0 is phase modulated by a signal of average frequency f 1 that is itself modulated at frequency f 2 . The modulated beam is passed through a filter to a detector to produce a detector output signal that has components at linear integral sums of f 1 and f 2 . A pair of control signals are generated that are proportional to the amplitude of two of the components of the detector output signal. These control signals are separately used in a pair of servo loops to separately establish fixed values of f 0 /f f and f 1 /f f , where f f is a characteristic frequency of the filter. A method is presented for stepping the value of f 0 /f f to another value and measuring f 1 /f 2 at each of these values, thereby enabling the value of f 0 to be determined.

Pitch detection using the short-term phase spectrum

Abstract: A new frequency domain method for determining the fundamental frequency of speech is presented in this paper. This method uses the information contained in the short-term phase spectral whereas the previous methods were limited to the amplitude spectrum. The short-term spectrum is computed by DFT and it is interpreted as the output of a bank of band-pass overlapping filters. Harmonic components are detected by searching for sets of three contiguous filters having the same instantaneous frequency. The frequency of a detected harmonic is given by the instantaneous frequency itself. A conventional harmonic numbering algorithm is used to convert the set of detected harmonics to a value of the fundamental frequency. Preliminary results show the validity of the method.

Dispersion of Transient Signals in Microstrip Transmission Lines

Abstract: The distortion of an electrical pulse caused by dispersion as it propagates along a microstrip line is investigated. A model for dispersion of the phase constant is selected to meet the frequency, accnracy, and microstrip parametric requirements. Numerical integration and Taylor series expansion approximation techniques are used to compute the shape of dc dispersed pulses having square and Gaussian envelope shapes. Taylor series expansion methods are more convenient for the analysis of RF pulses.

Centralized control receiver

Abstract: Centralized control receiver for power distribution networks, includes an input section containing at least one digital filter, an evaluating device, and an output section, the digital filter having a frequency response effecting selective damping of harmonic frequencies of at least one of the frequency of a respective network and control frequencies of at least one of adjacent centralized control services and of network-specific interference frequency ranges.

Characterisation of frequency response of 1.5 μm InGaAsP DFB laser diode and InGaAs PIN photodiode by heterodyne measurement technique

Abstract: The frequency response of an InGaAs PIN photodiode and the ratio of the frequency modulation (FM) index to the intensity modulation (IM) index of a 1.5 μm InGaAsP vapour-phase-transported DFB laser diode have been measured by an optical heterodyne measurement technique. From the response of the photodiode to the laser radiation beat frequency, a 20 GHz detector bandwidth is determined. The ratio of the FM and IM indices at 3 mW laser output power per facet decreases from 60 at 100 MHz modulation frequency to 3.3 above 2 GHz.

Low Frequency Characterization of PWM Converters

Abstract: Low frequency components of states or outputs in pulse-width modulation (PWM) dc and ac converters can be characterized by differential equations called describing state-space equations. These equations are derived by inspection of converter topology and use of switching functions and duty ratios. Their steady-state and small-signal dynamic solutions show how energy-storage elements in a converter/load system shape the frequency response of conversion functions established by the switches.

Analysis of coefficient quantization errors in state-space digital filters

Abstract: In this paper, we examine the sensitivity of state-space digital filters to coefficient quantization errors. A cost function using an L p norm criteria is used to measure the deviation in frequency response of the filter. The cost function is used to indicate the connection between roundoff noise and filter sensitivity to coefficient quantization errors. Then based on this cost function it is shown that low roundoff noise state-space digital filters, filters in balanced coordinates, and filters based on polynomials orthogonal on the unit circle have low sensitivity to coefficient quantization errors. Furthermore, the sensitivity of the filters is shown to depend on the second-order modes thereby exhibiting certain robustness and immunity to filter bandwidth.

Small-Signal Frequency Response Theory for piecewise-constant two-switched-network dc-to-dc converter systems

Abstract: Small-Signal Frequency Response Theory is a theory for calculating the output spectrum of ideal dc-to-dc converter systems, i.e. systems with system coefficients piecewise constant in time, for a given spectrum of the signal injected into the control-input, in the small-signal limit. This theory, unlike other methods, can be applied to both resonant and PWM converters, and gives analytic results in closed form for ideal converters. This paper discusses the special case of ideal two-switched-network converter systems in PWM, programmed, and bang-bang operation. For the examples under study, theoretical prediction and experimental results are found to differ by at most 2dB in amplitude and 10 degrees in phase at most frequencies up to three times the switching frequency. Examples are given in this paper for which the theory gives the correct prediction, while other methods fail.

On digital smoothing filters: a brief review of closed form solutions and two new filter approaches

Abstract: The concept of smoothing noisy data using appropriate polynomials turns out to be equivalent to the application of suitable nonrecursive digital filters having the following properties: They process the data in such a way that the moments are conserved up to a desired order while the energy of their impulse response is minimum. Flatness constraints of their frequency response at Ω=0 are equivalent to the moment condition. By using orthogonal polynomials, an explicit solution is known from the literature. A second approach which uses a special decomposition also yields closed form solutions. The realization is simplified, especially in the case where a large number of moments is supposed to be conserved.

Measured Lateral Response of Mass on Single Pile in Clay

Abstract: The results of dynamic lateral load tests on a cantilevered mass supported by a single 10.75-in. (273-mm) diameter steel pipe pile embedded in stiff, overconsolidated clay are presented. These tests were conducted to provide a basis for evaluation of mathematical models that predict the relatively low-frequency dynamic pile response that is representative of systems in which the primary resonance frequency is controlled by the mass and stiffness of the superstructure. Frequency sweep shear forcing functions were applied at the top of the mass, which simulated a simple structure. The responses of the pile-supported mass, points on the embedded pile, and points in the supporting soil were recorded to determine frequency response functions. Frequency response functions between the applied load and pile cap-mass were then examined to aid in the identification of the pile–soil system parameters which most strongly influence response. The measured pile cap frequency response function peak amplitude was 0.0022 in./lb (0.0126 mm/N), or about ten times the static flexibility, and the resonance frequency was approximately 2.2 Hz.

A.F.C. system for broad-band FM receiver

Abstract: An A.F.C. control system for reception of wide-band F.M. transmission such as satellite transmissions, in which a center frequency of an F.M. I.F. signal is repetitively and alternately compared with an upper and a lower frequency limit value so long as the center frequency lies between these values, with the results of the comparisons being respectively stored in two latch memories (28, 29), whose contents thereby indicate any error of the center frequency relative to the frequency limits. Any departure of the center frequency from between the limits is corrected by successive frequency shifts of the local oscillator (4) frequency, with the results of correction being indicated by the latch memory contents and with the number of frequency shifts being determined accordingly.

Properties of the feedback system controlling the coxa-trochanter joint in the stick insect carausius morosus

Abstract: The angle of the coxa-trochanter (C-T) joint in the stick insect Carausius morosus is controlled by a negative feedback mechanism. It is shown that the trochanteral hair plate alone functions as the feedback transducer and that the rhomboid hair plate is not involved in the feedback loop. The properties of the C-T control system were investigated by means of force measurements. The results cannot be adequately described in all details by either a fractional differentiator model, a model which fits many sensory systems, or a nonlinear bandpass filter, a model which fits the force response of the femur-tibia feedback loop. The fractional differentiator model adequately describes the frequency response of the open-loop system to sinusoidal stimulation with 34 deg stimulus amplitude. However, the responses to sinusoidal and steplike stimulation with 10 deg stimulus amplitude do not fit this model. They are better described by the model of a nonlinear bandpass filter. The possible contribution of mechanical properties of the musculature and the joint to the total force response is discussed. It is suggested that cocontractions occurring at higher stimulus frequencies alters the muscle properties and enables the animal to respond to stimulus frequencies above the upper corner frequency of the active feedback loop.

Frequency response of an InGaAsP vapor phase regrown buried heterostructure laser with 18 GHz bandwidth

Abstract: The frequency response of a 1.3‐μm InGaAsP vapor phase regrown buried heterostructure laser with an 18‐GHz cw bandwidth is analyzed in detail. The intrinsic bandwidth of the device is shown to be 22 GHz and the 3‐dB RC roll‐off frequency due to electrical parasitics is found to be 10 GHz.

Design of an active flutter suppression system

Abstract: An active control law is synthesized for the suppression of wing flutter for a mathematical model of a flight test vehicle. Eigenvalue placement is used to synthesize a full state controller that satisfies performance specifications on control surf ace activity and that exhibits excellent gain and phase margins. A simple frequency response matching technique is used to design a realizable compensator which approximates the feedback properties of the full state controller. The performance of the control system using this compensator is evaluated at various flight conditions and found to be satisfactory. In addition, eigenvector shaping is used to enhance the gust load alleviation capabilities of the flutter control system.

Frequency modulated (FM) time delay photoacoustic and photothermal wave spectroscopies. Technique, instrumentation, and detection. Part III: Mirage effect spectrometer, dynamic range, and comparison to pseudo‐random‐binary‐sequence (PRBS) method

Abstract: A detailed comparison is presented between the time delay and the pseudo‐random‐binary‐sequence (PRBS) methods of excitation and mirage effect response. Both time delay domain dynamic system response and frequency domain spectral functions were calculated via FFT methods. The results show that the FM time delay spectrometer exhibits superior performance to the PRBS device and is optimally suitable for nondestructive and depth‐profiling studies. The detailed examination of, and comparison between, the time delay and spectral dynamic functions of our FM time delay photothermal wave spectrometer and those of a PRBS‐driven device has proven that the former apparatus is capable of producing superior quality time delay and spectral function information when tested on a fast, flat frequency response mirage effect system. The FM time delay photoacoustic/photothermal wave technique and instrumentation of this work holds excellent promise for nondestructive evaluation and depth‐profiling applications in scientific ...

Analysis and optimization of integrated-optic travelling-wave modulators using periodic and non-periodic phase reversals

Abstract: An analysis is given of phase-reversal electrode structures used for phase matching in travelling-wave integrated-optic phase modulators. Both modulus and argument of the phase shift are obtained; both are required for applications involving broadband excitation. Periodic and non-periodic lossy structures are treated and the advantage of non-periodic structures for wide-band operation is demonstrated. Optimum structure arrangements and upper bounds to phase shift and figure of merit are derived.

Time and frequency response of the conventional avalanche photodiode

Abstract: An analytical expression for the time course of the average impulse response function for a conventional avalanche photodiode is derived. Delta-function absorption of a single photocarrier and single-carrier-initiated/single-carrier multiplication conditions are assumed. The result is obtained as a limiting case of a previously derived equation for the staircase avalanche photodiode. The initial exponential growth of the curves is shown to represent electron and hole contributions arising from multiplication in the avalanche region whereas the subsequent exponential decay arises from residual holes transiting backward across the multiplication region. The associated frequency response function is obtained by Fourier transformation. The analytical results are shown to be in good accord with average impulse response functions obtained by Riad and Hayes by means of simulation from the transport equations. The results should also apply to the channeling avalanche photodiode and to related structures in which the carriers are spatially separated and the multiplication is essentially single-carrier like.

Laser stabilization servo system

Abstract: A method and means for stabilizing the difference in frequencies between the frequency components of a two frequency laser beam influenced by Zeeman effect frequency splitting, accurately determines the frequency separation independently of the individual frequencies or intensities of either of the frequency components. Frequency stabilization is accomplished by mechanical and thermal adjustments to the lasing chamber length of the laser by a closed loop servo control referencing the frequency difference between laser beam components and a reference signal having a frequency equal to the desired frequency difference.