水中脉冲电晕放电的声学特性研究

为研究水中脉冲电晕放电的声学特性,由水听器测量了放电产生的压力信号,在以放电电极为圆心、电极到水听器的距离为半径的球面对压力信号积分,得到放电的声能和放电的声效率;利用快速傅立叶变换(FFT)得到同轴电极下电晕放电的频谱分布;比较尖—尖电极下电弧放电晕放电的频谱发现电晕放电声信号的主频比电弧放电的高。

Investigation of Acoustic Characteristics of Pulsed Corona Discharge in Water

Crona discharge occurred in salted water.Compared with spark discharge,distance between two electrodes in coroa discharge is more long.Current forms between two electrodes at the begainning.Due to the high density of current at the point of electrode,liquid around the electrode is vapoured.Like the process in the air,ionization appears at the point.Then at the high voltage electrode point,bush-like plasma forms.But the plasma does not connect two electrodes.Because of high temperature,bubble forms outside of plasma.Firstly,the bubble expands until to its biggest diameter.Then the bubble begins to shrink until breakdown.Along with this process,pressure waves are formed. A system was established to investigate the acoustic characteristics of pulsed corona discharge in salted water.Fig.1 is the system sketch.Pressure signals are sampled through a hydrophone.The frequency bandwidth of hydrophone is wide enough to accept pressure signal.Using Newton-Cores formula,we get the acoustic energy of the discharge process.Current is sampled through a sampling resistance.Voltage wave is sampled through a divider.A Tektronix scope is used to accept and storage the signals.Acoustic efficiency is calculated,and the efficiency from electrical energy to acoustic energy is approximately 2%.Compared with spark discharge in the same conditions,this efficiency is more high.This result indicates that corona discharge can replace spark discharge in some application fields.Spectra distribution of corona discharge under coaxial electrodes and arc discharge under point-point electrodes are obtained through fast Fourier transform algorithm(FFT).Aiming at different application,we can analyze different frequency in corona discharge.Compared with spark discharge,corona discharge does not generate multiple pressure pulses,and pressure signal has more high frequency energy,which can be used in high resolution seismic exploration.This feature is advantage over spark discharge in some using conditions.With high frequency pressure waves,we can get more clear information of object detected.