The effect of series and parallel connection of a correcting circuit’s elements on the duration of a piezoelectric probe’s acoustic signal

A piezoelectric plate with a series or parallel correcting RL circuit connected to the input is considered. The transducer is excited by a half-sinusoidal electric voltage pulse at the eigenfrequency of the plate. The calculated possibility of reducing the duration of an acoustic pulse is compared for each type of correcting-circuit connection to a probe radiating into a liquid or a solid. In each case, the optimal (in view of the shortest radiated pulses) parameters that characterize this radiating system are determined and the durations and amplitudes of the radiated acoustic pulses are estimated.     

An experimental setup for exciting semiconductors and dielectrics with picosecond electron-beam and electric-field pulses

An experimental facility for forming high-voltage pulses with amplitudes of 30–250 kV and durations of 100–500 ps and electron beams with a current density of up to 1000 A/cm² is described. The facility was built using the principle of energy compression of a pulse from a nanosecond high-voltage generator accompanied by the subsequent pulse sharpening and cutting. The setup is equipped with two test coaxial chambers for exciting radiation in semiconductor crystals by an electron beam or an electric field in air at atmospheric pressure and T = 300 K. Generation of laser radiation in the visible range under field and electron pumping was attained in ZnSSe, ZnSe, ZnCdS, and CdS (462, 480, 515, and 525 nm, respectively). Under the exposure to an electric field (up to 10⁶ V cm^?1), the lasing region was as large as 300–500μm. The radiation divergence was within 5°. The maximum integral radiation power (6 kW at λ = 480 nm) was obtained under field pumping of a zinc selenide sample with a single dielectric mirror.     

Influence of the character of electric excitation on the parameters of transient processes in piezoelectric transducers with plate elements

A pulsed operating mode of a piezoelectric plate placed into a liquid is considered. The problem is solved for the application of exciting electric pulses with a duration that is a multiple of the duration of a sinusoid half-period at the natural frequency of a piezoelectric plate. For different degrees of plate damping, the dynamics of changes in the shape of an acoustic pulse are studied as a function of an electrically excited pulse duration. The durations and amplitudes of acoustic signals are evaluated. The problem is solved by the calculation-theoretical method via application of both the apparatus of schemes-analogues of piezoelectric transducers and the spectral method based on a Fourier transform.     

Noncontact excitation of sound in metals by a video pulse of electric field

An acoustic signal that is excited without acoustic contact by an excitation electrode in a metal sample has been studied. A constant electric voltage close to the breakdown value was applied between the electrode and the sample. A video pulse of electric field with a duration of 0.4 μs was used to excite sound in the sample. The ratio k of signals that were registered with noncontact and contact excitation proved surprisingly large (k = 0.14) when compared to the value expected from the literature data. A strong dependence of the noncontact acoustic signal on the filling frequency f of the excitation pulse has been observed. For f > 10 MHZ, the signal dropped to the level of noises. An explanation for this frequency dependence is proposed. It is based on the assumption of quasi-atomic thickness of the charged metal layer that is created by the electric field.     

Optimization of high-voltage devices for energy compression of nanosecond pulses

Designs of compact converters intended for compression of high-voltage pulses with durations of a few nanoseconds and operating in a traveling wave mode were examined. The energy compression unit contained two lines-high-impedance and forming-with a high -pressure gas spark discharger used as a switch. A traditional serial connection of lines was replaced by a parallel connection to increase the energy compression efficiency. The power of the initial pulse (amplitude, 145 kV; half-height duration, 4 ns; and rise time, 1.5 ns) at a load of 45 Ω was increased by a factor of 1.8, while the calculated value was 2.5. The amplitude was as great as -195 kV, and the power was 17% higher relative to the circuit with a serial connection of lines. When shaped, the pulse was compressed in time to 0.8 ns. Two modifications of devices converting the initial pulse with an amplitude of -160 kV and a rise time of 0.3 ns into pulses with amplitudes of -210 and -250 kV and durations of 0.80 and 0.45 ns, respectively, were tested. Waveguide components of the converters were developed, with which it was possible to minimize the dimensions of the device in order to avoid excitation of higher harmonics while maintaining the electric strength.     

Test Results for Leakage and Rotordynamic Coefficients of Floating Ring Seals in a High-Pressure,High-Speed Turbopump

Test results are presented for short floating ring seals (D = 53.0 mm, L/D = 0.15) using a smooth surface and a round-hole pattern defined as a damper floating ring seal (h/C_r = 3, γ = 0.34: the ratio of hole area to surface area) for supplied pressures of 3.0, 5.0, and 7.0 MPa, respectively, with the shaft operating speed up to 24,800 rpm. The measured data includes leakage, attitude angle, eccentricity ratio, and rotordynamic coefficients such as stiffness, damping, and inertia. When the floating ring seals are locked up, the eccentricity ratio of the smooth surface floating ring seal is lower than that of the damper floating ring seal. The attitude angle increases linearly with the operating speeds. The damping coefficients of the damper floating ring seal are higher than those of the floating ring seal. Whirl frequency ratios of the floating ring seal are lower than the damper floating ring seal with high eccentricity ratio at low operating speed range. The design parameters determined from these test results will be used for high-pressure and high-speed turbopump seals in a liquid rocket engine system.     

Exact solutions for vibration and buckling of an SS-C-SS-C rectangular plate loaded by linearly varying in-plane stresses

Exact solutions are presented for the free vibration and buckling of rectangular plates having two opposite edges (x=0 and a) simply supported and the other two (y=0 and b) clamped, with the simply supported edges subjected to a linearly varying normal stress σ_x=−N₀[1−α(y/b)]/h, where h is the plate thickness. By assuming the transverse displacement (w) to vary as sin(mπx/a), the governing partial differential equation of motion is reduced to an ordinary differential equation in y with variable coefficients, for which an exact solution is obtained as a power series (the method of Frobenius). Applying the clamped boundary conditions at y=0 and b yields the frequency determinant. Buckling loads arise as the frequencies approach zero. A careful study of the convergence of the power series is made. Buckling loads are determined for loading parameters α=0,0.5,1,1.5,2, for which α=2 is a pure in-plane bending moment. Comparisons are made with published buckling loads for α=0,1,2 obtained by the method of integration of the differential equation (α=0) or the method of energy (α=1,2). Novel results are presented for the free vibration frequencies of rectangular plates with aspect ratios a/b=0.5,1,2 subjected to three types of loadings (α=0,1,2), with load intensities N₀/N_cr=0,0.5,0.8,0.95,1, where N_cr is the critical buckling load of the plate. Contour plots of buckling and free vibration mode shapes are also shown.     

The effectiveness of squeeze-film damper bearings supporting rigid rotors without a centralising spring

A method has been devised for comparing the effectiveness of squeeze-film damper bearings of various configurations. The analysis in this report is limited to the case of rigid-rotors without parallel flexible supports, but is to be extended to the case of flexible rotors. The performance of squeeze-film damper bearings can be expressed in terms of three independent system parameters, B the bearing parameter ( ), the gravity parameter ( ) and U the unbalance ratio ( ). For a rigid rotor it would appear that the design of an effective squeeze-film damper bearing would require to be less than 0·1, and B to be around 0·2. Also it is seen that for some range of the system parameters the effectiveness of the device increases with increasing unbalance ratio U.As an extension of the present investigation, it is shown that very small values of B produce unstable orbits or non-synchronous whirl components. Also, it is shown that the orbits and maximum transmitted forces produced by squeeze-film damper bearings with similar ratios of differ considerably, and that the determination of the performance of a squeeze-film damper bearing relies upon the absolute values of these two parameters.     

CdTe-based detectors for recording X-ray pulses with a subnanosecond resolution

Characteristics and manufacturing methods of semiconductor detectors made of pressed cadmium telluride are given. The sensitivity of the detectors is ∼(1–5) × 10⁻¹⁹ A cm² s/quantum. SPPD29k and SPPD29-02 detectors are calibrated by subnanosecond X-ray pulses generated by the СПИН-2 accelerator. The measured pulse durations are τ_0.5 = 0.29 and 0.47 ns, respectively. The X-ray pulse shape of the APCA accelerator is recorded.     

In situ study of electric field‐induced magnetization in multiferroic BiFeO3 nanowires

In this work, we have studied electric field‐induced magnetization effect of multiferroic BiFeO₃ (BFO) nanowires in situ using magnetic force microscopy (MFM). Changes in magnetic domain contrast have been observed in the MFM phase images under applied electric potential, which indicate local magnetoelectric (ME) coupling in the nanowires. The values of saturation and magnetization at different applied electric fields were evaluated. These results suggest that one‐dimensional multiferroic BFO nanowires are potential candidates for realizing multiferroic devices at nanoscale with unique functionalities. SCANNING 36:224–230, 2014. © 2013 Wiley Periodicals, Inc.     

A new probe for atmospheric electric field mill

介绍了一种由大气电场采集部分、前置放大电路和相敏检波电路构成的差动式大气电场仪探头的设计。采集部分采用了由双定子构成的差动输入电路,使精度提高一倍;前置放大电路部分由I-V转换电路、差分放大电路和次级放大电路构成;相敏检波电路用于检验电场的极性。经过Multisim仿真,得到了较为理想的仿真结果,证明了设计的有效性。     

Instruments for detecting electric breakdowns in proportional drift chambers of the transition radiation tracker in the ATLAS experiment

The transition radiation tracker is a part of the ATLAS facility at the LHC accelerator at CERN and operates as a position detector and a detector of transient radiation. It consists of approximately 400000 proportional drift chambers (PDCs) filled with a mixture of Xe + CO₂ + O₂. During its operation, electric breakdowns may occur, which may result in a failure of the detecting element. To diagnose and find broken-down PDCs, an instrument has been developed that makes it possible, by analyzing signals from the anode, to detect defective PDCs and exclude them from the working detector.     

The finite expansion of a circular hole in an infinite plate: A dynamic solution

The problem of dynamic expansion of a finite circular hole in an infinite plate, of uniform initial thickness, in a state of plane stress is worked out by solving the equation of motion. A numerical solution is obtained for a strain-hardening material using (i) a continuous three-parameter stress-strain relation and (ii) Nadai's J₂-deformation theory of plasticity. The solution is obtained by the method of characteristics for both ramp velocity and ramp pressure prescribed at the hole boundary.     

A stabilized pulsed repetition-rate CO<Subscript>2</Subscript> laser for a laser-plasma generator of multiply charged ions

The design of a laser oscillator with a stabilized frequency composition and a stabilized intensity of output radiation is described. The oscillator’s basic component is a TEA CO₂ module pumped by a self-maintained discharge and operating in a repetition-rate mode at a frequency of up to 3 Hz. A circuit for the formation of a self-maintained homogeneous discharge in the working volume of a CO₂ + N₂ + He mixture at atmospheric pressure is the basic component of the gas-discharge module. This circuit is based on the generation of a high-voltage pulse with a special profile, which provides high-reliability excitation of a discharge and pulse-to-pulse reproducibility of the discharge characteristics. The use of a hybrid circuit in the optical oscillator allows selection of a single longitudinal mode in the output radiation spectrum, thus eliminating undesirable interference phenomena, which lead to instability of the instantaneous values of the radiation intensity. During the development of the oscillator, the optimal operating parameters of the hybrid circuit were obtained, which ensure the high quality and reproducibility of the spatiotemporal and energy parameters of laser radiation.     

Radiated noise analysis via human body for intra-body communication

The transmission path of intra-body communication is composed of capacitance coupling among nodes. Therefore, a channel model of the communication is expressed by capacitive ambient elements. Such a communication is greatly affected by external noise because the balance of the transmission path deteriorates due to environmental factors. There is a serious problem in that radiated noise via the human body emitted from an electric light or peripheral electronic equipment is likely to be transmitted along the same path as a signal by capacitance coupling. We investigated a channel model and estimated radiated noise via the human body based on experiments and circuit simulation. The validity of the channel model was clarified from noise measurement. When an additional electrode was connected to a ground electrode in a measurement system for a practical scene, the noise reduction rating was 5.11 dB. However, actually, reducing the noise is difficult. Therefore, reducing the noise source in such a communication is necessary.     

On the problem of the frequency dependences of the input electric impedance of a broadband immersion transducer

A piezoelectric plate with a damper and a matching layer is considered. Water was chosen as an acoustic load. On the basis of the use of the apparatus of circuits-analogues of piezoelectric transducers (PETs), the relationships were obtained that determine the frequency dependences of the modulus and phase of the input electric impedance of the considered transmitter. Numerical investigations of the aforementioned electric characteristics of the PET were performed within a wide band of relative frequencies and the interrelationships of these characteristics with the shape of the frequency characteristics of the PET-transmitted acoustic power were studied.     

An experimental study on laminar CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> premixed flames under an electric field

This work investigates the electric field effect on gas temperature, radiative heat flux and flame speed of premixed CH₄/O₂/N₂ flames in order to gain a better insight into the mechanism of controlling the combustion process by electrophysical means. Experiments were performed on laminar Bunsen flames (Re<2200) of lean to rich mixture composition (φ =0.8–1.2) with slight oxygen enrichment (Ω=0.21-0.30). The Schlieren flame angle technique was used to determine the flame speed, and thermocouple measurements at the post flame gas were conducted. The radiative heat flux was measured by using a heat flux meter. At high field strengths, coincident with the appearance and enhancement of flame surface curvatures, an apparent change in flame speed and gas temperature was observed. However, the application of an electric field had no significant effect on flame speed and temperature when the flame geometry was unaltered. This was supported by radiative heat flux showing negligible electric field effects. The modification in flame temperature and flame speed under electric field was attributed to the field-induced flame stretch due to the body forces produced by the ionic winds. This additional flame stretch, coupled with the influence of non-unity Lewis number, accounts for such changes. This reinforces the idea that the action of an electric field on flames with a geometry that remains practically undeformed produces very minimal effect on flame speed, temperature and radiative heat flux. A possible mechanism of combustion control by the application of flame stretch using electric field was introduced.     

A high-performance source of high-power nanosecond ultrawideband radiation pulses

A source of high-power nanosecond ultrawideband electromagnetic pulses is described. The 3-ns-long bipolar voltage pulse with a 90-kV amplitude is applied to the input of four-element antenna array. The effective radiation potential values E _p R = 560 kV were obtained at a 100-Hz pulse repetition rate.     

Determination of experimental and theoretical kASi factors for a 200-kV analytical electron microscope

The relative sensitivity of an analytical electron microscope and energy-dispersive x-ray detector to x-rays of various elements is investigated through an extensive k_ASi factor study. Elemental standards, primarily National Bureau of Standards multielement research glasses, were dry-ground into submicrometer-sized particles and analyzed at 200 kV accelerating potential. The effect of self-absorption of x-rays by the particle has been corrected for, allowing the experimental k_ASi factors from this study to approximate those that could be obtained from “infinitely thin” specimens. Whenever possible, elemental k-factors were determined by the analysis of many (up to a maximum of nine) different standard materials. Experimental k_ASi factors were calculated for a wide range of K_α, L_α, and M_α x-ray lines. For comparison, theoretical k_ASi factors, employing a variety of ionization cross sections, were computed. Good agreement is obtained between several of the theoretical k-factor models and the experimental results. Mass volatilization of Na and K from the small glass particles during analysis is discussed, as are observations that the grinding and/or dispersing of standard materials in a liquid (such as ethanol) may promote leaching of certain elements from the particle matrix.     

Stress and electric potential fields in piezoelectric smart spheres

Piezoelectric materials produce an electric field by deformation, and deform when subjected to an electric field. The coupling nature of piezoelectric materials has acquired wide applications in electric-mechanical and electric devices, including electric-mechanical actuators, sensors and structures. In this paper, a hollow sphere composed of a radially polarized spherically anisotropic piezoelectric material, e.g., PZT_5 or (Pb) (CoW) TiO₃ under internal or external uniform pressure and a constant potential difference between its inner and outer surfaces or combination of these loadings has been studied. Electrodes attached to the inner and outer surfaces of the sphere induce the potential difference. The governing equilibrium equations in radially polarized form are shown to reduce to a coupled system of second-order ordinary differential equations for the radial displacement and electric potential field. These differential equations are solved analytically for seven different sets of boundary conditions. The stress and the electric potential distributions in the sphere are discussed in detail for two piezoceramics, namely PZT_5 and (Pb) (CoW)TiO₃. It is shown that the hoop stresses in hollow sphere composed of these materials can be made virtually uniform across the thickness of the sphere by applying an appropriate set of boundary conditions.