PATENT DOCUMENT

Publication Number: US-10117587-B2
Application Number: US-201615139133-A
Country: US
Kind Code: B2

Title: Dynamically reconfigurable apertures for optimization of PPG signal and ambient light mitigation

Abstract:
This relates to an electronic device with dynamically reconfigurable apertures to account for different skin types, usage conditions, and environmental conditions and methods for measuring the user&#39;s physiological signals. The device can include one or more light emitters, one or more light sensors, and a material whose optical properties can be changed in one or more locations to adjust the optical path and the effective separation distances between the one or more light emitters and one or more light sensors or the size, location, or shape of the one or more dynamically reconfigurable apertures. In some examples, the material can be a liquid crystal material, MEMS shutter layer, or light guide, which can form the one or more dynamically reconfigurable apertures. In some examples, the light emitters or light sensors or both can be an array of individually addressable optical components.

Claims:
What is claimed is: 
     
       1. An electronic device for measuring physiological information, the device comprising:
 one or more light emitters configured to emit light; 
 one or more light sensors configured to detect a reflection of the emitted light and generate one or more signals indicative of the detected reflected light; 
 a device component capable of forming dynamically reconfigurable apertures having a configuration to allow light to be transmitted from at least one of the one or more light emitters to at least one of the one or more light sensors, each aperture including a center location; and 
 a processor configured to:
 dynamically adjust a separation distance between the center locations of at least two of the apertures; and 
 determine the physiological information based on the one or more signals. 
 
 
     
     
       2. The electronic device of  claim 1 , wherein the electronic device is capable of dynamically reconfiguring one or more of a size of the apertures, a location of the apertures, and a shape of the apertures. 
     
     
       3. The electronic device of  claim 1 , wherein the one or more light sensors includes at least two light sensors capable of sensing different wavelengths. 
     
     
       4. The electronic device of  claim 1 , wherein the one or more light emitters includes at least two light emitters capable of emitting at different wavelengths. 
     
     
       5. The electronic device of  claim 3  or  claim 4 , wherein:
 wherein a sensing wavelength of at least one of the one or more light sensors or an emission wavelength of at least one of the one or more light emitters and separation distance associated with a second configuration is longer than a sensing wavelength of the at least one of the one or more light sensors or an emission wavelength of the at least one of the one or more light emitters and separation distance, respectively, associated with a first configuration. 
 
     
     
       6. The electronic device of  claim 1 , wherein the processor is further configured to: change one or more optical properties of the device component to form the apertures. 
     
     
       7. The electronic device of  claim 6 , wherein the device component comprises a liquid crystal layer capable of forming the apertures. 
     
     
       8. The electronic device of  claim 6 , wherein the device component comprises a plurality of microelectromechanical (MEMS) shutters capable of forming the apertures. 
     
     
       9. The electronic device of  claim 6 , wherein the one or more optical properties of the device component are different in a location corresponding to the center locations than a location outside of the apertures. 
     
     
       10. The electronic device of  claim 1 , wherein the one or more light emitters are formed from an array of individually addressable light emitters. 
     
     
       11. The electronic device of  claim 1 , wherein the one or more light sensors are formed from an array of individually addressable light sensors. 
     
     
       12. The electronic device of  claim 1 , further comprising at least one optical filter, wherein at least one of the one or more light emitters is a broadband source coupled to the at least one optical filter. 
     
     
       13. The electronic device of  claim 1 , wherein the device component comprises a light guide configured to receive at least one of the emitted light and the reflected light. 
     
     
       14. The electronic device of  claim 13 , wherein at least one of the emitted light and the reflected light enters or exits the light guide in a location different from a location corresponding to the one or more light emitters or the one or more light sensors. 
     
     
       15. The electronic device of  claim 13 , wherein the light guide is located on a same layer as at least one of the one or more light emitters and the one or more light sensors. 
     
     
       16. The electronic device of  claim 1 , wherein the one or more light emitters are located on a different layer than the one or more light sensors. 
     
     
       17. An electronic device for measuring physiological information, the device comprising:
 one or more light emitters configured to emit light; 
 one or more light sensors configured to detect a reflection of the emitted light and generate one or more signals indicative of the detected reflected light; and 
 a device component capable of forming dynamically reconfigurable apertures having a configuration to allow light to be transmitted from at least one of the one or more light emitters to at least one of the one or more light sensors, 
 a processor configured to:
 determine the physiological information based on the one or more signals; 
 
 wherein: 
 during a first configuration:
 the one or more light emitters are configured to emit a first light, 
 the one or more light sensors are configured to receive a second light, the second light being a reflection of the first light, and 
 the apertures, each having a center location, are configured to: 
 allow the first light to be transmitted from the one or more light emitters, and 
 allow the second light to be received at the one or more light sensors; and 
 
 during a second configuration:
 the one or more light emitters are configured to emit a third light, 
 the one or more light sensors are configured to receive a fourth light, the fourth light being a reflection of the third light, 
 the apertures are configured to: 
 allow the third light to be transmitted from the one or more light emitters, and 
 allow the fourth light to be received at the one or more light sensors; and 
 
 wherein the processor is further configured to compare a signal from the second light to a signal from the fourth light and dynamically adjust a separation distance between the center locations of the apertures from the first configuration to the second configuration. 
 
     
     
       18. The electronic device of  claim 17 , wherein the processor is further configured to:
 determine a PPG signal from the first configuration; and 
 determine a perfusion index from the second configuration. 
 
     
     
       19. The electronic device of  claim 17 , wherein the processor is further configured to: dynamic reconfigure the apertures one or more of a different size of the apertures, a different location of the apertures, and a different shape of the apertures. 
     
     
       20. The electronic device of  claim 17 ,
 wherein the apertures of the second configuration block light at a location of the first light emitted by the one or more light emitters during the first configuration, and the apertures of the first configuration block light at a location of the third light emitted by the one or more light emitters during the second configuration. 
 
     
     
       21. The electronic device of  claim 17 , wherein the apertures are configured with a third configuration, the third configuration based on the compared signals and being one of the configurations used in the comparison. 
     
     
       22. The electronic device of  claim 17 , wherein the first configuration is associated with a first determination of aperture size, location, and shape, and the second configuration is associated with a second determination of aperture size, location, and shape,
 wherein the first determination is coarser than the second determination. 
 
     
     
       23. The electronic device of  claim 17 , wherein the apertures are capable of being dynamically reconfigured from the first configuration to the second configuration during an initial calibration procedure. 
     
     
       24. The electronic device of  claim 17 , wherein the processor is further configured to: control a voltage of a liquid crystal material to dynamically reconfigure the apertures. 
     
     
       25. The electronic device of  claim 17 , wherein the device component includes a plurality of individual sections, wherein the processor is further configured to control each individual section. 
     
     
       26. The electronic device of  claim 25 , further comprising:
 a plurality of electrodes, wherein the processor is further configured to apply a voltage difference to control the plurality of individual sections to dynamically change one or more of a size, number, location, and shape of the apertures. 
 
     
     
       27. The electronic device of  claim 17 , further comprising:
 a window located at or near an external housing of the electronic device, 
 wherein an active area of the one or more light emitters and an active area of the one or more light sensors face the external housing, and the device component is located proximate to the window. 
 
     
     
       28. The electronic device of  claim 17 , further comprising:
 an optical component layer including the one or more light emitters and the one or more light sensors. 
 
     
     
       29. The electronic device of  claim 17 , wherein the one or more light emitters are located on a different layer than the one or more light sensors.

Description:
FIELD 
     This application is a Non-Provisional application of U.S. Provisional Application No. 62/153,445, filed Apr. 27, 2015, which is hereby incorporated by reference in its entirety for all purposes. 
     FIELD 
     This relates generally to a device that measures a photoplethysmogram (PPG) signal, and, more particularly, to dynamically reconfigurable apertures for optimization of the PPG signal and ambient light mitigation. 
     BACKGROUND 
     A photoplethysmogram (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). In a basic form, PPG systems can employ a light source or light emitter that emits light through an aperture into the user&#39;s tissue. In addition, a light detector can be included to receive light through an aperture that reflects off and exits the tissue. However, determination of the user&#39;s physiological signals can be erroneous due to variations in the user&#39;s skin type, usage conditions, and environmental conditions affecting the signal of the reflected light. 
     For a given light emitter and light detector, the PPG signal can decrease as the separation distance between the light emitter and light detector increases. On the other hand, perfusion index can increase as the separation distance between the light emitter and light detector increases. Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index values (e.g., motion performance). Additionally, the size of the light emitter and/or light detector apertures can lead to insufficient PPG signal strength and/or excessive ambient light intrusion that can introduce noise into the signal and can saturate the signal. Both insufficient PPG signal strength and excessive ambient light intrusion can lead to erroneous measurements. Furthermore, the location or shape (or both) of the apertures may not account for variations in the user&#39;s skin that can negatively impact the measurements. While certain architectures, such as multiple path length architectures, can be employed to alleviate these issues, the path lengths and aperture sizes, locations, or shapes cannot be adjusted once the device is manufactured. To account for different skin types, usage conditions, and environmental conditions, a device with dynamically reconfigurable apertures may be needed. 
     SUMMARY 
     This relates to an electronic device with dynamically reconfigurable apertures to account for different skin types, usage conditions, and environmental conditions. The user&#39;s physiological signals can be measured with one or more light emitters and one or more light sensors. The device can include a material whose optical properties can be changed in one or more locations to adjust the optical path and the effective separation distance between one or more light emitters and one or more light sensors or the size, location, or shape of one or more dynamically reconfigurable apertures. In some examples, the material can be a liquid crystal material, MEMS shutter layer, or light guide, which can form the dynamically reconfigurable apertures. In some examples, the light emitters or light sensors or both can be an array of individually addressable optical components, where the selection or addressing of active optical components can change the properties of the light emitted towards the user&#39;s skin and the light reflected off the user&#39;s skin, vasculature, and/or blood that is received by the light sensors. In some examples, the device can include multiple light emitters or multiple light sensors or both with different emission or sensing wavelengths. 
     This also relates to methods for measuring the user&#39;s physiological signals. In some examples, a longer separation distance between the light emitter and light sensor can be used for PPG signal measurements, whereas a shorter separation distance can be used for perfusion index measurements. In some examples, the aperture sizes can be adjusted to account for the amount of noise, such as the amount of ambient light intrusion, introduced into the signal. In some examples, the location or shape of an aperture can be adjusted to account for variations in the user&#39;s skin. Examples of the disclosure include methods to optimize the properties of the dynamically reconfigurable apertures. These methods can include comparing the signal values of three (or more) configurations and selecting the configuration with the highest (or lowest) signal value. These methods can also include incrementally adjusting the properties of the apertures in a direction with the highest (or lowest) signal value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate systems in which examples of the disclosure can be implemented. 
         FIG. 2A  illustrates a top view of an exemplary electronic device including light sensors and light emitters for measuring a PPG signal according to examples of the disclosure. 
         FIG. 2B  illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for measuring a PPG signal according to examples of the disclosure. 
         FIG. 2C  illustrates a signal detected by a light sensor in PPG system according to examples of the disclosure. 
         FIG. 3A  illustrates a top view of an exemplary electronic device including light sensors and light emitters with increased aperture sizes for measuring a PPG signal according to examples of the disclosure. 
         FIG. 3B  illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters with increased aperture sizes for measuring a PPG signal according to examples of the disclosure. 
         FIG. 3C  illustrates a PPG signal and a signal detected by a light sensor with an increased aperture size in an exemplary device according to examples of the disclosure. 
         FIGS. 4A-4B  illustrate exemplary relationships for the separation distance between a light emitter and a light sensor and the PPG signal and perfusion index according to examples of the disclosure. 
         FIG. 5A  illustrates a top view of an exemplary device with multiple light paths for measuring a PPG signal according to examples of the disclosure. 
         FIG. 5B  illustrates a cross-sectional view of an exemplary device with multiple light paths for measuring a PPG signal according to examples of the disclosure. 
         FIG. 5C  illustrates a table of exemplary path lengths, relative PPG signal values, and relative perfusion index values for multiple light paths in an exemplary device according to examples of the disclosure. 
         FIGS. 6A-6B  illustrate top views of an exemplary electronic device capable of dynamically adjusting the path length between a light emitter and a light sensor according to examples of the disclosure. 
         FIG. 6C  illustrates an exemplary relationship for two apertures with different separation distances and the corresponding PPG signal and perfusion index according to examples of the disclosure. 
         FIGS. 6D-6E  illustrate top views of an exemplary electronic device capable of dynamically adjusting the aperture size according to examples of the disclosure. 
         FIG. 6F  illustrates an exemplary relationship for two apertures of increased size with different separation distances and the corresponding PPG signal and perfusion index according to examples of the disclosure. 
         FIGS. 6G-6H  illustrate top views of an exemplary electronic device capable of dynamically adjusting the number of apertures according to examples of the disclosure. 
         FIG. 6I  illustrates an exemplary relationship between aperture area and the PPG signal and perfusion index according to examples of the disclosure. 
         FIG. 7  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a liquid crystal layer according to examples of the disclosure. 
         FIG. 8  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a microelectromechanical systems (MEMS) layer according to examples of the disclosure. 
         FIG. 9  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a plurality of individually addressable optical components according to examples of the disclosure. 
         FIG. 10A  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a light guide according to examples of the disclosure. 
         FIG. 10B  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a light guide located on the same layer as the light emitter and light sensor according to examples of the disclosure. 
         FIGS. 11A-11C  illustrate exemplary flow diagrams for a process of dynamically adjusting one or more aperture sizes, one or more path lengths, one or more aperture shapes, or a combination in an electronic device according to examples of the disclosure. 
         FIG. 12  illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a signal associated with a user&#39;s physiological state according to examples of the disclosure. 
         FIG. 13  illustrates an exemplary configuration in which an electronic device is connected to a host according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the various examples. Numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     A photoplethysmographic (PPG) signal can be measured by PPG systems to derive corresponding physiological signals (e.g., pulse rate). Such PPG systems can be designed to be sensitive to changes in a user&#39;s tissue that can result from fluctuations in the amount or volume of blood or blood oxygen in the vasculature of the user. In a basic form, PPG systems can employ a light source or light emitter that emits light through an aperture into the user&#39;s tissue, and a light sensor to receive light that reflects and/or scatters and exits the tissue through another aperture. The PPG signal is the amplitude of reflected and/or scattered light that is modulated with volumetric change in blood volume in the tissue. However, in some examples, some of the reflected and/or scattered light can be lost, leading to a PPG signal measured by the light sensor having a low signal strength. Additionally, the PPG signal can be distorted by noise due to artifacts. Artifacts can result from, for example, the user&#39;s movement or ambient light intrusion that can saturate or degrade the signal by introducing noise into the signal. As a result, it can be difficult to accurately determine the user&#39;s physiological state. 
     This disclosure relates to an electronic device with dynamically reconfigurable apertures to account for different skin types, usage conditions (e.g., sedentary, active motion, etc.), and environmental conditions (e.g., indoors, outdoors, etc.). The user&#39;s physiological signals can be measured with one or more light emitters and one or more light sensors. The device can include a material whose optical properties can be changed in one or more locations to adjust the optical path and the effective separation distances between the one or more light emitters and one or more light sensors or the size, location, or shape of the one or more dynamically reconfigurable apertures. In some examples, the material can be a liquid crystal material, MEMS shutter layer, or light guide, which can form the one or more dynamically reconfigurable apertures. In some examples, the light emitters or light sensors or both can be an array of individually addressable optical components, where selection of the active optical components can change the properties of the light emitted towards the user&#39;s skin and the light reflected off the user&#39;s skin, vasculature, and/or blood. In some examples, the device can include multiple light emitters or multiple light sensors or both with different emission or sensing wavelengths. 
     This disclosure also relates to method for measuring the user&#39;s physiological signals. In some examples, a longer separation distance between the light emitter and light sensor can be used for PPG signal measurements, whereas a shorter separation distance can be used for perfusion index measurements. In some examples, the aperture size can be adjusted to account for the amount of noise, such as the amount of ambient light intrusion, introduced into the signal. In some examples, the location or shape of an aperture can be adjusted to account for differences in the user&#39;s skin. Examples of the disclosure can include methods to optimize the properties of the dynamically reconfigurable apertures. These methods can include comparing the signal values of three (or more) configurations and selecting the configuration with the highest (or lowest) signal value. These methods can also include incrementally adjusting the properties of the apertures toward a direction and/or size with the highest (or lowest) signal value. 
     Representative applications of the apparatus and methods according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. Other applications are possible, such that the following examples should not be taken as limiting. 
       FIGS. 1A-1C  illustrate systems in which examples of the disclosure can be implemented.  FIG. 1A  illustrates an exemplary mobile telephone  136  that can include a touch screen  124 .  FIG. 1B  illustrates an exemplary media player  140  that can include a touch screen  126 .  FIG. 1C  illustrates an exemplary wearable device  144  that can include a touch screen  128  and can be attached to a user using a strap  146 . The systems of  FIGS. 1A-1C  can utilize the reconfigurable apertures and methods for detecting a PPG signal as will be disclosed. 
       FIG. 2A  illustrates a top view and  FIG. 2B  illustrates a cross-sectional view of an exemplary electronic device including light sensors and light emitters for measuring a PPG signal according to examples of the disclosure. The top view in  FIG. 2A  can be viewed as the underside of wearable device  144  of  FIG. 1C , for example. A light sensor  204  can be located proximate to a light emitter  206  on a surface of device  200 . Additionally, another light sensor  214  can be located or paired with light emitter  216  on a surface of device  200 . Device  200  can be situated such that light sensors  204  and  214  and light emitters  206  and  216  are proximate to a skin  220  of a user. For example, device  200  can be held in a user&#39;s hand or strapped to a user&#39;s wrist, among other possibilities. 
     Light emitter  206  can generate light  222  and  224  exiting aperture  201 . Light  222  can be directed towards and incident upon the user&#39;s skin  220 . A portion of light  222  can be absorbed by skin  220 , vasculature, and/or blood, and a portion of light (i.e., light  223 ) can reflect back for detection by light sensor  204 . Light  224  can also be incident upon skin  220 , a portion of light  224  can be absorbed by skin  220 , vasculature, and/or blood, and a portion of light (i.e., light  225 ) can reflect back towards device  200 . However, light  225  can be incident on back crystal  218  and may not reach light sensor  204 . Similarly, ambient light  226  can be incident upon skin  220 . A portion of the ambient light (i.e., light  227 ) can reflect back towards device  200 , and light  227  can be absorbed by back crystal  218 . 
       FIG. 2C  illustrates a signal detected by a light sensor for determining the user&#39;s physiological state in an exemplary electronic device according to examples of the disclosure. Signal  250  can be a low intensity signal measured by light sensor  204 . The intensity of signal  250  can be low because the size, shape, or location of aperture  201  can block a portion of the reflected light, such as light  225 , and prevent the light from being incident on the active area of the light sensors, such as light sensor  204 . Such a signal may be too low for accurate determination of the user&#39;s physiological state. While the intensity of the detected signal  250  can be increased by increasing the intensity of light generated from light emitter  206 , such a solution may not be feasible especially in portable or compact-sized electronic devices, whose power consumption can be limited due to portability and size requirements. 
     One way to overcome or alleviate the problem of having low signal intensity can be to enlarge one or more aperture sizes.  FIGS. 3A and 3B  illustrate a top view and a cross-sectional view of an exemplary electronic device including light sensors and light emitters with increased aperture sizes for measuring a PPG signal according to examples of the disclosure. Device  300  can include light emitters  306  and  316  and light sensors  304  and  314  located on a surface of device  300 . In some examples, either light sensors  304  and  314  or light emitters  306  and  314  or both can be symmetrically placed with respect to the center of the back crystal  318 . Light emitters  306  and  316  and light sensors  304  and  314  can be facing towards a user&#39;s skin  320 . The light emitters  306  and  316  can emit light at and can detect light reflected from the user&#39;s skin  320 , vasculature, and/or blood by passing through apertures  301 . 
     Light emitter  306  can emit light  322  and  324  through aperture  301  towards skin  320 . Both light  322  and  324  can be partially absorbed by skin  320 , vasculature, and blood. Light  323  and  325  can represent the portions of light  322  and  324  that are not absorbed by skin  320  and instead, are reflected back towards device  300 . Both light  323  and  325  can be detected by light sensor  304  to generate a signal representing the modulated light. 
     Each aperture  301  can have a diameter (or area) greater than the diameter (or area) of aperture  201  of  FIGS. 2A and 2B . By increasing the aperture sizes, neither light  323  nor  325  is absorbed by back crystal  318 , which can lead to measured modulated light values with an increased intensity. The increased intensity can make the signal strength sufficient enough to make detection of the PPG signal realizable, unlike signal  250  illustrated in  FIG. 2C . While increasing the aperture sizes can effectively increase the modulated signal strength, the larger apertures may allow unwanted light to pass through to be sensed by light sensor  304 . For example, ambient light  326  can reflect off the user&#39;s skin  320 , enter into aperture  301 , and can reach the active area of the light sensor  304 . Ambient light can also directly enter into the aperture and onto the light sensor without striking the user&#39;s skin. With an increase in the ambient light  327  reaching the active area of the light sensor  304 , the unmodulated signal intensity can increase. An increase in unmodulated signal intensity can cause the perfusion index to decrease and the signal-to-noise ratio to decrease. 
       FIG. 3C  illustrates a signal detected by a light sensor with an increased aperture size used for measuring a PPG signal in an exemplary device according to examples of the disclosure. Signal  350  can be the measured total signal (i.e., sum of the measured modulated light and unmodulated light, including ambient light) detected by light sensor  304 . Signal  360  can be the actual PPG signal that accurately represents the user&#39;s physiological state. 
     Device  300  can take the actual PPG signal, such as signal  360 , and determine the user&#39;s perfusion index. The perfusion index can be the ratio of received modulated light (ML  364 ) to unmodulated light (UML  366 ) (i.e., ratio of blood flow modulated signal to static, parasitic DC signal) and can give extra information regarding the user&#39;s physiological state. The modulated light (ML) can be the peak-to-valley value, and the unmodulated light (UML) can be the zero-to-average (average 362) value of the PPG signal  360 . As shown in  FIG. 3C , the perfusion index can be equal to the ratio of ML  364  to UML  366 . 
     Both signals  350  and  360  can have an amplitude that is modulated as a result of pulsatile blood flow (i.e., “signal”) and parasitic, unmodulated, non-signal light (i.e., DC). However, the unmodulated light UML  356  of signal  350  can be higher than the unmodulated light UML  366  of signal  360  due to signal  350  including noise. Noise can be generated from motion artifacts, ambient light intrusion (e.g., due to light sensor  304  detecting ambient light  327 ), or light that has not penetrated a blood layer, for example. The added noise or unmodulated light values can distort the determination of the user&#39;s physiological state. This can be particularly true in situations where the unmodulated light can saturate the total signal detected by light sensor  304 . For example, as shown in the figure, signal  350  can reach the saturation level  355 . As a result, the modulated light ML  354  detected by the light sensor can be lower in value (e.g., truncated), so the PPG signal can be incorrect. Given that the unmodulated light UML  356  can be erroneously high in value (e.g., saturated) and the modulated light ML  354  can be erroneously low in value (e.g., truncated), the perfusion index, being equal to the ratio of ML  354  to UML  356 , and the PPG signal may be incorrectly determined. 
     One way to increase the signal intensity or signal strength without increasing the unmodulated light intensity can be to reduce the distance between light sensors and light emitters such that light travels a shorter distance. Generally, for a given light emitter and light sensor pair, the signal strength decreases with increasing separation distance between the light emitter and the light sensor. On the other hand, the perfusion index generally increases with increasing separation distance between the light emitter and the light sensor. A higher perfusion index can correlate to better rejection of artifacts caused by, for example, motion or ambient light. Therefore, shorter separation distances between a light emitter and a light sensor can favor high PPG signal strength, while longer separation distances can favor high perfusion index. That is, a trade-off can exist, making it difficult to optimize separation distance for particular user skin/tissue types, usage conditions, and environmental conditions. 
       FIGS. 4A-4B  illustrate exemplary relationships for the separation distance between a light emitter and a light sensor and the PPG signal and perfusion index according to examples of the disclosure. Light sensor  404  can have a separation distance  411  from light emitter  406 . Light sensor  414  can have a separation distance  413  from light emitter  406 . Light sensor  424  can have a separation distance  415  from light emitter  406 . Light sensor  434  can have a separation distance  417  from light emitter  406 . Light sensor  444  can have a separation distance  419  from light emitter  406 . Separation distances  411 ,  413 ,  415 ,  417 , and  419  can be different. In some examples, the light emitter  406  and light sensors  404 ,  414 ,  424 ,  434 , and  444  can be placed directly upon the user&#39;s skin, and the separation distances  411 ,  413 ,  415 ,  417 , and  419  can be directly correlated to the distance the light travels within the skin. As plotted in  FIG. 4B , a shorter separation distance can lead to a lower perfusion index and a higher PPG signal, whereas a longer separation distance can lead to a higher perfusion index and lower PPG signal. 
     To alleviate the trade-off issues between signal strength and perfusion index, multiple light paths with various distances between the light emitters and the light sensors can be employed.  FIG. 5A  illustrates a top view and  FIG. 5B  illustrates a cross-sectional view of an exemplary device with multiple light paths for determining the user&#39;s physiological state according to examples of the disclosure. Device  500  can include light emitters  506  and  516  and light sensors  504  and  514  located on a surface of device  500 . The edge of the aperture associated with light emitter  506  can have a separation distance  513  from the edge of the aperture associated with light sensor  504 , and the edge of the aperture associated with light emitter  516  can have a separation distance  511  from the edge of the aperture associated with light sensor  504 . 
     Light  522  from light emitter  516  can be incident upon skin  520  and can reflect back as light  523  detected by light sensor  504 . Similarly, light  524  from light emitter  506  can be incident upon skin  520  and can reflect back as light  525  detected by light sensor  504 . In some examples, light emitters  506  and  516  and light sensor  504  can be placed directly upon the user&#39;s skin, and the separation distances  511  and  513  can be directly correlated to the distance the light travels within the skin. Separation distance  511  can be shorter than separation distance  513 , and as a result, light  523  can have a higher PPG signal strength than light  525 . However, light  525  can have a higher perfusion index than light  523  due to the longer separation distance. In some examples, light  522  and  523  can travel a shorter distance through the skin than light  524  and  525  travels. This shorter distance that light  522  and  523  travel can be associated with the shorter separation distance  511 . Similarly, the longer distance that light  524  and  524  travel can be associated with the longer separation distance  513 . Light emitter  516  and light sensor  504  can be employed for applications requiring a high PPG signal, whereas light emitter  506  and light sensor  504  can be employed for applications requiring a high perfusion index. Due to the different separation distances  511  and  513 , information extracted from light  523  and  525  can provide various combinations of PPG signals and perfusion index values to allow the device to dynamically select light information for particular user skin types, usage conditions, and environmental conditions. 
     Light emitters  506  and  516  can be symmetrically placed, while light sensors  504  and  514  can be asymmetrically placed. Light emitters  506  and  516  and light detectors  504  and  514  can be arranged such that there are four light paths with four different separation distances, for example. In some examples, a separation distance can be the distance between the edge of an aperture associated with a light emitter and an edge of an aperture associated with a light sensor. Light path  551  can be coupled to light emitter  506  and light sensor  514 . Light path  553  can be coupled to light emitter  506  and light sensor  504 . Light path  555  can be coupled to light emitter  516  and light sensor  504 . Light path  557  can be coupled to light emitter  516  and light sensor  514 . 
       FIG. 5C  illustrates a table of exemplary path lengths, relative PPG signals levels, and relative perfusion index values for light paths  551 ,  553 ,  555 , and  557  of device  500  according to examples of the disclosure. As shown, relative PPG signal levels can be higher for shorter path lengths because there can be less light loss when the light emitter and light sensor are located close together such that light can travel through a shorter distance of the user&#39;s skin. For example, light path  555  can have a higher PPG signal of 1.11 than light path  557  with a PPG signal of 0.31 due to the shorter path length (the path length of light path  555  can be 4.944 mm, whereas the path length of light path  557  can 6.543 mm). For applications that require high PPG signal levels, device  500  can favor information from light paths  555  or  551  over information from light paths  553  or  557 . However, relative perfusion index values can be higher for longer path lengths because light that travels along a greater distance in the skin can include a higher fraction or percentage of pulsatile signal and a smaller fraction or percentage of parasitic signal. For example, light path  553  can have a higher perfusion index value of 1.23, whereas light path  551  can have a lower perfusion index value of 1.10 due to the longer path length (the path length of light path  553  can be 5.915 mm, whereas the path length of light path  551  can be 5.444 mm). For applications that require high perfusion index values, device  500  can favor information from light path  553  over information from light path  551 , for example. While  FIG. 5C  illustrates exemplary values for path lengths  551 ,  553 ,  555 , and  557  along with exemplary PPG signal levels and perfusion index values, examples of the disclosure are not limited to these values. 
     Information obtained from the multiple light paths can be used both for applications requiring a high PPG signal strength and for applications requiring a high perfusion index value. In some examples, information generated from all light paths can be utilized. In some examples, information generated from some, but not all light paths can be utilized. In some examples, the “active” light paths can be dynamically changed based on the application(s), available power, user type, and/or measurement resolution. 
     Although the path lengths or aperture sizes or both of the one or more exemplary devices disclosed above may be adjusted in consideration of the trade-off between PPG signal and perfusion index, the path lengths and aperture sizes cannot be adjusted once the device has been manufactured. Many users desire a portable electronic device that can be used for multiple activities (i.e., usage conditions) and can be used in a variety of environmental conditions. Additionally, the skin types can vary from user to user, so a device that has fixed path lengths and aperture sizes may have limited capabilities. For example, the melanin content can vary significantly from user to user. The skin of a user with high melanin content can absorb a large amount of emitted light from the light emitter, so less light can reflect and/or scatter back towards the light sensor. As a result, a device that can favor a high PPG signal over perfusion index can be desirable only for users with high melanin content, for example. On the other hand, a device may not need to favor a high PPG signal if the user&#39;s skin has low melanin content. Usage conditions can also vary. For example, a user can be exercising or engaging in high movement activities. A device that can sacrifice a high PPG signal and can favor a high perfusion index for reducing the motion artifacts can be desired, but only for the time when the user is active. Furthermore, environmental conditions can vary. For example, the device can be located outdoors under sunny conditions. A device that can account for ambient light intrusion and can prevent the ambient light from saturating the signal can be desired. If the user and the device move to an indoor location with low ambient light levels, a device that can account for the change in ambient light without compromising signal level can be desired. In some examples, the temperature of the environment can cause a change in the blood volume in the user&#39;s skin surface. A lower blood volume due to a colder temperature environment can require additional light power to obtain the PPG signal, for example. To account for the different skin types, usage conditions, and environmental conditions, a device with dynamically reconfigurable apertures may be needed. 
       FIGS. 6A-6B  illustrate top views of an exemplary electronic device capable of dynamically adjusting the path length between a light emitter and a light sensor according to examples of the disclosure. Device  600  can include a light emitter  606  and a light sensor  604 . Device  600  can optionally include an optical isolation (not shown) to prevent direct optical cross talk between the light emitter  606  and light sensor  604 . Light emitter  606  can be any type of light source, including but not limited to, light emitting diodes (LEDs), incandescent lights, fluorescent lights, organic light emitting diodes (OLEDs), and electroluminescent diodes (ELDs). Light sensors  604  can be any type of optical sensing device such as a photodiode. In some examples, light emitter  606  and light sensor  604  can be fixed in location. Aperture  603  can be located above light emitter  606  such that light emitted from light emitter  606  can transmit through aperture  603 . Aperture  601  can be located above light sensor  604  such that light entering aperture  601  can transmit through and be incident upon the active area of light sensor  604 . Device  600  can further include material  630  located above light sensor  604 , light emitter  606 , or both. In some examples, material  630  can be opaque, and apertures  601  and  603  can be transparent. In some examples, the optical properties of material  630  can be dynamically adjusted or can vary amongst different locations or both. For example, material  630  can block light (can be opaque) in one or more locations (e.g., areas outside of apertures  601  and  603 ), while transmitting light (can be transparent) in one or more locations (e.g., apertures  601  and  603 ). Although the figure illustrates only one light emitter and only one light sensor, examples of the disclosure can include a device with multiple light emitters or multiple light sensors or both. 
     The distance or path length between the light sensor  604  and light emitter  606  can be dynamically adjusted. As shown in  FIG. 6A , the properties of material  630  can change such that aperture  601  can be located a distance  611  away from light emitter  606 . As shown in  FIG. 6B , the properties of material  630  can be adjusted such that aperture  601  can be located a distance  619  away from light emitter  606 . In both figures, the light emitter  606  and light sensor  604  can remain in the same location. Additionally, apertures  601  and  603  can retain their shape and size. 
     At an instance in time, a high PPG signal can be detected when apertures  601  and  603  are located the shorter distance  611  away from each other, as shown in  FIG. 6A . At another instance in time, a high perfusion index can be detected when apertures  601  and  603  are located the longer distance  619  away from each other, as shown in  FIG. 6B . In some examples, device  600  can change the location of the aperture based on the amount of ambient light detected. For example, if the amount of ambient light detected through an aperture at a first location exceeds a threshold value, the device can relocate the aperture to a second location, different from the first location, where the ambient light value can be less than the threshold value in the second location. In some examples, the second location can be further away from the ambient light source then the first location. By dynamically adjusting the location of apertures  601  and  603  relative to each other through a change in the optical properties of material  630 , both a high PPG signal and a high perfusion index can be achieved, as illustrated in  FIG. 6C . 
     In addition to adjusting the path length, the aperture size can be adjusted.  FIGS. 6D-6E  illustrate top views of an exemplary electronic device capable of dynamically adjusting the aperture size according to examples of the disclosure. Device  600  can include a light emitter  606  and an aperture  603  located above light emitter  606  such that light emitted from light emitter  606  can transmit through aperture  603 . Device  600  can also include light sensor  604  and an aperture  605  located above light sensor  604  such that light entering aperture  605  can transmit through and be incident upon the active area of light sensor  604 . In some examples, apertures  603  and  605  can be formed through one or more dynamic changes in the optical properties of material  630 . In some examples, material  630  can be transparent in the same locations as aperture  603  and  605 . In some examples, material  630  can be opaque in one or more areas located outside of apertures  603  and  605 . 
     As illustrated in  FIG. 6D , a PPG signal or perfusion index or both can be determined by locating apertures  603  and  605  with a separation distance  613 . Aperture  605  can be relocated such that the separation distance between apertures  603  and  605  changes to separation distance  617 , as illustrated in  FIG. 6E . In some examples, separation distance  613  can be shorter than separation distance  617 . In this manner, a high PPG signal can be measured when apertures  603  and  605  are located the shorter distance  613  apart, and a high perfusion index can be measured when apertures  603  and  605  are located the longer distance  617  apart. Device  600  can obtain both an accurate PPG signal and perfusion index, as illustrated in  FIG. 6F , by using the same optical components. 
     Device  600  can have fewer optical components for multiple path length measurements. Compared to device  500  of  FIG. 5A  where four different optical components (e.g., light sensors  504  and  514  and light emitters  506  and  516 ) were needed to generate four different path lengths (e.g., lengths associated with paths  551 ,  553 ,  555 , and  557 ), device  600  may need only two optical components (e.g., light sensor  604  and light emitter  606 ) to generate four different path lengths (e.g., distances  611 ,  613 ,  617 , and  619 ). Fewer optical components can lead to not only lower costs and more compact devices, but also the optical sensing capabilities can be enhanced. The optical sensing capabilities can be enhanced because the size of the optical components may not be constrained or “crowded,” and there can be a lower likelihood for optical crosstalk. Device  600  can also include an optical isolation  602  to prevent direct optical cross talk between the light emitter  606  and light sensor  604 . 
     Not only can one or more path lengths or separation distances be dynamically adjusted, but also one or more aperture sizes can be dynamically adjusted. For example, aperture  601  (illustrated in  FIGS. 6A-6B ) can have a different size or area than aperture  605  (illustrated in  FIGS. 6D-6E ). In some examples, aperture  605  can have an area A 2 , greater than the area A 1  of aperture  601 . In some examples, device  600  can make two or more adjustments to the size or area of the aperture. For example, device  600  can have an aperture  609  with an area A 3 , greater than both A 1  and A 2 , as illustrated in  FIG. 6G . 
     The device can change one or more aperture sizes for any number of reasons. For example, if the device determines that a higher intensity modulated light is desired or needed, the device can increase one or more aperture sizes. In some examples, the device can determine that ambient light is saturating the signal, so the device can reduce one or more aperture sizes.  FIG. 6I  shows a plot illustrating the effect aperture area has on signal intensity and ambient light intrusion according to examples of the disclosure. As the aperture area increases, the signal intensity increases. However, the trade-off to a higher signal intensity can be higher ambient light intrusion, which can distort the detected signal. Since the relative signal intensity to ambient light intrusion can vary depending on many factors, such as the user&#39;s skin type, usage conditions, and environmental conditions, a device with one or more fixed aperture areas may limit the accuracy of the PPG signal and perfusion index. 
     In some examples, the device can adjust the aperture size based on a calibration procedure custom tailored to the user&#39;s skin type or the location on the user&#39;s skin that the device is attached to, held with, or touching. In some examples, the device can adjust the aperture size based on the type of desired measurement(s) or the application. 
     In some examples, the number of apertures can by dynamically adjusted, as illustrated in  FIGS. 6G-6H . Device  600 , as illustrated in  FIG. 6G , can include one aperture  609 . Aperture  609  can allow light emitted from light emitter  606  to transmit through to the user&#39;s skin (not shown), and the same aperture  609  can allow light reflected and/or scattered from the user&#39;s skin to transmit through to be detected by light sensor  604 . In some examples, the size of aperture  609  can be such that the active areas of both light emitter  609  and light sensor  604  are exposed to the user&#39;s skin. 
       FIG. 6H  illustrates a top view of an exemplary electronic device including multiple apertures and multiple optical components according to examples of the disclosure. Device  600  can include light emitters  606  and  616 , light sensors  604  and  614 , and material  630 . Material  630  can be configured with multiple apertures  631 ,  633 , and  635 . Aperture  631  can be associated or coupled with both light emitter  616  and light sensor  614 . Aperture  633  can be associated with light emitter  606 , and aperture  635  can be associated with light sensor  604 . Aperture  633  can be located a separation distance  623  away from aperture  635 . Light emitted from light emitter  616  and exiting aperture  631  can be located a separation distance  621  away from light entering aperture  631  and detected by light sensor  614 . In some examples, distances  621  and  623  can be different. In some examples, distance  621  and  623  can be the same. In some examples, light sensors  604  and  614  can be a single detector that is apportioned into two or more sections. 
     In some examples, light sensor  604  and  615  can be a single large detector, such as light sensor  604  illustrated in  FIG. 6G . In a first time period, material  630  can be reconfigured such that light is allowed to transmit through the first aperture (e.g., aperture  631 ), while preventing light from transmitting through the second aperture (e.g., aperture  635 ). Light emitter  606  or light emitter  616  or both can be “active” by emitting light whose reflection is captured by aperture  631 . In a second time period, material  630  can be reconfigured such that light is allowed to transmit through the second aperture (e.g., aperture  635 ), while preventing light from transmitting through the first aperture (e.g., aperture  631 ). The “active” light emitters for the second period can be the same as the first period or can be different, where the reflection of the “active” light emitters are captured by aperture  635 . 
     A light path can exist between light emitter  606  and light sensor  604 , and another light path can exist between light emitter  616  and light sensor  614 . The paths can be located such that different areas of the user&#39;s skin are intentionally measured. For example, the device can be configured with two light paths with the same separation distances, but different locations. One light path can be associated with an area of the user&#39;s skin that has a different level of skin pigmentation or melanin content than the other light path. Device  600  can utilize the measurements from both light paths to extract out the effects that the skin pigmentation or melanin content can have on the PPG signal. 
     In some examples, the shape of one or more apertures can be changed. In some examples, the shapes of the apertures in device  600  can be different. For example, the shape of aperture  635  can be an oval, whereas the shape of aperture  633  can be circular. The device can adjust the shape of each aperture based on variations in the user&#39;s skin at those locations where the light reflects, for example. 
     In some examples, light emitters  606  and  616  can be different light sources. Exemplary light sources can include, but are not limited to, light emitting diodes (LEDs), incandescent lights, and fluorescent lights. In some examples, light emitters  606  and  616  can have different emission wavelengths. For example, light emitter  616  can be a green LED, and light emitter  606  can be an infrared (IR) LED. A user&#39;s blood can effectively absorb more light from a green light source than an IR source. Thus, the light path coupled to light emitter  616 , with the shorter separation distance  621 , can be used to measure a PPG signal when a user is sedentary, for example. An IR light source can effectively travel further distances through a user&#39;s skin than other light sources, so light emitter  606 , located the longer distance  623  away from associated light sensor  604 , can be used. In some examples, light emitters  606  and  616  can have different emission intensities. 
       FIG. 7  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a liquid crystal layer according to examples of the disclosure. Stackup  700  can include an optical component layer  761 , a liquid crystal layer  760 , and a window  762 . Optical component layer  761  can include a light emitter  706  and a light sensor  704 , where the active area of both the light emitter  706  and the light sensor  704  can be facing the user&#39;s skin  720 . In some examples, light emitter  706  and light sensor  704  can be located on different layers. In some examples, optical component layer  761  can include a back crystal  718 . Window  762  can be any material or substrate that is at least partially transparent. 
     Liquid crystal layer  760  can include a liquid crystal material and transparent electrodes. Liquid crystal layer can include components from any type of liquid crystal technology including, but not limited to, in-plane switching (IPS), fringe field switching (FFS), or twisted nematic (TN). Liquid crystal layer  760  can further include a thin-film transistors (TFTs) layer adjacent to the liquid crystal material. Individual sections of the liquid crystal material can variably allow light to pass through when an electric field is applied to the liquid crystal material. The electric field can be generated based upon a voltage difference between the transparent electrodes. For example, a voltage difference can be applied to the sections of the liquid crystal layer  760  located substantially near apertures  701  and  703 . Applying the voltage difference substantially near aperture  703  can allow light  722  emitted from light emitter  706  to pass through aperture  703  (i.e., sections of liquid crystal layer  760  that are transparent) and through window  762  towards user&#39;s skin  720 . The user&#39;s skin  720 , vasculature, and/or blood can absorb a portion of the light and another portion of the light can reflect back as light  723 . Light  723  can transmit through window  762  and aperture  701  (i.e., another or the same section of the liquid crystal layer  760  that is transparent) towards light sensor  704 . By controlling whether light can be transmitted through each of the individual sections, the size, number, location, and shape of apertures  701  and  703  can be dynamically changed. 
       FIG. 8  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a microelectromechanical systems (MEMS) layer according to examples of the disclosure. Stackup  800  can include an optical component layer  861 , a MEMS layer  860 , and a window  862 . Optical component layer  861  can include a light emitter  806  and a light sensor  804 , where the active areas of both the light emitter  806  and the light sensor  804  can be facing the user&#39;s skin  820 . 
     MEMS layer  860  can include a plurality of MEMs shutters  863 . Each MEMS shutter  863  can either allow or prevent light from passing through, depending on the position of the shutter. The position of each MEMS shutter  863  can be controlled by two lines, where the first line can be a conductive line attached to each shutter. A source (not shown) can provide a current to the first line, which can become electrically attracted to the second line such that the position of the shutter physically moves. Since each MEMS shutter can be coupled to a different source, each MEMS shutter can be individually controlled such that the position of one or more MEMS shutters can allow light to pass through forming apertures  805  and  807 , while the position of other MEMS shutters can block light. With aperture  805 , the location and amount of the light emitted from the light emitter  806  that is directed towards the user&#39;s skin  820  as light  822  can be changed. Similarly, the location and amount of the light  823  that has reflected off the user&#39;s skin  820 , vasculature, and/or blood and reaches light sensor  804  through aperture  807  can be changed. As a result, the sizes, shapes, and locations of apertures  805  and  807  can be changed. Individual control of the MEMS shutters can be used to tailor device  800  to meet the specific needs of the user, usage condition, and environmental conditions at any given time. 
       FIG. 9  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a plurality of individually addressable optical components according to examples of the disclosure. Stackup  900  can include an optical component layer  961  and a window  962 . Optical component layer  961  can include an array of light emitters  906  and an array of light sensors  904 . In some examples, optical component layer  961  can include a single light emitter or a single light sensor. Either one or both arrays can include a plurality of individually addressable light emitters or light sensors. The size, location, and shape of the light emitted from the array of light emitters  906  and the size, shape, and location of the light detected by the array of light sensors  904  can be determined by individually addressing the appropriate optical components. Additionally, individually addressing the appropriate optical components can also determine the separation distance between the light emitter and light sensor of a given light path. 
     For example, the size of the light  922  emitted from the array of light emitters  906  can be increased by increasing the number in the array of light emitters  906  that are addressed (i.e., turned on). To change the location or path length or both, the device can change which light sensor or light emitter (or both) to address. For example, path  911  can be selected by addressing light emitter  905  and light sensor  907 . Path  919 , different from  911 , can be selected by addressing light emitter  905  and light sensor  909 . In some examples, stackup  900  can include an array of light sensors, but only one light sensor can be employed. In some examples, stackup  900  can include an array of light emitters, but only one light emitter can be employed. 
     In some examples, the array of light emitters can include a plurality of individual light emitters. In some examples, the array of light sensors can include a plurality of individual light sensors. In some examples, the light emitters included in the array of light emitters  906  can have different emission properties, such as wavelength and intensity. In some examples, the light sensors included in the array of light sensors  904  can have different sensing properties, such as wavelength and intensity. In some examples, one or both of the light emitters and light sensors can have broadband sensing or emission capabilities. In some examples, the light emitter or light detector or both can be coupled to one or more optical filters. For example, at least one light emitter can be a broadband source. Some of the light emitters included in the array of light emitters can be coupled to a green optical filter, and others of the light emitters included in the array of light emitters can be coupled to an infrared optical filter. In some examples, the light emitter or light detector or both can be coupled to an adjustable diffuse layer, aperture layer, window, mask or filter that selectively allows or blocks light to transmit through. 
       FIG. 10A  illustrates a cross-sectional view of a partial stackup of an electronic device capable of dynamically adjusting one or more aperture sizes, one or more path lengths, and one or more aperture shapes through a light guide according to examples of the disclosure. Stackup  1000  can include an optical component layer  1061 , a light guide  1060 , a reconfigurable layer  1064 , and a window  1062 . Optical component layer  1061  can include one or more light emitters, such as light emitter  1006 , and one or more light sensors, such as light sensor  1004 , such that the active areas are directed towards the user&#39;s skin  1020 . Both light emitter  1006  and light sensor  1004  can be coupled to light guide  1060 . 
     Light guide  1060  can be a component configured to transport light from one location to another location. As illustrated in the figure, light from the light emitter  1006  can be incident upon top surface  1063  of light guide  1060 , can exit out of bottom surface  1065  of light guide  1060 , can enter through aperture  1009  located on reconfigurable layer  1064 , can transmit through window  1062 , and can enter the user&#39;s skin  1020  as light  1022 . A portion of light can reflect back as light  1023 , can transmit through window  1062 , can enter through aperture  1010  located on reconfigurable layer  1064 , and can enter light guide  1060  at a location  1012  located on the bottom surface  1065  of light guide  1060 . Due to total internal reflections, the light hitting each interface of light guide  1060  can reflect back and travel through. In some examples, the reflected light entering into the light guide can be reconfigured (e.g., by controlling the entrance aperture into the light guide  1060  using, for example, a liquid crystal layer, MEMS shutter, etc.) such that the optical distance through the skin is being controlled. Light guide  1060  can transport the reflected light to light sensor  1004 . Although light emitter  1006  can be located a distance  1018  away from light sensor  1004 , the PPG signal and perfusion index can be determined based on the distance of the light exiting (e.g., light  1022 ) and the light entering (e.g., light  1023 ) the device. Since light  1022  exited the device at aperture  1009  and light  1023  entered the device at aperture  1010 , separation distance  1017  can be representative of the optical distance through the skin. 
     Locating one or more optical components in a location different from the locations where light exits and enters the device can lead to more flexible placement of the optical components. In turn, more flexible placement of the optical components can lead to a thinner, more lightweight portable electronic device. An exemplary configuration is illustrated in  FIG. 10B . For example, the light  1022  generated from light emitter  1006  can transmit through aperture  1009  located on reconfigurable layer  1064 , can transmit through window  1062 , and can be incident upon user&#39;s skin  1020 . Light sensor  1004  can be an edge-sensing component. Reflected light  1023  can transmit through window  1062 , can transmit through aperture  1010  located on reconfigurable layer  1064 , and can enter light guide  1060  at location  1012 . Light guide  1060  can be configured to allow the reflected light to travel through the light guide and exit out of the edge of the light guide towards the active area of light sensor  1004 . In some examples, the reflected light entering into the light guide can be reconfigured (e.g., by controlling the entrance aperture into the light guide  1060  using, for example, a liquid crystal layer, MEMS shutter, etc.) such that the optical distance through the skin is being controlled. Light guide  1060  can transport the reflected light to light sensor  1004 . Although light emitter  1006  can be located a distance  1019  away from light sensor  1004 , the PPG signal and perfusion index can be determined based on the distance of the light exiting (e.g., light  1022 ) and the light entering (e.g., light  1023 ) the device. Since light  1022  exited the device through aperture  1009  and light  1023  entered the device at through aperture  1010 , separation distance  1017  can be representative of the optical distance through the skin. With this configuration, light guide  1060 , light emitter  1006 , and light sensor  1004  can be located on the same layer, eliminating at least one extra layer in the stackup  1000  thereby making the device thinner. In some examples, the light guide  1060  can be a waveguide, one or more lenses, or one or more reflectors. 
     Although examples of the disclosure illustrate dynamic adjustment using a liquid crystal layer, MEMS shutters, individually-addressable optical components, or a light guide, one skilled in the art would understand that any adjustable window or filter could be used. Examples of the disclosure can include one or more moveable apertures, irises, or windows. Additionally, examples of the disclosure can include adjusting the percentage of transmitted light through one or more apertures. 
       FIGS. 11A-11C  illustrate exemplary flow diagrams for a process of dynamically adjusting one or more aperture sizes, one or more path lengths, one or more aperture shapes, or a combination in an electronic device according to examples of the disclosure. Process  1100  can be used as an initial calibration procedure or for a coarse determination of the optimal aperture size, location, and shape, for example. Process  1100  can begin by setting the aperture size, location, and shape to a first configuration (step  1102 ). A processor or controller coupled to the light sensor can calculate a first figure of merit associated with the first configuration (step  1104 ). In some examples, the figure of merit can be the signal-to-noise ratio. In some examples, the figure of merit can be the modulated signal intensity, PPG signal value, or perfusion index value. The aperture size, location, shape, or a combination can be changed to a second configuration (step  1106 ). A second figure of merit associated with the second configuration can be calculated (step  1108 ). The aperture size, location, shape, or combination can be changed to a third configuration (step  1110 ). A third figure of merit associated with the third configuration can be calculated (step  1112 ). The first, second, and third figures of merit can be compared (step  1114 ), and the aperture size, location, and shape can be set based on the comparison (step  1116 ). 
     Process  1140 , illustrated in  FIG. 11B , can be used to adjust the aperture size, location, and shape while the device is being used by the user and after the calibration procedure, for example. Process  1140  can begin by setting the aperture size, location, and shape to a pre-determined or previously determined configuration (step  1142 ). A processor or controller can determine a figure of merit associated with the pre- or previously determined configuration (step  1144 ). The processor can determine whether the figure of merit, use condition, user type, or environmental condition has changed (step  1146 ). If not, the configuration of the apertures can remain unchanged. If so, the processor can check whether the amount of ambient light saturates the signal (step  1148 ). If the ambient light levels saturate the signal, the device can decrease the aperture size and/or relocate the aperture until some or all of the ambient light is blocked from reaching the light sensors (step  1150 ). Alternatively or additionally, the aperture can be relocated to a location where the ambient light levels are lower (e.g., a location further away from the ambient light source). The processor can check if the signal intensity is high enough (step  1152 ). If the signal intensity is not high enough, the device can increase the aperture size and/or relocate the aperture to allow more reflected light to reach the active area of the light sensors (step  1154 ). The processor can also check if the user has become more active (step  1156 ). If the user has become more active, the device can relocate the aperture and/or change the separation distance between the light sensors and light emitters (step  1158 ). If desired, the processor can repeat the process. 
     Process  1170 , illustrated in  FIG. 11C , can be used to adjust the aperture size, location, and shape while the device is being used by the user and after the calibration procedure, for example. In some examples, process  1170  can be used to fine-tune the properties of the one or more apertures. Process  1170  can begin with setting the aperture properties (e.g., size, location, shape, etc.) to a pre-determined or previously determined configuration (step  1172 ). A processor or controller can determine an initial figure of merit associated with the pre-determined or previously determined configuration (step  1174 ). The device can change the aperture properties in a first direction (step  1176 ). A first direction can include, but is not limited to, increasing the size, separation distance, or location of the apertures away from a reference point. A first figure of merit associated with the first direction can be determined (step  1178 ). The processor can compare the initial figure of merit with the first figure of merit to determine if the change in the first direction is desired (step  1180 ). If the change in the first direction led to a better figure of merit, then the aperture properties can be continually changed towards the first direction. In some examples, a better figure of merit is one where the initial figure of merit is greater than the first figure of merit. In some examples, a better figure of merit is one where the initial figure of merit is less than the first figure of merit. If the change in the first direction was not favorable, then the device can revert back to the previous aperture properties (step  1182 ). The device can change the aperture properties in a second direction (step  1184 ). In some examples, the second direction can be opposite the first direction. The processor can determine a second figure of merit associated with the second direction (step  1190 ) and can compare the second figure of merit to the previous figure of merit (step  1192 ). If the second figure of merit is better than the previous figure of merit, then the aperture properties can be continually changed towards the second direction. In some examples, a better figure of merit is one where the second figure of merit is greater than the previous figure of merit. In some examples, a better figure of merit is one where the second figure of merit is less than the previous figure of merit. If the change in the second direction was not favorable, then the device can revert back to the previous aperture properties (step  1194 ). If there are no changes that result in a more favorable figure of merit, then the optimization process can cease. 
     In some examples, the processor can adjust the aperture size, location, and shape based on a tracking history. The processor can maintain a record of the user&#39;s typical use conditions or environmental conditions and can adjust the aperture based on this record. Although the drawings illustrate process flows for optimizing one aperture size, location, shape, or combination, examples of the disclosure include optimization for multiple apertures. Examples of the disclosure can include optimization of the number of apertures and consideration of whether an aperture transmits light to multiple components. Additionally, the use of the term “aperture” or “apertures” is meant to include any opening or material where light is selectively allowed to transmit through. 
     Although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
       FIG. 12  illustrates an exemplary block diagram of a computing system comprising light emitters and light sensors for measuring a signal associated with a user&#39;s physiological state according to examples of the disclosure. Computing system  1200  can correspond to any of the computing devices illustrated in  FIGS. 1A-1C . Computing system  1200  can include a processor  1210  configured to execute instructions and to carry out operations associated with computing system  1200 . For example, using instructions retrieved from memory, processor  1210  can control the reception and manipulation of input and output data between components of computing system  1200 . Processor  1210  can be a single-chip processor or can be implemented with multiple components. 
     In some examples, processor  1210  together with an operating system can operate to execute computer code and produce and use data. The computer code and data can reside within a program storage block  1202  that can be operatively coupled to processor  1210 . Program storage block  1202  can generally provide a place to hold data that is being used by computing system  1200 . Program storage block  1202  can be any non-transitory computer-readable storage medium, and can store, for example, history and/or pattern data relating to PPG signal and perfusion index values measured by one or more light sensors such as light sensors  1204 . By way of example, program storage block  1202  can include Read-Only Memory (ROM)  1218 , Random-Access Memory (RAM)  1222 , hard disk drive  1208  and/or the like. The computer code and data could also reside on a removable storage medium and loaded or installed onto the computing system  1200  when needed. Removable storage mediums include, for example, CD-ROM, DVD-ROM, Universal Serial Bus (USB), Secure Digital (SD), Compact Flash (CF), Memory Stick, Multi-Media Card (MMC) and a network component. 
     Computing system  1200  can also include an input/output (I/O) controller  1212  that can be operatively coupled to processor  1210 , or it can be a separate component as shown. I/O controller  1212  can be configured to control interactions with one or more I/O devices. I/O controller  1212  can operate by exchanging data between processor  1210  and the I/O devices that desire to communicate with processor  1210 . The I/O devices and I/O controller  1212  can communicate through a data link. The data link can be a one-way link or a two-way link. In some cases, I/O devices can be connected to I/O controller  1212  through wireless connections. By way of example, a data link can correspond to PS/2, USB, Firewire, IR, RF, Bluetooth or the like. 
     Computing system  1200  can include a display device  1224  that can be operatively coupled to processor  1210 . Display device  1224  can be a separate component (peripheral device) or can be integrated with processor  1210  and program storage block  1202  to form a desktop computer (e.g., all-in-one machine), a laptop, handheld or tablet computing device of the like. Display device  1224  can be configured to display a graphical user interface (GUI) including perhaps a pointer or cursor as well as other information to the user. By way of example, display device  1224  can be any type of display including a liquid crystal display (LCD), an electroluminescent display (ELD), a field emission display (FED), a light emitting diode display (LED), an organic light emitting diode display (OLED) or the like. 
     Display device  1224  can be coupled to display controller  1226  that can be coupled to processor  1210 . Processor  1210  can send raw data to display controller  1226 , and display controller  1226  can send signals to display device  1224 . Data can include voltage levels for a plurality of pixels in display device  1224  to project an image. In some examples, processor  1210  can be configured to process the raw data. 
     Computing system  1200  can also include a touch screen  1230  that can be operatively coupled to processor  1210 . Touch screen  1230  can be a combination of sensing device  1232  and display device  1224 , where the sensing device  1232  can be a transparent panel that is positioned in front of display device  1224  or integrated with display device  1224 . In some cases, touch screen  1230  can recognize touches and the position and magnitude of touches on its surface. Touch screen  1230  can report the touches to processor  1210 , and processor  1210  can interpret the touches in accordance with its programming. For example, processor  1210  can perform tap and event gesture parsing and can initiate a wake of the device or powering on one or more components in accordance with a particular touch. 
     Touch screen  1230  can be coupled to a touch controller  1240  that can acquire data from touch screen  1230  and can supply the acquired data to processor  1210 . In some cases, touch controller  1240  can be configured to send raw data to processor  1210 , and processor  1210  can process the raw data. For example, processor  1210  can receive data from touch controller  1240  and can determine how to interpret the data. The data can include the coordinates of a touch as well as pressure exerted. In some examples, touch controller  1240  can be configured to process raw data itself. That is, touch controller  1240  can read signals from sensing points  1234  located on sensing device  1232  and can turn the signals into data that the processor  1210  can understand. 
     Touch controller  1240  can include one or more microcontrollers such as microcontroller  1242 , each of which can monitor one or more sensing points  1234 . Microcontroller  1242  can, for example, correspond to an application specific integrated circuit (ASIC), which works with firmware to monitor the signals from sensing device  1232 , process the monitored signals, and report this information to processor  1210 . 
     One or both display controller  1226  and touch controller  1240  can perform filtering and/or conversion processes. Filtering processes can be implemented to reduce a busy data stream to prevent processor  1210  from being overloaded with redundant or non-essential data. The conversion processes can be implemented to adjust the raw data before sending or reporting them to processor  1210 . 
     In some examples, sensing device  1232  can be based on capacitance. When two electrically conductive members come close to one another without actually touching, their electric fields can interact to form a capacitance. The first electrically conductive member can be one or more of the sensing points  1234 , and the second electrically conductive member can be an object  1290  such as a finger. As object  1290  approaches the surface of touch screen  1230 , a capacitance can form between object  1290  and one or more sensing points  1234  in close proximity to object  1290 . By detecting changes in capacitance at each of the sensing points  1234  and noting the position of sensing points  1234 , touch controller  1240  can recognize multiple objects, and determine the location, pressure, direction, speed and acceleration of object  1290  as it moves across the touch screen  1230 . For example, touch controller  1290  can determine whether the sensed touch is a finger, tap, or an object covering the surface. 
     Sensing device  1232  can be based on self-capacitance or mutual capacitance. In self-capacitance, each of the sensing points  1234  can be provided by an individually charged electrode. As object  1290  approaches the surface of the touch screen  1230 , the object can capacitively couple to those electrodes in close proximity to object  1290 , thereby stealing charge away from the electrodes. The amount of charge in each of the electrodes can be measured by the touch controller  1240  to determine the position of one or more objects when they touch or hover over the touch screen  1230 . In mutual capacitance, sensing device  1232  can include a two layer grid of spatially separated lines or wires (not shown), although other configurations are possible. The upper layer can include lines in rows, while the lower layer can include lines in columns (e.g., orthogonal). Sensing points  1234  can be provided at the intersections of the rows and columns. During operation, the rows can be charged, and the charge can capacitively couple from the rows to the columns. As object  1290  approaches the surface of the touch screen  1230 , object  1290  can capacitively couple to the rows in close proximity to object  1290 , thereby reducing the charge coupling between the rows and columns. The amount of charge in each of the columns can be measured by touch controller  1240  to determine the position of multiple objects when they touch the touch screen  1230 . 
     Computing system  1200  can also include one or more light emitters such as light emitters  1206  and one or more light sensors such as light sensors  1204  proximate to skin  1220  of a user. Light emitters  1206  can be configured to generate light, and light sensors  1204  can be configured to measure a light reflected or absorbed by skin  1220 , vasculature, and/or blood of the user. Device  1200  can include dynamically reconfigurable apertures  1247  coupled to light emitters  1206  and light sensors  1204 . Light sensor  1204  can send measured raw data to processor  1210 , and processor  1210  can perform noise and/or artifact cancelation to determine the PPG signal and/or perfusion index. Processor  1210  can dynamically activate light emitters and/or light sensors and dynamically reconfigure the aperture properties based on an application, user skin type, and usage conditions. In some examples, some light emitters and/or light sensors can be activated, while other light emitters and/or light sensors can be deactivated to conserve power, for example. In some examples, processor  1210  can store the raw data and/or processed information in a ROM  1218  or RAM  1222  for historical tracking or for future diagnostic purposes. 
     In some examples, the light sensors can measure light information and a processor can determine a PPG signal and/or perfusion index from the reflected or absorbed light. Processing of the light information can be performed on the device as well. In some examples, processing of light information need not be performed on the device itself.  FIG. 13  illustrates an exemplary configuration in which an electronic device is connected to a host according to examples of the disclosure. Host  1310  can be any device external to device  1300  including, but not limited to, any of the systems illustrated in  FIGS. 1A-1C  or a server. Device  1300  can be connected to host  1310  through communications link  1320 . Communications link  1320  can be any connection including, but not limited to, a wireless connection and a wired connection. Exemplary wireless connections include Wi-Fi, Bluetooth, Wireless Direct and Infrared. Exemplary wired connections include Universal Serial Bus (USB), FireWire, Thunderbolt, or any connection requiring a physical cable. 
     In operation, instead of processing light information from the light sensors on the device  1300  itself, device  1300  can send raw data  1330  measured from the light sensors over communications link  1320  to host  1310 . Host  1310  can receive raw data  1330 , and host  1310  can process the light information. Processing the light information can include canceling or reducing any noise due to artifacts and determining physiological signals such as a user&#39;s heart rate. Host  1310  can include algorithms or calibration procedures to account for differences in a user&#39;s characteristics affecting PPG signal and perfusion index. Additionally, host  1310  can include storage or memory for tracking a PPG signal and perfusion index history for diagnostic purposes. Host  1310  can send the processed result  1340  or related information back to device  1300 . Based on the processed result  1340 , device  1300  can notify the user or adjust its operation accordingly. By offloading the processing and/or storage of the light information, device  1300  can conserve space and power-enabling device  1300  to remain small and portable, as space that could otherwise be required for processing logic can be freed up on the device. 
     In some examples, an electronic device is disclosed. The device can comprise: one or more light emitters configured to emit light; one or more light sensors configured to detect a reflection of the emitted light; and a material capable of forming one or more dynamically reconfigurable apertures to allow light to be transmitted from at least one of the one or more light emitters to at least one of the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises one or more light paths, each light path associated with one of the one or more light emitters and one of the one or more light sensors, wherein the electronic device is capable of dynamically reconfiguring one or more of a separation distance of the one or more light paths, a size of the one or more dynamically reconfigurable apertures, a location of the one or more dynamically reconfigurable apertures, and a shape of the one or more dynamically reconfigurable apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, one or more optical properties of the material is changed to form the one or more dynamically reconfigurable apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the material comprises a liquid crystal layer capable of forming the one or more dynamically reconfigurable apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the material comprises a plurality of microelectromechanical (MEMS) shutters capable of forming the one or more dynamically reconfigurable apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the material comprises a light guide configured to receive at least one of the emitted light and the reflection of the emitted light. Additionally or alternatively to one or more examples disclosed above, in other examples, at least one of the emitted light and the reflection of the emitted light enters or exits the light guide in a location different from the one or more light emitters or the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the light guide is located on a same layer as at least one of the one or more light emitters and the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the optical properties of the material are different in a location corresponding to the one or more dynamically reconfigurable apertures than a location outside of the one or more dynamically reconfigurable apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light sensors includes at least two light sensors capable of sensing different wavelengths. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters includes at least two light emitters capable of emitting at different wavelengths. Additionally or alternatively to one or more examples disclosed above, in other examples, the device further comprises: a first light path associated with at least one of the one or more light sensors and at least one of the one or more light emitters and having a first separation distance; and a second light path associated with at least one of the one or more light sensors and at least one of the one or more light emitters and having a second separation distance greater than the first separation distance, wherein a sensing wavelength of the at least one of the one or more light sensors or an emission wavelength of the at least one of the one or more light emitters associated with the second light path is longer than a sensing wavelength of the at least one of the one or more light sensors or an emission wavelength of the at least one of the one or more light emitters associated with the first light path. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters are located on a different layer than the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light emitters are formed from an array of individually addressable light emitters. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more light sensors are formed from an array of individually addressable light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the electronic device further comprises at least one optical filter, wherein at least one of the one or more light emitters is a broadband source coupled to the at least one optical filter. 
     In some examples, a method of determining a user&#39;s physiological state with an electronic device, including one or more light emitters and one or more light sensors, is disclosed. The method can comprise: emitting a first light from the one or more light emitters; receiving a second light by the one or more light sensors, the second light being a reflection of the first light; and dynamically reconfiguring one or more apertures to a first configuration to allow the first light to be transmitted from the one or more light emitters, and to allow the second light to be received at the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises associating a light path with one of the one or more light emitters and one of the one or more light sensors, wherein the dynamic reconfiguration of the one or more apertures leads to at least one of a different separation distance between the one or more light emitters and the one or more light sensors, a different size of the one or more apertures, a different location of the one or more apertures, and a different shape of the one or more apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: emitting a third light from the one or more light emitters; receiving a fourth light by the one or more light sensors, the fourth light being a reflection of the third light; and dynamically reconfiguring one or more apertures to a second configuration to allow the third light to be transmitted from the one or more light emitters, and to allow the fourth light to be received at the one or more light sensors, wherein a separation distance for the first configuration is different from a separation distance different for the second configuration. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining a PPG signal from the first configuration; and determining a perfusion index from the second configuration. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more apertures of the second configuration block the second light and wherein the one or more apertures of the first configuration block the fourth light. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining an amount of noise from a signal of the second light; and dynamically reconfiguring the one or more apertures to a second configuration when the amount of noise or the signal of the second light is greater than or equal to a first threshold, the second configuration having a lower amount of noise than the first configuration. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining a signal value of the second light; and dynamically reconfiguring the one or more apertures to a second configuration when the signal value of the second light is less than or equal to a second threshold, the signal value of the second light being higher than a signal value of the first light in the first configuration. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises controlling a voltage of a liquid crystal material to dynamically reconfigure the one or more apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises controlling a position of one or more microelectromechanical (MEMS) shutters to dynamically reconfigure the one or more apertures. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises controlling an addressing of one or more individually addressable light emitters to dynamically change properties of one or more light paths, each light path associated with one of the one or more light emitters and one of the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises controlling an addressing of one or more individually addressable light sensors to dynamically change properties of one or more light paths, each light path associated with one of the one or more light emitters and one of the one or more light sensors. Additionally or alternatively to one or more examples disclosed above, in other examples, the properties of the one or more light paths include at least one of a separation distance, a size, a location, and a shape. Additionally or alternatively to one or more examples disclosed above, in other examples, the dynamic reconfiguration is based on a user activity. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: emitting a third light from the one or more light emitters; receiving a fourth light from the one or more light sensors, the fourth light being a reflection of the third light; dynamically reconfiguring one or more apertures to a second configuration to allow the third light to be transmitted from the one or more light emitters, and to allow the fourth light to be received at the one or more light sensors; emitting a fifth light from the one or more light emitters; receiving a sixth light from the one or more light sensors, the sixth light being a reflection of the fifth light; dynamically reconfiguring one or more apertures to a third configuration to allow the fifth light to be transmitted from the one or more light emitters, and to allow the sixth light to be received at the one or more light sensors; and comparing a signal from the second light to a signal from the fourth and sixth light. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.

Metadata:
Filing Date: 20160426
Publication Date: 20181106
Grant Date: 20181106
Priority Date: 20150427
Inventors: HAN, Chin San
Assignee: APPLE INC
CPC Classifications: [{"code": "A61B5/14552", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/02427", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/7214", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2560/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2560/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/7214", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/14552", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/02427", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/02427", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/14552", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2562/0242", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/02427", "inventive": true, "first": true, "tree": "[]"}, {"code": "A61B5/6898", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/14552", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/7214", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/681", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2560/0252", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B5/7214", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B5/6898", "inventive": true, "first": false, "tree": "[]"}, {"code": "A61B2562/0238", "inventive": false, "first": false, "tree": "[]"}, {"code": "A61B2560/0252", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 56084343