Showing papers on "Fundamental frequency published in 1995"

Impact Formulas for Vehicles Moving over Simple and Continuous Beams

Abstract: In this paper, a new set of impact formulas are developed for simple and continuous beams subjected to moving vehicle loads. By modeling a vehicle as sprung masses and a bridge structure by beam elements, a parametric study is performed for various simple and continuous beams traversed by five-axle trucks. Central to this study is the adoption of a nondimensional speed parameter s , which is defined as the ratio of the driving frequency of the vehicle, as represented by πv/L, with v denoting the velocity of the vehicle and L the characteristic length of the beam, to the fundamental frequency ω of the beam. From the numerical study, it is concluded that the impact factors for the deflections, bending moments, and shear forces at the midpoints of simple beams are linearly proportional to the speed parameter, and that these formulas can be multiplied by certain modification factors to yield results for continuous beams and support shears. Other parameters studied herein include the vehicle/bridge frequency r...

On the spatial structure of global modes in wake flow

Abstract: Numerical simulations of wake flow behind an equilateral triangular obstacle are presented. The form of global modes and their dependence on the Reynolds number found in this study are in accordance with recent experimental results of Goujon–Durand et al. [Phys. Rev. E 50, 308 (1994)]. A scaling law of the amplitude oscillating with the fundamental frequency corresponding to the maximum of the global mode is found to agree with the Landau model in a range of Reynolds Re numbers larger than in previous studies. The position of the maximum amplitude of the fundamental modes scales as (Re−Rec)−1/2. The amplitude of the second harmonic of the longitudinal component of the velocity as well as the correction to the mean flow have different critical behavior than the velocity components oscillating with fundamental frequency. During linear growth the position of the maximum of the global modes is constant and moves only in the nonlinear regime. The effects of the blockage and the boundary conditions on the side ...

Techniques for measuring difference of an optical property at two wavelengths by modulating two sources to have opposite-phase components at a common frequency

Abstract: A technique for making precise spectrophotometric measurements illuminates a sample with two or more modulated light sources at two or more, typically closely spaced, wavelengths. Light from the sources is combined, homogenized, and directed to the sample, and the light from the sample is collected and detected by a photodetector. The optical output powers of two sources are modulated with the same periodicity and with a reversed amplitude. Variations in the concentrations of species in the sample affect the modulation amplitude representing the sum of the optical powers from two sources in such a way as to produce an output signal. That output signal, based on an electrical component varying with a periodicity at the fundamental frequency, provides a measure of the difference in the transmissions (or other optical properties) of the sample at the two wavelengths. Feedback methods, such as null-point detection, provide stable, sensitive measurements. Wavelength-division multiplexing--required for simultaneous measurements at many wavelengths--is achieved by modulating different pairs of sources at different frequencies.

Sealed-cavity resonant microbeam pressure sensor

Abstract: A quasi-digital pressure sensor based on polysilicon resonant microbeams has been demonstrated. Pressure sensitivities of nearly 4000 counts per second per psi have been attained on a 10 psi device with a base frequency of 233 000 Hz. Short-term stability as low as 0.01 ppm of the base frequency is typical. The microbeams are fabricated with their own integral vacuum cavities, allowing high-Q operation in the differential pressure mode or in contact with liquids such as silicone oil. Design considerations include the effects of internal strain and lead to a push-pull layout configuration independent of microbeam strain or diaphragm thickness. Fabrication technology incorporates fine-grained polysilicon, surface micromachining, bulk micromachining, and reactive sealing. Packaging into precision avionics headers is being used for preliminary testing. Testing results indicate suitability for precision avionics, industrial, and commercial applications. Optical methods have been used to test resonant microbeam pressure sensors and verify the push-pull design methodology. Testing methods developed under this effort include electrostatic drive/piezoresistive sensing, optical drive/optical sensing, substrate piezoelectric drive/optical sensing, and electrostatic drive/laser vibrometer sensing. Wafer-level testing of 200 μm×46 μm×1.9 μm microbeams shows an average fundamental frequency of 553 150 and first overtone of 1 332 550 Hz. The standard deviations across the wafer are 0.15 and 0.10%, respectively. The internal strain and effective thickness can be determined with high resolution. Laser vibrometer measurements through the microbeam shell verify the fundamental frequency and reveal at least ten overtones up to 25 MHz.

Method for the measurement of the modulation transfer function of sampled imaging systems from bar-target patterns

Abstract: A rigorous and simple method for the determination of the modulation transfer function (MTF) of a sampled imaging system is presented. One calculates the MTF by imaging bar patterns and calculating the reduction in amplitude of the fundamental frequency components. The optimal set of bar-pattern frequencies that reduce errors from aliased frequency components is derived. Theoretical and experimental data are presented.

Experiments on subharmonic resonance in a shear layer

Abstract: The subharmonic resonance phenomenon is studied using hot-wire measurements and flow visualization in an initially laminar shear layer forced with two-frequencies for various choices of the fundamental frequency f and its subharmonic f/2 with controlled initial phase difference ϕin between them. We explore the effects of the controlling parameters, namely: (i) forcing frequencies and their initial amplitudes, (ii) initial phase difference ϕin, and (iii) detuning (i.e. when the second forcing frequency is slightly different from f/2). While several of our experimental observations support predictions based on weakly nonlinear theory, others do not. We explain our data in terms of vortex dynamics concepts.

A new self-tuning algorithm for the frequency estimation of distorted signals

Abstract: This paper introduces a new self-tuning digital signal processing algorithm for local power system frequency deviation measurement. The algorithm is derived using the nonrecursive least error square technique accompanied with an updating procedure, which generally improves the algorithm properties: the measurement range; the immunity to a random noise; and the accuracy. The algorithm developed takes into account the components of the fundamental frequency, the second through the M-th harmonics and a decaying DC component, so it could be used for the real-time distorted signals frequency estimation as well as for the harmonics measurement. To demonstrate the efficiency of the algorithm proposed, the results of the computer simulated, experimentally obtained and real-life data records tests are presented. >

Harmonics tracking and pitch extraction based on instantaneous frequency

Abstract: This paper proposes a technique for estimating the harmonic frequencies based on instantaneous frequency (IF) of a speech signal. The main problem is how to decompose the speech signal into the harmonic components. For this purpose, we use a set of bandpass-filters, each of whose center frequencies changes with time in such a way that it tracks the instantaneous frequency of its output. As a result, the outputs of the band-pass filters become the harmonic components, and the instantaneous frequencies of the harmonics are accurately estimated. To evaluate the effectiveness of the approach, we apply it to pitch extraction. The pitch extraction is simply accomplished by selecting the correct fundamental frequency out of the harmonic frequencies. The most significant feature of the pitch extractor is that the extracted pitch contour is smooth and it requires no post-processing such as nonlinear filtering or any smoothing processes.

Differences in frequency modulation detection and fundamental frequency discrimination between complex tones consisting of resolved and unresolved harmonics

Abstract: Three experiments investigated the finding [Shackleton and Carlyon, J Acoust Soc Am 95, 3529–3540 (1994)] that listeners are very poor at detecting frequency modulation (FM) imposed on complex‐tone carriers consisting of harmonics unresolved by the peripheral auditory system In the first experiment, stimuli consisted of the harmonics of a 625‐ or 250‐Hz fundamental (f0) passed through a bandpass filter with cutoff frequencies of 1375 and 1875 Hz This produced two complexes, one with resolved and one with unresolved harmonics Threshold measurements confirmed that listeners were very poor at detecting 5‐Hz FM imposed on a 200‐ms unresolved group, but that performance was relatively good for the resolved group In addition, the results revealed that, for the unresolved group, thresholds for detecting FM were similar to thresholds for detecting an f0 difference between two static 50‐ms complex‐tone bursts presented 50 ms apart The second experiment added a third complex consisting of the harmonics of

Time‐domain simulation of sound production in the brass instrument

Abstract: Sound production in brass instruments is formulated physically with two different models of lip vibration: the ‘‘transverse’’ model, where lips strike laterally to the direction of the air flow, and the ‘‘swinging‐door’’ model, where lips execute an outwardly striking motion. This formulation is used to carry out time‐domain simulation, which indicates that self‐excitation of the brass instrument is possible with both of these lip models. Changing the lip resonance frequency provides sustained oscillation at the first through eighth air column resonance modes, which correspond to the musical tones in the harmonic series played on the brass instrument without valve manipulation. Oscillation probably also occurred at higher modes, but that region was not investigated. The harmonic structure of the simulated sound varies according to the fundamental frequency and sound level, as is the case in the sound produced by actual brass instruments. Unusual regimes of oscillation are also obtained: the pedal tone, whose fundamental does not participate in its sound production, a tone an octave below the third mode, whose odd harmonics do not contribute to the regime of oscillation, and a multiphonic, which is an oscillation perceived as having two fundamentals simultaneously.

Large amplitude sinusoidal voltammetry

Abstract: A large amplitude sine wave is applied as the excitation potential to a amperometric measurement to produce a current output that is a phase shifted sine wave containing faradaic information at many frequencies. A current obtained from a conventional potentiostat coupled to the electrode is coupled to a lock-in amplifier that monitors the signal at one frequency at a specified phase angle. Since most of the background remains at the fundamental frequency, a higher harmonic of the fundamental frequency of the sinusoidal sweep frequency is monitored. By locking in on the higher harmonic components, the faradaic signal is therefore distinguished from the background signal. The background is diminished thereby allowing signal recognition at low analyte concentrations and increasing the signal-to-noise ratio.

Electronic ballast for operating lamps in parallel

Abstract: An electronic ballast for powering at least two rapid start, parallel connected fluorescent lamps. Associated with each lamp is a serially connected choke and capacitor combination. A train of pulses of alternating polarity having a fundamental frequency, which is generated by an inverter, is applied to each serially connected combination. Each combination is characterized by a resonant frequency which is other than an odd harmonic of and at least two times and preferably √ 5 times greater than the fundamental frequency. Reduction in filament heating, following lamp ignition, is provided through the addition of voltages applied to each filament which are substantially out of phase with each other.

Deer repellent system

Abstract: An animal repelling system, especially for deer which generates a square wave signal output in the ultrasonic frequency range, and which has a piezo-electric driver utilizing a horn type device that produces harmonic distortion so that at any given time the fundamental frequency and harmonic distortion is present in the audio output, and the system is capable of frequency switching to at least 10 different frequencies

A novel computerized multiharmonic active load-pull system for the optimization of high efficiency operating classes in power transistors

Abstract: A fully automated multiharmonic load-pull system allowing accurate measurement and control of the first three harmonic load terminations of RF and microwave transistors is presented in this paper. The technical originality of the proposed system lies in that the first, second and third harmonic load terminations can be independently and automatically monitored and fixed while varying the input power driving the transistor at the fundamental frequency. Appropriate hardware and software allow fast and automatic plots of power/efficiency performances of DUTs versus input power for different harmonic loadings. To demonstrate an attractive application of the system, measurements of a 1800 /spl mu/m gate periphery MESFET at 1.8 GHz for mobile communication applications are presented. Both suitable harmonic load terminations and nonappropriate ones yielding respectively optimum and poor power added efficiency are given. >

Apparatus and method for generating a signal representative of total harmonic distortion in waveforms of an A/C electrical system

Abstract: A microprocessor based device (1) for generating a representation of the total harmonic distortion in an ac waveform (W) derives from digital samples of the waveform a fundamental signal (F) representing the value of the fundamental frequency component of each sample. A harmonic signal is then generated as the difference between the sample value and the fundamental component of the sample. An output signal representing total harmonic distortion is then generated as the ratio of the RMS value of the harmonic signal to the RMS value of the fundamental signal converted to a percentage.

50-Gbit / s optical pulse storage ring using novel rational-harmonic modulation.

Abstract: 50-Gbit/s, 3.8-kbit packets of optical return-to-zero data have been stored in a unidirectional fiber storage ring by use of a novel modulation scheme in which the ratio of the fundamental modulation frequency to the cavity fundamental frequency is rational (nonintegral). The modulation technique should be applicable to lasers and to soliton transmission.

Miniaturized self-q-switched frequency-doubled laser

Abstract: A diode-pumped monolithic laser is fabricated from a self-doubling host material co-doped with two ionic species, where one ionic dopant converts pump radiation to continuous radiation at a fundamental frequency and the other dopant acts as a saturable absorber to Q-switch the fundamental radiation which is then frequency doubled to produce pulsed high-intensity green light, the green light being either outputted or further frequency-doubled, into pulsed coherent UV radiation, by means of a non-linear crystal.

System and method for phasor estimation and frequency tracking in digital protection systems

Abstract: A method and system for estimating phasors and tracking the frequency of a signal is provided. The method uses a variable N-point DFT to compute one or more phasors based on data acquired from one or more sampled signals. At each sampling interval the change in phasor angle between the current sampling interval and the previous sampling interval is determined and used to estimate the instantaneous frequency of the signal. Instantaneous frequencies are averaged over a cycle of the signal. In addition, a number of discrete frequencies and corresponding DFT windows based on a fixed sampling rate and a predetermined fundamental frequency of the signal are defined and used in estimating the instantaneous frequency. Once the average cycle frequency is determined the DFT window is adjusted by setting it equal to the DFT window corresponding to the discrete frequency closest to the average cycle frequency.

Transistor action through nonlinear cascading in Type II interactions.

Abstract: Based on cascading through Type II second-harmonic generation, I show how all-optical amplitude modulation and switching can be obtained by utilizing an input wave at the fundamental frequency with unequal orthogonal spatial components. The proposed all-optical transistor/switch is insensitive to the inputs’ relative phase, representing a step forward with respect to previously suggested configurations for transparent photonic networks.

Harmonic-based verifier device for a magnetic security thread having linear and non-linear ferromagnetic characteristics

Abstract: A security thread for use in a paper-based value document, such as currency or banknote paper, includes a plastic substrate coated with one or more regions of "soft" magnetic material. A device for verifying both the authenticity and the denomination of the document includes a coil that is driven by an alternating current to thereby provide a uniform magnetic field within a predetermined spatial region. As the document passes in proximity to the drive coil, the applied magnetic field saturates the regions of magnetic material on the security thread. The magnetic regions provide a response magnetic field that, because of the saturation of the magnetic regions, is a non-linear response containing a multiple of frequency components, including a component at the fundamental or drive frequency and various harmonic frequency components. A receive coil senses the response magnetic field. A signal processor connected to the receive coil utilizes the response signals at the fundamental frequency and the low-order harmonic frequencies to determine both the type of magnetic material on the security thread and the denomination of the document from the spatial distribution of the magnetic regions on the security thread.

Applications of one-dimensional bubbles to lithotripsy, and to diver response to low frequency sound

Abstract: Experimental, analytical, and numerical investigations into the dynamics of a cylindrical gas pocket in a liquid (a "one-dimensional" bubble) are described . One wall of the bubble (the gas-liquid interface) may move. The other walls (the curved wall, and the other end of the cylinder) are bounded by rigid surfaces. The equation of motion of a damped , forced, one-dimensional bubble is obtained, a nonlinearity arising through the amplitude-dependence of the oscillator stiffness. Analytical solutions to reduced forms of this equation give the natural frequency of undamped oscillations in the linear limit. [n the nonlinear regime of finite-amplitude free oscillation the fundamental frequency is found to be amplitude-dependent . Whilst analytical solutions of the undamped , un forced form of the equation of motion can be obtained in phase space, the full nonlinear damped forced equation must be solved numerically. These solutions are compared with those of the linear undamped analysis, and with experimental measurements. Two relevant cases of such bubbles arc studied: First, air bubbles trapped within the ear canals of divers and driven by high-amplitude low frequency sound; second, the theoretical potential of bubbles in blood to cause haemorrhage of lung blood vessels during lithotripsy

Method and device for determining the primary pitch of a music signal

Abstract: A method and device for very quickly and accurately determining the fundamental frequency of an input analog electrical signal. The method first uses sparse range autocorrelation to determine the note which is closest to the fundamental frequency. It then uses fine range autocorrelation and interpolation to calculate more precisely the exact pitch. Smoothing is employed for both the sparse range determination and the subsequent fine range determination to reject spurious signals. Because the sparse autocorrelation produces good results with merely one or two full cycles of the fundamental frequency, the initial sparse determination can be made in less than ten milliseconds and this is updated with a fine determination less than two milliseconds later.

A detailed analysis of a time-domain formant-corrected pitch-shifting algorithm

Abstract: A novel algorithm to perform real-time pitch shifting of quasiperiodic musical tones in such a way as to preserve the apparent spectral envelope has been proposed by Lent in 1989. A functional and analytical comparison is made of this method and most commercial methods of pitch shifting that shift the spectral envelope along with the fundamental frequency. Analytical results show that this method indeed attempts to preserve the spectral envelope similarly to frequency-domain methods that interpolate between discrete spectral lines and resample the interpolated spectrum at the output fundamental and its harmonics

An All Solid-State 1 THz Radiometer For Space Applications

Abstract: A heterodyne receiver at 1 THz is described, whose components are waveguide mixer and frequency multipliers with Schottky-diodes as mixing and multiplying elements. Most important is the breakthrough in local-oscillator development: The power at the fundamental frequency is generated by an InP-Gunn-Oscillator which delivers 70 mW at 111.2 2 GHz. The output power from two cascade triplers (at the 9th-harmonic) was 60 1.1W (min.) Coupling of signaland I—O.-power is achieved by a Martin-Puplett Interferometer. System noise temperature was determined with absorbers at room temperature and 77 K yielding Tsys = 8800 K (DSB) and total conversion loss = 13dB. Atmospheric losses appear to account for half of the noise temperature and 3dB conversion loss. The mixer is prepared for cooling to liquid nitrogen from which we hope for a further reduction in system noise of approximately a factor of two.