Sensor module

Abstract

A sensor module (1) is specified herein, comprising: - an emitter (2) that emits electromagnetic radiation (3) during operation, and - a detector (4) that detects electromagnetic radiation (3) emitted by the emitter (2) during operation, wherein - the emitter (2) and the detector (4) are arranged on a carrier (5), and - a main emission direction (21) of the emitter (2) and a main detection direction (41) of the detector (4) are inclined away from each other.

Description

[0001] Description

[0002] SENSOR MODULE

[0003] A sensor module is speci fied herein .

[0004] At least one obj ect of certain embodiments is to speci fy a sensor module with an improved sensitivity . This obj ect is achieved by the sensor module according to the independent claim .

[0005] Advantageous embodiments and further developments of the method are speci fied in the dependent claims .

[0006] According to an aspect , the sensor module comprises an emitter that emits electromagnetic radiation during operation . In particular, the emitter at least partially converts an electric operating current into the electromagnetic radiation .

[0007] For example , the emitter comprises a semiconductor layer sequence with a pn-j unction for converting the electric operating current into the electromagnetic radiation during operation . For example , the electromagnetic radiation comprises wavelengths in a spectral range between infrared light and ultraviolet light .

[0008] For example , the electromagnetic radiation emitted by the emitter comprises or consists of electromagnetic laser radiation . In particular, electromagnetic laser radiation is generated by stimulated emission . Compared to electromagnetic radiation generated by spontaneous emission, electromagnetic laser radiation has a longer coherence length, a smaller spectral bandwidth, and / or a higher degree of polari zation, for example .

[0009] According to a further aspect , the sensor module comprises a detector that detects electromagnetic radiation emitted by the emitter during operation . In particular, the detector at least partially converts incident electromagnetic radiation emitted by the emitter into an electric voltage and / or an electric current . For example , the detector comprises a semiconductor layer sequence with a pn-j unction for converting the incident electromagnetic radiation into the electric voltage and / or the electric current during operation .

[0010] According to a further aspect of the sensor module , the emitter and the detector are arranged on a carrier . In particular, the emitter and the detector are arranged on a common carrier . For example , the emitter and the detector are arranged laterally adj acent to each other on a main surface of the carrier . For example , the main surface of the carrier is flat . Here and in the following " lateral" refers to a direction parallel to the main surface of the carrier . It is also possible that the main surface of the carrier is curved . For example , the main surface of the carrier has a convex shape .

[0011] For example , the carrier comprises or consists of a semiconductor substrate or a printed circuit board . In particular, the carrier comprises electrical contact pads on the main surface for electrically contacting the emitter and / or the detector . For example , the emitter and the detector are surface mountable . For example , the emitter and the detector are arranged such that a light emission surface of the emitter and a light transmitting surface of the detector are facing away from the carrier. For example, the light emission surface and the light transmitting surface are flat surfaces.

[0012] For example, the sensor module further comprises an integrated circuit for controlling the emitter and / or the detector during operation. In particular, the integrated circuit is an application specific integrated circuit (short: ASIC) . For example, the integrated circuit is arranged on the main surface of the carrier, or the integrated circuit is arranged on a backside of the carrier that is opposite the main surface, or the integrated circuit is integrated into the carrier using a complementary metal-oxide-semiconductor process (short: CMOS process) .

[0013] It is also possible that the emitter and the detector are arranged on different sides of the carrier. For example, the emitter is arranged or mounted on the main surface of the carrier and the detector is arranged or mounted on a surface of the carrier that is opposite to the main surface, or vice versa .

[0014] According to a further aspect of the sensor module, a main emission direction of the emitter and a main detection direction of the detector are inclined away from each other. In particular, the main emission direction and the main detection direction are not parallel to each other. For example, an angle between the main emission direction and the main detection direction is larger than 0° and smaller than 180°, or between 40° and 140°, inclusive, or between 60° and 120°, inclusive, or between 80° and 100°, inclusive, or is 90°. In particular, the main emission direction and the main detection direction do not cross in a hal f space above the main surface of the carrier .

[0015] It is also possible that the main emission direction and the main detection direction cross in a hal f space above the main surface of the carrier . For example , the emitter and the detector are remotely mounted and imaged onto an obj ect to be sensed using e . g . a proj ection optics . For example , the sensor module is configured as a biomonitoring sensor and the emitter and the detector are imaged onto biological tissue , such as skin, using the proj ection optics . For example , the sensor module is part of an augmented reality and / or virtual reality headset .

[0016] In particular, the main emission direction of the emitter corresponds to a direction where a directional characteristics of the emitter or a directivity of the emitter is maximal . For example , the directional characteristics of the emitter speci fies a power of the emitted electromagnetic radiation per unit solid angle . For example , the main emission direction is perpendicular to the light emission surface of the emitter .

[0017] In particular, the main detection direction of the detector corresponds to a direction where a directional characteristics of the detector or a directivity of the detector is maximal . For example , the directional characteristics of the detector speci fies a sensitivity of the detector as function of the solid angle . For example , the main detection direction is perpendicular to the light transmitting surface of the detector . Here and in the following, the main detection direction is defined as a direction against the propagation direction of the electromagnetic radiation incident on the detector. In other words, the main detection direction is defined as pointing away from the detector rather than towards the detector.

[0018] Using a spherical coordinate system centered at the emitter with a z-axis or a zenith direction parallel to a surface normal of the main surface of the carrier and the detector arranged at a distance from the emitter along the x-axis, the main emission direction and / or the main detection direction has a polar angle larger than 0° and smaller than 90°, or between 10° and 80°, inclusive, or between 20° and 70°, inclusive, or between 30° and 60°, inclusive, for example. For example, the main emission direction and / or the main detection direction has a polar angle of 45°.

[0019] Moreover, if the azimuthal angle of the spherical coordinate system is measured from the x-axis, such that the x-axis is at an azimuthal angle of 0°, the main emission direction has an azimuthal angle larger than 90° and smaller than 270°, or larger than 135° and smaller than 225°, for example, whereas the main detection direction has an azimuthal angle larger than -90° and smaller than 90°, or larger than -45° and smaller than 45°, for example. Preferably, the main emission direction has an azimuthal angle of 180° and the main detection direction has an azimuthal angle of 0°.

[0020] According to an embodiment, the sensor module comprises:

[0021] - the emitter that emits electromagnetic radiation during operation, and

[0022] - the detector that detects electromagnetic radiation emitted by the emitter during operation, wherein

[0023] - the emitter and the detector are arranged on the carrier, and - the main emission direction of the emitter and the main detection direction of the detector are inclined away from each other .

[0024] The sensor module described herein is based on the idea to arrange the emitter and the detector such that the main emission direction and the main detection direction are inclined away from each other, such that the sensitivity and / or a signal-to-noise ratio of the sensor module can be increased compared to a sensor module where the main emission direction and the main detection direction are parallel to each other . In particular, a higher sensitivity of the sensor module advantageously lowers signal-to-noise ratio requirements of the sensor module , for example , and thus makes it possible to operate the sensor module with reduced power, prolonging battery li fe and / or reducing the overall system form factor, for example .

[0025] For example , the sensor module is a biomonitoring sensor configured for measuring a pulse and / or a blood oxygen saturation of a person or an animal . In particular, the sensor module emits electromagnetic radiation that is at least partially reflected at and / or inside a biological tissue , such as skin, and subsequently detected by the detector . For example , the sensor module is part of a wearable device , such as a watch or an in-ear earphone .

[0026] Due to space constraints , a separation between the emitter and the detector might be particularly small , for example at most a few millimeters . Accordingly, a substantial fraction of the electromagnetic radiation emitted by the emitter that is detected by the detector may originate from crosstalk between the emitter and the detector, and / or from a reflection at the surface of the biological tissue, for example, such that the reflected electromagnetic radiation has not interacted with deeper layers of the biological tissue. Consequently, the signal-to-noise ratio and / or the sensitivity of the sensor module can be reduced if the separation between the emitter and the detector is decreased.

[0027] By inclining the main emission direction and the main detection direction away from each other, both crosstalk and the amount of detected electromagnetic radiation that is reflected directly at the surface of the biological tissue can be decreased. Accordingly, the signal-to-noise ratio and / or the sensitivity of the sensor module can be advantageously increased.

[0028] According to a further aspect of the sensor module, the main emission direction of the emitter and / or the main detection direction of the detector is inclined with respect to a surface normal of the main surface of the carrier. For example, using the spherical coordinate system introduced above, the polar angle of the main emission direction of the emitter is larger than 0° and smaller than 90°, or between 10° and 80°, inclusive, or between 20° and 70°, inclusive, or between 30° and 60°, inclusive, for example.

[0029] For example, using the spherical coordinate system introduced above, the polar angle of the main detection direction of the detector is larger than 0° and smaller than 90°, or between 10° and 80°, inclusive, or between 20° and 70°, inclusive, or between 30° and 60°, inclusive, for example.

[0030] According to a further aspect of the sensor module, an angle between the main emission direction of the emitter and a direction from the emitter to the detector is larger than 90 ° and smaller than 180 ° , or larger than 100 ° and smaller than 170 ° , or larger than 120 ° and smaller than 150 ° . In particular, the direction from the emitter to the detector is a direction from a center of the emitter to a center of the detector .

[0031] According to a further aspect of the sensor module , an angle between the main detection direction of the detector and a direction from the detector to the emitter is larger than 90 ° and smaller than 180 ° , or larger than 100 ° and smaller than 170 ° , or larger than 120 ° and smaller than 150 ° . In particular, the direction from the detector to the emitter is a direction from the center of the detector to the center of the emitter .

[0032] According to a further aspect of the sensor module , a distance between the emitter and the detector is at most 3 millimeter, or at most 2 millimeter, or at most 1 millimeter . In particular, the distance is an edge-to-edge distance between the emitter and the detector . It is also possible that the distance between the emitter and the detector is larger than 3 millimeter . For example , the distance between the emitter and the detector is at most 5 millimeter or at most 10 millimeter .

[0033] According to a further aspect of the sensor module , the emitter comprises or consists of a light emitting diode chip ( LED chip ) or a vertical cavity surface emitting laser diode chip (VCSEL chip ) . In particular, the LED chip comprises a semiconductor layer stack with a pn-j unction for converting the electric operating current into electromagnetic radiation . For example , the LED chip has a Lambertian directional characteristics . For example , the LED chip is comprised by a LED package .

[0034] In particular, the VCSEL chip comprises a semiconductor layer stack with a pn-j unction for converting the electrical operating current into electromagnetic radiation . In particular, the VCSEL chip emits electromagnetic laser radiation in a direction perpendicular to a main extension plane of the semiconductor layers of the semiconductor layer stack . For example , an optical axis of an optical resonator of the VCSEL chip is arranged perpendicular to the main extension plane of the semiconductor layers of the semiconductor layer stack . For example , the VCSEL chip has a directed directional characteristics that deviates from a Lambertian directional characteristics . For example , the VCSEL chip is comprised by a VCSEL package .

[0035] It is also possible that the emitter comprises or consists of an incandescent light source , a Xenon light source , a laser driven or laser pumped light source , or an edge emitting laser diode , for example .

[0036] According to a further aspect of the sensor module , the detector comprises or consists of a photodiode chip or a phototransistor chip . In particular, the photodiode or phototransistor comprises a semiconductor layer stack with a pn-j unction for at least partially converting incident electromagnetic radiation into an electric voltage and / or an electric current . For example , the photodiode chip or the phototransistor chip is comprised by a photodiode package or a phototransistor package , respectively . According to a further aspect of the sensor module , the electromagnetic radiation emitted by the emitter is in the infrared spectral range . It is also possible that the emitter emits electromagnetic radiation in the red or green spectral range , for example .

[0037] According to a further aspect of the sensor module , the emitter comprises a first optical element for collimating the emitted electromagnetic radiation . In particular, the first optical element changes the directional characteristics and / or the main emission direction of the electromagnetic radiation emitted by the emitter . For example , the first optical element reduces a crosstalk between the emitter and the detector .

[0038] According to a further aspect of the sensor module , the first optical element is arranged of f-centered from a light emission surface of a light source of the emitter . For example , "of f-centered" refers to a lateral displacement between a center of the light source and a center of the first optical element . For example , the light source is the light emitting diode or the VCSEL .

[0039] In particular, by arranging the first optical element of f- centered from the light emission surface of the light source , the main emission direction of the emitter can be adj usted . For example , the light emission surface of the light source is arranged parallel to the main surface of the carrier, while the main emission direction of the emitter is inclined with respect to the surface normal of the main surface of the carrier . According to a further aspect of the sensor module , the detector comprises a second optical element for focusing the electromagnetic radiation onto a light transmitting surface of a photosensitive element of the detector . For example , the photosensitive element is the photodiode or the phototransistor . In particular, the second optical element changes the directional characteristics and / or the main detection direction of the detector . For example , the second optical element reduces a crosstalk between the emitter and the detector .

[0040] According to a further aspect of the sensor module , the second optical element is arranged of f-centered from the light transmitting surface of the photosensitive element . For example , "of f-centered" refers to a lateral displacement between a center of the photosensitive element and a center of the second optical element .

[0041] In particular, by arranging the second optical element of f- centered from the light transmitting surface of the photosensitive element , the main detection direction of the detector can be adj usted . For example , the light transmitting surface of the photosensitive element is arranged parallel to the main surface of the carrier, while the main detection direction of the detector is inclined with respect to the surface normal of the main surface of the carrier .

[0042] According to a further aspect of the sensor module , the first optical element and / or the second optical element comprises or consists of a refractive optical element or a di f fractive optical element . For example , the refractive optical element comprises or consists of a lens or a Fresnel lens . For example , the di f fractive optical element comprises or consists of a di f fraction grating or a metalens . In particular, the metalens comprises a nanostructured surface with an aperiodic array of nano-pillars that imparts a spatially dependent phase onto incident electromagnetic radiation .

[0043] According to a further aspect of the sensor module , the emitter comprises a first reflective element for tuning the directional characteristics of the emitter . For example , the first reflective element comprises or consists of a mirror or a metallic layer . For example , the first reflective element has a reflective surface that is arranged inclined or perpendicular to the main surface of the carrier . For example , the reflective surface of the first reflective element is flat or curved .

[0044] According to a further aspect of the sensor module , the first reflective element is arranged on a side of the emitter facing the detector . Accordingly, the first reflective element reduces a crosstalk between the emitter and the detector, for example . Moreover, the first reflective element directs the emitted electromagnetic radiation away from the detector, for example .

[0045] According to a further aspect of the sensor module , the detector comprises a second reflective element for tuning the directional characteristics of the detector . For example , the second reflective element comprises or consists of a mirror or a metallic layer . For example , the second reflective element has a reflective surface that is arranged inclined or perpendicular to the main surface of the carrier . For example , the reflective surface of the second reflective element is flat or curved . According to a further aspect of the sensor module , the second reflective element is arranged on a side of the detector facing the emitter . Accordingly, the second reflective element reduces a crosstalk between the emitter and the detector, for example . Moreover, the second reflective directs the main detection direction of the detector away from the emitter, for example .

[0046] According to a further aspect of the sensor module , a barrier for reducing crosstalk between the emitter and the detector is arranged on the main surface of the carrier . For example , the barrier comprises or consists of an absorptive material that at least partially absorbs the electromagnetic radiation emitted by the emitter . For example , an absorbance of the barrier for the electromagnetic radiation emitted by the emitter is at least 50% , or at least 80% , or at least 90% .

[0047] According to a further aspect of the sensor module , the barrier comprises or consists of a material that reflects the electromagnetic radiation emitted by the emitter . For example , the barrier has a reflectance of at least 80% , or of at least 90% , or of at least 99% for the electromagnetic radiation emitted by the emitter . For example , the barrier can be used for adj usting or changing the directional characteristics of the emitter and the detector .

[0048] According to a further aspect , the sensor module is configured as a photoplethysmography ( short : PPG) sensor . In particular, the sensor module measures a heart rate , a blood oxygen saturation ( short : SpO2 ) , a blood pressure , and / or an arterial sti f fness during operation . According to a further aspect , the sensor module further comprises a second emitter and a third emitter, wherein the emitter emits electromagnetic radiation in an infrared spectral range during operation, the second emitter emits electromagnetic radiation in a red spectral range during operation, and the third emitter emits electromagnetic radiation in a green spectral range during operation . For example , the infrared spectral range comprises wavelengths between and including 780 nanometer and 1500 nanometer, whereas the red spectral range comprises wavelengths between and including 640 nanometer and 780 nanometer, and the green spectral range comprises wavelengths between and including 490 nanometer and 570 nanometer . For example , detector readings corresponding to emissions in the above mentioned spectral ranges are combined in order to determine the blood oxygen saturation, the blood pressure and / or the arterial sti f fness .

[0049] It is also possible that the sensor module comprises one emitter, two emitters , three emitters or a plurality of emitters . For example , at least two of the emitters emit electromagnetic radiation at the same or at di f ferent wavelengths . For example , all emitters emit electromagnetic radiation at the same or at di f ferent wavelengths .

[0050] According to a further aspect of the sensor module , the detector detects electromagnetic radiation emitted by the emitter, the second emitter and the third emitter during operation . In particular, the detector is a broadband detector that can detect incident electromagnetic radiation in a spectral range between infrared light and green light . For example , the detector at least partially converts electromagnetic radiation with wavelengths between and including 490 nanometer and 1500 nanometer into the electric voltage or the electric current . It is also possible that the detector at least partially converts electromagnetic radiation with wavelengths between 490 nanometer and 1100 nanometer, inclusive , or between 490 nanometer and 2200 nanometer, inclusive , or between 490 nanometer and 2500 nanometer, inclusive , into the electric voltage or the electric current . For example , the semiconductor layer sequence of the detector comprises or consists of silicon or indium gallium arsenide phosphide , Inx-xGax SyPi-y with 0<x<l and 0<y<l . For example , the emitter, the second emitter and the third emitter emit electromagnetic radiation in a time- multiplexed manner, such that the electromagnetic radiation detected by the detector can be uniquely assigned to the respective emitter .

[0051] It is also possible that the sensor module comprises a dedicated detector for each emitter . For example , the sensor module further comprises a second detector and a third detector, wherein the detector detects electromagnetic radiation in the infrared spectral range , the second detector detects electromagnetic radiation in the red spectral range and the third detector detects electromagnetic radiation in the green spectral range .

[0052] It is also possible that the sensor module comprises , one detector, two detectors , three detectors or a plurality of detectors . For example , at least two of the detectors detect electromagnetic radiation in the same or in di f ferent wavelength ranges . For example , all detectors detect electromagnetic radiation in the same or in di f ferent wavelength ranges . For example , each detector detects electromagnetic radiation in a wavelength range that corresponds to the wavelength of the electromagnetic radiation emitted by an associated emitter, respectively .

[0053] According to a further aspect of the sensor module , the detector comprises a bandpass filter for filtering the incident electromagnetic radiation . For example , the emitter is a VCSEL and the bandpass filter of the associated detector is matched to a spectral linewidth of the emitter . For example , the bandpass filter is a Bragg filter, i . e . a filter comprising a stack of dielectric layers with alternating refractive indices . In particular, the bandpass filter is arranged on the light transmitting surface of the detector .

[0054] According to a further aspect of the sensor module , the bandpass filter is configured for tuning the main detection direction of the detector . For example , the main detection direction and / or the directional characteristics of the detector can be adj usted using the bandpass filter . For example , the bandpass filter has an angular characteristic or directional characteristic, wherein a central transmission wavelength of the bandpass filter changes with an angle of incidence of the incident electromagnetic radiation . For example , the bandpass filter of the detector can be adj usted such that the electromagnetic radiation emitted by the associated emitter can only be detected by the detector i f it is incident on the light transmitting surface of the detector under a preferred detection angle and / or a preferred angle of incidence .

[0055] Further advantageous embodiments and further embodiments of the sensor module may become apparent from the following exemplary embodiments described in connection with the figures . Figure 1A shows a schematic cross section of a sensor module according to an exemplary embodiment .

[0056] Figure IB shows a schematic cross section of an arrangement of a sensor module according to an exemplary embodiment on a person' s body part .

[0057] Figures 2 , 3 and 4 show examples of detector signals of a sensor module according to an exemplary embodiment .

[0058] Figures 5A, 5B, 6A and 6B show a normali zed perfusion index PI / PIo as function of an emitter angle or a detector angle of a sensor module according to an exemplary embodiment .

[0059] Figure 7 shows a schematic illustration of light propagation from an emitter to a detector of a sensor module according to an exemplary embodiment .

[0060] Figures 8 to 14 show schematic cross sections of sensor modules according to further exemplary embodiments .

[0061] Elements that are identical , similar or have the same ef fect , are denoted by the same reference signs in the figures . The figures and the proportions of the elements shown in the figures are not to be regarded as true to scale . Rather, individual elements may be shown exaggeratedly large for better representability and / or better understanding .

[0062] The sensor module 1 according to the exemplary embodiment in Figure 1A comprises an emitter 2 and a detector 4 arranged on a flat main surface 51 of a carrier 5 . The emitter 2 comprises a light emitting diode ( short : LED) or a VCSEL, whereas the detector 4 comprises a photodiode or a phototransistor . The emitter 2 and the detector 4 are arranged laterally adj acent to each other at an edge-to-edge distance d of at most 3 millimeters .

[0063] The carrier 5 is a printed circuit board with electrical contact pads for electrically contacting the emitter 2 and the detector 4 . For example , the emitter 2 is a packaged LED or a packaged VCSEL, while the detector is a packaged photodiode or a packaged phototransistor . For example , the package comprises or consists of a base plate , a semiconductor chip mounted on the base plate , a frame mounted on the base plate such that it completely surrounds the semiconductor chip in all directions parallel to the base plate , and an encapsulation disposed on and around the semiconductor chip, respectively . The semiconductor chip is the LED chip, the VCSEL chip, the photodiode chip, or the phototransistor chip, respectively .

[0064] It is also possible that the emitter 2 consists of the LED chip or the VCSEL chip, whereas the detector 4 consists of the photodiode chip or the phototransistor chip . In other words , the semiconductor chips of the emitter 2 and / or the detector 4 can be directly mounted on the carrier 5 of the sensor module 1 without using a separately packaged emitter 2 and / or detector 4 .

[0065] The emitter 2 emits electromagnetic radiation 3 in an infrared, red or green spectral range . The emitter 2 has a directional characteristics 26 with a main emission direction 21 . In particular, a power per unit solid angle of the emitted electromagnetic radiation 3 is maximal along the main emission direction 21 . For example , the light emitting diode has a Lambertian directional characteristics , whereas the VCSEL has a directional characteristics that deviates from the Lambertian directional characteristics in that it has a strong elliptical distortion with a maj or axis along the main emission direction, for example .

[0066] The detector 4 has a directional characteristics 46 with a main detection direction 41 . In particular, a sensitivity per unit solid angle of the detector 4 for the incident electromagnetic radiation 3 is maximal along the main detection direction 41 . Per convention, the main detection direction 41 is directed away from the detector 4 instead of towards the detector 4 , i . e . opposite to the propagation direction of the incident electromagnetic radiation 3 .

[0067] The main emission direction 21 of the emitter 2 forms an emission angle 0Ewith the surface normal 52 of the main surface 51 of the carrier 5 , such that it is inclined away from the detector 4 and / or form the main detection direction 41 . Preferably, the emission angle 0Eis between and including 30 ° and 60 ° . In order to adj ust the emission angle 0E, the emitter 2 can be mounted with a tilt with respect to the main surface 51 of the carrier 5 , for example .

[0068] The main detection direction 41 of the detector 4 forms a detection angle 0Dwith the surface normal 52 of the main surface 51 of the carrier 5 , such that it is inclined away from the emitter 2 and / or form the main emission direction 21 . Preferably, the detection angle 0Dis between and including 30 ° and 60 ° . In order to adj ust the detection angle 0D, the detector 4 can be mounted with a tilt with respect to the main surface 51 of the carrier 5 , for example . The main emission direction 21 and the main detection direction 41 lie in a plane that is perpendicular to the main surface 51 of the carrier 5 . In particular, using a spherical coordinate system with the zenith direction or z-axis parallel to the surface normal 52 of the main surface 51 , with the emitter 2 centered at the origin, the detector 4 arranged on the x-axis and the azimuthal angle measured from the x-axis , the main emission direction 21 has an azimuthal angle of 180 ° and the main detection direction 41 has an azimuthal angle of 0 ° .

[0069] It is also possible that the emission angle 0Eis non- zero and the detection angle 0Dis zero , or vice versa, as long as an angle between the main emission direction 21 and the main detection direction 41 is non zero , and the main emission direction 21 and the main detection direction 41 do not cross each other in a hal f space 53 above the main surface 51 of the carrier 5 . In particular, the angle between the main emission direction 21 and the main detection direction 41 equals 0E+ 0Eand is larger than zero and smaller than 180 ° , or between 40 ° and 140 ° , inclusive , or between 60 ° and 120 ° , inclusive , or between 80 ° and 100 ° , inclusive , or is 90 ° .

[0070] It is also possible that the main surface 51 of the carrier 5 has a convex shape , such that the main emission direction 21 and the main detection direction 41 are inclined away from each other when the emitter 2 and the detector 4 are mounted on the main surface 51 . In this case , the angle between the main emission direction 21 and the main detection direction 41 can be adj usted by changing the distance d between the emitter 2 and the detector 4 , or by changing a curvature of the main surface 51 of the carrier 5 , for example . Figure IB shows a schematic arrangement , where a sensor module 1 according to the exemplary embodiment described in connection with Figure 1A is arranged on a finger 7 of a person . In particular, the sensor module 1 is configured as a photoplethysmography sensor for measuring the person' s heart rate , blood oxygen saturation, blood pressure , and / or arterial sti f fness during operation . Furthermore , the sensor module 1 comprises an electrical control circuit 8 for controlling the emitter 2 and the detector 4 . For example , the electrical control circuit 8 is an analog front end and / or an AS IC . Here , the electrical control circuit 8 is arranged externally from the carrier 5 . It is also possible that the electrical control circuit 8 is arranged on the carrier 5 or integrated into the carrier 5 .

[0071] Figure 2 shows an example of a detector signal 47 as function of time t . The detector signal 47 is an electrical voltage generated by the detector 4 in response to incident electromagnetic radiation 3 emitted by the emitter 2 of the sensor module 1 as described in connection with the exemplary embodiment in Figure 1A. In particular, the emitter 2 emits electromagnetic radiation 3 in the green spectral range at a constant intensity . The detector signal 47 is displayed in units of a number of counts C of an analog-digital converter that takes the detector voltage as an input .

[0072] Here , the sensor module 1 is a photoplethysmography sensor that is attached to the skin of a person . The detector signal 47 exhibits an amplitude modulation due to the person' s heart beat . A characteristic figure of merit of the sensor module 1 is the perfusion index PI that corresponds to a ratio between an AC part of the detector signal 47 and a DC part of the detector signal 47 . In other words , the perfusion index PI corresponds to a di f ference of a maximum value max and a minimum value min of the detector signal 47 , divided by an average value of the detector signal . In particular, the perfusion index PI is speci fied in percent . The perfusion index PI of the detector signal 47 shown in Figure 2 is approximately 1 , 9% .

[0073] In particular, the perfusion index PI contains the primary information about the heart beat and therefore is of particular importance for photoplethysmography sensors . The sensor module 1 described in connection with Figure 1A advantageously allows to increase the measured perfusion index PI compared to a sensor module 1 where the main emission direction 21 and the main detection direction 41 are parallel . Accordingly, the performance of the sensor module 1 can be increased, the power consumption of the sensor module 1 can be reduced, and / or the sensor module 1 can have a particularly small si ze .

[0074] Figure 3 shows an example of a detector signal 47 analogous to Figure 2 , but the emitter 2 of the sensor module 1 emits electromagnetic radiation in the red spectral range . In this case the perfusion index PI is approximately 0 , 3% .

[0075] Figure 4 shows an example of a detector signal 47 analogous to Figures 2 and 3 , but the emitter 2 of the sensor module 1 emits electromagnetic radiation in the infrared spectral range . In this case , the perfusion index PI is approximately 0 , 5% .

[0076] Figures 5A and 5B show a normali zed perfusion index PI / PI0of a sensor module 1 according to the exemplary embodiment described in connection with Figure 1A. Speci fically, the normalized perfusion index PI / PI0is shown as a function of the detection angle 0Dat a fixed emission angle 0Eof -10° and at a fixed distance d of 3 millimeter between the emitter 2 and the detector 4. The perfusion index PI is plotted relative to a nominal reference value Pio of the perfusion index PI that is measured at an emission angle 0Eof -10° and a detection angle 0Dof -10°. Here and in the following, negative emission angles 0Ecorrespond to main emission directions 21 that are inclined towards the detector 4 and / or towards the main detection direction 41. Analogously, here and in the following negative detection angles 0Dcorrespond to main detection directions 41 that are inclined towards the emitter 2 and / or towards the main emission direction 21. In Figures 5A and 5B, the emitter 2 is a VCSEL and three data sets DS1, DS2 and DS3 of the normalized perfusion index PI / PIo are shown corresponding to three different emitters 2 emitting electromagnetic radiation 3 at wavelengths of 520 nanometer (DS1) , 637 nanometer (DS2) and 940 nanometer (DS3) , respectively .

[0077] The data in Figure 5A shows that the perfusion index PI is increased for positive detection angles 0D, i.e. if the main emission direction 21 and the main detection direction 41 are inclined away from each other. By contrast, as shown in Figure 5B, the perfusion index PI decreases for negative detection angles 0D, i.e. if the main detection direction 41 is inclined towards the emitter 2. In particular, the enhancement of the perfusion index PI for detection angles 0Dbetween 35° and 55°, inclusive, is about 20% for electromagnetic radiation 3 in the red (DS2) and infrared (DS3) spectral ranges. For electromagnetic radiation 3 in the green spectral range (DS1) , the perfusion index PI is enhanced as well, albeit the enhancement is not as large as for electromagnetic radiation 3 in the red and infrared spectral range.

[0078] Figures 6A and 6B show the normalized perfusion index PI / PI0of a sensor module 1 according to the exemplary embodiment described in connection with Figure 1A. Here, the distance d between the emitter 2 and the detector 4 is 2 millimeters. The data for the perfusion index PI is plotted relative to a nominal reference value Pio- The nominal reference value Pio of the perfusion index PI is taken at an emission angle 0Eof -10° and a detection angle 0Dof -10°.

[0079] Figure 6A shows data of the normalized perfusion index PI / PI0for five different emission angles 0Ebetween 25° and 65°, inclusive, at a fixed detection angle 0Dof -10°, whereas Figure 6B shows data of the normalized perfusion index PI / PI0for five different detection angles 0Dbetween 25° and 65°, inclusive, at a fixed emission angle 0Eof -10°. For each emission angle 0E(Figure 6A) or detection angle 0D(Figure 6B) , respectively, data is shown for three different wavelengths of the electromagnetic radiation 3, namely 530 nanometer, 637 nanometer and 940 nanometer.

[0080] In all cases, the perfusion index PI increases by at least 15%, if the main emission direction 21 and the main detection direction 41 are inclined away from each other, i.e. if 0E+ 0D> 0, in particular if 55° > 0E+ 0D> 15°. Specifically, if the detection angle 0Dis between 35° and 65°, inclusive, the perfusion index PI for electromagnetic radiation 3 at a wavelength of 940 nanometer increases by at least 50% relative to the nominal reference value Pio of the perfusion index PI. Moreover, the increase of the perfusion index PI is asymmetric with respect to changing the emission angle 0E ( Figure 6A) , or the detection angle 0D( Figure 6B ) . In particular, this is due to the di f ferent directional characteristics of the emitter 2 and the detector 4 .

[0081] Figure 7 shows a schematic cross section of a sensor module 1 according to an exemplary embodiment arranged on a person' s skin 7 and schematically illustrates the propagation of electromagnetic radiation 3 from the emitter 2 to the detector 4 inside the skin . In particular, the electromagnetic radiation 3 is repeatedly scattered and / or reflected by plasma and / or red blood cells 71 , for example , such that it is at least partially redirected from the emitter 2 to the detector 4 .

[0082] The sensor module 1 according to the exemplary embodiment in Figure 8 comprises an emitter 2 and a detector 4 arranged on a main surface 51 of a carrier 5 . The carrier 5 is a printed circuit board, while the emitter 2 is a packaged LED or a packaged VCSEL comprising a light source 24 , such as a LED chip or a VCSEL chip, with a light emission surface 23 that is parallel to the main surface 51 of the carrier 5 . The emitter 2 further comprises a first optical element 22 that is configured to adj ust the main emission direction 21 and the directional characteristics 26 (not shown here , c . f . Fig . 1 ) of the emitter 2 . The first optical element 22 is a convex lens that is arranged of f-centered from the light source 24 . In particular, a center of the first optical element 22 and a center of the light emission surface 23 are laterally displaced by an of fset aO . For example , the of fset aO is at most hal f of a diameter of the convex lens 22 and / or hal f of a diameter of the light emission surface 23 . For example , the main emission direction 21 can be adj usted by changing the of fset aO . The detector 4 is a packaged photodiode or a packaged phototransistor comprising a photosensitive element 44 , such as the photodiode chip or the phototransistor chip, with a light transmitting surface 43 that is parallel to the main surface 51 of the carrier 5 . The detector 4 further comprises a second optical element 42 that is configured to adj ust the main detection direction 41 and the directional characteristics 46 (not shown here , c . f . Fig . 1 ) of the detector 4 . The second optical element 42 is a convex lens that is arranged of f-centered from the photosensitive element 44 . In particular, a center of the second optical element 42 and a center of the light transmitting surface 43 are laterally displaced by an of fset aO . The of fset aO of the detector 4 can be the same or di f ferent from the of fset aO of the emitter 2 . For example , the of fset aO is at most hal f of a diameter of the convex lens 42 and / or hal f of a diameter of the light transmitting surface 43 . For example , the main detection direction 41 can be adj usted by changing the of fset aO .

[0083] Compared to the sensor module described in connection with Figure 8 , the sensor module 1 according to the exemplary embodiment in Figure 9 further comprises a barrier 6 that is arranged on the carrier 5 between the emitter 2 and the detector 4 . The barrier 6 comprises an absorptive material for the electromagnetic radiation 3 emitted by the emitter 2 and reduces optical crosstalk between the emitter 2 and the detector 4 , thereby increasing a signal-to-noise ratio of the sensor module 1 .

[0084] The sensor module 1 according to the exemplary embodiment in Figure 10 comprises an emitter 2 and a detector 4 arranged on a main surface 51 of a carrier 5 . Compared to the exemplary embodiment described in connection with Figures 8 and 9 , the carrier 5 is a semiconductor substrate , and the emitter 2 and the detector 4 are not packaged . Rather the LED chip or VCSEL chip 24 of the emitter 2 and the photodiode chip or phototransistor chip of the detector 4 are directly arranged on the main surface 51 of the carrier 5 .

[0085] Compared to the sensor module 1 described in connection with Figure 10 , the sensor module 1 according to the exemplary embodiment in Figure 11 comprises Fresnel lenses as first and second optical elements 22 , 42 .

[0086] Compared to the sensor module described in connection with Figure 1A, the sensor module 1 according to the exemplary embodiment in Figure 12 comprises an emitter 2 and a detector 4 that are arranged on the main surface 51 of the carrier 5 in a tilted manner . In particular, the light emission surface 23 of the emitter 2 and the light transmitting surface 43 of the detector 4 are not parallel to the main surface 51 of the carrier 5 . The emitter 2 is a LED with a Lambertian directional characteristics 26 and the main emission direction 21 is perpendicular to the light emission surface 23 . The detector 4 also has a Lambertian directional characteristics 46 and the main detection direction 41 is perpendicular to the light emission surface 23 . The emitter 2 and the detector 4 are arranged in a tilted manner such that an angle is formed between the main emission direction 21 and the main detection direction 41 . Furthermore , a barrier 6 for reducing optical crosstalk is arranged between the emitter 2 and the detector 4 . Compared to the sensor module described in connection with Figure 12 , the sensor module 1 according to the exemplary embodiment in Figure 13 comprises a VCSEL instead of an LED as emitter 2 . The VCSEL emits electromagnetic laser radiation 3 and has a directional characteristics 26 that deviates from a Lambertian characteristics of an LED . In particular, the directional characteristics 26 is elliptically distorted with a maj or axis along the main emission direction 21 .

[0087] Compared to the sensor module described in connection with Figure 8 , the sensor module 1 according to the exemplary embodiment in Figure 14 comprises an emitter 2 with a first reflective element 25 instead of a first optical element 22 , and a detector 4 with a second reflective element 45 instead of a second optical element 42 . The first reflective element 25 is arranged on a side of the emitter 2 facing the detector 4 , while the second reflective element 45 is arranged on a side of the detector 4 facing the emitter 2 . The first and second reflective elements 25 , 45 comprise metallic layers that reflect the electromagnetic radiation 3 emitted by the light source 24 . Accordingly, the first reflective element 25 changes the main emission direction 21 of the emitter 2 away from the detector 4 , whereas the second reflective element 45 changes the main detection direction 41 of the detector 4 away from the emitter 2 . Moreover, the first and second reflective elements 25 , 45 reduce optical crosstalk between the emitter 2 and the detector 4 .

[0088] This patent application claims the priority of German patent application DE 102023124796 . 4 , the disclosure content of which is hereby incorporated by reference . The invention is not restricted to the exemplary embodiments by the description on the basis of said exemplary embodiments . Rather, the invention encompasses any new feature and also any combination of features , which in particular comprises any combination of features in the patent claims and any combination of features in the exemplary embodiments , even i f this feature or this combination itsel f is not explicitly speci fied in the patent claims or exemplary embodiments .

[0089] References

[0090] 1 sensor module

[0091] 2 emitter

[0092] 21 main emission direction

[0093] 22 first optical element

[0094] 23 light emission surface

[0095] 24 light source

[0096] 25 first reflective element

[0097] 26 directional characteristics of the emitter

[0098] 202 second emitter

[0099] 203 third emitter

[0100] 3 electromagnetic radiation

[0101] 4 detector

[0102] 41 main detection direction

[0103] 42 second optical element

[0104] 43 light transmitting surface

[0105] 44 photosensitive element

[0106] 45 second reflective element

[0107] 46 directional characteristics of the detector

[0108] 47 detector signal

[0109] 5 carrier

[0110] 51 main surface

[0111] 52 surface normal

[0112] 53 hal f space

[0113] 6 barrier

[0114] 7 skin

[0115] 71 red blood cell

[0116] 8 electrical control circuit

[0117] 0Eemission angle

[0118] 0Ddetection angle aO of fset

[0119] C counts d distance t time

[0120] PI perfusion index max maximum value of the detector signal min minimum value of the detector signal

[0121] DS 1 first dataset

[0122] DS2 second dataset

[0123] DS3 third dataset

Claims

Claims1. A sensor module (1) , comprising:- an emitter (2) that emits electromagnetic radiation (3) during operation, and- a detector (4) that detects electromagnetic radiation (3) emitted by the emitter (2) during operation, wherein- the emitter (2) and the detector (4) are arranged laterally adjacent to each other on a flat main surface (51) of a carrier ( 5 ) ,- a main emission direction (21) of the emitter (2) and a main detection direction (41) of the detector (4) are inclined away from each other, and- the main detection direction (41) of the detector (4) is inclined with respect to a surface normal (52) of the main surface (51) of the carrier (5) .

2. The sensor module (1) according to the previous claim, wherein the main emission direction (21) of the emitter (2) is inclined with respect to the surface normal (52) of the main surface (51) of the carrier (5) .

3. The sensor module (1) according to any of the previous claims, wherein an angle between the main emission direction (21) of the emitter (2) and a direction from the emitter (2) to the detector (4) is larger than 90° and smaller than 180°.

4. The sensor module (1) according to any of the previous claims, wherein an angle between the main detection direction (41) of the detector (4) and a direction from the detector(4) to the emitter (2) is larger than 90° and smaller than5. The sensor module (1) according to any of the previous claims, wherein a distance (d) between the emitter (2) and the detector (4) is at most 3 millimeter.

6. The sensor module (1) according to any of the previous claims, wherein- the emitter (2) comprises a light emitting diode chip or a vertical cavity surface emitting laser diode chip, and- the detector (4) comprises a photodiode chip or a phototransistor chip.

7. The sensor module (1) according to any of the previous claims, wherein the electromagnetic radiation (3) emitted by the emitter (2) is in the infrared spectral range.

8. The sensor module (1) according to any of the previous claims, wherein- the emitter (2) comprises a first optical element (22) for collimating the emitted electromagnetic radiation (3) , and- the first optical element (22) is arranged off-centered from a light emission surface (23) of a light source (24) of the emitter ( 2 ) .

9. The sensor module (1) according to any of the previous claims, wherein- the detector (4) comprises a second optical element (42) for focusing the electromagnetic radiation (3) onto a light transmitting surface (43) of a photosensitive element (44) of the detector (4) , and- the second optical element (42) is arranged off-centered from the light transmitting surface (43) of the photosensitive element (44) .

10. The sensor module (1) according to claims 8 or 9, wherein the first optical element (22) and / or the second optical element (42) comprises a refractive optical element or a diffractive optical element.

11. The sensor module (1) according to any of the previous claims, wherein- the emitter (2) comprises a first reflective (25) element for tuning a directional characteristics (26) of the emitter ( 2 ) , and- the first reflective element (25) is arranged on a side of the emitter (2) facing the detector (4) .

12. The sensor module (1) according to any of the previous claims, wherein- the detector (4) comprises a second reflective element (45) for tuning a directional characteristics (46) of the detector ( 4 ) , and- the second reflective element (45) is arranged on a side of the detector (4) facing the emitter (2) .

13. The sensor module (1) according to any of the previous claims, wherein a barrier (6) for reducing crosstalk between the emitter (2) and the detector (4) is arranged on a main surface (51) of the carrier (5) .

14. The sensor module (1) according to the previous claim, wherein the barrier (6) comprises a material that reflects the electromagnetic radiation (3) emitted by the emitter (2) .

15. The sensor module (1) according to any of the previous claims, wherein the sensor module (1) is configured as a photoplethysmography sensor.

16. The sensor module (1) according to any of the previous claims, further comprising a second emitter (202) and a third emitter (203) , wherein- the emitter (2) emits electromagnetic radiation (3) in an infrared spectral range during operation,- the second emitter (202) emits electromagnetic radiation(3) in a red spectral range during operation,- the third emitter (203) emits electromagnetic radiation in a green spectral range during operation, and- the detector (4) detects electromagnetic radiation (3) emitted by the emitter (2) , the second emitter (202) and the third emitter (203) during operation.

17. The sensor module (1) according to any of the previous claims, wherein- the detector (4) comprises a bandpass filter for filtering the incident electromagnetic radiation (3) , and- the bandpass filter is configured for tuning the main detection direction (41) of the detector (4) .

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