RU2297640C2 - Method of measurement of electric pulse parameters - Google Patents

Abstract

FIELD: measurement of electrical and optical parameters.

SUBSTANCE: method can be used while testing different technical systems for registration of electrical signals of physical value detectors under extreme conditions. Method of measurement of parameters of electric pulse is based upon effect of tested pulse onto piezoelectric converter and degree of change of parameters is measured. Degree of change is used to judge on parameters of tested pulse. As converter the non-resonant electromechanical converter is used which converter has electromechanical coupling factor being equal to K²≪1. Change in parameters of mentioned converter is found from amplitude-time dependences of shift or speed of its movement by laser interferometry methods. Noise immunity of method of measured is improved in relation to electro-magnetic interference and mechanical influences. Self-descriptiveness of method is improved due to ability of registering of electric pulse shape.

EFFECT: improved noise immunity; widened area of application; improved self-descriptiveness.

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Description

The invention relates to measuring equipment, and more particularly to the field of electrical and optical measurements of pulsed loads, including mechanical loads in vibroacoustics and physics of fast processes, and can be used in testing various technical systems for recording electrical signals of physical quantity sensors in extreme conditions.

A known method of measuring the parameters of a single electric pulse / A.C. USSR No. 892323, IPC 7 G01R 19/04, BI No. 47, 1981 /, based on the measurement of a parameter of a sensing element changed under the influence of the studied pulse, according to which the studied pulse acts on the semiconductor element, causing it to irreversible thermal or avalanche-thermal breakdown, measure the residual resistance of the punched semiconductor element and the predetermined experimental dependence between the pulse amplitude and the residual resistance of the semiconductor element determines the amplitude of the studied Pulse.

The disadvantage of this method is its low information content, since it does not allow simultaneously with the amplitude of the pulse to register its duration or shape.

The closest in technical essence to the claimed (prototype) is a method developed earlier by the applicant for measuring the parameters (amplitude and duration) of an electric pulse / Tolstikov I.G. A method of recording parameters of a single rectangular electric current pulse. Patent RU No. 2029311, G01R 19/04, BI No. 5, 1995 / using a piezoelectric device (piezoelectric transducer) made of a ferroelectric piezomaterial made in the form of a passive registrar (storage device) of a capacitor type containing several electrically parallel sensitive memory elements (ferroelectric capacitors) ) The sensitive elements (SE) of this recorder change their physical state (namely, the magnitude of the residual polarization) when exposed to a pulsed electric field. This allows us to establish the relationship between the parameters of the measured electric pulse and the degree of change under its influence of the residual polarization of ferroelectric CEs. The direct measurement method is as follows. Connect the recorder to the load. Then, the test pulse is supplied to the load. The impact of the pulse on the SE leads to the appearance of electric fields of different magnitude in their volume, which leads to a change in the residual polarization of individual SEs to various degrees, the realized values of which can remain for a long time. After the passage of the pulse, the residual polarization in each SE is measured by known methods (for example, by the magnitude of the direct piezoelectric effect). The parameters (amplitude and duration) of the studied pulse are then determined from the previously obtained experimental dependence between these parameters and the degree of change under its influence of the residual polarization of ferroelectric CEs.

A disadvantage of the known methods is that the elements of the system that perform the functions of converting (reading) information and its long-term storage are structurally combined in one device. This leads to the need for additional measures using long measuring lines to protect the device from external electromagnetic and mechanical influences in extreme conditions of measurements, for example in an explosive experiment, in order to save information, which in some cases is an impossible task.

The disadvantage of the prototype is the lack of registration of the shape of the investigated pulse simultaneously with its amplitude and duration.

The problem to which the claimed invention is directed is to create a simple noise-immune method for measuring the parameters of a single electrical pulse of the micro- and submicrosecond range, generated, for example, by sensors of physical quantities under pulsed loads, under extreme conditions when exposed to strong electromagnetic and mechanical interference.

The technical result achieved by the implementation of the present invention is to increase the noise immunity of the measurement method from electromagnetic interference and mechanical stress, expand its field of application, as well as increase its information content due to the possibility of detecting the shape of an electric pulse.

This is achieved by the fact that in the method of measuring the parameters of the electric pulse, which consists in the fact that the studied pulse acts on the piezoelectric transducer, determine the degree of change in its parameters, the value of which judges the parameters of the studied pulse, the new is that non-resonant electromechanical converter with the electromechanical coupling coefficient K ² «1 with the change of said parameters of the converter is determined by the amplitude-time nnym dependencies displacement or velocity of the surface laser interferometric techniques.

The technical essence of the invention consists, on the one hand, in using the inverse piezoelectric effect under special conditions of its manifestation, in which it is possible to establish a simple relationship between the parameters of the electric loading pulse and the mechanical response of the piezoelectric, namely, when the interference is local (secondary, arising from the repeated manifestation of direct and the inverse piezoelectric effects) of acoustic waves in the volume of the latter does not significantly affect the mechanical response. Such conditions can be created using the so-called quartz approximation (the piezoelectric effect is weakly manifested, the electromechanical coupling coefficient K is sufficiently small so that K ² ≪ 1). When condition K ² ≪1 is fulfilled, the equivalent piezoelectric transducer circuit can be represented as a capacitor with a source of voltage applied to it / see, for example, Kayno G. Acoustic waves: Devices, visualization and analog signal processing: Per. from English - M .: Mir, 1990, 656 p., See p. 58 /. Therefore, in the quartz approximation, the temporary form of mechanical stress, and hence the velocity of the (front) surface of the piezoelectric transducer, repeats the temporal form of the applied electric voltage (field) during the half-period (T) of its own acoustic vibrations, and it is also determined with sufficient accuracy for practice at boundary conditions during all the above registration time / cm. also Ultrasonic piezoelectric transducers for non-destructive testing. Under the total. ed. Ermolova I.N. - M.: Mechanical Engineering, 1986, 280 p., See p. 33, p. 61 /. In the latter case, using well-known methods of filtering ultrasonic signals, one can easily exclude the contribution of reflected (primary) acoustic waves to the information signal, since the natural frequencies of the piezoelectric transducer are known / see, for example, Perov D.V., Rinkevich AB Filtering the ultrasonic signals of a laser interferometer using a dyadic wavelet transform. Flaw detection 2002, No. 4, pp. 78-98 /. Therefore, according to the amplitude-time dependences of the velocity (or displacement with subsequent differentiation) of the surface motion of the piezoelectric transducer, one can judge the parameters of the electric pulse under study.

On the other hand, the technical essence of the invention consists in the use of a non-resonant electromechanical piezoelectric transducer having a simple structure, for example, in the form of a piezoelectric element (quartz piezoelectric crystal), small geometric dimensions and low cost, and also having good electromagnetic compatibility with physical quantity sensors . This allows you to constructively combine the named piezoelectric transducer (information conversion device) with these sensors, and to store the information storage device (laser interferometer) outside the zone of external influences. Moreover, during the registration process, for a few microseconds, the piezoelectric transducer (in contrast to the SE of the sensor) is exposed only to electromagnetic interference, and immediately after registration it can be destroyed by mechanical action.

The use of a non-resonant electromechanical piezoelectric transducer to measure the parameters of a single electric pulse by precision measuring the parameters (nature) of its surface motion by laser interferometric methods is unknown to the applicant.

Note that if a voltage of 1 V is applied to the piezoelectric plate, then its deformation will be equal to 2.3 · 10 ^-3 nm for quartz, 16.2 · 10 ^-3 nm for lithium niobate, 225 · 10 ^{- for} barium titanate ³ nm, for PZT piezoceramics - 200-500 · 10 ^-3 nm, respectively, significantly exceeding the resolution of modern interferometric methods (at least 10 ^-4 nm, see links below). We also note that the working frequency band of non-resonant electromechanical piezoelectric transducers reaches many hundreds of megahertz. For example, using the so-called thick piezoelectric transducers, acoustic pulses of nano- and picosecond durations can be emitted / Ultrasonic piezoelectric transducers for non-destructive testing. Under the total. ed. Ermolova I.N. - M.: Mechanical Engineering, 1986, 280 p., See p. 47 /. The speed of piezoelectric transducers is theoretically limited only by the time it takes for the ionic polarization to be established in the piezoelectric materials and lies in the range of 10 ^-10 -10 ^-13 s. In practice, the minimum duration of acoustic pulses emitted by ordinary thick piezoelectric transducers from piezoceramics is a few nanoseconds and is limited by the purely technical capabilities of creating electronic circuits of nanosecond duration generators and the cleanliness of the processing of the radiating surface of the piezoelectric element. The frequency characteristics of piezoelectrics can also be judged, for example, by their use in piezoelectric resonators and filters. For crystalline resonators, the frequency range is limited from above to a frequency of 500-1000 MHz / Piezoelectric resonators. Directory. Ed. Kandyby P.E. and Pozdnyakova P.G. - M.: Radio and Communications, 1992.394 s. /. Band-pass filters for surfactants (surface acoustic waves) are widely used in the frequency range 2-10 GHz / Res I.S., Poplavko Yu.M. Dielectrics. Basic properties and applications in electronics. - M.: Radio and Communications, 1989, 288 pp. /.

It is also important that modern laser interferometric methods make it possible to detect mechanical vibrations with a minimum amplitude of the order of 10 ^-4 -10 ^-5 nm in the frequency band from units of hertz to hundreds of megahertz, while the probe beam can be focused into a spot with a diameter of several tens of microns / cm. , for example, 1. A.I. Kondratiev, Yu.M. Krinitsyn, S. A. Gusakov. Laser interferometers for measuring ultrasonic vibrations. Autometry. 2000, No. 4, p. 116-123; 2. P.V. Bazylev. Two-channel laser receiver of ultrasonic vibrations. PTE, 2003, No. 1, pp. 110-111; 3. Patent (USA) US 5909279 A dated 03/17/1997. Ultrasonic sensor with a coherent radiation source and method of its application.

The above parameters of the known piezoelectric transducers and interferometers indicate the fundamental possibility of implementing the proposed method in the development of electro-piezoelectric information converters for physical quantity sensors generating an informative electric pulse with characteristic amplitude and duration, respectively, belonging to the ranges 10 ^-2 -10 ⁺² V and 10 ^-1 - 10 ⁺² MHz and higher.

The main interferometric systems used under extreme conditions during explosive experiments are considered in monograph / 4. Methods for studying the properties of materials under intense dynamic loads (Chap. 9. Laser Doppler measuring systems and their application in shock wave studies.). Monograph. Under the total. ed. Dr. Phys.-Math. Sciences M.V.Zhernokletova. - Sarov: FSUE RFNC-VNIIEF, 2003, 403 p., See p. 372 /. Such systems are used here to measure the speed of a moving surface, as well as the distribution of speed over the surface in both single-frame and continuous multi-channel modes.

A positive point is that the proposed method allows you to expand the functionality of these systems and the scope of their application due to the possibility of recording other physical characteristics of the studied processes, for example, pressure (voltage) pulse profiles, and also helps to unify modern measuring systems based on multichannel interferometers. In some cases, the use of the method improves the characteristics of the sensors themselves by reducing their parasitic inductance or may be the only possible way to obtain information. The expected economic effect when implementing the proposed method in the considered measuring interferometric systems is associated with the possibility of using conventional low-power (tens of MW) laser receivers for measuring ultrasonic vibrations / 1, 2 / instead of specialized powerful (10 ² -10 ⁴ W) laser interferometers / 4 /, the cost of which is approximately an order of magnitude greater.

Thus, the use of the proposed method allows to increase the noise immunity of the measurement method from electromagnetic interference and mechanical stresses, to expand its scope, and also to increase its information content due to the possibility of registering the shape of an electric pulse.

Figure 1 presents a variant of the setup of the experiment for recording the parameters of the shock wave in an explosive experiment in which the inventive method is implemented.

Figure 2 presents the piezoelectric circuit of a non-resonant electromechanical piezoelectric transducer in the form of a piezoelectric element with a damper on the back side, explaining its operation.

Figure 3 presents the amplitude-time dependence of the velocity w (t) of the front surface of the indicated non-resonant electromechanical piezoelectric transducer.

The inventive method can be implemented as follows. In an explosive experiment (see Fig. 1), a physical quantity sensor (for example, a pulse pressure sensor) 2, an electric signal U (t) from which is fed to the input of a non-resonant electromechanical transducer (electropiezo-optical transducer), is placed on the path of shock wave (HC) 1 propagation 3. The sensor 2 and the converter 3 are structurally combined and placed in one housing 4, while the converter 3 is located behind the sensor 2 so that the shock wave acts on it after the arrival of the signal U (t). Using the converter 3, the electric information signal U (t) is converted into an optical analogue J (t) and fed to the input of the laser receiver (interferometer) 5 via a fiber optic fiber 6. The receiver 5 is protected from the effects of an explosion by a screen 7. The information signal is converted in this case along the following path: HC parameter (pressure pulse p (t)) - electric pulse U (t) of the sensor - electric field pulse E (t) in the piezoelectric material of the transducer - pulse σ (t) of mechanical stress in the piezoelectric material due to the inverse piezoelectric defects - motion parameter (amplitude and time dependence of the displacement x (t) or the velocity w (t) ultrasonic waves) surface nonresonant transmitter - optical information signal J (t).

As a non-resonant electromechanical transducer 3 (with an electromechanical coupling coefficient K ² ≪1) having the simplest design, for example, a piezoelectric element 8 in the form of a thin x-cut quartz disk (see Fig. 2) with thickness d with electrodes can be used on the bases 9 and 10, placed close to the damper 11. The damper 11, made, for example, of epoxy resin with a tungsten powder filler, is acoustically matched with the piezoelectric element 8 and provides fast absorption of acoustic waves entering it. The operation of such a transducer is based on the fact that acoustic signals arise on surfaces (bases) carrying electrodes 9 and 10. If the transducer is excited with a short electric pulse U (t) of duration t ₀ <d / c (where c is the speed of elastic waves in quartz) , then free electric charges appear on the electrodes 9 and 10, and due to the inverse piezoelectric effect, both of its bases are set in motion. Each base acts as a source of two ultrasonic waves (compression and tension, indicated by dashed lines in FIG. 2) emitted in two directions (indicated by arrows) in the piezoelectric element (waves σ _TP and σ _LP ) and into the external environment (waves σ _td and σ _ln ). As a result, for the case shown in Fig. 2 and determined by the direction of the velocity vector w (t), two acoustic pulses arise on the front surface 9: the first pulse (tensile wave σ _ln in the piezoelectric element) emitted by the front side from the moment of time t = 0; the second pulse (compression wave σ _TP in the piezoelectric element) emitted from the moment t = 0 by the rear surface 10 and arriving on the front surface 9 at the time t = Т = d / c, i.e. with a delay corresponding to the propagation time of the elastic wave through the piezoelectric element. The timing diagram of these pulses σ (t) has the form of two pulses of mutually opposite polarity following through the time interval T (see Fig. 3). Moreover, the relations σ ₁ (t) ~ E (t) ~ U (t) ~ w ₁ (t) are valid for the first pulse, and σ ₂ (tT) ~ E (t) ~ U (t) ~ w _{2 for the second} (t-T). For both pulses, the law of conservation of momentum is written in the form σ (t) = - w (t) · Z, where Z is the acoustic impedance of quartz. Due to various boundary conditions (acoustic matching conditions) on the back and front surfaces of the piezoelectric element, the amplitude of the second pulse is approximately two times less than the first. However, the shape of both pulses is the same and coincides with the shape of the studied pulse U (t), since for quartz the relation K ² = 0.009≪1 and the above reasoning are valid. Note that all the waves that passed to the left through the back surface 10 are absorbed by the damper 11, and there is no reflection on the back surface 10.

A precision measurement of the velocity of the front surface w (t) directly or its displacement, followed by differentiation and determination of w (t) by calculation, is carried out using an optical channel containing (reflecting) the front surface of the electrode 9 and a fiber waveguide 6, the end of which is directed to the center of the piezoelectric element 8 Fiber optic fiber 6 provides the transmission of optical signals to an optical recorder, such as a laser interferometer for measuring ultrasonic vibrations / see, for example, the above links 1, 2 /. The parameters of the studied pulse U (t) can be determined from a simple relation resulting from the equation of the inverse piezoelectric effect and the law of conservation of momentum for an elastic wave under the considered boundary conditions, namely

U (t) = w (t) · d · Z / e ₁₁ at 0≤t <T,

where e ₁₁ is the piezoelectric constant for quartz.

Obviously, the pulse parameters U (t) can also be determined from the dependence w (t) for the second pulse in Fig. 3 (at t≥T). If the duration of the studied pulse t ₀ > d / c = T, then the pulses in figure 3 are superimposed on each other from the moment t = T and restoration (filtering) of the first pulse in the interval T <t≤t _{0 is} required. This operation is easy to carry out by calculation, proceeding from the similarity of both pulses and knowing the parameters of the first pulse in the interval 0≤t <T.

The expected error of pressure measurement in this example is 5-10%.

Thus, the use of the proposed method allows to increase the noise immunity of the measurement method from electromagnetic interference and mechanical stresses, to expand its scope, and also to increase its information content due to the possibility of registering the shape of an electric pulse.

Claims (1)

The method of measuring the parameters of the electric pulse, which consists in the fact that the studied pulse acts on the piezoelectric transducer, determine the degree of change in its parameters, the value of which is used to judge the parameters of the studied pulse, characterized in that a non-resonant electromechanical converter with an electromechanical coupling coefficient K ^{2 is used} ≪1, while changing the parameters of the specified transducer is determined by the amplitude-time dependences of the bias or the velocity of its surface by laser interferometric methods.

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