Numerical determination of electric field forces and capacitance of pressure condenser microphone

Nonuniform deflection of a pressure condenser microphone membrane causes nonlinearities of a relationship between peak deflection of the membrane and the induced voltage. This paper describes how the numerical analysis carried out with the finite element method can help in more accurate determination of this nonlinearity. The dependence of the inverse capacitance (proportional to the induced voltage) on the deflection can be well approximated with the third-order polynomial and the electric field force with the second-order polynomial. There is a major influence of the nonlinearity of the inverse capacitance compared to the nonlinearity of the overall force on the microphone's overall nonlinearity. The deflection profile of the analyzed microphone's membrane is deduced from the values for a 1" microphone.     

The influence of the tip structure and the electric field on BN nanocones

Different configurations for BN nanocones with 240° disclination are analysed through first-principles calculations based on the density-functional theory. The studied cone tips involve either four pentagons with two homonuclear bonds or two squares and two hexagons with no homonuclear bonds. The structures are both terminated by two three-coordinated atoms. Cohesive energy results show that the cone terminated in pentagons is slightly energetically preferred. The influence of a 1.7?V??(-1) external electric field, applied along the axis, on the structural changes and charge distributions is analysed. The responses of the charge distributions to the external electric field demonstrate the main role played by the B atoms for the applications of BN cones as probes in electronic microscopy as well as field emitters.     

The influence of electric field on the microstructure of nc-Si:H films produced by RF magnetron sputtering

Hydrogenated nanocrystalline silicon thin films were prepared by RF magnetron sputtering. Different bias fields (no bias-no ground, grounded and negative bias) were applied to the substrate. The effect of the ion bombardment on the structure, chemical and optical property were studied by Raman spectroscopy, X-ray diffraction, Rutherford backscattering (RBS) and optical transmission spectroscopy. The deposition rate and the optical bandgap decrease as the bias voltage increases from 0 to −50 V. The structural characterization indicates that compressive stress is developed in plane and tensile stress is induced in the growth direction. No significant variation on the chemical composition was observed.     

The influence of size and shape of microorganism on pulsed electric field inactivation

In this paper the effect of microorganism size and shape on the killing efficiency of pulsed electric field (PEF) is investigated both experimentally and using a transient finite element program. The effect of cell size, membrane thickness, cell shape (spherical, elliptical, and cylindrical) on the calculated transmembrane voltage is studied. It has been found that both the cell size and cell membrane thickness have significant effect on the induced field across the cell membrane. The findings of the simulation results have been evaluated by comparing the trends with some experimental results. Five different types of microorganisms that have different shapes and dimensions have been inoculated with water at a conductivity level of 100 μS/cm and have been treated with the application of a pulsed electric field of 70 kV/cm. Significant difference in bacteria reduction was noticed between the treated cells which could be attributed to the cell size and shape.     

氧化石墨结构对电容性能的影响

研究了层状结构氧化石墨的片状尺度、结晶态及不同表面官能团含量对其电化学电容性能的影响.以光谱纯和化学纯石墨为原料,采用改进的Hummer法制备氧化石墨(GO),并将部分氧化石墨球磨.用FT-IR和XPS,对氧化石墨表面官能团进行了分析;XRD、FE-SEM和氮气吸附等温线,对氧化石墨结构和形貌进行了分析.利用恒电流充放...     

The influence of electric field on heat transfer in a boiling cryogenic liquid

An experimental technique to investigate how an electric field affects heat transfer in boiling nitrogen is described. Experiments were performed in natural convection and nucleate boiling zones using cylindrical surfaces to simulate wires conducting a current.     

The nonlinear influence of an electric field on phase transitions in ferromagnetic semiconductors: Lanthanum manganite

We investigate nonequilibrium processes of self-heating induced by electric current in ferromagnetic semiconductors exhibiting colossal magnetoresistance (CMR) in the vicinity of the Curie temperature. The heat balance equation is solved taking into consideration localized states that appear as a result of scattering from magnetic inhomogeneities and are characterized by a percolation threshold proportional to the amplitude of spin fluctuations. The appearance of N-shaped current-voltage characteristics and hysteresis in the dependence of magnetization on electric potential difference, which are caused by the emergence of a “hot” (with respect to internal temperature) semiconductor paramagnetic phase, is revealed in the steady-state regime. The possibility of suppression of the effect of colossal magnetoresistance with increasing potential difference is indicated. The onset of self-oscillation of current and magnetization with decreasing transverse dimensions of the sample is demonstrated.     

不同工艺对活性炭电吸附脱盐性能的影响

以活性炭为电极材料是利用电吸附脱盐的重点.以热解法制备了活性炭,采用酸处理及二次活化处理活性炭,并将二次活化的活性炭利用不同的工艺制成电极.研究表明:二次活化法能够使活性炭获得更高的比表面积和更大的孔容,热压和炭化结合的工艺使活性炭电极有着高的比表面积和高的孔容,适合用于苦咸水脱盐.因此,活性炭具有脱盐效果好,脱附时间短,脱盐率达到90%,是一种优良的脱盐电极材料.     

改进电容测微仪稳定性的技术措施

简述了JDC系列精密电容测微仪的组成原理,介绍了为改进仪器的稳定性而对稳压电源、主放大器、参比电容、传感器、滤波电路等组成环节所采取的一些技术措施。     

Investigation of the electric field excited by a personal computer

The electromagnetic field produced by a personal computer at frequencies in the 20 Hz-30 MHz range is investigated experimentally. Data are obtained on the spectral composition and polarization of the electric component of the electromagnetic field. Measurements of the spatial structure and the field strength in the front half-space of the plane of the monitor are presented.Translated from Izmeritel'naya Tekhnika, No. 7, pp. 59–61, 1994.     

Enhancement of the steel quenching process by an electric field

An electric field is known to be able to increase considerably the heat flux during the boiling process by suppressing the occurrence of film boiling. This field enhancement technique can be applied to the steel quenching process to accelerate the cooling rate and thus increase the effective hardenability of the steel. This report describes a quench experiment performed with an electric field. The effective hardenability (depth of high hardness) of the samples quenched with the field was measured to be significantly higher than those quenched without the field. Examination of the microstructures showed that the application of the electric field increased the depth to which martensite formed in the sample.     

无电流电场沉积CdS纳米薄膜

针对普通电沉积制备纳米薄膜工艺中的电极析气、电解、电镀等有害电极反应对沉积过程和沉积膜造成不良影响的问题,提出了一种待沉积薄膜的基材及其上的沉积膜不与沉积电路组成闭合电流回路的电场沉积装置及电场沉积制备纳米薄膜的新方法.在自制的电场沉积装置上制备了CdS薄膜并用AFM表征了薄膜微观结构.获得了粒径约30nm的CdS微粒致密平整薄膜.研究结果表明,新方法具有薄膜质量好、无需使用贵金属电极、沉积速度快等优点.     

The influence of skin depth on crack measurement by the ac field technique

A general solution is given to describe the ac field around surface-breaking cracks for arbitrary values of the ratio of skin depth δ to crack depthd. This solution allows accurate interpretation of crack depth from voltage readings taken by a Crack Microgauge instrument in cases where δ andd are comparable. It is shown to agree with asymptotic formulae obtained for the cases where δ/d is very small and very large. Provided that the probe length Δ is large compared with δ, the calculations show that a very good approximation to the crack depth may be obtained, irrespective of the ratio δ/d, by using the thin-skin asymptotic formula $$d = \frac{1}{2}\Delta (V_2 - V_1 )/V_1 $$ whereV ₁ andV ₂ are probe voltages registered at positions just off and across the crack, respectively. The problem is solved for a crack of infinite aspect ratio which has no opening, but it can be applied with confidence at the centerline of cracks of fairly large aspect ratio.     

Detecting fiber oscillations by measuring electric field variations

A new method is proposed for determining the characteristics of thin (charged) fibers, which is based on the measurement of their transverse oscillations by means of the electric field monitoring. The phenomenon of a sharp decrease in the rate of charge leakage from damaged fibers has been observed, which can be used as a basis for the new method of nondestructive testing.     

Experimental study of electric field influence on low-temperature,long-time relaxation in crystalline ferroelectrics

Calorimetric measurements with polycrystalline Pb_0.915La_0.085. (Zr_0.65Ti_0.35)O₃ were performed at liquid helium temperatures in an electric fieldE (0E4.3 kV/cm). Heat released after cooling fromT ₁ (1.3 K<T ₁35 K) toT ₀=1.3 K is very similar to that in amorphous metals and dielectrics. Experimental results disagree with the standard tunneling model. The observed heat release may be explained assuming the existence of a maximum energy _f in the distribution function. The maximum relaxation time _max was found as a function ofT ₁. A similar heat release is observed after switching on or off the electric field, independent ofT for 1.1 KT3 K, proportional toE ² with _maxE. No heat release was observed in the KH₂PO₄ single crystal.On leave of absence from the Technical University, Dresden, German Democratic Republic.On leave of absence from the Institute of Physics, Czechoslovak Academy of Sciences, Prague, Czechoslovakia.On leave of absence from the Central Institute for Solid State Physics and Material Research, Dresden, German Democratic Republic.     

On the conductivity of metal films during coalescence and the influence of an electric field on their growth

The influence of an electric field normal to the substrate during film growth on the electrical resistance of thin silver deposits is investigated. For interpretation of the results, the coalescence processes are subdivided into three stages. In the first two stages the resistance of the channels determines the resistance of the film. In the first stage the islands gather after film deposition has been interrupted; in the second stage they form bridges between one another. In the third stage the resistance is determined by that of the tracks. Owing to the interaction of dipoles, an electric field causes repulsive forces between the islands without the influence of charged particles. Accelerated charge carriers in the vapour beam increase the resistance of the channels, decrease the growth rate and the mobility of the islands and change the density of the islands.     

The Kirkendall effect of the Al-Cu couple with an electric field

Abstracts are not published in this journal