US3569921A

US3569921A - Cylinder-rod dual resonant transducer array

Info

Publication number: US3569921A
Application number: US791542*A
Authority: US
Inventors: Willis A Teel
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1969-01-13
Filing date: 1969-01-13
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09

Abstract

This invention pertains to a piezoelectric transducer which employs toroidal piezoelectric transducer elements and a plurality of prismatic piezoelectric rod elements in a unitary assembly. By application of predetermined driving potentials to the aforesaid piezoelectric elements, their acoustic coupling may be varied to produce a low Q combination thereof. Because the basic relationship of the two types of piezoelectric elements is modular in nature, they may also be combined to produce a variety of radiation patterns.

Description

United States Patent 72] inventor Willis A. Teel Panama City, Fla.

[211 App]. No. 791,542

[22] Filed Jan. 13, 1969 [45] Patented Mar. 9, I971 [73] Assignee the United States of America as represented by the Secretary of the Navy [54] CYLINDER-ROD DUAL RESONANT TRANSDUCER ARRAY 10 Claims, 6 Drawing Figs.

[5 6] References Cited UNITED STATES PATENTS 2,405,604 8/1946 Pope 340/10 3,321,738 5/1967 Trott Primary Examiner-Richard A. Farley Assistant Examiner-Brian L. Ribando Attorneys-Louis A. Miller, Don D. Dotty and William T.

Skeer ABSTRACT: This invention pertains to a piezoelectric transducer which employs toroidal piezoelectric transducer elements and a plurality of prismatic piezoelectric rod elements in a unitary assembly. By application of predetermined driving potentials to the aforesaid piezoelectric elements, their acoustic coupling may be varied to produce a low Q combination thereof. Because the basic relationship of the two types of piezoelectric elements is modular in nature, they may also be combined to produce a variety of radiation patterns.

Patented March 9, 1971 3,569,921

2 Sheets-Sheet 2 IOO l l I l I I W////'s A. 752/ INVENTOR. BY almf /fgg amey The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

A common design goal for piezoelectric transducers is a broad frequency response over a finite range with steep sloped cut off at the limits of the desired frequency range. I-leretofore, this design goal has been approximated by altering the natural resonant frequency of the piezoelectric transducing elements.

One prior art construction, described by Sims and Henriquez (Journal of the Acoustical Society of America Vol. 34, No. 9; Sept, 1962) employs a cavity loaded piston made of aluminum or wolframium. This cavity loaded piston is resonated by a stack of piezoelectric elements cemented together. The above noted construction, while satisfactory for some applications, suffers from certain limitations inherent in the mechanical construction thereof. Prominent among these limitations are: difficulty in maintaining the cement joints at high power levels; corrosion of the aluminum piston by sea water; difficulty in machining the wolframium loading mass; difficulty in calculating the dimensions of the resonant cavity; and a limitation to a single direction of the acoustical output or direction of maximum sensitivity of input.

A second prior art type transducer is known as the open ceramic cylinder" resonator, and it is described by G. W. Mc- Mahon (Journal of the Acoustical Society of America; Vol. 36, No. 3; Man, 1964). This type of transducer, which employs a plurality of open cylindrically shaped elements longitudinally spaced apart in an open frame, has some operational limitations for certain applications. Among these limitations are: sensitivity to temperature changes; reduction in bandwidth due to the presence of nearby objects; and the adverse coupling effect of the rods of the mounting frame.

The foregoing discussion is not intended as an exhaustive analysis of the prior art, but merely an indication of two of the prior art constructions having a recognizable similarity in purpose to the invention described herein. The design of electroacoustic transducers remains a somewhat empirical art and a great many ostensibly promising constructions have been purposed, tried, and abandoned. Most require complex combinations of mechanical or fluid coupling devices to an electromechanical element. These systems are fragile and difficult to make, install, and operate.

The uncombined electromechanical vibrating elements of electroacoustical transducers, usually piezoelectric elements, have a rather sharp resonant peak, i.e., a high O, which makes them less than satisfactory where a wide frequency coverage is desired. This is particularly true in the acoustic frequency portion of the spectrum. What is needed is a simple, in the fashion of a single piezoelectric crystal, device which can cover a relatively wide portion of the spectrum with uniform efficiency, i.e., a low Q device. Such a device should desirably have provisions for adjustment of operation when in service so as to meet changing conditions.

Accordingly, an object of this invention is to provide an improved underwater electroacoustic transducer.

Another object of this invention is to provide an electroacoustic transducer having broad bandwidth characteristics without the aforestated disadvantages of the prior art devices. v

A further object of this invention is the provision of an electroacoustic transducer of simple construction without mass loading devices.

A still further object of this invention is the provision of an A still further object of the invention is the provision of an electroacoustic transducer which has a. variable acoustic loading capability. H

Other objects and many of the attendant advantages will be readily appreciated as the subject invention becomes better understood by reference to the following detailed description, when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a front elevational view of the transducer of the invention;

FIG. 2 is a section taken along line 2-2 of FIG. 1;

FIG. 3 is a schematic showing how the transducer of the invention is coupled to a driving amplifier;

FIG. 4 is a graphic showing of the bandwidth of the transducer of the invention as a plot of impedance versus frequency; and

FIGS. 5 and 6 show other forms of the electroacoustic transducer according to the invention arranged to produce alternate radiation patterns.

Referring to FIGS. l and 2, transducer 11 is seen to comprise a five-sided rectangular enclosure 12 having an open face corresponding to the sixth face of a rectangular solid. Enclosure ]12, which may be made of balsa wood, provides a pressure release confine and support for the piezoelectric elements enclosed thereby. At one end of enclosure 12 is located a plurality of piezoelectric rods, or prisms, 13. Positioned adjacent the acoustically active ends of rods 13, in afashion to be described, is a cylindrical toroid 14 made of piezoelectric material.

The various piezoelectric elements may be of any desired material appropriate to the specific application for which the unit is being designed. Satisfactory results have been obtained from a developmental model made of lead-zirconate and leadtitanate elements. The shape of rods 13 may also be varied somewhat from those which are shown, however, in general, they should be rather long in comparison with their transverse dimensions. In the developmental models, rods of rectangular cross section were employed with satisfactory results, and are illustrated herein. Rods of other cross-sectional configuration may be employed if desired.

The precise mechanical dimension of rods 13 and cylindrical toroid I4 depend upon the operating frequency and the material from which the piezoelectric elements are constructed. However, it has been discovered that optimum results are obtained if the resonant frequency of either the rods 13 or cylindrical toroid I4 is chosen so as to be 0.80 times the highest desired frequency and the other 0.64 times this frequency.

As best illustrated at FIG. 2, the individual rods 13 have electrodes 15 on each end thereof. Electrodes are fired-on laminae of silver, although other materials and methods of attachment may be employed, if desired. The individual rods 13 are electrically connected in a series-parallel arrangement by joining predetermined ones of electrodes l5 by suitable conductors 16. The fashion in which this series-parallel arrangement is made is considered a matter of design choice to the proficient electroacoustic artisan, depending on the desired impedance and phasing requirements of the particular installation. For purposes of clarity, the routing of the conductors 16 from one end of rods l3 to the other, necessary to the series-parallel connection, is not shown. The series-parallel configuration results in a two terminal arrangement, and all of rods 13 may be driven therethrough.

Similarly, fired-on laminar electrodes l7 are radially disposed about cylindrical toroid 14. Like electrodes 15, they are preferably made of silver, although other materials may be employed if desired. Conductors l8 and 1% connect alternate electrodes to provide energizing electrode pairs. Conductors l8 and E9 may be conveniently located on opposite ends of cylindrical toroid i l from each other, as shown in FlG. 2, but may be on the same end thereof, if desired. As illustrated, there are four electrodes 17 on each cylindrical toroid 14, however, the actual number depends on the physical size of the cylindrical toroid 14. For the frequency range of the models studied, 30--60 kI-Iz., four electrodes are satisfactory. The number of electrodes employed on larger toroids, i.e., those used at lower frequencies, should be chosen to provide a spacing of -30 mm. between electrodes.

Conductor 19 is joined to one of conductors 16, forming thereby a common energizing lead 21 for rods 13 and cylindrical toroid 14. Another lead 22 is attached to conductor 18 to provide a second driving connection for cylindrical toroid 14. A third lead 23 is joined to the remaining lead 16 to provide a second driving connection for rods 13. The resulting three wire connection permits a variation in driving energy to be applied to the individual piezoelectric components comprising the transducer. The difference of signals applied to the respective components effectively adjusts the loading of the elements with respect to each other and permits tailoring the output to meet specific design requirements.

When energized, cylindrical toroid 14 is polarized tangentially and rods 13 are polarized longitudinally. The relative position of the cylindrical toroid l4 and rods 13 may be adjusted to obtain an optimum position. This positional adjustment is primarily for centering the two components on a common acoustical axis. The spacing between the two components when less than one-half wavelength is less critical than the centering of the assemblies. In prior art devices the spacing between components is quite critical, but in the device of the invention the separate driving connections permit greater control over element loading than positional variation. In the embodiment shown in FIGS. 1 and 2, the optimum position is a relatively easily obtained, but in embodiments employing more than two component assemblies the optimum position is not'so readily determined. In such instances, the use of impedance bridges and X-y plotters may be employed to make the positioning a reasonably rapid procedure. The use of such devices is common knowledge to the electroacoustic worker and, accordingly, is not explained in detail herein. The relative positioning of the three or more components in a more complex transducer assembly, as will be described below, may be for the purpose of shaping the radiation pattern. Such adjustments are sometimes referred to as shading and-may result in some small variation in placement between elements.

Enclosure 12 is filled with an acoustically transparent potting material to secure the rods 13 and cylindrical toroid 14 together with the associated wiring in their predetermined optimum position. Any suitable material having satisfactory acoustic transparency combined with sufficient water impenetrability and dielectric properties to permit the use of relatively high voltages may be used. By way of example, a material marketed by the 3M Company of St. Paul, Minnesota, under the trade name Scotchcast 280 has proven satisfactory in developmental models.

In instances where the enclosure 12 is made of balsa wood, the entire transducer 11 may be encapsulated in the potting material. This technique seals the balsa enclosure 12 by providing a coating 24'thereabout. Coating 24, because of its aforementioned water impenetrability, prevents the balsa material of enclosure 12 from absorbing water and losing its acoustic pressure release properties.

A circuit utilizing transducer 11 as an insonifying unit is shown in FIG. 3. An amplifier 25 is coupled by transformer 26 to transducer 11. The secondary winding of transformer 26 may be tapped at several output points, as shown, for permitting a plurality of drive ratios between the rods 13 and the cylindrical toroid 14. Such an arrangement is of particular value for adjustment purposes during initial design but may not be necessary in production versions. The use of different combinations of taps permits the adjustment of transducer lls resonant loading-a very difficult task in the mechanically loaded devices of the prior art.

FIG. 4 shows a typical impedance versus frequency curve 27 obtained with a developmental construction of transducer 11 made according to the invention. Those familiar with the performance of electroacoustic transducers will appreciate the improvement over prior art devices of comparable simplicity. The curve represents a level of performance only obtainable with more complex transducers of the prior art which, because of their complexities, are much less reliable than that of the invention.

The simple construction of the instant invention, together with the ease at which the amount of acoustic coupling between elements may be varied, permits a variety of modified forms to be made so as to effectively produce radiation patterns not possible with the transducers of the prior art.

FIG. 5 illustrates one such embodiment. A four-sided enclosure 31, shown with one side removed for purpose of clarity, contains an assembly of rods 32 and

cylinders

33 and 34 at opposite ends thereof. The interconnecting wiring and electrode structure is omitted for purposes of brevity but it, for all intents and purposes, the same as the embodiment of FIGS. 1 and 2, previously described. Likewise, the operation is similar with the exception that the device is bidirectional. That is, unlike the device of FIGS. 1 and 2 which radiates only from one end, the device of FIG. 5 radiates acoustic energy from both ends in two similarly shaped, but oppositely directed, patterns. If enclosure 31 is made of a waterproof pressure release material, such as some plastic materials, the confining potting material 35 may be limited to the inner portions of the enclosure 31.

FIG. 6 shows the construction of another form of the device of the invention. This construction is analogous to two transducers of the type shown in FIGS. 1 and 2 arranged in parallel. A five-sided, rectangular enclosure 36 radiates energy from its open side, like the initially described construction of FIGS. 1 and 2. A plurality of piezoelectric rods 37 are series-parallel connected, by electrical wiring not shown, and have two piezoelectric cylindrical toroids 38 and 39 positioned thereabove. The piezoelectric rods 37 and toroids 38 and 39 are positioned relative to one another in such manner as to provide the optimum acoustic coupling therebetween. This predetermined relative positioning is maintained, as in the case of the construction of FIGS. 1 and 2, by filling enclosure 36 with potting material of the appropriate type, as noted above.

Some latitude exists in the various electrode wiring arrangements without departing from the scope of the invention. For example, in some applications it may be desirable to employ a four-terminal connection to the transducer rather than the three-terminal arrangement shown. In such an arrangement, the cylindrical piezoelectric elements and piezoelectric rods may be driven independently. Alternatively, if desired, a twoterminal arrangement may be fabricated by either directly paralleling the piezoelectric components, or by incorporation of a dropping resistor in series with one of the components. Similarly, transformer 26 may be incorporated within the transducer enclosure, if desired.

Too, driving arrangements other than transformer 26 may be employed. For example, an inductor may be employed with plural secondary windings. Such a unit is particularly applicable in the four terminal arrangement discussed above and in the transducer types employing plural sections, such as that of FIG. 6, for example. In some installations it may be possible to dispense with coupling inductances altogether and drive the transducers directly from suitable solid state circuitry.

From the foregoing, it may be seen that the present invention meets the objects of invention. The remarkably uncomplicated combination of elements produces an unexpectantly marked improvement in electroacoustic transducer arts. With the benefit of the teachings contained herein a proficient artisan in the electroacoustic ans may make and use the device to obtain the improved results therefrom.

I claim:

1. An electroacoustic transducer comprising:

a first piezoelectric component assembled of a plurality of individual elongated piezoelectric rods;

a first electrode system comprising a plurality of individual electrodes respectively attached to said elongated piezoelectric rods for transmitting electrical signals thereto and therefrom;

a first conductor system attached to said first electrode system for interconnecting said plurality of piezoelectric rods into a predetermined circuit configuration;

a second piezoelectric component comprising cylindrical toroidal piezoelectric means acoustically coupled to said first piezoelectric component for electroacoustic cooperation therewith;

a second electrode system comprising a plurality of individual electrodes spaced radially about the surface of said cylindrical toroidal piezoelectric means for transmitting electrical signals thereto and therefrom;

a second conductor system attached to said second electrode system for interconnecting segments of said cylindrical toroidal piezoelectric means lying between consecutive ones of said individual electrodes into a predetermined circuit configuration;

enclosure means positioned in predetermined spatial relationship to said first and second piezoelectric components and their associated electrode and conductor systems for support thereof and for restricting the acoustical energy transmitted therefrom and thereto, so as to effect a predetermined acoustical radiation pattern;

an electrical lead system electrically attached to said first and second conductor systems so as to connect said first and second piezoelectric components in a predetermined electrical configuration and extending outside said enclosure means for conducting electrical signals to and from said electroacoustic transducer; and

acoustically transparent potting material filling said enclosure for encapsulating and fixedly supporting said piezoelectric components and the associated electrode and conductor systems therein in a moisture proof configuration.

2. Am electroacoustic transducer according to claim 1 wherein said elongated piezoelectric rods are rectangular in cross section.

3. An electroacoustic transducer according to claim 1 wherein said first conductor system connects said plurality of rods in a series-parallel electrical circuit configuration.

4. An electroacoustic transducer according to claim 1 in which said second piezoelectric component comprises a plurality of cylindrical toroids positioned along a common face of said first piezoelectric component.

5. An electroacoustic transducer according to claim 1 in which said electrical lead system comprises three individual electrical leads.

6. An electroacoustic transducer according to claim 1 in which said enclosure means is made of balsa wood.

7. An electroacoustic transducer according to claim 1 in which said potting material encapsulates the exterior of said enclosure means. 5

8. An electroacoustic transducer according to claim 1 in which said enclosure means comprises a five-sided rectangular container having an open side.

9. An electroacoustic transducer according to claim 1 in which said second piezoelectric component comprises plural cylindrical piezoelectric toroids located at opposite sides of said first piezoelectric component.

10. An electroacoustic transducer according to claim 9 in which said enclosure comprises a four-sided rectangular container open on opposite sides.

Claims

1. An electroacoustic transducer comprising: a first piezoelectric component assembled of a plurality of individual elongated piezoelectric rods; a first electrode system comprising a plurality of individual electrodes respectively attached to said elongated piezoelectric rods for transmitting electrical signals thereto and therefrom; a first conductor system attached to said first electrode system for interconnecting said plurality of piezoelectric rods into a predetermined circuit configuration; a second piezoelectric component comprising cylindrical toroidal piezoelectric means acoustically coupled to said first piezoelectric component for electroacoustic cooperation therewith; a second electrode system comprising a plurality of individual electrodes spaced radially about the surface of said cylindrical toroidal piezoelectric means for transmitting electrical signals thereto and therefrom; a second conductor system attached to said second electrode system for interconnecting segments of said cylindrical toroidal piezoelectric means lying between consecutive ones of said individual electrodes into a predetermined circuit configuration; enclosure means positioned in predetermined spatial relationship to said first and second piezoelectric components and their associated electrode and conductor systems for support thereof and for restricting the acoustical energy transmitted therefrom and thereto, so as to effect a predetermined acoustical radiation pattern; an electrical lead system electrically attached to said first and second conductor systems so as to connect said first and second piezoelectric components in a predetermined electrical configuration and extending outside said enclosure means for conducting electrical signals to and from said electroacoustic transducer; and acoustically transparent potting material filling said enclosure for encapsulating and fixedly supporting said piezoelectric components and the associated electrode and conductor systems therein in a moisture proof configuration.

7. An electroacoustic transducer according to claim 1 in which said potting material encapsulates the exterior of said enclosure means.