Abstract:
A sensor includes a first plate, a second plate, and a piezoelectric material portions. The piezoelectric material portions are positioned between the first plate and the second plate. The area of the piezoelectric material portions is less than the area of the plates. The plates can be supported with a center support structure. The width of the sensor is significantly greater than its height. The interstitial space is filled with a flexible material. An outside wall isolates the inside from the outside

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. § 119(e) of prior U.S. Provisional Patent Application No. 61/503,843, filed Jul. 1, 2011, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    Various embodiments described herein relate to a system and a method for forming a pressure sensor (hydrophone), which can be used as part of an array that includes a number of pressure sensors. The sensors and the array are used for receiving acoustic sound in the water. In one embodiment, the sensors are used on vessels, such as a submarine, as part of a Sonar system. 
       BACKGROUND 
       [0003]    Sonar is a well known apparatus having both civilian and military applications. Sonar (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation, usually underwater, to navigate, communicate with or detect other vessels. Sonar uses sensors placed in arrays to receive sound. The arrays can be deployed in many ways. Some sonar arrays are towed behind a ship or submarine. Towing an array of sensors or hydrophones presents many problems. Another way to deploy an array is by mounting sensors to the hull of a ship, such as a submarine. Hull mounted sonar arrays are generally built up from separate components at several hull mount sites on a hull. Typically, there are a number of hull mount sites that are aligned along the starboard side of the hull and an equal number of hull mount sites aligned along the port side of the hull In many instances, the individual sensors are made from solid ceramic plates or solid ceramic blocks and so are also heavy. Heavy sensors results in a heavy array of sensors. The heavy arrays add to the weight of the assembly needed for a hull mounted array. 
         [0004]    Sensor hydrophone converts acoustic signal into an electrical signal using a piezoelectric material. The piezoelectric material is bound by first plate and a second plate. Acoustic pressure waves impinge on the first plate and the second plate or top and bottom surfaces of the sensor, respectively. The variation in pressure squeezes or strains the active piezoelectric material to generate a voltage which is substantially proportional to a voltage produced by the piezoelectric material, such as ceramic. The chemical properties of the piezoelectric material generate the voltage. The voltage potential resulting from the acoustic sound waves is measured an input to signal processing systems to produce useful information in locating other ships and other structures. Sonar can be used to locate ships above or below the surface and can also be used to determine characteristics of the ocean floor. For example, one use of the sensors or hydrophones can be for undersea exploration for oil or other natural resources. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a side view of a vessel including an array of sonar sensors, according to an example embodiment. 
           [0006]      FIG. 2  is a perspective of a portion of the array in which a baffle, SCP, and VIM are one molded piece, according to an example embodiment. 
           [0007]      FIG. 3  is a schematic cross sectional view of an individual acoustic pressure sensor, according to an example embodiment. 
           [0008]      FIG. 4  is a side section view of an acoustic pressure sensor, according to an example embodiment. 
           [0009]      FIG. 5  is a top view of an acoustic pressure sensor, according to an example embodiment. 
           [0010]      FIG. 6  is a blown up perspective view of an acoustic pressure sensor, according to an example embodiment. 
           [0011]      FIG. 7  is a perspective view of a finished acoustic pressure sensor, according to an example embodiment. 
           [0012]      FIG. 8  is a blown up perspective view of another embodiment of an acoustic pressure sensor, according to an example embodiment. 
           [0013]      FIG. 9  is a perspective view of a square acoustic pressure sensor partially assembled, according to an example embodiment. 
           [0014]      FIG. 10  is a perspective view of a square acoustic pressure sensor as assembled, according to an example embodiment. 
           [0015]      FIG. 11  is a perspective view of a round acoustic pressure sensor as assembled, according to an example embodiment. 
           [0016]      FIG. 12  is a blown up perspective view of a round acoustic pressure sensor, according to an example embodiment. 
           [0017]      FIG. 13  is a perspective view of the round acoustic pressure sensor encased in a viscioelastic material, according to an example embodiment. 
           [0018]      FIG. 14  is a perspective view of a partially assembled round acoustic pressure sensor, according to an example embodiment. 
           [0019]      FIG. 15  is a perspective view of a fully assembled round acoustic pressure sensor, according to an example embodiment. 
           [0020]      FIG. 16  is one possible cross-section view along line A-A in  FIG. 15 , according to an example embodiment. 
           [0021]      FIG. 17  is one possible cross-section view along line A-A in  FIG. 15 , according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  is a side view of a vessel  100  including an array of sonar sensors  120 , according to an example embodiment. The vessel  100  is a submarine. It should be understood that other types of vessels may also include an array of sonar sensors. The array of sonar sensors  120  includes a number of subarrays of sonar sensors that are added to other components to form a panel, such as panels  122 ,  124 ,  126 . The vessel&#39;s  100  port side is shown with three panels  122 ,  124 ,  126  that include sonar sensors. The panels  122 ,  124 ,  126  are positioned along the port side of the vessel  100 . The starboard side of the vessel  100  also includes three similarly positioned panels (not shown) of sonar sensors. In total, there are six panels on the vessel that form the array  120 . It should be noted that other arrays can have a different number of panels. Some vessels  100  may include more panels and some vessels may include fewer panels to form an array of sensors. 
         [0023]      FIG. 2  is a perspective of a portion of one of the panels, such as panel  122 , of the array of sonar sensors  120 , according to an example embodiment. The sensors may be laid out in a hexagonal pattern to increase packing density which increases performance. 
         [0024]      FIG. 3  is a schematic cross sectional view of an individual acoustic pressure sensor  600 , according to an example embodiment. The sensor  600  includes a first plate  610  and a second plate  612 . Sandwiched between the first plate  610  and the second plate  612  are columns of ceramic material, such as columns  632 ,  634 ,  636 . The columns can be of any shape. For example, the cross section may be circular or square or rectangular in shape and these are low cost readily available parts. The columns of ceramic material are a piezoelectric material that produces electricity in response to pressure or force placed on the material. An electrical charge accumulates in certain solid materials (such as the ceramic used for the columns  632 ,  634 ,  636  in the pressure sensor  600 ) in response to applied mechanical strain. Sound waves, whether in water, air, or otherwise, are pressure waves. When the sound wave or pressure wave strikes a first plate  610  the force is transferred to the columns  632 ,  634 ,  636  of piezoelectric material. 
         [0025]    In fact, the columns  632 ,  634 ,  636  act as pressure concentrators. Pressure is force per unit area. When the force passes through the columns  632 ,  634 ,  636 , the force is distributed over a smaller area and therefore pressure at the columns  632 ,  634 ,  636  is higher than the pressure on the first plate  610 . The columns  632 ,  634 ,  636  of piezoelectric material generate electricity when subjected to a pressure change. Electrical connections are made to the columns which produce signals in response to the variations of pressure caused by sound waves. 
         [0026]    In other embodiments, the ceramic or piezoelectric material need not be formed in columns. The first plate  610  and the second plate  612  have major surfaces with an area. The ceramic or piezoelectric material interacts with less than the full surface area of these major surfaces. The ceramic or piezoelectric material could be shaped as cubes or even shorter flat rectangles. 
         [0027]    The surface area of the ceramic or piezoelectric material interfacing with the major surface of one of the first plate  610  and the second plate  612  will be less than the surface area of the major surface. The piezoelectric material or ceramic material is heavy. In such an arrangement, less ceramic material is used and the resultant sensor formed is lighter than previous sensors. Previous sensors included a substantially solid plate of ceramic between a first plate and a second plate. Using portions of ceramic or piezoelectric material rather than a solid plate of ceramic between the first plate  610  and the second plate  612  lightens the sensor. The ratios between the surface area of the first plate  610  or the second plate  612  (caps) and the piezoelectric material portions is in a range of between 3:1 to 11:1. It has been found that surface area ratios within the above range provide at least as good if not superior performance in a sensor that is less costly to build and which has less weight. 
         [0028]      FIG. 4  is a side section view of an acoustic pressure sensor  700 , according to an example embodiment. The pressure sensor  700  includes a first plate  710  and a second plate  720 . Sandwiched between the first plate  710  and the second plate  720  are columns of piezoelectric material, three of which can be seen,  732 ,  734 ,  736 .  FIG. 5  is a top view of an acoustic pressure sensor  700  with the second plate  720  removed, according to an example embodiment. This shows that the piezoelectric columns, such as  732 ,  734 ,  736  are actually ring-shaped. The ring-shaped piezoelectric material portions have openings therein,  731 ,  733 ,  735 , respectively. The openings  731 ,  733 ,  735  in the middle of the piezoelectric portions  732 ,  734 ,  736  can receive a fastener, such a screw or bolt. The fasteners (not shown) pass through the openings  731 ,  733 ,  735  and attach the first plate  710  to the second plate  720 . 
         [0029]      FIG. 6  is a blown up perspective view of an acoustic pressure sensor  700 , according to an example embodiment. In this example embodiment, there are twelve piezoelectric portions, such as  732 ,  734 ,  736  that are ring-shaped. Each ring-shaped piezoelectric material portion  732 ,  734 ,  736  has an opening therein, such as openings  731 ,  733 ,  735 , respectively. The first plate  710  and the second plate  720  also include twelve openings. As shown plate  710  includes openings  711 ,  713 ,  715  amongst the twelve openings, and plate  720  includes openings  721 ,  723 ,  725  amongst the twelve openings on that plate  720 . The openings in the first plate  710  and the openings in the second plate  720  substantially align. In some embodiments of the pressure sensor  700 , a spacer can be provided. The spacer also includes twelve openings, such as openings  741 ,  743 , and  745 . The openings  741 ,  743 , and  745  are sized to receive the ring-shaped piezoelectric material portions, such as  732 ,  734 ,  736  and hold them in proper alignment so that a fastener can pass through opening  725  in plate  720 , opening  735  in ceramic piece  736 , and opening  715  in plate  710 . The sensor  700  includes an acoustic isolation wall around perimeter of the sensor plates  710 ,  720 . The wall can be a single part or a an assembly that includes several parts. As shown in  FIG. 6 , the wall  750  includes a first wall component  751  and a second wall component  752  that form the acoustic wall  750 . This wall must be sufficiently stiff to resist movement from the acoustic waves but decoupled from the first plate  710  and the second plate  720  (caps) with a flexible layer to prevent the two caps from being bonded together. In one embodiment, the wall can be molded directly into the cap to reduce part count. A shorter wall could be molded into both the first plate  710  and second plate  720  (caps). In this embodiment, when the two plates are caps are assembled a wall will formed. A flexible layer will be required in each of these configurations to prevent the two caps or plates from effectively bonding together. 
         [0030]    Fasteners, such as screws or bolts placed through the ceramic centers and the plates  710 ,  720  support alignment, coupling, and “bond” strength of the assembled sensor  700 . Once assembled, the sensor is placed in a mold and urethane plastic or some other waterproof material having the same or similar properties as water (seawater or fresh water) is pumped into the chamber, pressurized and held at temperature for an amount of time. The urethane or other material must not fill the interstitial spaces your between the components making up the sensor  700  to leave an essential air gap allowing for coupling of the incident acoustic wave with the piezoelectric material. In one example embodiment a flexible material spacer could fill the space between the piezoelectric pieces to prevent a material such as urethane or water from filling the space. In one example embodiment, a layer of electrically isolative material is inserted between the ceramic and one of the first plate  710  or the second plate  720 . In this example embodiment, the plate/wall housing can be used to achieve full electrical shielding for the sensor  700 . Of course, it is contemplated that in alternative embodiments, the shape and size of these sensors as well as the quantity of ceramics in each sensor assembly could be varied. The sensors discussed above deliver increased sensitivity above baseline through a unique low cost geometry of piezoelectric material to plate coupling. 
         [0031]      FIG. 7  is a perspective view of a finished acoustic pressure sensor  700 , according to an example embodiment. The sensor  700  is encased in urethane material  1000 . The resulting sensor  700  has a low-profile; and works in current reflecting plate scenarios. The example embodiment has no tabs to break so it is more rugged than some current designs. In addition, the sensor  700  is lightweight when compared to sensors having a solid ceramic plate and has a weight of approximately 7.5 g/cm 2 . In addition, noise figure of merit is  10  dB higher than sensors that have a lead titanate design. In another embodiment, the ceramic thickness of the piezoelectric portions is doubled, and the noise figure of merit increases 40%. The sensor  700  also substantially maximizes flow noise area averaging. 
         [0032]    The sensors  600 ,  700  or hydrophones are designed to work in frequency ranges where the wavelength is greater than the size of the transducer. This region results in a mostly omnidirectional transducer where the entire sensor is engulfed in each pressure wave. It should be noted, that other sensors that are less than ⅛ of the wavelength in thickness can benefit from reflection gain from a signal conditioning plate when in an array. The polarization direction in the embodiment of sensors  600 ,  700  is axial. In other words, the hydrophone or sensor  600 ,  700  ceramic is active in the 3-3 mode. When active in the 3-3 mode, the voltage is measured from electrodes in the same direction as the ceramic is polarized. The above described structure will work on other types of sensors. For example, the same geometry could also be expanded to use materials in the 3-1 mode where the polarization direction is orthogonal to the voltage electrode direction for materials that make this mode desirable. 
         [0033]      FIG. 8  is a blown up perspective view of another embodiment of an acoustic pressure sensor  800 , according to an example embodiment. The pressure sensor  800  and includes a first plate  810  and a second plate  820 . The pressure sensor  800  is substantially square in shape and includes  16  piezoelectric portions, such as  831 ,  833 ,  835 . Each of the PAs electric portions  831 ,  833 ,  835  includes an opening therein which is sized to receive a fastener, such as fasteners  841 ,  843 ,  845 . The first plate  810  also includes openings which correspond to the fasteners  841 ,  843 ,  845 . Similarly the second plate also includes openings which correspond to the fasteners  841 ,  843 ,  845 . Also included in the pressure sensor  800  is a wall  850 . The wall  850  is a unitary unit which provides acoustic isolation at the perimeter of the sensor plates  810 ,  820 . The wall  850  can be thought of as a frame sized to substantially match the perimeter of the sensor plates  810 ,  820 . The frame or wall  850  is sufficiently stiff to resist movement from the acoustic waves while being decoupled from the first plate  810  and the second plate  820 . The decoupling prevents the wall from joining or bonding the first plate  810  and the second plate  820  and maintains the acoustic isolation of the elements within the frame or wall  850 . 
         [0034]      FIG. 9  is a perspective view of a square acoustic pressure sensor partially assembled, according to an example embodiment. As shown, the fasteners  841 ,  843 ,  845  have passed through the first plate  810  and through the openings in the ring shaped piezoelectric portions  831 ,  833 ,  835 . To complete the assembly, the frame or wall  850  has to be placed about the perimeter of the first and second plates  810 ,  820 . As a practical matter, the frame  850  will be placed onto the outer perimeter of the first plate  810  as shown in  FIG. 9 . The second plate  820  will then be placed onto the fasteners, such as fasteners  841 ,  843 ,  845  to complete the assembly. It should be noted that is shown in  FIG. 9 , acoustically isolated material is placed between the piezoelectric portions during assembly so that it is captured between the first plate  810  the second plate  820  and the wall  850 .  FIG. 10  is a perspective view of a square acoustic pressure sensor as assembled, according to an example embodiment. In other words  FIG. 10  is a perspective view of the square acoustic pressure sensor  800  after the partial assembly of  FIG. 9  is completed. It should be noted that the first plate  810  second plate  820  are made of aluminum. In other embodiments of the invention the first plate and second plate are made of steel. The assembly shown in  FIG. 10  generally encased in urethane or a similar material so the sensor is sufficiently ruggedized to work in various environments, such as in an ocean or other environment. 
         [0035]      FIG. 11  is a perspective view of a round acoustic pressure sensor  1100  as assembled, according to an example embodiment.  FIG. 12  is a blown up perspective view of a round acoustic pressure sensor  1100 , according to an example embodiment. Now referring to both  FIGS. 11 and 12 , the round acoustic pressure sensor  1100  will be further detailed. As shown, the round sensor  1100  includes a first round plate  1110  and a second round plate  1120  and a wall  1150 . The wall  1150  is annular. The wall has an outside perimeter which is substantially the same as the outside perimeter of the first plate  1110  and the second plate  1120 . The sensor  1100  also includes a piezoelectric ring  1130 . The round sensor  1100  can also include a center support structure  1140  to stiffen the caps (first plate  1110  and second plate  1120 ). If the caps (first plate  1110  and second plate  1120 ) are too flexible, they will not effectively transfer the acoustic pressure into the piezoelectricity. The support structure  1140  is generally not made of a piezoelectric material and is made of a material that will support the first plate  1110  and the second plate  1120 . As shown in  FIG. 12 , the support structure  1140  is centered with respect to the first plate  1110  and the second plate  1120 . The support structure  1140  also is tubular in shape and has an opening which can receive a fastener  1141 . The fastener  1141  passes through the first plate  1110  the support structure  1140  and the second plate  1120 . As mentioned above, the support structure provide stiffness to the first plate  1110  and the second plate  1120  which is spanning the space between the wall  1150  and the piezoelectric element  1130 . The area ratio between the center support  1140  and the piezo-electric material  1130  should be at least 1:10 so that the center support  1140  does not interfere with transferring load through the piezo-electric material  1130 . In one embodiment the center support structure  1140  is a separate element. In another embodiment, the center support may be molded directly into the caps (the first plate  1110  and the second plate  1120 ) to reduce part count. Also included in the sensor  1100  is a flexible layer  1160  which prevents the wall  1150  from coupling or bonding together the first plate  1110  and the second plate  1120 . 
         [0036]      FIG. 13  is a perspective view of the round acoustic pressure sensor  1100  encased in a urethane material, according to an example embodiment. The urethane material ruggedized as the archer sensor  1100  so they can be used in various environments. The urethane material generally will not affect the ability of the sensor  1100  to detect pressure waves. The final assembly also includes electrically coupling the PAs electric element  1130  (shown in  FIG. 12 ). As shown in  FIG. 13 , wires attached to the ring provide the electrical coupling. 
         [0037]      FIG. 14  is a perspective view of a partially assembled round acoustic pressure sensor  1400 , according to an example embodiment. The acoustic pressure sensor  1400  is very similar to the acoustic pressure sensor  1100 . Rather than describe the pressure sensor  1400  in detail, for the sake of clarity and brevity, only the differences between the pressure sensor  1100  and the pressure sensor  1400  will be discussed. As shown in  FIG. 14  the piezoelectric element  1130  is encased in acoustically isolated material. In the pressure sensor  1100 , acoustically isolated material can also be placed about the piezoelectric element  1130 . Among the differences is that the ring  1160  of the coupling material between the first plate  1110  and the second plate  1120  is placed directly onto the second plate  1120 . This reduces the part count and eases assembly of the sensor  1400 . 
         [0038]      FIG. 15  is a perspective view of a fully assembled round acoustic pressure sensor  1500 , according to an example embodiment. Sensors  1500  could be assembled in a number of different ways. The basic idea of sensor  1500  is that the wall  1150  of the previous sensors  1100 ,  1400  can be incorporated into the first plate and the second plate. Now referring to both  FIGS. 16 and 17 , two possible cross-sectional areas of the first plate and the second plate will now be shown. 
         [0039]      FIG. 16  is one possible cross-section view along line A-A in  FIG. 15 , according to an example embodiment. The first plate  1610  includes a wall  1660  and a support structure  1640 . The wall  1660 , in one embodiment, is a half wall. In other words the second plate will be similarly shaped in dimensioned so that when the first plate  1610  and the second plate are connected they form the wall  1660 . Similarly the support structure  1640  is also a half wall or half support so that the first plate  1610  and second plate are similarly shaped. It should be understood that the wall  1660  of the first plate  1610  could also be a full wall and that the support structure  1640  can also be a full support structure. In this case, a flat second plate would be connected to the first plate  1610  to form the round sensor  1500 . 
         [0040]      FIG. 17  is one possible cross-section view along line A-A in  FIG. 15 , according to an example embodiment. In this particular embodiment, the first plate  1710  is provided with a wall  1760 . Unlike the first plate  1610 , the first plate  1710  does not include a support structure. The wall  1760  could be a half wall or a full wall. A separate support structure, such as support structure  1140  (shown in  FIG. 12 ) could be used. Of course, during assembly the first plate and second plate must be separated by a dampening material so as not to bond or unify the first plate and the second plate. 
         [0041]    This has been a detailed description of some exemplary embodiments of the invention(s) contained within the disclosed subject matter. Such invention(s) may be referred to, individually and/or collectively, herein by the term “invention” merely for convenience and without intending to limit the scope of this application to any single invention or inventive concept if more than one is in fact disclosed. The detailed description refers to the accompanying drawings that form a part hereof and which shows by way of illustration, but not of limitation, some specific embodiments of the invention, including a preferred embodiment. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to understand and implement the inventive subject matter. Other embodiments may be utilized and changes may be made without departing from the scope of the inventive subject matter. Thus, although specific embodiments have been illustrated and described herein, any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.