Abstract:
A three-dimensional array of acoustic sensors. The array can be used for both the transmission and reception of acoustic signals. The array comprises electroplated piezoelectric polymer layers that are laminated with a non-conductive epoxy to form individual multi-layer array transducer elements. Circuit support layer layers are incorporated between the multi-layer array transducer elements. Because of the three-dimensional configuration of the array, logical transducers can be created from multiple transducer elements, and transmission and reception of acoustic signals in any direction can be realized.

Description:
STATEMENT OF GOVERNMENT INTEREST  
       [0001] 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. 
     
    
     
       CROSS REFERENCE TO OTHER PATENT APPLICATIONS  
         [0002]    Not applicable.  
         BACKGROUND OF THE INVENTION  
         [0003]    (1) Field Of The Invention  
           [0004]    The present invention generally relates to a sonar array, and more particularly to a three dimensional array of sonar sensors.  
           [0005]    (2) Description of the Prior Art  
           [0006]    Arrayed transducers are known in the art. Specifically, Hill et al., U.S. Pat. No. 4,380,808, describes a sparse or “thinned” array of mass loaded PZT elements. Hill et al. further describes a particular uniform element placement scheme that is utilized to achieve three half-wave element spacings for three separate operating frequencies. Francis, U.S. Pat. No. 4,638,468, describes a polymer hydrophone array with printed circuit wiring. Ehrlich et al., U.S. Pat. No. 4,766,575, describes a cylindrical sonar array that employs rectangular planar array segments that extend in the axial direction when assembled on a cylindrical conducting plate having flat longitudinal portions to which the planar array segments are attached. Each planar array segment comprises two columns of planar transducer elements with each column extending in the axial direction of the cylinder. Peloquin, U.S. Pat. No. 5,550,791, describes a composite hydrophone array assembly that is made from a compliant mandrel such as a hollow tube and at least one wrap of piezoelectric film adhered to the compliant hollow tube at a plurality of locations thereon. Lindberg, U.S. Pat. No. 5,530,683, describes an acoustic transducer that is constructed as a stacked configuration of multi-layer transducer elements. Each layer within the transducer contains elements in (along) one-dimension. Furthermore, the transducer elements are limited to high-frequency operation.  
           [0007]    What is needed is a sonar array system that provides a relatively greater spatial operational capability than the prior art, and provides single or double resonance frequency elements.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention is directed to a three-dimensional array of acoustic sensors for underwater imaging applications. The array utilizes electroplated layers of piezoelectric polymer (PVDF), or any other electrostrictive polymer, in conjunction with interleaved circuit support layers to providing a volumetric three-dimensional array whereby individual transducer elements may be formed between parallel circuit support layer layers. The three-dimensional configuration of transducers allows formation of acoustic beams in any direction. The individual transducer elements can be grouped into logical transducers operating in a different frequency band. The array can be used for both transmitting and receiving.  
           [0009]    The sonar array of the present invention has many applications, e.g., smart acoustic countermeasure devices and unmanned underwater vehicle SONAR systems. The three-dimensional array elements provide a SONAR user with a relatively increased operational field of view as compared to prior art two-dimensional arrays.  
           [0010]    A feature of the array of present invention is the use of piezoelectric or electrostrictive polymers (i.e. PVDF) as an active transduction material. An advantage of this feature is that the specific acoustic impedance of piezoelectric polymer is very closely matched to that of water. When the acoustic impedance of the array elements of the volumetric array of the present invention are closely matched to the surrounding fluid (e.g., ocean water), transmission and reception of very wide-band acoustic signals can be realized.  
           [0011]    Another important feature of the present invention is that the array can be configured to have a planar or cylindrical geometry.  
           [0012]    In one aspect, the present invention is directed to a sonar array comprising a transducer element having a plurality of layers of acoustically transparent electro-acoustic transducer material in a laminated configuration. Each of the layers has a first side with a plurality of electrically conductive portions that are (i) electrically isolated from each other, (ii) arranged in a two-dimensional arrangement, and (iii) configured to have a first polarization. The second side has a plurality of electrically conductive portions that are (i) electrically isolated from each other and the conductive portions on the first side, (ii) arranged in a two-dimensional arrangement that is the same as the two-dimensional arrangement in which the conductive portions of the first side are arranged such that the conductive portions of the second side are substantially aligned with the conductive portions of the first side, and (iii) configured to have a second polarization opposite the first polarization. The layers are arranged so that opposite polarizations do not confront each other. The end layers of the laminated configuration have exposed sides which have different polarities. The electrically conductive first side portions corresponding to the same location within the two-dimensional arrangement are electrically connected together and the electrically conductive second side portions that correspond to the same location within the two-dimensional arrangement are also electrically connected together.  
           [0013]    The sonar array can also have a pair of circuit support layers attached to a corresponding exposed side. Each of the circuit support layers has a plurality of electrically conductive regions that are electrically isolated from each other. Each of the regions is electrically connected to a corresponding electrically conductive portion of the exposed side. A plurality of electrically conductive terminal members are attached to each circuit support layer and electrically connected to a corresponding region.  
           [0014]    In a preferred embodiment, the acoustically transparent electro-acoustic transducer material is selected from the group consisting of urethane, electrostrictive polyurethane, polyvinylidene fluoride, and polyvinylidene trifluoroethylene.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The features of the invention are believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a perspective view of a completed laminate volumetric array assembly made in accordance with one embodiment of the present invention;  
         [0017]    [0017]FIG. 2A is a plan view of one side of piezoelectric polymer layer used in the array of the present invention;  
         [0018]    [0018]FIG. 2B is a plan view of the opposite side of the piezoelectric polymer layer of FIG. 1;  
         [0019]    [0019]FIG. 3 is a cross-sectional view taken along line  3 - 3  in FIG. 2A;  
         [0020]    [0020]FIG. 4 is an exploded view illustrating a laminate assembly of the piezoelectric polymer layers of FIGS. 2A and 2B which form a laminate array element of the sonar array of the present invention;  
         [0021]    [0021]FIG. 5 is a plan view of one side of a circuit support layer used in the array of the present invention;  
         [0022]    [0022]FIG. 6A is a enlarged, partial plan view of the side of the circuit support layer shown in FIG. 3;  
         [0023]    [0023]FIG. 6B is a cross-sectional view taken along line  4 B- 4 B in FIG. 4A.  
         [0024]    [0024]FIG. 6C is a cross-sectional taken along line  4 C- 4 C in FIG. 4A;  
         [0025]    [0025]FIG. 7 is an exploded view illustrating a laminate array assembly comprising a plurality of the laminate array elements of FIG. 4 and a plurality of circuit support layers of FIG. 5 that, when completely assembled, form one embodiment of the volumetric array of the present invention; and  
         [0026]    [0026]FIG. 8 is a perspective view of a volumetric array in accordance with another embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    In describing the preferred embodiments of the present invention, reference will be made herein to FIGS.  1 - 8  of the drawings in which like numerals refer to like features of the invention.  
         [0028]    Referring to FIG. 1, there is shown the completed volumetric sonar array  10  fabricated in accordance with one embodiment of the invention. Sonar array  10  generally comprises transducer layers  12   a ,  12   b  and  12   c , and circuit support layers  14 . Circuit support layers  14  are bonded to the transducer layers  12   a ,  12   b  and  12   c  to form the completed array  10 . Transducer layers  12  form a two dimensional array of individual transducers  15 . Each of these transducers has an operating frequency band determined by the Nyquist criteria; however, it is understood that one could group a plurality of these transducers in a three dimensional region to form a logical transducer having a lower operating frequency band. Each circuit support layer  14  includes terminals  16  that are configured to be electrically connected to wires or conductors (not shown) to enable transfer of signals to and from transducers  15  in array  10 . Thus, other sonar components and systems can receive or transmit signals from or to, respectively, array assembly  10 . The three-dimensional configuration of transducers elements  15  allows formation of acoustic beams in any direction. Array  10  can be used for both transmitting and receiving. The construction of array  10  is discussed in detail in the ensuing description.  
         [0029]    Referring to FIGS. 2A, 2B and  3 , there is shown a portion of one transducer layer  12  having a piezoelectric layer  18  made from a piezoelectric polymer (such as polyvinylidene fluoride (PVDF) or the like). Layer  18  comprises side  20  and side  22 . Sides  20  and  22  are substantially the same in construction. Either side  20  or  22  can be designated as the positive-polarity side or negative polarity side. For purposes of explaining the present invention, sides  20  and  22  are designated as the positive and negative polarity sides, respectively. It is to be understood that other suitable materials that can achieve the same results also can be used to fabricated piezoelectric layer  18 . Such materials include electrostrictive polyurethanes, and polyvinylidene difluoroethylene and polyvinylidene trifluoroethylene.  
         [0030]    Side  20  comprises an electrically non-conductive portion  24  and electrically conductive portions  26  that are formed by electro-depositing adhesive films (or any other technique known in the art) onto layer  24 . Conductive portions or electrodes  26  are spaced apart and electrically isolated from one another. In a preferred embodiment, conductive portions  26  have the same geometrical shape. In one embodiment, each conductive portion  26  has a generally rectangular shape, includes a first plated through-hole  28  in the upper left hand corner thereof. Thus, each plated through-hole  28  is in electrical contact with conductive portion  26  associated with that plated through-hole  28 . A portion of each conductive portion  26  is notched or cut away, as indicated by numeral  30 . A second plated through-hole  32  is located in the notched portion  30  of conductive portion  26 . Second plated through-holes  32  are electrically isolated from the conductive portions  26 . In a preferred embodiment, plated through-holes  28  and  32  are configured as copper-plated through-holes. In one embodiment, a photo-etched pattern is used to effect electrical isolation of the second through-holes  32 . In another embodiment, second through-holes  32  are positioned in the non-conductive portion near an associated conductive portion  26 .  
         [0031]    Side  22  (FIG. 2B) comprises electrically non-conductive portion  24  and electrically conductive portions or electrodes  34 . Conductive portions  34  are equidistant and electrically isolated from one another. In a preferred embodiment, conductive portions  34  have the same geometrical shape. In one embodiment, each conductive portion  34  has a generally rectangular shape. Each conductive portion  34  includes a corresponding second plated through-hole  32  in electrical contact with the corresponding conductive portion  34 . A portion of each conductive portion  34  is notched or cut away, as indicated by numeral  36  so as to provide space for first plated through-hole  28 . As above, other embodiments can feature different arrangements for avoiding conduction between conductive portion  34  and first through-hole  28 .  
         [0032]    Thus, each conductive portion  26  is located directly opposite, but is electrically isolated from, a corresponding conductive portion  34 . In a preferred embodiment, conductive portions  26  and  34  are arranged in a row-column (i.e. two-dimensional) arrangement as shown in FIGS. 1 and 2A. Thus, each conductive portion  26  and  34  may be referred to by its row-column location. For example, conductive portion  26   a  is located at row-column location ( 1 ,  4 ). Similarly, conductive portion  34   a  is located a row column location ( 2 ,  2 ). Although FIGS. 1 and 2A show twelve columns and three rows, it is to be understood that the actual number of conductive portions  26  and  34  required depends upon the particular application for which the volumetric array of the present invention is to be used. In one embodiment, electrically non-conductive portion  24  is fabricated from piezoelectric plastic. Conductive portions  26  can be formed by metallic layers that are electroplated or electro deposited on layer  24 . In one embodiment, layer  18  has a length L 1  of about four feet, a width W 1  of about eighteen inches, and an overall thickness of about 0.20 inch. However, layer  18  may be configured to have other dimensions depending upon the required number of conductive portions  26  and the particular application for which the volumetric array of the present invention is to be used. Layer  18  further includes fiducial marks  33  located on sides  20  and  22 .  
         [0033]    Referring to FIG. 4, a plurality of layers  18 , designated by  18   a ,  18   b ,  18   c ,  18   d ,  18   e , and  18   f , are joined together to form a multi-layer transducer  15 . The view shown in FIG. 4 is a partial, exploded view, in cross-section, of one transducer layer  12 . In a preferred embodiment, a z-axis conductive film  40  is positioned between layers  18   a ,  18   b ,  18   c ,  18   d ,  18   e , and  18   f  to bond the layers together. Film  40  serves two purposes: bonding layers together and allowing conduction in vertical direction between layers. This allows conduction between conductive portions  26  as shown by  38   a  while preventing conduction between conductive portions  26  and conductive portions  34  having an opposite polarity. Other embodiments of this invention can feature other structures known in the art which provide these functions separately or in combination. Layers  18  are arranged such that the positive polarity sides of layers  18   b - f  face the positive polarity side of the adjacent layer and the negative polarity sides of layers  18   b - f  face the negative polarity side of adjacent layers  18 . Thus, electrodes having opposite polarizations never confront each other. Lines  48   a  show the electrical connection of the positive (+) polarity conductive portions  26 . Lines  38   b  show the electrical connection between the negative (−) polarity conductive portions  34 . Line  38   c  shows the connection formed among the positive polarity conductive portions  26  of a different transducer  15 . Layers  18  are bonded together such that the rows and columns of conductive portions  26  and  34  of the layers  18  are substantially aligned. Although six layers  18  are shown in FIG. 4, it is to be understood that this is merely exemplary and that the actual number of layers  18  and conductive portions  26  and  34 , depend upon the actual application (i.e., frequency band) for which the array of the present invention is to be used. Furthermore, the element aperture will also vary according to the frequencies of operation. For example, for relatively high frequencies, the number of layers  18  utilized can be five or six with element apertures on the order of about 0.39 inch. Lines  38   a ,  38   b  and  38   c  provide conductive joining.  
         [0034]    Referring to FIGS. 2A and 4, each conductive portion  26  of each layer  18   a - f  that corresponds to the same row-column location is electrically connected together via a conductive connector, such as a line  38   a  shown in FIG. 2A. Preferably, line  38   a  is a conductive path provided by a well known z-axis conductive film; however other techniques well known in the art can be used to provide this conductive path. Referring to FIGS. 2B and 4, each conductive portion  34  of each layer  18   a - f  that corresponds to the same row-column location is electrically connected together via the conductive path  38   b  shown in FIG. 2A. Preferably, line  38   b  is a z-axis conductive film as discussed above.  
         [0035]    Referring to FIGS.  5 , and  6 A-C, there is shown circuit support layer  14  used in the array of the present invention. Circuit support layer  14  is a single-sided circuit and comprises electrically non-conductive layers  44 . Layer  44  has side  44   a  and  44   b . In one embodiment, layers  44  are fabricated from Kapton™. Circuit support layer  14  further includes conductive portions  48  which are electrically isolated from one another. Each conductive portion  48  is positioned so that it is substantially aligned with a particular row-column location on an element  26  on the piezoelectric polymer layer  18 . Circuit support layer  14  further includes terminal portions  16  which are attached to or formed on the periphery of circuit support layer  14 . An arbitrary number of conductive terminals  16  allow wires to be attached to the circuit support layer which connects to the conductive portions  26  that are in each column (see FIG. 1). Circuit support layer  14  further includes conductive traces  54 . Each conductive trace  54  is between layers  44  and extends from a particular terminal portion  16  to a particular conductive portion  48 . Side  44   b  has no electrically conductive material thereon. Preferably, layers  44  are configured from a material that enables the portions of layers  44  having no conductive trace  54  therebetween to bond to each other. Since circuit support layer  14  is a single-sided flex circuit, side  44   b  does not have any conductive portions thereon. In a preferred embodiment, circuit support layers  14  are used as the outer most layers of the array wherein side  44   b  is the exposed side. Circuit support layer  14  is just one example of a suitable single-sided circuit support layer that can be used in the sonar array of the present invention. Other suitable single sided circuit support layer configurations can used as well. In order to utilize single-sided circuit support layer  14  in the array&#39;s interior wherein conductive portions of the piezoelectric polymer layers  18  (i.e. conductive portions  26  or  34 ) are on both sides of circuit support layer  14 , two circuit support layers  14  are bonded together using a non-conductive adhesive film so as to function as a double-sided circuit support layer. In another embodiment, double sided-circuit support layers can be used in the interior of the array. In an alternate embodiment, stiffening plates (not shown) are attached to circuit support layers  14  to provide structural rigidity.  
         [0036]    Referring to FIG. 7, a plurality of laminate transducer layers  12  and circuit support layers  14  are joined together to form a laminate array assembly  10 . It should be understood that FIG. 7 is not to scale, and the layers may be much thinner than those shown in this figure. An adhesive film  58  is used to bond circuit support layers  14  to layers  12 . In one embodiment, adhesive film  58  is configured as the commercially available Z-axis adhesive film which conducts electrical current in the direction perpendicular to the surface of the film. Other types of suitable adhesives may be used as well, such as B-stage adhesive films. For purposes of identification and to facilitate understanding of the present invention, the designations  12   a ,  12   b ,  12   c  and  12   d  refer to particular transducer layers  12  that are part of array assembly  10 , while the designations  18   a ,  18   b ,  18   c ,  18   d ,  18   e ,  18   f  and  18   g  refer to particular ones of layers  18  that are part of each transducer layer  12 . The individual transducers  15  are the combined columns of transducer material layers  18  positioned on a transducer layer  12 . Circuit support layers  14  are used as the outermost layers of assembly  10 . Circuit support layers  14  are also used in the interior of assembly  10 . As described above, two circuit support layers  14  are bonded together to form a double-sided circuit support layer. A non-conductive adhesive film  60  is used to bond the two single-sided circuit support layers  14  together. Adhesive film  58  is disposed over layer  18   a  of transducer layer  12   a  and bonds circuit support layer  14  to layer  18   a . When circuit support layer  14  is bonded to layer  18   a , the conductive portions  48  are electrically connected to the exposed corresponding conductive portions (i.e. portions  26  or  34 ) of layer  18   a . Similarly, adhesive film  58  bonds the other circuit support layer  14  to layer  18   g  of transducer layer  12   c . When the circuit support layer  14  is bonded to layer  18   g , the conductive portions  48  are electrically connected to the exposed corresponding conductive portions (i.e., portions  26  or  34 ) of layer  18   g.    
         [0037]    All positive polarity conductive portions  26  of layers  18   a - 18   g  of transducer layer  12   a  that correspond to a particular row-column location are electrically connected together and to the conductive portion  48  of the top circuit support layer  14  that has the same row-column location. Similarly, all negative polarity conductive portions  34  of layers  18   a - 18   g  of transducer layer  12   a  that correspond to a particular transducer layer  12  and column location are electrically connected together and to the conductive portion  48  of the bottom circuit support layer  14  that corresponds to that same particular row-column location. Together, the positive and negative portions of a single row-column location form individual transducer  15 . Columns of layers  18   a - 18   g  on layers  12   b  and  12   c  are joined together in a similar manner to form a plurality of transducers  15  in a three dimensional array.  
         [0038]    Array assembly  10  has a generally planar geometry. However, other geometrical shapes are possible. For example, FIG. 8 shows a sonar array  100  of the present invention which has a generally cylindrical shape. Array  100  generally comprises circuit support layers  102   a ,  102   b ,  102   c  and  102   d , and multi-layer array transducer elements  104   a ,  104   b  and  104   c  that are rolled about backing member  106  to provide the cylindrical shape. Circuit support layers  102   a  and  102   d  are configured as single sided circuit support layers and form the outermost and innermost layers, respectively, of assembly  100 . Circuit support layers  102   b  and  102   c  are double-sided circuit support layers. Adhesive layers, not shown but similar to adhesive layers  58 , bond the circuit support layers to the array transducer elements. Each transducer layer  104   a ,  104   b  and  104   c  is generally the same in construction as transducer layer  12 . However, the precise location or placement of the conductive portions of the layers of particular layers  104   a - c  as well as the conductive portions of particular circuit support layers  102   a - d  are shifted to account for the overall thickness of array  100  as the aforesaid circuit support layers and transducer elements are rolled about backing member  106 . Electronics cavity  108  is located in the center of backing member  106 . In a preferred embodiment, the aforementioned components are wound in a scroll-like fashion in order to achieve the cylindrical shape of array  100 .  
         [0039]    In accordance with one aspect of the invention, the components described in the foregoing description are arranged so as to provide a volumetric or three-dimensional sonar array. The three-dimensional array elements of the array of the present invention provide a relatively greater spatial operational capability. The utilization of plastic components such as the piezoelectric polymer layers, the thin Kapton™ copper circuit support layers and then the thin adhesive layers provide the individual array layers  12   a ,  12   b  and  12   c  with very wide operational bandwidths, and acoustic transparency needed to form a volumetric array.  
         [0040]    While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.