US3454459A - Manufacture of ferroelectric parts,more particularly of transducers - Google Patents

Description

United States Patent 3 454,459 MANUFACTURE OF FERROELECTRIC PARTS, MORE PARTICULARLY 0F TRANSDUCERS Marie-Therese Louise Jeanne Munier, Paris, France, assignor to Societe Anonyme: Societe Alsacienne de Constructions Atomiques de Telecommunications et dElectronique Alcatel, Paris, France, a corporation of France No Drawing. Filed July 13, 1965, Ser. No. 471,741 Claims priority, application France, July 17, 1964, 982,152 Int. Cl. B32b 5/16 US. Cl. 161-168 7 Claims ABSTRACT OF THE DISCLOSURE Similar hexagonal ferroelectric elements are bonded laterally to each other to form an assembly having large flat end faces; end faces of two identical assemblies are bonded together or to an interposed metal plate to form a bimorph transducer.

The present invention relates to the manufacture of ferroelectric parts and more particularly to the manufacture of transducers.

It is known that for the manufacture of such parts use is currently made of certain ferroelectric compounds, such as the titanates, zirconates, stannates, hafnates, niobates, vanadates, tantalates, etc., of usually monovalent or divalent metals, these compounds being used in the pure state or with the addition of oxides of metals such as those of the rare earth group, alone or in mixtures which may or may not form solid solutions, in the form of microcrystalline ceramics prepared with the aid of the conventional techniques of the ceramic industry.

These techniques however do not enable parts having large surfaces to be produced, because of the considerable pressure which it would be necessary to apply. The assembly of a large number of parts of small drmenslons with the aid of adhesives could obviously be considered, but the adhesive film would create a break in the continuity of the material, thus disturbing its ferroelectric, piezoelectric, dielectric, and other properties, which would a priori lead to the rejection of this solution to the problem.

It is however desirable in certain cases to have avallable ferroelectric parts of large surface dimensions. Th1s is particularly so when it is desired to produce blmorph transducers, that is to say transducers formed either by two plates of piezoelectric material or of one plate of piezoelectric material and a metal plate, or else formed by two piezoelectric plates placed one on each side of a metal plate, the various plates being secured together by adhesive bonding; it is known that transducers of this type have numerous advantages over single or composite transducers of the bar type, particularly with regard to adaptation to the outside medium and dimensions. For an equal radiating surface, the relations WhlCh make it possible to compare conventional transducers and transducers of the bimorph type are:

bimorph mechanical impedance 5 bar mechanical impedance a where a=radius of bimorph transducer hzthickness of transducer l=length of bar vibrating at the same frequency as the bimorph transducer.

It is therefore advantageous to make the radius a of the part as large as possible in relation to its thickness h, because for example if the ratio h/a is only equal to 0.2, the ratio of the lengths, and therefore of the weights, is already 50 and the ratio of mechanical impedances is 17.

Moreover it has already been proposed (cf. Study of Piezoelectric Textures by A. V. Shubnikov and I. S. Zheludev, Paris 1958) to prepare ferroelectric parts, and more particularly piezoelectric parts, by agglomerating powders of the abovementioned ferroelectric compounds with the aid of thermosetting resins, such as resins of the ethoxyline, polyester, polyurethane, silicone, methacrylic, etc., type, either alone or mixed with one another. Nevertheless, the radial dimensions of such agglomerated parts are limited by problems of homogeneity in the mass and of mechanical strength.

The present invention has as an object a process which makes it possible to obtain ferroelectric plates of large surface which can in particular be used for the production of bimorph transducers.

This method consists fundamentally in assembling side by side a multiplicity of elements constituted by an agglomeration of ferroelectric material adhered together with the aid of a thermosetting resin, such elements having relatively small transversal dimensions and a crosssection of a shape such that they can interlock with one another after the style of tiling, and in connecting together the elements thus assembled by the application to their faces, which are in contact, of a thin layer of the same thermosetting resin as that used for the agglomeration of the individual elements said layer being then polymerized by heating.

It is thus possible to obtain homogeneous assemblies of large surface which can in particular be used for the production of bimorph transducers. To this end, according to the invention an assembly, produced as described above, is adhesively bonded by one of its large faces, preferably with the aid of the same resin as that used for the agglomeration of the individual elements and for the assembly of the latter, either on another similar assembly or on a face of a metal plate, on the other face of which a similar assembly may be adhesively bonded in the same manner.

Bimorph transducers produced in this manner provide two advantages:

(a) The mechanical impedance is much lower than in single or composite bar type transducers vibrating longitudinally in extension, and this permits better adaptation to the outside medium, particularly in aerial applications;

(b) The small dimensions make it possible to work at low frequency without attaining prohibitive weights or volumes.

For the performance of the invention use is preferably made of individual agglomerated elements of regular hexagonal cross-section, having for example a diameter of the order of 20-100 mm. and a thickness of the order of 2-15 mm. After the style of tiling, one or more rings of identical elements are assembled around a central element, so as to obtain plates formed of seven, ten, nineteen, thirty-seven, etc., elements.

This embodiment of the invention is illustrated by the three examples of practical performance given below. In these examples parts are indicated by weight.

Example 1 A composition containing:

parts of barium titanate modified by calcium titanate (5%) and lead titanate (5% 4 parts of ethoxyline resin (Araldite 556 of St. Go-

bain),

1 part of hardener (HY 951 of St. Gobain) was prepared by rapidly mixing the ingredients.

This composition Was compressed in steel moulds at a pressure of 80 kg. per square cm. so as to obtain 19 elements having the shape of regular hexagonal prisms having a side length of 25 mm. and a thickness of 8 mm. These elements Were then placed in a stove at 150 C. for 14 hours. After cooling, the large faces of the elements were coated with a thin coating of silver, applied by means of a brush, and then polarized at 120 C. at a voltage of 5000 v. per mm.

The elements thus treated were assembled by disposing a first ring of six elements around a central element, the side faces of said elements in contact with one another being previously coated with a thin layer of the same ethoxyline resin, with the addition of hardener, as was used in their manufacture. The assembly thus obtained was placed for 3 hours in a stove at 100 C., and then after cooling a second ring of 12 pieces was disposed concentrically to this first assembly and adhesively bonded in the same manner. After a further stay of 3 hours in a stove at 100 C., the assembly was adhesively bonded by means of a thin film of the same resin to a stainless steel plate of a thickness of 2 mm., which had previously been cut to the exact shape of the assembly of 19 hexagonal prisms. The whole assembly was placed in a stove for 14 hours at 100 C. The bimorph transducer thus obtained vibrated at a frequency close to 1100 c.p.s.

Example 2 Fourteen hexagonal prismatic parts of a similar composition to those described in Example 1 were prepared, silvered, and polarized in the same manner. Their dimensions were:

Side length: 20 mm.

Thickness: 10 mm.

They were assembled in the following manner:

6 similar parts were disposed and adhesively bonded as previously described around a central part. Two identical assemblies of 7 elements were thus prepared separately and subjected for 3 hours to a temperature of 100 C. After cooling these two assemblies were accurately superimposed and adhesively bonded with the aid of the same ethoxyline resin. The assembly was placed in a stove for 14 hours at 100 C.

The resulting bimorph transducer vibrated at a frequency close to 1900 c.p.s.

Example 3 A composition containing:

92.5 parts of lead titanate modified by lead zirconate (45%) and strontium zirconate (5% 6 parts of ethoxyline resin (Araldite 556 of St. Go-

bain),

1.5 parts of hardener (HY 951 of St. Gobain) was prepared and used to manufacture hexagonal parts under the conditions described in Example 1.

The parts were polarized at 135 C. at a voltage of 7000 v. per mm. The parts obtained had the shape of regular hexagons having a side length of 25 mm. and a thickness of 4 mm. They were assembled in the following manner:

37 of these parts were assembled as described above.

A first ring of 6 parts was disposed around a central part. They were joined by their side faces with the aid of a thin film of the ethoxyline resin used for their preparation. The assembly was placed for 3 hours in a stove at 100 C.

After cooling, 12 other parts were disposed concentrically and adhesively bonded in the same manner and the assembly was kept for 3 hours in a stove at 100 C. Finally, 18 other parts were adhesively bonded in the same manner around this assembly of 19 parts, and the assembly was kept for 3 hours in a stove at 100 C.

A second identical assembly was prepared in the same manner.

The first of these assemblies was adhesively bonded with the aid of the same ethoxyline resin to an aluminium plate having a thickness of 2 mm. and previously cut to the exact shape of the assembly of 37 hexagons. The whole assembly was kept in a stove for 3 hours at C.

After cooling, the second assembly of 37 hexagonal parts was adhesively bonded to the second face of the aluminium plate referred to above, and the whole arrange ment was kept in a stove for 14 hours at 100 C. The bimorph transducer thus obtained vibrated at a frequency close to 500 c.p.s.

What is claimed is:

1. Large surface ferromagnetic parts formed of elements of ferromagnetic material adhered into an agglomeration by means of a thermosetting resin, comprising a number of individual similar angular elements having small longitudinal dimensions and joined side by side to one another by respective surfaces of complementary lateral faces of the elements, the surfaces of said elements which are in contact with one another being covered With a thin polymerized coating of said resin.

2. The large surface ferromagnetic parts of claim 1 wherein the elements are regular prisms defining hexagonal transverse sections and flat parallel end faces.

3. The method of preparing large surface ferroelectric parts from elements of ferroelectric material adhered in an agglomeration by means of a thermosetting resin, comprising: providing elements having relatively small transverse dimensions and having lateral interlocking faces, applying to the lateral faces of said elements a thin coating of said thermosetting resin, assembling said elements by reciprocal engagement of their respective lateral faces so as to form a part having the desired shape and dimensions, and heating the part to polymerize said coating, thus bonding the elements together.

4. The method according to claim 3 in which said elements have cross sectional shapes of regular hexagons.

5. The method according to claim 3 in which the assembling and heating steps comprise assembling at least one ring of elements around a central element, heating and polymerizing said ring of elements, applying at least one other ring of elements around said first ring of elements, and heating and polymerizing said other ring of elements.

6. The method of claim 3 further comprising applying to end faces of said adhered elements a thin coating of said thermosetting resin, applying to end faces of another assembly of adhered elements a thin coating of said thermosetting resin, joining the coated end faces of the elements together, thus forming large surfaces of ferroelectric parts, heating the parts and polymerizing the resin, thereby binding the parts together and forming a bimorph transducer.

7. The method of claim 6 further comprising interposing a metal plate between the said ferroelectric parts and bonding large surfaces of the parts to opposite faces of the metal plate.

References Cited UNITED STATES PATENTS 2,324,024 7/1943 Ream 3l08.9 2,384,541 9/1945 Fruth 1l7-17 2,489,393 11/1949 Argabrite et a1. 161182 2,589,403 3/1952 Kurie 310--9 2,618,579 11/1952 Brajer 156-8 2,639,257 5/1953 Szegvari et a1 1563l0 3,073,732 1/1963 Hunsdiecker 161168 X 3,258,387 6/1966 Brown et a1. 161171 X BERNARD ANSHER, Primary Examiner.

US. Cl. X.R.

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