Photoplethysmography sensor system, wearable device and pulse oximeter device

Abstract

The utility model relates to a photoplethysmography sensor system, wearable equipment and pulse oximeter equipment. The utility model provides a PPG sensor system, which comprises an optical waveguide and is beneficial for transmitting light from a light source to the far end of the waveguide. In this manner, light from a light source may be emitted at a location separate from the location of the light source. By employing the optical waveguide, light can be emitted at a point in the PPG sensor system that is not proximate to the light source. For example, light may be emitted from the waveguide at a point opposite and directed to the light detector, such that a transmissive PPG may be enabled. By using the optical waveguide, the light source and the light detector can be integrated in the same circuit board and housing, thereby improving the efficiency of the PPG sensor system.

Description

Technical Field

[0001] The utility model relates to a photoplethysmography (PPG) sensor system. Background Art

[0002] PPG measurement has long been used to easily obtain vital signs. Initially, this was limited to obtaining heart rate, but over the years, more vital signs have been able to be extracted from the acquired data. The principle is that a light (usually an LED) shines through the subject's tissue and thus through the blood vessels, while a photodiode or light detector placed on the other side can capture the transmitted light. This is called transmissive PPG. Based on the changes in the amount of light reaching the photodiode, the subject's heart rate can be determined. Today, by using LEDs of different colors and advanced algorithms, other vital signs such as respiratory rate and SpO2 can be obtained. In other words, in a transmissive PPG sensor, the LED and photodiode are positioned on opposite sides of the subject's tissue. Therefore, in order to measure the transmissive PPG signal, the LED light needs to penetrate the human tissue to reach the photodiode located on the other side of the tissue.

[0003] However, for certain applications (such as smartwatches where waterproofing is important), integrating an LED opposite a photodiode is difficult. Therefore, for cost-effectiveness and ease of manufacturing, it is desirable to have the LED(s) separate from the photodiode so that they can be integrated into the same waterproof circuit board and housing. To this end, reflective PPG measurement methods have been developed, in which algorithms detect and process variations in light reflections from a subject's veins. In other words, in a reflective PPG sensor, the LED and photodiode are positioned on the same side of the subject's tissue, so that the LED light reflects off the tissue and reaches the photodiode on the same side. This is quite effective for acquiring heart rate and some other vital signs, but it is less accurate and presents challenges, particularly with aspects like SpO2 measurement. This is because reflective PPG sensor technology is sensitive to the contact state of the sensor with the human skin. Specifically, the exact sensor wearing configuration can affect PPG signal quality, and thus the accuracy of vital sign tracking. For example, movement and pressure changes are particularly likely to cause erratic / inaccurate SpO2 measurements.

[0004] US 2023 / 114269 A1 describes a method for blood oxygen measurement, comprising receiving a first photoplethysmogram (PPG) signal of a user via a wearable device.

[0005] US 2013 / 035562 A1 describes a medical sensor assembly configured to switch between a transmission mode and a reflection mode. Utility Model Content

[0006] The utility model is defined by the claims.

[0007] According to an example of one aspect of the present invention, there is provided a PPG sensor system, comprising: a first light source configured to emit light; a light detector configured to detect light incident on the light detector; and a light waveguide comprising: a light input at a proximal end of the light waveguide and a light output at a distal end of the light waveguide, the light input being configured to receive light emitted from the first light source, the light output being configured to emit light received via the light input; wherein the light waveguide is flexible so as to permit adjustment of a direction of the light output so that, in use, received light is emitted from the light output in a direction toward the light detector.

[0008] The present invention proposes using an optical waveguide to transmit light from a light source to the distal end of the waveguide. In this way, light from the light source can be emitted at a location separate from the light source. The waveguide can receive only a portion of the light emitted from the light source, or it can receive all of the light emitted from the light source.

[0009] By employing an optical waveguide, light can be emitted from a point in a PPG sensor system that is not close to the light source. For example, light can be emitted from the waveguide at a point opposite and directed toward a light detector, enabling transmissive PPG. By using an optical waveguide, the light source and light detector can be integrated into the same circuit board and housing, thereby improving system performance.

[0010] In other words, by using an optical waveguide, a system capable of transmissive PPG is provided, in which the light source and light detector can be integrated into the same circuit board and thus housed together. The housing can be waterproof, thereby advantageously enabling the PPG system to be integrated into wearable devices such as smart sports watches. Furthermore, since no electrical connections are required in and out of the housing, the system is more resistant to electromagnetic interference.

[0011] Embodiments may be based on the recognition that a transmissive PPG light source need not actually be positioned remotely from, i.e., opposite, a light detector, such that the light passes through tissue on its way to the detector. Instead, a waveguide may be used to transmit light from the light source to a point remote from the light detector, where it can be emitted from the distal end of the waveguide as if it were emitted from the light source located at that point. Thus, a configuration may be provided that allows for transmissive PPG while still housing the light source and light detector together on the same circuit board.

[0012] In summary, the use of an optical waveguide allows light to be emitted from a certain location without having to mount a light source at that point. The waveguide can be flexible so as to allow the position of the distal end of the waveguide to be adjusted, essentially allowing the position of the virtual light source to be adjusted. In this way, adjustable transmissive or reflective PPG can be implemented in the system, which can also be made waterproof and resistant to electromagnetic interference. The system can be particularly useful for integration into wearable devices such as smart watches or baby monitors (e.g., baby monitor socks). The system can also be integrated into a pulse oximeter device. Utilizing a pulse oximeter device of the present invention would be beneficial in environments with strong magnetic fields, such as in an MRI machine.

[0013] Being flexible allows the waveguide to be easily adjusted, for example, to bend around a subject's wrist, finger, or ankle, and still emit light from its distal end in a beneficial direction. Furthermore, configuring the waveguide so that, in use, received light is emitted from the light output in a direction toward a light detector enables transmissive PPG, which requires light to be transmitted toward the detector so that it can be detected. This allows for the implementation of a rigid PPG sensor system (e.g., such as a rigid bracelet) without the user having to configure the system themselves. Alternatively, if the waveguide is flexible so as to permit adjustment of the direction of the light output, the user can adjust the waveguide to ensure that light is emitted toward the light detector, and the system can then be adapted to the different anatomical geometries of different users.

[0014] In some embodiments, the system may further include a processor configured to generate at least one vital sign parameter value based on the light received by the light detector. This allows for the utilization of information contained in the light received by the light detector. Thus, using the system provides an efficient, non-invasive way to generate vital sign parameter values.

[0015] In some embodiments, the vital sign parameter values may include at least one of: a heart rate value; a respiratory rate value; and a pulse oximetry (SpO2) value. These are clinically useful vital sign parameters to be determined and can be determined based on light detected by a light detector in the PPG sensor system.

[0016] In some embodiments, the first light source and the light detector can be integrated into the same circuit board. This allows the positions of the first light source and the light detector to be fixed relative to each other. This can also simplify the system and reduce manufacturing costs, while minimizing the need for long wires and making the system more resilient to electromagnetic interference.

[0017] In some embodiments, the system may further include a housing, wherein the first light source and the light detector are housed within the housing. This improves the effectiveness of the system by allowing the first light source and the light detector to be housed together, so that the first light source and the light detector can be located on the same circuit board. This also allows the system to be completely sealed and / or waterproof, without any electrical connections entering or exiting. Since the housing does not have any electronic connections, the design can be more effectively resistant to electromagnetic interference. Long wires and interfaces are susceptible to such interference. For example, a circuit board with the first light source and the light detector integrated thereon can be housed within the housing.

[0018] In some embodiments, the housing can be waterproof. This allows the system to be integrated into a smart sports watch device, such as one that a user might want to wear while swimming. Thus, the system can be configured to allow wireless data transfer and charging.

[0019] In some embodiments, the system may further include a transparent window positioned between the first light source and the light input of the waveguide. This allows the waveguide to be located outside of the housing and still receive light from the light source.

[0020] In some embodiments, the optical waveguide may comprise at least one of the following: glass; acrylic fiber; polycarbonate; quartz; plastic; silicone; carbon; and silicon dioxide. These have been found to be beneficial materials for optical waveguides. For example, the waveguide may be an optical fiber comprising some or all of these materials.

[0021] In some embodiments, the first light source may be proximate to the light detector, and wherein the light waveguide may be configured such that, in use, a portion of the light emitted by the first light source is not received by the light input of the light waveguide and is suitable for reflective PPG. This allows a single light source to be used for both reflective and transmissive PPG. The portion of light not received by the waveguide may be reflected from the surface or superficial tissue of the subject and used for reflective PPG. Conversely, the portion of light received by the waveguide may be emitted through the subject's tissue towards the detector so as to be used for transmissive PPG. Thus, this provides an efficient system capable of both reflective and transmissive PPG using only a single light source.

[0022] In some embodiments, the system may further include a second light source configured to emit light having a wavelength within a second wavelength range, wherein the light input may be configured to also receive light emitted from the second light source. This allows the waveguide to receive and transmit light from the second light source as well as the first light source. This may allow a greater amount of light to be transmitted through the waveguide.

[0023] In some embodiments, the first light source can be configured to emit light having a wavelength within a first wavelength range that is different from a second wavelength range. This enables the waveguide to receive and transmit at least two different wavelengths of light (e.g., both red and infrared light), both of which are beneficial for a transmissive PPG.

[0024] In some embodiments, the system may further include a reflective light source configured to emit light in a reflective wavelength band, wherein the reflective light source may be proximate to the light detector so that, in use, the light detector can receive light emitted from the reflective light source and reflected from the surface of the subject. This allows a light source more suitable for reflective PPG to be used in the same system as the first light source, which may be configured for transmissive PPG. For example, green light has been found to be beneficial for reflective PPG but not particularly effective for transmissive PPG. Thus, the system may include different light sources suitable for different PPG sensing purposes, thereby providing a more efficient system.

[0025] In some embodiments, a second light source may also be housed within the housing.

[0026] In some embodiments, a reflective light source may also be housed within the housing.

[0027] In some embodiments, the transparent window may also be configured to be positioned between the second light source and the light input.

[0028] In some embodiments, the system may comprise a further transparent window configured to be located, in use, between the reflective light source and the surface of the subject.

[0029] In some embodiments, the system may include an additional transparent window configured to be positioned between the light detector and the surface of the subject in use. This may allow the light detector to still receive light emitted from outside the housing (e.g., from the distal end of the optical waveguide).

[0030] In some embodiments, the additional transparent window may be a transparent window. For example, only one large transparent window may be provided, which covers the light source and the light detector.

[0031] In some embodiments, the first light source and the light detector may be integrated into the same flat circuit board.

[0032] Also provided is a wearable device comprising any of the PPG sensor systems disclosed herein.

[0033] In some embodiments, the wearable device may include a smart watch or a baby monitor. For example, a baby monitor may be a device wearable by a baby, such as smart baby socks or smart baby gloves.

[0034] In another aspect of the present invention, a PPG sensor system is provided, comprising: a first light source configured to emit light; a light detector configured to detect light incident on the light detector; and a light waveguide comprising: a light input at a proximal end of the light waveguide and a light output at a distal end of the light waveguide, the light input configured to receive light emitted from the first light source, and the light output configured to emit light received via the light input.

[0035] Also provided is a pulse oximeter device comprising any of the PPG sensor systems disclosed herein.

[0036] A PPG sensing method is also provided, the method comprising: receiving light at an optical input at a proximal end of an optical waveguide; and emitting the received light at an optical output at a distal end of the optical waveguide; and detecting the emitted received light with a light detector.

[0037] Therefore, the concept of a PPG sensor system can be proposed.

[0038] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] For a better understanding of the present invention and to more clearly show how the present invention may be implemented, reference is now made, by way of example only, to the accompanying drawings, in which:

[0040] Figure 1 shows a simplified block diagram of a PPG sensor system according to the proposed embodiment;

[0041] Figure 2 shows a simplified diagram of a PPG sensor system according to the proposed embodiment;

[0042] Figure 3 shows a simplified view of a PPG sensor system attached to a subject's finger according to the proposed embodiment;

[0043] Figure 4 shows a simplified view of a PPG sensor system attached to a subject's foot according to the proposed embodiment;

[0044] Figure 5 shows a simplified diagram of a wearable device attached to a subject's limb, the wearable device including a PPG sensor system, according to the proposed embodiment; and

[0045] Figure 6 A flow chart of a PPG sensing method according to the proposed embodiment is shown. DETAILED DESCRIPTION

[0046] The present invention will be described with reference to the accompanying drawings.

[0047] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are intended for illustrative purposes only and are not intended to limit the scope of the present invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, the appended claims, and the accompanying drawings. It should be understood that the drawings are merely schematic and not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to indicate the same or similar components.

[0048] The present invention provides a PPG sensor system including an optical waveguide that facilitates the transmission of light from a light source to the distal end of the waveguide. In this manner, light from the light source can be emitted at a location separate from the location of the light source. The waveguide can receive only a portion of the light emitted from the light source, or it can receive all of the light emitted from the light source. By employing an optical waveguide, light can be emitted at a point in the PPG sensor system that is not close to the light source. For example, light can be emitted from the waveguide at a point opposite to and directed toward a light detector, enabling the use of a transmissive PPG. By using an optical waveguide, the light source and light detector can be integrated into the same circuit board and housing, thereby improving the efficiency of the system.

[0049] Now see Figure 1 , depicts a simplified block diagram of a PPG sensor system 100 according to the proposed embodiment. The system 100 includes: a first light source 110 configured to emit light; a light detector 120 configured to detect light incident on the light detector; and a light waveguide 130 including a light input at a proximal end of the light waveguide and a light output at a distal end of the light waveguide, the light input being configured to receive light emitted from the first light source 110, and the light output being configured to emit light received via the light input.

[0050] The light detector 120 may include at least one photodiode. The light source 110 may include at least one LED. The optical waveguide 130 is a device in which light can enter at one end and, due to refraction by the waveguide walls, be captured and guided to the other end of the waveguide, where it can be emitted. Thus, the waveguide 130 essentially allows the system 100 to operate in a manner similar to that in which the first light source 110 is located at the far end of the waveguide.

[0051] Essentially, the present invention allows for the manufacture of a PPG sensor system that is very similar to a purely reflective PPG setup, where the light source(s) and light detector(s) are located on the same circuit board, but where transmissive PPG sensing is also possible.

[0052] Now see Figure 2 , depicts a simplified diagram of a PPG sensor system 200 according to the proposed embodiment. The system 200 includes a first light source 210 configured to emit light, and an optical waveguide 230 including a light input 230a at a proximal end of the optical waveguide and configured to receive the light emitted from the first light source 210. The waveguide 230 also includes a light output 230b at a distal end of the optical waveguide and configured to emit light received via the light input 230a.

[0053] In this embodiment, optical waveguide 230 is flexible to allow adjustment of the direction of light output 230b. This allows the waveguide to be easily adjusted, for example, to bend around a subject's wrist, finger, or ankle, while still emitting light from its distal end 230b in a beneficial direction. Thus, the direction of light output 230b can be adjusted, for example, to ensure that light is emitted toward light detector 220, thereby facilitating transmissive PPG. The flexible waveguide 230 also makes it easier for system 200 to adapt to the varying anatomical geometries of different subjects. Preferably, light output 230b contacts the subject's tissue to ensure good penetration of the emitted light, and to this end, waveguide 230 is flexible, allowing for this to be advantageous in various situations. However, waveguide 230 need not be flexible. For example, waveguide 230 can be rigid, eliminating the need for the subject or clinician to configure system 200 themselves. For example, waveguide 230 can be housed within a rigid wristband that the subject can easily wear.

[0054] In this embodiment, the optical waveguide 230 is further configured such that, in use, received light is emitted from the optical output 230b in a direction toward the optical detector 220 of the system 200. Preferably, the optical output 230b should be configured to be between 20 and 35 mm from the center of the optical detector 220. These distances are the distances as if the waveguide 230 were arranged straight in the same plane as the optical detector 220 (i.e., flat and not curved). Ideally, this distance should be 25 mm. In other words, preferably, the length of the waveguide 220 should be such that its length plus the length from the center of the optical detector 220 to the optical input 230a totals between 20 and 35 mm, and ideally is 25 mm.

[0055] In this embodiment, optical waveguide 230 comprises an optical fiber. Optical fiber includes glass and plastic. In other embodiments, optical waveguide 230 may comprise at least one of the following: glass; acrylic fiber; polycarbonate; quartz; plastic; silicone; carbon; and silicon dioxide. These materials have been found to be beneficial for optical waveguides.

[0056] Now see Figure 3, provides a simplified view of a PPG sensor system 300 attached to a subject's finger 360 according to the proposed embodiment.

[0057] System 300 includes a first light source 310, a second light source 315, and a light detector 320. These components are integrated into the same circuit board 350, such that the positions of the first and second light sources 310, 315, and the light detector 320 are fixed relative to each other. The light detector 320 also communicates with a processor 340. Light from the two light sources 310 and 315 passes through an optical waveguide 330 and is then emitted from the optical waveguide opposite the light detector 320. The emitted light 335 passes through the subject's finger 360 and through a vein 365 before being detected by the light detector 320. Thus, system 300 enables transmissive PPG. Processor 340 is configured to generate at least one vital sign parameter value based on the light 335 received by the light detector 320. This allows the use of information contained in the light received by the light detector. Therefore, utilizing system 300 provides an efficient and non-invasive method for generating vital sign parameter values. The vital sign parameter values include at least one of the following: heart rate value; respiratory rate value; and pulse oximetry (SpO2) value. These are clinically useful vital sign parameters to be determined, and can be determined based on the light 335 detected by the light detector 320 in the PPG sensor system 300 .

[0058] In some embodiments, system 300 may also include an analog-to-digital converter.

[0059] In this embodiment, the system 300 includes a second light source 315 configured to emit light having a wavelength within a second wavelength range, wherein the light input of the waveguide 330 is configured to also receive light emitted from the second light source 315. This allows the waveguide 330 to receive and transmit light from the second light source 315 as well as the first light source 310.

[0060] In this embodiment, the first light source 310 is configured to emit light having a wavelength within a first wavelength range that is different from a second wavelength range. This allows the waveguide 330 to receive and transmit at least two different wavelengths of light (e.g., red light and infrared light), both of which are advantageous for transmissive PPG. Typically, PPG measurements of SpO2 utilize the difference between red and infrared light measurements. In this embodiment, the first light source 310 is therefore configured to emit light having a wavelength within a first wavelength range of 620 nm to 750 nm (i.e., red light). Accordingly, the second light source 315 is configured to emit light having a wavelength within a second wavelength range of 750 nm to 1 mm (i.e., infrared light).

[0061] Now see Figure 4, depicts a simplified view of a PPG sensor system 400 according to the proposed embodiment, attached to a subject's foot 460. For example, the system 400 can be integrated into a smart baby sock.

[0062] The system 400 includes a first light source 410 and a second light source 415, Figure 3 The depicted first light source 310 and second light source 315 are nearly identical. The light guide 430 comprising a light input 430a and a light output 430b is nearly identical to the waveguides previously described. The system 400 also includes a reflective light source 418.

[0063] The reflected light source 418 is configured to provide sufficient light output at a distance between 3.5 mm and 5 mm from the center of the light detector 420. This distance is preferably 4 mm. In other words, the center of the reflected light source 418 should preferably be 3.5 mm to 5 mm laterally from the center of the light detector 420, and ideally 4 mm.

[0064] In this embodiment, the system 400 also includes a housing 470, wherein the first light source 410, the second light source 415, the reflective light source 418, and the light detector 420 are housed within the housing. This increases the effectiveness of the system 400 by allowing all of the light sources 410, 415, 418 and the light detector 420 (which may be located on the same circuit board) to be housed together. This also allows the system to be completely sealed and / or easily waterproofed without any electrical connections entering or exiting. By not having any electronic connections leave the housing, the design is also more resistant to electromagnetic interference. Long wires and interfaces are easily susceptible to such interference. Therefore, by eliminating any external light sources that require electrical connections, this interference point can be eliminated.

[0065] However, in some embodiments, the light sources 410, 415, 418 may not all be located in the same housing 470. The light sources may be located in separate housings, or some light sources may not be in a housing at all.

[0066] In this embodiment, housing 470 is waterproof. This allows system 400 to be integrated into, for example, a smart sports watch device that a subject may wish to wear while swimming. System 400 can also be integrated into a baby monitor, such as a baby monitor sock or baby monitor glove. Thus, system 400 can be configured to allow for wireless data transfer and charging. By eliminating electrical connections in and out of the housing, it is easier and more cost-effective to fully seal the housing and make it completely waterproof.

[0067] The reflective light source 418 is configured to emit light in a reflective wavelength band, wherein the reflective light source is proximate to the light detector 420 so that, in use, the light detector is able to receive light emitted from the reflective light source 418 that is reflected by surface or shallow tissue of the subject (such as a vein close to the skin). This allows light sources that are more suitable for reflective PPG to be used in the same system 400 as the first light source 410 and the second light source 415, which are configured for transmissive PPG. For example, green light has been found to be useful in reflective PPG (especially in determining pulse rate and respiration rate), but is not particularly effective in transmissive PPG. Therefore, the system 400 includes a separate reflective light source 418 having a wavelength in the wavelength range of 495nm to 570nm (i.e., green light).

[0068] In this embodiment, the entire housing 470 is transparent. The term "transparent" refers to a material or substance that allows light to pass through it without significant scattering, absorption, or reflection, so that light can be transmitted through the material without being significantly affected. In other words, a transparent material is a material that is transparent or see-through. Transparency varies depending on the material and its thickness, as well as the properties of the light passing through the material (such as wavelength and intensity). Some examples of transparent materials include glass, water, air, and certain plastics.

[0069] In some embodiments, alternatively, the housing 470 can be opaque and include a transparent window positioned between the light sources 410, 415, 418 and the light input 430a of the waveguide 430. This allows the waveguide 430 to be located outside the housing and still receive light from the light sources. In some embodiments where the housing 470 is opaque, the system 400 can also include an additional transparent window configured to be positioned between the light detector 420 and the surface of the subject during use. In some embodiments, the additional transparent window can be a transparent window such that, for example, there is one large transparent window proximate all of the light sources and light detectors.

[0070] Together with any other embodiment disclosed herein, this embodiment may form part of a wearable device such as a smartwatch, sports watch, sleep monitor, or baby monitor. For example, a baby monitor may be a device wearable by a baby such as a smart baby sock or a smart baby glove. Together with any other embodiment disclosed herein, this embodiment may alternatively form part of a pulse oximeter device. Utilization of the pulse oximeter device of the present invention may be beneficial in environments with strong magnetic fields, such as in an MRI machine.

[0071] Now see Figure 5, depicts a simplified view of a wearable device 500 including a PPG sensor system according to the proposed embodiment attached to a subject's limb 560. The limb 560 may be the subject's arm or leg.

[0072] Wearable device 500 includes a housing 570, which itself includes a transparent window 575. Within the housing are a first light source 510 and a light detector 520. Transparent window 575 is positioned between first light source 510 and light input 530a of optical waveguide 530. Transparent window 575 is also positioned between light detector 520 and the surface of a subject. In some embodiments, wearable device 500 can be a smartwatch with a flexible strap or a rigid wristband.

[0073] In this embodiment, a first light source 510 is proximate to a light detector 520, and an optical waveguide 530 is configured such that, in use, a portion 535a of the light emitted by the first light source 510 is not received by the light input 530a of the optical waveguide 530 and is suitable for reflective PPG. This portion of light 535a can then be reflected from the surface of a subject (e.g., a superficial vein in a subject's limb 560) and detected by the light detector 520. The remaining portion 535b can then be emitted from the distal end 530b of the waveguide 530. In other words, this allows a single light source 510 to be used for both reflective and transmissive PPG. The portion of light 535a not received by the waveguide 530 can be reflected from the surface of the subject and used for reflective PPG, while the portion of light 535b received by the waveguide 530 can be emitted through the subject's tissue toward the detector 520 to be used for transmissive PPG. Thus, this provides an efficient device 500 capable of both reflective and transmissive PPG using only a single light source.

[0074] Now see Figure 6 , a flow chart of a PPG sensing method 600 according to a proposed embodiment is provided. Method 600 begins with step 610 of receiving light at an optical input at the proximal end of an optical waveguide. Step 620 includes emitting the received light at an optical output at the distal end of the optical waveguide. Finally, step 630 includes detecting the emitted received light with a light detector. This method can be implemented using any of the embodiments disclosed herein according to the present invention.

[0075] Those skilled in the art can understand and implement variations of the disclosed embodiments when practicing the claimed utility model by studying the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0076] The functions implemented by a processor may be implemented by a single processor or by multiple separate processing units, which may be collectively considered to constitute a “processor.” In some cases, such processing units may be remote from each other and communicate with each other in a wired or wireless manner.

[0077] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0078] The computer program may be stored / distributed on appropriate media (such as optical storage media or solid-state media provided with or as part of other hardware), but may also be distributed in other forms (such as via the Internet or other wired or wireless telecommunications systems).

[0079] If the term "suitable for" is used in the claims or the specification, it should be noted that the term "suitable for" is intended to be equivalent to the term "configured to". If the term "arranged" is used in the claims or the specification, it should be noted that the term "arranged" is intended to be equivalent to the term "system", and vice versa.

[0080] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A photoplethysmography sensor system (100), characterized in that include: a first light source (110) configured to emit light; a light detector (120) configured to detect light incident on the light detector; as well as an optical waveguide (130) comprising an optical input (230a) at a proximal end of the optical waveguide and an optical output (230b) at a distal end of the optical waveguide, the optical input (230a) being configured to receive light emitted from the first light source and the optical output (230b) being configured to emit light received via the optical input; The optical waveguide (130) is flexible to permit adjustment of the direction of the light output (230b) so that, in use, received light is emitted from the light output (230b) in a direction towards the light detector (120).

2. The photoplethysmography sensor system according to claim 1, wherein: Also included is a processor (340) configured to generate at least one vital sign parameter value based on the light received by the light detector (120).

3. The photoplethysmography sensor system according to claim 2, wherein: The vital sign parameter values include at least one of the following: a heart rate value; a respiratory rate value; and a pulse oximetry (SpO2) value.

4. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that The first light source (110) and the light detector (120) are integrated into the same circuit board.

5. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that Also included is a housing (570), wherein the first light source and the light detector are housed within the housing.

6. The photoplethysmography sensor system according to claim 5, wherein: The housing (570) is a waterproof housing.

7. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that Also included is a transparent window (575) positioned between the first light source and the light input of the waveguide (530a).

8. The photoplethysmography sensor system according to claim 7, wherein: Also included is a further transparent window configured to be positioned, in use, between the light detector and a surface of the subject.

9. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that The optical waveguide (130) comprises at least one of: glass; acrylic fiber; polycarbonate; quartz; plastic; silicone; carbon; and silicon dioxide.

10. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that The first light source (110) is proximate to the light detector (120), and wherein the light guide (130) is configured such that, in use, a portion of light emitted by the first light source is not received by the light input (230a) of the light guide.

11. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that Also included is a second light source (315) configured to emit light having a wavelength within a second wavelength range, wherein the light input is configured to also receive light emitted from the second light source.

12. The photoplethysmography sensor system according to claim 11, wherein: The first light source is configured to emit light having a wavelength within a first wavelength range different from the second wavelength range.

13. The photoplethysmography sensor system according to any one of claims 1 to 3, characterized in that Also included is a reflective light source (418) configured to emit light in a reflective wavelength band, wherein the reflective light source is proximate to the light detector so that, in use, the light detector can receive light emitted from the reflective light source and reflected from a surface of the subject.

14. A wearable device (500), characterized in that Comprising a photoplethysmography sensor system according to any one of claims 1 to 13.

15. A pulse oximeter device, characterized in that Comprising a photoplethysmography sensor system according to any one of claims 1 to 13.

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