DE2148555B2 - Cable-shaped piezoelectric element and method of making such an element - Google Patents

Description

The invention relates to a cable-shaped piezoelectric element which, for. B. in order to detect L · measurement of Dmckandingen vibration phenomena, for generating ultrasonic vibrations and the like can be used.

^ ^ sjsfis SffiÄ ^"vet -SnXheEtaflüsse ice the usual mitElek" ~ ", _{enes κδκρβ Γ} of ceramic material. ^ ^ _is due to the radial polarization for detection and no matter from what RICH ^ J ^ ™ measured or vibration delektierende ^, Zlcheinung is caught. ^^ *; "^ _{l lectr} is _C he element according to the invention uab Ρ" ~ " ^," ^ εη shape from a central TTTI ! L ^ axis coincides with the axis of a cylindri- ^. "Jacket ; such an element scnen ^ "" ^ Koaxalkabek can be any · f '° have as piezoelectric materials ^ sP * _ka ·, ^^ erhälüichen ceramic piezoMateriaüen such. B. lead-doped f B with 5 percent by weight lead titanate) of lead titanate and lead zirconate in _the so-called lead titanate *> form tester * y. _mo difizierter form of ^W ^ ^{U "g} _n fnd piece of a cable of this type can

^A « ^a * ⁿ * there _{will be a} difference between the middle and a voltage _{reversal> if that}

»5 conductors and aem e ^ _{mechanically stressed}

Cable on an oenc g

will. _{are temperature sensitive} .

^{Known from} f "^, which have the same design as ¹ ^ ff ^^^ ^ 'invention', where the elements ^ η« * ^ _Mmt ^ _{md the mitüeren}

the space ^ ^ _e ^s _m ⁿ _p ^he _{ulverförmigen material having an I} negative Temperaturkoefnzienten is filled. The materials mentioned in this patent also include materials with piezoelectric properties. The elements according to US-PS 33 39 164 are "but gJ ^ J way po ansiert. G« ® ™ J ^ S der

30th

40th Ub-r radial polarization Ekmente

At best they consist of short rods with angular

That for

sä?

partly w ^^ metals ζ B titanium, copper bh

• fessiss »; sä - *

solved that it consists of at least one elongated elec-

Irish conductor is made of elec- Metals ζ B, p

Trfcch conductive material existing cylindrical 55. The invention relates

Sheath lies, with the space between the head drive for manufacture

powder of a kel compressed into the jacket

Ramic piezoelectric material that contains is radially nolarized

fahe g

Irish element according to ^^ ξ

driving is characterized by the fact that

one made of an electrically conductive material

Outer jacket a more or less corrosion-resistant element can be obtained. Through his Forin can be used to measure and detect phenomena that have previously occurred is not certain, as is the case with traffic counts, where Was attached material, followed by the en erhalte- "whole of the diameter by processing ^_(me ch ^ani Be specific purpose of compressibility, of the powder and the reduced kabekormge EIement thus formed to a temperature near the Urne-

point of the piezoelectric material is heated, while between the electrical conductor and the jacket a voltage to polarize the piezoelectric Material is applied, * after which the material is cooled.

In this method, the techniques known per se for reducing the cross-sectional surface applied by elongated bodies, b ° j which are sandwiched between a central conductor and a sheath an electrically insulating ceramic material is located, such as. B. with coaxial heating cables. These operations consist of rolling, drawing and / or hammering. The filling can be made of powder or consist of pearls that are pushed onto the central conductor. Between the different Machining, the whole thing can be annealed in a suitable atmosphere if desired. To mechanical cross-section reduction is carried out the element to a temperature close to the Curie point of the ceramic material used brought. Such a DC voltage is now generated between the jacket and the central electrical conductor applied that the piezoelectric material is polarized. This polarization is directed radially. When determining the amount of voltage to be applied, the following factors should be considered are: When a polarization voltage is applied, the electric field between the jacket and the central conductor near the central conductor to its maximum value. The ceramic piezoelectric Materials have a negative temperature coefficient of resistance. When heated the resistance of the ceramic increases to the temperature at which polarization will take place Materials. From this it can be deduced that preferably those ceramic piezoelectric Materials are to be used which have the highest electrical resistance at the Curie point; when polarizing, the permissible field strength is highest with these materials. In this context the piezoelectric materials mentioned above, for example, have proven to be particularly suitable proven.

It should also be mentioned that from GB-PS 8 07 019 a method is known for the production of disk-shaped Elements, possibly also piezoelectric elements, in which a cable-shaped Structure of a similar structure as is divided into discs according to the invention. During the manufacture of the Cable-shaped structure is heated so honh that sintering occurs and a vitreous structure from the ceramic material is created. Such an element is not flexible. Moreover, it does not follow from this that the polarization of the material in powder form is maintained as in the element according to the invention remain.

The invention is explained in more detail below with reference to the drawing and an exemplary embodiment. It shows

F i g. 1 shows a cross section through an element in the form of a coaxial cable according to the invention,

F i g. Fig. 2 is a graph showing the relationship between various pressure changes and the consequently, stress differences generated in an element subjected to these pressure changes according to the invention.

The element according to FIG. I contains a core 1 formed by a central conductor, with its axis the axis of a cylindrical shell 2 coincides, which is also made of electrically conductive material consists. A ceramic piezoelectric material is located between the jacket 2 and the core 1, that is radially polarized. This is shown in the figure in the usual way by "+" and "-" signs, specify the directional dipoles.

_ις embodiment

In a tube made of titanium (outer diameter 13 mm, inner diameter 10 mm) became a central conductor made of titanium in the axis (Diameter 3.5 mm) attached. The room in that

ao tube was charged with a commercially available powder of a strontium titanate zirconate of the composition _[o Sr, Pb _{q5 o 9S} (Ti _{0 47} Zr _{0. s,)} O _3] filled existing ceramic piezoelectric material.

The diameter of the whole was reduced mechanically until an element with an outer diameter of 2 mm, an inner diameter of the shell 2 of 1.54 mm and one Diameter of 0.61 mm of the core 1 was obtained.

The element thus obtained was brought to a temperature of 300 ° C. A direct voltage of 500 V was then applied between the jacket 2 and the core 1. While maintaining this tension, the element was cooled to room temperature. The piezoelectric properties of the element obtained in this way prove to be permanent at temperatures between - 20 and + 7O ⁰ C.
An element according to this embodiment with a length of 70 cm was placed in a tube filled with oil. The oil was pressurized. The pressure was then quickly released. The maximum voltage difference that occurred between the cladding and the core was measured at various pressure changes using an oscilloscope with known impedance. From Fig. 2, in which the pressure change in kg / cm ² is plotted as the abscissa and the maximum voltage difference is plotted as the ordinate, it can be seen that the signal thus obtained is proportional to the pressure change.

The piezoelectric elements in the form of coaxial cables according to the invention can, among other things for measuring and detecting pressure changes, vibration phenomena and the like,

z. B. when checking the vibration level of machines, during traffic control, with underwater listening devices, be used. The cable can also be used to generate vibrations, e.g. B. Ultrasonic vibrations, be used; to this

For this purpose, a suitable alternating electric field is applied between the middle conductor and the jacket.

1 sheet of drawings

Claims (2)

Patent claims: 1. Cable-shaped piezoelectric element, characterized in that it consists of at least one elongated electrical conductor (l) consists, which lies within a cylindrical jacket (2) made of electrically conductive material, the space between the conductor and the shell contains compressed powder of a ceramic piezoelectric material (3) which is radially polarized. . 2. A method for producing a kabelfonmgea piezoelectric element according to claim 1, characterized in that within a zyhn- «Irish jacket (2) at least one wire-shaped electrical conductor (1) arranged axially and in the free space between the electrical conductor and the sheath is a powder of a ceramic piezoelectric material (3) is applied, after which the diameter of the whole thus obtained is reduced by mechanical processing for the purpose of compressing the powder and the thus formed cable-shaped element is heated to a temperature in the vicinity of the Curie point of the piezoelectric material, while between the electrical conductor and the jacket a voltage is applied to polarize the piezoelectric material, after which the material is cooled. ? 5 aar direction of travel to zäblen-Sch its structure has a higher resistance to harvest use ice cream the usual with elekh M.