Driver Frequency Research Articles

Hydrodynamic mode selection due to the electrocapillary effect: the mercury beating heart in neutral and basic solutions

The electrocapillary mechanism driving the oscillatory hydrodynamic modes of a «clean» (i.e., without organic contaminants) mercury drop in the absence of oxygen and in neutral and basic solutions was investigated. The electrocapillary driver can be mimicked by imposition of an external field oscillating with frequency ν max and amplitude ΔV about an appropriate voltage V 0 , where V 0 is referenced to a standard potential. The hydrodynamic mode selection for a given V 0 is controlled in a strictly reproducible and reversible manner by adjustment of the driver frequency ν max and the voltage ΔV

Performance-based measurements among elderly drivers and nondrivers.

Although driving is an important ability for maintaining independence in the later years, clinical factors that determine driving status are unknown. Aged male veterans (mean age, 70 years) were recruited from an outpatient clinic (N = 143), including 77 frequent drivers, 41 infrequent drivers, and 25 who drove rarely or not at all. There were 116 (84%) who completed a comprehensive performance-based assessment. There were no significant differences between the three groups in age, formal cognitive testing, or prevalence of stroke history. However, there were significant differences in grip strength, reaction time, static visual acuity, dynamic visual acuity, and peripheral vision. Using stepwise ordinal logistic regression, dynamic visual acuity, nondominant hand grip strength, and total horizontal peripheral visual field were significantly associated with driving frequency (P less than .05), and together explained approximately 45% of the variance. Subtle motor and visual deficits that can be detected by a performance-based assessment may play an important role in determining driving frequency in the elderly.

A device to generate high frequency noise from commercially available low frequency acoustic drivers

A device has been developed to generate high frequency noise with low frequency acoustic drivers. The principle behind this mechanism is the use of the non-linear propagation effects of high intensity sound waves inside hard-walled ducts, which alter the shape of the sound wave. This modification makes the sound wavefront steeper and, thereby, extends the frequency range of the wave signature. Two means are used to achieve this objective. In the first case, a converging duct is connected to an acoustic driver, where use is made of the fact that for a fixed acoustic power output from the driver, the intensity of the sound wave increases as the duct cross-sectional area decreases. In turn, a strong non-linear effect is produced. Thus, the larger the contraction ratio, the stronger the non-linear effect and the higher will be the frequency range. In the second case, a long, hard-walled duct of constant cross-sectional area is connected to the acoustic driver. In this second case, a reasonably strong sound wave emanating from the driver propagates through the long duct and, thereby, experiences non-linear propagation effects for a longer time. Therefore, the longer the duct, the greater the non-linear effects and the higher will be the frequency range. This paper presents the results obtained by using these two methods to generate high frequency noise from a low frequency driver. Higher frequencies can also be generated by combining both the means of creating non-linear effects: i.e., using a long and converging hard-walled duct. Examples of such devices developed for specific applications are illustrated in this paper.

Phase-pulling and breather instability in an AC driven-damped one-dimensional sine-Gordon system

Abstract An AC-driven damped sine-Gordon system, in the nonlinear Schrodinger regime, may converge into various nontrivial space-time attractors. One of them is breather riding on top of flat profile, both locked to the driver frequency. Using collective-coordinate ansatz for this attractor, and a multiple-scale perturbation technique, we study the location and nature of its instability. Among the various characteristics, this study includes understanding the role of the breather-background coupling, the structure of the associated unstable modes, the scaling structure of the instability boundary, etc. Most strikingly we find the instability mechanism and the above features to be strongly sensitive to the asymptotic phase-difference between the spatially localized breather and the spatially extended uniform background. We call this phenomenon “phase-pulling”.

Phase-pulling and breather instability in an AC-driven damped one-dimensional sine-Gordon system

An AC-driven damped sine-Gordon system, in the nonlinear Schrödinger regime, may converge into various nontrivial space-time attractors. One of them is breather riding on top of flat profile, both locked to the driver frequency. Using collective-coordinate ansatz for this attractor, and a multiple-scale perturbation technique, we study the location and nature of its instability. Among the various characteristics, this study includes understanding the role of the breather-background coupling, the structure of the associated unstable modes, the scaling structure of the instability boundary, etc. Most strikingly we find the instability mechanism and the above features to be strongly sensitive to the asymptotic phase-difference between the spatially localized breather and the spatially extended uniform background. We call this phenomenon “phase-pulling”.

Tokamak Power Systems Studies at ANL

A number of advances in plasma physics and engineering promise to greatly improve the reactor prospects of tokamaks. The following features, in particular, are examined: (a) large aspect ratio (A approx. = 6), which may ease maintenance; (b) high beta (..beta.. greater than or equal to 0.20) without indentation, which brings the maximum toroidal field down to about 7 T; (c) low toroidal current (I approx. = 5MA), which reduces the cost of the current drive and equilibrium field system; and (d) steady state operation with current density control via fast and slow wave current drive. The key to high beta operation with low toroidal current lies in utilizing second stability regime equilibria with the required current distributions produced by an appropriate selection of wave driver frequencies and power spectra. The ray tracing and current drive calculation is self-consistent with the actual magnetic fields produced in the plasma. In addition to matching desirable high-beta equilibria, this method is capable of producing a large variety of new equilibria, many of which look attractive. The impurity control activities in TPSS have emphasized the self-pumping concept as applied to using the entire first wall or ''slot'' limiters. The blanket design effort has emphasizedmore » liquid metal and Flibe concepts. The reference concept is a liquid lithium/vanadium, self-cooled configuration. Overall, there exists a number of major design improvements which will substantially improve the attractiveness of tokamak reactors.« less

Dummy load technique for power efficiency estimation in rf discharges

We have developed a simulated load technique for estimating power dissipation and effective impedance of the discharge which is useful over a wide range of driver frequencies. This is used to calculate the power delivered to the plasma and plasma current for frequencies from 0.12 to 13.56 MHz. This technique allows an efficiency calibration curve to be made for a given match circuit which can be quickly applied to any new discharge condition to give match efficiency.

Resonant Excitation of High Amplitude Oscillations and Hydrodynamic Wave Breaking in a Streaming Cold Plasma

The excitation of large amplitude electron oscillations in a streaming cold plasma and the minimum threshold of wave breaking in the resonant region are investigated analytically as a function of flow velocity. The problem is reduced to the solution of a driven harmonic oscillator with time varying eigenfrequency ωp(t) in a self-consistent, stationary ion density profile. An analytical solution is presented and applied to the correct wave breaking criterion in a streaming plasma. Wave breaking sets in when the driver amplitude Êd obeys the inequality which shows that the threshold is proportional to the driver frequency ω and to the flow velocity at the resonance point, vc; however, it is independent of the density scale length. Resonance ends at η = π/2. The denominator assumes there the value 2.759. η is a dimensionless time which measures the transit time of a volume element through resonance.

Volumetric inspection of moderately thick austenitic stainless steels by multifrequency eddy currents

This paper describes the initial phase of a project to develop eddy-current methods to inspect welds joining sections of austenitic stainless steel pipe having walls up to 13 mm (0.5 in.) thick. The objective of this phase was to demonstrate the feasibility of detecting and characterizing flaws in austenitic stainless steel base metals. These materials and welds present challenging eddy-current problems because of their relatively large thickness and ferromagnetism. Multiparameter analysis shows that a reflection coil probe operated with three discrete driver frequencies and phase detection can locate and size a cracklike defect in a single conductor in the presence of variations in conductor resistivity, permeability, and thickness and in the probe-conductor spacing (liftoff). Experiments were performed with a modular three-frequency instrument. Flat-plate specimens of types 304L and 347 stainless steel machined to 12.7 to 15.9 mm thickness simulated pipe walls; saw-cut slots 10 to 30% of nominal specimen thickness simulated cracklike defects. The same slots were used in duplicate experiments as near-side (directly under the test probe) or far-side (in the face opposite the probe) defects. Flaw detection and characterization capability was demonstrated by a series of experimental measurements fitted to specimen properties by least squares techniques. The quality of the fit determined the expected accuracy of measurement. Comparison of accuracy estimates determined the best choice of operating frequencies. From the 1,2,5 sequence of frequencies between 0.5 and 20 kHz, the optimum set of operating frequencies was selected to be 0.5, 2, and 10 kHz. Estimates of measurement accuracy for combined near- and far-side defect cases were: plate thickness, 0.74 mm; probe liftoff, 0.03 mm; defect location (depth of material above defect), 3.48 mm; and defect size (vertical slot depth), 1.09 mm. A few property values were back-calculated from instrument readings; the errors in these values were somewhat larger than the measurement accuracy estimates because of instrument drift and the absence of calibration circuits.

Compensated crossover network

The signal from the crossover network of an audio output circuit is applied to certain of the audio system's low, middle and high frequency speakers through particular compensation circuits that are associated with the crossover network and the speaker driver coils. These compensation networks include: a resistor-inductor-capacitor sequence of selected values connected across the terminals of a high frequency or other driver whose resonant impedance peak must be compensated to a resistive impedance for optimum crossover; a resistor-capacitor sequence of selected values connected across the terminals of a low frequency or other driver whose inductance must be compensated to a resistive impedance for optimum crossover; and a variable inductor connected in series with one or more of the terminals of any driver where a "roll off" at higher frequency may be desired. The result is more faithful audio reproduction.

The Active Control of Higher-Order Modes in Cylindrical Ducts

Higher-order modes in a cylindrical duct were generated by an planar array of electro-mechanical sound drivers (Spinning Mode Synthesizer) by appropriate phase and amplitude control of the array. Predictions of the sound field generated show excellent agreement with measurements. Active control of the sound field was achieved by the introduction of a properly phased second coplanar array of sound drivers resulting in substantial reduction in the primary sound field. The analytical models agree well with experiment and furthermore clearly delineate the limitation on the complexity of the higher-order modes that can be controlled as a function of the number of drivers in the arrays and the driver frequency. Although substantial reduction of the primary modes was achieved, both analysis and experiment show that secondary higher-order modes are generated, again, depending on the number of drivers in the array and the frequency of excitation.

Parametric Excitation of Ultrasonic Waves

It has been reported [J. Acoust. Soc. Amer. 46, 94(A) (1969)] that the observed fractional harmonics in a liquid-filled resonant ultrasonic cavity are parametrically excited ultrasonic waves. This excitation is produced by instabilities introduced through the vibration of the driver transducer that forms one end of the cavity. The theoretically derived threshold criterion that defines the range of amplitudes for such excitation is now tested experimentally. Since the theory predicts that the transducer voltage at threshold is a function of the driver frequency, the absorption per wavelength of the medium, and the cavity length, a change in either of these parameters causes a corresponding change in the transducer voltage at threshold. There is reasonable agreement between theory and experiment. To develop the model further, a nonlinear equation of parametric action is derived. The solution of the equation including the first nonlinear terms confirms the experimental observation that the nonlinearity of the medium does not affect the magnitude of the threshold for parametric oscillation. [Research sponsored by the U. S. Office of Naval Research.]

Spectrum Produced by an Ultrasonic Resonant Cavity

A spectrum analyzer is used to examine the ultrasonic spectra produced when large-amplitude ultrasonic waves are caused to resonate in a water-filled cavity. The cavity, consisting of a plane transducer and concave reflector, produces frequency components that in some cases are neither integral submultiples, nor integral overtones, of the driver frequency. [Research sponsored by the Office of Naval Research.]

A SUBSTITUTION METHOD FOR THE ABSOLUTE CALIBRATION OF VIBRATION PICK‐UPS

By making use of the general relations between input and output currents and voltages in four‐terminal networks of bilateral impedances a relationship is derived between the velocity response of a reversible vibration pick‐up and the velocity output of the same device, when used as a source of mechanical vibrations. It is then shown that any vibration pick‐up may be calibrated in absolute terms as a function of frequency by purely electrical measurements (input current and output voltage) made on the given pick‐up, an auxiliary reversible pick‐up, and a variable frequency driver.