US2980811A - Ceramic transducer elements - Google Patents

Description

April 18, 1961 J. M. JACQUE CERAMIC TRANSDUCER ELEMENTS Original Filed Sept. 10, 1956 INVENTOR BY ATTORN Y 1 2,980,81 1 Ice Patented Ag r 1961 CERAMIC TRANSDUCER ELEMENTS James M. 'Jacque, Conneaut, Ohio, assignor to The Astatic Corporation, Conneaut, Ohio, a corporation of Ohio Original application Sept. 10, 1956, Ser. No. 608,934. Divided and this application Jan. 4, 1960, Ser. No. 311

6 Claims. (Cl. 310-94) This application is a division of my co-pending application, Serial No. 608,934, filed September 10, 1956, which is assigned to the assignee of the present application.

This invention relates generally to the art of converting mechanical vibrations and movements into proportional electrical signals and has particular reference to improvements in the manufacture and design of ceramic piezoelectric transducer elements of the type commonly employed in phonograph apparatus, microphones, ultrasonic apparatus and the like.

Probably the best known type of transducer in commercial use at the present time is the Bimorph. This type of electro-mechanical transducer has opposite faces of active piezo-electric material and is mounted in such a manner that when a movement is transmitted to the transducer one of the sides is compressed and the other expanded thereby producing an electrical signal at its electrodes. In the manufacture of such Bimorphs prior art practice has been to fabricate relatively thin sheets of ceramic piezo-electric material, comprising one of the earth titanates, for example, maturing these sheets at high temperatures in a firing kiln, applying a silver electrode face to the major faces of each of the ceramic sheets and again firing the coatedsheets to set the conductive electrodes. A metal vane, usually brass, is prepared by tinning both faces thereof and carefully prepared chips of the coated and matured ceramic piezo-electric sheets are soldered to this metal vane, one on each'side thereof. The resultant sandwich is then heated to fuse the various elements and polarized according to well known principles to provide a small commercially acceptable transducer element. It will be appreciated that the multiple steps involved in the above outlined process must be completed with extreme care and precision and consequently this has resulted in high reject rates and a correspondingly high cost for such elements.

As an overall object, the present invention seeks to provide an improved method for manufacturing Bimorph transducer elements in a more expeditious manner than has heretofore been possible in the prior art.

A further object is the provision of a method for fabricating transducer elements whereby laborious, time consuming and expensive multiple assembly operations are eliminated. This is accomplished in the present instance by utilizing extrusion techniques and processing a series of Bimorphs prior to severing them into individual transducer elements.

More specifically, it is the object of the present invention to provide a new and novel transducer element of practical design, having improved physical and electrical characteristics rendering the element more suitable for specific intended uses and applications.

These, as well as other objects and advantages of the invention, will become more readily apparent upon consideration of the following specification and accompanying drawing wherein there is shown and described cer' tain representative embodiments of my invention.

In the drawing:

Figure 1 is a perspective view of an extruded body strip of my new and novel transducer; and

Figure 2 is a perspective view of a completed individual Bimorph transducer element constructed in accordance with the teachings of the present invention.

Referring now to the drawing, thereference numeral 10 indicates generally an extruded raw body strip which is generally rectangular in cross section and comprises a relatively thintop wall 11, athin bottom wall 12, aleft edge wall 13 and a groovedright edge wall 14. These walls enclose acentral aperture 15 which extends longitudinally through the extruded section ofbody strip 10.

In accordance with the method of the present invention thebody section 10 of Figure 1 is extruded in continuous fashion and severed in lengths suitable for handling in a firing kiln, not shown. After suitable preliminary drying the body section is fired to bring about ceramic maturation. Upon removal from the firing kiln, the interior surfaces of theaperture 15 are coated with a suitableconductive metal paint 16 and the top andbottom walls 11 and 12 are coated with relatively narrow strips ofmetal paint 17 and 18, respectively, which extend the entire length of thematured body strip 10. The painted body strip is again returned to a kiln for setting of the painted portions 16-18 and reducing the same to its final conductive metallic character.

The separate metallizing operation and second firing described above may be consolidated in a single firing as completely described and claimed in a co-pending patent application of Claude A. Lindquist, Jr., Serial No. 608,898, filed September 10, 1956, and assigned to the assignee of the present invention, wherein a suspension of noble metal, such as platinum or palladium, is applied directly to the unfired ceramic body and is reduced simultaneously with the firing thereof for curing.

The long tubular body section shown in Figure 1 of the drawing, with the ceramic material and the metal paint forming the electrodes 16-18 having been properly matured, is next polarized by the application of high voltage electrical potential. One terminal of polarizing voltage source, not shown, is connected to theinner electrode 16 while the other terminal is electrically connected with both of theelectrodes 17 and 18. The electrostatic field generated in the top andbottom walls 11 and 12 of the body section create a condition of electrical stress in these walls which is retained after removal of the external polarizing potential source and thus the body section is conditioned to exhibit the requisite piezo-electric characteristics.

Thebody section 10 is next severed transversely to the direction of extrusion as along the plurality ofbroken lines 19 to produce a series of small commercially acceptable Bimorphs 20, one of which is illustrated in Figure 2 of the drawing.

A preferred method of utilizing a Bimorph 20 of the present invention as a mechanical-electrical transducer, as in a phonograph pick-up, for example, is to clamp the rear end of theedge wall 13 between opposed suitable resilient clamping pads 23 and to apply the mechanical driving force through adrive lever 24 which is operative attached to a phonograph needle or stylus, not shown. Theedge wall 14 is suitably grooved as at 25 to accommodate thedrive lever 24, which, in the present instance, is shown as being a thin rectangular bar.

If an alternating motion is imparted to thedrive lever 24 as represented by arrow 26 a functional piezo-electric plane of the element, represented by thebroken lines 27, will also move in an alternating fashion. This causes alternating opposite stresses of tension and compression in thetop wall 11 and thebottom wall 12 thereby resulting in a charge of alternating sign on theelectrodes 17 and 18. It is noted that thefunctional plane 27 of the Bimorph transducer is disposed transversely to the extrusion axis of the body strip and the physical axis of the individual transducer element. The electric charges appearing on the electrodes '17 and 18 are conducted via suitable "lead wires, not shown, to an associated amplifier for reproduction as audible vibration.

In order to control'the mechanical compliance of the Bimorph transducer element described above it is possible to fill theelongated aperture 15 in the body strip before the same is severed with molten metal or various liquid plastics by dipping one end of the tube in such a solution and evacuating the internal aperture to draw the solution into this portion of the body section. This operation, of course, would be completed after metallizing of the electrodes but prior to polerization of the body strip as clearly set forth in the co-pending patent application of Charles L. Maxon, Serial No. 469,794, filed November 18, 1954-, now abandoned, and in a divisional application thereof, Serial No. 668,199, filed June 26, 1957, which are assigned to the assignee of the present invention.

It should thus be apparent that I have accomplished the objects initially set forth by providing a method of fabricating a plurality of Bimorph elements without the laborious operations used in the prior art. All operations, such as applying electrodes, and polarizing, are carried out prior to the severing of the body stock into individual units which allows ease of handling and working in an efiicient manner. In addition, the specific Bimorph transducer assembly disclosed herein is well adapted for use in phonograph reproducing systems.

As many changes may be made in the method and transducer disclosed and shown herein, reference should be had to the following appended claims in determining the scope of my invention.

I claim:

1. A piezo-electric ceramic transducer comprising a tubular section having top and bottom walls and two end walls, electrode areas on said top and bottom walls, means for securely anchoring one of said end walls, means for applying a driving force to the other of said end walls, said means for applying a driving force comprising a drive lever, said other end wall being formed with a groove-like recess therein to receive said drive lever, and the functional piezo-electric axis of said element being disposed transversely to the physical axis of said tubular section.

2. A piezo-electric ceramic transducer of generally rectangular cross section and having an aperture extending therethrough, said transducer having top and bottom walls and two end walls, said top and bottom walls being relatively thinner than said two end walls, the axis of piezo-electric action of said transducer being disposed transversely to the axis of said aperture, means for anchoring one of said end walls, electrode areas on said top and bottom walls, means to apply a driving force to the other of said end walls to place said top and bottom walls in tension and compression, said'means to apply a driving force comprising a drive lever, and said other end wall being formed with a depression therein to receive and support said drive lever.

3. A piezo-electric transducer element comprising a tubular section of piezo-electric material, electrodes on surface areas of said tubular section, means for securely anchoring one portion of said transducer element, means for applying a driving force to another portion of said transducer element, said means for applying a driving force comprising a coupling member, and said another portion of said transducer element having a depression therein for receiving and supporting said coupling member. i

4. A piezo-electric transducer element comprising a mass of piezoelectric material, electrodes on surface areas of said mass of piezo-electric material, means for securely anchoring one portion of said mass of piezo-electric material, means for applying a driving force to another, portion of said mass of piezo-electric material, said means for applying a driving force comprising a coupling memher, and said another portion of said mass of piezoelectric material having a depression therein for receiving and supporting said coupling member.

5. A transducesr element according to claim 4 further characterized in that said depression comprises an elongated groove, said coupling member comprising a drive lever, and one end of said drive lever being received in said groove.

6. A piezo-electric ceramic transducer of generally rectangular cross section and having an aperture extending therethrough, said transducer having top and bottom walls and two end walls, said top and bottom walls being relatively thinner than said two end walls, the axis of piezo-ele'ctric action of said transducer being disposed transversely to the axis of said aperture, means for anchoring one of said end walls, electrode areas on said top and bottom walls, means to apply a driving force to the other of said end walls to place said top and bottom walls in tension and compression, said means to apply a driving force comprising a drive lever, and said other end wall being formed with a depression therein to receive and support said drive lever.

No references cited.

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