Abstract:
An electro-active transducer for sonic applications includes a ferroelectric material sandwiched by first and second electrode patterns to form a piezo-diaphragm coupled to a mounting frame. When the device is used as a sonic actuator, the first and second electrode patterns are configured to introduce an electric field into the ferroelectric material when voltage is applied to the electrode patterns. When the device is used as a sonic sensor, the first and second electrode patterns are configured to introduce an electric field into the ferroelectric material when the ferroelectric material experiences deflection in a direction substantially perpendicular thereto. In each case, the electrode patterns are designed to cause the electric field to: i) originate at a region of the ferroelectric material between the first and second electrode patterns, and ii) extend radially outward from the region of the ferroelectric material (at which the electric field originates) and substantially parallel to the plane of the ferroelectric material. The mounting frame perimetrically surrounds the peizo-diaphragm and enables attachment of the piezo-diaphragm to a housing.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
   This patent application is co-pending with one related patent application entitled “ELECTRO-ACTIVE TRANSDUCER USING RADIAL ELECTRIC FIELD TO PRODUCE/SENSE OUT-OF-PLANE TRANSDUCER MOTION”, Ser. No. 10/347,563, filed Jan. 16, 2003, and owned by the same assignee as this patent application. 

   ORIGIN OF THE INVENTION 
   The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor. Pursuant to 35 U.S.C. §119, the benefit of priority from provisional application No. 60/365,014, with a filing date of Mar. 15, 2002, is claimed for this non-provisional application. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to sonic transducers. More specifically, the invention is an electro-active device for acoustic applications comprising a piezo-diaphragm that undergoes out-of plane deflection when a radial electric field is induced in the plane of the piezo-diaphragm. 
   2. Description of the Related Art 
   Sonic transducers such as loudspeakers, hydrophones, and microphones made from active piezo-elements typically require the mounting of these piezo-elements to hold them in place for directed mechanical action and electrical contact. In general, the mounting affects the performance of the device because it becomes an integral part of the piezo-element. More specifically, the mounting influences the piezo-element by restricting its movement and changing the mechanical resonance frequency and response of the piezo-element. Additionally, the mounting fixture and any additional mechanical elements are subjected to mechanical fatigue as the piezo-element vibrates and exerts mechanical strain on the fixture. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention, an electro-active sonic transducer includes at least one piece of ferroelectric material defining a first surface and a second surface opposing the first surface. The first and second surfaces lie in substantially parallel planes. A first electrode pattern is coupled to the first surface and a second electrode pattern is coupled to the second surface. When used as a sonic actuator such as a loudspeaker, the first and second electrode patterns are configured to introduce an electric field into the ferroelectric material when voltage is applied to the electrode patterns. The electrode patterns are designed to cause the electric field to: i) originate at a region of the ferroelectric material between the first and second electrode patterns, and ii) extend radially outward from the region of the ferroelectric material (at which the electric field originates) and substantially parallel to the parallel planes defined by the ferroelectric material. As a result, the ferroelectric material deflects symmetrically about the region of the ferroelectric material at which the electric field originates. In other words, the ferroelectric material deflects in a radially symmetric fashion and in a direction that is substantially perpendicular to the electric field. 
   When used as a sonic sensor such as a hydrophone or microphone, the first and second electrode patterns are configured to produce an induced electric field in the ferroelectric material when the ferroelectric material experiences deflection in a direction substantially perpendicular to the first and second surfaces. The induced electric field originates at the region of the ferroelectric material between the first and second electrode patterns and extends radially outward from the region substantially parallel to the first and second surfaces. As a result, a current is induced in each of the first and second electrode patterns, with the current being indicative of the deflection. 
   The ferroelectric material and first and second electrode patterns combine to form a piezo-diaphragm. A region for attaching, made in one embodiment of dielectric material, is coupled to the piezo-diaphragm and extends radially outward about the outer perimeter of the piezo-diaphragm. That is, the region perimetrically borders the piezo-diaphragm. A housing may be connected to the region. Because the piezo-diaphragm may be attached mechanically around its perimeter without impacting the strain behavior of the ferroelectric material, the piezo-diaphragm reduces the addition of mechanical resonance or vibration to the loudspeaker, hydrophone, or microphone during operation of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic side view of a sonic transducer mounted to a housing in accordance with the present invention; 
       FIG. 2A  is a plan view taken along line  2 — 2  of  FIG. 1  showing one embodiment of the present invention having a circular mounting frame; 
       FIG. 2B  is a plan view taken along line  2 — 2  of  FIG. 1  showing another embodiment of the present invention having a rectangular mounting frame; 
       FIG. 3A  is a plan view taken along line  2 — 2  of  FIG. 1  showing another embodiment of the present invention having a rectangular piezo-diaphragm and a circular mounting frame; 
       FIG. 3B  is a plan view taken along line  2 — 2  of  FIG. 1  showing another embodiment of the present invention having a triangular piezo-diaphragm and a circular mounting frame; 
       FIG. 4  is a side view of a sonic transducer functioning as a loudspeaker; 
       FIG. 5  is a side view of a sonic transducer functioning as a hydrophone or microphone; 
       FIG. 6  is a schematic view of a piezo-diaphragm according to the present invention; 
       FIG. 7  is a side, schematic view of the piezo-diaphragm shown in  FIG. 6  illustrating the radial electric field and out-of-plane displacement generated thereby; 
       FIG. 8  is a side view of a layered construction of the piezo-diaphragm&#39;s ferroelectric material; 
       FIG. 9  is a side view of a piece-wise construction of the piezo-diaphragm&#39;s ferroelectric material; 
       FIG. 10  is a diagrammatic view of a radial electric field originating from a point in the X-Y plane of the piezo-diaphragm&#39;s ferroelectric material; 
       FIG. 11  is a diagrammatic view of a radial electric field originating from the periphery of a circle in the X-Y plane of the piezo-diaphragm&#39;s ferroelectric material; 
       FIG. 12  is a diagrammatic view of a radial electric field originating from the periphery of a square in the X-Y plane of the piezo-diaphragm&#39;s ferroelectric material; 
       FIG. 13A  is an isolated view of an upper electrode pattern using circular intercirculating electrodes; 
       FIG. 13B  is an isolated view of a lower electrode pattern using circular intercirculating electrodes; 
       FIG. 13C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 13A and 13B ; 
       FIG. 14A  is an isolated view of an upper electrode pattern using square intercirculating electrodes; 
       FIG. 14B  is an isolated view of a lower electrode pattern using square intercirculating electrodes; 
       FIG. 14C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 14A and 14B ; 
       FIG. 15A  is an isolated view of an upper electrode pattern using circular interdigitated ring electrodes; 
       FIG. 15B  is an isolated view of a lower electrode pattern using circular interdigitated ring electrodes; 
       FIG. 15C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 15A and 15B ; 
       FIG. 16A  is an isolated view of an upper electrode pattern using square interdigitated ring electrodes; 
       FIG. 16B  is an isolated view of a lower electrode pattern using square interdigitated ring electrodes; 
       FIG. 16C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 16A and 16B ; 
       FIG. 17A  is an isolated view of an upper electrode pattern using a spiraling electrode; 
       FIG. 17B  is an isolated view of a lower electrode pattern using a spiraling electrode; 
       FIG. 17C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 17A and 17B ; 
       FIG. 18A  is an isolated view of an upper electrode pattern using concentric ring electrodes; 
       FIG. 18B  is an isolated view of a lower electrode pattern using concentric ring electrodes; 
       FIG. 18C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 18A and 18B ; 
       FIG. 19A  is an isolated view of another upper electrode pattern based on intercirculating electrodes; 
       FIG. 19B  is an isolated view of another lower electrode pattern based on intercirculating electrodes; 
       FIG. 19C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 19A and 19B ; 
       FIG. 20A  is an isolated view of another embodiment of an electrode pattern based on intercirculating electrodes; 
       FIG. 20B  is an isolated view of another embodiment of an electrode pattern based on intercirculating electrodes; 
       FIG. 20C  is a cross-sectional view of a portion of the piezo-diaphragm having the upper and lower electrode patterns depicted in  FIGS. 20A and 20B ; 
       FIG. 21  is an exploded view of a piezo-diaphragm of the present invention encased in a dielectric material package; 
       FIG. 22  is a side view of the piezo-diaphragm of  FIG. 21  after construction thereof has been completed; 
       FIG. 23  is a perspective view of another embodiment of the present invention showing an array of sonic transducers; 
       FIG. 24  shows another embodiment of the present invention having an omni-directional transducer array; 
       FIG. 25  shows another embodiment of the present invention having a three-axis directional transducer array; and 
       FIG. 26  shows another embodiment of the present invention having an omni-directional transducer array. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , a top-level schematic drawing of one embodiment of an electro-active device for sonic applications in accordance with the present invention is shown and referenced generally by numeral  100 . Depending on its particular configuration, electro-active device  100  can function as an actuator or as a sensor. However, in each case, the work-performing structure thereof will be the same. More specifically, electro-active device  100  has a piezo-diaphragm  10  coupled with a means for attaching  30  the piezo-diaphragm about its perimeter to a housing  40 . The means for attaching  30  may comprise a rigid mounting frame  32 A,  32 B as shown in  FIGS. 2A and 2B  with holes  34 A,  34 B for receiving a bolt, screw, rivet, etc. to connect the frame to a housing. The circumferential shapes of piezo-diaphragm  10  and means for attaching  30  can be tailored to suit a particular application. Further, piezo-diaphragm  10  and means for attaching region  30  can have their circumferential shapes correspond with one another or be different from one another. Several examples of possible geometries are illustrated in  FIGS. 2A ,  2 B,  3 A, and  3 B. Examples of correspondence between the geometries of the piezo-diaphragm  10  and the mounting frame are illustrated in  FIGS. 2A and 2B , whereas examples of differences therebetween are illustrated in  FIGS. 3A and 3B . 
   Because electro-active device  100  is a sonic transducer, it can function as either a sonic actuator or as sonic sensor.  FIG. 4  illustrates a side view of electro-active device  400 , which is functioning as a sonic actuator or loudspeaker. Device  400  is connected to a power supply  402  which provides a voltage to actuate movement of the piezo-diaphragm, thereby producing sound waves  410 . 
   On the other hand,  FIG. 5  shows a side view of electro-active device  500 , which is functioning as a sonic sensor such as a hydrophone or microphone. Device  500  has electrical leads  504 A,  504 B which connect to an electronic system  506 . The electronic system  506  analyzes the electrical signals or current generated by the piezo-diaphragm of device  500 , thereby enabling measurement of the acoustic energy or force  510  incident upon device  500 . 
   The common features between each of the above-described sonic transducers are that piezo-diaphragm  10  has a mounting region  30  mechanically coupled thereto for attachment to a housing  40 . In these embodiments, the out-of-plane deflection experienced by piezo-diaphragm  10  is not constrained by housing  40  and does not mechanically strain housing  40 . Thus, all mechanical work produced by piezo-diaphragm  10  when functioning as an actuator can be applied to the production of sound. Similarly, the acoustic energy or force incident upon piezo-diaphragm  10  when functioning as a sensor is dissipated primarily by the piezo-diaphragm  10 , thereby increasing sensitivity of the sensor. 
   The construction of piezo-diaphragm  10  is described in the cross-referenced U.S. patent application Ser. No. 10/347,563, the contents of which are hereby incorporated by reference. For a complete understanding of the present invention, the description of piezo-diaphragm  10  will be repeated herein. The essential elements of piezo-diaphragm  10  are a ferroelectric material  12  sandwiched between an upper electrode pattern  14  and a lower electrode pattern  16 . More specifically, electrode patterns  14  and  16  are coupled to ferroelectric material  12  such that voltage applied to the electrode patterns is coupled to ferroelectric material  12  to generate an electric field as will be explained further below. Such coupling to ferroelectric material  12  can be achieved in any of a variety of well-known ways. For example, electrode patterns  14  and  16  could be applied directly to opposing surfaces of ferroelectric material  12  by means of vapor deposition, printing, plating, or gluing, the choice of which is not a limitation of the present invention. 
   Ferroelectric material  12  is any piezoelectric, piezorestrictive, electrostrictive (such as lead magnesium niobate lead titanate (PMN-PT)), pyroelectric, etc., material structure that deforms when exposed to an electrical field (or generates an electrical field in response to deformation as in the case of an electro-active sensor). One class of ferroelectric materials that has performed well in tests of the present invention is a ceramic piezoelectric material known as lead zirconate titanate, which has sufficient stiffness such that piezo-diaphragm  10  maintains a symmetric, out-of-plane displacement as will be described further below. 
   Ferroelectric material  12  is typically a composite material where the term “composite” as used herein can mean one or more materials mixed together (with at least one of the materials being ferroelectric) and formed as a single sheet or monolithic slab with major opposing surfaces  12 A and  12 B lying in substantially parallel planes as best illustrated in the side view shown in FIG.  7 . However, the term “composite” as used herein is also indicative of: i) a ferroelectric laminate made of multiple ferroelectric material layers such as layers  12 C,  12 D,  12 E ( FIG. 8 ) or ii) multiple ferroelectric pieces bonded together such as pieces  12 F,  12 G,  12 H (FIG.  9 ). Note that in each case, major opposing surfaces  12 A and  12 B are defined for ferroelectric material  12 . 
   In general, upper electrode pattern  14  is aligned with lower electrode pattern  16  such that, when voltages are applied thereto, a radial electric field E is generated in ferroelectric material  12  in a plane that is substantially parallel to the parallel planes defined by surfaces  12 A and  12 B, i.e., in the X-Y plane. More specifically, electrode patterns  14  and  16  are aligned on either side of ferroelectric material  12  such that the electric field E originates and extends radially outward in the X-Y plane from a region  12 Z of ferroelectric material  12 . The size and shape of region  12 Z is determined by electrode patterns  14  and  16 , a variety of which will be described further below. 
   The symmetric, radially-distributed electric field E mechanically strains ferroelectric material  12  along the Z-axis (perpendicular to the applied electric field E). This result is surprising and contrary to related art electro-active transducer or piezo-diaphragm teachings and devices. That is, it has been well-accepted in the transducer art that out-of-plane (i.e., Z-axis) displacement required an asymmetric electric field through the thickness of the active material. The asymmetric electric field introduces a global asymmetrical strain gradient in the material that, upon electrode polarity reversal, counters the inherent induced polarity through only part of the active material to create an in-situ bimorph. This result had been achieved by having electrodes on one side of the ferroelectric material. However, tests of the present invention have shown that displacement is substantially increased by using electrode patterns  14  and  16  that are aligned on both sides of ferroelectric material  12  such that the symmetric electric field E originates and extends both radially outward from region  12 Z and throughout the thickness of the ferroelectric material. 
   Electrode patterns  14  and  16  can define a variety of shapes (i.e., viewed across the X-Y plane) of region  12 Z without departing from the scope of the present invention. For example, as shown in  FIG. 10 , region  12 Z could be a point with radial electric field E extending radially outward therefrom. The periphery of region  12 Z could also be a circle ( FIG. 11 ) or a rectangle ( FIG. 12 ) with radial electric field E extending radially outward therefrom. Other X-Y plane shapes (e.g., triangles, pentagons, hexagons, etc.) of region  12 Z could also be defined without departing from the scope of the present invention. 
   In accordance with the present invention, radially-extending electric field E lies in the X-Y plane while displacement D occurs in the Z direction substantially perpendicular to surfaces  12 A and  12 B. Depending on how electric field E is applied, displacement D can be up or down along either the positive or negative Z-axis, but does not typically cross the X-Y plane for a given electric field. The amount of displacement D is greatest at the periphery of region  12 Z where radial electric field E originates. The amount of displacement D decreases with radial distance from region  12 Z with deflection of ferroelectric material  12  being symmetric about region  12 Z. That is, ferroelectric material  12  deflects in a radially symmetric fashion and in a direction that is substantially perpendicular to surfaces  12 A and  12 B. 
   As mentioned above, a variety of electrode patterns can be used to achieve the out-of-plane or Z-axis displacement in the present invention. A variety of non-limiting electrode patterns and resulting local electric fields generated thereby will now be described with the aid of  FIGS. 13-20  where the “A” figure depicts an upper electrode pattern  14  as viewed from above, the “B” figure depicts the corresponding lower electrode pattern  16  as viewed from below, and the “C” figure is a cross-sectional view of the ferroelectric material with the upper and lower electrode patterns coupled thereto and further depicts the resulting local electric fields generated by application of a voltage to the particular electrode patterns. 
   In  FIGS. 13A-13C , upper electrode pattern  14  and lower electrode pattern  16  comprise intercirculating electrodes with electrodes  14 A and  16 A connected to one polarity and electrodes  14 B and  16 B connected to an opposing polarity. For illustrative purposes, electrodes  14 A and  16 A have a positive polarity applied thereto and electrodes  14 B and  16 B have a negative polarity applied thereto. 
   Patterns  14  and  16  are aligned such that they are a mirror image of one another as illustrated in FIG.  13 C. The resulting local electric field lines are indicated by arced lines  18 . In this example, the radial electric field E originates from a very small diameter region  12 Z which is similar to the electric field illustrated in FIG.  10 . 
   The spiraling intercirculating electrode pattern need not be based on a circle. For example, the intercirculating electrodes could be based on a square as illustrated in  FIGS. 14A-14C . Other geometric intercirculating shapes (e.g., triangles, rectangles, pentagons, etc.) could also be used without departing from the scope of the present invention. 
   The electrode patterns may also be fabricated as interdigitated rings. For example,  FIGS. 15A-15C  depict circular-based interdigitated ring electrode patterns where upper and lower electrode patterns  14  and  16  are positioned to be aligned with one another in the Z-axis so that their polarities are aligned as shown in FIG.  15 C. Once again, the interdigitated ring electrode patterns could be based on geometric shapes other than a circle. Accordingly,  FIGS. 16A-16C  depict square-based interdigitated ring electrode patterns as an example of another suitable geometric shape. 
   The upper and lower electrode patterns are not limited to mirror image or other aligned patterns. For example,  FIGS. 17A-17C  depict the use of spiraling electrodes in which upper and lower electrode patterns are staggered with respect to one another when viewed in the cross-section shown in FIG.  17 C. Each electrode pattern is defined by a single polarity electrode pattern so that local electric field  18  extends between surfaces  12 A and  12 B of ferroelectric material  12 . Note that the resulting staggered or cross pattern could be achieved by other electrode patterns such as the ring-based electrode patterns illustrated in  FIGS. 18A-18C . 
   For applications requiring greater amounts of out-of-plane displacement D, the electrode patterns can be designed such that the induced radial electric field E enhances the localized strain field of the piezo-diaphragm. In general, this enhanced strain field is accomplished by providing an electrode pattern that complements the mechanical strain field of the piezo-diaphragm. One way of accomplishing this result is to provide a shaped piece of electrode material at the central portion of each upper and lower electrode pattern, with the shaped pieces of electrode materials having opposite polarity voltages applied thereto. The local electric field between the shaped electrode materials is perpendicular to the surfaces of the ferroelectric material, while the remainder of the upper and lower electrode patterns are designed so that the radial electric field originates from the aligned edges of the opposing-polarity shaped electrode materials. 
   For example,  FIGS. 19A-19C  depict spiral-based intercirculating electrode patterns in which a shaped negative electrode  14 C is aligned over a shaped positive electrode  16 C at the center portions of upper electrode pattern  14  and lower electrode pattern  16 . Under this embodiment, a circularly shaped region  12 Z (aligned with the perimeters of electrodes  14 C and  16 C) is defined in ferroelectric material  12  with the radial electric field E extending radially outward therefrom. Note that such strain field enhancement is not limited to circularly-shaped electrodes  14 C and  16 C, as these shapes could be triangular, square, hexagonal, etc. Further, the remaining portions of the electrode patterns could be based on the above-described interdigitated ring or cross-pattern (staggered) electrode patterns. 
   Enhancement of the piezo-diaphragm&#39;s local strain field could also be achieved by providing an electrode void or “hole” at the center portion of the electrode pattern so that the radial electric field essentially starts from a periphery defined by the start of the local electric fields. For example,  FIGS. 20A-20C  depict spiral-based intercirculating electrode patterns that define centrally-positioned upper and lower areas  14 D and  16 D, respectively, that are void of any electrodes. As a result, the induced radial electric field E originates at the points at which local electric field  18  begins, i.e., about the perimeter of aligned areas  14 D and  16 D. Once again, the central electrode void areas  14 D and  16 D are not limited to circular shapes, and the electrode patterns could be based on the above-described interdigitated ring or cross-pattern electrode patterns. 
   Regardless of the type of electrode pattern, construction of the piezo-diaphragm can be accomplished in a variety of ways. For example, the electrode patterns could be applied directly onto the ferroelectric material. Further, the piezo-diaphragm could be encased in a dielectric material to form the means for attaching (mounting region)  30  as well as waterproof or otherwise protect the piezo-diaphragm from environmental effects. By way of non-limiting example, one simple and inexpensive construction is shown in an exploded view in FIG.  21 . Upper electrode pattern  14  is etched, printed, plated, or otherwise attached to a film  20  of a dielectric material. Lower electrode pattern  16  is similarly attached to a film  22  of the dielectric material. Films  20  and  22  with their respective electrode patterns are coupled to ferroelectric material  12  using a non-conductive adhesive referenced by dashed lines  24 . Each of films  20  and  22  is larger than ferroelectric material  12  so that film portions  20 A and  22 A that extend beyond the perimeter of ferroelectric material  12  can be joined together using non-conductive adhesive  24 . When the structure illustrated in  FIG. 21  is pressed together, piezo-diaphragm  10  is encased in dielectric material  20 / 22  with portions  20 A/ 22 A forming mounting region  30  as illustrated in  FIG. 22  (with the non-conductive adhesive being omitted for clarity of illustration). 
   Irrespective of the particular construction thereof, the present invention allows the work-producing piezo-diaphragm to be held in a fixture without strain on the piezo-diaphragm or the fixture. The devices can be fabricated using thin-film technology thereby making the present invention capable of being installed on circuit boards. 
   The present invention is not limited to a single electro-active transducer as has been described thus far. More specifically, the teachings of the present invention can be extended to a plurality of sonic transducers  100  functioning together in an array. Examples of such arrays include a two-dimensional, omni-directional transducer array  2300  as shown in  FIG. 23 , a three-dimensional, omni-directional transducer array  2400  as shown in  FIG. 24 , a three-axis directional array  2500  as shown in  FIG. 25 , and a spherical omni-directional transducer array  2600  as shown in FIG.  26 . 
   Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function and step-plus-function clauses are intended to cover the structures or acts described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.