Low Kilohertz Frequencies Research Articles

Analysis of an inverse weak-value tiltmeter in the kilohertz regime.

We present a follow-on experiment to the recent study from The University of Rochester [Opt. Lett.42, 2479 (2017)OPLEDP0146-959210.1364/OL.42.002479], which reported a new architecture for an inverse weak-value tiltmeter. We recreate the Rochester tiltmeter and specifically investigate mirror oscillations in the low-kilohertz frequency regime, which is relevant to certain potential applications, such as Coriolis vibratory gyroscopes. We find that the inverse weak-value amplification effect persists in this regime, although our measured noise floors are higher than those obtained in the Rochester experiment-approximately 2prad/Hz for mirror oscillation frequencies between 1 and 25 kHz.

Quantum Hamiltonian daemons: Unitary analogs of combustion engines.

Hamiltonian daemons have recently been defined classically as small, closed Hamiltonian systems which can exhibit secular energy transfer from high-frequency to low-frequency degrees of freedom (steady downconversion), analogous to the steady transfer of energy in a combustion engine from the high terahertz frequencies of molecular excitations to the low kilohertz frequencies of piston motion [L. Gilz, E. P. Thesing, and J. R. Anglin, Phys. Rev. E 94, 042127 (2016)2470-004510.1103/PhysRevE.94.042127]. Classical daemons achieve downconversion within a small, closed system by exploiting nonlinear resonances; the adiabatic theorem permits their operation but imposes nontrivial limitations on their efficiency. Here we investigate a simple example of a quantum mechanical daemon. In the correspondence regime it obeys similar efficiency limits to its classical counterparts, but in the strongly quantum mechanical regime the daemon operates in an entirely different manner. It maintains an engine-like behavior in a distinctly quantum mechanical form: a weight is lifted at a steady average speed through a long sequence of quantum jumps in momentum, at each of which a quantum of fuel is consumed. The quantum daemon can cease downconversion at any time through nonadiabatic Landau-Zener transitions, and continuing operation of the quantum daemon is associated with steadily growing entanglement between fast and slow degrees of freedom.

Consolidation of metallic hollow spheres by electric sintering

This paper considers peculiarities of the technology of production of structures from metallic hollow spheres (MHS) using magnetic fields and electric sintering. In these studies, the raw material was MHS obtained by burning of polystyrene balls coated by carbon steel. MHS had an outer diameter of 3-5 mm and a steel wall thickness of 70-120 microns. Pulsed current generators were used for electric sintering of MHS to obtain different spatial structures. Since MHS have small strength, the compressive pressure during sintering should be minimal. To improve the adhesion strength and reduce the required energy for sintering, hollow spheres were coated with copper by ion-plasma sputtering in vacuum. The coating thickness was 10-15 microns. The ferromagnetic properties of MHS allowed using of magnet fields for orientation of the spheres in the structures, as well as using of perforated tapes acting as orienting magnetic cores. Ultrasonic testing of MHS structures has been tried using through propagation of ultrasound in low kilohertz frequency range. Sensitivity of the propagation parameters to water filling of inter-spheres space and sintering temperature was demonstrated.

Measurement of atmospheric sound propagation and meteorological parameters to support development of an acoustic propagation model

Acoustic propagation over long distances is affected by many conditions including atmospheric properties, topography, vegetation, source characteristics, and frequency content. This work presents the results of a set of measurements of acoustic propagation of impulsive sound in the low kilohertz frequency range. These measurements are made over flat ground with limited vegetation at propagation ranges of up to 400 m. At multiple locations along the propagation path, the temperature, pressure, and relative humidity, along with altitude and GPS position are recorded to provide high spatial resolution characterization of the air column in the propagation path. A mast-mounted weather station at the acoustic source provides a record of wind speed and direction at ground level. These measurements are intended to inform related efforts developing a model of acoustic propagation that uses a Crank-Nicolson Parabolic Equation implementation. The measured transmission loss will be compared to preliminary results fro...

Electrical and optical emission measurements of a capillary dielectric barrier discharge

We report a capillary dielectric barrier discharge (Cap-DBD) plasma operated in atmospheric pressure air. The plasma reactor consists of metal wire electrodes inside quartz capillary tubes powered with a low kilohertz frequency AC high voltage power supply. Various reactor geometries (planar, 3-D multilayer, and circular) with wall-to-wall separation ranging from zero up to 500 micron were investigated. For the electrical and spectral measurements, three reactors, each with six tubes, six inches in length, were assembled with gap widths of 500 micron, 225 micron, and 0 micron (i.e. tubes touching). The discharges appear homogenous across the whole device at separations below 225 micron and turned into filamentary discharges at larger gap spaces. The operating voltage was generally around 3–4 kV (rms). The power consumption by the Cap-DBD was calculated using voltage/charge Lissajous figures with observed powers of a few watts to a maximum of about 14 W for the reactor with no gap spacing. Further studies of optical emission spectroscopy (OES) were employed to evaluate the reactive species generated in the microplasma source. The observed emission spectrum was predominantly within the second positive system of $\mbox{N}_2$ ( $\mbox{C}^3$ $\Pi_u$ – $\mbox{B}^3$ $\Pi_g$ ) and the first negative system of $\mbox{N}^+_2$ ( $\mbox{B}^2$ $\Sigma^+_u$ – $\mbox{X}^2$ $\Sigma^+_g$ ).

The underwater acoustic testing of modest sized panel materials using a multi-element array technique in a laboratory test vessel

The underwater acoustic properties of materials can be assessed in panel form via a simple single hydrophone measurement technique which is ideally conducted on large test panels in open water. Alternatively measurements may be conducted in a laboratory test vessel which is capable of simulating ocean conditions. However, physical limitations imposed by the constraints of the vessel, including a reduction in test panel dimensions, require modification of the traditional technique to allow measurements to be made down to low kilohertz frequencies. This can be achieved by, in addition to a directional source, the use of a directional receiver in the form of a planar multi-hydrophone array. The technique is described and illustrated with measurements of reflection loss and insertion loss between 1 kHz and 7 kHz performed on a test panel in a pressure vessel through changing hydrostatic pressure from ambient to 2.8 MPa. The efficacy of this technique is considered with simulated multi-hydrophone array measurements on a scaled panel in an open tank.

Calibration sphere for low-frequency parametric sonars

The problem of calibrating parametric sonar systems at low difference frequencies used in backscattering applications is addressed. A particular parametric sonar is considered: the Simrad TOPAS PS18 Parametric Sub-bottom Profiler. This generates difference-frequency signals in the band 0.5-6 kHz. A standard target is specified according to optimization conditions based on maximizing the target strength consistent with the target strength being independent of orientation and the target being physically manageable. The second condition is expressed as the target having an immersion weight less than 200 N. The result is a 280-mm-diam sphere of aluminum. Its target strength varies from -43.4 dB at 0.5 kHz to -20.2 dB at 6 kHz. Maximum excursions in target strength over the frequency band due to uncertainty in material properties of the sphere are of order +/-0.1 dB. Maximum excursions in target strength due to variations in mass density and sound speed of the immersion medium are larger, but can be eliminated by attention to the hydrographic conditions. The results are also applicable to the standard-target calibration of conventional sonars operating at low-kilohertz frequencies.

Using buried vector sensors to examine seabed layering in sandy sediment

There is considerable interest within the underwater acoustics community in quantifying the sound-speed dispersion in sandy sediments at low kiloHertz frequencies. To address this, data were collected during the SAX04 experiment (a US Office of Naval Research Departmental Research Initiative) using projectors and directional (vector) receivers buried in the top 1 m of the seabed, in conjunction with a water-borne source directly above the buried sensor field. Although using buried sensors significantly increased the complexity of the experimental setup, it should enable a direct time-of-flight measurement of acoustic wave speed, which simplifies interpretation of the results. However, initial analysis of the time-of-flight results indicates the existence of a buried layer, which increases the complexity of the data. In this paper, the vector sensors are used to steer beams to confirm the existence of the layer and to isolate the direct and reflected arrivals to improve the estimate of sound speed dispersion. [Work partially funded by US Office of Naval Research.]

Acoustic backscatter measurements from littoral seabeds at shallow grazing angles at 4 and 8 kHz

Direct measurement of acoustic scattering from the seabed at shallow grazing angles and low kilohertz frequencies presents a considerable challenge in littoral waters. Specifically, returns from the air-water interface typically contaminate the signals of interest. To address this issue, DRDC Atlantic has developed a sea-going research system for measuring acoustic scatter from the seabed in shallow-water environs. The system, known as the wideband sonar (WBS), consists of a parametric array transmitter and a superdirective receiver. In this paper, backscatter measurements obtained with the WBS at two sandy, shallow-water sites off North America's Atlantic coast are presented. Data were collected at 4 and 8 kHz at grazing angles from 3 degrees-15 degrees. The backscattering strength is similar at both sites and, below about 8 degrees, it appears to be independent of frequency within the statistical accuracy of the data. The measurements show reasonable agreement with model estimates of backscatter from sandy sediments. A small data set was collected at one of the sites to examine the feasibility of using the WBS to measure the azimuthal variability of acoustic scatter. The data set--although limited--indicates that the parametric array's narrow beamwidth makes the system well-suited to this task.

Wide-frequency-range dielectric response of polystyrene latex dispersions

In this work we analyze the dielectric properties of dilute colloidal suspensions of nonconducting spherical particles with a thin electrical double layer from experimental data obtained by performing impedance spectroscopy experiments over a broad frequency range, from 20 Hz to 1 GHz. The electrode polarization correction was made by fitting a circuit model in the complex impedance plane (impedance spectrum) using a constant phase angle (CPA) element to fit the electrode polarization in series with the sample impedance. This simple procedure is found to be effective in eliminating the electrode contribution. The dielectric response shows two different dispersions, the α relaxation (counterion relaxation) that occurs at low kilohertz frequencies, and the δ relaxation (Maxwell–Wagner effect) found in the MHz range. These are reasonably well fitted over a broad frequency range by the theoretical expressions given by a simplified standard model (not including anomalous conduction) and a generalized model (including anomalous conduction) for the low-frequency dispersion, plus Maxwell–Wagner–O'Konski theory for the δ relaxation in the mid-frequency range. An analysis was also made of the need to include, for these latices, the effects of ion mobility in the Stern layer in order for the values of the ζ-potential obtained from electrophoretic and dielectric data to be compatible with each other.

Nuclear magnetic resonance using DC SQUIDs with APF

We are using low- T c multiloop DC SQUIDs with additional positive feedback (APF), operating in a flux-locked loop mode out to several megahertz, to perform nuclear magnetic resonance on low temperature samples. The optimum input configuration depends on the sample under investigation. For systems with short T 2 and low frequencies a broadband input circuit is best, with the NMR pickup coil forming a flux transformer with the input coil of the SQUID. This system has been used to perform NMR on several metals, including UPt 3 in the superconducting state, and on submonolayer 3 He films at low kilohertz frequencies. For systems with narrow lines a tuned input configuration offers improved sensitivity, especially when the pickup coil can be cooled to millikelvin temperatures. Here the NMR pickup coil forms part of a series resonant tank circuit, attached to the input coil of the SQUID. We are presently using such a system, tuned to 880 kHz, to detect signals from thin 3 He films (of thickness 100 nm) adsorbed on a surface area of 1 cm 2 . Cooling these films to below 1 mK will enable the study of superfluidity in 3 He films thinner than the bulk superfluid coherence length.

On the relative role of sea-surface roughness and bubble plumes in shallow-water propagation in the low-kilohertz region

In the low-kilohertz frequency range, acoustic transmission in shallow water deteriorates as wind speed increases. Although the losses can be attributed to two environmental factors, the rough sea surface and the bubbles produced when breaking- or spilling waves are present, the relative role of each is still uncertain. For simplicity, in terms of an average bubble population, the time- and space-varying assemblage of microbubbles is usually assumed to be uniform in range and referred to as “the subsurface bubble layer.” However the bubble population is range- and depth-dependent. In this article, results of an experiment [Weston et al., Philos. Trans. R. Soc. London, Ser. A 265, 507–606 (1969)] involving fixed source and receivers, and observations during an extended period of time under varying weather conditions are re-examined by exercising a numerical model that allows for the dissection of the problem. Calculations are made at 2- and 4-kHz. It is shown that at these frequencies and at wind speeds capable of generating breaking waves the main mechanism responsible for the excess loss in the shallow-water waveguide is the patchy nature of the subsurface bubble field. Refraction and attenuation within the pockets of high void fraction are minor contributors to the losses.

Quantitative assessment of the germicidal efficacy of ultrasonic energy

Propagated (free-field) ultrasonic energy at a frequency of 26 kHz was used to expose aqueous suspensions of bacteria (Escherichia coli, Staphylococcus aureus, Bacillus subtilis, and Pseudomonas aeruginosa), fungus (Trichophyton mentagrophytes), and viruses (feline herpesvirus type 1 and feline calicivirus) to evaluate the germicidal efficacy of ultrasound. There was a significant effect of time for all four bacteria, with percent killed increasing with increased duration of exposure, and a significant effect of intensity for all bacteria except E. coli, with percent killed increasing with increased intensity level. There was a significant reduction in fungal growth compared with that in the controls, with decreased growth with increased ultrasound intensity. There was a significant reduction for feline herpesvirus with intensity, but there was no apparent effect of ultrasound on feline calicivirus. These results suggest that ultrasound in the low-kilohertz frequency range is capable to some degree of inactivating certain disease agents that may reside in water. The physical mechanism of inactivation appears to be transient cavitation.

Sensitivity of the schlieren method for the visualization of low-frequency ultrasonic waves

Schlieren visualization of ultrasonic waves is usually carried out at megahertz frequencies since it is generally realized that lower-frequency waves are much more difficult to observe. This paper considers the factors involved in the frequency dependence of the sensitivity of an ideal diffraction-limited schlieren system. The results indicate that relatively low-amplitude sound waves can be visualized even at low-kilohertz frequencies. A techique is suggested which would make the sensitivity at these low frequencies comparable to that at the higher frequencies.

Composite bar technique applied to measurement of the internal friction of small samples of alkali halides crystals at low kilohertz frequencies

A technique using a composite bar is described which enables measurements to be carried out at low kilohertz frequencies in small alkali halide crystals. The technique allows measurements to be made over a range of frequencies on a small sample of an alkali halide and thus the acoustic relaxation process associated with the divalent cation-vacancy dipole can be examined.

Critical Acoustic Relaxation in EuO

Acoustic damping and dispersion in EuO have been measured at low kilohertz frequencies near the ferromagnetic critical point. The experimental observations are discussed in terms of thermoelastic and critical dissipative processes. Bounds are established for the critical relaxation rate for sound, $2\ifmmode\times\else\texttimes\fi{}{10}^{5}<{{\ensuremath{\tau}}_{c}}^{\ensuremath{-}1}<2\ifmmode\times\else\texttimes\fi{}{10}^{7}$ ${\mathrm{sec}}^{\ensuremath{-}1}$, in order-of-magnitude agreement with the EuO spin-lattice relaxation rate calculated by Huber.