Abstract:
A system for inspecting the surface of a curved object is provided. This system includes an object having a curved surface; at least one substantially flat interdigital transducer, wherein the interdigital transducer is operative to generate surface energy waves; and at least one coupling device disposed between the curved surface and the substantially flat interdigital transducer, wherein the coupling device is operative to conform to the curved surface, support the interdigital transducer, and provide a medium through which the surface energy waves can effectively travel from the interdigital transducer to the curved surface and across the curved surface in a predetermined direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/662,717 filed on Jun. 21, 2012 and entitled “Acoustic Coupling Shoes for Use in Inspecting Non-Flat Surfaces”, the disclosure of which is hereby incorporated by reference herein in its entirety and made part of the present U.S. utility patent application for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    An interdigital transducer, interdigitized transducer, or interdigitated transducer, is a device or sensor which typically consists of two interlocking comb-shaped metallic coatings or structures that have been applied to a piezoelectric substrate, such as quartz, lithium niobate, or piezoelectric ceramics, for the purpose of converting electrical or electromagnetic energy (e.g., microwaves) into acoustic energy (e.g., surface acoustic waves (SAW)) or vice versa. Interdigital transducers may be used to generate and receive ultrasonic surface waves for the purpose of inspecting the surface condition of a particular item or for measuring its acoustic properties. 
         [0003]    Currently, there are no known effective means for transferring surface waves generated by a flat interdigital transducer to a curved, contoured, or otherwise non-flat surface of an object. A custom-designed curved interdigital transducer may be fabricated for use on a curved surface of a part being inspected. However, creating complex contoured interdigital transducers is difficult and increases manufacturing costs considerably. Furthermore, a custom-designed interdigital transducer or sensor is only compatible with the specific contoured part or surface for which the sensor was originally designed. Accordingly, there is a need for a means by which flat interdigital transducers or sensors may be easily and inexpensively adapted for use with curved or contoured items that are to be inspected. 
       SUMMARY OF THE INVENTION 
       [0004]    The following provides a summary of certain exemplary embodiments of the present invention. This summary is not an extensive overview and is not intended to identify key or critical aspects or elements of the present invention or to delineate its scope. 
         [0005]    In accordance with one aspect of the present invention, a first system for inspecting the surface of a curved object is provided. This system includes at least one object having a curved surface; at least one substantially flat interdigital transducer, wherein the interdigital transducer is operative to generate surface energy waves; and at least one coupling device disposed between the curved surface and the substantially flat interdigital transducer, wherein the coupling device is operative to conform to the curved surface, support the interdigital transducer, and provide a medium through which the surface energy waves can effectively travel from the interdigital transducer to the curved surface and across the curved surface in a predetermined direction. 
         [0006]    In accordance with another aspect of the present invention, a second system for inspecting the surface of a curved object is provided. This system includes at least one object having a curved surface; at least one substantially flat interdigital transducer, wherein the interdigital transducer is operative to generate and receive surface acoustic waves; and at least one coupling device disposed between the curved surface and the substantially flat interdigital transducer, wherein the coupling device is operative to conform to the curved surface, support the interdigital transducer, and provide a medium through which the surface acoustic waves can effectively travel from the interdigital transducer to the curved surface and across the curved surface in a predetermined direction. 
         [0007]    In yet another aspect of this invention, a coupling device for transmitting surface energy waves is provided. This device includes a substantially flat top surface, wherein the substantially flat top surface is adapted to receive at least one surface energy wave generating device; a curved bottom surface, wherein the curved bottom surface is of greater length than the top surface and is adapted to conform to a curved surface of an object to be inspected; and a least two angled side surfaces between the top and bottom surfaces, wherein the angled side surfaces are operative to direct surface energy waves generated by the at least one surface energy wave generating device onto and across the curved surface of an object to be inspected. 
         [0008]    Additional features and aspects of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the exemplary embodiments. As will be appreciated by the skilled artisan, further embodiments of the invention are possible without departing from the scope and spirit of the invention. Accordingly, the drawings and associated descriptions are to be regarded as illustrative and not restrictive in nature. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated into and form a part of the specification, schematically illustrate one or more exemplary embodiments of the invention and, together with the general description given above and detailed description given below, serve to explain the principles of the invention, and wherein: 
           [0010]      FIG. 1  illustrates the appearance of a flat interdigital transducer placed on the curved surface of a part to be tested or analyzed; 
           [0011]      FIG. 2  illustrates the appearance of a flat interdigital transducer that has been mounted on the substantially flat top surface of an exemplary embodiment of the coupling shoes of present invention for purposes of dramatically increasing the contact surface between the curved part and the interdigital transducer; 
           [0012]      FIGS. 3   a - b  illustrate two possible geometries for the coupling shoes of the present invention; 
           [0013]      FIGS. 4   a - c  illustrate different possible mounting positions and alternate geometric configurations for the coupling shoes of the present invention; 
           [0014]      FIG. 5  is a block diagram of an exemplary pitch/catch detection system in accordance with the present invention; and 
           [0015]      FIGS. 6   a - b  illustrates the inspection results of cylindrically shaped test samples; one with no crack and the other with a surface breaking crack occurring on the side wall section thereof. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    Exemplary embodiments of the present invention are now described with reference to the Figures. Although the following detailed description contains many specifics for purposes of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention. 
         [0017]    With reference to the Figures, this invention provides various interchangeable devices that effectively accommodate single or multiple substantially flat interdigital transducers (also referred to as “sensors”) and which operate to transfer surface wave energy generated by the interdigital transducer(s) to one or more non-flat surfaces of a part to be inspected or otherwise analyzed. The devices of the present invention, which are referred to as “acoustic coupling shoes”, are operative to eliminate air gaps that typically occur between the curved surface of a part to be inspected and a flat or substantially flat interdigital transducer (IDT). The acoustic coupling shoes of this invention may be manufactured from any number of materials, such as polymethyl methacrylate (PMMA), that will: (i) support an IDT sensor or similar device; (ii) uniformly contact a contoured surface of a part; and (iii) effectively transmit and/or receive surface acoustic waves or similar energy. Once surface wave energy has been transferred onto a curved surface of a part using such coupling shoes, that energy can then be used for inspecting surface conditions or measuring material properties of the item. This invention provides an acoustic coupling system and devices for both transmission and reception of surface waves induced by IDT sensors for use with non-flat surfaces. 
         [0018]      FIG. 1  illustrates the appearance of a flat IDT  40  placed on a curved surface of part  10  and shows the air gaps that the present invention eliminates when in use. In  FIG. 1 , the contact surface between part  10  and IDT  40  is too small to effectively transfer surface waves generated by the IDT to the curved surface of part  10  for purposes of inspecting the part.  FIG. 2  illustrates an IDT  40  that has been mounted on an exemplary embodiment of coupling shoe  20  for allowing surface waves to travel from IDT  40  onto the curved surface of part  10 . In the embodiment shown in  FIG. 2 , coupling shoe  20  includes flat upper/top surface  20 , first angled surface  24 , second angled surface  26 , and lower/bottom surface  28 . As indicated by the arrows in  FIG. 2 , surface waves generated by top-mounted IDT  40  travel from IDT  40  downward and across angled surface  24  and  26  and onto the curved surface of part  10 . The shape of coupling shoe  20  dramatically increases the contact surface between part  10  and IDT  40  and as shown in  FIGS. 3   a - b , coupling shoe  20  may be configured for mounting parallel to the longitudinal axis of part  10  ( FIG. 3   a ) or perpendicular to the longitudinal axis of part  10  ( FIG. 3   b ). 
         [0019]      FIGS. 4   a - c  illustrate different possible mounting positions and alternate geometric configurations for coupling shoes  20 . In  FIG. 4   a , coupling shoe  20  is shown in a forward slanting orientation with IDT  40  mounted on an angled top surface. In this embodiment, surface waves generated by IDT  40  travel circumferentially through part  10  in the direction indicated by the arrow inside the circular structure of part  10 . In  FIG. 4   b , coupling shoe  20  is mounted perpendicular to the longitudinal axis of part  10  and IDTs  40 ,  42 , and  44  are mounted on the top surface and angled side surfaces respectively of coupling shoe  20 . In this embodiment, surface waves generated by IDTs  40 ,  42 , and  44  travel circumferentially through part  10  in both directions as indicated by the arrows inside the circular structure of part  10 . In  FIG. 4   c , acoustic coupling shoe  20  is mounted parallel with the longitudinal axis of part  10  and the surface waves generated by IDT  40  travel in parallel with the longitudinal axis of part  10  as shown by the arrows in  FIG. 4   c.    
         [0020]      FIG. 5  provides a block diagram of an exemplary pitch/catch detection system in accordance with the present invention. This system includes test assembly  100 , which further includes transmitting subassembly  200  and receiving subassembly  300 . Both transmitting subassembly  200  and receiving subassembly  300  include at least one coupling shoe  20  and at least one IDT  40 . Additional system components include gain amplifier  400 ; digital oscilloscope  500 , RF signal generator  600 ; and RF power amplifier  700 . As shown in  FIGS. 6   a - b , this system is useful for generating information about the condition of test specimen  100 . With reference to  FIG. 6   a , transmitting subassembly  200  generates a surface wave that travels across the surface of part  10  and that is received by receiving subassembly  300 . In this example, the distance between transmitting subassembly  200  and receiving subassembly  300  is about three inches. The received surface wave signal is displayed on a digital oscilloscope screen as shown and the image of the surface wave indicates that part  10  does not include a crack or other problematic structural flaw. With reference to  FIG. 6   b , transmitting subassembly  200  generates a surface wave that travels across the surface of part  10  toward receiving subassembly  300 . However, because a received surface wave signal is not displayed on the digital oscilloscope screen, the conclusion is that a surface breaking crack or other structural flaw is present in part  10  and is reflecting or otherwise preventing receiving subassembly  300  from receiving and displaying the surface wave. Accordingly, the acoustic coupling shoes of the present invention permit accurate characterization of a curved surface using flat IDT sensors. 
         [0021]    The coupling shoes of the present invention may be manufactured from metal, plastics, composite materials, polymers, nanomaterials, or various combinations thereof. The coupling shoes may further include incident angles ranging from about 1 to 89 degrees and may be polygonal in shape. Each coupling shoe typically includes least one flat surface and the interdigital transducer is attached to that flat surface. The placement of the coupling shoes and the interdigital transducers on the curved surface determines if the acoustic surface waves are transmitted longitudinally or circumferentially across the object being characterized. 
         [0022]    While the present invention has been illustrated by the description of exemplary embodiments thereof, and while the embodiments have been described in certain detail, it is not the intention of the Applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to any of the specific details, representative devices and methods, and/or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.