Abstract:
A sensor able to detect shearing forces as well as simple pressure includes a substrate, a support secured to the substrate, and shear force sensing unit located at an exterior surface of the support facing away from the substrate. The support can be elastically deformed in proportion to the shearing force or pressure. The shear force sensing unit includes first piezoelectric films on outer opposing shoulders of each support, the first piezoelectric film being elastically deformed with the support and outputting a signal accordingly. The magnitude of simple pressure is recorded by similar deformation of a second piezoelectric film entirely covering its support.

Description:
FIELD 
     The subject matter herein generally relates to sensors, and particularly, to a sensor capable of sensing a shear force. 
     BACKGROUND 
     A piezoelectric sensor is configured to elastically deform and thereby generate a voltage when pressure is applied to the piezoelectric sensor. Additionally, the piezoelectric sensor can also elastically deform when a voltage is applied to the piezoelectric sensor. The piezoelectric sensor can have one or more piezoelectric film located therein. The piezoelectric film can itself respond such that when it is elastically deformed it generates a voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementations of the present technology will now be described, by way of example only, with reference to the attached figures. 
         FIG. 1  is a diagrammatic view of an embodiment of a sensor capable of sensing a shear force. 
         FIG. 2  is an isometric view of a support included in the sensor of  FIG. 1 . 
         FIG. 3  is cross-sectional view taken along line III-III of  FIG. 2 . 
         FIG. 4  is a diagrammatic view showing the support of  FIG. 2  before and after a shear force F 1  is applied. 
         FIG. 5  is cross-sectional view taken along line IV-IV of  FIG. 2 . 
         FIG. 6  is a diagrammatic view showing the support of  FIG. 2  before and after a pressure F 2  is applied. 
         FIG. 7  is similar to  FIG. 1 , but showing a sensor of another 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 can 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 “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. 
       FIG. 1  illustrates an embodiment of a sensor  1  capable of sensing a shear force and electrically connected to a mobile terminal  2 . The mobile terminal  2  can be a tablet computer or a cell phone. The sensor  1  includes a substrate  10  and at least one support  20  located on and secured to the substrate  10 . Each support  20  is a three-dimensionally arched structure which can be elastically deformed. In at least one embodiment, the substrate  10  is a printed circuit board (PCB), and more specifically, the substrate  10  can be a flexible printed circuit board (FPC). Each support  20  is made of stainless steel. The sensor  1  further includes a casing  30  located on the substrate  10 . The substrate  10  and the casing  30  cooperatively form a receiving space  100  for receiving each support  20 . The substrate  10  further includes a vibrator  11  and a processor  12  located on and secured to the substrate  10 . 
       FIG. 2  illustrates that each support  20  includes two opposite flange portions  201  and an arched portion  202  located between the two flange portions  201 . Each support  20  is secured to the substrate  10  via the two flange portions  201 . The arched portion  202  is arched away from the substrate  10 , thereby forming a space  2020  between the arched portion  202  of each support  20  and the substrate  10 . 
     An exterior surface  2000  of each support  20  facing or positioned away from the substrate  10  includes at least one shear force sensing unit  21 . In at least one embodiment, the exterior surface  2000  of each support  20  can further include at least one pressure sensing unit  22 . Each of the shear force sensing unit  21  and the pressure sensing unit  22  is connected to wires  2210 . 
       FIG. 3  illustrates that each shear force sensing unit  21  includes a first piezoelectric film  210  sandwiched between two first electrodes  211 . The first piezoelectric film  210  partially covers the support  20 , with an upper end being secured to a top point of the arched portion  202  and a lower end being secured to a flange portion  201  of the support  20 . As such, each shear force sensing unit  21  is three-dimensionally arched. 
       FIG. 4  illustrates that when a shear force F 1  is applied to the support  20 , the support  20  is elastically deformed along a direction substantially parallel to the substrate  10  (that is, along −X or +X direction,  FIG. 4  showing the support  20  being elastically deformed along +X direction), causing an elastic deformation in the first piezoelectric film  210  of each shear force sensing unit  21 . The first piezoelectric film  210  outputs a signal corresponding to a degree of deformation thereof via one of the first electrodes  211 . The output signal can be an electrical vibration corresponding to a vibration produced in the first piezoelectric film  210 . The output signal can also be a voltage signal. 
     In at least one embodiment, each support  20  includes two shear force sensing units  21  (shown in  FIG. 2 ). Two top points of the arched portion  202  with a distance between them anchor the upper ends of the first piezoelectric films  210  and two opposing flange portions  201  of the support  20  anchor the lower ends of the first piezoelectric films  210 . As such, the first piezoelectric films  210  of the two shear force sensing units  21  can be elastically deformed in opposing directions parallel to the substrate  10  (that is, along −X and +X directions) when shear forces F 1  are applied along the two directions. 
       FIG. 5  illustrates that each pressure sensing unit  22  includes a second piezoelectric film  220  sandwiched between two second electrodes  221 . The second piezoelectric film  220  partially covers the support  20 , with each end being secured to an opposing flange portion  201  of a support  20 . As such, each pressure sensing unit  22  is also three-dimensionally arched. 
       FIG. 6  illustrates that when a pressure F 2  is applied to the support  20 , the support  20  is elastically deformed toward the substrate  10  (that is, substantially along −Z direction), causing an elastic deformation in the second piezoelectric film  220  of each pressure sensing unit  22 . The second piezoelectric film  220  outputs a signal corresponding to a degree of deformation thereof via one of the second electrodes  221 . The output signal can be an electrical vibration corresponding to a vibration produced in the second piezoelectric film  220 . The output signal can also be a voltage signal. The output signal can also be a voltage signal. The casing  30  (shown in  FIG. 1 ) is made of elastic material such as rubber or polyformaldehyde, and can effectively transmit a representation of the shear force F 1  and the pressure F 2  to each shear force sensing unit  21  and each pressure sensing unit  22 . 
     The first piezoelectric film  210  and the piezoelectric film  220  can be made of organic piezoelectric material. The organic piezoelectric material is selected from a group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polytetrafluoro ethylene (PFA), polychlorotrifluoro ethene (PCTFE), polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET). The first piezoelectric film  210  and the second piezoelectric film  220  can also be made of inorganic material such as lead zirconate titanate (PZT). The first electrodes  211  and the second electrodes  221  can be made of a material selected from a group consisting of gold (Au), silver (Ag), platinum(Pt), aluminum (Al), nickel (Ni), copper (Cu), titanium (Ti), and selenium (Se). 
     In at least one embodiment, the output signal from the shear force sensing unit  21  and the pressure sensing unit  22  is an electrical vibration. In this embodiment, referring to  FIG. 1 , the vibrator  11  is electrically connected to one end of the first electrode  211  of each shear force sensing unit  21  via the wire  2110 , and one end of the second electrode  221  of each pressure sensing unit  22  via the wire  2210 . The processor  12  is electrically connected to the opposite end of the first electrode  211  of each shear force sensing unit  21  via a wire  2110 , and the opposite end of the second electrode  221  of each pressure sensing unit  22  via a wire  2210 . The vibrator  31  outputs a reference electrical vibration with a reference frequency to each shear force sensing unit  21  and each pressure sensing unit  22 . If one shear force sensing unit  21  or one pressure sensing unit  22  is elastically deformed, the shear force sensing unit  21  or the pressure sensing unit  22  will change the frequency of the reference electrical vibration. The processor  12  obtains an actual vibration from each shear force sensing unit  21  and each pressure sensing unit  22 , and determines whether the actual frequency of the obtained actual electrical vibration equals the reference frequency. If so, the processor  12  determines that no deformation is being experienced by the first piezoelectric film  210  or the second piezoelectric film  220  (that is, that no shear force F 1  or pressure F 2  is applied to the shear force sensing unit  21  and the pressure sensing unit  22 ). Otherwise, the processor  12  calculates a difference between the actual frequency and the reference frequency and calculates a value of the shear force F 1  or the pressure F 2  being applied according to calculated difference. The processor  12  then outputs the calculated value of the shear force F 1  or the pressure F 2  to the mobile terminal  2 . 
     In another embodiment, the output signal from the shear force sensing unit  21  and the pressure sensing unit  22  is a voltage signal. The value of the voltage signal is proportional to the value of the shear force F 1  or the pressure F 2 . In the embodiment illustrated by  FIG. 7 , the vibrator  11  is omitted. The substrate  10  further includes a signal amplifier  13 . The signal amplifier  13  is electrically connected to the first electrode  211  of each shear force sensing unit  21  via a wire  2110 , and is electrically connected to the second electrode  221  of each pressure sensing unit  22  via a wire  2210 . The signal amplifier  13  obtains the voltage signal from each shear force sensing unit  21  and each pressure sensing unit  22 , and amplifies the obtained voltage signal. The processor  12  filters the amplified voltage signal, and calculates the value of the shear force F 1  or the pressure F 2  being applied according to the voltage signal after filtered. The processor  12  then outputs the calculated value of the shear force F 1  or the pressure F 2  to the mobile terminal  2 . 
     In at least one embodiment, the sensor  1  includes two supports  20 . The flange portions  201  of the two supports  20  are perpendicular to each other (shown in  FIG. 1 ). That is, the first piezoelectric films  210  of the shear force sensing units  21  located on the two supports  20  can be elastically deformed along four different directions substantially parallel to the substrate  10  (that is, along −X, +X, −Y, and +Y directions). Thus, the shear force sensing units  21  located on the two supports  20  can also sense shear forces F 1  along the same four different directions. 
     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.