US3732535A

US3732535A - Spherical acoustic transducer

Info

Publication number: US3732535A
Application number: US00850478A
Authority: US
Inventors: S Ehrlich
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1969-08-15
Filing date: 1969-08-15
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08

Abstract

A spherical acoustic transducer formed from electromechanically active material and having a common electrode attached to one surface as a voltage reference and a distribution of electrodes attached to other surfaces so that the radial and circumferential vibrating modes of the acoustically excitable sphere are detectable and resolvable as to bearing angle over 4 pi steradians.

Description

mite States Ehrlich 51 May 8,1973

[54] SPHERICAL ACOUSTIC TRANSDUCER [75] Inventor: Stanley L. Ehrlich, Middletown, R.l.

[73] Assignee: Raytheon Company, Lexington,.

Mass.

[22] Filed: Aug. 15, 1969 [21] Appl. No.: 850,478

[52] U.S. Cl ..340/10, 340/6 [51] Int. Cl. ..G0lv 1/00 [58] Field of Search ..340/l0, 6

[56] References Cited UNITED STATES PATENTS 2,565,158 8/1951 Wi11iams... ..340/1O UX 2,939,970 6/1960 Dranete et a1. ..340/1O X 2,966,656 12/1960 Bigbie et al ..340/1O 3,221,296 11/1965 Milne ..340/1O 3,444,508 5/1969 Granfors et al ..34l)/1O X Primary Exa minerBenjarn'in A. Borchelt Assistant Examiner-H. J Tudor Att0rney-Harold A. Murphy and Joseph D. Pannone [57] ABSTRACT A spherical acoustic transducer'formed from electromechanically active material and having a common electrode attached to one surface as a voltage reference and a distribution of electrodes attached to other surfaces so that the radial and circumferential vibrating modes of the acoustically excitable sphere are detectable and resolvable as to bearing angle over 41r steradians.

17 Claims, 7 Drawing Figures l as l INS ms) I SPHERICAL 90 commas/non I 5 ROTATION OF SUMMING 92 AXIS ciRculTs [Ta 5 OPTIONAL (re) 96 1 5 SLOPE 0mm PHASE CORRECTION REE PHASE SHIFT 1 S l as l l h zmmwssi PATENTEDHAY 181913 3, 7 32 53 5 sum 1 BF 3 Z=rCOS9 FIG 2 11 x r snveaoscp INVENTOI? STANLEY L. EHRL/CH Wm lei/Wa ATTORNEY PATENTED HAY I 8|975 sum 2 or 3 F/Gl 4 INVENTOI? STANLEY L EHRL ICH ATTORNEY BACKGROUND OF THE INVENTION This invention relates to spherical acoustic transducers and, more particularly, to the utility of such transducers for resolving bearing angle of incident acoustic waves over 411- steradians.

In the prior art, as for example Underwater Acoustics Handbook by V. M. Albers, Penn. State University Press, 1965, LC. 64-15069, at page 157, only fleeting reference is made to the use of a sphere shaped acoustic transducer. While the spherical transducer has been discussed theoretically as an acoustic radiator, i.e., P. M. Morse in Vibrations and Sound, published by McGraw-Hill Book Company, New York, in 1936, pages 240-255, such transducers when reduced to practice were limited to the radial mode of vibration. This limitation in the art derived from the number and placement of electrodes. Typically, one outer surface and one internally placed electrode were used.

Non-spherically shaped transducers vibrating in two modes have been reported. Reference may be made to Stanley L. Ehrlich et al., US. Pat. Nos. 3,176,262 and 3,290,646 issued on Mar. 30, 1965 and Dec. 6, 1966, respectively. In these patents, cylindrically shaped transducers were employed for obtaining azimuth and elevation angle bearings. When such cylindrical transducers were used as a set of four, it was possible to determine two angles. However, only one angle was available from the basic single cylinder. As described with multiple cylindrical elements, it was possible to divide them into two or more groups to get the second angle. However, the beam patterns in the second direction were frequency dependent. Additionally, the cylindrical transducers had a cardioid type beam directionality, the notches of which form a limitation on the system sensitively. A related pattern appears in the magnetostrictive transducer'of R. L. Peek, U.S. Pat. No. 2,468,837, issued May 3, 1949 at FIGS. 7 and 8.

SUMMARY OF THE INVENTION it is, accordingly, an object of this invention to devise an acoustic transducer having a spherical shell formed from electromechanically active material in which at least two or more vibrating modes of the shell may be utilized for acoustic signal processing purposes.

It is a related object to devise a spherical acoustic transducer adapted to discriminate among bearing and elevation angles over 411' steradians. It is still another object of this invention to devise a spherical acoustic transducer which may be utilized for moderate to deep water commercial and research applications over a wide range of signal levels and in applications where separation of multipath arrivals by angle is of importance.

The above-mentioned objects are satisfied in one embodiment comprising a spherical shell formed from electromechanically active material; a plurality of electrodes attached to the shell outer surface and regularly spaced over equal area segments thereof; another electrode connected to the shell inner surface to provide a common voltage reference point; and combining means coupling the outer electrodes and inner electrodes for generating n orthogonally phased output dipoled voltages and an omnidirectional pattern voltage upon vibration of the spherical shell.

The even distribution of the outer shell electrodes permits the detection of the electrical manifestations of both the radial mode and the circumferential mode of vibration inducible in the spherical shell. Furthermore, the multimode shell vibration is detectable independent of the incident acoustic signal bearing angle anywhere within 411 steradians.

In another embodiment, the shell is divided into a plurality of elemental surface areas such as two hemispheres connected at its elemental surface areas boundaries by a common metallic locus. The metallic locus serves as a common voltage reference line. Here, as in the first embodiment, a plurality of electrodes are attached to the shell outer surface and regularly spaced over equal area segments thereof. This type of construction has particular advantage of ease of manufacture because hemispheres rather than complete spheres need be fabricated.

Another embodiment may be formed by dividing the spherical shell into a plurality of elemental surface areas such as octants. A pair of electrically insulated electrodes is assigned to each elemental area, with one electrode of each pair serving as a reference voltage point. The other electrode is subjected to a positive biasing voltage. A common electrode is attached to the shell inner surface for maintaining a substantially radial electric field. This embodiment offers a reduced interelectrode capacitance between each surface electrode pair. The capacitance reduction enables the design of preamplifier-s to meet low noise requirements.

All of the embodiments would serve to increase the pressure capability and improve the pressure release design which would become internal to the sphere. Furthermore, reversibility of the multimocle effect and its use as a transmitter in the light of the teachings of the disclosure should not present any difficulties. In-

deed, in the transmission context, beam directivity may be improved by reducing beam width through the capacity to concentrate readily vibration energy from different modes into a narrow beam.

The foregoing aspects and advantages of the invention as well as additional aspects thereof will be understood more clearly and fully from the description of the preferred embodiments taken with reference to the accompanying drawing of which the following is a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS tant inner electrodes and two outer electrodes per octant.

FIG. 5 shows the spherical transducer with attached electrodes in combination with the combining means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1A and 1B of the drawing, there are shown the extensional vibration patterns for cylinders and spheres in the zero and first vibration modes. The zero and first order terms of the Bessel function series expansion of plane waves interacting with a cylindrical or spherical obstacle are the principal ones associated with the multimode transducer configurations to be subsequently described. As previously mentioned, the vibration modes of interest are primarily extensional. For the cylinder, the vibration may be represented as in FIG. 1A. The

solid lines

1 and 3 are the neutral positions of the inner and outer walls respectively. The dashed lines 2 and 4 are their instantaneous positions at another time.

In FIG. 18, if the figure is viewed as representing the cross section of a cylinder, then its vibration in the n 1 mode is twofold degenerate (sin (b and cos (b). This plan view is the same for all planes normal to the cylinder axis. Since there is vibration along one nodal diameter, then this is determinative of the order of the vibration mode. If a spherical shell is substituted for the cylinder in FIG. IE, it also may be made to vibrate in the m 1 mode. For a sphere, such a vibration mode is three-fold degenerate (cos 0, sin 6 sin dz, and sin 0 cos 4)). In this regard, FIG. 18 represents the view of a figure of revolution about a diametrical axis through the direction of maximum radial displacement. Relatedly, the trace diameter of the one nodal plane is perpendicular to the axis of symmetry.

Referring now to FIG. 2A of the drawing, there is shown a spherical multimode transducer framework with three normally intersecting circular rings. Rings 7,

8, and 9 are shown mutually orthogonal and intersecting at points 10 through 15. The three normally intersecting circular rings have equal radii and a common center 16. They support eight identical spherical shell octants of electromechanically active material such as barium titanate (BaTiO Each of the octants is securely, i.e., acoustically, attached to respective octant boundaries. The individual octants may be polarized identically with the positive potential on the inner spherical surface. Each of the inner spherical surface electrodes may be electrically connected. to the metal framework prior to the octant being mechanically attached. This provides a common ground for all octants. The common ground may be brought out through the metal framework. The electrodes attached to the outer surface for each octant become the signal leads required to form the basic beam pattern.

Referring now to FIG. 3, there is shown a simpler mechanical configuration using a single metal ring and two hemispheres (only one of which, 17, is shown). The inner electrodes 18 of each hemisphere may be continuous and connected to the metal ring 19 as a common ground. The four outer electrodes 20 (only one of which is shown) are electrically insulated from each other. It is possible to have a small hole in the spherical assembly of the two hemispheres cut through so that a wire may be connected to the inner electrodes 18.

Referring now to FIG. 4 of the drawing, there is shown a hemisphere 17 in which a single octant of the sphere divides the'outer electrode into two equal electrode areas. The octant, which is, of course, formed from electromechanically active material, is polarized by the application of a positive voltage to one of the outer electrodes with the use of the other outer electrode as a ground. The inner electrode 21 serves as an inaccessible center tap so that the electric field is effectively radial and the capacitance C between the two outer electrodes is, at maximum, one-fourth the capacitance C plus C between the two outer electrodes connected electrically and the inner electrodes. Illustratively, C represents the capacitance between the first outer electrode and the inner electrode. C is the capacitance between the inner electrode and the other outer electrode. C and C are serially connected. Thus, C (C C /C -i-C If C C then C C /2 C /2 (C, C /4). Each of the eight octants may be characterized by a high outer electrode, a ground outer electrode, and a floating inner electrode. The inner electrodes for each quadrant should be isolated from each other. They do not have any external connection. The ground outer electrodes for each quadrant may be connected together to form a common ground. The eight high outer electrodes will yield the required signals. Note, of course, that the impedance levels are higher as well as the sensitivity because of the series connection of the half octants. Mechanical fabrication of the sphere may be in any of the forms for which the inner electrode is required. If it is not possible to separate the inner electrode into octants, then cross talk may be minimized by making the outer ground electrode substantially larger than the outer high electrode.

Referring now to FIG. 5 of the drawing, there is shown a spherical transducer with attached electrodes terminating in a combining means. In this regard, spherical transducer 50 is coupled to combining means 52 over

paths

54, 56, 58, 60, 62, 64, 66, 68.

The combining means comprises a plurality of

amplifiers

70, 72, 74, 76, '78, 80, 82, and $4 and summing circuits. Summing circuits 86 terminate the amplifiers and their corresponding electrical paths for purposes of forming four directional signals on

paths

83, 90, 2, 1100 that are orthogonal in the form of voltages that are all in phase or out of phase with each other. Three directional signals labelled NS, EW, and TB, are respectively applied over

paths

88, 90, and Q2 to a spherical compensator 94. An omnidirectional phase reference is applied on path 96 to a slope correction phase shift circuit 98 to obtain the desired relative phase at 100.

The resonant modes of spherical shell 50 can be used to produce a multimode system. The sphere is divided into hemispheres for all three orthogonal axes. The bearing angle information is obtained by the simultaneously appropriate summing of the output 8 octants of the sphere. It is, of course, possible to use basic multimode displays such as used with cylinder systems found, for example, in US. Pat. No. 3,176,262. Spherical compensator 94 with linkages or external friction drive may be used to allow maximum rotation for rotating the effective axes of a hydrophone for target tracking or to compensate for roll, pitch, and yaw of a ship or platform.

The beam patterns of shell 50 in multimode are insensitive to frequency because they are dependent only on the specific orthogonal modes for which the shell is designed and are capable of a complete 4w solid angle coverage. The signals appearing on

lines

54, 56, 58, 60, 62, 64, 66, and 68 may be characterized as voltages responsive to the modal vibrations incurred by the corresponding octant transducer sections. For purposes of relating the voltage signal on a particular line to the compass orientation of the vibrating octant, the leads have also been designated respectively as NE, NW, etc. It will be noted that the first four leads 54, 56, 58, and 60 represent the top hemisphere octants while the remaining four leads 62, 64, 66, and 68 represent the bottom hemisphere octants. These may be appropriately designated top T and bottom B with respect to compass and tilt sensor orientation. Such top and bottom designation also provides a complete solid angle orientation.

The signals on each of these lines represent complex magnitudes. More specifically, the radial vibration component of the sphere R and the circumferential vibration component of the sphere C are each complex magnitudes distributed among the octants such as R/8 and C/8 may be considered representative values for the octant in question for purposes of description. Measurements have shown that the relationship between R and C is itself substantially orthogonal and may be represented as a complex quantity. Accordingly, the signals appearing on each of the lines 54 through 68 may be represented as follows:

Top NE (R/8) +j (C/8) (sin cos (b sin 0 sin cos 0) Top SW (R/8) +j (C/8) (sin 0 cos d; sin 6 sin e:

+ cos 0) 7 Top NW (R/8) +j (C/8) (sin 0 cos (i) -sin 0 sin (b cos 0) Bottom NE (R/8) +j (C/8) (sin 0 cos 4; sin 0 sin b cos 0) Bottom SE (R/8) +j (C/8) (sin 6 cos d: sin 0 sin cos 0) Bottom SW (12/8) +j (C/8) (sin 6 cos d: sin 0 sin cos 0) Bottom NW (R/8) +j (C/8) (sin 0 cos 11 sin 0 sin (I) cos 6) 7 As previously mentioned, the circumferential vibration mode is degenerate in three degrees of freedom so that its component magnitude C must be modified by the angular projection in terms of sines and cosines of (b and 6. Note that the circumferential components of opposite octants such as Top SE and Bottom NW are 180 out of phase.

The summing circuit is organized in a manner substantially according to US. Pat. No. 3,176,262 such that the resultant sum signals appearing on lines 88, 9t), 92, and 96 may be algebraically represented also by a complex quantity having orthogonal components. To this extent, the eight independent signals applied to the summing circuits are reduced to four output signals from the summing circuits; Three of the outputs are designated as geographical, such as NS (north south), EW (east west), TB (top bottom). The fourth signal designated by omniphase reference is applied on path 96. The resultant sum signals NS, EW, TB, and OMNI may be represented as:

NS (TNE-i-BNE) (TNW+BNW) (TSE+BSE) (TSW+BSW) =j C sin 6 cos 4:

EW (TNE+BNE) (TNW-FBNW) (TSE-i-BSE) (TSW+BSW) ==j Csin 0 sin d:

TB (TNE-BNE) (TNW-BNW) (TSE-BSE) (TSW-BSW) =j C cos 6 OMNl (TNE+BNE) (TNW+BNW) (TSE+BSE) (TSW+BSE) R It should be observed that the transducer 50 is divided into equal area octant segments having positioned thereon a corresponding one of the

surface electrodes

102, 104, 106, 108, 110, 112, 114, and 116. The radial or circumferential vibration will induce voltages on corresponding paths 54 through 68 which in turn will be summed by summing circuits 86 through corresponding amplifiers 70 through 84. The summing circuits effectively algebraically combine the eight signals applied thereto to produce four output signals. As is apparent from the mathematical exposition of the resultant sum signals, each said sum signal is formed from a portion or contribution of each of the eight input signals.

Attention is directed to US. Pat. Nos. 3,176,262 and 3,290,646 for a detailed discussion of the construction of the summing circuits.

The present invention has been described for use as an underwater acoustic receiver and by analytic extension as an acoustic transmitter. It is contemplated that such transducer is useful in environments other than water where compression wave energy may be utilized to vibrate such a transducer as, for example, in gas or air. it is realized that modifications may be made, and it is desired that it be understood that no limitations on the invention are intended other than may be imposed by the scope of the appended claims.

I claim:

1. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material;

a plurality of electrodes attached to the shell outer surface and regularly spaced over equal area segments thereof;

an electrode connected to the shell inner surface to provide a common voltage reference point; and

combining means coupling the outer electrodes and the inner electrode for generating at least one dipole voltage upon vibration of the spherical shell.

2. An acoustic transducer according to claim 1, in which the combining means generates n orthogonally phased dipole voltages and an omnidirectional pattern voltage upon vibration of the spherical shell.

3. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material;

a plurality of electrodes attached to the shell outer surface and evenly distributed thereover for detecting the electrical manifestations of radial mode and circumferential mode vibration inducible in the spherical shell;

an electrode attached to the shell inner surface for providing a common voltage reference point; and

combining means coupling the outer electrodes and the inner electrode for generating at least two orthogonally phased dipole voltages upon vibration of the spherical shell.

. An acoustic transducer comprising:

spherical shell formed from electromechanically active material and having its elemental surface area boundaries joined at a common metallic locus, the metallic locus serving as a common voltage reference line;

a plurality of electrodes attached to the shell outer surface and regularly spaced over equal area segments thereof; and

combining means coupling the electrodes and the metallic locus for generating an output dipole voltage upon vibration of the spherical shell.

5. An acoustic transducer according to claim 4,

wherein the elemental surface areas form hemispheres.

6. An acoustic transducer comprising:

a spherical shell formed from electromechanically active material and divided into a plurality of elemental surface areas;

a plurality of electrodes attached to the shell outer surface and distributed such that a pair of electrically insulated electrodes is assigned to each elemental area, one electrode of each pair'serving as a reference voltage point thereof;

a common electrode attached to the shell inner surface for maintaining a substantially radial electric field; and

combining means coupling the electrode pairs for generating a dipole voltage upon vibration of the spherical shell.

7. An acoustic transducer according to claim 6, wherein the plurality of elemental surface areas consists of octant segments.

8. An acoustic transducer according to claim 6, wherein the common electrode reduces the inter-electrode capacitance between each surface electrode pair.

9. An acoustic transducer according to claim 6, wherein the reference voltage point electrode of each pair is connected together to form a common ground.

10. An acoustic transducer according to claim 6, wherein the reference voltage point electrodes of each pair are connected in predetermined connectable groups.

11. An acoustic transducer according to claim 6, wherein the transducer includes means for applying a positive biasing voltage to the remaining electrode of each pair.

12. An acoustic transducer according to claim 6, wherein the electromechanically active material is selected from the group of piezoelectric material.

13. An acoustic transducer according to claim 6, wherein the electromechanically active material is selected from the group of magnetostrictive materials.

14. An acoustic system comprising:

a transducer body comprising a shell having an outer radiating surface curved about a plurality of mutually orthogonal axes and an inner surface;

a plurality of electrical means coupled respectively to different regions of at least one of said surfaces of said body;

each of said regions extending for a sufficient distance to provide for substantial curvature along said surface in all directions;

means for coupling a voltage reference to the other of said surfaces;

signal combinin means and means for coup mg different phase signals between said combining means and said plurality of electrical means coupled to said body.

15. The system in accordance with claim 14 in which said combining means are coupled with said plurality of electrical means coupled respectively to different regions of said body in a format which generates at least a plurality of radiation patterns along different axes.

16. The system in accordance with claim 14 in which the combining means generate an orthogonally phased dipole voltage and an omnidirectional pattern voltage.

17. The system in accordance with claim 15 in which at least a plurality of said radiation patterns are directive.

Claims

1. An acoustic transducer comprising: a spherical shell formed from electromechanically active material; a plurality of electrodes attached to the shell outer surface and regularly spaced over equal area segments thereof; an electrode connected to the shell inner surface to provide a common voltage reference point; and combining means coupling the outer electrodes and the inner electrode for generating at least one dipole voltage upon vibration of the spherical shell.

3. An acoustic transducer comprising: a spherical shell formed from electromechanically active material; a plurality of electrodes attached to the shell outer surface and evenly distributed thereover for detecting the electrical manifestations of radial mode and circumferential mode vibration inducible in the spherical shell; an electrode attached to the shell inner surface for providing a common voltage reference point; and combining means coupling the outer electrodes and the inner electrode for generating at least two orthogonally phased dipole voltages upon vibration of the spherical shell.

4. An acoustic transducer comprising: a spherical shell formed from electromechanically active material and having its elemental surface area boundaries joined at a common metallic locus, the metallic locus serving as a common voltage reference line; a plurality of electrodes attached to the shell outer surface and regularly spaced over equal area segments thereof; and combining means coupling the electrodes and the metallic locus for generating an output dipole voltage upon vibration of the spherical shell.

5. An acoustic transducer according to claim 4, wherein the elemental surface areas form hemispheres.

6. An acoustic transducer comprising: a spherical shell formed from electromechanically active material and divided into a plurality of elemental surface areas; a plurality of electrodes attached to the shell outer surface and distributed such that a pair of electrically insulated electrodes is assigned to each elemental area, one electrode of each pair serving as a reference voltage point thereof; a common electrode attached to the shell inner surface for maintaining a substantially radial electric field; and combining means coupling the electrode pairs for generating a dipole voltage upon vibration of the spherical shell.

14. An acoustic system comprising: a transducer body comprising a shell having an outer radiating surface curved about a plurality of mutually orthogonal axes and an inner surface; a plurality of electrical means coUpled respectively to different regions of at least one of said surfaces of said body; each of said regions extending for a sufficient distance to provide for substantial curvature along said surface in all directions; means for coupling a voltage reference to the other of said surfaces; signal combining means; and means for coupling different phase signals between said combining means and said plurality of electrical means coupled to said body.