Electroacoustic Transducers Of The Mass Loaded Vibratile Piston Type

Abstract

A cylindrical, piezoelectric, ceramic transducer is clamped between an electrically conductive mass element and a vibratile piston. The electrical connection is completed from the piston via a stress bolt to a terminal near the mass element. This arrangement enables sturdy electrical connections to be made to electrodes on the ceramic material and eliminates soldered wire, or foil electrical connections to the ceramic.

Description

The invention relates to electroacoustic piezoelectric ceramic transducers of the mass loaded vibratile piston type, and more particularly to such transducers for use in very deep water.

This type of transducer generally comprises a piezoelectric cylindrical transducer element rigidly cemented between a vibratile piston and an inertial mass element. One of the problems which must be solved in such transducer structures concerns the need for making reliable electrical connections to electrode surfaces of the piezoelectric element. This reliability is generally accomplished by soldering flexible leads to the electrodes or by providing conducting foil electrodes which are held in mechanical contact with the electrode surfaces. However, the vibrations of the structure are likely to break these connections. In addition, a relatively high cost is required for the construction of these conventional electrode connections. These and other problems are especially severe in high power transducers which are likely to be subjected to intense vibration of the piezoelectric element while submerged in deep water.

Accordingly, an object of this invention is to improve the means for making electrical connection to the electrode surfaces of a piezoelectric element in a transducer.

Another object of this invention is to eliminate wire leads making direct electrical connection to the electrode surfaces of the piezoelectric element in a transducer.

A still further object of this invention is to utilize the basic component elements of the transducer vibrating assembly to complete the electrical connections to the piezoelectric element. Here, an object is to avoid using electrical conductors or foil electrodes in direct contact with the piezoelectric element.

Yet another object of this invention is to simplify the construction of mass loaded vibratile piston-type transducers, whereby a lower cost and an increased reliability is achieved, as compared to prior art structures.

In keeping with an aspect of the invention, these and other objects are accomplished by providing connections between electrodes on a piezoelectric transducer element and near-by metallic parts, thereby eliminating wire-like connections. More particularly, the terminals for the individual electrodes on the transducer element assemblies are two terminal lugs conveniently located at the rear of the assembled element. One lug attaches directly to the mass element, and the other lug attached to a stress bolt threaded into the vibratile piston. Thus, the invention provides a simplified construction of a transducer element assembly and completely eliminates the necessity for any direct wiring to electrode surfaces on the ceramic. This elimination enables a more reliable and less costly structure.

For a better understanding of the invention itself, together with further features and advantages thereof, reference is made to the accompanying description and drawings in which:

FIG. 1 is a rear plan view of a mass loaded transducer assembly incorporating an illustrative embodiment of this invention;

FIG. 2 is a cross-sectional side view taken along the line 2--2 of FIG. 1;

FIG. 3 is an end view of a first embodiment of a polarized ceramic transducer element that may be used in the transducer element assembly of FIG. 2;

FIG. 4 is a cross-sectional side view taken along the line 4--4 of FIG. 3;

FIG. 5 is an end view of another embodiment of a polarized ceramic transducer element that may be used in the transducer element assembly of FIG. 2;

FIG. 6 is a cross-sectional side view taken along the line 6--6 of FIG. 5;

FIG. 7 is a longitudinal partial cross-sectional view of a deep water transducer employing several of the element assemblies illustrated in FIG. 2; and

FIG. 8 is a cross-sectional view of the transducer assembly of FIG. 7 taken along the line 8-8 thereof.

In the various figures, the reference character 11 identifies a vibratile piston which might be made of any suitable electrically conductive material, such as aluminum, for example. A cylindrical transducer element 12 may be made of any well known piezoelectric materials, such as barium titanate or lead-zirconate-titanate. As best seen in FIGS. 3 and 4, the ceramic 12 has electrode surfaces 13 and 14 (such as fired silver) formed on each end of the cylinder. An electrically conductive cylindrical inertial mass element 15 (FIG. 2) may be made of steel, for example.

The electrode on one end of the hollow, polarized, piezoelectric ceramic cylinder 12 is bonded to one side of the piston 11. The mass element 15 is bonded to the electrode 14 on the opposite end of the ceramic cylinder. On each end, the bonding is accompished by means of a conducting cement, such as an epoxy mixed with a silver dust.

The inertial mass element 15 has a clearance hole passing through its axis for receiving a stress bolt 19 for completing the assembly. As a result, an assembly may be completed by placing an insulating collar 17 over the stress bolt 19 and then putting a terminal lug 16 over the collar. Another terminal lug 18 is placed between the top of collar 17 and the bottom of the head on the stress bolt 19. All these parts are secured together by means of the stress bolts 19, which is tightened into a tapped hole machined into the piston 11. Any suitable spring means, such as a Belleville spring washer (not shown) may be placed under the head of the screw 19 to control the compression stress applied to the ceramic cylinder 12.

When the assembly of FIG. 2 is completed, a negative electrical potential appears on electrode 13 and at the terminal lug 18, the circuit being completed via the stress bolt 19. An electrical connection is also completed from the positive electrode 14 to the terminal lug 16, which is in contact with the inertial tail mass 15.

Thus, the assembly of FIG. 2 provides means for conveniently making electrical connections to the ceramic without requiring any direct connections of wires or foil to the electrodes. All electrical potentials appear at the terminal lugs 16 and 18 on the rear of the transducer assembly. This arrangement enables the wiring together of multiple transducer elements, when they are assembled as an array inside a housing structure.

The ceramic cylinder 12 (FIGS. 2 and 4) has electrode surfaces on each of its two ends. The ceramic is axially polarized with the polarizing potentials (+) and (-) applied to the electrodes 13 and 14, as indicated.

Another type of polarization for the ceramic element is illustrated in FIGS. 5 and 6. Here, the tubular ceramic cylinder 20 has an electrode surface 21 on its inside wall and an electrode surface 22 on its outside wall. The ceramic material is radially polarized through the ceramic wall, with the polarizing potentials (+) and (-) applied as indicated. The positive (+) electrode continues from the inside cylindrical wall and wraps over a portion of one end of the ceramic cylinder. Likewise, the negative (-) electrode continues from the outside cylindrical wall and wraps over a portion of the opposite end of the ceramic cylinder, as illustrated in FIG. 6. This radially polarized ceramic element 20 may be substituted for the ceramic element 12 in FIG. 2. Other types of electroacoustic transducer elements, such as an X-cut quartz plate, for example, may also be substituted for the ceramic cylinder 12, in FIG. 2.

FIGS. 7 and 8 show an illustrative embodiment of the inventive transducer assembly in a single transducer housing. A number of these transducer assemblies are arranged with their pistons 11 cemented to a sound conducting window 23, such as rubber or neoprene, for example. This cementing may be accomplished by means of epoxy (or another suitable cement).

These transducer assemblies are electrically wired together by means of a conductor 24, which is soldered to each of the common positive potential terminal lugs 16. Likewise, a conductor 25 is soldered to each of the common negative potential terminal lugs 18. The conductors 24 and 25 are soldered to the terminals 26 and 27, which are sealed in a conventional insulated manner through the wall of the rigid housing structure 28.

After making these electrical connections, the periphery of the rubber window 23 is bonded to the open end of the housing 28, again by means of a suitable cement, such as epoxy.

If the transducer assembly is to be used for deep underwater applications, the space within the housing 28 is preferably filled with a rubbery potting compound 29, such as polyurethane or with a liquid such as castor oil. This filling is inserted into the housing through an opening, after which it is sealed by means of a threaded plug 30.

The described invention eliminates direct wiring or foil connections to the electrode surfaces on the ceramic element. There is a simple, convenient, and reliable means for making a transducer assembly, which has great advantages over prior art structures.

While specific embodiments have been shown, it should be understood that various modifications and alternative constructions may be made without departing from the true spirit and scope of the invention. Therefore, the appended claims are intended to cover all modifications and equivalents which fall within the true spirit and scope of the invention.

Claims

I claim:

1. An electroacoustic transducer comprising an electrically conductive vibratile piston having at least one plane surface on one side thereof, an electrically conductive inertial mass element having at least one plane surface on one side thereof, piezoelectric transducer means for converting electrical oscillations into mechanical vibrations, said transducer means having a pair of opposite plane surfaces, separate electrode means formed directly on each of said pair of opposite plane surfaces of said transducer means, said integral electrode means being free of external connections, means for rigidly fastening said plane surface on said one side of said vibratile piston directly to one of said opposite plane surfaces of said transducer means and fastening said plane surface on said one side of said inertial mass element directly to said separate electrode means on the opposite surface of said transducer means, a first electrical terminal means connected to said inertial mass element, an electrically conductive bolt member attached to said piston, passing through said inertial mass member, and insulated from said mass member, and a second electrical terminal means electrically connected to said bolt member, whereby an electrical connection is made directly to said transducer means only via said plane surfaces on said one sides.

2. The invention of claim 1 wherein said transducer means comprises a polarized ceramic cylinder with said separate electrode on said opposite surfaces of said transducer means.

3. The invention in claim 2 wherein said rigid fastening means includes a stress bolt for holding said piston and said inertial mass element tightly against the opposite end surfaces of said ceramic, whereby said ceramic is held in mechanical compression.

4. The invention in claim 3 wherein said stress bolt is threaded into the piston and insulated from said inertial mass element.

5. The invention in claim 4 and first terminal lug means in electrical contact with the surfaces of said inertial mass element and said ceramic cylinder and a second terminal lug means in electrical contact with said stress bolt.

6. The invention in claim 5 wherein said first and said second terminal lugs and said stress bolt are separated by an electrical insulator with said stress bolt in contact with one of said lugs and holds said terminal lugs securely in position.

7. An electroacoustic transducer comprising a vibratile piston having a pair of opposite plane surfaces, an inertial mass element having at least one plane surface, transducer means for converting electrical oscillations into mechanical vibrations, said transducer means having two parallel plane surfaces, electrode means integrally formed on at least a portion of each of said two parallel plane surfaces on said transducer means, mechanical fastening means for securely holding said piston, said inertial mass element, and said transducer means in direct physical contact free of any discrete electrode members having tabs for making external electrical connections thereto; said piston, said mass, and said transducer being held in axial alignment, one of said parallel plane surfaces of said transducer means being held in intimate mechanical contact with said plane surface of said inertial mass element, the other of said parallel plane surfaces of said transducer means being held in intimate mechanical contact with one of said plane surfaces of said piston means, a first electrical terminal means being connected to said inertial mass element, said mechanical fastening means comprising an electrically conductive bolt member attached to said piston, passing through said inertial mass member, and insulated from said mass member, and a second electrical terminal means electrically connected to said bolt member, whereby an electrical connection is made directly to said transducer means only via said plane surfaces of said inertial mass element and said piston which are in intimate contact with the electrode surfaces on said transducer means.

8. The invention in claim 7 wherein said transducer means is a hollow ceramic cylinder.

9. The invention in claim 8 wherein the ceramic cylinder is polarized axially between electrode surfaces placed over each end plane face of said hollow cylinder.

10. The invention in claim 8 wherein the ceramic cylinder is polarized radially between electrode surfaces placed over the inside and outside cylindrical walls of the ceramic.

11. The invention in claim 8 wherein said inertial mass element has an axial hole, said mechanical fastening means including a stress bolt passing through said axial hole and applying axial compressive stress to said ceramic cylinder.

12. A plurality of electroacoustic transducer assemblies as defined in claim 7 and an open-sided housing closed by a sheet of sound transparent material, means for bonding an exposed plane surface of each of said vibratile pistons in said transducer assemblies to one side of said sheet of sound transparent material, insulated terminal means sealed through the wall of said housing, electrical connection means interconnecting said transducer assemblies to each other and to said insulated terminal means, and means for sealing the periphery of said sheet of said sound transparent material to the open side of said housing, whereby said transducers are attached to one surface of said sound transparent material and completely sealing the enclosure.

13. The invention in claim 12 and a non-electrically-conductive fluid filling the space within said sealed enclosure.

14. The invention in claim 12 and a non-electrically-conductive potting compound filling the space within said sealed enclosure.

15. A plurality of electroacoustic transducer assemblies as defined in claim 7 and a housing with an open side, means for positioning the exposed plane surfaces of said vibratile pistons of said transducer assemblies in alignment at the open side of said housing, potting means for sealing said assemblies inside of said housing and for closing said open side of said housing, insulated terminal means extending through the wall of said housing, and electrical connection means for interconnecting said transducer assemblies and said insulated terminal means.

16. A deep water transducer comprising a plurality of electrically conductive plate pistons flexibly connected to each other in a substantially planar alignmnt, a housing with an open side and one side of said planar alignment facing outwardly from said housing, a plurality of piezoelectric transducing elements, each element being held with one side in intimate contact with the other side of each of an individually associated one of said pistons, an electrically conductive inertial mass element held in intimate contact with the other side of each individually associated transducing element, a stress bolt interconnecting each of said mass elements and insulated from said mass elements and the associated plate piston for applying a stress to the associated one of said piezoelectric elements, said stress bolt making electrical contact with the associated plate piston, and means for electrically interconnecting said piezoelectrical elements via said mass elements and said stress bolts.

17. The transducer of claim 16 wherein said flexible connection is a sheet of elastic material sealing the open side of said housing.