PIEZOELECTRIC DEVICE HAVING AT LEAST ONE PIEZOELECTRIC ELEMENT

Abstract

Aspects of the present disclosure relate to a piezoelectric device having at least one piezoelectric element, which has a support plane oriented to a force introduction element, wherein in the event of a thermal loading of the piezoelectric device in the support plane, expansion differences between the piezoelectric element and the force introduction element occur. To compensate for shear loadings, at least one transition element is arranged between the piezoelectric element and the force introduction element, the E-module of which is smaller than the E-module of the piezoelectric element in the support plane.

Claims

1. A piezoelectric device comprising: at least one piezoelectric element, a force introduction element, a support plane aligned with the force introduction element, wherein expansion differences occur between the at least one piezoelectric element and the force introduction element in the support plane when the at least one piezoelectric device is thermally loaded, and at least one transition element is arranged between the at least one piezoelectric element and the force introduction element, wherein a modulus of elasticity of said at least one transition element is smaller than a modulus of elasticity of the at least one piezoelectric element in the support plane thereof.

2. The piezoelectric device according to claim 1, wherein the at least one piezoelectric element has an anisotropic thermal expansion and an anisotropic modulus of elasticity which can be described by an elasticity tensor, wherein the modulus of elasticity of the at least one transition element is smaller than the components of the elasticity tensor associated with the support plane.

3. The piezoelectric device according to claim 1 wherein the at least one transition element has a compressive strength in a direction of a force acting on the at least one piezoelectric element of at least 30% of the compressive strength of the at least one piezoelectric element.

4. The piezoelectric device according to claim 1, wherein the at least one transition element together with the at least one piezoelectric element is pretensioned to absorb shear forces.

5. The piezoelectric device according to claim 1, wherein the at least one transition element consists largely of sintered hexagonal boron nitride.

6. The piezoelectric device according to claim 5, wherein the at least one transition element contains one or more of the following: silicon carbide (SiC), zirconium(IV) oxide (ZrO2) and silicon oxide (SiO2).

7. The piezoelectric device according to claim 5, wherein the at least one transition element contains boron oxide as a binder.

8. The piezoelectric device according to claim 2, wherein the at least one transition element has an anisotropic modulus of elasticity and is oriented in such a way that the anisotropic thermal expansion of the at least one piezoelectric element is optimally compensated in its support plane.

9. The piezoelectric device according to claim 1, wherein the at least one piezoelectric element consists of: GaPO4, langasite, langatate or tourmaline.

10. The piezoelectric device according to claim 1, wherein the at least one piezoelectric element consists of a piezoceramic.

11. The piezoelectric device according to claim 1, wherein the thickness of the at least one transition element in a measuring arrangement for utilizing the longitudinal piezoelectric effect is between 20% and 500% of the thickness of the at least one piezoelectric element.

12. The piezoelectric device according to claim 1, wherein the thickness of the at least one transition element in a measuring arrangement for utilizing the transverse piezoelectric effect is between 5% and 200% of the height of the at least one piezoelectric element.

13. The piezoelectric device according to claim 1, wherein the at least one piezoelectric device is a pressure sensor having a support, a piezoelectric element, a sensor membrane and a thrust piece acted upon by the sensor membrane, wherein a first transition element of the at least one transition element is arranged between the support and the at least one piezoelectric element and a second transition element of the at least one transition element is arranged between the at least one piezoelectric element and the thrust piece.

14. Piezoelectric device according to claim 1, wherein the piezoelectric device is a force or acceleration sensor having a support, piezoelectric element and a seismic mass, wherein a first transition element of the at least one transition element is arranged between the support and the at least one piezoelectric element and a second transition element of the at least one transition element is arranged between the at least one piezoelectric element and the seismic mass.

15. The piezoelectric device according to claim 3, wherein the at least one transition element has a compressive strength in the direction of a force acting on the at least one piezoelectric element of more than 90% of the compressive strength of the at least one piezoelectric element.

16. The piezoelectric device according to claim 10, wherein the at least one piezoelectric element consists of bismuth titanate.

17. The piezoelectric device according to claim 11, wherein the thickness of the at least one transition element in a measuring arrangement for utilizing the longitudinal piezoelectric effect is between 50% and 300% of the thickness of the piezoelectric element.

18. The piezoelectric device according to claim 12, wherein the thickness of the at least one transition element in a measuring arrangement for utilizing the transverse piezoelectric effect is between 10% and 50% of the height of the at least one piezoelectric element.

Description

[0029] The invention is explained in more detail in the following by means of embodiment examples, wherein:

[0030] FIG. 1 shows a piezoelectric device according to the invention in a schematic, three-dimensional representation;

[0031] FIG. 2 shows a first embodiment variant of the invention based on a pressure sensor (longitudinal piezoelectric effect) in a partial sectional view;

[0032] FIG. 3 shows a second embodiment variant of the invention based on a force or acceleration sensor in a lateral view;

[0033] FIG. 4 shows a third embodiment variant of the invention based on a pressure sensor (transverse piezo effect) in a partial sectional view;

[0034] FIG. 5 shows a fourth embodiment variant of the invention based on an acceleration or vibration sensor in a three-dimensional representation; and

[0035] FIG. 6 shows a simplified side view of the fourth embodiment variant.

[0036] Parts with identical functions are marked with the same reference numerals in the embodiment variants.

[0037] The piezoelectric device 1 schematically shown in FIG. 1 has at least one piezoelectric element 2, for example a crystal element made of GaPO.sub.4, which has an anisotropic thermal expansion in its parallel support planes 4 aligned with the two force introduction elements 3, such that expansion differences between the piezoelectric element 2 and the force introduction elements 3 occur in the support planes 4 when the piezoelectric device 1 is thermally loaded. In order to minimize or compensate for shear forces and shear stresses that occur when the device 1 is heated or cooled, a transition element 5 is arranged between the piezoelectric element 2 and the force introduction elements 3, whose modulus of elasticity is smaller than the modulus of elasticity of the piezoelectric element 2 in its support plane 4. Shear stresses in the piezoelectric element 2 are thus reduced by expansion or compression of the transition element 5 and do not reach values that can lead to damage to the piezoelectric element 2. F is the force acting on the upper force introduction element 3 and G is the counter force resulting from the lower force introduction element 3 (for example a support or housing part).

[0038] The embodiment variant of the invention shown in FIG. 2 shows a pressure sensor 10 with a sensor membrane 11, wherein the lower force introduction element 3 is designed as a support 12 of the sensor 10. The upper force introduction element 3 is designed as a thrust piece 14 acted upon by the sensor membrane 11, wherein between the support 12 and the lower piezoelectric element 2 of a stack of e.g. four piezoelectric elements 2 a first, disc-shaped transition element 5 and between the upper, membrane-side piezoelectric element 2 and the thrust piece 14 a second, disc-shaped transition element 5 is arranged, so that the shear stresses and shear forces occurring in the critical support planes 4 of the edge-side piezoelectric elements 2 can be effectively compensated. The central area of the membrane 11 can also lie directly against the membrane-side transition element 5.

[0039] The diameter of the transition element essentially corresponds to the diameter of the piezoelectric elements, which in the variant shown according to FIG. 2 are arranged in a stack using the longitudinal piezoelectric effect. Depending on the application, the thickness of the transition element 5 can be between 20% and 500%, preferably between 50% and 300%, of the thickness of the piezoelectric element 2. In any case, a thin coating of the piezoelectric elements 2, for example of boron nitride, is not suitable to compensate for the shear forces described above.

[0040] The housing of the pressure sensor 10 is welded to the edge of the sensor membrane 11 and fixed to a centering flange 15 of the support 14.

[0041] The transition elements 5 also serve as electrical insulating elements. Charges of the same name on the piezoelectric elements are collected from a foil material via thin, ductile electrode plates 16 and dissipated by means of signal lines 17. In FIG. 2 and FIG. 3 only the connecting loops of the electrode plates 16 are visible.

[0042] The embodiment variant of the invention shown in FIG. 3 shows a force or acceleration sensor 20, wherein the lower force introduction element 3 is designed as support 12 of the sensor 20. The upper force introduction element 3 is designed as a seismic mass 21, wherein a first transition element 5 is arranged between the support 12 and the lower piezoelectric element 2 of a stack of, for example, four piezoelectric elements 2 and a second transition element 5 is arranged between the upper piezoelectric element 2 and the seismic mass 21, so that the shear stresses and shear forces occurring in the critical support planes 4 of the edge-side piezoelectric elements 2 can also be effectively compensated here. The two transition elements 5 and the piezoelectric elements 2 arranged between them are of annular design to accommodate a pretensioning element (not shown) acting on the support 12 and on the seismic mass 21.

[0043] The embodiment variant of a pressure sensor 30 shown in FIG. 4 essentially corresponds to the variant shown in FIG. 2, wherein here the piezoelectric elements 2 are cuboidal in shape and arranged vertically using the transverse piezoelectric effect. The sensor housing and the sensor membrane have been omitted for a better overview. The thickness of the transition element 5 is between 5% and 200%, preferably between 10% and 50%, of the height of the piezoelectric element 2.

[0044] The embodiment variant of the invention shown in FIG. 5 and FIG. 6 shows a force or acceleration sensor 40, wherein a central, for example T-shaped force introduction element 3 is designed as a support 12 of the sensor 40 and has a mounting surface 22 for attachment to a component not further shown here. Two laterally arranged force introduction elements 3 are designed as seismic masses 21, wherein a stack with piezoelectric elements 2 is arranged in each case between each seismic mass 21 and the support 12 and the outer piezoelectric elements 2 of each stack rest on the support 12 or on the seismic masses 21 with the interposition of a transition element 5. The four transition elements 5 and the piezoelectric elements 2 arranged between them are, for example, of annular design to accommodate a prestressing element 23 acting on the support 12 and the two seismic masses 21. The device is suitable, for example, for recording shear and vibration forces that occur in the measuring direction x and introduce a shear load into the transition elements 5 (see FIG. 6).

[0045] The electrical contact is made via thin electrode plates 16 made of a foil material.