RU2013782C1 - Device for spatial distribution of electric charge in solid dielectrics - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: device for spatial distribution of electric charge in solid dielectrics has pulse generator of optical radiation and unit for registration of acoustic-induced electric signal having electric coupling with dielectric sample, meter of parameters of laser radiation and unit for conversion and processing of signals. Generator of optical radiation has two channels. One of channels is coupled to optical input of meter of parameters of laser radiation which electric output is linked to first input of unit for conversion and processing of signals. Its second input is connected to output of unit for registration of acoustic-induced electric signal. EFFECT: increased accuracy of measurement. 1 dwg

Description

 The invention relates to techniques for measuring internal electrostatic fields in solid dielectrics and can be used in the radio engineering and electronic industries, as well as in research laboratories for non-destructive testing of electrostatic fields in solid dielectrics.

 A device for measuring the distribution of potential in solid dielectrics, containing a source of β-radiation, a detector and a recording device [1]. The operation of the device is based on determining the current in the external circuit of the test sample, resulting from the interaction of the flow of fast electrons with the substance of the dielectric in the presence of electric fields of space charges.

 A disadvantage of the known device is the destruction of the test sample in the process of determining the spatial distribution of charge in the volume of the dielectric.

 Closest to the technical nature of the present invention is a device [2], containing a pulsed optical radiation generator and a unit for recording an acoustically induced electric signal having electrical connection with a dielectric sample. The operation of the device consists in the excitation of sounding acoustic vibrations in a dielectric sample and registration of an electrical signal characterizing the distribution of space charge. The device allows measurements to be made without destroying the sample or introducing additional probes into it, disturbing the spatial distribution of electric charge under study.

 A disadvantage of the known device is the low accuracy of the measurement, as well as the impossibility of obtaining the desired charge distribution in absolute values, since in this case the final value of the duration of the acoustic pressure pulse acting on the test sample is not taken into account.

 The aim of the invention is to improve the accuracy of determining the spatial distribution of electric charge in solid dielectrics.

 In accordance with the proposed technical solution, the goal is achieved by the fact that in the device for determining the spatial distribution of electric charge in solid dielectrics containing a pulsed optical radiation generator and an acoustically-induced electric signal recording unit having electrical connection with a dielectric sample, a laser radiation pulse parameter meter is additionally introduced and a signal conversion and processing unit, and the optical radiation generator is made two-channel m, wherein one of the channels connected to the optical input measuring laser pulse parameters on the electrical output connected to the first input of the signal converting and processing unit, the second input coupled to the output registration unit acoustically induced electrical signal.

 In laser technology and laser technology, it is known to implement an optical radiation generator with two outputs [3]. However, the use of this optical radiation source in combination with a laser pulse parameter meter in the technique of measuring internal electric fields makes it possible to implement a two-channel version of the device for determining the spatial distribution of charge in solid dielectrics and to achieve qualitatively new results and, accordingly, increase the measurement accuracy. Together, these blocks make it possible in the proposed device to actually determine the temporal shape of the laser pulse, the maximum density of absorbed energy in the excitation zone, and, accordingly, the amplitude of the acoustic pressure pulse in a solid dielectric, which can be further used in the calculations made using the conversion unit introduced into the device and data processing, allows with a fairly high degree of accuracy to take into account the spatio-temporal characteristics of the probe pulse acoustic Cesky signal, having a direct impact on improving the accuracy of determining the desired spatial charge distribution in the sample. The introduction of a data conversion and processing unit into a new set of features into the device makes it possible to determine the desired spatial charge distribution in solid dielectrics with minimal distortions of its spatiotemporal structure and in real time, since in this case the final value of the acoustic pressure pulse duration is used in the calculation, which improves the accuracy of determining the spatial distribution of charge in solid dielectrics.

 Thus, the analysis of the totality of significant differences showed that the claimed technical solution meets the criterion of "significant differences".

 The drawing shows a block diagram of a device for determining the spatial distribution of charge in solid dielectrics.

 A device for determining the spatial distribution of charge in solid dielectrics contains a two-channel pulsed generator of optical radiation 1, electrodes 2 and 3, mounted on the ends of the dielectric sample 4 and connected at the input of the unit 5 for recording an acoustically induced electric signal (for example, a broadband amplifier, storage oscilloscope C 8- 12, an interface unit of the oscilloscope with a multi-channel analyzer [4], a multi-channel analyzer AI-1024-95 [5]), connected to the first input b OKA 6 data conversion and processing (for example, an information and computer complex for converting and processing multichannel measurement data [6]), at the second input connected to the output of the meter 7 parameters of the laser pulse, providing simultaneous measurement of the maximum density of absorbed energy and the temporal shape of the laser pulse .

 The device operates as follows.

C_oχG(ε_r)P

S_e(t-t′)

J(t′)dt′, (1)
где χ =

- модуль всесторонней объемной упругости [8] (где Е - модуль Юнга; μ - коэффициент Пуассона) ;
G(ε_r) =

-

- функция относительной диэлектрической проницаемости, учитывающая ее возможное изменение от величины приложенного акустического давления и для случая линейного акустического воздействия является величиной постоянной (где ε - диэлектрическая проницаемость исследуемого диэлектрического образца);
S_е - скорость продольных акустических волн;
С_о - емкость незаряженного образца;
Р_о - максимальная величина амплитуды давления в бегущей акустической волне;
J(t′) - функция, описывающая изменение импульса лазера во времени, причем

J(t)

≅ 1;
ρ (S_e(t-t′)) - распределение плотности заряда вдоль оси пучка лазерного излучения.When power is applied to the high-voltage unit of the pulse generator 1 of optical radiation, two laser pulses of equal duration and amplitude are formed at its output. When the first laser pulse acts on the electrode 2 mounted on the front side of the test sample 4, the laser radiation energy is almost instantly absorbed in the local volume, determined by the depth of laser radiation penetration into the substance and the transverse dimensions of the laser pulse. This, in turn, taking into account the unsteady nature of the radiation, leads to the formation of a field of thermoelastic mechanical stresses, which are unloaded by radiation from the excitation zone of the compression wave, which propagates with sound velocity at first along electrode 2, then due to additional matching of the wave acoustic impedances of electrode 2 and the test sample 4 freely passes into the volume of the test sample 4. When the compression wave propagates through the dielectric sample 4, some of the the following sample 4, which leads, firstly, to a spatial displacement of charges, secondly, to a change in the spatial concentration of charges and dipoles, and thirdly, to a change in the relative dielectric constant of the material of the studied sample 4. As a result of the processes occurring on the electrodes 2 and 3, induced charges appear, and changes in the magnitude of the induced charges depend on the distribution of real charges in the volume of the sample 4 and the parameters of the laser pulse. Depending on the value of the input impedance of the acoustically induced electric signal recording unit 5, the acoustically induced electric signal parameters are expressed through changes in potentials or currents, which allows, in principle, to estimate the characteristics of the charge distribution in the volume with the known spatio-temporal structure of the laser pulse [7]:
I (t) =

C _o χG (ε _r ) P

S _e (tt ′)

J (t ′) dt ′, (1)
where χ =

- modulus of comprehensive bulk elasticity [8] (where E is Young's modulus; μ is Poisson's ratio);
G (ε _r ) =

-

- the function of relative permittivity, taking into account its possible change from the value of the applied acoustic pressure, and for the case of linear acoustic exposure is a constant value (where ε is the dielectric constant of the investigated dielectric sample);
S _e is the velocity of longitudinal acoustic waves;
With _about - the capacity of the uncharged sample;
P _about - the maximum value of the amplitude of the pressure in a traveling acoustic wave;
J (t ′) is a function that describes the change in the laser pulse in time, and

J (t)

≅ 1;
ρ ( _Se (tt ′)) is the charge density distribution along the axis of the laser beam.

) =

χC_oG(ε_r)

(k)

(ω), (2)
следовательно,

(k) =

, (3)
где I^~( ω ) - спектр импульса электрического сигнала, снимаемого с электродов 2 и 3;
ρ^~ (k) - пространственный спектр распределения электрического заряда внутри диэлектрика;
k - пространственная частота, равная ω/S_e;
P

) =

P(t)e^iωtdt - спектр зондирующего акустического сигнала (где P(t)= P_oJ(t), где P_o= ГЕ_m; Г =

- безразмерная постоянная Грюнайзена; α - коэффициент теплового расширения; ρ - плотность диэлектрика; С - теплоемкость; κ - модуль всесторонней объемной упругости; Еm, J(t) - максимальная плотность поглощенной энергии в зоне возбуждения и функция, описывающая изменение импульса лазера во времени, соответственно, определяемые с помощью измерителя 7 параметров импульса лазерного излучения с выхода которого сигналы подаются на вход блока 6 преобразования и обработки данных, в котором происходит расчет по заданной программе спектра зондирующего акустического сигнала Р^~( ω ) с использованием полученных ранее файлов данных.The electric signal I (t) is supplied to the input of the data conversion and processing unit 6 by means of a unit 5 for recording an acoustically induced electric signal, in which the pulse spectrum of the electric signal I ^~ (ω) is calculated using a given program. As can be seen from formula (1), the amplitude of the electric signal taken from electrodes 2 and 3 and characterizing the spatial charge distribution in the volume of a charged dielectric is described by the expression of the convolution type. This circumstance allows, using the Borel theorem known from spectral analysis, to obtain the following expression:
I

) =

χC _o G (ε _r )

(k)

(ω), (2)
hence,

(k) =

, (3)
where I ^~ (ω) is the spectrum of the pulse of an electrical signal taken from electrodes 2 and 3;
ρ ^~ (k) is the spatial spectrum of the distribution of electric charge inside the dielectric;
k is the spatial frequency equal to ω / S _e ;
P

) =

P (t) e ^iωt dt is the spectrum of the sounding acoustic signal (where P (t) = P _o J (t), where P _o = ГЕ _m ; Г =

- dimensionless Grüneisen constant; α is the coefficient of thermal expansion; ρ is the density of the dielectric; C is the specific heat; κ is the modulus of comprehensive bulk elasticity; Em, J (t) is the maximum density of absorbed energy in the excitation zone and a function that describes the change in the laser pulse in time, respectively, determined using a meter 7 of parameters of the laser radiation pulse from the output of which the signals are fed to the input of the conversion and data processing unit 6, in which is calculated according to a given program of the spectrum of the probing acoustic signal P ^~ (ω) using previously obtained data files.

k)e^ikxdx, (4) можно рассчитать реальное распределение электрического заряда в объеме твердого диэлектрика по формуле
ρ(S_et) =

e^iωt _dω
Таким образом, алгоритм работы блока 6 преобразования и обработки данных заключается в следующем.Next, using the calculated spectra I ^~ (ω) and P ^~ (ω) in the data conversion and processing unit 6, the calculation is performed according to a given program in accordance with formula (3) of the spatial spectrum of the distribution of electric charge inside the dielectric ρ ^~ (k) and, applying the inverse Fourier transform, namely
ρ (x) =

k) e ^ikx dx, (4) we can calculate the actual distribution of electric charge in the volume of a solid dielectric by the formula
ρ (S _e t) =

e ^iωt _dω
Thus, the algorithm of the block 6 conversion and data processing is as follows.

и постоянной Грюнайзена Г =

.Introduction to the memory block of the values of the constant values: μ, E, C _o , _Se , G (ε _r ), ρ, C, α;
Calculation of the modulus of comprehensive bulk elasticity χ =

and the Grüneisen constant G =

.

According to the measured values of I (t), the calculation according to a given program of the spectrum of the pulse of the electric signal I ^~ (ω).

) =

P(t)e^iωtdt.From the measured values of the maximum density of the absorbed energy E _m and the temporal shape of the laser pulse J (t), the calculation according to the given program P (t) = P _o J (t) = GE _m J (t) and the determination of the spectral composition of the generated acoustic pulses by non-periodic expansion functions P (t) in the Fourier integral:
P

) =

P (t) e ^iωt dt.

k) =

Применяя обратное преобразования Фурье, расчет по заданной программе реального распределения электрического заряда в объеме твердого диэлектрика:
ρ(S_et) =

e^iωtdω
Таким образом, измеряя амплитуды акустоиндуцированного сигнала, а также плотность поглощенной энергии в зоне возбуждения зондирующих акустических сигналов, проводя с помощью блока преобразования и обработки данных вычисление спектра импульса электрического сигнала и, определение спектрального состава генерируемых акустических импульсов, а также рассчитывая пространственный спектр распределения электрического заряда внутри диэлектрика, а затем применяя обратное преобразование Фурье, можно получить реальное распределение электрического заряда в объеме заряженного диэлектрика.Calculation according to a given program of the spatial spectrum of the distribution of the electric charge inside the dielectric:

k) =

Applying the inverse Fourier transform, the calculation according to a given program of the real distribution of electric charge in the volume of a solid dielectric:
ρ (S _e t) =

e ^iωt dω
Thus, by measuring the amplitudes of the acoustically induced signal, as well as the density of the absorbed energy in the excitation zone of the probing acoustic signals, using the conversion and data processing unit, calculating the spectrum of the pulse of the electric signal and determining the spectral composition of the generated acoustic pulses, as well as calculating the spatial spectrum of the distribution of electric charge inside the dielectric, and then applying the inverse Fourier transform, you can get the real distribution of elec charge in the volume of a charged dielectric.

 In the proposed device, the accuracy of determining the spatial distribution of charge in solid dielectrics is much higher than in the prototype (Rozno A.G., Gromov V.V. Measurement of the density of the distribution of space charge in solid dielectrics. - Letters in ZhTF, 1979, v. 5, issue . 11, p. 168), containing a pulsed optical radiation generator, two electrodes mounted on the end faces of the dielectric sample, and an electric signal pickup unit that does not take into account the parameters of laser radiation acting on the surface of the sample of the electric sample, and the parameters of ultrasonic vibrations excited by laser pulses in the sample, which leads to the determination of the desired spatial distribution of charge in relative values and with significant distortions of its spatio-temporal structure. In addition, the proposed device makes it possible to automate the measurement procedure not only of the spatial charge distribution, but also of the distribution of electric field strength and potential in the volume of dielectric materials. (56) 1. B. Gross "The effect of irradiation in borosilicate glass." Plus Rev. , 1957, v. 107, p. 368.

 2. Rozno AG, Gromov VV. Measurement of the density distribution of space charge in solid dielectrics. - Letters to the ZhTF, t. 5, N 11, p. 648, 1978.

 3. Handbook of laser technology. / Ed. Yu. V. Bayborodina and others K.: Technique, 1978, p. 268, fig. 195, p. 270, fig. 198.

 4. R. Weber. D. Smith. Pairing an oscilloscope with a multi-channel analyzer // Instruments for Scientific Research, 1986, N 12, p. 161, FIG. 1.

 5. Technical description of the multi-channel amplitude pulse analyzer AI-1024-95.

 6. Zayka V. A., Mokhnach A. T., Babitskaya L. D. Information-computer complex for the conversion and processing of data of multivariate measurements // Instruments and experimental equipment. - 1983, N 6, p. 194.

 7. Leiviner I. Les charges electrostatiques clansles isolants une meilleure connaissance par de nou velles methodes de messure / Rev. General Del. , Electr. 1987, N 2, pp. 57-59.

 8. Yavorsky B. M., Detlaf A. A. Handbook of Physics. M.: Science, 1977, p. 284.

 9. Rozno AG, Gromov VV Acoustic sounding - a new method for measuring electric charge and field in the volume of dielectrics / Izv. USSR Academy of Sciences. Ser. Physical, 1986, v. 5, N 3, p. 447.

Claims (1)

 DEVICE FOR DETERMINING SPATIAL DISTRIBUTION OF ELECTRIC CHARGE IN SOLID DIELECTRICS, containing a pulsed generator of optical radiation and a unit for recording an acoustically-induced electric signal, which is in electrical communication with a dielectric sample, characterized in that, in order to increase the accuracy of determining the spatial distribution of electric charge, the meter is introduced into it a laser pulse and a signal conversion and processing unit, an optical generator The radiation is made two-channel, one of the channels being connected to the optical input of the laser pulse meter, via an electrical output connected to the first input of the signal conversion and processing unit, and a second input connected to the output of the acoustically-induced electric signal recording unit.

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