飞行器GNSS接收机静电放电干扰效应分析

针对飞行器全球卫星导航系统接收机易受静电放电干扰的问题,研究了机体表面电晕放电与机务维修火花放电对接收机的干扰效应。分析了静电放电的时频域特征,使用针球电极与高压源组成的模拟器开展了电晕放电对接收机的前门耦合实验,证明了电晕脉冲产生的辐射场对接收机无明显干扰效应。基于人体金属ESD模型开展了火花放电对接收机的干扰效应实验,发现浪涌电流易导致接收机串口转换芯片电位波动,读写程序主循环卡死,应针对串口端进行静电阻抗器防护。     

A new method for generation of synchronised capacitive sparks of low energy

Conventional tests for investigating the minimum ignition energy (MIE) of dust clouds are restricted to energies above a few mJ, due to the challenges of producing sparks of very low energies that can be synchronised with a transient dust cloud. In this paper, a new circuit for generating capacitive sparks of significantly lower energies than 1 mJ is presented. A measurement system for capturing voltage and current waveforms has been integrated in the circuit, offering the energy delivered to the spark by integration of the power-versus-time curve. When working with such low energy discharges, which are highly transient phenomena, attention must be paid to the measurement technique and methods of noise reduction in the measurement instruments.The measured spark energies range from 0.03 to 7 mJ, and they were found to constitute between 60 and 90 per cent of the energy stored on the discharge capacitors prior to breakdown. Losses to the measurement resistors are increasingly significant at higher energies and larger electrode gaps, due to the relatively large currents, and correspondingly small spark resistances.A simple circuit simulation, in which the spark conductivity is assumed proportional to the spark energy, offers voltage and current waveforms in good agreement with the measured ones, indicating that the spark is mainly resistive. In addition, the discharge channel's ability to carry current depends strongly on the supplied energy. The proportionality factor is found to depend on the breakdown voltage.     

Comparison of ESD from metal sphere electrodes and tribocharged insulators of both polarities using two ESD probes

Electrostatic discharge (ESD) is an important source of accidental ignitions in process industries and damage to semiconductor electronic devices. There is a need to understand the time-varying ESD event and interaction between ESD probe and source in order to understand the important parameters in ESD measurements for evaluation of these phenomena.This paper compares measured peak current, waveform, risetime and charge transferred in ESD from charged isolated spherical conductors with and without a ground plane (spark), and triboelectrically charged polyethylene and polyamide samples (brush discharge). Measurements made using two recently developed ESD probes are compared.     

Ignition of a cloud of dry powder using super brush discharges

Ignition of a cloud of dry powder is a major concern in the field of industrial process safety. The different types of discharges are already defined (spark discharges, brush discharges, propagating discharges, cone discharges, corona discharges) such as their ignition properties in a gas or a dust atmosphere. For example, it is known that a classic brush discharge cannot ignite a cloud of dry flammable dust [6,13]. Glor and Schwenzfeuer performed direct ignition tests using brush discharges and defined that even if the energy released by this kind of discharge equaled the one of a spark, the power released by the brush discharge is too low to trigger an ignition.However, some doubts remained for super brush discharges. A brush discharge as a super brush discharge occurs between a charged insulating object and a conductive electrode. The main difference lies in the surface charge density reached on the insulator that is much higher for a super brush discharge than for a brush discharge. A high charge density can be reached for example using pipes of polyethylene individually charged by tribo-charging piled one above another. Such a configuration was evocated by Lüttgens [12] and tested by Larsen [11] who performed direct ignition tests in oxygen enriched atmospheres.This study is relevant with the actual safety problems since pharmaceutical and chemical powders are well known to generate electrostatic charges during their transport or handling and since the same configuration of independent polyethylene fibers can be found in flexible bulk containers that are one of the most common solutions to package this kind of powder.This paper presents the experimental set-up and the results of direct ignition tests performed with a polyethylene wax whose MIE is lower than 1  mJ at ambient conditions. The electric field reached at 1 m and the charge transfer were also registered and are described. Finally, numerical simulations are carried out to define the original surface charge density in order to help to understand the phenomenology of this discharge and its frequency of occurrence in industry.     

Characteristics and application of laser-generated acoustic shock waves in air

When a high-power laser beam is focused at a point, the air at the focal point is heated to temperatures of thousands of degrees within several nanoseconds and breaks down. This generates a spark that, in turn, is accompanied by an acoustic shock wave. The acoustic shock waves generated by focussing the beam from a pulsed laser with a 1064 nm wavelength and a power of 800 mJ per pulse have been measured using 1/4″ and 1/8″ B&K microphones. Nonlinear sound levels are observed up to 1.5 m from the laser-induced sparks. Beyond a certain region close to the source, levels are found to decrease in a manner consistent with spherical spreading plus nonlinear hydrodynamic losses. Analysis of the waveforms shows that the acoustic pulses associated with the laser-induced sparks are more repeatable and have higher intensity than those from an electrical spark source. Laser-generated acoustic shock waves are ideal for simulating a blast wave or a sonic boom in the laboratory and for studying the associated propagation effects. To illustrate this application, the propagation of the laser generated shock waves over a series of different hard, rough surfaces has been investigated. The results show the distinctive influences of ground roughness on the propagation of the shock wave.     

Two Dimensional Generalization of Raizer's Analysis for the Subsonic Propagation of Laser Sparks

An extension to two dimensions of Raizer's analysis for the steady state, subsonic propagation of laser sparks is presented. A solution in closed form is obtained for a simplified, two dimensional energy equation, yielding both axial and radial temperature profiles as well as the relationship between incident laser intensity, laser radius and propagation velocity. The propagation mechanism is assumed to be thermal conduction and radiation losses are included in a phenomenological manner. The solution is obtained for a laser spark propagating in a channel and therefore can be used to investigate the effect of a boundary on spark propagation. The solution also allows calculation of the radial heat conduction parameter A introduced by Raizer for use in one dimensional approximations. Sample calculations are presented for air sparks of .15 and .50 cm radius.     

Some parameters of a spark channel with preionization of the gas

Spark discharges in a preionized gas gap were studied. Preionization was produced by breaking down the spark gap directly before the main discharge, which was used to ignite fuel gas mixtures. The resulting experimental and computed data are compared with theoretical data and with results obtained in an investigation of spark discharge parameters.It is shown that, as in the case of self-breakdown, the volume energy density in discharges in a preionized gas remains constant in order of magnitude (10¹⁹ eV/cm³).The studies were carried out in order to obtain certain spark characteristics for the purpose of increasing the thermal efficiency of discharges in igniting fuel mixtures.The authors are grateful to Doctor of Engineering Sciences Professor I. V. poroikov for his advice.     

Complex chemistry simulations of spark ignition in turbulent sprays

Three-dimensional DNS of two-phase flows with the point-source approximation and with complex chemistry for n-heptane has been used to extract physical information on the structure of igniting kernels following localised heat deposition in turbulent monodisperse sprays. Consistent with experiment, small sparks fail to ignite and sprays ignite later than premixed gaseous mixtures. Reaction rates are intense in spherical zones near droplets and much lower in the interdroplet spacing, resulting in a highly wrinkled flame surface. The propagation of these reaction zones was observed. The flame shows a locally non-premixed character, with reactions proceeding at a wide range of mixture fractions, which increases as evaporation progresses. The distribution of various chemical species is presented. The results constitute a database for model validation and physical analysis.     

Effect of needle cone angle and air flow rate on electrostatic discharge characteristics of a corona-needle ionizer

In this study, the corona-needle ionizer was designed, constructed, and characterized. Experimental characterizations of the electrostatic discharge in terms of current–voltage relationships of the corona ionizer, including the effects of discharge electrode cone angle and air flow rate were presented. It was found that the charging current and ion concentration in the charging zone increased monotonically with corona voltage. Conversely, discharge currents decreased with increasing angle of the needle cone. The negative corona was found to have higher current than the positive corona. At higher air flow rates, the ion current and concentration were found to be relatively high for the same corona voltage. The effect of air flow rate was more pronounced than the corona voltage. It was also shown that the ion penetration through the ionizer decreased with increasing corona voltage, and increased with increasing air flow rate. The highest ion penetration through the ionizer of the 10° needle cone angle was found to be about 93.7 and 7.7% for positive and negative coronas, respectively. The highest ion penetration for the needle cone angle of 20° was found to be 96.6 and 6.1% for positive and negative coronas, respectively.     

A 300 Hz TEA CO<Subscript>2</Subscript> Laser

We present a design and construction of a high pulse repetition rate (PRR) transversely excited atmospheric (TEA) CO₂ laser with ultraviolet preionization. We use a new combination of spark and corona preionizations. Under semi-sealed off condition, we obtained 220 W at 300 Hz with 7.7% efficiency in a 735 mJ/pulse. The best results we have obtained in different experiments are a 1.07 J/pulse, 320 Hz PRR, 11 MW peak power, and 10.6% efficiency.