Patent Publication Number: US-2023132801-A1

Title: Thin film loudspeaker and electronic device with loudspeaker

Description:
The present application is based on, and claims priority from, China application number 202111263561.7, filed Oct. 28, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     FIELD 
     The subject matter herein generally relates to a loudspeaker and an electronic device having the loudspeaker. 
     BACKGROUND 
     Electronic devices having sound playback function, such as mobile phones, computers, televisions, etc., need to be equipped with loudspeakers to realize the sound playback function. Traditional loudspeakers produce sound by mechanical vibration. A traditional loudspeaker includes many electronic components to realize mechanical vibration, resulting in a large overall volume. For small electronic devices (such as mobile phones) having traditional loudspeakers leaves little internal space for other components. Further, a traditional loudspeaker is limited by achievable vibration frequency and the sound volume is not high. Holes in a shell of the electronic device are usually required to facilitate a propagation of sound. 
     Thin film loudspeakers are widely used in various electronic devices due to their small size, however. sound generation by thin film loudspeakers is not optimal. Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of embodiments only, with reference to the attached figures. 
         FIG.  1    is an isometric view of an electronic device according to a first embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view of the electronic device in  FIG.  1    along line II-II. 
         FIG.  3    is an isometric view of a loudspeaker of the electronic device in  FIG.  1   . 
         FIG.  4    is a bottom view of a screen of the electronic device in  FIG.  1    and a piezoelectric layer of the loudspeaker in  FIG.  2   . 
         FIG.  5    is a variation curve of a volume of the loudspeaker in  FIG.  2    with the vibration frequency of the piezoelectric layer. 
         FIG.  6    is a bottom view of a screen and a piezoelectric layer of the electronic device according to a second embodiment of the present disclosure. 
         FIG.  7    is a variation curve of a volume of the loudspeaker with the vibration frequency of the piezoelectric layer in the second embodiment. 
         FIG.  8    is a bottom view of a screen and a piezoelectric layer of the electronic device according to a third embodiment of the present disclosure. 
         FIG.  9    is a variation curve of a volume of the loudspeaker with the vibration frequency of the piezoelectric layer in the third embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure. 
     The term “coupled” is defined as coupled, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently coupled or releasably coupled. The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. 
     First Embodiment 
     Referring to  FIG.  1   , an electronic device  100  includes a loudspeaker  10  to realize a sound playback function. The electronic device  100  may be a device with a sound playback function such as a mobile phone, a computer, a television, a radio, etc. In this embodiment, the electronic device  100  is a mobile phone. 
     The electronic device  100  defines a display area AA and a non-display area NA surrounding and connected to the display area AA. The display area AA is an area where an image can be displayed, the non-display area NA cannot display images. The electronic device  100  includes a housing  200  and a screen  300 . As shown in  FIG.  2   , the housing  200  and the screen  300  cooperate to form a closed receiving space  400 , and the loudspeaker  10  is located in the closed receiving space  400 . The screen  300  is partially located in the display area AA and the speaker  10  is at least partially located in the display area AA. That is, in the present embodiment, the loudspeaker  10  is arranged under the screen. 
     In this embodiment, the loudspeaker  10  is a thin film loudspeaker. The loudspeaker  10  includes piezoelectric material, and the loudspeaker  10  makes sound by mechanical vibration generated by the piezoelectric material under the action of an electric field. 
     As shown in  FIG.  3   , in this embodiment, the loudspeaker  10  includes a first electrode layer  11 , a second electrode layer  12 , and a piezoelectric layer  13  between the first electrode layer  11  and the second electrode layer  12 . The first electrode layer  11  and the second electrode layer  12  are arranged opposite to each other. The piezoelectric layer  13  is located in an area the first electrode layer  11  directly opposite to the second electrode layer  12 . The first electrode layer  11  and the second electrode layer  12  are made of conductive material, such as metal. The piezoelectric layer  13  is a thin film formed of piezoelectric material. In this embodiment, the piezoelectric layer  13  is formed of a flexible piezoelectric material, such as polyvinylidene fluoride (PVDF). In this embodiment, the piezoelectric layer  13  is composed of flexible PVDF, allowing the piezoelectric layer  13  to be cut into various shapes and durable. 
     The first electrode layer  11  is used to receive a first driving voltage, and the second electrode layer  12  is used to receive a second driving voltage. When the first driving voltage and the second driving voltage are different, a voltage difference is formed between the first electrode layer  11  and the second electrode layer  12 , and an electric field is formed between the first electrode layer  11  and the second electrode layer  12 . The piezoelectric layer  13  generates mechanical vibration under the electric field and moves the surrounding air to realize sound generation. 
     In this embodiment, both the first electrode layer  11  and the second electrode layer  12  are continuous as conductive structures. That is, the first electrode layer  11  and the second electrode layer  12  have no etching or patterns and no hollow areas. 
     Referring to  FIG.  1    to  FIG.  3   , in this embodiment, shapes of the first electrode layer  11 , the second electrode layer  12  and the piezoelectric layer  13  are the same. That is, the projections of the first electrode layer  11 , the second electrode layer  12  and the piezoelectric layer  13  on the screen  300  completely coincide. 
     In at least one embodiment, projections of the first electrode layer  11  and the second electrode layer  12  on the screen  300  completely coincide, and the projection of the first electrode layer  11  and the projection of the second electrode layer  12  on the screen  300  is greater than the projection of the piezoelectric layer  13  on the screen  300 . That is, the projection of the piezoelectric layer  13  on the screen  300  is completely overlapped by the projection of the first electrode layer  11  and the projection of the second electrode layer  12  on the screen  300 , and the projection area of the piezoelectric layer  13  on the screen  300  is less than the projection area of the first electrode layer  11  and the projection area of the second electrode layer  12  on the screen  300 . Near the edges of the first electrode layer  11  and the second electrode layer  12 , the electric field may be weak. In at least one embodiment, by setting the projection of the first electrode layer  11  and the projection of the second electrode layer  12  on the screen  300  to completely overlap the projection of the piezoelectric layer  13  on the screen  300 , problems of performance of the piezoelectric layer  13  in a weak field are avoided. 
     The electronic device  100  also includes a flexible circuit board (not shown) electrically connected to both the first electrode layer  11  and the second electrode layer  12  to apply the first driving voltage to the first electrode layer  11  and the second driving voltage to the second electrode layer  12 . 
     By changing a voltage difference between the first electrode layer  11  and the second electrode layer  12 , the vibration frequency of the piezoelectric layer  13  can be changed, and the volume of the loudspeaker  10  can also be changed. 
     In this embodiment, the first driving voltage on the first electrode layer  11  keeps constant, and the voltage difference between the first electrode layer  11  and the second electrode layer  12  is changed by changing the second driving voltage on the second electrode layer  12 . 
     In at least one embodiment, the second driving voltage on the second electrode layer  12  may keep constant, and the voltage difference between the first electrode layer  11  and the second electrode layer  12  may be changed by changing the first driving voltage on the first electrode layer  11 . Alternatively in at least one embodiment, both the first driving voltage and the second driving voltage may be changed to change the voltage difference between the first electrode layer  11  and the second electrode layer  12 . 
     In this embodiment, according to different shapes, sizes, materials, etc. of the piezoelectric layer  13 , the vibration frequency of the piezoelectric layer  13  can be different under the driving of the same voltage difference, resulting in different volume of the loudspeaker  10 . In this embodiment, the piezoelectric layer  13  is parallel to the screen  300 , and the shape of the piezoelectric layer  13  refers to the shape of the projection of the piezoelectric layer  13  on the screen  300 . 
     As shown in  FIG.  4   , in this embodiment, the shape of the piezoelectric layer  13  is rectangular. That is, the projection  130  of the piezoelectric layer  13  on the screen  300  is rectangular in shape. The long side of the piezoelectric layer  13  is defined as L and the short side is defined as W. In this embodiment, the electronic device  100  has a handset (not shown), and the edge  310  of the screen  300  is the edge closest to the handset. The geometric center of the projection  130  is defined as O, and the vertical distance between the geometric center O and the edge  310  is defined as D. 
     When the projection  130  has a fixed area, changing an aspect ratio of the projection  130  (that is, changing the L and W aspect ratio of the piezoelectric layer  13 ) changes the vibration frequency of the piezoelectric layer  13 , and the sound volume of the loudspeaker  10  at different aspect ratios and different vibration frequencies are detected. In this embodiment, the closer that the projection  130  can be to a 1:1 aspect ratio, the better the sound generation effect of the loudspeaker  10 . 
     The horizontal axis of  FIG.  5    represents the vibration frequency (frequency/Hz) of the piezoelectric layer  13 , and the vertical axis represents the sound volume (SPL/DB) of the loudspeaker  10 .  FIG.  5    shows the variation curve of sound volume with vibration frequency at three values of distance D. In  FIG.  5   , curve a represents the variation curve of sound volume with vibration frequency when d = 5 mm, curve b represents the variation curve of sound volume with vibration frequency when d=50 mm, and curve c represents the variation curve of sound volume with vibration frequency when d=55 mm. As can be seen from  FIG.  5   , the greater the distance D, the better the sound generation effect of the loudspeaker  10 . That is, the greater the distance between the loudspeaker  10  and the edge  310  closest to the handset on the screen  300 , the better the sound generation effect of the loudspeaker  10 . 
     The electronic device  100  of the present embodiment saves space in the electronic device  100  and miniaturizing and lightening the electronic device  100  by using a thin-film loudspeaker  10 . By setting the size and position of the piezoelectric layer  13  in the loudspeaker  10 , the sound generation effect of the loudspeaker  10  is improved (the volume is higher when driven by the same driving voltage). 
     Second Embodiment 
     For convenience of description, the same elements in the second embodiment and the first embodiment adopt the same symbols. A main difference between the electronic device in this embodiment and the electronic device  100  in the first embodiment is the different shape of the piezoelectric layer  13  of the loudspeaker in the electronic device. 
     As shown in  FIG.  6   , in this embodiment, the piezoelectric layer  13  is a rectangle with a chamfer. That is, the projection  130  of the piezoelectric layer  13  on the screen  300  is shaped as a rectangle with chamfer. That is, the projection shape of the piezoelectric layer  13  on the screen  300  is rectangular, and each adjacent two edges are connected by an arc  131  rather than a right angle. 
     In this embodiment, the two adjacent edges being connected by an arc  131  rather than by a right angle allows the two adjacent edges to connect smoothly. When the piezoelectric layer  13  mechanically vibrates under the electric field, the two adjacent edges connect smoothly, so that the obstruction against vibration of the connection area of the two adjacent edges being at right angles is reduced by having the arc  131  instead. 
     Therefore, when the voltage differences on both sides of the piezoelectric layer  13  are the same, compared with the first embodiment in which the two adjacent edges are connected by the right angle, the present embodiment using the arc  131  connections increases the vibration frequency and the volume of the piezoelectric layer  13 . That is, in this embodiment, the two adjacent edges of the piezoelectric layer  13  are connected by the arc  131 . 
     In this embodiment, a radius r1 of the arc  131  between each adjacent two edges is the same. In this embodiment, the radius r1 is 20 mm, and three variation curves of the sound volume with the vibration frequency are drawn when the distance D is taken as three values of D. In  FIG.  7   , curve a is a curve of sound volume varying with vibration frequency when d=45 mm, curve b is a curve of sound volume varying with vibration frequency when d=50 mm, and curve c is a curve of sound volume varying with vibration frequency when d=55 mm. A horizontal axis of  FIG.  7    represents the vibration frequency (frequency/Hz) of the piezoelectric layer  13 , and the vertical axis represents the sound volume (SPL/DB) of the loudspeaker  10 . As can be seen from  FIG.  7   , the greater the distance D, the better the sound generation effect of the loudspeaker  10 . That is, the greater the distance between the loudspeaker  10  and the edge  310  closest to the handset on the screen  300 , the better is the sound generation effect of the loudspeaker  10 . 
     The electronic device of the present embodiment realizes all the beneficial effects of the electronic device  100  in the first embodiment. In this embodiment, the two adjacent edges of the piezoelectric layer  13  are connected by the arc  131 , which is conducive to further improving the sound generation effect of the loudspeaker. 
     Third Embodiment 
     A main difference between the electronic device in this embodiment and the electronic device  100  in the first embodiment is in the different shape of the piezoelectric layer  13  of the loudspeaker in the electronic device. 
     As shown in  FIG.  8   , in this embodiment, the piezoelectric layer  13  is circular. That is, a projection  130  of the piezoelectric layer  13  on the screen  300  is circular in shape. When the piezoelectric layer  13  is circular, the overall contour of the piezoelectric layer  13  is smoother than when the piezoelectric layer  13  is rectangular with chamfer. Therefore, compared with the second embodiment, the present embodiment further improves the sound generation effect of the loudspeaker. 
     In this embodiment, a radius of the piezoelectric layer  13  is r2. The radius r2 is 28 mm, and three variation curves of the sound volume with the vibration frequency are drawn when the distance D is taken as three values of D. In  FIG.  9   , curve a is a curve of sound volume varying with vibration frequency when d=45 mm, curve b is a curve of sound volume varying with vibration frequency when d=50 mm, and curve c is a curve of sound volume varying with vibration frequency when d=55 mm. A horizontal axis of  FIG.  9    represents the vibration frequency (frequency/Hz) of the piezoelectric layer  13 , and the vertical axis represents the sound volume (SPL/DB) of the loudspeaker  10 . As can be seen from  FIG.  9   , when the distance d=50 mm, the sound generation effect of loudspeaker  10  is better. 
     The electronic device of this embodiment can realize all the beneficial effects of the electronic device in the second embodiment. The present embodiment is conducive to further improving the sound generation effect of the speaker by setting the piezoelectric layer  13  as circular. 
     In other embodiments, the piezoelectric layer  13  may be a shape with a smooth outer contour rather than a circle and a rectangle with a chamfer. That is, the projection  130  of the piezoelectric layer  13  on the screen  300  may be other shapes having a smooth outer contour. In the present embodiment, the outer contour of the piezoelectric layer  13  is the outer contour of the projection pattern of the piezoelectric layer  13  on a plane parallel to the screen  300  (or parallel to the first or second electrode layers  11  and  12 ). 
     The “smooth outer contour” described in the present disclosure, that is, the outer contour of the piezoelectric layer  13 , does not have sharp corners. In some embodiments, the projection of the outer contour of the piezoelectric layer  13  on the screen  300  is a closed curve, such as an ellipse, a circle in the third embodiment, or other irregular shape formed by the enclosure of the closed curve. In some embodiments, the projection of the outer profile of the piezoelectric layer  13  on the screen  300  includes at least one curved line segment and at least one straight line segment alternatively connected, such as the rectangle with chamfer described in the second embodiment (the rectangle with chamfer in the second embodiment can be regarded as being connected by the end of four curved segments and four straight segments in turn) or other irregular shape surrounded by curved line segments and straight line segments. 
     Due to sharp corners being a large obstruction against vibration, the piezoelectric layer  13  in the disclosure has a smooth outer contour, which is conducive to reducing the vibration obstruction of the low-voltage electric layer  13 , so as to improve the sound generation effect of the loudspeaker  10  where the piezoelectric layer  13  is located. 
     It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.