Photoplethysmographic module

Abstract

A photoplethysmographic module comprising at least one LED and a photodetector, characterized in that it comprises at least two subassemblies consisting of an alignment of a photodetector associated on either side with two green LEDs, and an infrared sensor. Figure 1

Description

Title of the invention: Photoplethysmographic module Scope of the invention

[0001] The present invention relates to the field of detecting an individual's physiological activities, in particular for capturing, identifying, and analyzing that individual's emotions in order to enable automatic characterization, for example, for the purpose of amplifying emotions in a person, or for interacting with an external interactive system providing an immersive experience for a user. The principle is described, for example, in patent FR3100972B1 or patent application FR3123487Al of the applicant

[0002] The electrophysiological signals used to deduce correlations with emotional state are acquired by skin sensors, often in the form of a photoplethysmographic bracelet whose general principle is as follows: green LEDs send a beam of light through the skin. Part of this light is absorbed by the artery. The rest is reflected back to the watch and captured by the photodiodes located on the back of the watch. The less light is received, the more dilated the artery will be. Conversely, during vasoconstriction, a lot of light is reflected back to the watch. The heart rate monitor then records the time elapsed between each heartbeat, an interval called RR in medical jargon. Thanks to this raw vascular information, an algorithm is then able to calculate the user's heart rate and track it over time. State of the art

[0003] Prior art patent application EP3964127 describes a photoelectric pulse sensor component capable of reducing the divergence angle of light emitted by an electroluminescent component comprising a substrate; at least one electroluminescent component configured to emit light of at least one wavelength band; at least one lens disposed on the light-emitting side of at least one electroluminescent component; each lens corresponding to at least one electroluminescent component, and each lens can reduce the divergence angle of the light emitted by the at least one electroluminescent component to which the lens corresponds. The photoelectric pulse sensor component can be mounted in the wearable article such that the wearable article, when worn on a target organism, can measure the heart rate and blood oxygen saturation of the target organism.

[0004] US patent 10420470B2 describes another example of a biological information sensor comprising a light-emitting part and a photodetector, the part light emission comprising at least two light-emitting elements having light-emitting angles of different sizes, the photodetector being configured to detect light generated by the light-emitting part and modulated by a subject, and a data processor configured to extract and analyze biological information from the subject from the data measured by the biological signal measurement unit.

[0005] Patent EP3057138B1 describes an optical sensor module comprising a substrate, a light source disposed on the substrate, a first encapsulant formed on the light source, a photodetector disposed on the substrate, a second encapsulant formed on the photodetector, and a partition coupled to the substrate and located between the light source and the photodetector. The two encapsulants are separated from the partition. Each of the first and second encapsulants comprises a median surface extending directly from the substrate and facing the partition. At least one of the median surfaces has an optical directional component. The optical directional component of the first encapsulant is configured to direct the light from the light source in a direction intended toward the photodetector.The optical directional component of the first encapsulating agent is configured as an inclined plane; the inclined plane defines a refracting interface that refracts incident light emitted by the light source. An angle facing the light source is formed between a top surface of the substrate and the medial surface of the first encapsulating agent; the angle is greater than 20 degrees and less than 90 degrees. The incident light projected onto the refracting interface of the medial surface is concentrated above the partition. The partition is configured to block stray light directly from the light source to the photodetector.

[0006] US patent application 20170311856 describes a sensor comprising a light guiding element having a diffraction structure designed to direct incident light towards an object, and an optical sensing element designed to detect light reflected by said object.

[0007] Patent application EP3954274 describes a photoplethysmography sensor comprising a housing, a mounting hole formed on the housing; an optical device, housed in the mounting hole; and a light transmission element, comprising a central portion and a circumferential portion surrounding the central portion. The circumferential portion comprises at least one end face having a textured layer, the textured layer being used to scatter and / or absorb light. The central portion has an end face provided without a textured layer. The light transmission element is connected to the housing and is positioned outside the optical device. The end face of the central portion is configured to to correspond to the optical device, and the end face of the circumferential portion is configured to correspond to the surface provided without the optical device. The end face of the central portion that is near the optical device protrudes from the end face of the circumferential portion that is near the optical device.

[0008] We also know the document “GUIDELINES FOR THE OPTO-MECHANICAL

[0009] INTEGRATION OF HEART-RATE MONITORS IN WEARABLE EARBUD "DEVICES AN6847" from Maxim Integrated™ describes the opto-mechanical integration of a heart rate monitor, for example, a MAX86160 or MAX86161 module (trade names). Signal quality can be influenced by choosing designs that minimize crosstalk and maximize the signal. Disadvantages of prior art

[0010] Prior art sensors do not allow for totally satisfactory coupling with the wearer's epidermis, which leads to parasitic light beams and fluctuations in the light source.

[0011] The skin consists of three main layers from the surface: the bloodless epidermis (100 µm thick), the vascularized dermis (1 mm to 2 mm thick), and the subcutaneous adipose tissue (1 mm to 10 mm thick depending on the body area). Generally, the optical properties of these layers are characterized by absorption (pa), diffusion coefficients ps, and anisotropy factor (g).

[0012] The absorption coefficient characterizes the average number of absorption events per unit path length of photons traveling through the tissue. The main absorbers in the visible spectral range are melanin, which is blood composed of oxyhemoglobin (Hb), deoxyhemoglobin (HbO2), and lipids. In the IR spectral range, water absorption dominates the absorption properties of the dermis.

[0013] To reliably acquire the light signal interacting with the blood flow, it is necessary to improve the coupling between the "LED - Photodetector" pair and the patient's skin, particularly in the case of a sensor mounted on a bracelet, to minimize parasitic reflections in the opto-mechanical part of the sensor, and to ensure optimal intradermal interaction to take into account the variation of the vascular profusion index at the wrist, from one individual to another. Solution provided by the invention

[0014] To overcome these drawbacks, the invention relates to a photoplethysmographic module comprising at least one LED and a photodetector characterized in that it comprises at least two subassemblies consisting of a alignment of a photodetector associated on either side with two green LEDs and an infrared sensor.

[0015] According to variants: - said two sub-assemblies include a common green LED - said two subsets are activated alternately - The activation time of a subset is 10 ms ±5 ms - The duration of one cycle is 40 ms ± 10 ms - an opaque barrier is placed between each photodetector and the adjacent LEDs.

[0016] Detailed description of a non-limiting example of embodiment

[0017] The present invention will be better understood upon reading the following description, concerning non-limiting examples of embodiments illustrated by the accompanying drawings where:

[0018] [Fig. 1] [Fig. 1] represents a front view of a photoplethysmographic sensor according to the invention

[0019] [Fig.2] [Fig.2] represents the timing diagram of the operating cycle of a photoplethysmographic sensor according to the invention

[0020] [Fig.3] [Fig.3] shows a cross-sectional view of an "LED / photodetector" pair of a first example of a photoplethysmographic sensor according to the invention

[0021] [Fig.4] [Fig.4] represents a cross-sectional view of an "led / photodetector" pair of a second example of a photoplethysmographic sensor according to the invention.

[0022] [Fig.5] [Fig.5] represents a cross-sectional view of a photoplethysmographic sensor according to the invention. General principles of the invention

[0023] The invention relates to a photoplethysmographic module comprising an alternation of green light-emitting diodes (3, 4, 5) and photodetectors (6, 7), as well as an infrared temperature sensor (1) aligned behind a transparent window (25) of a length between 15 and 20 mm.

[0024] This module can be placed on the inner surface of a bracelet so that the transparent window (25) comes into contact with the skin of the wrist.

[0025] The principle of the invention is to cyclically control the switching on and off of the LEDs to alternate the subsets formed by a photodetector surrounded by two LEDs, with a frequency at least ten times greater than the typical heart rate of 70 to 75 beats per second.

[0026] Another feature relates to the treatment of parasitic light reflections in order to improve the signal-to-noise ratio; For this purpose, each LED (10) is surrounded by opaque partitions laterally masking the LED (12), and forming a window cut out in the upper surface (12) to collimate the light emitted by the LED. The photodetector (20) is also surrounded by opaque partitions (21) and an opaque separation (15) preventing the direct transmission of light emitted by the LED (10) to the photodetector (20). This opaque barrier is advantageously extended (16) to the transparent glass (25) to avoid interference from reflections at the air-glass interface.

[0027] Detailed description of the photoplethysmographic module

[0028] The module according to the example described with reference to Figures 1 and 2 consists of a component formed by a housing (8) closed by a glass pane (1). The glass pane (1) has high transmission (greater than 90%) in the wavelengths used (green and infrared) in order to maximize the light emitted into the skin and the signal reflected by the skin. To minimize transmission loss, the transparent glass pane (1) must be as thin as possible while being sufficiently robust to withstand normal wear. In addition, it must have a refractive index close to that of human skin (approximately 1.4) in order to minimize transmission losses due to Fresnel reflections.

[0029] Corning® Gorilla® Glass is an example of a material for the production of the window (1). Its refractive index is 1.5, the transmission at the operating wavelengths of the module (532 nm and 880 nm) is greater than 91%, and the glass provides a structurally sound covering with a thickness as thin as 200 µm. Other possible materials are acrylics, silicones, and polycarbonates.

[0030] Another method of integrating the module into the industrial design consists of encapsulating the module in a transparent material. Such a product also offers a certain "flexibility" which increases the contact area and pressure with the skin.

[0031] The module comprises a printed circuit board (9) on which are mounted an infrared sensor (2), and an array comprising a first green LED (3), a first photodetector (6) and a central green LED (4), then a second photodetector (7) and a third LED (5). This forms two sub-assemblies which are activated alternately, the first consisting of the first green LED (3), the first photodetector (6) and the central green LED (4), the second sub-assembly consisting of the third green LED (5), the second photodetector (7) and the central green LED (4).

[0032] These two subsets are alternately activated for durations of 10 ms, as illustrated in [Fig. 2], to form alternating cycles providing information on the light absorption characteristics of the wrist tissues, allowing for better compensation of ambient light and motion artifacts. This also improves the quality and accuracy of the signal when measuring physiological parameters such as heart rate or the pulse wave, due to a sampling frequency at least ten times higher than the usual heart rate.

[0033] Figure 2 illustrates an operating mode where each pair of LEDs surrounding a photodetector is alternately activated, with periods of extinction for all LEDs. The cycle is: • The first pair (3, 4) of LEDs is illuminated for 10 ms • All LEDs are switched off for 10 ms • Illumination of the second pair (4, 6) of LEDs for 10 ms • All LEDs are switched off for 10 ms • Etc...

[0034] Detailed description of the protection of the photodetectors

[0035] To improve the signal-to-noise ratio of the photodetectors (20), they are protected by an opaque casing (21) closed by a cover (22) opening through a window the size of the sensitive area of ​​the photodetector (20). An opaque barrier (15) prevents the direct propagation of stray light from an adjacent LED (10). This barrier (15) can be extended by a barrier (16) extending to the glass (25).

[0036] The glass (25) is kept away from the surface of the LEDs (10) and photodetectors (20) by an air gap. Alternative implementation

[0037] Figure 5 shows a cross-sectional view of an alternative embodiment. The module comprises a printed circuit board (9) on which an infrared sensor (2) is mounted, and an array comprising a first green LED (3), a first photodetector (6) and a central green LED (4), then a second photodetector (7) and a third LED (5). This forms two sub-assemblies that are activated alternately, the first consisting of the first green LED (3), the first photodetector (6) and the central green LED (4), the second sub-assembly consisting of the third green LED (5), the second photodetector (7) and the central green LED (4).

[0038] Partitions (18) extending between the printed circuit board (9) and the transparent glass (1) form light barriers preventing the direct transmission of light between an LED diode (3, 4, 6) and the photodetectors (5, 7).

[0039] The case (8) is mounted on a watch strap (19) applying the transparent glass (1) against the wearer's skin.

Claims

Demands

1. Photoplethysmographic module comprising at least one LED (10) and at least one photodetector (20) characterized in that it comprises at least two sub-assemblies consisting of an alignment of a photodetector (6, 7) associated on either side with two green LEDs (3, 4; 4, 5), and an infrared sensor (1).

2. Photoplethysmographic module according to claim 1 characterized in that said two subassemblies comprise a common green LED (4).

3. Photoplethysmographic module according to claim 1 characterized in that said two subsets are activated alternately, the first of said subsets consisting of a first green LED (3), a first photodetector (6) and a median green LED (4), the second of said subsets consisting of a third green LED (5), a second photodetector (7) and a median green LED (4).

4. Photoplethysmographic module according to the preceding claim characterized in that the activation time of a subset is 10 ms ±5 ms.

5. Photoplethysmographic module according to claim 4 characterized in that said two subsets are alternately activated for durations of 10 ms ±5 ms to form alternating cycles, the duration of said cycle being 40 ms ±10 ms.

6. Photoplethysmographic module according to claim 1 characterized in that an opaque barrier is placed between each photodetector (20) and the adjacent LEDs (10).

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