Patent Publication Number: US-2022218279-A1

Title: Photoplethysmography sensor and terminal

Description:
This application claims priority to Chinese Patent Application No. 201910521035.2, filed with the China National Intellectual Property Administration on Jun. 17, 2019 and entitled “PHOTOPLETHYSMOGRAPHY SENSOR AND TERMINAL”, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     Embodiments relate to the field of intelligent terminal technologies, and in particular, to a photoplethysmography sensor and a terminal. 
     BACKGROUND 
     A photoplethysmography sensor can detect a sport heart rate of a human body by using a photoplethysmography (photoplethysmograph or PPG) technology, can detect a difference of intensity of light reflected after absorption performed by blood and tissue of a human body, and record changes of a vessel volume during a cardiac cycle, so that a heart rate can be calculated from a pulse waveform. The photoplethysmography sensor is an application of an infrared nondestructive detection technology in biomedicine. 
     The photoplethysmography sensor is disposed in an existing smartwatch or smart band, and heart rate detection may be performed by using the photoplethysmography sensor. The photoplethysmography sensor includes an optical device and a photoelectric sensor. Light may be emitted to a human body by using the optical device, and light reflected after absorption performed by blood and tissue of the human body is detected by using the photoelectric sensor to detect a change of a heart rate of a wearer. 
     However, the light emitted by the optical device is very likely to leak, and consequently a light crossover between the optical device and the photoelectric sensor is severe. This affects heart rate measurement precision and affects user experience. 
     SUMMARY 
     Embodiments provide a photoplethysmography sensor and a terminal, so as to ensure heart rate measurement precision and also resolve a problem of a light crossover inside the photoplethysmography sensor. 
     To achieve the foregoing objectives, the following solutions are used in the embodiments: 
     According to a first aspect of the embodiments, a photoplethysmography sensor is provided, including: a housing, a cover plate, an optical device configured to emit light outwards, and a photoelectric sensor configured to receive an external optical signal. The housing and the cover plate form an enclosed space, and the optical device and the photoelectric sensor are accommodated in the enclosed space. The cover plate includes a first area used by the optical device to emit the light outwards and a second area used by the photoelectric sensor to receive the external optical signal. The cover plate further includes a third area, a shielding structure is disposed on the third area, and the shielding structure is configured to isolate light between the optical device and the photoelectric sensor. Therefore, the shielding structure is disposed in the third area, thereby improving isolation between the optical device and the photoelectric sensor, avoiding a light crossover between the optical device and the photoelectric sensor, improving measurement precision of the photoelectric sensor, and improving user experience. 
     In an optional implementation, the photoplethysmography sensor further includes a light insulating plate, the light insulating plate is disposed around the optical device, and one end of the light insulating plate is connected to the cover plate. Therefore, the light insulating plate may be configured to isolate the optical device and the photoelectric sensor, thereby further avoiding the light crossover between the optical device and the photoelectric sensor in the enclosed space. 
     In an optional implementation, the shielding structure includes a groove, and the groove is disposed around the first area. Therefore, a thickness of the cover plate at a position of the groove is less than a thickness of the cover plate at another position, and a light propagation path changes at the position of the groove, thereby reducing total reflection of light at the groove, and improving the light crossover between the optical device and the photoelectric sensor. 
     In an optional implementation, a depth of the groove is 0.002 mm to 0.2 mm Therefore, a proper groove depth may be selected provided that strength of the cover plate is not affected, and this is conducive to improving the light crossover between the optical device and the photoelectric sensor, and also improving the isolation between the optical device and the photoelectric sensor. 
     In an optional implementation, an inner surface of the groove is provided with a grain. Therefore, roughness of the inner surface of the groove is increased, a specular reflection phenomenon at the position of the groove is reduced, the light crossover between the optical device and the photoelectric sensor is further improved, and the isolation between the optical device and the photoelectric sensor is improved. 
     In an optional implementation, the inner surface of the groove is covered with a coating for absorbing light. Therefore, when light emitted by the optical device reaches the position of the groove, the light is absorbed by the coating, thereby avoiding the light crossover between the optical device and the photoelectric sensor. 
     In an optional implementation, the third area is also covered with a coating for absorbing light, and the coating is located on a side, of the third area, facing the housing. Therefore, when light emitted by the optical device reaches the third area, the light is absorbed by the coating, thereby preventing the light of the optical device from leaking out of the housing through the cover plate, and avoiding user experience deterioration caused by blinding due to light leakage. 
     In an optional implementation, the coating is black ink. Therefore, light that reaches the coating can be fully absorbed, a light shielding effect can be enhanced, and the cover plate does not need to be carved, thereby ensuring completeness of appearance of the cover plate. 
     In an optional implementation, the shielding structure includes a light-shielding ring, the light-shielding ring is disposed around the first area, the light-shielding ring is carved through a laser process, and the light-shielding ring is injected with a light-shielding material. Therefore, while impact-resistance performance of the cover plate is ensured, the light crossover between the optical device and the photoelectric sensor is improved. 
     In an optional implementation, the housing includes a bottom housing and a convex part, the bottom housing and the convex part are integrally formed, the cover plate is flat-shaped, the convex part is provided with a first opening, and the cover plate is clamped to the first opening. Therefore, the housing uses an integrally-forming process, has higher strength, and can withstand external impact, and the cover plate may be formed into a flat shape, so that a height of the cover plate is less than a height of the surrounding housing, and the surrounding housing can bear as much external impact as possible, thereby improving the impact-resistance performance of the cover plate. 
     In an optional implementation, the housing includes a bottom housing, the bottom housing is provided with a second opening, the cover plate is convex, and the cover plate is clamped to the second opening. Therefore, the housing has a simple structure, and this reduces processing difficulty, and is conducive to mass production. 
     In an optional implementation, a recess is provided on a side of the cover plate facing the optical device, and the optical device is disposed in the recess. Therefore, a thickness of the cover plate at the recess is relatively small, a height difference is generated between the area of the cover plate at the recess and a cover plate area corresponding to the photoelectric sensor, and light emitted by the optical device may be directly emitted through the cover plate at the recess, thereby further avoiding the light crossover between the optical device and the photoelectric sensor, and improving the isolation between the optical device and the photoelectric sensor. 
     In an optional implementation, a side of the cover plate facing away from the optical device is provided with a planar face, and the planar face is opposite to the recess. Therefore, the cover plate at the recess is set to a flat shape, so that a height of the position may be less than a height of a surrounding cover plate, and a surrounding thick cover plate may bear as much external impact as possible, thereby improving the impact-resistance performance of the cover plate. 
     In an optional implementation, the optical device is fastened in the recess through glue injection. Therefore, the optical device and the cover plate are injection-molded into an integrated module, thereby improving strength of the cover plate at the position of the recess, enhancing the impact-resistance performance of the cover plate, improving stability of the optical device, and avoiding fall-off of the optical device caused by external impact. 
     In an optional implementation, the second area includes one or more light transmission windows, each light transmission window corresponds to one photoelectric sensor, and the light transmission windows are uniformly arranged around the first area. Therefore, the photoelectric sensor can fully receive light emitted from the optical device and reflected from a to-be-detected part of a human body, thereby improving working efficiency of the photoplethysmography sensor. 
     In an optional implementation, a material of the housing is ceramic or plastic. Therefore, the housing may be integrally formed by injection molding, thereby enhancing strength of the housing, and improving impact-resistance performance of the housing. 
     In an optional implementation, a material of the cover plate is sapphire or toughened glass. Therefore, the strength of the cover plate is enhanced, and the impact-resistance performance of the cover plate is improved. 
     According to a second aspect of the embodiments, a terminal is provided. The terminal includes a body and a fastening part, the body includes the photoplethysmography sensor as described above, the fastening part is configured to fasten the body to a to-be-detected body part of a user, and, when the body is fastened to the to-be-detected body part of the user, the cover plate of the photoplethysmography sensor faces the to-be-detected body part. Therefore, the terminal uses the photoplethysmography sensor. This avoids blinding due to light leakage, avoids an internal light crossover phenomenon, and improves user experience. 
     In an optional implementation, the terminal is a smartwatch, a smart band, or a smartphone. Therefore, the photoplethysmography sensor is integrated into the terminal, and a heart rate change status of a wearer can be detected provided that the wearer wears the terminal, thereby improving user experience. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic structural diagram of a terminal according to an embodiment; 
         FIG. 2  is an exploded view of a photoplethysmography sensor according to an embodiment; 
         FIG. 3  is a cross-sectional view of a photoplethysmography sensor according to an embodiment; 
         FIG. 4  is a schematic structural diagram of a cover plate according to an embodiment; 
         FIG. 5  is a schematic structural diagram of another cover plate according to an embodiment; 
         FIG. 6  is a schematic structural diagram of another cover plate according to an embodiment; 
         FIG. 7  is a schematic structural diagram of another cover plate according to an embodiment; 
         FIG. 8  is a schematic structural diagram of another photoplethysmography sensor according to an embodiment; 
         FIG. 9  is a schematic structural diagram of another photoplethysmography sensor according to an embodiment; and 
         FIG. 10  is a structural block diagram of a terminal according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following describes the solutions in the embodiments with reference to the accompanying drawings in the embodiments. To clearly describe the solutions in the embodiments, terms such as “first” and “second” are used in the embodiments to distinguish between same items or similar items that have basically the same functions or purposes. A person of ordinary skill in the art may understand that the terms such as “first” and “second” do not limit a quantity or an execution sequence, and the terms such as “first” and “second” do not mean being definitely different either. 
     To facilitate understanding of a photoplethysmography sensor provided in the embodiments, the following first describes an application scenario of the photoplethysmography sensor. The photoplethysmography sensor may be applied to a terminal, for example a common electronic device such as a mobile phone, a tablet computer, a digital camera, or a wearable device. An optical device in the photoplethysmography sensor may emit light outwards, a part of the light is reflected after absorption performed by blood and tissue of a human body of a user, and a photoelectric sensor in the photoplethysmography sensor may receive light reflected from the human body of the user. Further, a change status such as a heart rate of a wearer can be determined based on reflected light received by the photoelectric sensor. 
     Usually, in the terminal, the optical device and the photoelectric sensor are disposed adjacent to each other. When the optical device is used, light emitted by the optical device is likely to leak to cause blinding, and this affects user experience. In addition, a light crossover between the optical device and the photoelectric sensor is severe, and this affects power consumption of the entire system of the terminal and heart rate measurement precision. 
     To this end, an embodiment provides an improved terminal. 
     The following describes the terminal provided in this embodiment with reference to the accompanying drawings.  FIG. 1  is a schematic structural diagram of a terminal according to an embodiment. As shown in  FIG. 1 , the terminal  10  includes a body  11  and a fastening part  12 . The body  11  is fixedly connected to the fastening part  12 . The body  11  includes a photoplethysmography sensor, the fastening part is configured to fasten the body  11  to a to-be-detected body part of a user, and when the body  11  is fastened to the to-be-detected body part of the user, the photoplethysmography sensor faces the to-be-detected body part. 
     For example, the terminal is a smartwatch, the body is a watch face, the fastening part is a watch band, the photoplethysmography sensor is disposed on a back surface of the watch face, and, when the user uses the smartwatch, a human body of the user is in contact with the back surface of the watch face. The photoplethysmography sensor faces the to-be-detected body part of the user. 
     Therefore, the photoplethysmography sensor is integrated into the smartwatch, and a heart rate change status of a wearer can be detected provided that the wearer wears the terminal, thereby improving user experience. 
       FIG. 2  is an exploded view of a photoplethysmography sensor according to an embodiment.  FIG. 3  is a cross-sectional view of a photoplethysmography sensor according to an embodiment. As shown in  FIG. 2  and  FIG. 3 , the photoplethysmography sensor  100  includes a housing  102 , a cover plate  101 , an optical device  103 , configured to emit light outwards, and a photoelectric sensor  105 , configured to receive an external optical signal. The housing  102  and the cover plate  101  form enclosed space, and the optical device  103  and the photoelectric sensor  105  are accommodated in the enclosed space. 
     Specific structures of the optical device  103  and the photoelectric sensor  105  are not limited in this embodiment. For example, the optical device  103  may be, for example, a light emitting diode, and the photoelectric sensor  105  may be, for example, a photodiode. When the photoplethysmography sensor works, the optical device may emit light outwards, a part of the light is reflected after absorption performed by blood and tissue of a human body of a user, and the photoelectric sensor may receive light reflected from the human body of the user. 
     A specific material of the cover plate  101  is not limited in this embodiment, provided that light transmission requirements of the optical device  103  and the photoelectric sensor  105  can be met. In a specific implementation, a material of the cover plate  101  is sapphire or toughened glass. The sapphire and the toughened glass have good light transmission and relatively high strength and improve impact-resistance performance of the cover plate while ensuring the light transmission. 
     A specific structure of the cover plate  101  is not limited in this embodiment. The cover plate  101  includes a first surface and a second surface that are opposite to each other. For example,  FIG. 4  shows the first surface of the cover plate  101 , and  FIG. 5 ,  FIG. 6 , and  FIG. 7  show the second surface of the cover plate. The first surface faces the housing  102  and forms the enclosed space with the housing  102 , and the second surface faces away from the housing  102 . 
     As shown in  FIG. 4 ,  FIG. 5 ,  FIG. 6 , and  FIG. 7 , the cover plate  101  may be divided into a first area  1011  and a second area  1012  based on fields of vision (FOV) of the optical device  103  and the photoelectric sensor  105  on the cover plate  101 . For example, a field of vision of the optical device  103  on the cover plate  101  is the first area  1011 , and the optical device  103  transmits an optical signal through the first area  1011 . A field of vision of the photoelectric sensor  105  on the cover plate  101  is the second area  1012 , and the photoelectric sensor  105  receives an optical signal through the second area  1012 . 
     There are relatively high requirements on light transmission of the first area  1011  and the second area  1012 . A structure that can enhance light transmission of the two may be disposed in the first area  1011  and the second area  1012 , or no processing needs to be performed. 
     A quantity, a shape, and a position of the first area  1011  and the second area  1012  are not limited in this embodiment. The first area  1011  includes, for example, one first light transmission window, the second area  1012  includes, for example, one or more second light transmission windows, and the second light transmission windows are disposed around the first light transmission window. The first light transmission window is, for example, circular or square, and the second light transmission window is in a concentric ring shape, a square shape, or an irregular shape. 
     For example, as shown in  FIG. 4 , the first area  1011  includes, for example, one first light transmission window, the first light transmission window is circular, and the first light transmission window is located in the center of the cover plate  101 . The second area  1012  includes four second light transmission windows, the second light transmission windows are in an irregular shape, each second light transmission window corresponds to one photoelectric sensor  105 , and the second light transmission windows are evenly arranged around the first light transmission window. 
     Therefore, the photoelectric sensor can fully receive light emitted from the optical device and reflected from a to-be-detected part of a human body, thereby improving working efficiency of the photoplethysmography sensor. 
     As shown in  FIG. 5 , the first area  1011  includes one first light transmission window, the first light transmission window is circular, and the first light transmission window is located in the center of the cover plate  101 . The second area  1012  includes six second light transmission windows, the second light transmission windows are in an irregular shape, and the second light transmission windows are evenly arranged around the first light transmission window. 
     As shown in  FIG. 6 , the first area  1011  includes one first light transmission window, the first light transmission window is circular, and the first light transmission window is located in the center of the cover plate  101 . The second area  1012  includes eight second light transmission windows, the second light transmission windows are in an irregular shape, and the second light transmission windows are evenly arranged around the first light transmission window. 
     As shown in  FIG. 7 , the first area  1011  includes one first light transmission window, the first light transmission window is square, and the first light transmission window is located in the center of the cover plate  101 . The second area  1012  includes four second light transmission windows, the second light transmission windows are square, and the second light transmission windows are evenly arranged around the first light transmission window. 
     The cover plate  101  further includes, for example, a third area  1013 , and the third area  1013  is an area on the cover plate  101  other than the first area  1011  and the second area  1012 . For example, the cover plate  101  is made of glass. When light emitted by the optical device  103  reaches the cover plate  101 , due to different refractive indexes of the glass and air, a total reflection phenomenon occurs in the cover plate  101 . In addition, because a surface of the cover plate  101  is relatively smooth, specular reflection occurs. 
     The total reflection phenomenon and the specular reflection phenomenon cause a part of the light emitted by the optical device  103  to directly enter a collection range of the photoelectric sensor  105  without passing through the to-be-detected human body part, thereby affecting detection accuracy of the photoelectric sensor  105 . 
     In order to improve measurement precision of the photoelectric sensor  105 , for example, a shielding structure is disposed on the third area  1013 , and the shielding structure is configured to isolate light between the optical device  103  and the photoelectric sensor  105  to prevent light that reaches the first area  1011  of the cover plate  101  from entering the second area  1012  through the third area  1013 , and prevent light that reaches the second area  1012  from reaching the first area  1011  through the third area  1013 , thereby improving isolation between the optical device  103  and the photoelectric sensor  105 , and improving measurement precision of the photoelectric sensor  105 . 
     According to the photoplethysmography sensor provided in this embodiment, the shielding structure is disposed in the third area, so that the isolation between the optical device and the photoelectric sensor is improved, the light crossover between the optical device and the photoelectric sensor is avoided, the measurement precision of the photoelectric sensor is improved, and user experience is improved. 
     A specific structure of the shielding structure is not limited in this embodiment. In a specific implementation, as shown in  FIG. 4 ,  FIG. 5 ,  FIG. 6 , and  FIG. 7 , the shielding structure includes, for example, a groove  1014 . The groove  1014  is located between the first area  1011  and the second area  1012 , and the groove  1014  is disposed around the first area  1011 . Therefore, when light emitted by the optical device  103  reaches a position of the groove  1014 , a thickness of the cover plate  101  at the position of the groove  1014  is less than a thickness of the cover plate at another position, and a light propagation path changes at the position, thereby reducing total reflection of light at the groove  1014  and improving the light crossover between the optical device  103  and the photoelectric sensor  105 . 
     A specific structure of the groove  1014  is not limited in this embodiment. In a specific implementation, the groove  1014  is located in the third area  1013  of the first surface of the cover plate  101 . In another implementation, the groove  1014  is located in the third area  1013  of the second surface of the cover plate  101 . In other implementations, the groove  1014  is disposed in both the third area  1013  of the first surface and the third area  1013  of the second surface of the cover plate  101 , and the groove of the first surface and the groove of the second surface are opposite to each other. 
     A depth of the groove  1014  is, for example, 0.002 mm to 0.2 mm, and the groove  1014  may be formed on the cover plate  101  by, for example, laser carving or groove milling. Therefore, a proper groove depth may be selected provided that strength of the cover plate is not affected, and this is conducive to improving the light crossover between the optical device and the photoelectric sensor and improving the isolation between the optical device and the photoelectric sensor. 
     For example, an inner surface of the groove  1014  is provided with a grain. For example, a rough grained-surface ring is disposed on the inner surface of the groove  1014 , and this increases roughness of the inner surface of the groove  1014 , reduces a specular reflection phenomenon at the position of the groove  1014 , and further improves the light crossover between the optical device  103  and the photoelectric sensor  105 . 
     The inner surface of the groove  1014  is also covered with, for example, a coating for absorbing light, the coating may be in a relatively dark color such as black, and the coating may cover the inner surface of the groove  1014  by printing, evaporation, or spraying. For example, the coating is, for example, black ink. For example, the black ink may cover the inner surface of the groove  1014  by spraying. 
     A disposing range of the groove  1014  is not limited in this embodiment. For example, a range of the groove  1014  is less than or equal to a range of the third area  1013 . If the range of the groove  1014  is equal to the range of the third area  1013 , the groove  1014  is disposed in all the third areas  1013 . If the range of the groove  1014  is less than the range of the third area  1013 , all areas of the third area  1013  other than the groove  1014  are covered with, for example, a coating for absorbing light, and the coating may be formed by using the same material and process as those of the coating in the groove  1014 . The light crossover between the optical device  103  and the photoelectric sensor  105  is further improved, and the isolation between the optical device  103  and the photoelectric sensor  105  is improved. 
     As shown in  FIG. 4 , in an implementation, the coating covers the third area  1013  of the first surface of the cover plate  101 . Therefore, when light emitted by the optical device  103  reaches the third area  1013 , the light is absorbed by the coating, thereby avoiding the light crossover between the optical device  103  and the photoelectric sensor  105 , also preventing the light of the optical device  103  from leaking out of the housing  102  through the cover plate  101 , and avoiding user experience deterioration caused by blinding due to light leakage. 
     In another implementation, the third area  1013  of the second surface of the cover plate  101  is also covered with the coating. Therefore, incidence of other light in an external environment is avoided, impact of the external environment on the photoplethysmography sensor is reduced, and the measurement precision of the photoelectric sensor  105  is improved. 
     However, the cover plate at the position of the groove is relatively thin and impact-resistance performance is poor. To this end, an embodiment provides a new shielding structure. As shown in  FIG. 8 , the shielding structure includes, for example, a light-shielding ring  1015 , and the light-shielding ring is injected with a light-shielding material. For a specific position of the light-shielding ring  1015 , refer to the groove. Details are not described herein. Processing of the light-shielding ring includes, for example, the following steps: first, deep micro carving is performed on the cover plate  101  through a laser process, and then the black light-shielding material is injected to form a black ring-shaped light-shielding structure. In this way, while the impact-resistance performance of the cover plate is ensured, the light crossover between the optical device  103  and the photoelectric sensor  105  is improved. 
     In this embodiment, a disposing range of the light-shielding ring  1015  is not limited. For example, a range of the light-shielding ring  1015  is less than or equal to a range of the third area. If the range of the light-shielding ring  1015  is equal to the range of the third area  1013 , the foregoing light-shielding processing is performed on all the third areas. If the range of the light-shielding ring  1015  is less than the range of the third area  1013 , no processing may be performed on an area in the third area other than the light-shielding ring  1015 , or the area may be covered with a layer of coating for absorbing light as described above. 
     To further improve isolation of the photoplethysmography sensor, as shown in  FIG. 3 ,  FIG. 8 , and  FIG. 9 , for example, a light insulating plate  106  is further disposed in the housing  102 , and the light insulating plate  106  is disposed around the optical device  103 . One end of the light insulating plate  106  extends to a root of the optical device  103 , and the other end is connected to the cover plate  101 . 
     In an implementation, the light insulating plate  106  and the housing  102  are integrally formed. 
     In another implementation, the light insulating plate  106  is an independent part, and the light insulating plate  106  may be assembled around the optical device  103 . The light insulating plate is configured to isolate the optical device  103  and the photoelectric sensor  105 , so as to avoid a light crossover between the optical device  103  and the photoelectric sensor  105  in the enclosed space. 
     In this embodiment, a specific material of the light insulating plate is not limited. The light insulating plate may be made of any non-transparent material, provided that the light insulating plate may implement light blocking. 
     A structure of the housing  102  is not limited in this embodiment. In an implementation, as shown in  FIG. 3 , the housing  102  includes a bottom housing  1021  and a convex part  1022 . The bottom housing  1021  and the convex part  1022  are integrally formed. The cover plate  101  is flat-shaped, a first opening is disposed on the convex part  1022 , and the cover plate  101  is clamped to the first opening. 
     For example, a support component is further disposed on the convex part  1022  at a position of the first opening. For example, the cover plate  101  is fixedly connected to the support component in an adhesive dispensing manner. 
     For example, the bottom housing  1021  and the convex part  1022  may be integrally formed by injection molding without cutting or the like, thereby reducing processing costs of the part. However, the bottom housing  1021  and the convex part  1022  may be separately formed, and then assembled into a whole by using a lamination process, as desired. 
     In another implementation, as shown in  FIG. 9 , the housing  102  includes a bottom housing  1021 , a second opening is disposed on the bottom housing  1021 , the cover plate  101  is convex, and the cover plate  101  is clamped to the second opening. 
     For example, a support component is further disposed on the bottom housing  1021  at a position of the second opening. For example, the cover plate  101  is fixedly connected to the support component in an adhesive dispensing manner. 
     For example, the cover plate  101  may be integrally formed by injection molding, and a protrusion does not need to be disposed on the bottom housing  1021 , thereby reducing process difficulty. 
     Next, referring to  FIG. 9 , for example, a recess is further disposed on a side, of the cover plate  101 , facing the optical device  103 , and the optical device  103  is disposed in the recess. Therefore, a thickness of the cover plate at the recess is relatively small, a height difference is generated between the area of the cover plate at the recess and a cover plate area corresponding to the photoelectric sensor, and light emitted by the optical device may be directly emitted through the cover plate at the recess, thereby further avoiding the light crossover between the optical device and the photoelectric sensor, and improving the isolation between the optical device and the photoelectric sensor. 
     A side of the cover plate  101  facing away from the optical device  103  is provided with a planar face, and the planar face is opposite to the recess. Therefore, a position that is of the second surface of the cover plate  101  and that is opposite to the recess is flattened, so that a height of the position may be less than a height of a surrounding cover plate  101 , and a surrounding thick cover plate  101  may bear as much external impact as possible, thereby improving the impact-resistance performance of the cover plate  101 . 
     The optical device  103  is fastened in the recess through glue injection. For example, the optical device  103  may be glue-injected and sealed in the recess by using transparent adhesive. After solidification, the optical device  103  and the cover plate  101  form an integrated module, thereby improving strength of the cover plate  101  at the position of the recess, improving stability of the optical device  103 , and avoiding fall-off of the optical device  103  caused by external impact. 
     A material of the housing  102  is not limited in this embodiment, and a material of the housing  102  is ceramic or plastic. For example, the housing  102  may be integrally formed by injection molding. 
     Next, referring to  FIG. 2 , the photoplethysmography sensor further includes, for example, a PCB board  104 , and the circuit board is located in the enclosed space and fixedly disposed on the housing  102 . The optical device  103  and the photoelectric sensor  105  may be fastened onto the PCB  104 , for example, in a welding or cementing manner, where the PCB  104  may be a common printed circuit board. 
     In another implementation, the PCB includes, for example, a first PCB board and a second PCB board, the optical device is fastened onto the first PCB board, the photoelectric sensor is fastened onto the second PCB board, for example, the first PCB board is circular, and for example, the second PCB board is annular. The first PCB board is fastened onto the second PCB board, and the first PCB board is electrically connected to the second PCB board. 
       FIG. 10  is a structural block diagram of a terminal according to an embodiment. The terminal further includes a display screen  13 , at least one processor  14 , a communications bus  15 , at least one communications interface  16 , and a memory  17 . It may be understood that the terminal in  FIG. 10  is merely an example of the terminal and does not constitute any limitation on the terminal. The terminal may include more or fewer components than those shown in the figure, or combine some components, or have different components. Although not shown, the terminal may further include a battery, a camera, a Bluetooth module, a global positioning system (GPS) module, and the like. Details are not described herein. 
     The processor  14  is communicatively connected to the at least one communications interface  16 , the memory  17 , and the display screen  13  by using the communications bus  15 . The processor  14  may be a central processing unit (CPU), or may be another general purpose processor  14 , a digital signal processor  14  (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or another programmable logic device, a discrete gate or transistor logic device, or a discrete hardware component. The general-purpose processor  14  may be a microprocessor  14 , or the processor  14  may be any conventional processor  14 , or the like. The processor  14  is a control center of the terminal and connects all parts of the entire terminal by using various interfaces and lines. 
     The display screen  13  may be configured to display information entered by a user or information provided for a user, and various menus of the terminal. The display screen  13  may be in a form of a liquid crystal display (LCD), an organic light-emitting diode (OLED), or the like. 
     The communications bus  15  may include a path to transmit information between the foregoing components. 
     The communications interface  16  is any apparatus such as a transceiver, and is configured to communicate with another device or a communications network, such as the Ethernet, a radio access network (RAN), or a wireless local area network (WLAN). 
     The memory  17  may be configured to store a computer program and/or a module. The processor  14  implements various functions of the terminal by running or executing the computer program and/or the module stored in the memory  17  and invoking data stored in the memory  17 . The memory  17  may mainly include a program storage area and a data storage area. The program storage area may store an operating system, an application program (such as a sound playing function or an image playing function) that is required by a plurality of functions, and the like. The data storage area may store data (such as audio data or a phone book) that is created based on use of the terminal, and the like. In addition, the memory  17  may include a high-speed random access memory  17 , and may further include a non-volatile memory  17 , for example, a hard disk, a memory, a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, a plurality of magnetic disk storage devices  17 , a flash memory, or another volatile solid-state storage device  17 . The memory  17  may exist independently and be connected to the processor  14  by using the communications bus  15 . Alternatively, the memory  17  may be integrated with the processor  14 . 
     During specific implementation, in an embodiment, the processor  14  may include one or more CPUs, for example, a CPU  0  and a CPU  1  in the figure. 
     During specific implementation, in an embodiment, the terminal may include a plurality of processors  14 , for example, the processor  14  in the figure and a processor  141 . Each of these processors  14  may be a single-core (single-CPU) processor  14  or may be a multi-core (multi-CPU) processor  14 . The processor  14  herein may be one or more devices, circuits, and/or processing cores used to process data (for example, a computer program instruction). 
     In the embodiment, the processor  14  is separately connected to the optical device  103  and the photoelectric sensor  105 , and when the user triggers the photoplethysmography sensor to start working, the processor  14  controls the optical device  103  to emit light outwards, a part of the light is reflected after absorption performed by blood and tissue of a human body of the user, and the photoelectric sensor  105  may receive light reflected from the human body of the user, convert the optical signal into an electrical signal, and send the electrical signal to the processor  14 . The processor  14  can determine a change status such as a heart rate of a wearer based on the reflected light received by the photoelectric sensor  105  and display the change status by using the display screen  13 . 
     The foregoing descriptions are merely specific implementations of embodiments, but are not limiting. Any variation or replacement within the scope disclosed in the embodiments shall fall within the scope of the embodiments.