Kilohertz Frequency Research Articles

不連続的インピーダンス変化特性を有した薄膜ＧＭＩセンサと微分回路を組合せた磁界検出方法に関する検討

A giant magnetoimpedance sensor with a step-like impedance property was obtained in the case of amorphous Co85Nb12Zr3 soft magnetic thin film in a rectangle shape with an in-plane uniaxial easy axis in a direction nearly 60 degrees relative to the width direction of the element. It was shown experimentally that the magnetic field in which the step-like impedance change occurs has an almost constant value with a standard deviation in the microtesra (μT) range. The magnetic field in which the step-like change occurs includes information on the external magnetic field. To realize a magnetic field sensor with an accuracy of nT/Hz1/2 by using this step-like phenomenon, a differential circuit was studied in combination with an alternating bias field in the kilohertz (kHz) frequency range. The aim of the differential circuit was to make the driving circuit into a digital logic circuit, by using pulse signals timed to coincide with the step-like changes. The alternating bias field increases the sampling number, because of the step-like changes in the bias frequency. The aim of the ac bias is to improve the sensor accuracy by using an averaging effect. This paper reports a first trial of the method. As a result, a high-linearity sensor without hysteresis was obtained, which had a linearity error of less than 0.5% in the range of ±100 μT. A measurement accuracy of 460 nT was achieved with a 20 Hz time constant of the output low pass filter (LPF).

Comparative Performance of Passively Q-Switched Diode-Pumped Yb $^{3+}$-Doped Tungstate and Garnet Lasers Using Cr $^{4+}$:YAG Saturable Absorber

We investigated the continuous wave (CW) free-running and repetitive modulation in the kilohertz frequency domain of a passively Q-switched diode-pumped Yb:YAG, Yb:GGG, and Yb:KYW lasers by using Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> :YAG as a saturable absorber. The results presented in this paper are focused on the design of a passively Q-switched Yb-doped garnets or Yb-doped tungstates microlasers. The free-running performance of Yb:YAG, Yb:GGG, Yb:KGW, and Yb:KYW were characterized, and experimental parameters such as gain and loss were evaluated. We carried out a fit between our experimental results and an existing numerical model, which relates the experimental and the physical parameters of the ytterbium diode-pumped system to the minimal threshold pumping power. The best performance among the laser crystals was obtained for Yb:YAG laser. A maximum peak power of ap4.5 kW at an average output power of 1.32 W was extracted with an extraction efficiency of ap25%.

Wave biomechanics of the skeletal muscle

Results of acoustic measurements in skeletal muscle are generalized. It is shown that assessment of the pathologies and functional condition of the muscular system is possible with the use of shear waves. The velocity of these waves in muscles is much smaller than the velocity of sound; therefore, a higher symmetry type is formed for them. In the presence of a preferential direction (along muscle fibers), it is characterized by only two rather than five (as in usual media with the same anisotropy) moduli of elasticity. A covariant form of the corresponding wave equation is presented. It is shown that dissipation properties of skeletal muscles can be controlled by contracting them isometrically. Pulsed loads (shocks) and vibrations are damped differently, depending on their frequency spectrum. Characteristic frequencies on the order of tens and hundreds of hertz are attenuated due to actin-myosin bridges association/dissociation dynamics in the contracted muscle. At higher (kilohertz) frequencies, when the muscle is tensed, viscosity of the tissue increases by a factor of several tens because of the increase in friction experienced by fibrillar structures as they move relative to the surrounding liquid; the tension of the fibers changes the hydrodynamic conditions of the flow around them. Finally, at higher frequencies, the attenuation is associated with the rheological properties of biological molecules, in particular, with their conformational dynamics in the wave field. Models that describe the controlled shock dissipation mechanisms are proposed. Corresponding solutions are found, including those that allow for nonlinear effects.

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.]

Temporal variability of the telluric sodium layer

The temporal variability of the telluric sodium layer is investigated by analyzing 28 nights of data obtained with the Colorado State University LIDAR experiment. The mean height power spectrum of the sodium layer was found to be well fitted by a power law over the observed range of frequencies, 10 microHz to 4 mHz. The best-fitting power law was found be be 10(beta)nu(alpha), with alpha=-1.79+/-0.02 and beta=1.12+/-0.40. Applications to wavefront sensing require knowledge of the behavior of the sodium layer at kilohertz frequencies. Direct measurements at these frequencies do not exist. Extrapolation from low-frequency behavior to high frequencies suggests that this variability may be a significant source of error for laser guide star adaptive optics in large-aperture telescopes.

The quantized Hall resistance: towards a primary standard of impedance

In this paper, it is shown that a quantum Hall resistor (QHR) which exhibits a proportionality relationship between the deviation of the Hall resistance from RK/i and the ac dissipation in the system, represented by ρxx, can be used as a primary standard of ac resistance. As an example, a calculable quadrifilar resistor was calibrated against the QHR at kilohertz frequencies. The agreement between the calibration using the QHR and the calculated frequency dependence of the quadrifilar resistor is better than 4 parts in 108 at 1 kHz. This result is achieved despite the frequency and current dependence of the ac-QHR. The most important criterion to achieve accurate measurements using an ac-QHR standard is to extrapolate the value of the Hall resistance to zero dissipation.

Phase transitions and electric properties of imidazolium chlorobismuthate(III): [C 3H 5N 2] 6[Bi 4Cl 18

[C 3H 5N 2] 6[Bi 4Cl 18] crystallizes at room temperature in the monoclinic space group; C2/m. It undergoes two solid–solid phase transitions of first-order type at 221/218 K (heating–cooling) from phase I to II and at 195/145 K from phase II to III. The dielectric relaxation process was found to appear in a kilohertz frequency region over the phase III with the activation energy c.a. 14 kJ/mol. A polydispersive character of the dielectric dispersion indicates a presence of complex molecular motions of dipolar groups in the crystal. The mechanism of the phase transitions in [C 3H 5N 2] 6[Bi 4Cl 18] is proposed.

Dielectric and ferroelectric properties of c-axis oriented strontium bismuth tantalate thin films applied transverse electric fields

The in-plane dielectric and ferroelectric properties of c-axis oriented epitaxial strontium bismuth tantalate (SBT) thin films were investigated by interdigital surface electrode measurement. The four types of SBT thin films, which have various Sr∕Bi atomic ratios, were prepared on MgO substrates by pulsed laser deposition. The dielectric properties at kilohertz and megahertz frequencies were studied from 20to870K. Above room temperature, all the films show the phase transition. Sr0.99Bi1.61Ta2O9, Sr0.97Bi2.10Ta2O9, and Sr0.88Bi1.79Ta2O9 thin films show frequency dispersions near phase transition temperature. At low temperatures, dielectric and ferroelectric properties of Sr0.97Bi2.10Ta2O9 and Sr0.83Bi2.08Ta2O9 thin films were investigated. Both dielectric constant and remanent polarization show a tendency to decrease as temperature decreases, and the rapid change, which may indicate a phase transition, was observed in Sr0.97Bi2.10Ta2O9 near 80K.

Guiding of dynamically modulated signals in arrays of photorefractive spatial solitons

As the formation of spatial optical solitons in photorefractive mediad is governed by modification of the refractive index, every single solitons in complex configurations of solitons can act as a single waveguide for other light beams. In this article, we demonstrate guiding of amplitude-modulated beams in complex configurations of photorefractive solitons carrying information; we analyze the received signal in the kilohertz frequency range. The possibility of data transmission combined with waveguide couplers opens the route to all-optical networks.

Progress toward a thousandfold reduction in 1∕f noise in magnetic sensors using an ac microelectromechanical system flux concentrator (invited)

The potential advantage of some magnetic sensors having a large response is greatly decreased because of the 1∕f noise. We are developing a device, the microelectromechanical system (MEMS) flux concentrator, that will mitigate the effect of this 1∕f noise. It does this by placing flux concentrators on MEMS structures that oscillate at kilohertz frequencies. By shifting the operating frequency, the 1∕f noise will be reduced by one to three orders of magnitude depending upon the sensor and the desired operating frequency. We have succeeded in fabricating the necessary MEMS structures and observing the desired kilohertz normal-mode resonant frequencies. Only microwatts are required to drive the motion. We have used spin valves for our magnetic sensors. The measured field enhancement provided by the flux concentrators agrees to within 4% with the value estimated from finite element calculations. No difference was detected in noise measurements on spin valves with and without the flux concentrators. This result provides strong evidence for the validity of our device concept. Solutions to the sole remaining fabrication problem will be discussed.

Crystal structure and phase transitions in dipropylammonium hexachloroantimonate(V): [N(C 3H 7) 2H 2][SbCl 6

The crystal structure of dipropylammonium hexachloroantimonate(V), [N(C 3H 7) 2H 2][SbCl 6] (DPACA) has been determined by means of X-ray diffraction at 290 K. The compound crystallizes in the monoclinic space group: P2 1 / n. The crystal undergoes three structural phase transitions: two first-order type at 388/376 K (heating-cooling) from phase (I) to (II) and at 157/144 K from phase (III) to (IV), and one second-order type at 210 K from phase (II) to (III). The dielectric relaxation process has been found to appear in a kilohertz frequency region over the phases (II) and (III) with the activation energy ca. 28 kJ mol −1. A polydispersive character of the dielectric dispersion indicates a presence of complex molecular motions of dipolar groups in the crystal. The mechanism of the phase transitions in DPACA is proposed.

Characteristic features of the sound field formation near the bottom of a shallow sea

Detailed calculated data are presented for the angular, temporal, and energy structures of the sound field at the points of localtion of a horizontal line array of receivers (at 250-m intervals) in a shallow sea. The array is deployed near the bottom of a 200-m-deep waveguide along a sound propagation track, at distances from 20 to 30 km from a source generating a signal in the kilohertz frequency range. The influence of a sand or mud bottom on the intensity of signals arriving along single rays is numerically estimated for winter and summer conditions of sound propagation in a specific region of the Barents Sea.

Ultrasonic nanoimprint lithography: a new approach to nanopatterning

We report an ultrasonic nanoimprint lithography (U-NIL) method that can overcome the drawbacks of energy consumption and long process times that occur in conventional nanoimprint lithography (NIL) methods. Instead of using heaters in conventional NIL, the proposed U-NIL employs an ultrasonic source located on the top of the mold to generate high-frequency vibrations, causing the increase of temperature to soften and melt the thermoplastic polymer. The ultrasonic source is induced by the transducer, consisting of a number of piezoelectric ceramic disks sandwiched between two aluminum metal blocks. Since the ultrasonic source provides a vibration with tens of kilohertz frequencies, the temperature of the polymer can increase rapidly. Consequently, the process time is significantly reduced. The experimental results demonstrate that vibratory energy could be concentrated in transferring the topography of a mold's surface into the polymer. In addition, we found that under appropriate conditions, such as ultrasonic time, imprinted pressure/force, frequency, and amplitude of vibration, the feature on the mold can replicate into the polymer film in a few seconds. We conclude that the proposed U-NIL process has the potential to become a novel nanoimprinting method with high productivity, energy efficiency, and low cost.

Acoustic propagation in the subsurface sound channel

Experimental data obtained in the kilohertz frequency band for the sound propagation in the subsurface channel formed by the wind-caused mixing of subsurface waters are discussed. The data were obtained in different years in the northeastern region of the Atlantic Ocean, where the subsurface waters down to the depths of 40–70 m are mixed by both wind waves and the swell that arrives from distant ocean areas. The hydrological conditions in the subsurface waters of this region are characterized by a good reproducibility. The spatial structure of the sound field and the attenuation of sound propagating in the subsurface channel are analyzed. The origin of the additional attenuation (in comparison with the absorption in sea water) is discussed. The data of our experiments are compared with those obtained by other experimenters and with the calculations performed using the computer code by Avilov. The necessity of improving the computer codes to allow for the scattering of sound beyond the channel under the influence of the swell, whose parameters are unrelated to the wind regime at the experimental site, is emphasized.

Elementos Arquiteturais do Substrato da Lagoa dos Patos Revelados por Sísmica de Alta Resolução

A high-resolution seismic survey was performed on the Lagoa dos Patos, southern Brazil. The survey was conducted aboard the research vessel LARUS of the Fundação Universidade Federal do Rio Grande. The seismic profiles were obtained using a 3.5 kilohertz frequency, which provided a rather good penetration depth and resolution of the records. Results of the seismic records allowed the determination and mapping of seismic facies and seismic sequences, as well as related architectural elements, which were identified basically through the configuration patterns of the seismic reflectors. The analysis of the seismic records allowed the identification of the architectural elements that build up the sedimentary pile accumulated in the coastal prism of the State of Rio Grande do Sul, contributing to a better understanding of the geological evolution of the southern Brazilian coastal plain during the Quaternary period.

Low-power optical vibration detection by photoconductance monitoring with a laser speckle pattern

We present a quantitative evaluation of the performance of a photoconductance-monitoring sensor array in a speckle-based vibration detection configuration. The device is found to be capable of detecting nanometer-amplitude vibrations in a single shot with incident intensities of only a few microwatts per square centimeter at kilohertz frequencies. This performance indicates that the photoconductance-monitoring array requires approximately 3 orders of magnitude lower intensity to achieve the same displacement sensitivity as competing technologies, such as photo-electromotive-force detectors.

Mechanical spectra measurement to probe the magnetolattice coupling in cupric oxide

Mechanical spectra (complex Young's modulus Y*=Y′+i Y″ versus frequency and temperature) of polycrystalline cupric oxide CuO were measured by vibrating reed method from liquid nitrogen temperature to room temperature at the kilohertz frequency. The abnormal behavior of internal friction and the change of slope of the real part of the complex Young's modulus versus temperature are observed around 213 and 230 K, where two successive magnetic transitions were established. At low temperatures, below 130 K, a higher internal friction platform with the decrease of temperature was clearly observed which might show a phase transition. Our study indicates that mechanical spectrum is an effective tool to detect subtle phase transitions and there is a strong magnetolattice coupling in CuO.

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.

Defect structure of the high-dielectric-constant perovskiteCaCu3Ti4O12

Using transmission electron microscopy (TEM) we studied $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}$, an intriguing material that exhibits a huge dielectric response, up to kilohertz frequencies, over a wide range of temperature. Neither in single crystals, nor in polycrystalline samples, including sintered bulk and thin films, did we observe the twin domains suggested in the literature. Nevertheless, in the single crystals, we saw a very high density of dislocations with a Burger vector of [110], as well as regions with cation disorder and planar defects with a displacement vector $\frac{1}{4}[110]$. In the polycrystalline samples, we observed many grain boundaries with oxygen deficiency, in comparison with the grain interior. The defect-related structural disorders and inhomogeneity, serving as an internal barrier layer capacitance in a semiconducting matrix, might explain the very large dielectric response of the material. Our TEM study of the structure defects in $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Ti}}_{4}{\mathrm{O}}_{12}$ supports a recently proposed morphological model with percolating conducting regions and blocking regions.

Hydrogen diffusion and interpretation of the 200K anelastic relaxation in NiTi alloys

The internal friction, the Young’s modulus, and the heat flow have been measured as a function of temperature (20–360K) at kilohertz frequencies in a H-free and H-doped Ni50.8Ti49.2 alloy, solubilized under vacuum and rapidly furnace cooled. The chemical H-diffusion coefficient DC has been deduced from absorption experiments (323–1063K) and has been compared with the Einstein diffusion coefficient DE derived from a Snoek (or Zener)-type relaxation PH. The comparison has allowed the interpretation of the so-called 200K relaxation as a Snoek (or Zener)-type relaxation due to hydrogen.