Showing papers on "Frequency response published in 2003"
TL;DR: In this article, a nonlinear model is used to account for the midplane stretching, a DC electrostatic force, and an ACharmonic force in the response of a resonant microbeam to an electric actuation.
Abstract: An investigation into the response of a resonant microbeam to anelectric actuation is presented. A nonlinear model is used to accountfor the mid-plane stretching, a DC electrostatic force, and an ACharmonic force. Design parameters are included in the model by lumpingthem into nondimensional parameters. A perturbation method, the methodof multiple scales, is used to obtain two first-order nonlinearordinary-differential equations that describe the modulation of theamplitude and phase of the response and its stability. The model and theresults obtained by the perturbation analysis are validated by comparingthem with published experimental results. The case of three-to-oneinternal resonance is treated. The effect of the design parameters on the dynamic responses isdiscussed. The results show that increasing the axial force improves thelinear characteristics of the resonance frequency and decreases theundesirable frequency shift produced by the nonlinearities. In contrast,increasing the mid-plane stretching has the reverse effect. Moreover,the DC electrostatic load is found to affect the qualitative andquantitative nature of the frequency-response curves, resulting ineither a softening or a hardening behavior. The results also show thatan inaccurate representation of the system nonlinearities may lead to anerroneous prediction of the frequency response.
452 citations
TL;DR: In this paper, two sets of aluminum beams were used for this experimental study each set consisted of seven beams, the first set had fixed ends, and the second set was simply supported Cracks were initiated at seven different locations from one end to the other end (along the length of the beam) for each set, with crack depth ratios ranging from 01 d to 07 d (d is the beam depth) in steps of 01, at each crack location.
282 citations
TL;DR: In this paper, a lumped element model of a piezoelectric-driven synthetic jet actuator is presented, where the individual components of a synthetic jet are modeled as elements of an equivalent electrical circuit using conjugate power variables.
Abstract: : This paper presents a lumped element model of a piezoelectric-driven synthetic jet actuator. A synthetic jet, also known as a zero net mass-flux device, uses a vibrating diaphragm to generate an oscillatory flow through a small orifice or slot. In lumped element modeling (LEM), the individual components of a synthetic jet are modeled as elements of an equivalent electrical circuit using conjugate power variables. The frequency response function of the circuit is derived to obtain an expression for Q(sub out)/V(sub AC), the volume flow rate per applied voltage. The circuit is analyzed to provide physical insight into the dependence of the device behavior on geometry and material properties. Methods to estimate the model parameters are discussed, and experimental verification is presented. In addition, the model is used to estimate the performance of two prototypical synthetic jets, and the results are compared with experiment.
279 citations
TL;DR: In this paper, a series of numerical simulations on a simple beam are made in order to compare various damage detection methods based on mode shape changes and a generalisation of these methods to the whole frequency ranges of measurement is proposed.
275 citations
TL;DR: In this article, the time and frequency response characteristics of two-arm micromachined thermal actuators were examined and the thermal time constants and frequency responses were measured experimentally and compared to analytical predictions.
Abstract: This paper examines the time and frequency response characteristics of two-arm micromachined thermal actuators. Two types of thermal actuators are considered: hot/cold arm actuators and 'V' or 'chevron' shaped actuators. A heat transfer equation governing the temperature profile along the thermal actuators is derived. Equations for the thermal time constants and the frequency responses are presented. The thermal time constants and frequency responses are measured experimentally and compared to analytical predictions.
216 citations
TL;DR: In this article, the authors measured the impedance of transformer windings over a wide frequency range and compared the results with reference data using a network analyzer to sweep the frequency range, make the measurements, and analyze the results.
Abstract: This technique measures the impedance of transformer windings over a wide frequency range and compares the results with reference data The author used a network analyzer to sweep the frequency range, make the measurements, and analyze the results
202 citations
TL;DR: In this article, an injection-locked uncooled tunable vertical cavity surface emitting laser (VCSEL) was shown to have a reasonable modulation performance in a wide abient temperature range.
Abstract: Injection locking has been actively researched for its possibility to improve laser performance for both digital and analog applications. When a modulated follower laser (also termed "slave" laser) is locked to the master laser, its nonlinear distortion and frequency chirp may be reduced. As well, the resonance frequency can increase to several times higher than its free running case. In this paper, we show that the frequency response (S21) of an injection-locked laser is similar to a parasitic-limited laser with a high resonance frequency. The S21 was studied experimentally and the condition to achieve a flat, enhanced frequency response was identified. For analog applications, a record 112 dB-Hz/sup 2/3/, single-tone third harmonic spur-free dynamic range of a 1.55-/spl mu/m vertical cavity surface emitting lasers (VCSEL) was demonstrated. An improvement was attained for a wide-injection parameter space. In a 50-km 2.5-Gb/s digital link, a 2-dB power penalty reduction at 10/sup -9/ bit error rate was also demonstrated. As a novel application, an injection-locked uncooled tunable VCSEL was shown to have a reasonable modulation performance in a wide abient temperature range. The VCSEL was locked to a designated wavelength and the injection compensated the temperature-induced performance degradation. This concept can be extremely attractive for low-cost dense wavelength division muliplexed transmitters.
179 citations
TL;DR: In this paper, a frequency domain approach was proposed to identify the Hammerstein model in the frequency domain using sampled input-output data, and its convergence was shown for both the linear and nonlinear subsystems in the presence of noise.
Abstract: Discusses Hammerstein model identification in the frequency domain using sampled input-output data. By exploring the fundamental frequency and harmonics generated by the unknown nonlinearity, we propose a frequency domain approach and show its convergence for both the linear and nonlinear subsystems in the presence of noise. No a priori knowledge of the structure of the nonlinearity is required and the linear part can be nonparametric.
135 citations
TL;DR: In this article, the response of a microbeam-based resonant sensor to superharmonic and subharmonic electric actuations using a model that incorporates the nonlinearities associated with moderately large displacements and electric forces is investigated.
Abstract: We investigate the response of a microbeam-based resonant sensor to superharmonic and subharmonic electric actuations using a model that incorporates the nonlinearities associated with moderately large displacements and electric forces. The method of multiple scales is used, in each case, to obtain two first-order nonlinear ordinary-differential equations that describe the modulation of the amplitude and phase of the response and its stability. We present typical frequency–response and force–response curves demonstrating, in both cases, the coexistence of multivalued solutions. The solution corresponding to a superharmonic excitation consists of three branches, which meet at two saddle-node bifurcation points. The solution corresponding to a subharmonic excitation consists of two branches meeting a branch of trivial solutions at two pitchfork bifurcation points. One of these bifurcation points is supercritical and the other is subcritical. The results provide an analytical tool to predict the microsensor response to superharmonic and subharmonic excitations, specifically the locations of sudden jumps and regions of hysteretic behavior, thereby enabling designers to safely use these frequencies as measurement signals. They also allow designers to examine the impact of various design parameters on the device behavior.
130 citations
TL;DR: In this article, a new type of measurement microphone that is based on MEMS technology is presented, which is tested on a number of key parameters for measurement microphones: sensitivity, noise level, frequency response, and immunity to disturbing environmental parameters, such as temperature changes, humidity, static pressure variations and vibrations.
Abstract: This paper presents a new type of measurement microphone that is based on MEMS technology. The silicon chip design and fabrication are discussed, as well as the specially developed packaging technology. The microphones are tested on a number of key parameters for measurement microphones: sensitivity, noise level, frequency response, and immunity to disturbing environmental parameters, such as temperature changes, humidity, static pressure variations, and vibration. A sensitivity of 22 mV/Pa (-33 dB re. 1 V/Pa), and a noise level of 23 dB(A) were measured. The noise level is 7 dB lower than state-of-the-art 1/4-inch measurement microphones. A good uniformity on sensitivity and frequency response has been measured. The sensitivity to temperature changes, humidity, static pressure variations and vibrations is fully comparable to the traditional measurement microphones. This paper shows that high-quality measurement microphones can be made using MEMS technology, with a superior noise performance.
121 citations
TL;DR: This work investigates two iterative channel estimators for mobile orthogonal-frequency division multiplexing and finds that the superior iterative estimator is superior and its performance is independent of whether the chosen time-frequency pilot grid satisfies the two-dimensional sampling theorem or not.
Abstract: We investigate two iterative channel estimators for mobile orthogonal-frequency division multiplexing. The first estimator is based on iterative filtering and decoding whereas the second one uses an a posteriori probability (APP) algorithm. The first method consists of two cascaded one-dimensional Wiener filters, which interpolate the unknown time-varying two-dimensional frequency response in between the known pilot symbols. As shown, the performance can be increased by feeding back the likelihood values at the output of the APP-decoder to iteratively compute an improved estimate of the channel frequency response. The second method applies two APP estimators, one for the frequency and the other one for the time direction. The two estimators are embedded in an iterative loop similar to the turbo decoding principle. As shown in detail, this iterative estimator is superior and its performance is independent of whether the chosen time-frequency pilot grid satisfies the two-dimensional sampling theorem or not. The bit-error rate as a function of the signal-to-noise ratio is used as a performance measure. In addition, the convergence of the iterative decoding loop is studied with the extrinsic information transfer chart.
TL;DR: In this article, the authors proposed a novel four-degrees-of-freedom (DOF) nonresonant micromachined gyroscope design concept based on utilizing dynamical amplification both in the 2DOF drive-direction oscillator and the 2-DOF sense direction oscillator to achieve large oscillation amplitudes without resonance.
Abstract: This paper reports a novel four-degrees-of-freedom (DOF) nonresonant micromachined gyroscope design concept that addresses two major MEMS gyroscope design challenges: eliminating the mode-matching requirement and minimizing instability and drift due to mechanical coupling between the drive and sense modes. The proposed approach is based on utilizing dynamical amplification both in the 2-DOF drive-direction oscillator and the 2-DOF sense-direction oscillator, which are structurally decoupled, to achieve large oscillation amplitudes without resonance. The overall 4-DOF dynamical system is composed of three proof masses, where second and third masses form the 2-DOF sense-direction oscillator, and the first mass and the combination of the second and third masses form the 2-DOF drive-direction oscillator. The frequency responses of the drive and sense direction oscillators have two resonant peaks and a flat region between the peaks. The device is nominally operated in the flat regions of the response curves belonging to the drive and sense direction oscillators, where the gain is less sensitive to frequency fluctuations. This is achieved by designing the drive and sense anti-resonance frequencies to match. Consequently, by utilizing dynamical amplification in the decoupled 2-DOF oscillators, increased bandwidth and reduced sensitivity to structural and thermal parameter fluctuations and damping changes are achieved, leading to improved robustness and long-term stability over the operating time of the device.
Patent•
29 Oct 2003TL;DR: In this paper, the frequency response of a wireless channel in an OFDM system is estimated based on a pilot transmission received via the subbands in the first group and an estimate of the impulse response of the wireless channel is then derived based on the initial frequency response estimate.
Abstract: Techniques to estimate the frequency response of a wireless channel in an OFDM system. In one method, an initial estimate of the frequency response of the wireless channel is obtained for a first group of subbands based on a pilot transmission received via the subbands in the first group. An estimate of the impulse response of the wireless channel is then derived based on the initial frequency response estimate. An enhanced estimate of the frequency response of the wireless channel is then derived for a second group of subbands based on the impulse response estimate. The first and second groups may each include all or only a subset of the usable subbands. Subband multiplexing may be used to allow simultaneous pilot transmissions by multiple terminals on their associated groups of subbands.
18 Apr 2003
TL;DR: In this paper, a millimetre wave uni-travelling-carrier photodiode with a monolithically integrated matching (impedance transform) circuit utilising a coplanar-waveguide short stub is presented.
Abstract: The design and characterisation of a millimetre wave uni-travelling-carrier photodiode with a monolithically integrated matching (impedance transform) circuit utilising a coplanar-waveguide short stub are presented. The device with the matching circuit shows about 50% higher efficiency at 100 GHz than the one without it. The frequency response was characterised through time-domain measurement by means of an electro-optic sampling technique. The 1 dB down bandwidth of the device is as wide as 40 GHz, and the frequency response characteristics are in good agreement with circuit model calculations. The maximum saturation output power is 20.8 mW at 100 GHz for a bias voltage of -3 V, which is the highest output power ever generated directly from a photodiode in the W-band.
Patent•
20 May 2003
TL;DR: In this article, a method of characterizing a tissue present in a predetermined location of a body of a subject was proposed, the method comprising: generating mechanical vibrations at a position adjacent to the predetermined location, the mechanical vibrations are at a frequency ranging from 10 Hz to 10 kHz; scanning the frequency of the mechanical vibration; and measuring a frequency response spectrum from the predetermined position, thereby characterizing the tissue.
Abstract: A method of characterizing a tissue present in a predetermined location of a body of a subject, the method comprising: generating mechanical vibrations at a position adjacent to the predetermined location, the mechanical vibrations are at a frequency ranging from 10 Hz to 10 kHz; scanning the frequency of the mechanical vibrations; and measuring a frequency response spectrum from the predetermined location, thereby characterizing the tissue.
TL;DR: In this article, the frequency response of optoelectronic devices is measured using a calibrated optical reference receiver, a modulated optical source, and a calibrated electrical vector network analyzer.
Abstract: Describes the most straightforward method for accurately measuring the frequency response of optoelectronic devices. The method uses a calibrated optical reference receiver, a modulated optical source, and a calibrated electrical vector network analyzer.
01 Dec 2003
TL;DR: A simulator that efficiently generates correlated complex Gaussian variates with a power spectral density as described by Jakes (Jakes, Jr., 1974) is presented.
Abstract: This paper presents a simulator that efficiently generates correlated complex Gaussian variates with a power spectral density as described by Jakes (Jakes, Jr., 1974). The simulator consists of a fixed IIR filter followed by a variable polyphase interpolator, to accommodate different Doppler rates. The IIR filter was designed using an iterative optimization technique known as the ellipsoid algorithm, following an optimization technique that is more generally applicable and can be used to approximate any given magnitude frequency response. Software to implement both the IIR filter design technique and the complex Rayleigh fading simulator itself are available at the author's Website or by email.
TL;DR: In this paper, a series of experiments are performed to assess the validity of an equivalent circuit model of ionic polymer transducers, where the fundamental parameters of the model are the dielectric permittivity of the material, the viscoelastic modulus, and the effective strain coefficient of the transducers.
Abstract: A series of experiments are performed to assess the validity of an equivalent circuit model of ionic polymer transducers. The fundamental parameters of the model are the dielectric permittivity of the material, the viscoelastic modulus, and the effective strain coefficient of the transducer. The results demonstrate the validity of a simplifying assumption regarding the reflected impedance of the polymer. This allows us to use a simpler set of expressions to predict the time and frequency response of the polymer. The expressions for sensing and actuation are verified in a series of step response and frequency response tests of cantilevered transducers. The curvefit algorithm used for parameter identification works well but there is always a tradeoff in accuracy between the time domain and frequency domain measurements. This could imply the existence of an input-level dependence on the parameters. In spite of this level dependence, the linear model is able to predict the response of an input-output pair tha...
TL;DR: In this paper, a resonant shunt damper was modeled from piezoelectric sensor/actuator equations and the shunt voltage equation was derived from the charge generated in PZT due to beam vibration.
TL;DR: In this article, the velocity related frictional hysteresis terms fHðd; ’ dÞ were modified to define fðdÞ that will include velocity-related frictional terms fÞðd ðd; ǫðdǫÞ for the sgn function.
TL;DR: In this paper, the frequency-dependent response of a photo detection system based on a Si-PIN photodiode and a laser with wavelength 1064 nm was characterized, and the diode response was characterized as a first-order low-pass filter with a 3dB-frequency of 8-9 kHz, depending on laser intensity.
Abstract: We characterize the frequency-dependent response of a photo detection system based on a Si-PIN photodiode and a laser with wavelength 1064 nm, a system commonly used with optical tweezers We chopped the laser beam with chopper frequencies from 200 Hz to 14 kHz, and found an exponentially delayed response of the detection system with a characteristic delay time of ∼20 μs The physical mechanism causing this time delay is silicon’s transparency to 1064 nm light: Photons are absorbed and create charge carriers not only in the diode’s depletion layer, where they are detected within nano-seconds, but predominantly in the n-layer, where they remain undetected till transported out by thermal diffusion The diode’s response is dominated by this delay which can be characterized as a first-order low-pass filter with a 3dB-frequency of 8–9 kHz, depending on laser intensity Measurements exploiting frequencies near or above this 3dB-frequency must be corrected for this unintended filter effect We describe how to do
TL;DR: In this article, a 60-MS/s phase-encoded optical sampling (PES) system was used to down-sample two different FM chirp signals: 1) a baseband (0-250 MHz) linear-chirp waveform and 2) a nonlinear-chircp waveforms having a 10-GHz center frequency and a frequency excursion of 1 GHz.
Abstract: Phase-encoded optical sampling allows radio-frequency and microwave signals to be directly down-converted and digitized with high linearity and greater than 60-dB (10-effective-bit) signal-to-noise ratio. Wide-band electrical signals can be processed using relatively low optical sampling rates provided that the instantaneous signal bandwidth is less than the Nyquist sampling bandwidth. We demonstrate the capabilities of this technique by using a 60-MS/s system to down-sample two different FM chirp signals: 1) a baseband (0-250 MHz) linear-chirp waveform and 2) a nonlinear-chirp waveform having a 10-GHz center frequency and a frequency excursion of 1 GHz. We characterize the frequency response of the technique and quantify the analog bandwidth limitation due to the optical pulse width. The 3-dB bandwidth imposed by a 30-ps sampling pulse is shown to be 10.4 GHz. We also investigate the impact of the pulse width on the linearity of the phase-encoded optical sampling technique when it is used to sample high-frequency signals.
TL;DR: In this paper, the authors investigated computing air damping in a comb-drive resonator by numerically solving the three-dimensional Stokes equation for the entire resonator using the FastStokes solver.
Abstract: In this paper, we investigate computing air damping in a comb-drive resonator by numerically solving the three-dimensional (3-D) Stokes equation for the entire resonator using the FastStokes Solver. In addition, we used a recently developed computer microvision system to directly measure resonator frequency response. By comparing the measured results to those generated by one dimensional analytic models and by numerical solution of the 3-D Stokes' equation, we demonstrate that numerically solving the Stokes' equation is fast and also generates a model that matches quality the factor to within 10%. We also show that results based on one-dimensional (1-D) models mispredict quality factor by more than a factor of two. In addition, the detailed drag force distribution generated by the FastStokes solver is used to identify sources of errors in the 1-D models.
TL;DR: It is shown that there is a single critical rod in the optimized bend structure that exhibits an extraordinary high sensitivity at a given frequency, and power reflection becomes tunable from 0 % up to 100 % involving only small changes in the critical rod's properties.
Abstract: We perform a simple sensitivity analysis of a W1 waveguide bend in a photonic crystal (PhC) where we use the information obtained to optimize the PhC bend's frequency response. Within a single optimization step we already achieve very low power reflection coefficients over almost the entire frequency range of the photonic bandgap (PBG), i.e., an achromatic bend. A further analysis shows that there is a single critical rod in the optimized bend structure that exhibits an extraordinary high sensitivity at a given frequency. Hence power reflection becomes tunable from 0 % up to 100 % involving only small changes in the critical rod's properties. This opens the door to novel topologies for compact switches and sensor applications.
04 Jun 2003
TL;DR: In this paper, an LPV model is derived by using measured Frequency Response Functions at different positions, fitting a parametric model on each measurement and combining these models by linking parameters via a fit as a function of operating point.
Abstract: The objective of this paper is to show how experimentally based modelling can be used for designing Linear Parametrically Varying (LPV) controllers. As a test system we use an industrial pick and place unit with one linear X-drive and two independent linear Ydrives. The dynamics of the Y-axes depend on the Xposition. An LPV model is derived by using measured Frequency Response Functions at different positions, fitting a parametric model on each measurement and combining these models by linking parameters via a fit as a function of operating point. Rewriting the LPV model into a LFT structure and applying model reduction in the space of the scheduling variable finalizes the modelling phase. With this model an LPV controller is calculated and shows robust performance for the whole operating range, in contrast to local H∞ controllers.
08 Jun 2003
TL;DR: In this paper, a simple statistical path loss model was proposed for the residential channel that is based on over 300,000 frequency response measurements and the probability distributions of the model parameters for different locations were presented.
Abstract: In this paper, we describe a simple method for measurement of the Ultra-Wideband Band (UWB) frequency response for evaluation of the path loss and impulse response of the UWB indoor channel. We propose a simple statistical path loss model for the residential channel that is based on over 300,000 frequency response measurements. The probability distributions of the model parameters for different locations are presented.
01 Jan 2003
TL;DR: Convergence of truncated representations of the frequency-response operator of a linear time-periodic system is studied and the roll-off rates are shown to be determined by certain properties of Taylor and Fourier expansions of the periodic systems.
Abstract: In this report we study how a time-varying system with a time-periodic integral kernel (impulse response), g(t,\tau)=g(t+T,\tau+T), can be expanded into a sum of essentially time-invariant systems. This allows us to define a linear frequency response operator for periodic systems, called the Harmonic Transfer Function (HTF). The HTF is a direct analog of the transfer function for time-invariant systems, but it captures the frequency coupling of a time-periodic system. It can, for example, be used to compute the induced L_2-norm of periodic systems. The report also includes analysis of convergence of truncated HTFs, which is essential for practical computations as the HTF is an infinite-dimensional operator.
TL;DR: In this article, a method for finding sensitivities of the scattering matrix efficiently over a range of frequencies, from a finite-element analysis, is applied to the optimization problem of microwave devices with 1-4 design parameters: a rightangle miter bend, an E-plane U-bend, and a waveguide impedance transformer.
Abstract: Direct optimization of microwave devices is more efficient if sensitivities of the cost function are available. An earlier method for finding sensitivities of the scattering matrix efficiently over a range of frequencies, from a finite-element analysis, is applied here to the optimization problem. The method is tested on rectangular waveguide components with 1-4 design parameters: a right-angle miter bend, an E-plane U-bend, and a waveguide impedance transformer.
TL;DR: In this article, the authors describe how to significantly change the dynamic behavior of parametric resonance in a micromechanical oscillator, by varying the voltage amplitude of applied electrical signal.
Abstract: We describe how to significantly change the dynamic behavior of parametric resonance in a micromechanical oscillator. By varying the voltage amplitude of applied electrical signal, the frequency response of the first order parametric resonance changes dramatically. We attribute this variation to the tuning of effective cubic stiffness of the oscillator, which is a contribution of both structural and electrical cubic stiffness. This phenomenon is well explained by the first-order perturbation analysis of nonlinear Mathieu equation.
TL;DR: In this article, a topology optimization based approach is proposed to study the optimal configuration of stiffeners for the interior sound reduction, which is aimed at reducing the low frequency noise, a coupled acoustic-structural conservative system without damping effect is considered.
Abstract: A topology optimization based approach is proposed to study the optimal configuration of stiffeners for the interior sound reduction. Since our design target is aimed at reducing the low frequency noise, a coupled acoustic-structural conservative system without damping effect is considered. Modal analysis method is used to evaluate the interior sound level for this coupled system. To formulate the topology optimization problem, a recently introduced Microstructure-based Design Domain Method (MDDM) is employed. Using the MDDM, the optimal stiffener configurations problem is treated as a material distribution problem and sensitivity analysis of the coupled system is derived analytically. The norm of acoustic excitation is used as the indicator of the interior sound level. The optimal stiffener design is obtained by solving this topology optimization problem using a sequential convex approximation method. Examples of acoustic box under single frequency excitation and a band of low frequency excitations are presented and discussed. @DOI: 10.1115/1.1569512#