it is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding , while eliminating , for the purpose of clarity , many other elements found in typical slotted cylinder transducers and drive assemblies and methods of making and using the same . those of ordinary skill in the art may recognize that other elements and / or steps may be desirable in implementing the present invention . however , because such elements and steps are well known in the art , and because they do not facilitate a better understanding of the present invention , a discussion of such elements and steps is not provided herein . referring now to fig7 a , 7 b and 7 c there is shown a transducer 70 comprising an inert slotted cylinder or tubular shell structure 72 having a drive assembly 73 which applies stress to the inner diameter ( id ) or inner wall 75 of the inert slotted cylinder shell 72 . in one configuration ( e . g . fig7 a ) a magnetostrictive drive assembly comprises a vibratory member such as magnetostrictive stack 77 disposed within a coil 771 surrounding the stack . the stack may be a single rod of magnetostrictive material or a plurality of coaxial rod sections , for example . in another configuration ( e . g . fig7 b ) a ceramic drive assembly comprises a vibratory member such as one or more stacks of sectionalized vibratory elements 77 , such as piezoelectric elements . fig8 illustrates the shell structure 72 capable of receiving the corresponding drive assembly illustrated in fig7 a - 7c . in any event , the drive assembly comprises a vibratory member such as one or more stacks of sectionalized vibratory elements that may be formed from a suitable magnetostrictive material , or a piezoelectric material such as a ceramic having piezoelectric characteristics . each stack extends across the inner wall of shell 72 with the stacks linearly arranged along the longitudinal axis of the transducer . in the embodiment illustrated in fig7 b - 7c , the sectionalized elements 77 1 , 77 2 , . . . , 77 n are of the same length and thickness and are linearly stacked in abutting relationship to one another . electrical connectivity 770 to / from the stack for vibrating the elements is provided , as is known in the art . in the exemplary embodiment shown in fig7 b - 7c , the electrical connectivity is schematically depicted as positive 775 and negative 776 ( fig7 c ) conductor electrodes alternatively electrically coupled to corresponding element segments within each stack in order to apply the appropriate polarity to each element segment so as to cause the elements to vibrate when a biasing source such as an alternating current signal is introduced , as is known in the art . the stack of sectionalized elements 77 abuts at opposite ends 77 a , 77 b corresponding portions of inner wall 75 . more particularly , inner wall 75 of slotted , tubular or cylindrical shell 72 includes oppositely disposed , inwardly extending wall segments having ledge or channel portions 76 terminating in a journal bearing type surface 78 . the interface between the stack and shell comprises a layer 79 of solid lubricant material mounted on the journal bearing type surface 78 . solid lubricant layer 79 operates to minimize the erosion of the stack and the shell interface as well as allow rotational motion at the stack / shell interface . one or more backing or acoustic matching layers may be disposed at respective ends 77 a , 77 b of the drive assembly for providing the structural support and acoustic matching of the stack with the shell . in an exemplary embodiment , the use of low modulus drive materials , such as soft ceramic , high coupling pmn and terfenol , may be utilized in conjunction with lubricant layer 79 at the journal bearing interface retaining the stack within the shell structure . the cylindrical shell structure 72 may be made from a metal such as steel having elastic properties , as is understood by one skilled in the art . in an exemplary embodiment of the invention , the inwardly extending ledge portion and journal bearing type surface 78 is positioned about inner wall 75 such that the stack 77 is offset from the shell central longitudinal axis l a predetermined amount . in one configuration , the offset may be from about 5 % to 80 % from the central longitudinal axis l , with the horizontal center axis a orthogonal to the central longitudinal axis l and bisecting the circumferentially shaped cylindrical shell 72 . the stack placement enables improved shell displacement ( closer to the nodal region of the shell &# 39 ; s fundamental bending mode ). the resulting configuration permits a more favorable shell - to - stack stiffness ratio and higher electromechanical coupling . when alternating current signals are introduced to the sectionalized elements , typically via electrical connections or leads coupled to the corresponding stacks of elements as is known in the art , the elements vibrate and produce vibrations in the shell at positions adjacent to the gap 74 . the thickness and diameter of the shell is selected to produce the vibrations at a preselected frequency and / or over a wide range of frequencies in the infrasonic , audible and ultrasonic bands as such frequency ranges are understood by those skilled in the art . the solid lubricant and journal bearing approach is directly applicable to conventional flextensional projectors to avoid stack bending problems . a protective cover or boot 50 , typically made of rubber , surrounds the outer wall 175 of the transducer shell 72 , as is well known in the art . fig7 a illustrates an exemplary magnetostrictive implementation of the transducer drive assembly wherein the assembly may comprise materials such as terfenol - d , single crystal magnetostrictive alloys , and the like . fig7 b illustrates a ceramic implementation of the transducer drive assembly formed of pzt , pmn ( lead magnesium niobate ) or single crystal ceramic materials , for example . fig7 c provides a more detailed illustration of that depicted in fig7 b of an embodiment of the drive assembly 73 within the transducer shell 72 wherein a uniform layer 79 of solid lubricant is disposed about the cylindrical journal bearing 78 defining the interface between the wall portion 75 and the ceramic stack 77 of sectionalized elements mounted to optimize displacement and coupling with backing / acoustic matching layers 80 , 81 . in an exemplary embodiment , layer 80 represents an insulative layer that terminates the stack of sectionalized elements 77 . layer 80 is preferably formed of a ceramic material having substantially the same thickness as each of the sectionalized elements of the stack . layer 81 is preferably a metal such as steel or alumina , for example , that engages the inner wall at the journal bearing interface 78 for strengthening or reinforcing the flextensional transducer . the bearing surface 78 is coated with the solid lubricant 79 so that essentially no bending stresses are transferred to the stack ( enabling additional degrees of freedom provided by the bearing ). the stack is loaded by opening the shell , inserting the stack , and then releasing the shell , to thereby provide an interference fit between the stack / shell interface . the transducer is formed by providing a relatively soft and resilient ( relative to the stack ) shell structure 72 . the structure 72 is forcibly opened and the relatively rigid stack is inserted therein . in this manner the stack is compression fit into the shell ( as opposed to adhesively coupling or cementing the stack / shell interface ). fig9 a , 9 b , and 9 c illustrate alternative shell structures for use in accordance with the principles of the present invention . as shown in fig9 a , the cylindrical shell structure 72 is of uniform circumferential thickness t with inwardly extending wall segments and ledge portions 76 positioned such that the stack 77 is offset from the longitudinal central axis l of the device . fig9 b shows a cylindrical shell structure with inwardly extending wall segments and ledge portions 76 ′ in a linearly sloped configuration beginning at a position pa substantially along the longitudinal axis of the shell and terminating at position pb . the inner wall 75 ′ of the shell structure illustrated in fig9 b includes recessed portions pc symmetrically positioned about the lower portion 85 of shell 72 ′. as shown in fig9 b , the lower portion of the shell is of non - uniform circumferential thickness . fig9 c illustrates a further alternate configuration wherein the entire shell structure is of non - uniform circumferential thickness . more particularly , both the upper portion 87 ″ and lower portion 85 ″ of the shell 72 ″ are non - uniform in thickness . as illustrated in fig9 c , the inner wall forms an oval or elliptical configuration rather than the substantially circular geometry of fig9 a . further , the inner ledge portion 76 ″ forms a non - linearly sloped or curved segment terminating in journal bearing surface 78 . these transducers exhibit various displacements and sensitivities across each of the configurations and are adaptable according to the desired application . it is understood that driving slotted cylinders with a longitudinal ( bar ) type drivers as opposed to much more expensive and often failure prone wall driven approaches is desirable . the wall driven slotted cylinders have the advantage of a good impedance match between the inert shell and the active wall located on the inner diameter ( id ) of the inert shell . this results in effective transducer coupling in the range of about 0 . 28 to 0 . 38 . an improvement offered by the present invention results in electromechanical coupling which approaches these values when using softer ceramic drive materials presently available and should equal or surpass these values with high coupling pmn ( lead magnesium niobate ) and single crystal ceramic and magnetostrictive materials . the present invention provides a lower cost alternative to existing wall driven slotted cylinders by enabling them to be effectively driven in a longitudinal mode . the invention also provides remedies to the low coupling and poor performance of prior designs due to stack bending and fretting corrosion at the stack / shell interface due to micromotion in the direction orthogonal to the horizontal drive direction . the use of a lubricant such as the solid lubricant kapton or other polyimides or equivalent or similar solid lubricant material applied to the journal bearing type interface in conjunction with the offset ceramic or magnetostrictive stack enables a more efficient and improved transducer design . the present invention avoids stack bending problems to enable a stack mounting approach to be used in flextensional projectors in arrays which experience non symmetric radiation pressures , to avoid the “ banana ” mode exhibited in existing devices . the present invention finds applicability in both surface and subsurface platforms , sonobuoys , decoys , uuv &# 39 ; s , geophysical exploration , acoustic sweep anti mine operations , target simulators and the like . while the present invention has been described with reference to the illustrative embodiments , this description is not intended to be construed in a limiting sense . various modifications of the illustrative embodiments , as well as other embodiments of the invention , will be apparent to those skilled in the art on reference to this description . for example , the use of the solid lubricant and journal bearing approach may be implemented within a transducer structure having a vibratory member either centered or offset from the longitudinal central axis . it is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention .