Patent Publication Number: US-6984923-B1

Title: Broadband and wide field of view composite transducer array

Description:
STATEMENT OF GOVERNMENT INTEREST 
   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. 

   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present invention relates generally to transducer arrays, and more particularly to a composite transducer array that provides a broadband frequency response over a wide field of view. 
   (2) Description of the Prior Art 
   A variety of sonar applications such as vehicle homing require the steering of acoustic beams over a wide field-of-view. Existing homing array technology uses numerous narrowband and high-power longitudinal tonpilz resonators to form the aperture of an active transducer. Each tonpilz resonator consists of several active and inactive mechanical components that work together as a spring-mass, single degree-of-freedom system. Unfortunately, tonpilz resonators are expensive to fabricate and offer only a limited operational bandwidth above their first length mode resonance. 
   To address operational bandwidth limitations of tonpilz resonators, recent work has focused on constructing multi-resonance tonpilz elements that have significantly greater bandwidth than that of the original single-mode tonpilz resonators. However, the fixed-size radiation head inherent to tonpilz resonators prevent their use in a “frequency agile” design in which array apertures can be varied in size. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a transducer array that can operate in a broadband frequency range over a wide field-of-view. 
   Another object of the present invention is to provide a broadband, wide field-of-view transducer array that is inexpensive to fabricate. 
   Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
   In accordance with the present invention, a composite transducer array has a central portion thereof formed by a piezoelectric polymer composite panel with opposing first and second surfaces. A continuous electrode is coupled to the first surface and a plurality of electrode segments electrically isolated from one another are coupled to the second surface. Each electrode segment is shaped as an angular segment of a circular ring, while the plurality of electrode segments are arranged to define an array of concentric circular rings of electrode segments. Each electrode segment can by independently addressed so that the array&#39;s aperture can be varied in size. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
       FIG. 1  is a plan view of the segmented electrode side of an embodiment of a broadband and wide field-of-view composite transducer array in accordance with the present invention; 
       FIG. 2  is a side view of the composite transducer array taken along  2 — 2  of  FIG. 1 ; 
       FIG. 3  is a side view of another embodiment in which the composite transducer array is shaped or curved; and 
       FIG. 4  is a cross-sectional view of an assembly housing the composite transducer array for use in an underwater environment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
   Referring now to the drawings, simultaneous reference will be made to  FIGS. 1 and 2  where a composite transducer array is shown and referenced generally by numeral  10 . More specifically,  FIG. 1  is a plan view depicting the segmented electrode surface of the array and  FIG. 2  is a side view depicting construction details of the array. 
   In  FIG. 1 , the segmented electrode surface of array  10  is defined by concentric circular rings of electrode segments  12 . That is, each of electrode segments  12  is shaped as an angular segment (e.g., approximately 90° in the illustrated embodiment) of a circular ring of such electrode segments. Electrode segments  12  are electrically isolated from one another by means of spaces or gaps  14  therebetween. The size of spaces  14  between adjacent ones of electrode segments  12  is determined by diffraction theory as would be well understood by one of ordinary skill in the art. By way of illustrative example, four of electrode segments  12  are used to define an outermost circular ring of electrode segments. However, more or fewer electrode segments can be used in a circular ring thereof without departing from the scope of the present invention. 
   Each electrode segment  12  has a radial width W R  and an arc length L A . Within a given circular ring of electrode segments, the radial width W R  and/or arc length L A  can be the same (as shown) or different for each electrode segment in the circular ring without departing from the scope of the present invention. For example, in the outermost circular ring illustrated in  FIG. 1 , the radial width W R  is the same for each electrode segment  12  and the arc length L A  is the same for each electrode segment  12 . Radial width and arc lengths can be increased or decreased with interior ones of the circular rings of electrode segments. 
   Construction of array  10  will now be explained with additional reference to  FIG. 2 . Electrode segments  12  are supported on a first major surface of a piezoelectric polymer composite panel  20 . Details of a suitable composite panel  20  are described in U.S. Pat. No. 6,255,761, the contents of which are hereby incorporated by reference. Briefly, composite panel  20  is constructed using spaced-apart piezoelectric (e.g., a ferroelectric material such as piezoceramic materials lead zirconate titanate or lead titanate) columns or rods  22  that span the thickness or height H of composite panel  20 . Filling the spaces between rods  22  for the full height thereof is a viscoelastic material  24  such as a thermoplastic epoxy. 
   Each of electrode segments  12  can have a dedicated electrical lead coupled thereto. This can be accomplished by passing conductors (e.g., conductors  31  and  32  are illustrated in  FIG. 2 ) through a side of composite panel  20 . More specifically, conductors  31  and  32  are routed through viscoelastic material  24  and electrically coupled to one of electrode segments  12 . The second major surface of composite electrode panel  20  has a continuous electrode  40  coupled thereto. Typically, the height H of panel  20  is the same throughout so that planes defined by electrode segments  12  and continuous electrode  40  are parallel to one another. 
   Array  10  can also be shaped to conform to simple or complex contours if viscoelastic material  24  comprises a thermoplastic material such as thermoplastic epoxy. For example, as illustrated in  FIG. 3 , composite panel  20  has been shaped during heating thereof such that the planes defined by electrode segments  12  and continuous electrode  40  are curved in correspondence with one another. 
   The composite transducer array described herein can be used as part of an underwater array assembly such as assembly  100  illustrated in  FIG. 4  where like reference numerals are used to describe elements of array  10  incorporated into assembly  100 . A waterproof housing (e.g., a waterproof encapsulant)  50  has array  10  fitted and sealed therein such that electrode  40  is flush with and spans an opening  52  in housing  50 . That is, the plane defined by continuous electrode  40  faces out of housing  50  while the plane defined by electrode segments  12  faces into housing  50 . Abutting electrode segments  12  is an acoustic absorbing material  54  such as a particle-filled epoxy. Conductors  31  and  32  pass through both composite panel  20  (as described above) and acoustic absorbing material  54  before being coupled to appropriate signal electronics  56  that can be located within and/or outside of housing  50  as illustrated. 
   The advantages of the present invention are numerous. Broadband operation is achieved owing to the inherent broadband resonance of piezoelectric polymer composite panel  20  used to construct the transducer array of the present invention. The present invention also provides an improved spatial field-of-view since numerous elements may be formed by selectively applying electrodes over the array aperture to form elements having different (non-uniform) apertures. The invention teaches element apertures that can be varied in size by simply addressing electrode segments separately. High frequency responses are achieved using small sized electrode segments. The electrode segments can be combined for low frequency responses, or larger sized electrode segments could be used. The composite transducer array can be singly or doubly curved to any reasonable radii of curvature thereby providing a cost-effective means to realize truly conforming array apertures. 
   It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.