Patent Publication Number: US-7719926-B2

Title: Slotted cylinder acoustic transducer

Description:
FIELD OF THE INVENTION 
   This invention relates generally to underwater acoustic transducers and, more particularly, to a slotted cylinder acoustic transducer. 
   BACKGROUND OF THE INVENTION 
   A variety of types of conventional acoustic transducers are known. Acoustic transducers are used to convert electrical energy to acoustical energy, and vice-versa. An acoustic projector, a type of acoustic transducer, in operation, is used in one transduction direction, to convert electrical energy to acoustic energy. However, though usually not used in the opposite direction, an acoustic projector also does operate in the opposite direction, to convert acoustic energy into electrical energy. 
   Some conventional acoustic transducers have limitations. For example, many types of conventional acoustic transducers are not capable of producing large amounts of acoustic power at low frequencies, for example, on the order of two kHz or less, and, in particular, under 400 Hz. Similarly, many types of conventional acoustic transducers are unable to operate over a wide bandwidth at the low frequencies. 
   Physical limitations can complicate solving such deficiencies. For example, an ability to withstand high stresses is important for deep depth, high water pressure, survival and operation, as well as for the ability to produce high acoustic power levels. An ability to withstand high stresses can result in an inability to operate at the above-described low frequencies. 
   Known types of acoustic projectors that can operate as acoustic projectors at low frequencies include flextensional transducers, inverse flextensional transducers, bender disc transducers, wall-driven oval transducers (also know as “WALDOs”), and slotted cylinder acoustic transducers. 
   Slotted cylinder acoustic projectors can be characterized by various parameters, including, but not limited to, a center operating frequency, a bandwidth (associated with a mechanical Q), and an efficiency corresponding to a ratio of acoustic power output to electrical power input. 
   Referring to  FIG. 1 , one type of conventional slotted cylinder acoustic transducer  10 , here shown as a cross section, includes a cylindrical housing shell  12  having an inner surface  12   a , an outer surface  12   b , and a central major axis of curvature  14  (perpendicular to the page). The cylindrical housing shell  12  has a tapered thickness  12   c  between the inner surface  12   a  and the outer surface  12   b , wherein the thickness  12   c  is taken in a direction perpendicular to the central major axis of curvature  14 . The cylindrical housing shell  12  also has a slot  16  through the housing shell  14  extending in a direction parallel to the central major axis of curvature  14 , forming a gap  18  in the cylindrical housing shell  12 . The thickness  12   c  of the cylindrical housing shell  12  is greatest at a position opposite the slot  16  and smallest at positions proximate to the slot  16 . 
   The slotted cylinder acoustic transducer  10  also includes a plurality of ceramic elements  20 , of which a ceramic element  20   a  is but one example, having different solid shapes, and each having a respective central major axis (e.g.,  32 , perpendicular to the page). It will be recognized that the shapes of the ceramic elements  20  symmetrically on either side of and equidistant from an axis  22  can be the same. However, it will be recognized that there are approximately as many different shapes of ceramic elements  20  as half of a total number of ceramic elements  20 . 
   The slotted cylinder acoustic transducer  10  also includes a plurality of electrodes  24 , of which an electrode  24   a  is but one example, having different planar shapes. Each electrode  24  is disposed between two adjacent ceramic elements  20 . It will be recognized that the shapes of the electrodes  24  symmetrically on either side of and equidistant from an axis  22  can be the same. However, it will be recognized that there are approximately as many different shapes of electrodes  24  as half of a total number of electrodes. 
   The plurality of ceramic elements  20  and the plurality of electrodes  24  are interposed in a ceramic stack assembly  26 , one of the electrodes  24  between each two adjacent ceramic elements  20 . The ceramic stack assembly  26  has an inner surface  26   a , an outer surface  26   b , a central major axis of curvature  14   a  (perpendicular to the page) parallel to the central major axis of curvature  14  of the cylindrical housing shell, and tapered thickness  26   c  between the inner surface  26   a  and the outer surface  26   b , wherein the thickness  26   c  is in a direction perpendicular to the central major axis of curvature  14   a  of the ceramic stack assembly  26 . The central major axis of curvature  14   a  of the ceramic stack assembly  26  can be at the same position as the central major axis of curvature  14  of the cylindrical housing shell  26 , or it can be at a different position as shown. 
   A shape of the outer surface  26   b  of the ceramic stack assembly  26  matches a shape of the inner surface  12   a  of the cylindrical housing shell  12 . The outer surface  26   b  of the ceramic stack assembly  26  is disposed proximate to the inner surface  12   a  of the cylindrical housing assembly  12 . 
   The slotted cylinder acoustic transducer  10  can further include first and second tapered inserts  28 ,  30 , respectively. The tapered inserts  28 ,  30  have inner surfaces  28   a ,  30   a , respectively, outer surfaces  28   b ,  30   b , respectively, and central major axes  34 ,  36 , respectively (perpendicular to the page). Shapes of the outer surfaces  28   b ,  30   b  of the first and second tapered inserts  28 ,  30 , respectively, match the shape of the inner surface  12   a  of the cylindrical housing shell  12 . The outer surfaces  28   b ,  30   b  of the first and second tapered inserts  28 ,  30 , respectively, are disposed proximate to the inner surface  12   a  of the cylindrical housing shell  12 . The first tapered insert  28  is disposed proximate a first end of the ceramic stack assembly  26  and the second tapered insert  30  is disposed proximate to a second end of the ceramic stack assembly  26 . 
   The slotted cylinder acoustic transducer  10  can include end caps (not shown) and an outer boot (not shown) so as to be sealed from the water. 
   It will be appreciated that having so many different ceramic elements  20  with different shapes and so many electrodes  24  with different shapes tends to make the acoustic transducer  10  expensive. 
   As described above, the acoustic transducer  10  can be characterized by various parameters, including, but not limited to, a center operating frequency, a bandwidth (associated with a mechanical Q), and an efficiency corresponding to a ratio of acoustic power output to electrical power input. 
   It will be understood that the center operating frequency of the slotted cylinder acoustic transducer  10  is related to a number of parameters, including, but not limited to, a density, stiffness, and modulus of elasticity of the cylindrical housing shell  12 , a density, stiffness, and modulus of elasticity of the ceramic stack assembly  26 , and a density, stiffness, and modulus of elasticity of the first and second tapered inserts  28 ,  30 , respectively. As is known, stiffness is related to the modulus of elasticity of a material of an object, a shape of the object, and boundary conditions experienced by the object. A higher modulus of elasticity generally results in a higher operating frequency, and a higher density generally results in a lower operating frequency. 
   In order to design the slotted cylinder acoustic transducer  10  to achieve a particular center operating frequency, properties of the components, or of the entire slotted cylinder acoustic transducer  10 , can be modeled using a finite-element computer model. The finite element model should include a so-called “radiation loading” of the water around the slotted cylinder acoustic transducer  10 , which is related to an acoustic impedance. Finite element models can predict both static stresses and dynamic stresses upon elements of the transducer  10 . Finite element models can also predict dynamic behavior of the slotted cylinder acoustic transducer  10 . 
   It will be understood that the bandwidth of the slotted cylinder acoustic transducer  10  is related to a ratio of largest and smallest thicknesses  12   c  of the tapered cylindrical housing shell  12  and a ratio of largest and smallest thicknesses  26   c  of the tapered ceramic stack assembly  26  in combination with the tapered inserts  28 ,  30 . In addition, it is known that bandwidth of the slotted cylinder acoustic transducer  10  generally increases when a length of the cylindrical housing shell  12  of the slotted cylinder acoustic transducer  10  is increased relative its outer diameter. 
   An efficiency of the slotted cylinder acoustic transducer  10  is related to a variety of factors, including, but not limited to, characteristics of a rubber boot surrounding the slotted cylinder acoustic transducer, piezoelectric efficiency of the piezoelectric ceramics  20  (related to a dielectric loss resulting in heating), and losses in bondings associated with the ceramic elements  60 . 
   SUMMARY OF THE INVENTION 
   The present invention provides a slotted cylinder acoustic projector having a crescent-shaped insert that, in some embodiments, allows ceramic elements and electrodes all to have the same size. 
   In accordance with one aspect of the present invention, a slotted cylinder acoustic transducer includes a cylindrical housing shell having an inner surface, an outer surface, a central major axis of curvature, and a thickness between the inner surface and the outer surface, wherein the thickness is in a direction perpendicular to the central major axis of curvature. The cylindrical housing shell also includes a slot through the cylindrical housing shell extending in a direction parallel to the central major axis of curvature and forming a gap in the cylindrical housing shell. The slotted cylinder acoustic transducer also includes a crescent-shaped insert having an inner surface, an outer surface, a central major axis of curvature parallel to the central major axis of curvature of the cylindrical housing shell, and a tapered thickness between the inner surface and the outer surface. The thickness of the crescent-shaped insert is in a direction perpendicular to the central major axis of curvature. A shape of the outer surface of the crescent-shaped insert matches a shape of the inner surface of the cylindrical housing shell, and the outer surface of the crescent-shaped insert is disposed proximate to the inner surface of the cylindrical housing shell. The thickness of the crescent-shaped insert is greatest at a position opposite the slot. The slotted cylinder acoustic transducer also includes a plurality of piezoelectric ceramic elements, each having a respective solid shape, and each having a respective central major axis parallel to the central major axis of curvature of the cylindrical housing shell. The slotted cylinder acoustic transducer also includes a plurality of electrodes, each having a planar shape. The plurality of piezoelectric ceramic elements and the plurality of electrodes are interposed in a ceramic stack assembly. An electrode is between each two adjacent piezoelectric ceramic elements. The ceramic stack assembly has an inner surface, an outer surface, a central major axis of curvature parallel to the central major axis of curvature of the cylindrical housing shell, and a thickness between the inner surface and the outer surface. The thickness of the ceramic stack assembly is in a direction perpendicular to the central major axis of curvature. A shape of the outer surface of the ceramic stack assembly matches a shape of the inner surface of the crescent-shaped insert, and the outer surface of the ceramic stack assembly is disposed proximate to the inner surface of the crescent-shaped insert. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which: 
       FIG. 1  is a cross-sectional view showing a prior art slotted cylinder acoustic projector; 
       FIG. 2  is a cross-sectional view showing a slotted cylinder acoustic projector in accordance with the present invention; 
       FIG. 3  is a cross-sectional view showing the slotted cylinder acoustic projector of  FIG. 2  in another plane; 
       FIG. 3A  is a cross-sectional view showing two stacked slotted cylinder acoustic projectors of  FIG. 2  in the plane of  FIG. 3  and surrounded by end caps and a boot; and 
       FIG. 4  is a side view of the slotted cylinder acoustic projector of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Before describing the present invention, some introductory concepts and terminology are explained. As used herein, the term “central major axis of curvature” is used to describe an axis about which a solid object or surface curves. As used herein, the term “central major axis” is used to describe an axis passing through at least two centroids of at least two respective cross sections of a solid object. As used herein, the term “about the same as” is used to describe value within twenty percent of another value. 
   Referring now to  FIG. 2 , a slotted cylinder acoustic transducer  50 , here shown as a cross section, includes a cylindrical housing shell  52  having an inner surface  52   a , an outer surface  52   b , and a central major axis of curvature  54  (perpendicular to the page). The cylindrical housing shell  52  has a thickness  52   c  between the inner surface  52   a  and the outer surface  52   b , wherein the thickness  52   c  is taken in a direction perpendicular to the central major axis of curvature  54 . The cylindrical housing shell  52  also has a slot  56  with first and second slot surface  56   a ,  56   b , respectively, through the housing shell  54  extending in a direction parallel to the central major axis of curvature  54  and forming a gap  58  in the cylindrical housing shell  52 . 
   The slotted cylinder acoustic transducer  50  also includes a crescent-shaped insert  72  having an inner surface  72   a , an outer surface  72   b , a central major axis of curvature  54   a  parallel to the central major axis of curvature  54  of the cylindrical housing shell  52 , and a tapered thickness  72   c  between the inner surface  72   a  and the outer surface  72   b . The thickness  72   c  of the crescent-shaped insert  72  is in a direction perpendicular to the central major axis of curvature  54   a . A shape of the outer surface  72   b  of the crescent-shaped insert  72  matches a shape of the inner surface  52   a  of the cylindrical housing shell  52 . The outer surface  72   b  of the crescent-shaped insert  72  is disposed proximate to the inner surface  52   a  of the cylindrical housing shell  52 . The thickness  72   c  of the crescent-shaped insert  72  is greatest at a position opposite the slot  56 . 
   The slotted cylinder acoustic transducer  50  also includes a plurality of piezoelectric ceramic elements  60 , of which a piezoelectric ceramic element  60   a  is but one example. In some embodiments, such as the embodiment shown, and unlike the piezoelectric ceramic elements  20  of  FIG. 1 , each one of the piezoelectric ceramic elements  60  has the same solid shape. However, in other embodiments, like the piezoelectric elements  20  of  FIG. 1 , the piezoelectric elements  60  have different solid shapes. Each one of the piezoelectric ceramic elements  60  has a respective central major axis (e.g.,  84 , perpendicular to the page). 
   The slotted cylinder acoustic transducer  50  also includes a plurality of electrodes  64 , of which an electrode  64   a  is but one example. In some embodiments, and unlike the electrodes  24  of  FIG. 1 , each one of the electrodes  64  has the same planar shape. However, in other embodiments, like the electrodes  24  of  FIG. 1 , the electrodes  64  have different solid shapes. 
   The plurality of piezoelectric ceramic elements  60  and the plurality of electrodes  64  are interposed in a ceramic stack assembly  66 , one of the electrodes  64  between each two adjacent piezoelectric ceramic elements  60 . The ceramic stack assembly  66  has an inner surface  66   a , an outer surface  66   b , and a central major axis of curvature  54   b  (perpendicular to the page) parallel to the central major axis of curvature  54  of the cylindrical housing shell  52 . 
   The central major axis of curvature  54   b  of the ceramic stack assembly  66  can be at the same position as the central major axis of curvature  54  of the cylindrical housing shell  52 , or it can be at a different position as shown. The central major axis of curvature  54   a  of the crescent-shaped insert  72  can be at the same position as the central major axis of curvature  54  of the cylindrical housing shell  52 , or it can be at a different position as shown. 
   A shape of the outer surface  66   b  of the ceramic stack assembly  66  matches a shape of the inner surface  72   a  of the crescent-shaped insert  72 . The outer surface  66   b  of the ceramic stack assembly  66  is disposed proximate to the inner surface  72   a  of the crescent-shaped insert  72 . 
   In some embodiments, a material of the cylindrical housing shell  52  comprises a graphite-epoxy material. However, in other embodiments, the cylindrical housing shell  52  can be comprised of Aluminum, an Aluminum alloy, steel, or an Iron alloy. 
   In some embodiments, such as the embodiment shown, the cylindrical housing shell  52  is the same as or similar to the cylindrical housing shell  12  of  FIG. 1 . Therefore, in some embodiments, the thickness  52   c  of the cylindrical housing shell  52  is tapered, and the thickness  52   c  of the cylindrical housing shell  52  is greatest at a position opposite the slot  56  and smallest at positions proximate to the slot  56 . However, in other embodiments, the thickness  52   c  of the cylindrical housing shell  52  is constant. 
   In some embodiments, a material of the crescent-shaped insert  72  has a density and a modulus of elasticity about the same as (or otherwise similar to) a density and a modulus of elasticity of a material of the plurality of piezoelectric ceramic elements  60 . In some embodiments, a material of the crescent-shaped insert  72  has a density and a modulus of elasticity selected to achieve a predetermined operating frequency. To this end, a stiffer or a denser crescent-shaped insert  72  tends to increase the operating center frequency. Therefore, if a slotted cylinder acoustic transducer  50  is designed and tested and found to have an operating frequency different from that intended, the crescent-shaped insert  72  can be modified to adjust the operating frequency. It is similarly possible to make adjustments to the crescent-shaped insert  72  in order to achieve the desired operating frequency at different depths. The crescent-shaped insert  72  can be made of a material comprising at least one of a graphite-epoxy material, Aluminum, an Aluminum alloy, Copper, a Copper alloy, steel, or an Iron alloy. 
   In some embodiments, such as the embodiment shown, and unlike the ceramic stack assembly  26  of  FIG. 1 , the ceramic stack assembly  66  has a constant thickness  66   c  between the inner surface  66   a  and the outer surface  66   b , wherein the thickness  66   c  is in a direction perpendicular to the central major axis of curvature  54   b  of the ceramic stack assembly  66 . However, in other embodiments, like the ceramic stack assembly  26  of  FIG. 1 , the ceramic stack assembly  66  can have a tapered thickness  66   c.    
   In some embodiments, the slotted cylinder acoustic transducer  50  can further include first and second tapered inserts  68 ,  70 , respectively. The tapered inserts  68 ,  70  have inner surface  68   a .  70   a , respectively, outer surfaces  68   b ,  70   b , respectively, and central major axes  90 ,  92 , respectively (perpendicular to the page). Shapes of the outer surfaces  68   b ,  70   b  of the first and second tapered inserts  68 ,  70 , respectively, match the shape of the inner surface  52   a  of the cylindrical housing shell  52 . The outer surfaces  68   b ,  70   b  of the first and second tapered inserts  68 ,  70 , respectively, are disposed proximate to the inner surface  52   a  of the cylindrical housing shell  52 . The first tapered insert  68  is disposed proximate a first end of the ceramic stack assembly  66  and the second tapered insert  70  is disposed proximate to a second end of the ceramic stack assembly  66 . 
   In some embodiments, a material of the first and second tapered inserts  68 ,  70  has a modulus of elasticity about the same as a modulus of elasticity of a material of the plurality of piezoelectric ceramic elements  60 . In some embodiments, the material of the first and second tapered inserts  68 ,  70  has a density about the same as a density of the material of the plurality of piezoelectric ceramic elements  60 . In other embodiments, the material of the first and second tapered inserts  68 ,  70  has a density lower than the density of the material of the plurality of piezoelectric ceramic elements  60 . 
   A plurality of holes  80   a ,  80   b  through the tapered inserts  68 ,  70  and through the cylindrical housing shell  52  can be used in conjunction with screws, pins, rivets, or the like (not shown) to hold the tapered inserts  68 ,  70  to the cylindrical housing shell  52 . 
   The crescent-shaped insert  72  can be bonded to the cylindrical housing shell  52  using a two-component epoxy structural adhesive. Similarly, the ceramic stack assembly  66  can be bonded to the crescent-shaped insert  72  with the same or with a different two-component epoxy structural adhesive. 
   The slotted cylinder acoustic transducer  50  can include end caps (e.g.,  102  of  FIG. 3A ) and an outer boot (e.g.,  104  of  FIG. 3A ) so as to be sealed from the water. 
   It will be appreciated that embodiments having only one type, i.e., shape, of piezoelectric ceramic elements  60  and one shape of electrodes  64  tends to make the acoustic transducer  50  less expensive than the prior art slotted cylinder acoustic projector  10  of  FIG. 1 . 
   The slotted cylinder acoustic transducer  50  can include an insulating layer  82  disposed between the ceramic stack assembly  66  and the crescent-shaped insert. The insulating layer can be comprised of a variety of materials, including, but not limited to, a polyetherimide, for example, ULTEM®, or a polymide, for example, KAPTON®. In some arrangements, the insulating layer  82  can withstand at least ten thousand volts without breakdown. The insulating layer is tailored to be able to withstand at least a maximum operating voltage of the ceramic stack assembly  66 . 
   In some embodiments, a solid shape and a material of the crescent-shaped insert  72  are selected so that a bandwidth and a center frequency of the slotted cylinder acoustic transducer  50  are approximately the same as a bandwidth and a center frequency of a different slotted cylinder acoustic transducer, for example, the slotted cylinder acoustic transducer  10  of  FIG. 1 , which has no crescent-shaped insert, which has a plurality of different piezoelectric ceramic elements  20 , and which has a plurality of different electrodes  24 , each different piezoelectric ceramic element  20  and each different electrode  24  differently shaped to achieve a different ceramic stack assembly  26 . 
   In some embodiments, the cross section of the slotted cylinder acoustic transducer  50  taken in a direction perpendicular to the central major axis of curvature  54  of the cylindrical housing shell  52  as shown, has a round inner surface  52   a  of the cylindrical housing shell  52 , a round inner surface  72   a  of the crescent-shaped insert  72 , and a round inner surface  66   a  of the ceramic stack assembly  66 . However, in some embodiments, a cross section of the cylindrical housing shell  52  is elliptical. 
   In one particular embodiment, a cross section of the cylindrical housing shell  52  has a round outer shape with a diameter of about 7.5 inches, a round inner shape, and is made of a graphite epoxy material. In one particular embodiment, the thickest part of the cylindrical housing shell  52  has a thickness of about 0.60 inches, the thinnest parts of the cylindrical housing shell  52  near the slot  56  have a thickness of about 0.20 inches, and the gap  58  has a dimension of about 0.75 inches. In one particular embodiment, the crescent-shaped insert has a thickest dimension of about 0.30 inches, a thinnest dimension of about zero, and is made from Aluminum. In one particular embodiment, the ceramic stack assembly  66  has a constant thickness of about 0.38 in, the ceramic stack assembly  66  includes 56 ceramic elements  60 , each having the same bar shape, and each one of the ceramic elements  60  is made from Navy modified Type 3 ceramic material, which meets DOD standard 1376A, for example, type EC67 made by the EDO Corporation of Salt Lake City, Utah. Other ceramic materials can also be used, for example, Navy Type 4. 
   As described above, the acoustic transducer  50  can be characterized by various parameters, including, but not limited to, a center operating frequency, a bandwidth (associated with a mechanical Q), and an efficiency corresponding to a ratio of acoustic power output to electrical power input. In one particular embodiment the slotted cylinder acoustic transducer  50  has a center operating frequency of about 474 Hz, a bandwidth of about 96 Hz and an efficiency of about 82 percent when operating at a depth of about four hundred feet. 
   As described above, it will be understood that the center operating frequency of the slotted cylinder acoustic transducer  50  is related to a number of parameters, including, but not limited to, a density, stiffness, and modulus of elasticity of the cylindrical housing shell  52 , a density, stiffness, and modulus of elasticity of the ceramic stack assembly  66 , and a density, stiffness, and modulus of elasticity of the first and second tapered inserts  68 ,  70 , respectively. As is known, stiffness is related to the modulus of elasticity of a material of an object, a shape of the object, and boundary conditions experienced by the object. A higher modulus of elasticity generally increases operating frequency, and a higher density generally decreases operating frequency. 
   As also described above, in order to design the slotted cylinder acoustic transducer  50  to achieve a particular center operating frequency, properties of the components, or of the entire slotted cylinder acoustic transducer, can be modeled using a finite-element computer model. The finite element model should include the radiation loading of the water around the slotted cylinder acoustic transducer  50 , which is related to an acoustic impedance. Finite element models can predict both static stresses and dynamic stresses upon elements of the transducer  50 . 
   Finite element models can predict both static stresses and dynamic stresses upon elements of the transducer  10 . Finite element models can also predict dynamic behavior of the slotted cylinder acoustic transducer  50 . 
   In addition, it is known that bandwidth of the slotted cylinder acoustic transducer  50  is generally increased when a length of the cylindrical housing shell  52  of the slotted cylinder acoustic transducer  50  is increased relative its outer diameter. 
   An efficiency of the slotted cylinder acoustic transducer  50  is related to a variety of factors, including, but not limited to, characteristics of a rubber boot (e.g.,  102 ,  FIG. 3A ), surrounding the slotted cylinder acoustic transducer  50 , piezoelectric efficiency of the piezoelectric ceramics  60  (related to a dielectric loss resulting in heating), and losses in bondings associated with the ceramic elements  60 . 
   Referring now to  FIG. 3 , in which like elements of  FIG. 2  are shown having like reference designations, the slotted cylinder acoustic transducer  50 , here shown in a side cross-sectional view in accordance with a section line A-A of  FIG. 2 , includes the cylindrical housing shell  52  and the crescent-shaped insert  72  having the first and second surface  72   a ,  72   b , respectively. The slotted cylinder acoustic transducer  50  also includes the plurality of ceramic elements  60 , forming the ceramic stack assembly  66  having the first surface  66   a . Only one ceramic element  60   b  and one electrode  64   b  are explicitly shown for clarity. 
   The slotted cylinder acoustic transducer  50  also includes the tapered insert  68  having the first surface  68   a . The slotted cylinder acoustic transducer  50  also includes the first surface  56   a  of the gap  56  of  FIG. 2 , wherein it will be recognized that the gap  58  continues into the page. 
   A plurality of holes, for example, the above-described hole  80   a  through the tapered insert  68  and through the cylindrical housing shell  52  can be used in conjunction with screws, rivets, or the like (not shown) to hold the tapered inserts  68  to the cylindrical housing shell  52 . 
   In one particular embodiment, a height  92  of the ceramic stack assembly  66  is about four inches, a height  90  of the cylindrical housing shell  52  is about five inches and a height of the tapered insert  68  is about four inches. 
   Referring now to  FIG. 3A , like elements of  FIG. 2  are shown having like reference designations, but with an extra letter indicative of an instance of the element. For example, there are two slotted cylinder acoustic transducers  50  ( FIG. 2 ) designated  50   a  and  50   b.    
   The two slotted cylinder acoustic transducers  50   a ,  50   b  are coupled or stacked, forming a longer slotted cylinder acoustic transducer  100 . When stacked in this way, the term “ceramic/shell assembly” can be used to describe each portion  50   a ,  50   b  and the entire stacked assembly can be referred to as the slotted cylinder acoustic transducer  100 . The ceramic/shell assemblies  50   a ,  50   b  can be aligned with a guide pin  106  or the like. The slotted cylinder acoustic transducer  100  can be made water tight with end caps, here only an end cap  102  is shown, and with a boot  104 , which can, in some embodiments, be a rubber boot. While two ceramic/shell assemblies  50   a ,  50   b  are shown, it should be recognized that, in other arrangements, there can be one ceramic/shell assembly or more than two ceramic/shell assemblies stacked in a slotted cylinder acoustic transducer having end caps and a boot. 
   Referring now to  FIG. 4 , in which like elements of  FIG. 2  are shown having like reference designations, the slotted cylinder acoustic transducer  50  of  FIG. 2  is shown from a view looking into the slot  56 . In some embodiments, the slot  56  can have rounded regions, of which rounded regions  110   a ,  110   b  are examples. The rounded regions  110   a ,  110   b  can provide protection of a rubber boot, for example, the rubber boot  104  of  FIG. 3A , by eliminating sharp corners that could tear the boot. In other embodiments, the slotted cylinder acoustic transducer  50  can have additional rounded regions  112   a ,  112   b . However, when the slotted cylinder acoustic transducer  50  is but one of a plurality of stacked ceramic/shell assemblies, in some embodiments, the two end-most ceramic/shell assemblies each have rounded regions only on one end. 
   All references cited herein are hereby incorporated herein by reference in their entirety. 
   Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.