COMPRESSED SONAR ARRAY WITH INTERLEAVED STAVES

Abstract: A compressed sonar array with a plurality of substantially interleaved offset staves, each stave having a plurality of approximate half wave length individual transducer elements (31), the adjacent elements in each stave having a center to center spacing (31b) substantially greater than a half wave length. The elements of each stave substantially intrude into adjacent staves. The individual elements may be squares aligned vertex to vertex in each stave, or may be circular or take other shapes. The individual elements in each stave may be connected in parallel or simultaneously addressed, and a plurality of staves may be electrically connected in a predetermined manner for beam forming and scanning in the horizontal direction. The array may be cylindrical, planar, curved or conformal, and a plurality of staves of radiating elements is fitted into a space normally filled by a lesser number of staves with the same size radiating elements.

Description: COMPRESSED SONAR ARRAY WITH INTERLEAVED STAVES Background Of The Invention The invention relates to electronically operated sonar array in which the array is comprised of a plurality of discrete simila transducer elements arranged in operational entities of vertical staves (and horizontal rows) . Such arrays may be plariar, curved, cylindrical or conformal; may be used actively or passive]y; and operate in a liquid medium such as sea water at a predetermined frequency or band of frequencies. Transmit - receive circuitry means control the array. In the commonly used transmit and receive modes of beam forming and scanning in the horizontal direction with such arrays, the individual elements of each stave generally will either be electrically connected in parallel or will be simultaneously addressed. Each stave will be a unit separately connected from the other staves, and a number of stave normally will be selectively connected in a predetermined manner during such beam forming and scanning, i.e., in parallel, phase shifted or delayed with respect to one another, etc. In the design of such arrays, various conflicting criteria come into play. The electroacoustic elements (commonly those with piezoelectric characteristics) are designed with a desire to optimize (maximize) the radiating surface of the individual elements, taking into consideration such factors as acoustic signal wave length, the array packing factor, element acoustic loading, signal-to-noise ratio, signal coherence. cavitation, array size and weight, reliability, economics, etc. Further, a high array resolution requires a high number of beams and thus a high number of staves of such elements. This combination of optimized element radiating surfaces and large number of staves of course points to the need for large arrays. When installing arrays of the type here being considered for application with naval and other vessels, however, available space is often scarce. Such arrays are often mounted on the hulls of vessels, in domes positioned on the hulls, or in trailing towed bodies. Naval architects prefer sonar domes and towed bodies to be small in volume for hydrodynamic and other reasons. Small naval vessels dictate even smaller domes and thus smaller arrays such as cylindrical arrays. Accordingly, it is apparent that the somewhat empirical art of sonar array design requires design compromises, and particularly in the desire for large arrays as set forth above versus the array size constraints presented in relation to the array mounting. Common prior art sonar arrays with staves consist of closely packed rectangular or circular transducer elements with radiating surfaces of approximately a half wavelength (or less) on a side or diameter respectively, the elements in each stave (and each row) being spaced from each other at an essentially minimum spacing and thus having a center-to-center spacing of adjacent elements in each stave (and in each row) of approximately a half wavelength (or less) of the acoustic signal. Such a center-to-center spacing has been considered highly desirable to avoid undesirable beam pattern lobes. In a cylindrical array, the staves extend vertically on the housing surface parallel to and about the cylinder axis, and the elements of each stave do not make any significant intrusion into adjacent staves; the rows, consisting of elements from each adjacent stave, extend around the housing circumference perpendicular to the cylinder axis. While such prior art designs may be adequate in certain respects, it would be highly desirable for reasons of size constraint to be able to accommodate the same number of staves within a smaller area or volume than defined by such prior art arrays, while operating at the same given frequency (or frequency band) ; or, for better array resolution, to accommodate more staves within the same area or volume defined by such prior art arrays, while operating at the same given frequency (or frequency band) . In a cylindrical array of a given volume, more staves could then be accommodated; or, the same number of staves could be accommodated in a smaller volume to provide a reduced size of array. Prior to the present invention, no simple means has been apparent to achieve these objectives, attempts having required various complex electronic techniques, smaller transducer elements with attendant problems, etc. Summary Of The Invention The compressed sonar array of the present invention is of the type utilized in beam forming and scanning, and is comprised of a plurality of generally parallel staves. Each stave is forme of a plurality of individual transducer elements extending in a line, and the individual elements of each stave are offset along the stave from the individual elements of adjacent staves. As contrasted with the previously described prior art, each stave is substantially interleaved with its adjacent staves to obtain either a significantly larger number of staves in a given area or volume, or alternatively the same number of staves in a smaller area or volume. In the former instance a better array resolution can be obtained, and in the latter instance, a smaller array environment (such as a smaller ship dome) may be utilized. In either instance, a significant advance in beam forming and scanning array design is the result, with a plurality of staves fitted into a space normally filled by a lesser number of staves with the same size radiating elements. The interleaving of staves in the present invention is obtained, in contrast to the prior art, by positioning adjacent transducer elements in each vertical stave at a substantially greater than minimum (i.e., substantially greater than half wave length) center to center spacing to allow substantial intrusion into the stave by individual offset elements of adjacent staves. This substantial intrusion results in the interleaving of individual elements of adjacent staves and thus the interleaving of adjacent staves themselves. As observed, it has long been considered desirable and advantageous to provide the half wave length center to center spacing of transducer elements along the vertical staves (and horizontal rows) . Such a configuration is thought to be an optimal design for the best beam patterns and array loading, with each stave physically discrete from and non-interleaved with its adjacent staves. In the present invention the opening up of each stave in the vertical direction, by substantially increasing the center to center spacing of the adjacent stave elements, therefore would be expected by conventional theory to result in deteriorated vertical beam patterns. However, it surprisingly has been found that the present invention results in the obtaining of as good beam patterns as those obtained in the prior art. In applicant's invention, the transducer elements may take various shapes, one preferred embodiment comprising diamond-shaped individual transducers extending 'vertex to vertex along each stave line. Circumlinear, rectangular and other shapes are also applicable. The array may be cylindrical, planar, curved or conformal, and operate either actively or passively. Conventiona transmit-receive circuitry means are provided to electrically connect in parallel, or to simultaneously address, the individual transducer elements in each stave, as well as to electrically connect individual staves in parallel with other staves or phase shifted or delayed with respect to other staves, to obtain beam forming and scanning in a horizontal direction. Other combinations of staves and/or elements may be connected in variou well-known configurations to beam form and scan in other directions. Descriϋtion Of Drawings Fig. 1 is a perspective view of a prior art cylindrical sonar array; Fig. 2 is perspective view of a compressed cylindrical sonar array constructed accordingly to one embodiment of the present invention; Fig. 3 is a partial expanded view of Fig. 2; and. Fig. 4 is a partial expanded view corresponding to Fig. 3 but of another embodiment of the present invention. Description Of Embodiments Referring to Fig. 1, cylindrical sonar array 30 is an illustration of what has been considered to be an optimal prior art design for beam forming and scanning. The array 30 is comprised of similar individual transducer elements 31 (the radiating surfaces being shown) , piezoelectric in nature for example, of conventional construction and mounted into a cylindrical housing 32. The transducer elements 31 are respectively arranged in vertical staves 33 placed circumferentially around the cylindrical housing, the staves being parallel to each other and to the cylindrical axis 32a. Fig. 1 shows twenty-four staves in number, with each vertical stave having nine individual transducer elements 31. STAVE 1, STAVE 2 and STAVE 3 only are labelled, for purposes of illustration. It also is apparent that there are nine horizontal rows 34 of transducer elements 31 extending around the circumference of array 30 perpendicular to the cylindrical axis 32a. The transducer elements of each stave are not offset vertically from corresponding elements of adjacent staves, and each row 34 accordingly is comprised of elements from each adjacent stave. The radiating surfaces of transducer elements 31 of array 30 in Fig. 1 are squares (or approximate squares) , and dimensioned on each side at a half wave length of the acoustic signal (or approximate half wave length where a band of frequencies is involved) . Where such half wave length elements are being utilized, the elements 31 also are spaced at a minimum, half-wave length (or approximate half wave length where a band of frequencies is involved) center-to-center distance 31a from each other in the staves (and rows) , allowing for only a slight space between adjacent elements to allow each element to function as an entity separable from its adjacent elements. Also schematically illustrated in Fig. 1 is transmit - receive circuitry (and signal processing means) 35 with multiple conductor electrical cables 35a and 35b to array 30, all conventional and well-known in nature and thus not further described. Each transducer element 31 has conventional electrical connections allowing separate addressing for transmitting or receiving. In the common transmit mode of radiation beam forming and scanning in the horizontal direction, as well as beam forming and horizontally scanning in the receive mode, the individual elements 31 of each stave will generally be electrically connecte in parallel or simultaneously addressed and each stave will be separately connected and operable from the other staves. In such beam forming and scanning in the horizontal ό_,irection, a pluralit of staves normally will be electrically connected in predetermine fashion (i.e., in parallel or phase shifted or delayed or amplitude shaded with respect to one another) by the transmit - receive circuitry and signal processing means 35, for example STAVE 1 through STAVE 8 initially combined electrically, followed by STAVE 2 through STAVE 9 combined electrically, then STAVE 3 through STAVE 10 combined electrically, etc. When beam forming and scanning in non-horizontal directions, other combinations of staves and/or elements will be electrically connected in well- known configurations. It will be observed in Fig. 1 that none of the twenty-four staves is interleaved with its adjacent staves. Each stave in effect remains within its own proprietary territory about the cylinder circumference, separate and apart from its adjacent staves. Now referring to the present invention as shown in Figs. 2 and 3, a compressed cylindrical sonar array for beam forming and scanning is illustrated, wherein each stave is substantially interleaved with its adjacent staves. Twenty-four vertically extending staves 33 still remain, each in this case having five rather than nine individual transducer elements 31 (the radiatin surfaces being shown) for purposes of illustration. Here, however, the interleaving of the staves permits use of a cylindrical housing of considerably smaller diameter than Fig. 1, with the attendant advantages thereof. Alternatively, the design arrangement of Fig. 2 would allow considerably more staves than the Fig. 1 arrangement to be accommodated on a cylinder of the same diameter (for example, approximately thirty-two staves vs. twenty-four staves) . More specifically, in Figs. 2 and 3 each transducer element 31 is identical to that of Fig. 1 and thus its radiating surface is also a half wave length (or approximate half wave length where a band of frequencies is involved) square on each side. Here, however, the square elements 31 have each been rotated 45* in angle so to appear as diamond - shaped in the vertical direction. Each vertical stave 33 is now comprised of a plurality (five as shown) of transducer elements 31 extending vertex to vertex, rather than side to side. Where such half wave length elements are being utilized, it is therefore apparent that the adjacent transducer elements along each stave are now positioned with respect to each other at a substantially greater than minimum half wave length center to center spacing 31b, as opposed to the minimum half wave length center to center distance 31a described above in relation to Fig. 1. In effect, each stave in Figs 2 and 3 has been opened up in the vertical direction. Referring to Fig. 3 in particular, a partially expanded view of Fig. 2, STAVE 1 includes elements 1A, 1B,1C (and ID,IE not shown), STAVE 2 includes elements 2A,2B,2C (and 2D,2E not shown), STAVE 3 includes elements 3A,3B,3C (and 3D,3E not shown), STAVE 4 includes elements 4 A,4B,4C (and 4D,4E not shown), and STAVE 5 includes elements 5A,5B,5C (and 5D,5E not shown). Each vertical stave remains parallel to its adjacent staves, but as opposed to Fig. 1, here the individual transducer elements 31 in each stave are vertically offset along the stave from the individual elements 31 in adjacent staves. The extending vertex to vertex of the diamond - shaped transducer elements 31 in each opened-up stave, taken with the vertical offset of adjacent staves, then permits substantial intrusion into the proprietary territory of each stave by the individual offset elements of adjacent staves. Referring to Fig. 3 for example, transducer elements 2A,2B, and 2C of STAVE 2 intrude nearly halfway into the side-to-side ambit or proprietary territory of STAVE 1; transducer elements 3A,3B and 3C of STAVE 3 in turn intrude nearly halfway into STAVE 2; and so forth, around the circumference of the array. It thus can be seen that the individual elements of each stave substantially intrude into and are interleaved with the individual elements of its adjacent staves to create the compressed sonar array of substantially interleaved staves. The interleaving of the elements also makes it possible for the rear of the elements, on the inside of the cylinder opposite the radiating surfaces, to likewise interleave and allow the diameter of the cylinder to be decreased. Still referring to Figs. 2 and 3, it will be seen that the vertical center lines of adjacent interleaved staves are now substantially less than a half wave length apart, rather than a half wave length apart as shown in Fig. 1. It will also be noted that each row is now comprised of transducer elements 31 of every other stave. For example, ROW 1 is formed of elements 1A,3A,5A, etc. from STAVES 1,3,5, etc.; ROW 2 is formed of elements 2A,4A, etc. from STAVES 2,4, etc.; ROW 3 is formed of elements 1B,3B,5B, etc. from STAVES 1,3,5, etc.; and so forth. Fig. 2 also schematically includes the same conventional transmit - receive circuitry (and signal processing means) 35 with multiple conductor electrical cables 35a and 35b to operate the array in precisely the same manner as described above for Fig. 1. The individual elements 1A,1B,1C,1D arid IE of STAVE 1 may be electrically connected in parallel (or simultaneously addressed) , as may be the corresponding elements of STAVES 2,3,4,5,etc. , with each stave separately connected and operable from the other staves; a plurality of such staves may in turn be electrically connected in the same predetermined fashion (i.e., in parallel -or phase shifted or delayed or amplitude shaded with respect to one another) for beam forming and scanning in the horizontal direction as described above in reference to Fig. 1. Fig. 4 illustrates a partial expanded view corresponding to Fig. 3 but wherein the individual transducer elements 31 in each stave have radiating surfaces (as shown) that are circular rather than diamond - shaped. Each circular radiating surface is a half wave length in diameter. Here again, where using half wave lengths elements, the center to center spacing of adjacent elements in each stave is opened up to a substantially greater than half wave length center to center distance 31c to permit substantial intrusion into each stave by the offset circular transducer elements of adjacent staves. Otherwise, that which has been stated above in relation to Figs. 2 and 3 equally pertains to the embodiment of Fig. 4, and adjacent staves are again substantially interleaved. As will be seen in Fig. 4, STAVE 2 (transducer elements 2A,2B,2C, etc.) is substantially interleaved with STAVE 1 (transducer elements 1A,1B,1C, etc.), STAVE 3 (transducer elements 3A,3B,3C, etc.) is substantially interleaved with STAVE 2, etc. In the various embodiments of the compressed sonar array of the present invention, compared with the prior art of beam formin and scanning arrays having staves, considerably more staves can be accommodated in a given area or volume and the same number of staves can be accommodated in a smaller area or volume. The interleaving of staves permits this advantageous result, and surprisingly produces much better beam patterns and array loading than conventional array design would suggest. It will be understood that various modifications may be made in the present invention without departing from the spirit and scope of the invention as hereafter claimed. As one example, in certain less - common array applications, the interleaving of rows rather than staves may become the pertinent consideration, with the individual transducer elements of each row, and a plurality of rows, then electrically connected as described above with respect to staves.

Claims: What is claimed is: 1. A compressed sonar array for beam forming and scanning comprising in combination: a plurality of staves; the staves being generally parallel to each other; each stave being comprised of a plurality of individual transducer elements physically extending in a line; the individual elements of each stave being offset along the stave from the individual elements of adjacent staves; adjacent transducer elements in each stave being positioned in relation to each other at a substantially greater than minimum center to center spacing to permit substantial intrusion into the stave by the individual elements of adjacent staves; the individual elements of each stave substantially intruding into, and being interleaved with the individual elements of, adjacent staves; whereby a compressed sonar array of substantially interleaved staves is formed. 2. The invention of claim (1), wherein the individual transducer elements are polygonal in shape. 3. The invention of claim (2), wherein the individual transducer elements are parallelograms. 4. The invention of claim (2) or claim (3), wherein the individual transducer elements in each stave physically extend in a line vertex to vertex. 5. The invention of claim (1) , wherein the individual transducer elements are curvilinear in shape. 6. The invention of claim (2) or claim (3) or claim (4) or claim (5) , wherein the plurality of staves form a compressed cylindrical sonar array with the staves extending parallel to the cylinder array axis. 7. A compressed cylindrical sonar array, comprising in combination: a cylindrical housing; a plurality of staves positioned on the housing surface, the staves being parallel to each other and to the axis of the cylinder; each stave being comprised of a plurality of individual transducer elements each essentially square in shape and physically extending in a line, vertex to vertex; the individual elements of each stave being offset along the stave from the individual elements of adjacent staves; the individual elements of each stave substantially intruding into, and being interleaved with the individual elements of, adjacent staves; whereby a compressed cylindrical sonar array of substantially interleaved staves is formed. 8. The invention of claim (7), wherein the individual elements of every other stave form a series of rows of transducer elements extending around the circumference of the cylindrical housing perpendicular to the axis of the cylinder. 9. The invention of claim (8), wherein the transducer elements in each row extend vertex to vertex. 10. The invention of claim (9), wherein adjacent transducer elements in each row are spaced from each other a distance substantially the same as the distance the adjacent transducer elements in each stave are spaced from each other. 11. The invention of claim (1) or claim (7) , including means to electrically connect the individual elements of each stave in parallel and to electrically connect individual staves in predetermined manner with other staves. 12. The invention of claim (1) or claim (7), including means to simultaneously address the individual elements of each stave and to electrically connect individual staves in predetermined manner with other staves. 13. The invention of claim (7), wherein the squares are dimensioned on each side at a half wave length of the acoustic signal. 14. The invention of claim (1), wherein the individual transducer elements are dimensioned at a half wave length of the acoustic signal and the center to center spacing between adjacent elements in each stave is substantially greater than a half wave length.

Inventors: SCHILDKRAUT SID I, SCHILDKRAUT, SID, I.
Applicants: EDO CORP, EDO CORPORATION
Application year: 1986
Main classification: H04B1
IPC codes: B06B1