US3182284A

US3182284A - Interleaved electroacoustical transducer

Info

Publication number: US3182284A
Application number: US11113A
Authority: US
Inventors: Charles E Green
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-02-25
Filing date: 1960-02-25
Publication date: 1965-05-04
Anticipated expiration: 1982-05-04

Description

May 4, 1965 Filed Feb.

C. E. GREEN INTERLEAVED ELEGTROACOUSTICAL TRANSDUCER 2 Sheets-Sheet l l I I l l I 1 ul- /9 4 /6 2/ 0 /7 27 l ,5 i I 18 TRANSCEIVER PHASE SHIFTER I 2 lg. 3 as Fig. 4

INVENTDR.

CHARL 55 E'. GREEN k AZ'T R/VEYS y 4, 1965 c. E. GREEN 3,182,284

INTERLEAVED ELECTROACOUSTICAL TRANSDUCER Filed Feb. 25, 1960 2 Sheets-Sheet 2 Fig 5 FREE FIELD VOLTAGE (db) a i O O IN V EN TOR.

Fig 6 CHARLES E. GREEN L ATTO N YS United States Patent 3,182,284 INTERLEAVED ELECTRQACOUSTECAL TRANSDUCER Charles E. Green, San Diego, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Feb. 25, 1960, Ser. No. 11,113 11 Claims. (Cl. 340-9) (Granted under Title 35, US. Code (1952), see. 266) 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.

This invention relates generally to apparatus for radiating and receiving acoustical energy and in particular concerns a reversible electroacoustical transducer for directionally broadcasting and receiving energy in the acoustical frequency range within an aqueous medium.

Although it is known to use single piezoelectric elements and arrays of piezoelectric elements as acoustical projectors, and that they perform the function of converting electrical energy into acoustical energy and vice versa in a satisfactory manner for many operational purposes, it has been found to be difiicult to predetermine and con trol the directivity and power characteristics thereof without including elaborate associated supporting structure and perhaps appropriate reflectors and deflectors, etc. The present invention, however, requires only relatively simple associated supporting structure and need not be used in conjunction with expensive reflectors and deflectors in order to broadcast or receive energy patterns having desirable forms and power characteristics. The basic idea embodied in the structures constituting this invention is exceedingly simple per se, but when properly employed in appropriate structure it becomes profound indeed, inasmuch as it achieves exceptional operational results which are considerable improvements over the prior art for its intended purposes.

It is, therefore, an object of this invention to provide an electroacoustical transducer assembly that will produce substantially predetermined broadcast and reception radiation characteristics from nondirectional piezoelectric elements.

A further object of this invention is to provide an electroacoustical transducer whose relative phase and amplitude characteristics may be varied essentially as desired.

Another object of this invention is to provide an electroacoustical transducer operationally characterized by substantially free-field response patterns.

Another object of this invention is to provide an improved transducer that will produce a horizontal plane directivity pattern that is proportional to the total length of a plurality of stacked projector elements when operated in the fundamental mode.

A further object of this invention is to provide an improved electroacoustical transducer that cancels sound pressure in accordance with the direction of offset of a plurality of individual projecting elements.

Another object of this invention is to provide an electro acoustical transducer that produces a predetermined horizontal bi-directional or unidirectional sound beam within an operating medium.

Another object of this invention is to provide a transducer having sonic beam widths and beam attenuation characteristics dependent on the offset distance between the electroacoustical convertor units and the excitation frequency applied thereto.

A further object of this invention is to provide a sound projector that will efficiently operate in an acoustical spectrum band of at least 0.7 octave.

3,l82,284 Patented May 4, 1965 Last but not least, it is an object of this invention to provide an improved reversible submarine electroacoustical transducer that is easily and economically constructed and maintained.

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

FIG. 1 is a perspective view of a representative diagrammatic embodiment of the inventive idea of interleaving the piezoelectric cylinders of two stacks of piezoelectric cylinders with their respective axes parallel but displaced with respect to each other;

FIG. 2 is an elevational view, partly in section, of the transducer constituting this invention combined with a phase shifter circuit;

FIG. 3 is an elevational view, partly in section, of another embodiment of the transducer constituting this invention;

FIG. 4 is a schematic diagram of a phase shifter circuit which may be used with the subject transducers;

FIG. 5 is an exemplary graphical illustration of the horizontal radiation patterns that may be obtained from varying the relative phase of the two vertical projector stacks with signal wavelength and stack offset distance; and

FIG. 6 is a graphical representation of the free-field voltage response of the invention that may be obtained under various operational conditions.

Referring now to the drawing, there is shown in PEG. 1 a first stack of thin cylindrically shaped piezoelectric convertor elements 121. spacially aligned along a common axis 12. Alternately and partially interleaved between piezoelectric converter elements 11 is a second stack of thin cylindrical piezoelectric converter elements 13 spacially disposed along a common axis 14 which may be otfset a given desired distance d from axis 12.

The piezoelectric convertor elements disclosed as preferred embodiments herein are substantially cylindrical in shape with their diametrical planes essentially parallel; nevertheless, it should be understood that the shape and angular relationship therebetween may be varied to contain any desired geometrical configuration having any desired centroid offset distances without violating the spirit or scope of this invention. For example, in some instances, it may be to an advantage to make said piezoelectric elements cube in shape or oblong block in shape or irregular block in shape and so doing should be considered to be well within the purview of this disclosure. Likewise, the dimensions and angular relationships of the various disclosed elements of this invention may be varied as expedient. However, it has been determined that when cylindrical piezoelectric convert-or elements are operated at their gravest mode, that the diameter thereof should be approximately a wavelength across with the offset distance therebetween something less than a wavelength in order to establish the desired free-field response patterns. Obviously, to accomplish this, the interleaving feature must be employed.

Because stacks of individual cylinders are actually interrupted radiators along the axis of the stack, it becomes necessary to minimize the resulting interrupted radiation effect so that substantially continuous axial radiation will occur. This may be effected by using short or thin cylinders so that the axial distance between radiators of the same phase is less than one-third wavelength at any given frequency, thereby causing the sum of the individual radiators to appear as a continuous line.

FIG. 2 illustrates one of the preferred embodiments of the invention as a right hand axially aligned stack of piezoelectric converter elements 15 made of, for example,

I with. Each of the right hand convertor elements are respectively in direct contact with or are partially impregnated with upper and

lower electrodes

17 and 18 mounted to excite same when the subject transducer is being used as a sound projector and also mounted to be excited by said convertor elements when said transducer is being employed as an acoustical energy receiver. Likewise and for like purpose, upper and

lower electrodes

19 and 20, are respectively mounted on left hand convertor elements 16. Alternate convertor elements and their adjacently associated electrodes are separated by insulators 21. All convertor-electrode assemblies or projector units contain an aperture 22 normal to the diametrical planes thereof through which extends a hollow elongated insulating pipe 2 3. The entire transducer assembly is held together by a threaded shaft 24 extending through said hollow pipe and a pair of nuts 25 and 26 in such manner that each of the piezoelectric convertor elements and their respectively associated electrodes are physically and electrically insulated from each other as individual energy projecting units. I

Completely surrounding each of the projector units is an electrically insulating but substantially acoustically clear material 27 which serves to electrically insulate same from the ambient aqueous medium and still allow passage of sonic pressure waves therethrough. Such material may be of any appropriate resilient types such as rubber or the like, but preferably'it should have physical characteristics which enable it to pass sonic energy with minimum resistance and distortion.

An extension 28 of shaft 24 may be used as a means for fastening the entire transducer to any appropriate support structure such as, for example, the deck or hull of a ship or submarine boat.

The convertor elements of each stack of projector units are shown as having their respective associated electrodes electrically connected in parallel, forming two separate energy projectors which may be excited in any given .phase relationship as operational circumstances warrant, although series connection thereof may be used as well if so desired. A phase shifter 29, which was inserted by a previous amendment is appropriately coupled through insulated electrical conductors to the parallel connected electrodes of each stack of convertor units for this purpose. Any appropriate signal source or receiver may be used as the excitation means for the entire transducer or as a utilization means therefor, respectively. Accordingly, a transceiver 51 is optionally connected to the aforementioned phase shifter 29 for these purposes.

FIG. 3 depicts another preferred embodiment of the subject invention as having a pair of energy projectors and receivers each of which contain a stack of converter elements disposed along a common axis, the respective convertor elements of which are interleaved with the other. The stacks have a plurality of right hand and left hand

piezoelectric elements

30 and 31, respectively. Associated with elements 30 are a plurality of upper and

lower electrodes

32 and 33, and associated with elements 31 are 'a plurality of upper and

lower electrodes

34 and 35. Of course, these piezoelectric elements and their associated electrodes are also electrically insulated as units from their ambient environment by acoustically clear resilient material 36 such as rubber or the like in a manner similar to the projector units of FIG. 2 mentioned above. Separating the electrodes of adjacent projector units are shelves 37 of any suitable structural material such as, for example, rubber, metal, wood, plastic, etc. These shelves serve to isolate one projector unit from another as well as physically secure all of the projector units of both stacks when firmly clamped by a plurality of threaded shafts 38 passing through apertures 39 containedin suitable locations in said shelves and nuts 40. Extensions 41 of shafts 38 may be employed to fasten the entire transducer assembly to any appropriate supporting structure.

It should be noted that all of the cylindrical projector units need not be the same size. In particular, the embodiment shown in FIG. 3 discloses the

end projector units

61 and 62 to be somewhat larger than the others. Because the acoustic impedance of the end cylinders is different from the rest, compensation may be made therefor in one or two ways. Change of physical size of the end projector units is one way and, since a different acoustic impedance reflects a different electrical impedance as well, using a different electrical driver to excite the end piezoelectric convertors in another Way. In general, where an aligned plurality of identically sized cylinders are used, the end cylinders have a lower acoustic load and, consequently, will resonate at a higher frequency. To overcome this, the end cylinders of a line should be made larger in diameter and of the same resistive component to the complex impedance as the inner cylinders if they are to be driven from the same electrical driver. This may also provide the additional benefit that, if the transducer is to function at maximum power limited only by cavitation of the medium within which it is operated, the larger cylinders on the ends having greater radiating surfaces help compensate for the lower cavitation threshold of poorly loaded cylinders.

The device of FIG. 3 is also shown as having each individual projector unit of each stack coupled in parallel with both stacks adapted to being connected to effectively separate electrical driving means for exciting each stack with a phase relationship different from that of the other. Of course, the preferred embodiments disclosed herein employ only two stacks of axially aligned, parallel connected, energy projectors; but, it should be understood that any number of stacks or individual offset projector units may be used in conjunction with pertinent support and excitation and phase shifting means connected thereto without deviating from the scope and spirit of this invention, in event it becomes necessary to so do in order to obtain desired radiation patterns during either broadcast or receiving operations. Likewise, it should be noted that magnetostrictive elements and appropriate excitation means such as energized electrical coils or the like may be respectively substituted for the piezoelectric projector elements and their excitation means without deviating from the scope and spirit of this invention.

Referring now to FIG. 4, the phase shifter means thereof is illustrated as including a pair of input-output terminals 42 adapted to be connected to an external power source having electrical conductors leading therefrom with a variable resistor 43 and a capacitor 44 series connected thereacross. Also series coupled across said conductors is a variable inductance 45 and capacitor 46. The negative terminal of input-output terminals 42 is also the negative terminal of a plurality of terminals 47 which are adapted to being connected to like terminals of the transducer assembly through appropriate insulated conductors. The two positive terminals of the aforesaid plurality of terminals 47 are obtained from conductors connected to the junction of variable resistor 43 and capacitor 44 and the junction of variable inductance 45 and capacitor 46, respectively.

Operation of the subject invention is briefly as follows:

When the transducer is being operated as a sound source and acoustical energy projector within an aqueous medium, electrical driving power is applied across the electrodes of each projector unit of each stack. Each of the cylindrical piezoelectric convertors are thereby caused to change size in proportion to the potential difference applied thereto and produce an omnidirectional sonic pressure wave which radiates therefrom. As the radiating sonic pressure wave from one stack interferes with that of the other stack, cancellation thereof occurs, leaving a null area and resulting in a radiation pattern in accordance with the relative phase of the driving powers applied to the two stacks and the offset distance between stacks.

FIG. 5 indicates that control of the radiation pattern is feasible and illustrates some of the various and sundry radiation patterns that may be obtained by regulating variable resistance 43 and variable inductance 45 which, in turn, regulates the relative phase represented by the ordinant and the offset represented by the term d/)\ as an abscissa, where d is the distance between axes of the stacks, as measured parallel to said ordinant and is the wavelength of the acoustical signal being broadcast.

FIG. 6 shows the free-field voltage response where the offset in the cylinders was adjusted to make the cutofi frequency coincide with the resonant frequency and the relative phase between stacks equal to zero. The upper response curve is that of the main lobe. The lower curve is taken at a 90 horizontal rotation to the main lobe. The interleaved circles and arrows, of course, show the relative offsets and energy radiation directivity, respectively. This response then, for example, goes through the null as shown at approximately d/)\=.55. The differ ence between the curves shows the front-to-side ratio in directivity.

When the subject invention is acting as an energy receiving means or hydrophone, the process is essentially reversible as far as radiation patterns and response thereto are concerned. Of course, the energy transfer is reversed and the piezoelectric elements convert received acoustical energy into proportional electrical energy.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise then as specifically described.

What is claimed and desired to be protected by Letters Patent of the United States is:

l. A transducer comprising a plurality of stacks of acoustical energy projectors each of which is successively and alternately interleaved with the others along a like plurality of respective axes each of which is spatially disposed from the others, means connected to each of said acoustical energy projectors for timely electrical excitation thereof, and support means connected thereto for effectively securing same in a predetermined relationship.

2. A transducer comprising in combination a first stack of piezoelectric cylinders spatially disposed along a first common axis, a second stack of piezoelectric cylinders partially interleaved with said first stack of piezoelectric cylinders along a second common axis, spatially disposed from said first common axis, means coating said first and second stacks of piezoelectric cylinders for electrically insulating same from their ambient environment, insulated means extending through said coating means for timely conducting electrical energy to and from said first and second stacks of piezoelectric cylinders, and means connected to said coating means for supporting said first and second stacks of piezoelectric cylinders in a predetermined geometrical configuration.

3. A transducer comprising a plurality of stacks of axially aligned piezoelectric convertors, each of said piezoelectric convertors of said plurality of stacks of axially aligned piezoelectric convertors being alternately and consecutively interleaved with the others for spatial disposition of their respective axes a predetermined distance therebetween, means connected to each of said axially aligned convertors for electrical excitation thereof as a unitary stack projector having a predetermined relative phase relationship with the other stacks, and means con nected to said plurality of stacks of axially aligned piezoelectric convertors for mounting same in substantially fixed relationship.

4. A transducer comprising in combination a first plurality of sonic energy projectors spatially disposed along a first common axis, a second plurality of sonic energy projectors spatially disposed along a second common axis, said first and second common axes being separated from each other by a predetermined distance whereby said first and second sonic energy projectors are partially and alternately interleaved, means covering each projector of said first and second plurality of sonic projectors for electrically insulating same from its ambient environment, means connected to said first and second plurality of sonic projectors for electrically exciting same in a predetermined relative phase relationship, means connected to each projector of said plurality of sonic projectors for securing same in substantially fixed geometrical relationship, and means integrally connected to said projector securing means for mounting said transducer on a support structure.

5. A reversible electroacoustical transducer adapted to broadcast and receive predetermined acoustical energy patterns within an aqueous medium comprising in combination a first stack of cylindrically shaped piezoelectric elements having diameters equal to the wavelength of the acoustical energy to be broadcast and received, said piezoelectrical elements being spatially disposed along a common axis at a distance that is less than one-third wavelength therebetween, a second stack of axially aligned cylindrically shaped piezoelectric elements having diameters and distances therebetween equal to those of said first stack of cylindrically shaped piezoelectric elements, said first and second stacks being interleaved in such manner that the distance between their respective axes may be varied as desired, electrode means respectively connected to each of the piezoelectric elements of said first and second stacks, means connected to each of said electrode means for electrically exciting said first and second stacks as separate acoustical energy projector units, means covering the aforesaid piezoelectric elements and electrode means for electrically insulating same from said aqueous medium, and means effectively connected to said last mentioned means for securing said first and second stacks of cylindrically shaped piezoelectric elements in a predetermined relationship.

6. An electroacoustical transducer comprising in combination a first stack of piezoelectric elements centrically disposed along a first common longitudinal axis passing therethrough, a second stack of piezoelectric elements similarly disposed along a second common longitudinal axis passing therethrough, said first and second stacks of piezoelectric elements being partially interleaved for predetermined relative spatial disposition of said first and second axes, means respectively interconnecting the piezoelectric elements of said first and second stacks of piezoelectric elements for parallel electrical excitation thereof in predetermined phase relationship, and means connected to each piezoelectric element of said first and second stacks of piezoelectric elements for structurally supporting same in a predetermined geometrical configuration.

7. A transducer adapted to broadcast sonic signals within an aqueous medium upon electrical excitation and produce electrical signals upon sonic excitation received from within said aqueous medium comprising in combination, a plurality of electroacoustical converter means disposed about a longitudinal axis, each of said electroacoustical converter means being partially and alternately interleaved, each of said electroacoustical convertor means being characterized by a predetermined geometrical configuration, and alternate ones of said plurality of electroacoustical converter means having aligned centroids disposed at different positions about and parallel to the aforesaid longitudinal axis, means coupled to each of said electroacoustical converter means for electrically exciting same in a predetermined relative phase relationship when said sonic energy is being broadcast within said aqueous medium, means connected to said electrical excitation means for varying said relative phase relationship, and means connected to each of said electroacoustical converter means for rigidily positioning same in a desired geometrical configuration.

8. A reversible transducer comprising in combination, a first plurality of substantially identical piezoelectric cylinders. centrically disposed along a first common axis, a second plurality of substantially identical piezoelectric cylinders partially interleaved with said first plurality of substantially identical piezoelectric cylinders and centrically disposed along a second common axis that is spatially disposed from said first common axis, a pair of electrodes attached to each of the piezoelectric cylinders of said first and second plurality of substantially identical piezoelectric cylinders, conductor means coupled to each of said electrodes for connecting each of theaforesaid first and second plurality of substantially identical piezoelectric cylinders in electrical parallel, means coating each cylinder of said first and second plurality of substantially identical piezoelectric cylinders and the electrodes attached thereto and the aforesaid conductor means in such manner as to insulate same from their ambient environment, and

variable inductance'and capacitor connected between said pair of electrical conductors, and another pair of electrical conductors respectively connected to the junction of said series connected variable resistor and capacitor and the junction of the aforesaid series connected variable inductance and capacitance, said another pair of electrical conductors and one of said first mentioned electrical conductors constituting the outputs of said phase shifter which are respectively connected to the aforesaid conductor means.

11. The device of claim 9 further characterized by an electrical signal source connected to the input of said phase shifter.

References Cited by the Examiner UNITED STATES PATENT 2,405,604 8/46 Pope.

2,416,314 2/47 Harrison 340-10 2,466,112 4/49 Keller 34010 2,508,544 -5/50 Shaper.

2,697,822 1 2/54 Schuck et a1.

2,708,742 5/55 Harris 340--11 X 2,878,886 3/59 Overton.

CHESTER L. JUSTUS, Primary Examiner.

LEWIS H. MYERS, KATHLEEN H. CLAFFY, FRED- ERICK M. STRADER, Examiners.

Claims

1. A TRANSDUCER COMPRISING A PLURALITY OF STACKS OF ACOUSTICAL ENERGY PROJECTORS EACH OF WHICH IS SUCCESSIVELY AND ALTERNATELY INTERLEAVED WITH THE OTHERS ALONG A LIKE PLURALITY OF RESPECTIVE AXES EACH OF WHICH IS SPATIALLY DISPOSED FROM THE OTHERS, MEANS CONNECTED TO EACH OF SAID ACOUSTICAL ENERGY PROJECTORS FOR TIMELY ELECTRICAL EXCITATION THEREOF, AND SUPPORT MEANS CONNECTED THERETO FOR EFFECTIVELY SECURING SAME IN A PREDETERMINED RELATIONSHIP.