Showing papers on "Fundamental frequency published in 1998"

Tissue harmonic imaging : why does it work ?

Abstract: The recent utilization of harmonic frequencies in the imaging of both tissue and contrast agents has dramatically improved echocardiographic image quality. In contrast harmonics, the harmonic frequency energy is generated on reflection from the microbubble contrast agent. In tissue harmonics, the harmonic frequency energy is generated gradually as the ultrasonic wave propagates through the tissue. Critical to the utility of tissue-generated harmonic frequencies is their origin beyond the chest wall and their nonlinear relation to the fundamental frequency energy strength. These two characteristics of tissue-generated harmonics ensure that the echoes most likely to produce artifact are least likely to produce harmonic waves. Armed with an understanding of how these images are produced and with data emerging as to their clinical utility, we anticipate that harmonic imaging will become the standard for assessing regional and global left ventricular function in technically difficult studies.

Ultrasonic harmonic imaging system and method

Abstract: A method for imaging a target includes the steps of transmitting ultrasonic energy at a fundamental frequency and receiving reflected ultrasonic energy at a harmonic of the fundamental frequency. The ultrasonic energy is transmitted in power bursts (80), each having a respective envelope shape (82), wherein the envelope shapes rise gradually to a respective maximum value and fall gradually from the respective maximum value. Utrasonic energy in the transmit beam is focused in an elongated high power region, as for example by means of a line focus.

A new control method for 400 Hz ground power units for airplanes

Abstract: This paper presents a new control strategy for a ground power unit, which is used for airplanes on the ground. In such a system, the ratio between the switching frequency and the fundamental frequency is low and in order to obtain high output performance, the controller has to be digital. The control is performed by a pulsewidth modulator and a voltage controller in the synchronously rotating reference frame (d-q). Design roles are given and a simulation tool is used for investigation of the controller. A 90 kVA prototype is used for validation of the principle. It is concluded by the experiments that the new controller gives a high output performance both stationary and dynamically at linear and nonlinear loads. Synchronization with the airplane is also shown to work successfully.

Method and apparatus for frequency control of an ultrasound system

Abstract: A method and system for acquiring data in an ultrasound system are provided. A transducer is operatively connected to a transmit beamformer and a receive beamformer. The receive beamformer is configured to obtain a first value associated with a fundamental frequency interleaved with a second value associated with a harmonic frequency. A first transmit signal is transmitted at a first frequency. A first echo signal is received in response to the first transmit signal. At least the first value associated with the first frequency is obtained from the first echo signal. An interleaved second transmit signal is transmitted at the first frequency or a second frequency. A second echo signal is received in response to the second transmit signal. At least the second value associated with a third frequency is obtained from the second echo signal. Images are generated and displayed based on the at least one first value and the at least one second value.

Remote magneto-elastic analyte, viscosity and temperature sensing apparatus and associated methods of sensing

Abstract: An analyte, viscosity, or temperature sensing apparatus for operative arrangement within a time-varying magnetic field, including a sensor with an outer surface that is chemically, frictionally, or thermally responsive and adhered to a base magnetostrictive element, and a receiver to measure a first and second value for magneto-elastic emission intensity of the sensor taken at, respectively, a first and second interrogation frequency. A change in mass or a change in material stiffness of the sensor due to the responsiveness, the viscosity and mass density of a fluid therearound, or the temperature, can be identified. The receiver, alternatively, measures a plurality of successive values for magneto-elastic emission intensity of the sensor taken over an operating range of successive interrogation frequencies to identify a value for the sensor's magneto-elastic resonant frequency (a fundamental frequency or harmonic thereof). Several sensors in an ordered array will provide a “package” of information.

Ultrasound imaging method and apparatus for generating pulse width modulated waveforms with reduced harmonic response

Abstract: An improvement to the method for harmonic imaging including the steps of transmitting ultrasonic energy at a fundamental frequency, and receiving reflected ultrasonic energy at a harmonic of the fundamental frequency is provided. The transmitting step includes the step of transmitting a waveform comprising at least a sequence of at least a first and second pulse characterized by first and second pulse durations, respectively, where the second pulse duration is different than the first duration. This arrangement can reduce harmonic energy in the waveform. The system (10) includes a transmit beam former (12) that supplies high voltage transmit waveform in a plurality of channels via a TX/RX switch (14) to a transducer array (16).

Inherent structure theory of networks and power system harmonics

Abstract: The inherent structure theory of networks, already applied in the literature at the fundamental frequency to a variety of planning problems, is extended to the field of power system harmonics. In the context of this theory, the harmonic admittance matrices are reformulated in terms of their eigenvalues and eigenvectors, showing that these expansions can be useful to create a framework in which the power system response to harmonic disturbances can be better understood. After the presentation of the theoretical background, some power system harmonic problems are tackled to show possible applications of this theory. Numerical experiments on a 17-busbar distribution system give evidence of the significance of application to the field of power system harmonics.

HVDC device for converting between alternating voltages and direct current voltages

Abstract: A device for converting alternating voltage to direct voltage and, conversely, direct voltage into alternating voltage. A series connection between the poles of a direct voltage side has at least four units each having a semiconductor element of turn-off type and a first diode connected in anti-parallel therewith. A first midpoint of the series connection is connected to an alternating voltage phase line and forms a phase output. Second midpoints of the series connection are connected to a midpoint of the direct voltage side through such units. An apparatus is adapted to control the semiconductor elements with a pulse width modulation frequency of at least one order of magnitude higher than the fundamental frequency of the alternating voltage of the phase line and the rest of the semiconductor elements with a frequency substantially lower and within or close to the frequency range of one or a couple of times of the fundamental frequency.

Stabilizer for switch-mode powered RF plasma

Abstract: Circuitry and techniques designed to allow stable and continuous delivery of alternating power to a plasma with switch-mode power supply (16) include a variety of embodiments. Parallel, series, and other circuit elements connected across switching element (7) are tuned so that energy at other than the fundamental frequency is absorbed and dissipated. This energy may be only at the second harmonic or it may be across broad frequency ranges through selecting high impedance at the fundamental frequency and relatively low impedance at other frequencies. In overcoming instabilities, oscillations, and even changing class of operation of the switch-mode power supply, the stabilizing element absorbs the energy to avoid allowing it to affect switch (7) of power supply (16).

Accurately Characterizing Hard Nonlinear Behavior of Microwave Components with the Nonlinear Network Measurement System: Introducing “Nonlinear Scattering Functions”

Abstract: This paper describes an original way of dealing with the measuring and modeling of microwave transistor nonlinear behavior. Although generalizations are possible, the method described in this particular paper deals with transistor behavior under a large signal one-tone excitation, with arbitrary impedance terminations for the fundamental and the harmonics. First the mathematical theory of the “nonlinear scattering functions” is described. Next the measurement set-up and the actual extraction of the model parameters is highlighted. Finally the model is implemented in a commercial harmonic balance simulator. Using the simulator, model verification is performed by comparing measured and modeled behavior. INTRODUCTION There is a growing number of applications relying heavily on microwave technology: GSM, CDMA cellular phone, Local Multipoint Distribution Service, Japanese PCS and PDC, WCDMA, Wireless Local Loop,... The design of the power amplifiers used in these systems is often one of the toughest problems to solve. Powerful CAD tools potentially save a lot of time. It is important, however, to be aware that these simulators can only be as accurate as the mathematical models that are used. As a consequence a lot of time is spend on constructing good models for the components used. Especially constructing models that can accurately describe the large-signal hard-nonlinear behavior of power transistors is far from trivial. The state-of-the-art is to use technology dependent analytical models (e.g. Curtice Cubic, Materka, Statz, Tajima,...) or more general “small signal measurement based” models like the HP-Root model [1]. Despite the fact that a lot of effort goes into building models for power transistors, the result is often not accurate enough to satisfy the designer. In this case time consuming loadpull measurements are being used (often these loadpull measurements need to be iterated a few times during the design cycle). In this work another modeling approach is proposed, based upon the use of a black-box frequency domain model. The method is called “nonlinear scattering functions” and can be considered as an extension of “scattering parameters” into hard nonlinear behavior. The model can accurately simulate the behavior of a power transistor under large-signal one-tone excitation at the input, with any arbitrary impedances present at the output (fundamental and all harmonics). The model parameters are extracted based upon a relatively small set of measurements performed with an experimental loadpull set-up build around a “Nonlinear Network Measurement System” [2]. These measurements are actually a combination of passive and active harmonic loadpull measurements. There are mainly two reasons why one can expect this approach to be more simple and accurate. Firstly one has the advantage that the model parameters are directly extracted from large signal loadpull measurements, which are very close to the actual working conditions of the device. This implies that the behavior of the model in the simulator will be consistent with the measured harmonic loadpull behavior. Classical modeling approaches are based upon many small signal and DC measurements, which are far from the actual operating conditions. This often results in inconsistency between measured and modeled loadpull behavior. Secondly all parasitic effects are automatically included in the black-box model, while all parasitic effects have to be explicitly identified with the other models. This makes the “nonlinear scattering functions” really technology independent. A drawback of the method is of course that the model will only be valid for one-tone excitation, with a frequency corresponding to the frequency used to extract the model. MATHEMATICAL THEORY Mathematical notations Extending the concept of “scattering-parameters” [3] in order to describe nonlinear behavior is not trivial. One needs to go back to the basics. “Scattering parameters” are called this way because they relate incident and reflected (or scattered) travelling voltage waves at the signal ports, thereby completely describing the behavior of a linear microwave device. The “nonlinear scattering functions” have the same purpose: relating incident and reflected travelling voltage waves. Some necessary mathematical notations and concepts are introduced in the following. Incident voltage waves will be denoted by the symbol “a” and reflected voltage waves will be denoted by the symbol “b”. In many cases travelling voltage waves (and the corresponding sparameters) are defined in a characteristic impedance of 50 Ohm. When dealing with nonlinear behavior, however, it may be convenient to use different characteristic impedances. The characteristic impedance used for the definition of the waves will be indicated between brackets as a subscript. When the impedance is not indicated it is assumed to be 50 Ohm, or that the value is irrelevant for the given formula. The relationship between voltage “v”, current “i” (defined as being positive when flowing into the device-under-test, called DUT, signal port) and the travelling voltage waves is given by . (1) As mentioned in the introduction, we will describe the device behavior under sinusoidal (onetone) excitation. Excluding subharmonic and chaotic behavior, all signals appearing at the DUT ports will have the same periodicity (= the reciprocal of the fundamental frequency). The periodic signals will be described by their complex Fourier series coefficients, which are commonly called the “spectral components” of the signal. Each “spectral component” has an associated “harmonic index”, which denotes the ratio between the associated frequency and the fundamental. The “harmonic index” will be indicated by the last subscript. An “harmonic index” equal to zero corresponds to DC. The first subscript indicates the respective DUT signal port. Port 1 will typically correspond to the input (gate, base) and port 2 with the output (drain, collector) of the DUT. Some examples: • a(10)21 refers to fundamental of the incident voltage wave at port 2, defined with a characteristic impedance of 10 Ohm. • b13 refers to the third harmonic (with frequency equal to 3 times the fundamental frequency) at port 1, defined with a characteristic impedance of 50 Ohm. a Z ( ) v Zi + 2 -------------= b Z ( ) v Zi – 2 -------------= The black-box model Conceptually, writing down the black-box model equation is trivial. First thing to do is to “phase normalize” all signals by applying a time delay (applying a phase shift to the spectral components proportional to the harmonic index) such that a11 has zero phase. This way all spectral component phases are uniquely defined. This is done as follows: , with superscript “NN” denoting “not normalized”. (2) One can then simply write . (3) This equation simply states that the scattered voltage wave spectral components are complex functions of the real and imaginary parts of all the incident voltage wave spectral components. The functions “Skp” are called the “nonlinear scattering functions”. Note that Im(a11) does not appear in the equation since this value is always zero because of the phase normalization. The modeling problem is now transformed in identifying the functions Skp, for all scattered spectral components. In practice it will be sufficient to consider a limited number of harmonics (including up to the 4th harmonic has been enough for all practical cases investigated until now). Generally speaking identifying the functions Skp would imply the identification of a set of multidimensional nonlinear functions, which is practically very hard to do. In many cases, however, signal conditions are such that the functions Skp can be simplified. For a power amplifier with one dominant tone at the input, all harmonic signals will be relatively small compared to the fundamental signals. It is then possible to expand the functions Skp into a MacLaurin series [7] for all harmonic components (excluding the fundamental components at both signal ports). This results in . (4) In this equation N represents the highest harmonic index considered. Fkp, Gkpij and Hkpij are functions of Re(a11), Re(a21) and Im(a21) (= fundamental components) ,they are given by

Ultrasonic harmonic imaging system and method using waveform pre-distortion

Abstract: Improvements to a method for imaging a target, which method including the steps of (a) transmitting ultrasonic energy at a fundamental frequency, (b) receiving reflected ultrasonic energy at a harmonic of the fundamental frequency and (c) generating an image responsive to reflected energy at the harmonic, are provided. The transmitting step includes transmitting a waveform with a positive pulse spatially defined by first and second zero values. A positive peak amplitude of the positive pulse is a first distance from the first zero value that is less than half a second distance between said first and second zero values. Thus, the waveform includes a fundamental spectral component and a harmonic spectral component at the transducer. An attenuation normalized peak of the harmonic spectral component is reduced at a region spaced from the transducer as compared to the peak at a region adjacent to the transducer. A negative peak is also shifted or pre-distorted. Various pre-distortions of the waveform may compensate for propagation, scattering, or system non-linearities.

Temporal processing of the pitch of complex tones

Abstract: The effect of tone duration on fundamental frequency (F0) discrimination is greater for complexes containing unresolved harmonics than for those containing resolved harmonics [Plack and Carlyon, J. Acoust. Soc. Am. 98, 1355-1364 (1995)]. Three experiments explored this effect further. The first experiment measured sensitivity (as d') to fundamental frequency (F0) differences for two complexes, both with an F0 of 250 Hz. The first complex was low-pass filtered at 1875 Hz to create a resolved complex and the second was bandpass filtered between 5500 and 7500 Hz to create an unresolved complex. The harmonics for the resolved complex were selected so that no two harmonics were the same between the two observation intervals. Performance for both complexes was measured for tone durations of 20, 40, 80, and 160 ms. For the unresolved complex, the effect of duration was greater than that for the resolved complex and greater than the predictions of a "multiple-looks" model assuming either peripheral (before sampling) or central (after combining samples) sources of variance. The second experiment replicated these results using an F0 of 62.5 Hz with the cutoff frequencies of the bandpass filters divided by four, confirming that the effect is related to resolvability and not to spectral region. In the final experiment, F0 discrimination for pairs of complexes separated by a temporal gap was measured relative to that for one complex. Performance for the resolved and unresolved complexes was similar: Very little effect of gap duration was observed and the results were consistent with the predictions of the peripheral-variance multiple-looks model. Taken together, the results suggest that the pitch mechanism for resolved harmonics uses a relatively short sampling window of around 20 ms, while the mechanism for unresolved harmonics may use a more complex strategy for optimizing the combination of information over time, perhaps involving a flexible integration time.

Fundamental Frequency Estimation in the SMS analysis

Abstract: The particular approach of SMS is based on modeling sounds as stable sinusoids (partials) plus noise (residual component), therefore analyzing sounds with this model and generating new sounds from the analyzed data. The analysis procedure detects partials by studying the time-varying spectral characteristics of a sound and represents them with time-varying sinusoids. These partials are then subtracted from the original sound and the remaining “residual” is represented as a time-varying filtered white noise component [1].

Harmonic frequency analysis of SAW resonator chemical sensors: application to the detection of carbon dioxide and humidity

Abstract: We have investigated the possibility of increasing surface acoustic wave (SAW) gas sensor sensitivity and detection limit by operating a SAW device at its fundamental frequency (250 MHz for the devices used in this paper), while monitoring frequency changes at a higher harmonic. In particular we have compared frequency changes at the third harmonic with that of the fundamental mode, using carbon dioxide (CO2) and water vapor as our test gases. The results showed that sensitivity is increased by a factor of three and the detection limit is improved by a factor of two. Three different polymers were used in our investigations. Of the three polymer coatings studied—BMBT, PEI and Versamid 900—PEI gave the greatest frequency change per unit change in humidity, followed by Versamid 900 and BMBT, in that order. The frequency change yielded by PEI (5.7 kHz per percent change in humidity) was about a factor of ten increase compared with the other two polymers. PEI was also found to be relatively more sensitive to CO2 compared with the other polymers. A frequency shift of about 1 kHz was measured for 240 ppm of CO2 in nitrogen. This was comparable to the frequency shift obtained for Versamid 900. The corresponding frequency shift for BMBT was about 700 Hz.

A new tissue harmonic imaging scheme with better fundamental frequency cancellation and higher signal-to-noise ratio

Abstract: Tissue Harmonic Imaging (THI) is a new ultrasound imaging technique, which uses the harmonic components generated by nonlinear acoustic propagation through human tissues to form an image. Several factors affect THI image quality. First, strong suppression of the fundamental signals is necessary to allow the full dynamic range of the harmonic signals to be seen. This will allow the full benefits of harmonic imaging to be seen. Second, since the harmonic components are much weaker (15-20 dB lower) than the fundamental, they must be enhanced as much as possible relative to noise. This will allow the maximum possible image penetration. This paper will compare the phase inversion technique with another data acquisition and processing scheme from the literature in terms of suppression of fundamental frequencies, and signal-to-noise ratio (SNR) improvement. The comparison will be both theoretical, using a very simple model, and experimental, using data acquired in vitro. The phase inversion technique appears to be a better choice to realize THI in an ultrasound imaging system. This technique gives better cancellation of the fundamental frequencies while simultaneously improving SNR.

Self centering frequency multiplier

Abstract: A frequency multiplier (120) having a tunable resonant circuit (122), is anticipated for use with a frequency synthesizer (100) having a Voltage Controlled Oscillator (110). The VCO control line (116) voltage establishes the VCO (110) fundamental frequency (fo) as well as the resonant circuit (122) center frequency, such that the resonant circuit (122) frequency response will track a desired harmonic component within the multiplier output (130) even as the VCO control line (116) voltage and the fundamental frequency (fo) change in response to control line variation.

Diagnostic medical ultrasound system and method for using a sparse array

Abstract: A method and system for obtaining ultrasound data with a sparse array of transducer elements is provided. About one wavelength of a highest operating frequency separates the center of each transducer element from any adjacent transducer element. While this spacing may generate grating lobes, the beamformer of the ultrasound system is configured to filter and isolate information at a harmonic of a fundamental transmit frequency. The resultant two-way beam pattern is less effected by the grating lobes. The image generated as a function of the harmonic information has few artifacts created as a function of the sparse spacing of the transducer elements. Given a set number of beamformer transmit channels, the sparse spacing may allow for a larger aperture width with few artifacts as a result of sparse element spacing. The larger aperture width generates a narrower beam in the azimuthal dimension of a one-dimensional transducer. By generating a narrower beam, better azimuthal resolution may be obtained. Alternatively, the number of transmit channels may be reduced to provide a beam width that is the same or similar to a beam generated with a conventional phased array where transducer elements have a one-half of the wavelength spacing of the fundamental frequency. By using fewer transmit channels to obtain the same beam width, the space required by electrical traces connecting the transducer elements to the beamformer is reduced. The reduced required space is beneficially used on catheter or intravascular transducers.

High-Speed Scanning of Piezo-Probes for Nano-fabrication

Abstract: Low scanning speed of piezo-probes has been a fundamental limitation of scanning probe based nano-fabrication techniques. Typical scan-rates achieved are limited, by structural vibrations of the piezo-probe, to about 1/10th the fundamental vibrational frequency of the piezo-probe. Faster scanning of piezo-probes is achieved here (experimental results are presented) by using inversion of the piezo-dynamics—this approach uses a feedforward input voltage, applied to piezo-probe, to compensate for piezo vibrations.

Estimation of power system frequency using adaptive notch filters

Abstract: A new approach for frequency relaying in power system is presented in this paper. The approach consists of passing the power system voltage signal through a two stage adaptive notch filter, which produces an estimate of the fundamental frequency of the voltage waveform and its enhanced amplitude. The adaptive of the notch filter coefficients are obtained by a recursive least mean squares algorithm. The performance of the proposed algorithm is computationally efficient and it produces an accurate estimate of the fundamental frequency in the presence of harmonics and noise, which is a prerequisite to frequency relaying in power systems. Several computer simulation results are presented in the paper to show the effectiveness of the algorithm. The algorithm is simple and suitable for real time implementation. Further the accuracy of this approach in presence of harmonics and noise is improved considerably.

Series compensation of electric alternating current machines

Abstract: In a method of series compensating rotating electric alternating current machines (2) connected, directly or via a static current converter (28), to a three-phase distribution or transmission network (6), wherein the stator winding of the alternating current machine is Y-connected, a capacitive circuit (14) for the fundamental frequency of the voltage is connected in each phase between the down side of the winding and the earth point (20) of the distribution or transmission network (6). A device for such series compensation comprises a capacitive circuit (14) for the fundamental frequency of the voltage, connected between the down side of the winding and the earth point (20) of the distribution or transmission network (6).

Method and apparatus for acoustic subtraction imaging using linear and nonlinear ultrasonic images

Abstract: A method and an apparatus for imaging a nonlinear signal component isolated from the echo signal derived from transmission of a base waveform having fundamental frequency f0 and relatively high peak power. The nonlinear signal component is isolated by subtracting the linear signal component from the echo signal. This is accomplished using a second transmit firing derived from the same base waveform, but having different transmit characteristics, i.e., the base waveform is convolved with a code sequence to form a coded waveform. The coded waveform is transmitted at relatively low peak power. The beamsummed signal produced from the low-peak-power coded transmit is pulse compressed and then subtracted from the beamsummed signal produced from the high-peak-power uncoded transmit. The signals are scaled as necessary to achieve cancellation of the linear signal components when one beamsummed signal is subtracted from the other, leaving the nonlinear signal component for imaging.

Band centering frequency multiplier

Abstract: A frequency multiplier (120) having a tunable resonant circuit (122), is anticipated for use with a frequency synthesizer (100) having a Voltage Controlled Oscillator (110). The VCO control line (116) voltage establishes the VCO (110) fundamental frequency (ƒo) as well as the resonant circuit (122) center frequency, such that the resonant circuit (122) frequency response will track a desired harmonic component within the multiplier output (130) even as the VCO control line (116) voltage and the fundamental frequency (ƒo) change in response to control line variation.

Measurement of the modulation transfer function of paper.

Abstract: In recent years there has been a renewed interest in modeling the halftone microstructure to better control the colors produced in a halftone image. Diffusion of light within the paper has a significant effect on the halftone color; this effect is known as optical dot gain or the Yule–Neilsen effect. Because of diffusion, a photon may exit the paper from a different region of the halftone microstructure than that into which it entered the paper. To account rigorously for this effect requires knowledge of the paper’s point-spread function or, equivalently, the paper’s modulation transfer function (MTF). A new technique for measuring the MTF of paper—the series-expansion bar-target technique—is introduced. The method uses a bar target, but the analysis more closely resembles that of the edge-gradient technique. In the series-expansion method, bar-target image data are expanded into a Fourier series, and the paper’s MTF is given by the series-expansion coefficients. It differs from the typical bar-target analysis in that the typical method plots the amplitude of the fundamental frequency component for several targets of varying frequency, whereas the series-expansion method plots the amplitude of the fundamental and its harmonics for a single target. Two possible techniques for measuring the MTF with the bar-target series-expansion method are considered. In the first, the image of the bar target is projected onto the paper, and in the second, the bar target is placed directly on the paper, in close contact.

A new digital filter for phasor computation. I. Theory [power system protection]

Abstract: A new pair of orthogonal filters for power system phasor computation is presented They have excellent time-frequency characteristics for fault location and measurement Their impulse responses are obtained applying the inverse Fourier transform to a single-lobe function with a strong stopband From this process, a new window emerges Without side lobes, it overcomes the temporal barriers imposed by the rectangular window, implicit in digital Fourier filtering Its length is not restricted to a multiple of one cycle, and it can be adjusted to cover totally the available samples of the fault, extracting the fundamental component with growing precision On the other hand, its sampling frequency can be reduced to twice the fundamental frequency In particular, at this minimum sampling frequency, the digital Cosine filter rejects the even harmonics and the aperiodic component

Ultrasonic diagnostic imaging of harmonic frequencies with speckle reduction processing

Abstract: An ultrasonic diagnostic imaging system and methods are described which produces ultrasonic images from harmonic echo components of a transmitted fundamental frequency. Preferably, a programmable digital filter is used to pass harmonic echo components for image processing to the exclusion of fundamental frequency signals. In a preferred embodiment, artifacts are removed by producing decorrelated replicas of the harmonic signals, which are then combined and used for imaging. To produce an image in the presence of depth dependent attenuation of high frequency echo signals, both fundamental and harmonic echo signals are processed and used to produce an image blended from components of both fundamental and harmonic echo signals.

Testing the Nonlinearity of Piano Hammers Using Residual Shock Spectra

Abstract: Summary Force pulses and residual shock spectra of voiced, unvoiced (soft), and used (hard) piano hammers are compared. The peak frequency of the residual shock spectrum is related to the frequency range over which the hammer will be most effective in exciting string modes. Hammer speeds of 1 to 6 m/s, used in these experiments, span the normal dynamic range of the piano. Peak force is related to pulse duration and also to a nonlinearity exponent in the equation relating force to compression of the felt. For lower notes on the piano, is well above the fundamental frequency which helps to explain the dominance of higher partials in the bass notes. At the treble end, however, is comparable to the fundamental frequency, resulting in a strong fundamental and few partials in these notes on a piano. In addition to its usefulness in piano research, the residual shock spectrum could serve as a useful guide in the production and voicing of pianos.

Magnetic Sensor Using Second Harmonic Change in Magneto-Impedance Effect

Abstract: This study reports on a magnetic sensor composed of a Cu wire sandwiched between Co-based amorphous ribbons. The impedance of the Cu wire largely depends on the permeability of the amorphous ribbons and changes with an external field. This phenomenon results in a change in the voltage at the fundamental frequency (V1st) and that at the second harmonic frequency (V2nd) at both ends of the Cu wire. The maximum V2nd variation rate was ~150%/Oe which is about 15 times larger than that of V1st. The detection of the second harmonic voltage offers the potential for a great improvement in the magnetic field sensitivity.

Fundamental frequency coupling between HVAC and HVDC lines in the Quebec-New England multiterminal system-comparison between field measurements and EMTDC simulations

Abstract: Fundamental frequency coupling between HVAC and HVDC lines has been investigated through actual field measurements in the Quebec-New England multiterminal HVDC power system. These are the first field measurements which clearly exhibit the fundamental frequency coupling. The measurements covered the sections of interaction located along the Radisson-Des Cantons part (approximately 1120 km long) of the HVDC transmission line. In these sections, the distances between the AC and DC lines do not exceed 1.5 km. During the field measurements, the recorded fundamental frequency currents in the DC line ranged between 1.05 and 1.20 A RMS. An EMTDC computer model of the coupling phenomenon has been developed and validated based on these measurements. This article presents the computer model and the results of the validation.

Two new measuring algorithms for generator and transformer relaying

Abstract: This paper presents new digital measuring algorithms for generator and transformer protection. Two methods are proposed to make the estimation of amplitudes of the fundamental frequency component and the higher harmonics immune to frequency deviations. The first method is based on the software re-sampling of the physical data window and on the simultaneous iterative estimation of the frequency. The second algorithm employs the amplitude estimator having unique frequency response in the entire frequency spectrum and enables direct compensation for the frequency deviations. Also a new Volts/Hertz inverse-time algorithm is proposed which does not call for the direct measure of frequency. It relies on the second method and uses the amplitude estimator having the gain close to the inverse of the frequency; therefore, it acts as a direct amplitude-to-frequency estimator. The proposed algorithms were analyzed analytically and tested using EMTP simulations.