PPG sensor with high signal-to-noise ratio

Abstract

A photoplethysmography (PPG) sensor (100) configured to be worn on a user's body (300), the PPG sensor (100) comprising: a sensing portion (110) comprising an optical emitter (101) configured to emit emission light (201) toward the user's body (300), and an optical detector (102) for detecting detector light (202) reflected or scattered from tissue, thereby providing a PPG signal; and a docking portion (120) between the sensing portion (110) and the user's body (300), the docking portion (120) comprising a transparent interface element (104), the emission light (201) is transmitted through the transparent interface element (104) when traveling from the optical emitter (101) toward the body (300), and the detector light (202) is transmitted through the transparent interface element (104) when traveling from the body (300) to the optical detector (102), wherein the transparent interface element (104) has an interface transmittance (T1); the transparent interface element (104) includes an anti-reflection interface (106), and the anti-reflection interface (106) is configured so that the anti-reflection interface transmittance (T2) of the transparent interface element (104) including the anti-reflection interface (106) is at least 4% greater than the interface transmittance (T1).

Description

Technical Field

[0001] The present invention relates to a photoplethysmography (PPG) sensor to be worn on a user's body for measuring a PPG signal with a high signal-to-noise ratio. More particularly, the present invention relates to a PPG sensor comprising a sensing portion including an optical emitter and an optical detector, wherein the sensing portion is shielded from an external environment, and wherein the PPG sensor can be easily manufactured with good assembly tolerances. Background Art

[0002] According to the World Health Organization, one in three adults worldwide suffers from high blood pressure. High blood pressure can lead to serious complications, such as stroke and heart failure. Every year, the disease causes 7.5 million premature deaths worldwide. The paradox of high blood pressure is that most people who suffer from the disease are unaware of it.

[0003] Furthermore, the current "gold standard" of non-invasive blood pressure (BP) measurement is performed using a cuff placed around the arm. This 110-year-old technology is cumbersome and results in low compliance among patients who are prescribed self-monitoring. As a result, healthcare professionals are unable to obtain complete and high-quality data for their diagnosis and treatment of the disease.

[0004] The optimal technology to monitor BP should be non-invasive (it does not require penetration into the human body), non-occlusive (it does not require pressure around a body part), beat-to-beat (it allows BP values ​​to be measured with every heartbeat), available 24 / 7 in a home environment (it allows BP to be measured not only in a supervised clinical setting but also in real-life settings outside the clinic), and comfortable (it does not cause any disturbance to its user).

[0005] In search of such an optimal BP technique, PPG combined with pulse wave analysis (PWA) technology has recently attracted the interest of research institutions and industry. While photoplethysmography (PPG) is a sensor technology that provides a 24 / 7 available and comfortable measurement of arterial pulsation (the change in arterial diameter caused by the arrival of arterial pressure pulses) in a home environment, PWA is a signal processing tool that allows cardiovascular insights to be extracted from arterial pulsation patterns (such as heart rate and blood pressure). The combination of these two technologies is called optical blood pressure monitoring (OBPM). See, for example, reference: "DOI: 10.1109 / MPUL.2018.2856960".

[0006] Among the different possible implementations of OBPM solutions, one setting is particularly interesting: OBPM at the wrist. By embedding a PPG sensor into a wrist device (e.g., into a bracelet, smart band, or watch) and by applying PWA analysis techniques to the measured signals, a BP monitor can be built that is easily integrated into the user's life. Such a solution thus opens the door to the first-ever cuffless and beat-by-beat monitoring of BP in outpatient and clinical settings, providing clinicians with new insights into BP regulation and enabling revolutionary prevention and treatment strategies. See, for example, US20170360314A1.

[0007] Using an OBPM solution at the wrist requires the use of a special form of photoplethysmography - namely, reflection photoplethysmography (as opposed to transmission photoplethysmography). See, e.g., reference: ISBN-13: 978-0750304672.

[0008] A reflective PPG sensor illuminates a portion of the skin, for example by using an off-the-shelf LED, and retrieves a portion of the light that has propagated through the tissue, for example by using an off-the-shelf photodiode. Due to the presence of arterioles and other perfused structures in the skin, each time a pressure pulse reaches the illuminated portion of the skin, the amplitude of the retrieved portion of the light is modulated by the blood flow and locally occurring structural changes. Analysis of the modulation of the retrieved light is known to be relevant to identifying cardiovascular information from the user, such as heart rate, heart rate variability, blood composition, blood pressure, and other cardiovascular parameters. See, for example, reference: doi:10.1088 / 0967-3334 / 28 / 3 / R01.

[0009] EP3057138 discloses a reflective optical sensor module, an optical sensing accessory and an optical sensing device. The reflective optical sensor module includes a light source and a first package, a photodetector and a second package, and a substrate. The light source is configured to convert electrical energy into radiant energy and emit light to the surface of an object. The photodetector is configured to receive light from the surface of the object and convert the radiant energy into current or voltage. A partition is located between the light source and the photodetector. At least one intermediate surface of the package forms an optical directional component, which can be an inclined plane or a lens. The optical directional component promotes light extraction efficiency and light reception efficiency, respectively.

[0010] US2017311856 discloses a device and method for detecting light reflected from an object. The device includes: a light-guiding element including a diffractive structure configured to guide incident light to the object; and an optical sensing element configured to detect light reflected from the object.

[0011] Unfortunately, current state-of-the-art PPG sensors are associated with several drawbacks. In order to shield the electrical and optoelectronic components from external aggressions (humidity, dust, ...), reflective PPG sensors integrate a "transparent layer interface" between the PPG sensor and the body. This layer generates significant losses in the amount of light energy actually injected into and collected from the body, thus reducing the overall performance of the sensor.

[0012] In order to avoid the integration of such a "transparent layer interface", some manufacturers have provided means to create contact directly between the PPG sensor and the body. This approach is associated with safety (biocompatibility, electrical safety, ...), usability issues (cleaning and sterilization) and device assembly problems.

[0013] Finally, high manufacturing volumes of reflective PPG sensors (e.g., consumer-facing products) are associated with assembly tolerance issues from both optical and mechanical elements. Summary of the invention

[0014] The present disclosure relates to a PPG sensor, comprising: a sensing portion, comprising an optical emitter configured to emit emission light toward a user's body, and an optical detector for detecting detector light reflected or scattered from tissue, thereby providing a PPG signal; and a docking portion between the sensing portion and the user's body, the docking portion comprising a transparent interface element, through which the emission light is transmitted when traveling from the optical emitter toward the body, and through which the detector light is transmitted when traveling from the body to the optical detector, wherein the transparent interface element has an interface transmittance; a transparent interface element comprising an anti-reflection interface, configured such that the anti-reflection interface transmittance of the transparent interface element comprising the anti-reflection interface is at least 4% greater than the interface transmittance.

[0015] In one embodiment, the PPG sensor is configured to be worn on the wrist and used to determine blood pressure.

[0016] The PPG sensor disclosed herein increases the transmission of emitted light, resulting in a high signal-to-noise ratio of the PPG signal and reduced power consumption. In addition, the sensing portion is shielded from the external environment. The PPG sensor can be easily manufactured with good assembly tolerances. These and other advantages will become clear from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention will be better understood with the aid of the description of embodiments given by way of example and illustrated by the drawings, in which

[0018] Figure 1 illustrates a reflective PPG according to an embodiment, including an optical emitter, a transparent interface element, and an anti-reflective interface;

[0019] Figure 2shows the transmission of emission light emitted by an optical emitter through a transparent interface element and an anti-reflection interface according to an embodiment;

[0020] Figure 3 A PPG sensor is illustrated wherein the optical interface does not include an anti-reflection interface;

[0021] Figure 4 A PPG sensor is illustrated wherein the optical interface comprises an anti-reflective interface;

[0022] Figure 5 A PPG sensor including a flexible docking structure according to an embodiment is shown;

[0023] Figure 6 A PPG sensor having a docking configuration is shown; and

[0024] Figure 7 Another configuration of a PPG sensor with a docking structure is illustrated. DETAILED DESCRIPTION

[0025] Figure 1 A reflective PPG sensor 100 that is intended to be worn on a user's body 300 according to an embodiment is illustrated. The PPG sensor 100 includes a sensing portion 110 that includes an optical emitter 101 configured to emit emission light 201 toward tissue of the user's body 300 and an optical detector 102 to provide a PPG signal, the optical emitter 101 being configured to emit emission light 201 toward tissue of the user's body 300, and the optical detector 102 for detecting detector light 202 reflected or scattered from the tissue. The PPG sensor 100 further includes an interface portion 120 that is included between the sensing portion 110 and the user's body 300 when the PPG sensor 100 is worn. The interface portion 120 includes a transparent interface element 104 through which the emission light 201 is transmitted when traveling from the optical emitter 101 toward the tissue, and through which the detector light 202 is transmitted when traveling from the tissue to the optical detector 102.

[0026] The docking portion 120 includes a gap 150 between the sensing portion 110 and the transparent interface element 104. The gap 150 is filled with a medium. Preferably, the medium is air.

[0027] In one embodiment, the transparent interface element 104 includes an anti-reflective interface 106 .

[0028] The transparent interface element 104 can be made of a transparent material such as polycarbonate, acrylic, silicone, glass, metal oxide, ceramic, and any other suitable transparent material having a low absorption coefficient in the emission wavelength and a refractive index close to the refractive index of human skin. The low absorption coefficient can be in the green wavelength range (between 500 and 575 nm), in the infrared wavelength range (above 750 nm), in the red wavelength range (between 650 and 750 nm), in the yellow wavelength (between 575 and 650)), in the blue wavelength (between 420 and 500 nm), or in any other wavelength (between 400 and 1500 nm) that can penetrate the user's body 300. The transparent material can be biocompatible with human or animal tissue (skin). The transparent interface element 104 (with or without the anti-reflection interface 106) can be configured to exhibit a light transmittance greater than 70% or 80%, but preferably greater than 90%.

[0029] The anti-reflection interface 106 may include any suitable anti-reflection member or anti-reflection coating. For example, the anti-reflection interface 106 may include any one of a refractive index matching coating, a single-layer interference coating, a multi-layer interference coating, a textured layer, or any other type of anti-reflection coating, alone or in combination.

[0030] like Figure 2 As shown in , the optical emitter 101 emits emission light 201 with emission intensity I1. The emission light 201 is incident on the surface of the transparent interface element 104. The reflection part 203 of the emission light 201 with reflection intensity I3 is reflected, while the transmission part 207 of the emission light 201 with transmission intensity I2 is transmitted through the transparent interface element 104 (into the user's body 300).

[0031] When the emitted light 201 encounters the interface of the transparent interface element 104 at normal incidence (perpendicular to the surface), the reflected intensity I3 of the reflected light is given by the reflection coefficient or reflectivity R:

[0032] (1)

[0033] Where n1 and n2 are the refractive indices of the first and second media, ie, the refractive indices of the transparent interface element 104 and the gap 150, respectively.

[0034] If absorption is neglected, the transmittance (or transmission coefficient) T corresponds to 1-R. The gap 150 of the second refractive index travels to have In the case of the transparent interface element 104 having a first refractive index of , at a single reflection, the value of R is 0.04 or 4%. Therefore, the transparent interface element 104 has an interface transmittance T1 of 96%, that is, at most 96% of the light (T = 1-R = 0.96) actually enters the transparent interface element 104, and the rest is reflected from its surface.

[0035] The interface transmittance T1 corresponds to the ratio of the transmitted intensity I2 to the emitted intensity I1:

[0036] (2).

[0037] In other words, if emission light 201 with emission intensity I1 is incident on the surface of transparent interface element 104 (without anti-reflection interface 106 ), reflection portion 203 with reflection intensity I3 is reflected and transmission portion 207 with transmission intensity I2 is transmitted into the user's body 300 .

[0038] In the case where the transparent interface element 104 includes an anti-reflection interface 106, the anti-reflection interface 106 may be configured such that the anti-reflection interface transmittance T2, ie, the ratio of the transmission intensity I2 to the emission intensity I1, is at least 99%:

[0039] (3).

[0040] although Figure 2 Not shown, the detector light 202 may also be reflected at the surface of the transparent interface element 104 including the anti-reflection interface 106 , so that the anti-reflection interface transmittance of the transmitted portion of the detector light 202 will also be higher than the case without the anti-reflection interface 106 .

[0041] More generally, the anti-reflective interface 106 may be configured such that the transparent interface element 104 including the anti-reflective interface 106 has an anti-reflective interface transmittance T2 of at least 99%.

[0042] In one embodiment, the anti-reflective interface 106 is configured such that, for a transparent interface element 104 having a first refractive index n1 greater than a second refractive index n2 of the gap 150, the transparent interface element 104 including the anti-reflective interface 106 has an anti-reflective interface transmittance T2 of at least 99%.

[0043] In other words, the anti-reflection interface 106 is configured such that the anti-reflection interface transmittance T2 of the transparent interface element 104 including the anti-reflection interface 106 is at least 4% greater than the interface transmittance T1 of the transparent interface element 104, or:

[0044] (4).

[0045] The anti-reflection interface 106 is configured such that the anti-reflection interface transmittance T2 of at least 99% for the second refractive index n2 is at least 10%, such as about 20% or about 30%, greater than the first refractive index n1. The second refractive index n2 depends on the medium filling the gap 150. As mentioned, the medium may include air and any other low refractive index material, such as highly porous mirror SiO2 with a refractive index value as low as 1.05, or a low refractive index polymer with a refractive index value, for example, between 1.2 and 1.4.

[0046] Figure 3 The PPG sensor 100 is illustrated in which the optical interface 104 does not include an anti-reflection interface 106. In this configuration, the reflected portion 203 of the emitted light 201 is reflected back toward the sensing portion 110 on the transparent interface element 104, thereby reducing the transmission intensity I2 of the transmitted portion 207 of the emitted light 201 reaching the user's body 300 and the intensity of the detector light 202 reaching the optical detector 102. Figure 3 The reflected portion 203 of the emitted light 201 is shown as a single reflection path, but several reflection paths and reflection angles are possible.

[0047] Figure 4 The diagram illustrates how adding an anti-reflection interface 106 to the optical interface 104 reduces the reflected portion 203 of the emitted light 201 and increases the transmission intensity I2 of the transmitted portion 207 of the emitted light 201 reaching the user's body 300 and the intensity of the detector light 202 reaching the optical detector 102.

[0048] The increased transmission of the emitted light 201 results in an increased signal-to-noise ratio of the PPG signal. Thus, by reducing the intensity of the emitted light 201 and obtaining a measured PPG signal of similar amplitude, the PPG sensor 100 can have reduced power consumption (and therefore longer battery life).

[0049] For the same reasons as above, the transparent interface element 104 including the anti-reflection interface 106 also has an increased anti-reflection interface transmittance T2 for the detector light 202 that comes from the user's body 300 and travels toward the optical detector 102. Due to the increased anti-reflection interface transmittance T2 of both the emission light 201 and the detector light 202 when passing through the transparent interface element 104 including the anti-reflection interface 106, the emission intensity I1 of the emission light 201 generated by the optical emitter 101 and the intensity of the detector light can be lower than is possible in the case of a conventional PPG sensor for obtaining a PPG signal of the same signal-to-noise ratio.

[0050] like Figure 1As shown in the example of , the sensing portion 110 includes a substrate 105 on which an optical emitter 101 and an optical detector 102 are arranged. The substrate 105 may include a circuit board, a PCB, an electronic support, an adhesive patch, a textile, the skin itself, or any other support. The substrate 105 can be configured to be flexible or rigid, or partially flexible and rigid. The substrate 105 can be configured to support or / and connect to various electronic components, such as an analog front end (AFE), a microcontroller (MCU), a central processing unit (CPU), a memory, a wireless module, a power supply, and / or any other electrical component.

[0051] In a possible configuration, the sensing portion 110 may be integrated in a single chip, such as that manufactured by OSRAM. Sensor. The sensing portion 110 may be provided as a complete module with additional features and / or processing, such as the products MAX30100 / 1 / 2 or MAX86160 manufactured by Maxim Integrated, ADPD142 / 4RI, ADPD174 / 5GGI, or ADPD188BI manufactured by Analog Devices, BW1 / 2 / 4 or BE2 / 4 manufactured by Valencell, AS7000 or AS7024 manufactured by AMS, and Si1143 / 4 or Si1172 / 3 manufactured by SiLabs. The substrate 105, the optical emitter 101, and the optical detector 102 may also be provided or mounted as separate components.

[0052] The optical emitter 101 may include a single LED (such as SFH 4043, LT PWSG, CT DELSS1.12 or CH DELSS 1.22 from OSRAM), or multiple LEDs (such as SFH 7013 from OSRAM, VSMD66694 from Vishay and DLED-xxx / xxx-CSL-2 / 3 from OSIoptoelectronics), or any other light source, such as a diode, an organic diode, a polymer diode, a laser diode or all other similar sources. The wavelength of the emitted light of the optical emitter 101 may be in the green wavelength range (between 500 and 575 nm), in the infrared wavelength range (above 750 nm), in the red wavelength range (between 650 and 750 nm), in the yellow wavelength (between 575 and 650 nm), in the blue wavelength (between 420 and 500 nm) or in any other wavelength (between 400 and 1500 nm) that can penetrate the user's body.

[0053] The optical detector 102 may include a photodiode, a photodetector, a phototransistor, an optical chipset, a camera imaging device, a charge coupled device, or all other similar receivers (e.g., OSRAM's D5140 SFH 2200, SFH2440, BPW 34 S, SFH2201, or SFH 2704, Vishay's VCNL3036 or VEMD5010X01, ROHM's BH179XGLC, Analog Devices' ADPD221X, SiLabs' Si1181 / 2, and OSIoptoelectronics' PIN-0.81-LLS, PIN-4.0-LLS, or PIN-8.0-LLS). The optical detector 102 may be capable of collecting light at a large spectrum or at a notched spectrum window that matches the emission wavelength of the optical emitter 101.

[0054] The optical emitter 101 and the optical detector 102 may be separated by different distances from each other (1.33, 1.45, 2.18, 2.12, 2.32, 2.4, 2.51, 2.71, 2.72, 2.8, 2.83, 2.94, 2.95, 3.11, 3.5, and 5.3 mm) and may be configured to be at different distances (either in direct contact with the body or without contact) from the user's body 300. It is known that different distances between the optical emitter 101 and the optical detector 102 and different distances from the body 300 result in different penetration depths of the emitted light 201 and the detector light 202 reflected or scattered into the body 300.

[0055] In other variations, the transparent interface element 104 including the anti-reflective interface 106 may be flat or have a non-zero radius of curvature. For example, the transparent interface element 104 including the anti-reflective interface 106 may have a radius of curvature between 10 and 100 mm.

[0056] The shape of the transparent interface element 104 including the anti-reflection interface 106 can be configured so as to optimize the contact pressure with the user's body 300 when the PPG sensor 100 is worn so as to reduce possible movement between the PPG sensor 100 and the body 300. The shape and roughness of the transparent interface element 104 including the anti-reflection interface 106 can be further configured to optimize the contact between the transparent interface element 104 and the body 300 so as to maximize the transmission intensity I2 of the transmission portion 207 of the emission light 201 and the intensity of the detector light 202.

[0057] According to one embodiment, the anti-reflection interface 106 comprises a textured surface. Preferably, the anti-reflection interface 106 comprises a textured surface having a thickness between 0.025 and 0.40 According to the SPI mold surface finish standard or the VDI standard, such roughness corresponds to SPI finish A-2 to C-2. The textured surface can be produced by molding, forming, machining or any other suitable technology.

[0058] exist Figure 1 In the configuration shown in , the anti-reflective interface 106 is included on one side of the transparent interface element 104. Figure 1 In the specific example of FIG. 1 , the anti-reflection interface 106 is included on the side of the transparent interface element 104 closer to the sensing portion 110. Figure 1 In a specific example of the embodiment of the present invention, the side of the transparent interface element 104 without the anti-reflection interface 106 can be in direct contact with the tissue (such as skin) of the user's body 300. The latter configuration allows increasing the transmission of the emitted light 201 by reducing the reflected portion of the emitted light 203 caused by the change in the refractive index of the air and the transparent interface element 104 including the anti-reflection interface 106 (i.e., the surface of the transparent interface element 104 that is farther away from the sensing portion 110).

[0059] However, other arrangements of the docking portion 120 are contemplated (not shown). For example, the anti-reflective interface 106 may be included on a side of the transparent interface element 104 that is further away from the sensing portion 110, and therefore, is intended to be closer to the user's body 300 when the PPG sensor 100 is worn. Such a configuration allows the anti-reflective interface transmittance T2 of the transparent interface element 104 to be further increased.

[0060] In another possible arrangement, the anti-reflective interface 106 may be in direct contact with tissue (such as skin) of the user's body 300. In yet another possible arrangement, the docking portion 120 may be configured so that the anti-reflective interface 106 does not come into contact with the user's body 300 when the PPG sensor is worn.

[0061] In yet another arrangement, the anti-reflection interface 106 may be included on both sides of the transparent interface element 104. This configuration allows for increased transmission of the emitted light 201 by reducing the reflected portion of the emitted light 203 caused by the change in refractive index of the air and the transparent interface element 104 including the anti-reflection interface 106. The anti-reflection interface 106 on the side of the transparent interface element 104 further away from the sensing portion 110 increases the transmission of the emitted light 201 by reducing the reflected portion of the emitted light 203 caused by the change in refractive index of the tissue of the user's body 300 and the transparent interface element 104 including the anti-reflection interface 106.

[0062] The PPG sensor 100 may include a contact PPG sensor, in which a transparent interface element 104 is in contact (possibly direct contact) with the user's body 300, the transparent interface element 104 including an anti-reflection interface 106 on either side of the transparent interface element 104 or on both sides of the transparent interface element 104. Alternatively, the PPG sensor 100 may include a non-contact PPG sensor, in which the transparent interface element 104 is not in contact with the user's body 300, the transparent interface element 104 including an anti-reflection interface 106 on either side of the transparent interface element 104 or on both sides of the transparent interface element 104. Examples of non-contact PPG sensors 100 may include an emitting laser as a light source and a high-speed PiN photodiode as a photodetector (see, e.g., reference: oai:dspace.lboro.ac.uk:2134 / 22188).

[0063] In one embodiment, the docking portion 120 includes a docking structure 103 extending between the substrate 105 and the transparent interface element 104 to define a gap 150 between the sensing portion 110 and the transparent interface element 104. Figure 1-3 In the example shown in , the docking structure 103 includes an intermediate wall 130 between the optical emitter 101 and the optical detector 102 , and side walls 131 surrounding the optical emitter 101 and the optical detector 102 .

[0064] The docking structure 103 can be configured so that the gap 150 is completely enclosed between the base 105, the walls 130, 131 and the transparent interface element 104. The docking structure 103 can be configured so that the gap 150 is sealed and isolated from the external environment. In other variations, the docking structure 103 can be configured so that the gap 150 is open to the external environment. Here, the middle wall 130 and the side wall 131 may include openings, or may include pillars or any other open structures.

[0065] In a preferred embodiment, the docking structure 103 is flexible so that when pressure is applied to the substrate 105 or the transparent interface element 104 or both, the distance between the substrate 105 and the transparent interface element 104 and the height (or volume) of the gap 150 can change (see Figure 5 ).

[0066] The flexible docking structure 103 further allows compensating for assembly tolerances of the sensing portion 110 by correcting assembly defects of the different optical and mechanical elements forming the sensing portion 110 .

[0067] The flexible docking structure 103 facilitates the integration of a commercially available sensing portion 110 (such as the aforementioned The PPG sensor 100 can be integrated with other commercially available sensors) with great flexibility in design. Thus, the manufacture of the PPG sensor 100 is facilitated.

[0068] The transparent interface element 104 in combination with the docking structure 103 allows the sensing portion 110 to be shielded from the external environment (such as protecting the sensing portion 110 from dust, water and moisture). The transparent interface element 104, which may include an anti-reflective interface 106, can be cleaned. The transparent interface element 104 further allows the sensing portion 110 to be insulated from the tissue of the user's body 300 and provides biocompatibility when the PPG sensor 100 is in contact with the tissue of the user's body 300.

[0069] In known PPG sensor configurations, the optical emitter 101 and the optical detector 102 are in direct contact with the user's body 300 (such as skin) or via a dielectric material, where the dielectric material can be a transparent interface element 104 or any other material having a refractive index close to that of the user's body 300 (typically around 1.4 - 1.5).

[0070] In contrast, the PPG sensor 100 described herein includes a gap 150 between the optical emitter 101 and the optical detector 102 and the transparent interface element 104. As mentioned above, the gap 150 can be filled with air or another medium. In the case of air, and possibly for another medium, the refractive index can be close to 1, resulting in a large reflected portion 203 of the emitted light 201 at the interface between the gap 150 and the transparent interface element 104, and thus resulting in a low interface transmittance T1.

[0071] The transparent interface element 104 including the anti-reflection interface 106 allows a ratio of the transmitted intensity I2 to the emitted intensity I1 of 99% or greater to be obtained in the case where the gap 150 having a refractive index that may be close to 1 is included between the optical emitter 101 and the optical detector 102 and the transparent interface element 104. In other words, the anti-reflection interface 106 can be configured such that the anti-reflection interface transmittance T2 of the transparent interface element 104 including the anti-reflection interface 106 is at least 4% greater than the interface transmittance T1 of the transparent interface element 104 (without the anti-reflection interface 106).

[0072] The docking structure 103 can be further configured to prevent optical shunting, i.e., prevent the emitted light 201 from reaching the optical detector 102 without traveling through the transparent interface element 104 and the tissue of the user's body 300, and / or prevent the ambient light 206 from reaching the optical detector 102. In other words, the docking structure 103 can be used as an optical mask. Here, the ambient light 206 is light from the environment outside the PPG sensor 100.

[0073] like Figures 1 to 3 As shown in , the middle wall 130 optically shields the optical emitter 101 from the optical detector 102, thereby preventing the emitted light 201 from reaching the optical detector 102 without traveling through the transparent interface element 104 and the tissue of the user's body 300. The side wall 131 can be configured to prevent ambient light 206 from reaching the optical detector 102.

[0074] To this end, the docking structure 103 can be made of a light-shielding or / and light-reflecting material. The docking structure 103 can include a dark or light color and / or surface finish. The docking structure 103 can be made of a material that does not absorb light.

[0075] Figure 6 A variation of the PPG sensor 100 is shown in which the docking structure 103 does not include an intermediate wall and in which the diverted portion 204 of the emitted light 201 travels towards the optical detector 102 without passing through the transparent interface element 104 and the user's body 300 .

[0076] Figure 7 The optimal dimensions of the docking structure 103 are illustrated, wherein the intermediate wall 130 extends between the base 105 and the transparent interface element 104 and reduces the interface reflective portion 205 by preventing the interface reflective portion 205 from traveling from the optical detector 102 to the optical detector 102 without penetrating into the user's body 300. The dimensions of the docking structure 103 are also configured to prevent the emitted light 201 from reflecting at a surface of the transparent interface element 104 further away from the sensing portion 110 and not traveling further, i.e., not penetrating into the user's body 300. The dimensions of the docking structure 103 are based on the reflection and refraction angles of the emitted light 201 and the detector light 202.

[0077] The PPG sensor 100 with improved optical performance allows for the exploration of novel configurations suitable for different applications. For example, the PPG sensor 100 may be small in size (such as a PPG sensor 100 having an optical emitter 101 and an optical detector 102 spatially separated by 4 to 10 mm), or large in size (such as a PPG sensor 100 having an optical emitter 101 and an optical detector 102 separated by more than 10 mm). Alternatively or in combination, the wavelength or wavelength range of the optical emitter 101, and the filtering configuration of the optical detector 102 may be selected so as to allow the emitted light 201 to penetrate superficially or deeply in the tissue of the user's body 300, and measure arterial pulsations of different layers of the tissue of the user's body 300.

[0078] The PPG sensor 100 may be configured to be worn at a location on the user's body 300 , including any one of an armband, a wrist, a fingertip, or an ear.

[0079] The PPG sensor 100 can be configured to be integrated into a wearable device, which includes any of the following: a headband, an ankle bracelet, a necklace, a ring, a helmet, earplugs, a hearing aid, headphones, glasses, a shirt, a bra, clothing, gloves, underwear, socks, shoes, a wearable sensor, a patch attached to the user's skin, a pulsation signal sensor.

[0080] The PPG sensor 100 may be further configured so as to be integrated into a device intended to be in contact with a user's body 300, including any of a bed sensor, a chair sensor, a toilet sensor, a table sensor, a car sensor, a computer mouse sensor, or any other arrangement intended to measure a pulsating signal.

[0081] The PPG sensor 100 facilitates the measurement of local arterial pulsation due to the increased transmission of the emitted light 201 and the increased signal-to-noise ratio of the PPG signal. In fact, the increased signal-to-noise ratio of the PPG signal improves the performance of signal processing algorithms, such as time series analysis of local arterial pulsation for determining cardiovascular parameters such as blood pressure.

[0082] The PPG sensor 100 can be used to determine blood pressure, pulse pressure, central pulse wave velocity, peripheral pulse wave velocity, arterial stiffness, aortic pulse transit time, augmentation index, stroke volume, stroke volume variability, pulse pressure variability, cardiac output, systemic vascular resistance, venous pressure, systemic hemodynamic parameters, pulmonary hemodynamic parameters, cerebral hemodynamic parameters, heart rate, heart rate variability, heart beat interval, arrhythmia detection, ejection duration, SpO2, SpHb, SpMet, SpCO, respiratory rate, tidal volume, apnea detection, sleep quality, sleep score, sleep analysis, time in bed, sleep duration, rem sleep time, light sleep time, deep sleep time, time to wake up, sleep time, sleep efficiency, minutes awake after falling asleep, snoring duration, stress index, and general cardiovascular and health indexes.

[0083] Reference Number

[0084] 100 PPG Sensor

[0085] 101 Optical Transmitter

[0086] 102 Optical detector

[0087] 103 Docking structure

[0088] 104 Transparent interface elements

[0089] 105 Base

[0090] 106 Anti-reflection interface

[0091] 110 Sensing part

[0092] 120 Docking part

[0093] 130 Middle Wall

[0094] 131 Sidewall

[0095] 150 Clearance

[0096] 201 Emitted Light

[0097] 202 Detector light

[0098] 203 Reflected portion of emitted light

[0099] 204 Split portion of emitted light

[0100] 205 Interface reflection part of emitted light

[0101] 206 Ambient Light

[0102] 207 Transmitted portion of emitted light

[0103] 300 User Body

[0104] I1 emission intensity

[0105] I2 Transmittance Intensity

[0106] I3 Reflection intensity

[0107] n, n1, n2 refractive index

[0108] T1 interface transmittance

[0109] T2 Anti-reflection interface transmittance

Claims

1. A photoplethysmography (PPG) sensor (100) configured to be worn on or in contact with a user's body (300), the PPG sensor (100) comprising: a sensing portion (110) comprising an optical emitter (101) configured to emit emission light (201) toward a user's body (300), and an optical detector (102) for detecting detector light (202) reflected or scattered from tissue, thereby providing a PPG signal; as well as comprising an interface portion (120) between the sensing portion (110) and the user's body (300), the interface portion (120) comprising a transparent interface element (104), through which emission light (201) is transmitted when traveling from the optical emitter (101) toward the body (300), and through which detector light (202) is transmitted when traveling from the body (300) toward the optical detector (102), wherein the transparent interface element (104) has an interface transmittance (T1); The docking portion (120) includes a gap (150) between the sensing portion (110) and the transparent interface element (104), the transparent interface element (104) having a first refractive index of n1, and the gap (150) having a second refractive index of n2; Features The transparent interface element (104) includes an anti-reflection interface (106), and the anti-reflection interface (106) is configured so that when the second refractive index n2 is at least 10% greater than the first refractive index n1, the anti-reflection interface transmittance (T2) of the transparent interface element (104) including the anti-reflection interface (106) is at least 99%; and The sensing part comprises a substrate (105), an optical emitter (101) and an optical detector (102) are arranged on the substrate (105), wherein the substrate is flexible; and The docking portion includes a docking structure (103) extending between the substrate (105) and the transparent interface element (104), thereby defining a gap (150) between the sensing portion (110) and the transparent interface element (104); The docking structure (103) is flexible so that the distance between the substrate (105) and the transparent interface element (104) can be changed when pressure is applied to the substrate (105) or the transparent interface element (104) or both. 2 . The PPG sensor according to claim 1 , wherein the second refractive index n2 is 20% or 30% greater than the first refractive index n1 .

3. The PPG sensor of claim 1, wherein the anti-reflection interface (106) comprises a textured surface having a roughness Ra between 0.025 and 0.40 μm.

4. The PPG sensor of claim 1 , wherein the anti-reflection interface ( 106 ) comprises any one of a refractive index matching coating, a single-layer interference coating, a multi-layer interference coating, or any other type of anti-reflection coating.

5. The PPG sensor of claim 1, wherein the anti-reflection interface (106) is included on one side of the transparent interface element (104).

6. The PPG sensor according to claim 5, wherein the anti-reflection interface (106) is included on a side of the transparent interface element (104) closer to the sensing portion.

7. The PPG sensor according to claim 5, wherein the anti-reflection interface (106) is included on a side of the transparent interface element (104) further away from the sensing portion.

8. The PPG sensor of claim 1, wherein an anti-reflection interface (106) is included on both sides of the transparent interface element (104).

9. The PPG sensor according to claim 1, comprising a contact PPG sensor (100).

10. The PPG sensor according to claim 1, comprising a contactless PPG sensor (100).

11. The PPG sensor according to claim 1, wherein the docking structure (103) includes an intermediate wall (130) between the optical emitter (101) and the optical detector (102), and a side wall (131) surrounding the optical emitter (101) and the optical detector (102).

12. The PPG sensor according to claim 1, wherein the docking structure (103) is configured such that the gap (150) is sealed from the external environment.

13. The PPG sensor according to claim 1, wherein: The docking structure (103) is further configured to prevent the emitted light (201) from reaching the optical detector (102) without traveling through the transparent interface element (104) and the user's body (300).

14. The PPG sensor of claim 13, wherein the docking structure (103) is further configured to prevent ambient light (206) from reaching the optical detector (102).

15. The PPG sensor according to claim 1 is configured to be worn on a user's body (300), the location comprising any one of an armband, a wrist, a fingertip or an ear.

16. The PPG sensor of claim 1, configured to be worn on a wrist and used to determine blood pressure from the PPG signal.

17. The PPG sensor of claim 1 , configured to be integrated into a wearable device, the wearable device comprising any one of the following: a headband, an ankle bracelet, a necklace, a ring, a helmet, earplugs, a hearing aid, headphones, glasses, a shirt, a bra, clothing, gloves, underwear, socks, shoes, a wearable sensor, a patch attached to a user's skin, a pulsation signal sensor.

18. The PPG sensor according to claim 1 is configured to be integrated in a device intended to be in contact with a user's body (300), the device comprising any of the following: a bed sensor, a chair sensor, a toilet sensor, a table sensor, a car sensor, a computer mouse sensor.

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