RU2092934C1 - Ferroelectric ceramic polarizing technique - Google Patents

Abstract

FIELD: mass production of piezoids. SUBSTANCE: single voltage pulse is applied to ferroelectric ceramic specimen placed in insulating medium through inductance coil. Current passed through specimen is integrated and voltage is picked off specimen as soon as desired integral value is attained. EFFECT: facilitated procedure. 3 dwg

Description

 The invention relates to piezoelectric technology and can be used in the mass production of piezoelectric elements.

In the process of manufacturing frequency-selective devices (filters), one of the most important operations is to control the level of polarization of piezoceramics (PC). A known method of controlling the polarization of PCs in order to fine-tune their frequency characteristics by high-temperature aging (1). In this method, the piezoelectric element is heated to temperatures not reaching 30 100 ^o C to the Curie point, over a period of time, the duration of which is determined by the given resonance interval.

 A known method of fine-tuning the frequency characteristics by changing the level of polarization by the action of depolarizing pulses of electric voltage on a piezoceramic element (2).

 A common drawback of these methods is that initially the piezoceramic element is polarized by one of the known methods, and then the polarization level is adjusted to the desired value. This leads to high complexity and, consequently, low productivity of known methods.

 There is also a method of polarizing ferroceramic elements and a device for its implementation (3), in which the sample is exposed to a series of unipolar pulses of constant energy, and the degree of polarization is controlled by the amplitude of the voltage on the electrodes of the piezoelectric element.

 The disadvantage of this method is the need to apply a series of pulses to the sample, which leads to an increase in polarization time. In addition, the application of a series of polarizing pulses leads to a change in the polarization of the sample stepwise, which will affect the accuracy of polarization.

 As a prototype, the solution (4) was selected, which describes the installation for switching polarization by the action of a unipolar pulse voltage. However, the described setup does not allow us to solve the problem of achieving a given level of polarization in general and all the more with high accuracy.

 The aim of the invention is to increase the efficiency and accuracy of achieving a given level of polarization.

 The goal is achieved by the fact that in the continuous process of polarization control the formation of the trailing edge of the polarizing pulse upon reaching the integral of the polarization current of a given value.

 In FIG. 1 shows a diagram of the implementation of the proposed method; in FIG. 2 - timing diagrams of the installation; in FIG. Figure 3 shows the experimental dependence of the electromechanical coupling coefficient of the CTTs-19 samples (6 x 6 x 1) mm on the reference voltage.

 The main elements of the installation are a high-voltage voltage source 1, the first electronic switch 2, which connects the voltage source 1 to the polarizable piezoelectric element through inductance, the second electronic switch 3, which removes voltage from the sample by the moment the signal passes from the comparator 4, the current integrator 5, connected to the current-measuring resistor R .

 The method is as follows.

A piezoelectric sample, for example, from TsTS-19 is placed in a cell with a dielectric fluid. Then, by switching on the electronic switch 2, the leading edge of the high-voltage pulse is formed (Fig. 2a). In this case, a polarization current flows along the piezoceramic sample (Fig. 2b), which creates a voltage drop across the resistor R. The signal from the resistor R is fed to a current integrator 5 (voltage-current converter), the output of which is formed by a voltage U proportional to the polarization current integral Sf (t) dt (Fig. 2c). This voltage in the comparator 4 is compared with the reference voltage U _op corresponding to a given level of polarization. When performing UU _{op, the} comparator generates an electric signal (Fig. 2d), which is fed to the inputs of electronic keys 2 and 3. In this case, the key 2 is opened, and the key 3 is closed, thus forming the trailing edge of the high-voltage pulse (Fig. 2a). This completes the polarization process.

In the proposed method, the polarization for each sample is individual. By increasing, for example, the steepness of the polarization current for another sample due to technological factors, the comparator 4 generates an electrical signal at time tt ₂ , as shown in FIG. 2 by dashed lines, as a result of which the polarization process is completed earlier.

 Thus, for each specific sample, a well-defined duration of high-voltage pulse is formed, ensuring the achievement of a given level of polarization with high accuracy.

 Inductance L is included in the circuit of a polarizable sample to prevent an abrupt increase in the polarization current at the time of supply of the high-voltage pulse. A change in the inductance leads to a change in the polarization time, which allows the selection of the value of L to adjust the polarization time interval. For example, for a PZT-19 piezoceramic sample (10x1 mm), a change in L within (0.05 50) mg allows you to adjust the polarization time range in the range of 1 50 μs.

In FIG. Figure 3 shows the experimental dependence of the electromechanical coefficient K _{p of the} connection of industrial samples TsTS-19 (6 x 6 x 1) from the reference voltage.

The parameters of the TsTS-19 piezoceramic samples (10 x 1 mm) polarized by the proposed method: the amplitude of the high-voltage polarizing pulse 3 kV, the pulse duration of about 30 μs. In this case, the electromechanical coupling coefficient K _p amounted to 0.413 ± 0.008.

 Thus, the proposed method provides effective polarization of piezoceramic samples to a given level with a high degree of accuracy.

Claims (1)

 The polarization method of ferroceramics, which consists in applying a single unipolar voltage pulse to the sample through the inductance, integrating the current passing through the sample during the polarization process, characterized in that the voltage is removed from the sample upon reaching the specified value of the current integral.

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