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Share：| Relation between electrical system and mechanical system | ||||||||||||||||||||||||||||||||||
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 Impedance matching |
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| As the piezoelectric ceramic element has capacitive impedance at the resonance point, it cannot be driven effectively, if the electric power supplied from the oscillator. To achieve the supply of electric power effectively, it must need to counteract reactance by the same modulus induced reactance (chalk coil) with capacitive reactance of the piezoelectric ceramic element, and it must be put in the oscillator circuit with series or parallel connection against piezoelectric ceramic element. | ||||||||||||||||||||||||||||||||||
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Vector chart at the resonance of piezoelectric element
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Piezoelectric Ceramic Oscillator consist of  ,  ,  and Cd in the equivalent circuit. But as and deny at the point of resonance frequency, the equivalent circuit showed  and  only with parallel connection. Then, impedance  of the oscillator becomes  . Equivalent  to the numeric figure of this  is put in parallel to deny of it, and impedance of the oscillator assumed to be only  . In addition, if the output resistance of the oscillator is assumed to be  , the most effective drive to make of  can be done. This simple method need to adjust the wire wound ratio used  wire wound ratio output transformer to become  . |
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The value of R1 changes, too, if changes the size of the load because  corresponds to a mechanical load of the oscillator. For instance, the same water load makes great changes by the way of immersing in the water and generating the cavitation. It is necessary to measure close to the actual operating condition. |
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A parallel equivalent circuit can be converted into the series circuit of Rs and Cs. In this case,  can be denied by putting chalk coil  that the numeric figure is equal to  in the series. |
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Method of output calculation to given force  |
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The usage where charge  or voltage  by force is an application of electric energy conversion from the machinery energy. The all charged amount  where piezo-electric ceramics generated corresponds to add all force through the proportion constants such as the size, piezoelectric constants  , and  in electrostatic capacity. |
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At this time, output voltage  becomes the following relation from thickness t and sectional area  of piezoelectric constant  of piezoelectric element. |
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If force  is constant, charge  is also constant because charge  that a piezoelectric element is corresponding to the size of force  . However, because the value of the insulation resistance of a piezoelectric element also which assume a kind of capacitor is limited, generated charge is discharged according to the next expression. |
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  Apparent charge for real |
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For this, it should be careful attention that it has not static sensitivity when you apply a piezo-electric element to the pressure sensor etc. |
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Force  can be developed from the relation among mass  , acceleration  , amplitude  , and the corner frequency  with alternating current making like the next expression. |
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Method of calculation for amount of displacementon input voltage |
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There are applications to drive of distortion energy with input of voltage. As electric power input - mechanical power output application, there is the one which operates by alternating current as well as ultrasonic equipments, and by direct current or low frequency alternating current. The displacement  at a no load and generation force  becomes the following relations. |
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 Input voltage ,  Piezoelectric constant ,  Compliance ,  Thickness and sectional area of piezoelectric element |
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Anti-electric power |
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 The piezoelectric element obtains piezoelectricity by polarization of a high direct current, voltage giving directionality in the direction of an internal voluntary polarization, and giving the residual polarization. The voltage is put contrary to the direction of the polarization, and the value to which the residual polarization vanishes is anti-electric power  . The value of anti-electric power is different according to the kind of material of a piezoelectric element. When the plus voltage is impressed in the direction of a piezoelectric element where the residual polarization is promoted in a word, the plus display side when doing to actual use, it is unquestionable. When a high voltage of the minus is impressed to the plus display side, a remarkable attention is required. Therefore, the characteristic is different depending on the condition. Many hundreds of from tens of  electric field becomes a limit from tens of for the thickness between electrodes of a piezoelectric element. |
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The highest use temperature |
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| The characteristic of a polarized piezoelectric element is secure from remarkable changes on the low temperature range. But on a high temperature range, it has limitation in operational temperature range as there is a metabolic point of crystal axis (Curie point). The crystal becomes unstable at the Curie point due to the permittivity may infinity increase, and the crystal structure made phase transition. Because both voluntary polarizations and the residual polarizations disappear at that time, and piezoelectricity also disappeared. The residual polarization do not come to remain disappearing, but a voluntary polarization restores to remain from the loss of piezoelectricity when cooled below the Curie point afterwards. Because the disappearance of the residual polarization is different in the temperature time and the material, it is not categorically decided. About 1/2 to 1/3 of the Curie point becomes standards as a temperature of unquestionable as for continuous use. | ||||||||||||||||||||||||||||||||||
 High temperature characteristic of piezo-electric ceramic (C-6 system) |
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Physical constant at normal temperature
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Physical constant at normal temperature of [Pb(Zr • Ti)O3] ceramic
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Scanning
