Wearable device and method for determining a photoplethysmogram

Abstract

A wearable device for determining a photoplethysmogram, the wearable device comprising at least a first light source arranged to provide light to at least one entry point on the body of a proband when the wearable device is used by the proband. The wearable device further comprises at least a first light detector arranged to detect light received from the light source through the body of the proband. The wearable device further comprises a control device arranged to calculate a photoplethysmogram based on the detected light. The wearable device further comprises at least a first detector optical waveguide and a second detector optical waveguide arranged to detect light at at least two different positions on the body of the proband and feed the light to the at least first light detector when the wearable device is used by the proband.

Description

Technical Field

[0001] The present invention generally relates to the field of wearable devices for health monitoring; more particularly, to wearable devices and methods for determining photoplethysmograms. Background Art

[0002] Generally, photoplethysmography analyzes the change in blood volume of the underlying microvascular bed of tissue non-invasively by irradiating the skin of a subject. A photoplethysmogram provides valuable information about the cardiovascular and other physiological systems, such as changes in blood flow or blood opacity related to heart rate, respiration, blood oxygen level, etc. Currently, there are many technical problems with traditional devices used for determining photoplethysmograms and the sensing methods used therein for comprehensive health monitoring. One of the main problems is managing the power consumption of such traditional devices. Generally, a light emitter is used in photoplethysmography to achieve the irradiation purpose. In traditional devices, the light emitter (e.g., light-emitting diode) is usually the main power consumption source of photoplethysmography. For traditional wearable devices powered by size-limited batteries, managing the power consumption to power such a light emitter becomes more challenging. In one example, having multiple light emitters can provide better irradiation and output signals, but it may also have the adverse effect of rapid battery depletion, or may further lead to an increase in the size of traditional wearable devices, which is undesirable.

[0003] Another technical problem is inaccuracy in determining photoplethysmograms, which results in inaccurate health metrics, such as incorrect heart rate, respiration rate, etc. For example, almost everyone has different body characteristics at a specific body part, such as different vein or artery positions, and these characteristics can be carefully examined to determine the photoplethysmogram. The current sensing methods and optical devices used in traditional devices are error-prone and insufficient to handle such differences in body characteristic positions, and thus may not provide consistent and accurate measurement results for everyone. In some cases, when determining the photoplethysmogram, the subject wearing the traditional wearable device may perform certain physical activities, such as exercise, or may have some body movements, such as hand movements. Such movements may cause motion artifacts, resulting in much lower accuracy of the health metrics monitored using traditional wearable devices. For example, due to hand movements, heart rate monitoring through the wrist or finger is inaccurate. One way to improve accuracy during physical activities or any body movement can be to feed more power to the light emitter so that the resulting signal has an acceptable signal quality. However, the adverse effect of increased power consumption depletes the battery of the wearable device, resulting in the situation that even during non-exercise periods, traditional devices may not have enough power to measure the subject over a day or a week, which is undesirable.

[0004] Therefore, in view of the above discussion, there is a need to overcome the above disadvantages associated with conventional devices and methods for determining photoplethysmograms and for health monitoring. SUMMARY OF THE INVENTION

[0005] The present invention seeks to provide a wearable device and method for determining a photoplethysmogram. The present invention seeks to provide a solution to the existing inefficient power management problem and the error-prone sensing method currently used for determining photoplethysmograms, which results in health metrics that cannot be accurately monitored by conventional devices. The object of the present invention is to provide a solution that at least partially overcomes the problems encountered in the prior art and provides an improved wearable device and method capable of efficiently managing power consumption and accurately determining a photoplethysmogram to obtain accurate health metrics.

[0006] The object of the present invention is achieved by the solution provided in the appended independent claims. Advantageous implementations of the present invention are further defined in the dependent claims.

[0007] In a first aspect, the present invention provides a wearable device for determining a photoplethysmogram. The wearable device includes at least a first light source arranged to provide light to at least one entry point on the body of a proband when the wearable device is used by the proband. The wearable device further includes at least a first light detector arranged to detect light received from the light source through the body of the proband when the wearable device is used by the proband. The wearable device further includes control means arranged to calculate a photoplethysmogram based on the detected light. The wearable device further includes at least a first detector optical waveguide and a second detector optical waveguide arranged to detect light at at least two different positions on the body of the proband and feed the light to the at least first light detector when the wearable device is used by the proband.

[0008] The wearable device described in the first aspect can obtain an improved output signal while efficiently managing power consumption. For example, an improved pulsatile physiological waveform (i.e., the "AC" part of the signal) is obtained in the form of an output signal, which is generated due to changes in blood volume related to heartbeat, respiration, blood oxygen level, etc., so that a photoplethysmogram can be accurately determined. Since the first detector optical waveguide and the second detector optical waveguide are arranged to detect light at at least two different positions on the body of the subject, the opportunity to interact with relevant body features (such as arteries) on the body of the subject is significantly increased. This improved optical device and sensing method increases the number of reading (i.e., measuring) points covering different body features on the body of the subject, thereby improving the accuracy of determining the photoplethysmogram without any increase in the power consumption of a single first light source.

[0009] In the first implementation of the first aspect, the at least first light detector is a photodiode.

[0010] Since the light detected at at least two different positions on the body of the subject by the first detector optical waveguide and the second detector optical waveguide is fed to the photodiode, the signal quality of the output signal is significantly improved, thereby improving the accuracy of determining the photoplethysmogram.

[0011] In the second implementation of the first aspect, the at least first light source is a light-emitting diode. The wearable device further includes at least a first source optical waveguide and a second source optical waveguide, and the at least first source optical waveguide and the second source optical waveguide are arranged to receive light from the at least first light source. In use, the light of the at least first light source is guided by the at least first source optical waveguide and the second source optical waveguide to enter the body of the subject through at least two different entry points.

[0012] Using the first source optical waveguide and the second source optical waveguide to receive light from the at least first light source ensures the power efficiency of the wearable device while further improving the accuracy of determining the photoplethysmogram. Since multiple source optical waveguides are used to irradiate light at at least two different positions to enter the body of the subject, the opportunity to interact with relevant body features (such as arteries) on the body of the subject is significantly increased. This improves health index monitoring, for example, improves clinical physiological measurements, vascular assessments, and autonomic functions. In addition, enhancing the irradiation at at least two different positions also increases the sensing ability of the first light detector, which receives light from at least two different positions on the body of the subject from the first detector optical waveguide and the second detector optical waveguide.

[0013] In the third implementation of the first aspect, the wearable device includes one light source and two light detectors.

[0014] By having two optical detectors (e.g., multiple photodiodes), the power of the "AC" part of the output signal (i.e., the quality and signal intensity of the pulsatile physiological waveform of the photoplethysmogram waveform) increases without any increase in the power consumption of a single light source in the wearable device.

[0015] In a fourth implementation of the first aspect, the wearable device includes at least three source optical waveguides for each light source to separate the light from the light source.

[0016] Increasing the number of source optical waveguides increases the chance of interaction with relevant body features (such as arteries) on the body of the subject, without any increase in the power consumption of the light source. Additionally, increasing the interaction with relevant body features (such as arteries) on the body of the subject improves the accuracy of determining the photoplethysmogram, thereby accurately monitoring the health indicators of the subject.

[0017] In a fifth implementation of the first aspect, the wearable device includes at least three detector optical waveguides for each optical detector to detect light at different positions on the body of the subject.

[0018] Detecting light at different positions on the body of the subject using at least three detector optical waveguides increases the number of reading (i.e., measuring) points covering different body features on the body of the subject. Increasing the number of reading points improves the accuracy of determining the photoplethysmogram without increasing the power consumption of the light source.

[0019] In a sixth implementation of the first aspect, the first light source is a tunable laser. The wearable device further includes an optical waveguide that includes a metasurface, and the control device is arranged to control the wavelength of the laser to control the position of the at least one entry point.

[0020] In the case where the light source is a tunable laser, the optical waveguide with a metasurface can be used to direct different optical bands to different positions (i.e., different entry points) to enter the body of the subject. Thus, even if different people have different body features, such as different vein or artery positions, at a specific body part, the control device can adequately handle such body feature differences (due to irradiating different positions within a specific range) by using the optical waveguide, thereby providing consistent and accurate measurements for each person.

[0021] In a seventh implementation of the first aspect, the control device is arranged to calculate the photoplethysmogram based on the light detected by all detector optical waveguides of all optical detectors.

[0022] Since all the detector optical waveguides of all the photodetectors are used for detecting light, the cumulative signal intensity of the output signal (e.g., the power of the AC component of the output signal) increases, while there is no increase in the power consumption of a single light source in the wearable device. This improved optical device and sensing method increases the number of reading (i.e., measuring) points covering different body features on the body of the proband, thereby improving the accuracy of determining the photoplethysmogram, while there is no increase in the power consumption of a single first light source.

[0023] In eight implementations of the first aspect, the control device is arranged to select at least one detector optical waveguide to calculate the photoplethysmogram based on the light detected from the at least one selected detector optical waveguide.

[0024] Selecting at least one detector optical waveguide can obtain an output signal having a relatively high signal intensity (e.g., an increase in the power of the AC component of the output signal) measured from at least one point (associated with at least one detector optical waveguide) compared to other points on the body of the proband. Therefore, the accuracy of determining the photoplethysmogram is improved, while there is no increase in the power consumption of the first light source.

[0025] In the ninth implementation of the first aspect, the control device is arranged to select at least one source optical waveguide among the source optical waveguides to provide light to the body of the proband.

[0026] The control device can locate the appropriate position of a vascular feature (e.g., artery or vein) according to the selection of at least one of the source optical waveguides to provide light to the located position. Therefore, the interaction with the relevant vascular feature of the body of the proband improves the accuracy of determining the photoplethysmogram, enabling accurate monitoring of the health indicators of the proband.

[0027] In the tenth implementation of the first aspect, the wearable device is a watch, a bracelet or a ring.

[0028] In traditional wearable devices, due to challenges in hand movement and determining the appropriate position of traditional sensors on the skin surface, health indicator monitoring, especially through watches, bracelets or rings, is inaccurate. Compared with traditional wearable devices, the waveguide-enhanced optical device in the wearable device of the present invention improves the sensing ability by increasing the number of reading (i.e., measuring) points covering different body features on the body of the proband, thereby reducing any motion artifacts caused by hand movement. This further increases the accuracy of determining the photoplethysmogram without increasing the power consumption of the first light source.

[0029] In the second aspect, the present invention provides a use of a wearable device for determining the photoplethysmogram of a proband.

[0030] The wearable device described in the second aspect can accurately monitor the health indicators of the proband and achieve all the advantages and effects of the wearable device described in the first aspect.

[0031] In a third aspect, the present invention provides a method for determining a photoplethysmogram of a proband using a device. The method is implemented when the proband wears the device. The method includes: emitting light from a first light source to at least one point on the proband's body. The method further includes: receiving the light through at least a first detector optical waveguide and a second detector optical waveguide, the at least first detector optical waveguide and the second detector optical waveguide being arranged to detect light at at least two different positions on the proband's body; feeding the received light to a photodetector. The method further includes: calculating the photoplethysmogram based on the light received from at least one optical waveguide.

[0032] The method described in the third aspect achieves all the advantages and effects of the wearable device in the first aspect.

[0033] In a first implementation of the third aspect, the method further includes: steps performed for at least a first position and a second position of the device relative to the proband that are different, before the steps of the method described in the third aspect. The method further includes: emitting light from the first light source; receiving the light through the at least first detector optical waveguide and the second detector optical waveguide; feeding the received light to the photodetector. The method further includes: calculating the photoplethysmogram; determining which of the first position and the second position provides a better result relative to each other; positioning the device at the position that provides the better result.

[0034] When determining which of the first position and the second position provides a better result relative to each other, the signal quality of the output signal is significantly improved, thereby improving the accuracy of determining the photoplethysmogram. In other words, the quality and signal intensity of the pulsatile physiological waveform (i.e., the AC component) of the photoplethysmogram waveform are significantly increased, without any increase in the power consumption of a single light source in the wearable device.

[0035] It should be noted that all devices, components, circuits, units, and modules described in this application can be implemented by software or hardware components or any combination thereof. All steps performed by various entities described in this application and the functions described to be performed by various entities are intended to indicate that the corresponding entities are adapted or used to perform the corresponding steps and functions. Although in the description of the following specific embodiments, the specific functions or steps performed by external entities are not reflected in the description of the specific detailed components of the entity performing the specific step or function, those skilled in the art should be clear that these methods and functions can be implemented in the corresponding hardware or software components or any combination thereof. It should be understood that various combinations of the features of the present invention can be made without departing from the scope of the present invention defined by the appended claims.

[0036] Additional aspects, advantages, features, and objectives of the present invention become apparent from the accompanying drawings and the detailed description of the illustrative implementations explained in conjunction with the following appended claims. Brief Description of the Drawings

[0037] Reading in conjunction with the accompanying drawings can better understand the above overview and the detailed description of the following illustrative embodiments. To illustrate the present invention, an exemplary structure of the present invention is shown in the drawings. However, the present invention is not limited to the specific methods and tools disclosed herein. In addition, those skilled in the art should understand that the drawings are not drawn to scale. Where possible, the same elements are denoted by the same reference numerals.

[0038] Embodiments of the present invention will now be described by way of example only with reference to the following drawings, in which:

[0039] Figure 1 is a block diagram showing various exemplary components of a wearable device provided by an embodiment of the present invention;

[0040] Figure 2 is a diagram showing an exemplary scenario of a wearable device for implementing a photoplethysmogram determination provided by an embodiment of the present invention;

[0041] Figure 3 is a diagram showing different exemplary positions describing the vascular characteristics of body parts of different probands provided by an embodiment of the present invention;

[0042] Figure 4 is a diagram showing an output signal derived from multiple signals detected at different positions of a body part of a proband provided by an embodiment of the present invention;

[0043] Figure 5 is a diagram of an exemplary wearable device having a tunable laser as a light source and an optical waveguide provided by another embodiment of the present invention;

[0044] Figure 6 The flowchart shows a method for a device to determine the photoplethysmogram of a proband according to an embodiment of the present invention.

[0045] In the drawings, underlined numbers are used to denote the item in which the underlined number is located or the item adjacent to the underlined number. Non-underlined numbers refer to the item identified by the line connecting the non-underlined number and the item. When a number is non-underlined and has an associated arrow, the non-underlined number is used to identify the general item to which the arrow points. Detailed Description of the Invention

[0046] The following detailed description illustrates embodiments of the present invention and ways in which these embodiments can be implemented. Although some modes of implementing the present invention have been disclosed, those skilled in the art should recognize that there may be other embodiments for implementing or practicing the present invention.

[0047] Figure 1 The block diagram shows various exemplary components of a wearable device according to an embodiment of the present invention. Referring to Figure 1 , a wearable device 102 is shown. The wearable device 102 includes a first light source 104 and one or more light detectors, such as a first light detector 106. The wearable device 102 also includes a control device 108 and a plurality of detector optical waveguides 110, such as a first detector optical waveguide 110A and a second detector optical waveguide 110B. A proband 112 associated with the wearable device 102 is also shown. Optionally, in one implementation, the wearable device 102 further includes a plurality of source optical waveguides 114, such as a first source optical waveguide 114A and a second source optical waveguide 114B.

[0048] The wearable device 102 includes suitable logic, circuitry, interfaces, and / or code for determining, for example, the photoplethysmogram of the proband 112 when the wearable device 102 is used by the proband 112. The proband 112 refers to a person (e.g., a user or a given subject) or any living organism. The photoplethysmogram associated with the proband 112 may be used to measure (or indicate) one or more health metrics of the body of the proband (hereinafter referred to as the body of the proband 112). In other words, the wearable device 102 may be used to monitor various health metrics of the body of the proband 112 who may wear the wearable device 102 based on the determined photoplethysmogram. Examples of health metrics monitored by the wearable device 102 include, but are not limited to, the heart rate, heart rate variability (HRV), glucose level, blood pressure, and peripheral capillary oxygen saturation (SPO2) level of the body of the proband 112.

[0049] According to an embodiment, the wearable device 102 is a watch, a bracelet, or a ring. In such an embodiment, the wearable device 102 is worn by the proband 112 on the wrist or finger. The wearable device 102 may also be worn (or attached) on the earlobe, neck, or forehead of the proband 112's body, or on any other body part of the proband 112 suitable for performing photoplethysmography. Other examples of implementations of the wearable device 102 include, but are not limited to, smart clothing, fashion electronics, sports monitoring devices, identification devices (e.g., human identification based on specific health metrics), medical devices, military devices, gaming devices, or other wearable computing devices.

[0050] The first light source 104 is a semiconductor device (i.e., a light emitter) that emits light when powered. In other words, the first light source 104 is used to convert electrons when powered in the form of photons, which are emitted from the first light source 104 in the form of electromagnetic radiation (i.e., as light). The first light source 104 is arranged to provide light to at least one entry point on the body of the proband 112 when the wearable device 102 is used by the proband 112. According to an embodiment, at least the first light source 104 is a light-emitting diode. In one implementation, the light-emitting diode is an infrared light-emitting diode. In another implementation, the light-emitting diode is a green light-emitting diode. In yet another implementation, the light-emitting diode is a combination of an infrared light-emitting element and a green light-emitting element, which operate alternately according to a specified setting. For example, one type of color light-emitting element is "turned on" at a time to save power, but advantageously, green and infrared light wavelengths are used in health metric monitoring. According to another embodiment, at least the first light source 104 is a tunable laser. The tunable laser emits wavelengths of red or near-infrared light during operation for irradiating a body part (e.g., finger part, wrist part, etc.) of the proband 112 wearing the wearable device 102. Optionally, the tunable laser is used to emit wavelengths of green light or other wavelengths for irradiation purposes.

[0051] One or more light detectors (e.g., first light detector 106) are used to detect an optical signal (i.e., in the form of light) emitted by a light source (e.g., first light source 104) after the light has propagated through a medium (e.g., the body of the proband 112). The one or more light detectors act as light receivers in the wearable device 102. Thus, the first light detector 106 is arranged to detect light received from at least the first light source 104 through the body of the proband 112 when the wearable device 102 is used by the proband 112. According to an embodiment, at least the first light detector 106 is a photodiode. In one example, the photodiode is a positive-intrinsic-negative (PIN) diode, an avalanche photodiode, or other types of photodiodes capable of detecting light. For example, in the case where the first light source 104 is implemented as a tunable laser in the wearable device 102, the first light detector 106 can be implemented as an avalanche photodiode. According to an embodiment, the wearable device 102 includes one light source (e.g., first light source 104) and two light detectors (e.g., first light detector 106).

[0052] The control device 108 may include suitable logic, circuitry, interfaces, and / or code for calculating a photoplethysmogram based on the light detected by one or more light detectors (e.g., first light detector 106). Examples of the control device 108 may include, but are not limited to, a microprocessor, a microcontroller, a complex instruction set computing (CISC) processor, an application-specific integrated circuit (ASIC) processor, a reduced instruction set (RISC) processor, a very long instruction word (VLIW) processor, a central processing unit (CPU), a state machine, a data processing unit, and other processors or circuitry. Additionally, the control device 108 may refer to one or more individual processors, processing devices, or processing units that are part of the wearable device 102.

[0053] The plurality of detector optical waveguides 110 (e.g., a first detector optical waveguide 110A and a second detector optical waveguide 110B) are physical structures for guiding waves (e.g., electromagnetic waves in the form of light). The plurality of detector optical waveguides 110 (e.g., a first detector optical waveguide 110A and a second detector optical waveguide 110B) capture light at different positions on a body part (e.g., a finger part) and direct (or guide) the light captured from the different positions to a light detector (e.g., a first light detector 106) with minimal energy loss. In other words, the first detector optical waveguide 110A and the second detector optical waveguide 110B are arranged in the wearable device 102 to detect light at at least two different positions on the body of the proband 112 when the wearable device 102 is used by the proband 112 and feed the detected light to the first light detector 106. The first detector optical waveguide 110A and the second detector optical waveguide 110B may be waveguides with a constant cross-sectional area or a variable cross-sectional area. For example, the first detector optical waveguide 110A and the second detector optical waveguide 110B may be waveguides with a constant cross-sectional area, such as strip waveguides, rib waveguides, etc. In another example, the first detector optical waveguide 110A and the second detector optical waveguide 110B are waveguides with a variable cross-sectional area, such as segmented waveguides, photonic crystal waveguides, etc. In yet another example, the first detector optical waveguide 110A and the second detector optical waveguide 110B are laser scribed waveguides, light pipes, optical fibers, etc.

[0054] According to an embodiment, the wearable device 102 further includes at least a first source optical waveguide 114A and a second source optical waveguide 114B, and the at least first source optical waveguide 114A and the second source optical waveguide 114B are arranged to receive light from at least a first light source 104. Each of the first source optical waveguide 114A and the second source optical waveguide 114B is a physical structure (e.g., an optical fiber) similar to the first detector optical waveguide 110A and the second detector optical waveguide 110B. In one example, each of the first source optical waveguide 114A and the second source optical waveguide 114B has a first end and a second end. The first end of each of the first source optical waveguide 114A and the second source optical waveguide 114B is coupled to the first light source 104. In use, the second end of each of the first source optical waveguide 114A and the second source optical waveguide 114B is arranged in the wearable device 102 such that the light emitted by the first light source 104 is guided to enter the body of the proband 112 through at least two different entry points. In one example, in use, the second end of each of the first source optical waveguide 114A and the second source optical waveguide 114B may be close to or in contact with two different entry points on the body of the proband 112 (e.g., on the wrist, finger, neck, forehead, etc.). In other words, at least two different entry points are exposed to the light guided through the second ends of the first source optical waveguide 114A and the second source optical waveguide 114B. For example,Figure 2 Exemplary arrangements of a plurality of source optical waveguides 114 are shown and described. In one example, both the plurality of source optical waveguides 114 and the plurality of detector optical waveguides 110 are each constructed using photon components. Optionally, the cores of the plurality of source optical waveguides 114 and the plurality of detector optical waveguides 110 may be deposited with silicon nitride (SixNy) material to enable light to pass through efficiently.

[0055] According to another embodiment, the first source optical waveguide 114A and the second source optical waveguide 114B are optical waveguides having a metasurface. In use, the first source optical waveguide 114A and the second source optical waveguide 114B are used to guide light emitted by at least the first light source 104 to enter the body of the proband 112 through at least two different entry points. Figure 5 Examples of metasurfaces are shown and described. The metasurface of the optical waveguide provides a defined surface area that enables light to enter the body of the proband 112 through various entry points (e.g., two or more different entry points). An exemplary implementation of the first source optical waveguide 114A and the second source optical waveguide 114B is similar to the exemplary implementation of the first detector optical waveguide 110A and the second detector optical waveguide 110B described above.

[0056] According to an embodiment, the wearable device 102 includes at least three source optical waveguides for each light source to split the light from the light source. At least three source optical waveguides (e.g., the plurality of source optical waveguides 114) split the light from the light source (e.g., the first light source 104) and guide the light to at least three entry points on the body of the proband 112. The term "splitting" means receiving light from a single source point and guiding the received light to multiple destination points, which is similar to the splitting (or dividing) of a light-emitting point. According to an embodiment, the wearable device 102 includes at least three detector optical waveguide detectors for each light detector to detect light at different positions on the body of the proband 112. At least three detector optical waveguide detectors detect light at at least three different positions on the body of the proband 112 and feed the light to the light detector (e.g., the first light detector 106).

[0057] In operation, the proband 112 can wear the wearable device 102 and "power on" the wearable device 102. In one implementation, the wearable device 102 can be communicatively coupled to an external device, such as a smartphone or other display device, via a wired or wireless communication network. In this case, the wearable device 102 can be "powered on" or "powered off" based on user input provided by a user of the external device. In another implementation, a hardware button or user interface can be provided in the wearable device 102 to control the wearable device 102, such as "turning on" or "turning off" the wearable device 102.

[0058] The wearable device 102 includes a first light source 104 which is arranged to provide light to at least one entry point on the body of the proband 112 when the wearable device 102 is used by the proband 112. A first source optical waveguide 114A and a second source optical waveguide 114B are arranged to receive light from at least the first light source 104. In use, the light from the first light source 104 is guided by at least the first source optical waveguide 114A and the second source optical waveguide 114B to enter the body of the proband through at least two different entry points. Optionally, for each light source, at least three source optical waveguides are arranged to split the light from the light source at at least three entry points on the body of the proband 112. In the case where the first light source 104 is implemented as a tunable laser, the control device 108 is arranged to control the wavelength of the first light source 104 to control the position of at least one entry point (or multiple entry points) on the body of the proband 112. In other words, one or more entry points (or positions) on the body of the proband 112 are irradiated by the light from each source optical waveguide of the plurality of source optical waveguides 114. For example, different points on the skin surface such as fingers, wrists, earlobes, necks, etc. are irradiated by photons of light passing through the tissue microvascular bed under the exposed skin surface to non-invasively analyze blood volume changes and possible other changes in the blood vessels or the vascular structure in the blood or the exposed tissue. In addition, when different points on the skin surface are irradiated, the chance of interaction with relevant body features (such as arteries) on the body of the proband 112 is significantly increased.

[0059] A plurality of detector optical waveguides 110 (e.g., a first detector optical waveguide 110A and a second detector optical waveguide 110B) are arranged to detect light at at least two different positions on the body of the proband 112 and feed the light to a light detector (e.g., a first light detector 106) when the wearable device 102 is used by the proband 112. The arrangement of at least the first detector optical waveguide 110A and the second detector optical waveguide 110B for detecting light at at least two different positions on the body of the proband 112 is advantageous because this arrangement improves the sensing ability of the wearable device 102 by increasing the number of reading (i.e., measuring) points covering different body features (such as arteries and veins) on the body of the proband 112 without increasing the power consumption of the first light source 104. The first light detector 106 is arranged to detect the light received from at least the first light source 104 through the body of the proband 112 when the wearable device 102 is used by the proband 112. The first light detector 106 detects the light guided by the first detector optical waveguide 110A and the second detector optical waveguide 110B.

[0060] The wearable device 102 including the control device 108 is arranged to calculate a photoplethysmogram based on the light detected from the body of the proband 112. The accuracy of calculating the photoplethysmogram by the wearable device 102 depends on the number of interactions of the light with the body features (especially vascular features, such as arteries) on the body of the proband 112. It can be observed that the more the number of interactions, the higher the accuracy of the calculated photoplethysmogram.

[0061] According to an embodiment, the control device 108 is arranged to calculate a photoplethysmogram based on the light detected from all detector optical waveguides of all light detectors. A plurality of detector optical waveguides 110 (e.g., the first detector optical waveguide 110A and the second detector optical waveguide 110B) feed light to the corresponding light detectors. Generally, having a plurality of light detectors (e.g., the first light detector 106) increases the total power (or intensity) of the alternating current (AC) component of the signals (e.g., electromagnetic waves or electromagnetic signals in the form of light) detected at all light detectors. According to an embodiment, the control device 108 is used to perform summation on such signals detected at all light detectors to obtain a final output signal. The AC component of this summation signal (i.e., the final output signal) has increased power, thereby improving the accuracy of determining the photoplethysmogram without any increase in the power consumption of the first light source 104. For example, Figure 4 Exemplary summation operations are shown and described in

[0062] According to an embodiment, the control device 108 is arranged to select at least one source optical waveguide from the source optical waveguides (e.g., a plurality of source optical waveguides 114) to provide light to the body of the proband 112. In one example, the control device 108 selects one source optical waveguide from three source optical waveguides for guiding the light emitted from the first light source 104. The control device 108 may select the source optical waveguide arranged at a specific position (e.g., the optimal position or the entry point) on the body of the proband 112 that may interact with the vascular features (e.g., arteries). For example, based on simulation or trial operation, the control device 108 is used to locate the appropriate positions of one or more vascular features (e.g., arteries or veins) according to the selection of at least one source optical waveguide from the source optical waveguides (a plurality of source optical waveguides 114) to provide light to the located positions. In addition, such selection may be different for each proband (e.g., the proband 112). Therefore, the control device 108 is arranged to select one or more source optical waveguides from the plurality of source optical waveguides 114 for each proband so as to increase the interaction of the light with the arteries in the body of the corresponding proband. The interaction with the relevant vascular features of each proband improves the accuracy of determining the photoplethysmogram, thereby enabling consistent and accurate monitoring of health indicators for each proband.

[0063] According to an embodiment, the control device 108 is arranged to select at least one detector optical waveguide to calculate a photoplethysmogram based on the light detected from the at least one selected detector optical waveguide. The control device 108 may select a detector optical waveguide that captures a signal (i.e., an electromagnetic signal or an electromagnetic wave in the form of light) whose signal strength is greater than the signal strength of the signals captured by other detector optical waveguides. The selection is performed based on the interaction of light with the arteries in the body of the proband 112. In other words, selecting at least one detector optical waveguide enables obtaining an output signal having a relatively high signal strength (e.g., an increase in the power of the AC component of the output signal) measured from at least one point (associated with the at least one detector optical waveguide) compared to other points on the body of the proband 112. Therefore, the accuracy of determining the photoplethysmogram is improved without any increase in the power consumption of the first light source 104.

[0064] Figure 2 FIG. is a diagram of an exemplary scenario 200 for implementing a wearable device for determining a photoplethysmogram provided by an embodiment of the present invention. In combination with Figure 1 element description Figure 2 . Referring to Figure 2 , an exemplary scenario 200 including a wearable device 202 worn on a finger 204 is shown. In this embodiment, the wearable device 202 is in the form of a ring. The wearable device 202 includes a first light source 206, a first light detector 208, a second light detector 210, a set of source optical waveguides 212, a first set of detector optical waveguides 214, and a second set of detector optical waveguides 216. Also shown are the dorsal side 218A and the proximal side 218B of the finger 204, which includes an epidermis 218, a vein 220, an artery 222, a distal phalanx 224, a tendon 226, and a proximal phalanx 228.

[0065] According to the exemplary scenario 200, the wearable device 202 corresponds to the wearable device 102 ( Figure 1 ). In this embodiment, the first light source 206 is a light-emitting diode, and each of the first light detector 208 and the second light detector 210 is a photodiode. In addition, in this embodiment, each of the set of source optical waveguides 212, the first set of detector optical waveguide groups 214, and the second set of detector optical waveguide groups 216 is an optical fiber. In one example, the wearable device 202 may include a battery, a memory for data storage, a network interface, which are not shown for the sake of simplicity. The battery powers the first light source 206. In one example, the wearable device 202 may be communicatively coupled to an external device, such as a smartphone, via a network interface (e.g., wirelessly).

[0066] According to exemplary scenario 200, a first light source 206 is arranged to provide light to a proximal side 218B of a finger 204, as shown. The set of source optical waveguides 212 (e.g., five waveguides in this case) are arranged to receive light from the first light source 206 at their first ends during operation. The light from the first light source 206 is guided by the set of source optical waveguides 212 to enter the finger 204 through five different entry points through the epidermis 218 (e.g., through the second ends of each of the set of source optical waveguides 212 that are exposed to the epidermis 218, as shown). Thus, the epidermis 218 including the subcutaneous tissue (e.g., artery 222) is illuminated at five different points, without any additional power consumption by the first light source 206. For example, the reflected light from the artery 222 is detected by the first set of detector optical waveguides 214 and the second set of detector optical waveguides 216.

[0067] The first set of detector optical waveguides 214 is arranged at a defined distance from the set of source optical waveguides 212. The first set of detector optical waveguides 214 is arranged to detect light at five different locations on the finger 204 and feed the detected light to the first optical detector 208. Similarly, the second set of detector optical waveguides 216 is arranged at a defined distance from the set of source optical waveguides 212 and is generally opposite the first set of detector optical waveguides 214 to increase the coverage and detect the reflected light from the artery 222. The second set of detector optical waveguides 216 is arranged to detect light at five different locations on the finger 204 and feed the detected light to the second optical detector 210. Thus, the first optical detector 208 receives light (e.g., a first signal in the form of electromagnetic radiation, i.e., light) from the first set of detector optical waveguides 214, and the second optical detector 210 receives light (e.g., a second signal in the form of electromagnetic radiation, i.e., light) from the second set of detector optical waveguides 216. The control device 108 is configured to calculate a photoplethysmogram based on the light detected at the first optical detector 208 and the second optical detector 210. The light detected over a period of time indicates how the reflected light and scattered light intensities vary with each blood flow pulse. The scattered light intensity typically varies over time relative to changes in blood flow or blood opacity associated with heartbeats, respiration, blood oxygen level (SPO2), etc. Compared with traditional wearable devices, the waveguide-enhanced optical device in the wearable device 202 improves the sensing ability of the wearable device 202 by increasing the number of reading (i.e., measuring) points covering different vascular features (e.g., artery 222) on the body of the subject 112, thereby reducing any motion artifacts caused by hand movement and improving the accuracy of determining the photoplethysmogram without any increase in the power consumption of the first light source 206. In addition, increasing the number of reading (i.e., measuring) points covering different vascular features (e.g., artery 222) on the body of the subject 112 enables the measurement of even small or otherwise conventionally undetected changes in the number of scattered photons indicating changing blood flow.

[0068] According to an embodiment, the control device 108 is configured to perform a summation on the signals detected at the first photodetector 208 and the second photodetector 210 (i.e., the first signal and the second signal) to obtain a final output signal. Generally, the reflected light detected by the first photodetector 208 and the second photodetector 210 is converted into an electrical signal including an alternating current (AC) part and a direct current (DC) part by the corresponding photodetectors (e.g., the first photodetector 208 and the second photodetector 210). Thus, the photoplethysmogram waveform (i.e., the final output signal) includes a pulsatile (“AC”) physiological waveform that is typically superimposed on a slowly varying (“DC”) baseline. Accordingly, by adding all these signals together, the quality and intensity of the pulsatile physiological waveform (i.e., the “AC” component or part) of the final output signal generated due to, for example, cardiac blood volume changes that occur simultaneously with each heartbeat are significantly increased, without any increase in power consumption of the first light source 206 in the wearable device 202. In one example, the pulsatile (“AC”) physiological waveform of the output signal may be used to accurately measure an accurate heart rate, even when the proband (e.g., proband 112) is performing physical activity or hand movement. In another example, the slowly varying baseline waveform (i.e., the DC part) of the output signal may be used to measure certain other health metrics, such as respiration, sympathetic nervous system activity, and thermoregulation.

[0069] Figure 3 is a diagram showing different exemplary locations of vascular characteristics of body parts of different probands provided by an embodiment of the present invention. In combination with Figure 1 and Figure 2 element description Figure 3 . Refer to Figure 3, which shows the exemplary positions of different arteries 302A, 302B, 302C, 302D, and 302E in the corresponding finger portions 304A, 304B, 304C, 304D, and 304E of different probands. Thus, for different probands, the appropriate positions of the corresponding light sources 306A, 306B, 306C, 306D, and 306E are different. Similarly, the appropriate positions of the light detectors 308A, 308B, 308C, 308D, and 308E in the corresponding finger portions 304A, 304B, 304C, 304D, and 304E of different probands are different. In other words, the positions of vascular features (e.g., arteries 302A, 302B, 302C, 302D, and 302E) in the same body part (i.e., finger) vary among different probands. Therefore, the optimized positions for irradiating and detecting light also vary among different probands. Thus, the positions of the light-emitting diodes 310 (i.e., light sources) for emitting light and the positions of the photodiodes 312 for capturing signals in the form of light may be arranged or positioned within a specified range in the ring 314 (i.e., wearable device). This arrangement ensures enhanced coverage of different vascular features, thereby improving the accuracy of determining the photoplethysmogram without any increase in the power consumption of the battery-powered light-emitting diodes 310.

[0070] Figure 4 is a diagram showing an output signal derived from a plurality of signals detected at different positions of a body part of a proband provided by an embodiment of the present invention. In combination with Figure 1 , Figure 2 and Figure 3 element description Figure 4 . Referring to Figure 4 , a part of a wearable device 402 having a first light source 404 and four light detectors (e.g., a first light detector 406, a second light detector 408, a third light detector 410, and a fourth light detector 412) is shown. The AC components of each of the first signal 414A, the second signal 414B, the third signal 414C, and the fourth signal 414D are also shown. The first signal 414A, the second signal 414B, the third signal 414C, and the fourth signal 414D are detected at the first light detector 406, the second light detector 408, the third light detector 410, and the fourth light detector 412, respectively.

[0071] According to an embodiment, a microprocessor 416 (e.g., an example of the control device 108 of Figure 1 ) is used to perform summation on the first signal 414A, the second signal 414B, the third signal 414C, and the fourth signal 414D to obtain an output signal 418 with an increased power of the AC component, thereby improving the accuracy of the microprocessor 416 in determining the photoplethysmogram without any increase in the power consumption of the first light source 404.

[0072] Figure 5 FIG. is a diagram of an exemplary wearable device 502 provided by another embodiment of the present invention, having a tunable laser 504 as a light source and an optical waveguide 506 having a metasurface 508. In combination with Figure 1 , Figure 2 , Figure 3 and Figure 4 element descriptions Figure 5 . Referring to Figure 5 , a wearable device 502 including a tunable laser 504 as a light source is shown. An optical waveguide 506 is also shown, which has a metasurface 508 disposed on the inner side of the wearable device 502. In this embodiment, the wearable device 502 is in the form of a ring that can be worn on a finger portion 510. In one example, the tunable laser 504 can be a tunable hybrid silicon / III-V laser known in the art. The tunable hybrid silicon / III-V laser can include a silicon photonic integrated circuit emitter composed of a hybrid III–V / silicon laser and a silicon Mach-Zehnder modulator (MZM) operating in a specified wavelength window.

[0073] According to an embodiment, a control device 512 of the wearable device 502 is configured to control the wavelength of the tunable laser 504 to direct different light bands to different positions (i.e., different entry points towards the finger portion 510) through the optical waveguide 506 having a metasurface 508 disposed on the inner side of the wearable device 502.

[0074] Figure 6 FIG. is a flowchart of a method 600 for determining a photoplethysmogram of a proband using a device provided by an embodiment of the present invention. In combination with Figures 1 to 5 element descriptions Figure 6 . The method 600 is performed by, for example, the wearable devices 102, 202, 402, or 502 described in Figures 1 to 5 . The method 600 includes steps 602 and 608.

[0075] In step 602, light is emitted from a first light source towards at least one point on the body of a proband (e.g., proband 112). Examples of the first light source are the first light sources 104, 206, or 404, light sources 306A, 306B, 306C, 306D, or 306E, or the tunable laser 504 shown and described in Figures 1 to 5 .

[0076] In step 604, light is received by at least a first detector optical waveguide and a second detector optical waveguide, which are arranged to detect light at at least two different locations on the body of a proband. Examples of the first detector optical waveguide and the second detector optical waveguide are, for example, the multiple detector optical waveguides 110 (e.g., the first detector optical waveguide 110A and the second detector optical waveguide 110B), the first group of detector optical waveguides 214, the second group of detector optical waveguides 216, or the optical waveguide 506 shown and described in Figure 1 , Figure 2 and Figure 5 .

[0077] In step 606, the received light is fed to a light detector. Examples of the light detector are, for example, the first light detectors 106, 208 or 406, the second light detectors 210 or 408, the light detectors 308A, 308B, 308C, 308D and 308E, the third light detector 410 or the fourth light detector 412 shown and described in Figures 1 to 5 .

[0078] In step 608, a photoplethysmogram is calculated based on the light received from at least one optical waveguide. In one example, a photoplethysmogram is calculated based on the light received at the multiple detector optical waveguides 110. The control device 108 ( Figure 1 ) is arranged to calculate a photoplethysmogram based on the light detected from the body of the proband 112.

[0079] According to an embodiment, method 600 further includes performing certain operations or steps for at least different first and second positions of a device (such as wearable device 102, 202, 402, or 502) relative to a proband 112 before steps 602 to 608. These operations or steps include: emitting light from a first light source 104, 206, or 404; receiving the light through at least a first detector optical waveguide 110A and a second detector optical waveguide 110B; feeding the received light to a light detector (e.g., a first light detector 106, 208, or 406). Method 600 further includes calculating a photoplethysmogram and determining which of the first and second positions provides better results relative to each other. For example, control device 108 is used to perform a trial run (or simulation or experiment) to locate an appropriate position of a vascular feature (e.g., an artery or a vein) to provide light to the located position for different first and second positions of a device (such as wearable device 102, 202, 402, or 502) relative to a proband 112. A better result refers to the accuracy level of measuring a health metric according to the photoplethysmogram calculated for different first and second positions of a device (such as wearable device 102, 202, 402, or 502). Method 600 further includes positioning the device at the position that provides better results. When determining which of the first and second positions provides better results relative to each other, the device is positioned accordingly. As a result, the signal quality of the output signal is significantly improved, thereby increasing the accuracy of determining the photoplethysmogram. In other words, the quality and signal intensity of the pulsatile physiological waveform (i.e., the AC component) of the output signal (e.g., output signal 418) are significantly increased without any increase in the power consumption of the first light source 104, 206, or 404.

[0080] Without departing from the scope of the invention as defined by the appended claims, modifications may be made to the embodiments of the invention described above. Expressions such as "comprising", "combining", "having", "is", etc. used to describe and claim the invention are intended to be interpreted in a non-exclusive manner, i.e., allowing items, components, or elements not explicitly described to also be present. References to the singular should also be interpreted as relating to the plural. The term "exemplary" as used herein means "serving as an example, instance, or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as more preferred or advantageous than other embodiments, and / or excludes combinations of features of other embodiments. The term "optionally" as used herein means "provided in some embodiments but not in other embodiments". It should be understood that some features of the invention described in the context of separate embodiments for clarity may also be provided in combination in a single embodiment. Conversely, the various features of the invention described in the context of a single embodiment for brevity may also be provided separately, in any suitable combination, or in any other described embodiment suitable for the invention.

Claims

1. A wearable device (102, 202, 402, 502) for determining a photoplethysmogram, characterized in that, Comprising: At least a first light source (104, 206, 404), arranged to provide light to at least one entry point on the body of the proband when the wearable device (102, 202, 402, 502) is used by the proband (112); At least a first light detector (106, 208, 406), arranged to detect light received from the at least first light source (104, 206, 404) through the body of the proband when the wearable device (102, 202, 402, 502) is used by the proband (112); A control device (108), arranged to calculate a photoplethysmogram based on the detected light; At least a first detector optical waveguide (110A) and a second detector optical waveguide (110B), arranged to detect light at at least two different positions on the body of the proband and feed the light to the at least first light detector (106, 208, 406) when the wearable device (102, 202, 402, 502) is used by the proband (112); The at least first light source (104, 206, 404) is a tunable laser (504), the wearable device (102, 202, 402, 502) further includes an optical waveguide (506), the optical waveguide (506) of the metasurface (508) is configured to direct different optical bands of the tunable laser (504) to positions of different entry points on the body of the proband, and the control device (108) is arranged to control the wavelength of the tunable laser (504) to control the position of the at least one entry point.

2. The wearable device (102, 202, 402, 502) according to claim 1, characterized in that, The at least first light detector (106, 208, 406) is a photodiode.

3. The wearable device (102, 202, 402, 502) according to claim 1, wherein The at least first light source (104, 206, 404) is a light-emitting diode (310), the wearable device (102, 202, 402, 502) further includes at least a first source optical waveguide (114A) and a second source optical waveguide (114B), and in use, the at least first source optical waveguide (114A) and the second source optical waveguide (114B) are arranged to receive light from the at least first light source (104, 206, 404), and wherein the light of the at least first light source (104, 206, 404) is guided by the at least first source optical waveguide (114A) and the second source optical waveguide (114B) to enter the body of the proband through at least two different entry points.

4. The wearable device (102, 202, 402, 502) according to claim 3, characterized in that, Comprising one light source and two light detectors.

5. The wearable device (102, 202, 402, 502) according to claim 3 or 4, characterized in that, For each light source, including at least three source optical waveguides for separating the light from the light source.

6. The wearable device (102, 202, 402, 502) according to claim 3 or 4, characterized in that, For each light detector, including at least three detector optical waveguides for detecting light at different positions on the body of the proband.

7. The wearable device (102, 202, 402, 502) according to any one of claims 1 to 4, characterized in that, The control device (108) is arranged to calculate the photoplethysmogram based on the light detected from all detector optical waveguides of all light detectors.

8. The wearable device (102, 202, 402, 502) according to any one of claims 1 to 4, characterized in that, The control device (108) is arranged to select at least one detector optical waveguide to calculate the photoplethysmogram based on the light detected from the at least one selected detector optical waveguide.

9. The wearable device (102, 202, 402, 502) according to claim 3, wherein The control device (108) is arranged to select at least one source optical waveguide from the source optical waveguides to provide light to the body of the proband.

10. The wearable device (102, 202, 402, 502) according to any one of claims 1 to 4 and 9, characterized in that, The wearable device is a watch, bracelet or ring (314).

11. A wearable device (102, 202, 402, 502) according to any one of claims 1 to 10, characterized in that, For the use of determining the photoplethysmogram of a proband (112).

12. A method (600) for determining a photoplethysmogram of a proband (112) using the device according to any one of claims 1 to 10, characterized in that, Including the following steps when the proband (112) wears the device, Emitting light from a first light source (104, 206, 404) to at least one point on the body of the proband; Receiving the light through at least a first detector optical waveguide (110A) and a second detector optical waveguide (110B), the at least first detector optical waveguide (110A) and the second detector optical waveguide (110B) being arranged to detect light at at least two different positions on the body of the proband; Feeding the received light to a photodetector; Calculating the photoplethysmogram based on the light received from at least one optical waveguide; The at least first light source (104, 206, 404) is a tunable laser (504), the wearable device (102, 202, 402, 502) further includes an optical waveguide (506), the optical waveguide (506) includes a metasurface (508), and the method further includes: using the optical waveguide (506) including the metasurface (508) to direct different optical bands of the tunable laser (504) to different entry point positions on the body of the proband; controlling the wavelength of the tunable laser (504) guided by the optical waveguide (506) including the metasurface (508) by the control device (108) to control the position of the at least one entry point.

13. The method (600) according to claim 12, wherein Before the step of claim 12, for different first and second positions of the device relative to the proband (112), perform the following steps: Emitting light from the first light source (104, 206, 404); Receiving the light through the at least first detector optical waveguide (110A) and the second detector optical waveguide (110B); Feeding the received light to the photodetector; Calculating the photoplethysmogram; Determining which of the first position and the second position provides better results relative to each other; Positioning the device at the position providing the better result.

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