PATENT DOCUMENT

Publication Number: US-11482659-B2
Application Number: US-201816217951-A
Country: US
Kind Code: B2

Title: Composite piezoelectric actuator

Abstract:
A piezoelectric actuator including an upper piezoelectric bimorph beam having a first upper piezoelectric layer, a second upper piezoelectric layer and at least three upper electrode layers extending between a first end and a second end of the upper piezoelectric bimorph beam; a lower piezoelectric bimorph beam having a first lower piezoelectric layer, a second lower piezoelectric layer and at least three lower electrode layers extending between a first end and a second end of the lower piezoelectric bimorph beam, and wherein the first end of the lower piezoelectric bimorph beam is coupled to the first end of the upper piezoelectric bimorph beam by a first joint, and the second end of the lower piezoelectric bimorph beam is coupled to second end of the upper piezoelectric bimorph beam; and a base member coupled to a center region of the lower piezoelectric bimorph beam.

Claims:
What is claimed is: 
     
       1. A piezoelectric actuator comprising:
 an upper piezoelectric bimorph beam, the upper piezoelectric bimorph beam having a first upper piezoelectric layer, a second upper piezoelectric layer and at least three upper electrode layers extending between a first end and a second end of the upper piezoelectric bimorph beam, and wherein at least one of the three upper electrode layers is directly coupled to the first upper piezoelectric layer and the second upper piezoelectric layer; and 
 a lower piezoelectric bimorph beam coupled to the upper piezoelectric bimorph beam, the lower piezoelectric bimorph beam having a first lower piezoelectric layer, a second lower piezoelectric layer and at least three lower electrode layers extending between a first end and a second end of the lower piezoelectric bimorph beam, and wherein at least one of the three lower electrode layers is directly coupled to the first lower piezoelectric layer and the second lower piezoelectric layer, and 
 wherein the first end of the lower piezoelectric bimorph beam is coupled to the first end of the upper piezoelectric bimorph beam by a first joint, and the second end of the lower piezoelectric bimorph beam is coupled to the second end of the upper piezoelectric bimorph beam by a second joint. 
 
     
     
       2. The piezoelectric actuator of  claim 1  further comprising:
 a base member coupled to a center region of the lower piezoelectric bimorph beam along a side of the lower piezoelectric bimorph beam facing away from the upper piezoelectric bimorph beam, the base member is dimensioned to couple the lower piezoelectric bimorph beam to a structure, and when coupled, the first and second ends of the upper and lower piezoelectric bimorph beams are operable to move relative to the structure. 
 
     
     
       3. The piezoelectric actuator of  claim 1  wherein each of the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam have a same stiffness. 
     
     
       4. The piezoelectric actuator of  claim 1  wherein the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam bend in opposite directions upon application of a voltage. 
     
     
       5. The piezoelectric actuator of  claim 1  wherein the first joint and the second joint are dimensioned to be compliant to a rotational movement of the upper piezoelectric bimorph beam relative to the lower piezoelectric bimorph beam, and resistant to compression and tension. 
     
     
       6. The piezoelectric actuator of  claim 5  wherein at least one of the first joint and the second joint comprise a pressure sensitive adhesive. 
     
     
       7. The piezoelectric actuator of  claim 1  wherein a gap in the range of 300 microns or less is present between the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam. 
     
     
       8. The piezoelectric actuator of  claim 7  wherein the gap is an open space free of a filler material. 
     
     
       9. The piezoelectric actuator of  claim 1  wherein the lower piezoelectric bimorph beam is coupled to a fixed structure by a base member that serves as an only point of contact between the lower piezoelectric bimorph beam and the fixed structure, the upper piezoelectric bimorph beam is coupled to a movable structure, and upon application of a voltage, the movable structure produces a sound output within a low frequency range. 
     
     
       10. A composite piezoelectric actuator comprising:
 an upper piezoelectric actuator unit comprising a first upper piezoelectric bimorph beam and a second upper piezoelectric bimorph beam, the first and second upper piezoelectric bimorph beams are attached to each other at each of their respective ends by a joint directly connecting a conductive layer at each of their respective ends that allows for a rotational movement of the first upper piezoelectric bimorph beam relative to the second upper piezoelectric bimorph beam, and a base member is mounted to a center portion of the second upper piezoelectric bimorph beam along a side that faces away from the first upper piezoelectric bimorph beam; and 
 a lower piezoelectric actuator unit coupled to the upper piezoelectric actuator unit, the lower piezoelectric actuator unit comprising a first lower piezoelectric bimorph beam and a second lower piezoelectric bimorph beam, the first and second lower piezoelectric bimorph beams are attached to each other at each of their respective ends by a joint directly connecting a conductive layer at each of their respective ends that allows for a rotational movement of the first lower piezoelectric bimorph beam relative to the second lower piezoelectric bimorph beam, and a center portion of the first lower bimorph beam is mounted to the base member. 
 
     
     
       11. The composite piezoelectric actuator of  claim 10  wherein at least one of the first upper piezoelectric bimorph beam, the second upper piezoelectric bimorph beam, the first lower piezoelectric bimorph beam or the second lower piezoelectric bimorph beam comprises a stack up of a first electrode layer, a first piezoelectric layer, a second electrode layer, a second piezoelectric layer and a third electrode layer. 
     
     
       12. The composite piezoelectric actuator of  claim 10  wherein the upper piezoelectric actuator unit and the lower piezoelectric actuator unit are mounted together at only the base member. 
     
     
       13. The composite piezoelectric actuator of  claim 10  wherein the upper piezoelectric actuator unit and the lower piezoelectric actuator unit are symmetrically arranged. 
     
     
       14. The composite piezoelectric actuator of  claim 10  wherein a plurality of the upper piezoelectric actuator units and a plurality of the lower piezoelectric actuator units are symmetrically coupled together to achieve a desired force output without increasing an x and y dimension of the composite piezoelectric actuator unit. 
     
     
       15. The composite piezoelectric actuator of  claim 10  wherein application of a voltage causes a displacement of the upper piezoelectric actuator unit that is equal to a sum of a displacement of the upper piezoelectric actuator unit and the lower piezoelectric actuator unit combined. 
     
     
       16. A piezoelectric actuator comprising:
 a movable member; 
 a first piezoelectric bimorph beam having a first piezoelectric layer and a second piezoelectric layer that are arranged between electrode layers extending from a first end to a second end of the first piezoelectric bimorph beam, and at least one of the electrode layers is directly coupled to the first piezoelectric layer and the second piezoelectric layer, wherein the first piezoelectric bimorph beam is coupled to the movable member; 
 a second piezoelectric bimorph beam having a first piezoelectric layer and a second piezoelectric layer that are arranged between electrode layers extending from a first end to a second end of the second piezoelectric bimorph beam, and at least one of the electrode layers is directly coupled to the first piezoelectric layer and the second piezoelectric layer, and wherein the first and second ends of the second piezoelectric bimorph beam are coupled to the first and second ends of the first piezoelectric bimorph beam, respectively, by a joint that allows for a rotational movement of the first and second piezoelectric bimorph beams relative to each other; 
 a base member coupled to a center portion of the second piezoelectric bimorph beam along a side of the second piezoelectric bimorph beam facing away from the first piezoelectric bimorph beam; and 
 a fixed member coupled to the base member, and wherein the first and second piezoelectric bimorph beams are operable to move the movable member relative to the fixed member upon application of a voltage. 
 
     
     
       17. The piezoelectric actuator of  claim 16  wherein the first and second piezoelectric bimorph beams have a same thickness, length and width. 
     
     
       18. The piezoelectric actuator of  claim 16  wherein the joint comprises an adhesive running in a widthwise direction between the first and second ends of the first and second piezoelectric bimorph beams, and the adhesive provides an only attachment point between the first and second piezoelectric bimorph beams. 
     
     
       19. The piezoelectric actuator of  claim 16  wherein the base member is a rigid base member having a compliance that is less than a compliance of the second piezoelectric bimorph beam, and the rigid base member provides the only attachment point between the second piezoelectric bimorph beam and the fixed member. 
     
     
       20. The piezoelectric actuator of  claim 16  wherein the movable member is a speaker diaphragm and upon application of a voltage, displacement of the first and second piezoelectric bimorph beams cause the speaker diaphragm to generate a sound output within a low resonance frequency. 
     
     
       21. An electronic device comprising:
 an enclosure defining an enclosed space; 
 an upper piezoelectric bimorph beam positioned within the enclosed space, the upper piezoelectric bimorph beam having a first upper piezoelectric layer, a second upper piezoelectric layer and at least three upper electrode layers extending between a first end and a second end of the upper piezoelectric bimorph beam, and wherein at least one of the three upper electrode layers is directly coupled to the first upper piezoelectric layer and the second upper piezoelectric layer; and 
 a lower piezoelectric bimorph beam coupled to the upper piezoelectric bimorph beam, the lower piezoelectric bimorph beam having a first lower piezoelectric layer, a second lower piezoelectric layer and at least three lower electrode layers extending between a first end and a second end of the lower piezoelectric bimorph beam, and wherein at least one of the three lower electrode layers is directly coupled to the first lower piezoelectric layer and the second lower piezoelectric layer, and wherein the first end of the lower piezoelectric bimorph beam is coupled to the first end of the upper piezoelectric bimorph beam by a first joint, and the second end of the lower piezoelectric bimorph beam is coupled to the second end of the upper piezoelectric bimorph beam by a second joint. 
 
     
     
       22. The electronic device of  claim 21  further comprising:
 a base member coupled to a center region of the lower piezoelectric bimorph beam along a side of the lower piezoelectric bimorph beam facing away from the upper piezoelectric bimorph beam, the base member is dimensioned to couple the lower piezoelectric bimorph beam to the enclosure, and when coupled, the first and second ends of the upper and lower piezoelectric bimorph beams are operable to move relative to the structure. 
 
     
     
       23. The electronic device of  claim 21  wherein each of the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam have a same stiffness. 
     
     
       24. The electronic device of  claim 21  wherein the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam bend in opposite directions upon application of a voltage. 
     
     
       25. The electronic device of  claim 21  wherein the first joint and the second joint are dimensioned to be compliant to a rotational movement of the upper piezoelectric bimorph beam relative to the lower piezoelectric bimorph beam, and resistant to compression and tension.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/736,724, filed on Sep. 26, 2018, which is incorporated herein by reference. 
    
    
     FIELD 
     An aspect of the invention is directed to a piezoelectric actuator, more specifically, a piezoelectric actuator made up of a composite structure including symmetrically stacked piezoelectric bimorph beams. Other aspects are also described and claimed. 
     BACKGROUND 
     Piezoelectric materials are solid materials upon which large mechanical stresses can be induced by applying an electric field across the material. This conversion from electrical to mechanical energy makes them useful in electromechanical actuators. However, because piezoelectric materials can be very stiff, the large stresses induced, may yield only very small strains. As a result, in their most basic bulk form, piezoelectric materials are typically only suitable for actuator applications that involve extremely small displacements (e.g., vibrations). 
     SUMMARY 
     An aspect of the disclosure is directed to a low-stiffness piezoelectric actuator unit, or composite piezoelectric actuator unit, having geometric, and bandwidth, flexibility. For example, in one aspect, the piezoelectric actuator unit, or composite piezoelectric actuator unit, is suitable for use in a mobile audio speaker driver having a desired operating frequency bandwidth and which must fit into a relatively small package geometry that other electrodynamic and/or piezoelectric drivers cannot. By way of background, it should be noted that a mechanically compliant speaker (as close as possible to the compliance of air) is necessary to drive low frequency sound efficiently. Piezoelectric speakers made of a single plate of piezoelectric material must be very thin (compared to x and y dimensions) in order to increase the compliance of the plate, enabling low frequency sound production. Since maximum output power is closely related to the volume of piezoelectric material in the actuator, such a thin plate must have very large x and y dimensions to output sufficient power, which is necessary for both low and high frequency sound output. Aspects of this disclosure therefore provide for an actuator that can output equivalent sound levels, despite widely varying aspect ratios, making fitting the actuator into a desired geometry possible. In addition, aspects of the disclosure provide for an actuator which achieves an increased electric field per volt and reduced stiffness, making it suitable for low frequency applications. 
     More specifically, aspects of the disclosure include a piezoelectric actuator unit or composite piezoelectric actuator unit including piezoelectric bimorph cantilever beams that are symmetrically arranged (e.g., stacked) to provide an actuator with increased displacement while still maintaining relatively small x and y dimensions. The piezoelectric bimorph cantilever beams have a relatively low stiffness, and therefore when used in the actuator, help to increase displacement. Each bimorph cantilever beam may include two layers of piezoelectric material running parallel to the beam&#39;s axis. Each layer may be sandwiched between two layers of conductive material (e.g., electrodes). A voltage or signal can be applied to the conductive layers to apply electric fields across the piezoelectric layers thereby straining the two layers. When one layer is negatively strained, and the other is positively strained, a bending moment is induced. The bending of the beam yields a potentially large displacement, particularly at the tip of the beam. When a number of piezoelectric bimorph cantilever beams are arranged together, for example, in a stacked configuration, a relatively large displacement suitable for low-frequency output (e.g., 200 Hz or less) can be achieved, without changing a thickness/stiffness of each beam (e.g., making it longer and/or thinner), and in turn, the x and y dimensions of the actuator. 
     Representatively, in one aspect, a piezoelectric actuator unit is disclosed. The piezoelectric actuator may include an upper piezoelectric bimorph beam, the upper piezoelectric bimorph beam having a first upper piezoelectric layer, a second upper piezoelectric layer and at least three upper electrode layers extending between a first end and a second end of the upper piezoelectric bimorph beam. The piezoelectric actuator may further include a lower piezoelectric bimorph beam coupled to the upper piezoelectric bimorph beam, the lower piezoelectric bimorph beam having a first lower piezoelectric layer, a second lower piezoelectric layer and at least three lower electrode layers extending between a first end and a second end of the lower piezoelectric bimorph beam, and the first end of the lower piezoelectric bimorph beam is coupled to the first end of the upper piezoelectric bimorph beam by a first joint, and the second end of the lower piezoelectric bimorph beam is coupled to second end of the upper piezoelectric bimorph beam. In addition, a base member may be attached to a center region of the lower piezoelectric bimorph beam along a side of the lower piezoelectric bimorph beam facing away from the upper piezoelectric bimorph beam. The base member may be dimensioned to attach the lower piezoelectric bimorph beam to a structure, and when attached, the first and second ends of the upper and lower piezoelectric bimorph beams are operable to move relative to the structure. In addition, in some aspects, each of the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam may have a same stiffness. Still further, the first upper piezoelectric layer and the second upper piezoelectric layer may be stacked in an alternating arrangement with the at least three upper electrode layers. In other aspects, the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam may bend in opposite directions upon application of a voltage. In addition, in some aspects, the first joint and the second joint may be dimensioned to be compliant to a rotational movement of the upper piezoelectric bimorph beam relative to the lower piezoelectric bimorph, and resistant to compression and tension. In addition, at least one of the first joint and the second joint may include a pressure sensitive adhesive. In some aspects, a gap in the range of 300 microns or less is present between the upper piezoelectric bimorph beam and the lower piezoelectric bimorph beam. The gap may be an open space free of a filler material. In other aspects, the structure the lower piezoelectric bimorph beam is attached to is a fixed structure, the upper piezoelectric bimorph beam is attached to a movable structure, and upon application of a voltage, the movable structure produces a sound output within a low frequency range. 
     In another aspect, a composite piezoelectric actuator unit is disclosed. The composite piezoelectric actuator unit may include an upper piezoelectric actuator unit including a first upper piezoelectric bimorph beam and a second upper piezoelectric bimorph beam, the first and second upper piezoelectric bimorph beams are attached to each other at each of their respective ends by a joint that allows for a rotational movement of the first upper piezoelectric bimorph beam relative to the second upper piezoelectric bimorph beam, and a base member is mounted to a center portion of the second upper piezoelectric bimorph beam along a side that faces away from the first upper piezoelectric bimorph beam. The composite piezoelectric actuator unit may further include a lower piezoelectric actuator unit attached to the upper piezoelectric actuator unit, the lower piezoelectric actuator unit may include a first lower piezoelectric bimorph beam and a second lower piezoelectric bimorph beam, the first and second lower piezoelectric bimorph beams are attached to each other at each of their respective ends by a joint that allows for a rotational movement of the first lower piezoelectric bimorph beam relative to the second lower piezoelectric bimorph beam, and a center portion of the first lower bimorph beam is mounted to the base member. In some aspects, at least one of the first upper piezoelectric bimorph beam, the second upper piezoelectric bimorph beam, the first lower piezoelectric bimorph beam or the second lower piezoelectric bimorph beam may include a stack up of a first electrode layer, a first piezoelectric layer, a second electrode layer, a second piezoelectric layer and a third electrode layer. The upper piezoelectric actuator unit and the lower piezoelectric actuator unit may be mounted together at only the base member. In still further aspects, the upper piezoelectric actuator unit and the lower piezoelectric actuator unit are symmetrically arranged. Still further, a plurality of the upper piezoelectric actuator units and a plurality of the lower piezoelectric actuator units are symmetrically attached together to achieve a desired force output without increasing an x and y dimension of the composite piezoelectric actuator unit. In addition, in some aspects, the application of a voltage causes a displacement of the upper piezoelectric actuator unit that is equal to a sum of a displacement of the upper piezoelectric actuator unit and the lower piezoelectric actuator unit combined. 
     In another aspect, a piezoelectric actuator assembly is disclosed. The piezoelectric actuator assembly may include (1) a movable member; (2) a first piezoelectric bimorph beam having a first piezoelectric layer and a second piezoelectric layer that are arranged between electrode layers extending from a first end to a second end of the first piezoelectric bimorph beam, wherein the first piezoelectric bimorph beam is coupled to the movable member; (3) a second piezoelectric bimorph beam having a first piezoelectric layer and a second piezoelectric layer that are arranged between electrode layers extending from a first end to a second end of the second piezoelectric bimorph beam, and wherein the first and second ends of the second piezoelectric bimorph beam are coupled to the first and second ends of the first piezoelectric bimorph beam, respectively, by a joint that allows for a rotational movement of the first and second piezoelectric bimorph beams relative to each other; (4) a base member coupled to a center portion of the second piezoelectric bimorph beam along a side of the second piezoelectric bimorph beam facing away from the first piezoelectric bimorph beam; and (5) a fixed member coupled to the base member, and wherein the first and second piezoelectric bimorph beams are operable to move the movable member relative to the fixed member upon application of a voltage. In some aspects, the first and second bimorph beams have a same thickness, length and width. In addition, the joint may include an adhesive running in a widthwise direction between the first and second ends of the first and second piezoelectric bimorph beams, and the adhesive provides the only attachment point between the first and second piezoelectric bimorph beams. In still further aspects, the base member may be a rigid base member having a compliance that is less than a compliance of the second piezoelectric bimorph beam, and the rigid base member provides the only attachment point between the second piezoelectric bimorph beam and the fixed member. In some aspects, the movable member is a speaker diaphragm and upon application of a voltage, displacement of the first and second piezoelectric bimorph beams cause the speaker diaphragm to generate a sound output with a low resonance frequency. 
     The above summary does not include an exhaustive list of all aspects of the present invention. It is contemplated that the invention includes all systems and methods that can be practiced from all suitable combinations of the various aspects summarized above, as well as those disclosed in the Detailed Description below and particularly pointed out in the claims filed with the application. Such combinations have particular advantages not specifically recited in the above summary. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The aspects are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” aspect in this disclosure are not necessarily to the same aspect, and they mean at least one. 
         FIG. 1  illustrates a cross-sectional side view of a piezoelectric actuator unit. 
         FIG. 2  illustrates a perspective view of the piezoelectric actuator unit of  FIG. 1 . 
         FIG. 3  illustrates a cross-sectional side view of a piezoelectric actuator beam of a piezoelectric actuator unit. 
         FIG. 4  illustrates a cross-sectional side view of a bending movement of the piezoelectric actuator unit of  FIG. 1 . 
         FIG. 5  illustrates a cross-sectional side view of a composite piezoelectric actuator unit. 
         FIG. 6  illustrates a cross-sectional side view of one application for a piezoelectric actuator unit. 
         FIG. 7  illustrates a simplified schematic view of an electronic device in which a piezoelectric actuator unit may be implemented. 
         FIG. 8  illustrates a block diagram of some of the constituent components of an electronic device in which a piezoelectric actuator unit may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     In this section we shall explain several preferred aspects of this invention with reference to the appended drawings. Whenever the shapes, relative positions and other aspects of the parts described in the aspects are not clearly defined, the scope of the invention is not limited only to the parts shown, which are meant merely for the purpose of illustration. Also, while numerous details are set forth, it is understood that some aspects of the invention may be practiced without these details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the understanding of this description. 
     The terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting of the invention. Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper”, and the like may be used herein for ease of description to describe one element&#39;s or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     The terms “or” and “and/or” as used herein are to be interpreted as inclusive or meaning any one or any combination. Therefore, “A, B or C” or “A, B and/or C” mean “any of the following: A; B; C; A and B; A and C; B and C; A, B and C.” An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive. 
       FIG. 1  illustrates a cross-sectional side view of one aspect of a piezoelectric actuator unit. Piezoelectric actuator unit  100  may include a first piezoelectric bimorph beam  102  and a second piezoelectric bimorph beam  104 . First piezoelectric bimorph beam  102  may have a top side  114  and a bottom side  116  which extend between a first end  110 A and a second end  110 B. Similarly, second piezoelectric bimorph beam  104  may have a top side  118  and a bottom side  120  which extend between first end  112 A and second end  112 B. First piezoelectric bimorph beam  102  may be considered stacked on top of second piezoelectric bimorph beam  104  such that sides  116  and  118  are interfacing (although not directly touching), and sides  114  and  120  face away from each other. In this aspect, the first piezoelectric bimorph beam  102  may also be referred to as an upper piezoelectric bimorph beam and the second piezoelectric bimorph beam  104  may be referred to as a lower piezoelectric bimorph beam. The respective ends  110 A,  110 B,  112 A,  112 B of each beam are attached to one another by joints  106 A,  106 B. For example, when the beams  102 ,  104  are stacked as shown, first end  110 A of first piezoelectric bimorph beam  102  is connected by joint  106 A to first end  112 A of second piezoelectric bimorph beam  104 , and second end  110 B of first piezoelectric bimorph beam  102  is connected by joint  106 B to second end  112 B of second piezoelectric bimorph beam  104 . 
     Joints  106 A,  106 B allow for rotation of the ends of first and second piezoelectric bimorph beams  102  and  104 , respectively, with respect to one another as shown in  FIG. 4 . Joints  106 A,  106 B, however, should be resistant to compression and tension (e.g., horizontal stretching) such that the ends  110 A,  110 B,  112 A,  112 B of first piezoelectric bimorph beam  102  and second piezoelectric bimorph beam  104  do not slide or otherwise move horizontally with respect to one another. Representatively, in one aspect, each of joints  106 A,  106 B may be formed by a glue, adhesive, epoxy or the like, which secures only the beam ends along the interfacing sides  116 ,  118 . For example, joints  106 A,  106 B may be formed by a line of a pressure sensitive adhesive (PSA) applied in a widthwise direction on sides  116 ,  118 , at only the beam ends so that an open space or gap  122  is formed between the remaining portions of sides  116 ,  118 . Representatively, the PSA may be applied at a minimal thickness, for example, a thickness of 200 microns or less, such that a height (in the z direction) of the gap  122  is 200 microns or less. In addition, the PSA may be as narrow as possible, for example, the PSA may essentially be a line running in a widthwise direction across the beams. For example, a line having a width of ½ mm or less. The remaining area of gap  122  between the joints  106 A,  106 B is open. In addition, it is noted that so as not to take away, or otherwise reduce, a compliance of the stack up of beams  102 ,  104 , there is no filler, or other similar stabilizing material, between sides  116 ,  118  of beams  102 ,  104 , respectively. 
     This arrangement of first piezoelectric bimorph beam  102 , second piezoelectric bimorph beam  104  and joints  106 A,  106 B can be more clearly seen in the perspective view of actuator  100  illustrated in  FIG. 2 . In particular, from this view, it can be seen that beams  102 ,  104  have a length (L), a width (W) and a thickness (T). Joints  106 A,  106 B are formed across the width (W) of beams  102 ,  104  in a relatively narrow line, and attach only the ends  110 A,  110 B,  112 A,  112 B together. In addition, it can be understood from  FIG. 2  that the ends  110 A,  110 B,  112 A,  112 B that are attached together at joints  106 A,  106 B are the ends defining the length dimension (L) of each beam. In other words, it is the ends of each beam that are farthest apart that are attached together, therefore most of the beam is free to move. 
     Returning now to  FIG. 1 , piezoelectric actuator unit  100  may further include a base member  108 . Base member  108  may be a substantially rigid structure that can be used to connect the piezoelectric actuator unit  100  to another structure (e.g., another actuator unit or stationary structure). For example, the base member  108  may be considered “rigid” in that it is less compliant (or more stiff) than the second piezoelectric bimorph beam  104 . The base member  108  may provide the only connection point between the piezoelectric actuator unit  100  and another structure. In  FIG. 1 , base member  108  is shown attached (e.g. chemically or mechanically mounted) to second piezoelectric bimorph beam  104 , at side  120 , which faces away from first piezoelectric bimorph beam  102 . In other aspects, however, base member  108  could be attached to first piezoelectric bimorph beam  102 , for example, at side  114 . Still further, it is contemplated that base member  108  could be part of the structure that the unit  100  is coupled to, and could be any type of supporting structure that supports unit  100  on the structure such that the upper and lower beams do not contact the supporting structure anywhere except at the base member  108 . 
     Base member  108  is attached to the beam  104  (or beam  102 ) at its center  124 , and should generally be in contact with only a small fraction of the length of the lower beam  104  to avoid stiffening the beam vs. flapping. Base member  108  can, however, contact the full width of the beam to increase stiffness v. translation of the center. For example, base member  108  may be an elongated, beam like structure that extends along center  124 , in a widthwise direction across side  120 , of beam  104 , as shown in  FIG. 2 . In this aspect, when base member  108  is used to attach piezoelectric actuator unit  100  to another structure, the center portion of beam  104  may remain relatively stationary with respect to the structure, while the ends  112 A,  112 B of beam  104  are free to move with respect to the structure. For example, when a voltage is applied, ends  112 A,  112 B of beam  104  can move away from the structure as illustrated in  FIG. 4 . 
     Referring again to  FIG. 2 , it should be noted that in one aspect, piezoelectric beam  102  and piezoelectric beam  104  may have a same thickness (T) as shown. In addition, each of beams  102  and  104  may have a same width (W) and length (L). In this aspect, each of beams  102  and  104  may be understood to have a same stiffness and/or piezoelectric material volume. Accordingly, when a voltage is applied, an amplitude of the bend or deflection of each of the beams  102  and  104  is substantially the same, as illustrated by  FIG. 4 . 
     Referring now to  FIG. 3 ,  FIG. 3  illustrates a cross-sectional side view of one of the piezoelectric bimorph beams included in the actuator unit  100  of  FIGS. 1-2 . Representatively,  FIG. 3  is a cross-sectional view of piezoelectric bimorph beam  102 . It should be understood, however, that the description with respect to first piezoelectric bimorph beam  102 , also applies to second piezoelectric bimorph beam  104 . Piezoelectric bimorph beam  102  may include two piezoelectric layers  302 ,  304  running parallel to the length dimension of beam  102 . The piezoelectric layers  302 ,  304  may be made of a piezoelectric material, for example, a ceramic. The piezoelectric layers  302 ,  304  may be sandwiched between conductive or electrode layers  306 ,  308 ,  310 . Representatively, the piezoelectric bimorph beam  102  may include a stack up of electrode layer  306 , piezoelectric layer  302 , electrode layer  308 , piezoelectric layer  304  and electrode layer  310 , in that order. It should further be noted that the layers  302 - 310  are stacked directly on top of one another, and without any intervening substrate layers. It is further contemplated that although beam  102  is referred to herein as a piezoelectric bimorph beam  102 , in some aspects, beam  102  could be any type of electroactive beam, for example, a multilayer plate bender. 
     In  FIG. 3 , piezoelectric layers  302 ,  304  are further shown arranged so that beam  102  has a polarization direction as illustrated by arrow  318  (e.g., in a 3 direction). When a signal or voltage is applied to electrode layers  306 ,  308 ,  310  (e.g., via circuitry or wires  312 ,  314 ,  316 ), an electric field is applied across the piezoelectric layers  302 ,  304  as shown. This electric field strains the piezoelectric layers  302 ,  304 , for example, one layer is negatively strained and the other is positively strained. When this stress in the piezoelectric material acts in different directions (illustrated by the horizontal arrows), a bending moment is induced (illustrated by the curved arrow). Said another way, upon application of the voltage, the electric field causes piezoelectric layer  302  to contract inward, while piezoelectric layer  304  expands outward, causing beam  102  to bend. This bending of the beam  102  yields a relatively large displacement at the ends  110 A,  110 B of the beam (see, for example,  FIG. 4 ). 
     As previously discussed, this relatively large displacement (e.g., vibration) allows piezoelectric bimorph beam  102  to be used in an actuator (e.g., actuator unit  100 ) where vibrations of a particular frequency or bandwidth, for example, an audio speaker driver, are desired. However, the force output of the beam for a given volume, compliance and electric field input may be limited to a theoretical maximum defined by the piezoelectric material. Modifying aspects of the piezoelectric material and/or beam can be used to modify the output. For example, increasing the beam compliance allow the beam to radiate low frequency sounds (e.g., 200 Hz or less). Where the volume of the bimorph beam  102  is fixed, increasing compliance means the beam must be made longer. A longer beam, however, is not necessarily desirable because this increases the overall foot print of the actuator in the x and/or y direction. Alternatively, the width or thickness of the beam can be increased to increase the piezoelectric material volume, but then this may reduce the compliance of the beam making a low frequency range difficult to achieve. 
     It should be further understood that if beam  102  is fixed at one end (e.g., to a fixed structure) and connected to a mass at another end (e.g, a moving structure), when it is actuated at different frequencies, there will be a relatively large peak in the frequency response curve representing a lot of sound/acceleration of the mass at the resonance of the beam. Modifying the dimensions of the piezoelectric material or beam (e.g., changing the length, width or thickness) can therefore also be used to tune a force output and/or resonant frequency. For example, if the length of the beam is increased, the resonance can be lowered because the stiffness of the beam is decreased. This, however, may reduce the force output at higher frequencies. In addition, this increases the overall actuator foot print in the x and/or y directions making the actuator unsuitable for implementation in enclosures having a small form factor. 
     Piezoelectric actuator unit  100  solves many of these challenges by stacking piezoelectric bimorph beam  102  with one or more other beams (e.g., beam  104 ). Stacking beams  102  and  104  as disclosed herein increases displacement, while still achieving a high force output and maintaining a relatively small foot print (in the x and y dimensions). In particular, the stiffness decreases as the number of layers of bimorph beams increases. Said another way, the stiffness can be divided by the number of layers of bimorphs in the structure. Thus, the more beams that are stacked together, the more the compliance increases, and this in turn, leads to an increase in the displacement that can be achieved. In addition, as illustrated by  FIG. 2 , since beams  102  and  104  are stacked as shown, only the overall height (e.g. z-height or dimension along the z-axis) of the piezoelectric actuator unit  100  increases, while the overall length (L) (e.g., dimension along the x-axis) and width (W) (e.g., dimension along the y-axis) can remain the same. Thus, this increased displacement is achieved while still maintaining a same overall actuator footprint (in the x and y dimensions). 
       FIG. 4  illustrates one aspect of a deflection or displacement that can be achieved by the piezoelectric actuator unit  100 . Representatively,  FIG. 4  illustrates actuator unit  100  attached to a structure  402  by base member  108 . When a voltage is applied, first and second piezoelectric bimorph beams  102 ,  104 , respectively, bend in different directions. For example, ends  112 A,  112 B of second piezoelectric bimorph beam  104  bend upward, and ends  110 A,  110 E of first piezoelectric bimorph beam  102  bend downward such that the centers of each beam are farther apart. In addition, the amplitude of the displacement (or bend) of first piezoelectric bimorph beam  102  and second piezoelectric bimorph beam  104  alone may be substantially the same. The overall displacement of piezoelectric actuator unit  100 , however, may be greater than a single bimorph beam alone. For example, a displacement of the top side  114  of beam  102  may be the sum of the displacement of beams  102  and  104  combined. In addition, since the additional beams do not increase the overall stiffness, and in fact it is decreased (e.g., compliance is increased), the actuator  100  is suitable for low frequency applications, and without compromising the output force. 
     It should further be understood that characteristics of the joints  106 A,  106 B, which are used to attach first and second piezoelectric bimorph beams  102 ,  104  together, may also be critical to maintaining a desired force output. In particular, as previously discussed, joints  106 A,  106 B are low-rotational-stiffness joints. In other words, joints  106 A,  106 B are designed to allow for rotation of the ends of beams  102  and  104  with respect to one another, but resistant (or stiff) to compression and tension. For example, as can be seen from  FIG. 4 , joints  106 A,  106 B can stretch vertically (in a triangular fashion) to allow for rotation of ends  110 A,  112 A and ends  110 B,  112 B, with respect to one another, much like they were rotating around a pin. Joints  106 A,  106 B, however, maintain relatively the same width (e.g., resistant to stretching in a horizontal direction) because they are resistant to tension and sheer. This low-rotational-stiffness at joints  106 A,  106 B allows each of beams  102 ,  104  to deflect without adding unnecessary stiffness. In addition, the high out-of-plane stiffness (e.g., resistant to stretch in the horizontal direction) reduces force loss at the joint. 
     Still further, it should be understood that joints  106 A,  106 B only attach ends  110 A,  110 B,  112 A,  112 B (e.g. the short ends) of each of beams  102 ,  104  together. The remaining sides, edges and/or surfaces of beams  102 ,  104  are not connected and are free to move with respect to one another, which further reduces any unnecessary stiffness. 
     While  FIGS. 1-4  illustrate two piezoelectric bimorph beams  102 ,  104  symmetrically arranged to form a piezoelectric actuator unit  100  with increased displacement, an actuator with even greater displacement and/or force output (and without increasing x and y dimensions) can be achieved by symmetrically arranging more than one of piezoelectric actuator units  100  together.  FIG. 5  illustrates a cross-sectional side view of a composite piezoelectric actuator unit  500  made up of a number of piezoelectric actuator units  100 A  100 B and  100 C. Piezoelectric actuator units  100 A,  100 B and  100 C may be substantially the same as piezoelectric actor unit  100  previously discussed in reference to  FIGS. 1-4 . The piezoelectric actuator units  100 A- 100 C are stacked to form a symmetrical structure (e.g., along axis  318 ) as shown. For example, piezoelectric actuator units  100 A- 100 C are stacked such that the base member  108  of unit  100 A is connected to the top side  114  of second piezoelectric beam  104  of unit  100 B, and base member  108  of unit  100 B is connected to the top side  114  of first piezoelectric beam  104  of unit  100 C. It should be recognized that the only point of connection between each of units  100 A- 100 C may be at base members  108  as shown. In this aspect, a displacement of each of units  100 A- 100 C can be maximized upon application of a voltage or signal. The voltage or signal may be the same for all units, such that, for example, all the units  100 A- 100 C are driven at the same time. When arranged as shown, the displacement of the top side  114  of the upper most piezoelectric beam of the stack (e.g., beam  104  of unit  100 A) is displaced by the sum of the displacements of all the underlying units (e.g., units  100 B and  100 C). In this aspect, a composite piezoelectric actuator unit  500  having an increased piezoelectric material volume, and therefore increased force output, without increasing an overall footprint (e.g., an x and y dimension) can be achieved. 
     It should further be understood that although units  100 A- 100 C are shown stacked one on top of the other, any number of units  100  may be arranged together along an x, y and/or z axis, where an even greater deflection and/or force output is desired. For example, N number of units  100  may be stacked one on top of the other (e.g., along a z-axis or axis  318 ) and/or N number of units  100  may be arranged end to end (e.g., along an x-axis) and/or N number of units  100  may be arranged side by side (e.g., along a z-axis). Representatively, in one aspect, the composite unit  500  may include an arrangement of 8 side by side columns, each of the columns made up of 5 actuator units  100 , each vertically stacked one on top of the other. Still further, composite unit  500  could include three or more of this composite arrangement (including the 8 columns), arranged end to end with one another. Representatively, in some aspects, the composite unit  500  may include 2 or more of units  100  symmetrically arranged, for example, 24 of units  100  symmetrically arranged, 40 of units  100  symmetrically arranged, 80 of units symmetrically arranged or 120 of units  100  symmetrically arranged. It should be understood that the symmetry provides better rigid connection by reducing the torque load on the joints. 
       FIG. 6  illustrates a cross-sectional side view one exemplary application for a piezoelectric actuator unit. Representatively,  FIG. 6  shows piezoelectric actuator unit  100  coupled to a moving structure  602  and a fixed structure  604 . In this application, it is desirable to move the moving structure  602  with respect to the fixed structure  604 . The moving structure  602  could be any type of structure or mass that is desired to be moved with respect to another structure. Similarly, the fixed structure  604  could be any type of structure that is to remain relatively stationary or fixed while another structure is moving. For example, the moving structure  602  could be an audio speaker diaphragm and the fixed structure  604  could be a fixed portion of the speaker (e.g., portion of the speaker module or enclosure). Still further, the moving structure  602  and the fixed structure  604  may be portions of an electronic device enclosure, for example, a top enclosure wall and a bottom enclosure wall, respectively, in which it is desirable to move (e.g., vibrate) one wall with respect to the other. 
     As shown in  FIG. 6 , the top wall  114  of piezoelectric actuator unit  100  is attached to moving structure  602 , and the base member  108  is attached to fixed structure  604 . When a voltage is applied to piezoelectric actuator unit  100 , a displacement or vibration of unit  100 , as previously discussed, causes a corresponding displacement or vibration of moving structure  602 . Various aspects of the unit  100  can be tuned, as previously discussed, to cause the desired displacement or vibration of moving structure  602 . In addition, it is contemplated that although a separate moving structure  602  is shown in  FIG. 6 , in some aspects, the moving member  602  may be omitted and instead the top wall  114  of piezoelectric actuator unit  100  may serve as the moving structure. 
     Still further, it should be understood that while  FIG. 6  shows a single piezoelectric actuator unit  100  for driving moving structure  602 , any number of piezoelectric actuator units  100  may be used. For example, a composite piezoelectric actuator unit such as unit  500  described in reference to  FIG. 5  may be used to drive movement of moving structure  602 . 
       FIG. 7  illustrates a simplified schematic perspective view of an exemplary electronic device in which a composite piezoelectric actuator as described herein, may be implemented. As illustrated in  FIG. 7 , the composite piezoelectric actuator may be integrated within a consumer electronic device  702  such as a smart phone with which a user can conduct a call with a far-end user of a communications device  704  over a wireless communications network; in another example, the composite piezoelectric actuator may be integrated within the housing of a tablet computer  706 . These are just two examples of where the composite piezoelectric actuator described herein may be used; it is contemplated, however, that the composite piezoelectric actuator may be used with any type of electronic device in which movement of a mass is desired, for example, a home audio system, any consumer electronics device with audio capability, or an audio system in a vehicle (e.g., an automobile infotainment system). 
       FIG. 8  illustrates a block diagram of some of the constituent components of an electronic device in which the composite piezoelectric actuator disclosed herein may be implemented. Device  800  may be any one of several different types of consumer electronic devices, for example, any of those discussed in reference to  FIG. 8 . 
     In this aspect, electronic device  800  includes a processor  812  that interacts with camera circuitry  806 , motion sensor  804 , storage  808 , memory  814 , display  822 , and user input interface  824 . Main processor  812  may also interact with communications circuitry  802 , primary power source  810 , speaker  818  and microphone  820 . Speaker  818  may be a micro speaker assembly within which the piezoelectric actuator unit  100  is implemented. The various components of the electronic device  800  may be digitally interconnected and used or managed by a software stack being executed by the processor  812 . Many of the components shown or described here may be implemented as one or more dedicated hardware units and/or a programmed processor (software being executed by a processor, e.g., the processor  812 ). 
     The processor  812  controls the overall operation of the device  800  by performing some or all of the operations of one or more applications or operating system programs implemented on the device  800 , by executing instructions for it (software code and data) that may be found in the storage  808 . The processor  812  may, for example, drive the display  822  and receive user inputs through the user input interface  824  (which may be integrated with the display  822  as part of a single, touch sensitive display panel). In addition, processor  812  may send an audio signal to speaker  818  to facilitate operation of speaker  818 . 
     Storage  808  provides a relatively large amount of “permanent” data storage, using nonvolatile solid state memory (e.g., flash storage) and/or a kinetic nonvolatile storage device (e.g., rotating magnetic disk drive). Storage  808  may include both local storage and storage space on a remote server. Storage  808  may store data as well as software components that control and manage, at a higher level, the different functions of the device  800 . 
     In addition to storage  808 , there may be memory  814 , also referred to as main memory or program memory, which provides relatively fast access to stored code and data that is being executed by the processor  812 . Memory  814  may include solid state random access memory (RAM), e.g., static RAM or dynamic RAM. There may be one or more processors, e.g., processor  812 , that run or execute various software programs, modules, or sets of instructions (e.g., applications) that, while stored permanently in the storage  808 , have been transferred to the memory  814  for execution, to perform the various functions described above. 
     The device  800  may include communications circuitry  802 . Communications circuitry  802  may include components used for wired or wireless communications, such as two-way conversations and data transfers. For example, communications circuitry  802  may include RF communications circuitry that is coupled to an antenna, so that the user of the device  800  can place or receive a call through a wireless communications network. The RF communications circuitry may include a RF transceiver and a cellular baseband processor to enable the call through a cellular network. For example, communications circuitry  802  may include Wi-Fi communications circuitry so that the user of the device  800  may place or initiate a call using voice over Internet Protocol (VOIP) connection, transfer data through a wireless local area network. 
     The device may include a speaker  818 . Speaker  818  may be a speaker which includes an actuator, such as that described in reference to  FIG. 1 . Speaker  818  may be an electric-to-acoustic transducer or sensor that converts an electrical signal input (e.g., an acoustic input) into sound. The circuitry  312 - 316  of  FIG. 3  may be electrically connected to processor  812  and power source  810  to facilitate the speaker operations, including diaphragm displacement measurement and temperature compensation as previously discussed. 
     The device  800  may further include a motion sensor  804 , also referred to as an inertial sensor, that may be used to detect movement of the device  800 , camera circuitry  806  that implements the digital camera functionality of the device  800 , and primary power source  810 , such as a built in battery, as a primary power supply. 
     While certain aspects have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that the invention is not limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those of ordinary skill in the art. For example, in one aspect, the piezoelectric bimorph beams, piezoelectric actuator unit and/or composite piezoelectric actuator unit disclosed herein may be considered 3-1 bimorph actuators in that electric field is in the 3 direction (e.g., direction parallel to a z-axis) and the beam expansion is in the 1 direction (e.g., direction parallel to an x-axis). In other aspects, however, the piezoelectric bimorph beams, piezoelectric actuator unit and/or composite piezoelectric actuator unit may be arranged so that the expansion is in a same direction as the electric field, in other words the expansion is in the 3 direction or direction parallel to a z-axis, and may therefore be considered 3-3 bimorph actuators. Moreover, the devices and processing steps disclosed herein may correspond to any type of electromechanical actuator and any application including, but not limited to, an actuator for moving one part with respect to another, for example to reproduce audio sound, for example in a home audio system, any consumer electronics device with audio capability, or an audio system in a vehicle (e.g., an automobile infotainment system). The description is thus to be regarded as illustrative instead of limiting. In addition, to aid the Patent Office and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims or claim elements to invoke 35 U.S.C. 112(f) unless the words “means for” or “step for” are explicitly used in the particular claim.

Metadata:
Filing Date: 20181212
Publication Date: 20221025
Grant Date: 20221025
Priority Date: 20180926
Inventors: CORONA, DANIEL
Crosby, Justin D.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04R7/08", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R7/22", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04R2499/11", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L41/083", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L41/0471", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L41/094", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10N30/2042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10N30/2041", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10N30/50", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10N30/50", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10N30/871", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10N30/2041", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04R17/00", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 69883689