WO2023180205A1

WO2023180205A1 - Proximity sensing system, ear-mountable playback device and proximity sensing method

Info

Publication number: WO2023180205A1
Application number: PCT/EP2023/056924
Authority: WO
Inventors: Dalibor STOJKOVIC; Markus Arzberger
Original assignee: Ams-Osram Ag; Ams-Osram International Gmbh
Priority date: 2022-03-21
Filing date: 2023-03-17
Publication date: 2023-09-28

Abstract

A proximity sensing system (1) for a wearable or an ear-mountable playback device (100) comprises an optical proximity sensor (10) and a control unit (20). The proximity sensor (10) comprises an emitter structure (11) configured to emit light in a first wavelength range (r1) and in a second wavelength range (r2) from the near-infrared optical domain, and a detector structure (12) configured to detect light that is emitted by the emitter structure (11) and reflected by an object (3) arranged distant to the optical proximity sensor (10), and to generate a first and second photo signals based on light detected at the first and second wavelength ranges (r1, r2). The control unit (20) determines based on the first and second photo signals, whether the object (3) is within a threshold distance to the optical proximity sensor (10) and whether the object (3) is a user's body part.

Description

PROXIMITY SENSING SYSTEM, EAR-MOUNTABLE PLAYBACK DEVICE AND PROXIMITY SENSING METHOD

The present disclosure relates to a proximity sensing system for wearables and ear-mountable playback devices, an ear- mountable playback devices comprising such a system, and to a proximity sensing method.

BACKGROUND OF THE INVENTION

Accessory devices such as wearables, earphones and headphones are commonly used in connection with mobile electronic devices, such as media players, smartphones, tablets, laptop computers and the like. Such state-of-the-art devices are typically wireless, meaning that the accessory device is cordlessly coupled to a host device via wireless communication protocols such as Bluetooth. For convenience, modern wearables and earphone devices typically do not comprise any power switches but instead rely on means to detect whether the device is worn and an active operation, e.g. an output of sound via the earphone is desired. In other circumstances, e.g. during storage, an output and substantially all non-essential components, except for the above-mentioned detection mechanism, are preferably disabled in order to conserve battery power. However, present day solutions featuring ordinary proximity sensors are typically incapable of determining whether a wearable or an earphone device is actually placed on or within a user's body part, e.g. an ear, or whether a proximity to a different object is determined, e.g. a table top the earphone device is placed on or the inside of a pocket or bag. This causes significant power dissipation and unwanted output of audio signals even when the earphone device is not in use .

One approach is the employment of an optical proximity sensor operating in the short-wave infrared, SWIR, domain for determining the occurrence of water absorption in the reflected signal , hence indicating an organic obj ect , i . e . an ear of a user, in proximity to the earphone device . SWIR optical components , however, are fairly expensive in manufacturing due to special material requirements and complicated fabrication processes , and limit an evaluation of the recorded photo signals to the application of ear detection only .

An obj ect to be achieved is to provide a proximity sensing system for an ear-mountable playback device having an optical proximity sensor that is capable of skin detection, can be provided in a cost-ef ficient manner, and overcomes limitations of present day solutions . A further obj ect is to provide an ear-mountable playback device comprising such a proximity sensing system, and a proximity sensing method .

These obj ects are achieved with the subj ect-matter of the independent claims . Further developments and embodiments are described in dependent claims .

SUMMARY OF THE INVENTION

The improved concept is based on the idea of providing a proximity sensing system for an ear-mountable playback device that comprises an optical proximity sensor that relies on readily available optical components in the near-infrared, NIR, regime . Therein, said NIR optical components enable a reliable skin detection mechanism and in addition are characteri zed by being extremely energy ef ficient and cheap in production as processes , particularly compared to SWIR component processes , are well established and provide high yields . In particular, a proximity sensor according to the improved concept performs a reflection measurement for at least two di f ferent optical wavelengths and evaluates the at least two resulting photo signals for determining the type of obj ect that is in proximity to the ear-mountable playback device , e . g . whether it has a surface formed from an organic material and therefore most likely is an ear of a user or whether it is non-organic and therefore tantamount with the earphone device not being currently worn by the user .

Speci fically, a proximity sensing system for a wearable or an ear-mountable playback device according to the improved concept comprises an optical proximity sensor having an emitter structure configured to emit light in a first wavelength range and in a second wavelength range . The optical proximity sensor further comprises a detector structure that is configured to detect light that is emitted by the emitter structure and reflected by an obj ect arranged distant to the optical proximity sensor, and to generate a first photo signal based on light detected at the first wavelength range and a second photo signal based on light detected at the second wavelength range . Therein, the first wavelength range and the second wavelength range are di f ferent wavelength ranges but both situated within the near-infrared, NIR, domain .

The proximity sensing system further comprises a control unit that is electrically coupled to the optical proximity sensor and is configured to determine based on the first photo signal and the second photo signal , whether the obj ect is within a threshold distance to the optical proximity sensor and whether the obj ect is a user' s body part .

According to the improved concept , the proximity sensor comprises an optical emitter structure that is configured to emit light of two di f ferent wavelength ranges . For example , the emitter structure comprises a broadband emitter that emits light comprising the two wavelength ranges , or it comprises multiple light emitters , wherein each light emitter emits a distinct wavelength range of light with a certain emission bandwidth . Accordingly, the detector structure of the proximity sensor comprises a photodetector that is responsive to both the first and second wavelength ranges and generates respective photo signals . For example , the photodetector comprises separate spectral channels for distinguishing light of the first wavelength range from light of the second wavelength range . Alternatively, the photodetector is a broadband photodetector and generates the first photo signal while emission at the second wavelength of the emitter structure is disabled, i . e . the emitter structure only emits light in the first wavelength range , and vice versa .

The first and second photo signals are provided to a control unit . The control unit generates from the first and second photo signals a detection signal and determines from the detection signal in a first step whether an obj ect is in proximity to the proximity sensor, e . g . whether the obj ect is within a threshold distance to the proximity sensor, and in a second step whether the obj ect is a user' s body part , e . g . an ear . In other words , the proximity sensing system determines from the detection signal whether a wearable or an ear- mountable playback device the proximity sensing system is integrated into is currently worn by a user.

Compared to solutions that rely on a single wavelength measurement, distinguishing the received signal form different materials the light is reflected off of is often impossible as a one-point measurement typically does not carry enough information. In contrast, the improved concept realizes a two-point measurement, wherein the proximity sensor is operated at two different wavelengths. Due to different reflection behavior at different wavelength, the two-point measurement typically allows to easily distinguish between whether the wearable or ear-mountable playback device is in contact with the user' s body and whether it is in contact with inanimate objects such as cloth from a pocket or bag, a storage container or a table top, for instance. Thus, the respective device can reliably be power on, i.e. a sound output can be enabled in case of earphones, only if the device is actually in contact with the skin of the ear.

In an embodiment, the first wavelength range comprises an absorption wavelength of water, in particular a wavelength of 930 nm. A key difference of optical reflection behavior between a user's skin and surfaces of inanimate objects is a substantial water content in the composition and on a surface of the former. Thus, choosing the first wavelength range to be a narrowband wavelength range that includes an absorption band of water provides efficient means to determine whether the object located in proximity to the sensor, i.e. to the earphone device is actually the user's skin. Water shows strong absorption for light at a wavelength between 900 and 950 nm. Thus, the first wavelength range can be engineered to include a wavelength within this range. Specifically, the first wavelength range is centered around the absorption peak located at a wavelength of 940 nm and has a bandwidth (FWHM) of 10-50 nm .

In an embodiment, the second wavelength range comprises a wavelength in the range of 800-900 nm. In this range, organic surfaces, e.g. skin, typically experience less absorption compared to inanimate objects. Thus, particularly in combination with embodiments, in which the first wavelength range is chosen to correspond to an absorption range of water, the weaker absorption at 800-900 nm can provide strong evidence whether the detected surface is actually the user' s skin or a surface of an inanimate object such as a synthetic, wooden or plastic surface.

In an embodiment, for determining whether the object is the user's body part, the control unit is configured to calculate a difference of a signal derived from the first photo signal and a signal derived from the second photo signal, and compare the difference to a reflectance threshold. The signals derived from the first and second photo signals can be a normalized reflectance of the respective wavelength range. If the first wavelength range experiences a low degree of reflection for a human ear compared to other surfaces, while the second wavelength range experiences a comparable or higher degree of reflection, forming the difference from the two photo signals can provide sufficient distinction in determining whether the light is reflected from human skin or from an inanimate object. Thus, a predefined reflectance threshold can be used as a comparison value, such that if the difference signal is larger than the reflectance threshold, the light has been reflected of human skin with large confidence, while if the difference signal is lower than the reflectance threshold, the device is in close contact with an inanimate obj ect , i . e . it is not being worn .

In an embodiment , the control unit is configured to operate the emitter structure to selectively emit either light of the first wavelength range or light at the second wavelength range at a time . In embodiments , in which the detector structure comprises a single broadband photodetector, e . g . a silicon-based photodiode , which does not allow to distinguish whether a photo signal is generated based on the first or second wavelength range , the control unit can be configured to selectively activate and deactivate emission of the emitter structure regarding the two wavelength ranges . For example , the control unit activates an emission of the emitter structure at the first wavelength range , while an emission of the second wavelength range is deactivated, such that the reflected light detected by the detector structure is exclusively light of the first wavelength range , based on which the first photo signal is generated and provided to the control unit .

Subsequently, the control unit activates an emission of the emitter structure at the second wavelength range , while an emission of the first wavelength range is deactivated, such that the reflected light detected by the detector structure is exclusively light of the second wavelength range , based on which the second photo signal is generated and provided to the control unit . Alternatively, the detector unit has separate spectral channels and can distinguish between di f ferent wavelengths , such that the first and second photo signal can be generated concurrently . In this case , the emitter structure can emit broadband light , e . g . it is a broad-band LED covering wavelength range 800- 1050 nm . In an embodiment , the emitter structure comprises a first light emitter configured to emit the light at the first wavelength range , and a second light emitter configured to emit the light at the second wavelength range . Having separate light emitters allows for engineering the first and second emission bands suitably narrow such that indeed only reflections within a wavelength of interest , e . g . an absorption range of water, are recorded by the detector structure . For example , the first light emitter emits light at or around 930 nm, while the second light emitter emits light at or around 800 nm . Therein, the first and second wavelength ranges do not overlap each other .

In a further embodiment , the first light emitter and the second light emitter are NIR light-emitting diodes , LEDs . LEDs provide cost-ef fective and energy ef ficient means to provide light emitters of a certain center wavelength and bandwidth . For example , NIR LEDs with emission wavelengths comprising one of 800 , 930 and 1000 nm and spectral hal fwidths of 20- 60 nm are readily available .

In an alternative embodiment , the first light emitter and the second light emitter are vertical cavity surface-emitting lasers , VCSELs . I f speci fic narrowband emission in the first and second wavelengths ranges around a speci fic center wavelength is desired, VCSELs provide ef ficient and cost- ef fective means . For example , VCSEL can be designed to output an emission wavelength of 800 , 930 and 1000 nm with an emission bandwidth of as low as 10 GHz . Alternatively, the emitter structure can comprise an LED emitter for emitting light at the first wavelength range and a VCSEL for emitting light at the second wavelength range , or vice versa . In an embodiment , the detector structure comprises a photodiode , in particular a silicon-based photodiode . Silicon-based photodiodes are the most common type of photodiodes and experience sensitivities in the visible and NIR range . Thus , a silicon photodiode is not only suitable for detecting the NIR light emitted by the emitter structure but also enables further applications such as the sensing of vital signs typically performed with red or green light without the need for dedicated photo sensing structures .

In an embodiment , the emitter structure is further configured to emit light in a third wavelength range di f ferent from the first wavelength range and the second wavelength range , wherein the third wavelength range comprises a wavelength in the range of 950- 1050 nm, in particular in the range of 975- 1025 nm . Moreover, the detector structure is further configured to generate a third photo signal based on light detected at the third wavelength range , and the control unit is further configured to determine based on the first photo signal , the second photo signal and the third photo signal whether the obj ect is within the threshold distance and whether the obj ect is the user' s body part .

In order to further enhance the distinction between light that is reflected of f of a user' s skin and light that is reflected of the surface of an inanimate obj ect , a three point measurement can be performed . For example , the first wavelength range comprises 930 nm, the second wavelength range comprises 800 nm and the third wavelength range comprises 1000 nm with given respective bandwidths and without overlapping each other . As mentioned above , water absorbs light around 930 nm, while light at around 800 nm is reflected with a higher relative intensity compared to reflections from surfaces of inanimate objects. In addition, a reflection at lOOOnm is comparable for both types of surfaces. This enables a higher confidence in determining the nature of the object the light is reflected off of. For even larger confidence, additional wavelength ranges, e.g. a fourth and fifth wavelength range, can be introduced in an analogous manner.

In a further embodiment, for determining whether the object is the user's body part, the control unit is configured to calculate a sum of a difference of a signal derived from the first photo signal and a signal derived from the second photo signal and a difference of a signal derived from the third photo signal and the signal derived from the first photo signal, and compare the sum to a reflectance threshold. Thus, forming a first difference signal from the first and second photo signals as described above, forming a second difference from the first and third photo signals, and forming a sum signal from the first difference signal and the second difference signal leads to an increased distinction between an object with large water content, e.g. skin, and inanimate objects having low water contents.

In an embodiment, the optical proximity sensor comprises an optical stack that is arranged on a surface of the emitter structure and defines an angular range of emission of the emitter structure. In order to prevent light from directly reaching a detection surface of the detector structure, an aperture can be formed above the emitting surface of the emitter structure such that a light cone is defined that does not include the detector structure. Furthermore, the detection range of the proximity sensor can be limited by limiting the angle of the light cone leaving the proximity sensing system .

In an embodiment , the optical proximity sensor comprises an optical stack that is arranged on a surface of the detector structure and configured to define an angular range of detection, i . e . a f ield-of-view, of the detector structure . In addition or alternative to arranging an aperture structure above the emitter structure , an optical stack above a sensitive surface of the detector structure can likewise or additionally provide optical isolation between light emitter and detector structure . In addition, limiting the f ield-of- view of the detector structure can suppress stray environmental light that is not reflected from an obj ect from entering the sensor and falsi fying the generated photo signals .

In an embodiment , the control unit is further configured to determine a vital sign from the first photo signal and/or the second photo signal , the vital sign being at least one of : a heart rate , a heart rate variability, and a blood pressure . As mentioned above , an advantage of performing the proximity measurement in the NIR domain is the fact that likewise vital signs can be recorded in this regime . Thus , no additional emitters or detectors are required . Instead, the photo signals generated by the detector structure in response to light that is reflected of f a user' s ear can contain information about vital signs such as a heart rate .

In an embodiment , the emitter structure is further configured to emit light in a further wavelength range in the visible domain, in particular including a wavelength of 660 nm . Moreover, the detector structure is further configured to generate a further photo signal based on light detected at the further wavelength range , and the control unit is further configured to determine a blood oxygen content from the further photo signal . With the detector structure preferably comprising a silicon-based photodiode that is likewise sensitive in the NIR and VIS range , and enabling the emitter structure to also emit red light around 660 nm, for example , additional functionality in terms of vital sign monitoring is enabled as a blood oxygen level can be easily determined at this wavelength combined with 940 nm . The blood oxygen level is a relevant parameter indicating the fitness of a user . As earphone devices are commonly worn during workout sessions , monitoring vital signs such as heart beat and oxygen level provides ef ficient means for the user to analyze his or her workout performance . Furthermore , the detection of vital signs can further help in distinguishing whether the captured light is reflected of a user' s body part or from an inanimate but organic obj ect such as fruits , for instance . The vital signals can further be used to identi fy a user and to unlock a device in case of correct identi fication, for instance .

In an embodiment , the control unit is further configured to measure a distance to the obj ect via a proximity measurement of the proximity sensor using light at the first or second wavelength range . Moreover, the control unit is further configured to determine whether the obj ect is in contact with the housing and whether the obj ect the user' s body part only i f the measured distance is less than or equal to the threshold distance . For further enhancing an energy ef ficient operation of the respective wearable or ear-mountable playback device particularly in situations , in which it is not worn, the control unit can be configured to merely monitor a proximity to an obj ect arranged in front of the proximity sensor and only enable the obj ect identi fication via a two- or three-wavelength range measurement described throughout this disclosure i f an obj ect is within a certain distance , e . g . only i f an obj ect is in contact with a housing of the device .

The aforementioned obj ect is further solved by an ear- mountable playback device that comprises a housing configured to be placed in contact with a user ' s ear, a speaker arranged within the housing, and a proximity sensing system according to one of the embodiments described above .

The proximity sensing system is for example arranged in a housing of an ear-mountable playback device , e . g . an in-ear earbud or over-ear headphones . In particular, the ear- mountable playback device is a wireless device , meaning that it is cordlessly coupled to a host device and that it comprise a battery as power supply . The host device is a smartphone , media player, tablet computer, laptop or the like . The wireless connection can be established via common wireless communication interfaces , such as a Bluetooth interface , for instance .

The earphone device comprises a housing, e . g . formed by a main body, which houses a speaker that transduces electrical audio signals into sound, e . g . by means of a moving diaphragm as a sound driver . The speaker can be arranged in a cavity of the housing, wherein the cavity comprises a sound port facing an ear canal of the user when the earphone device is worn . The earphone device further comprises an optical proximity sensor arranged within the housing and that is coupled to an environment of the earphone device via a viewport or window that is transparent at the operating wavelengths of the proximity sensor or via the sound port. In particular, the proximity sensor is arranged such that light emitted by the sensor propagates to the outside of the earphone device. If an object, e.g. a user's ear, is in proximity to the earphone device and positioned on an optical path of the emitted light, at least a portion of the emitted light is reflected back towards the proximity sensor where it is detected. An amount of reflected light can give information about a distance of the object from the earphone device. For example, the aforementioned threshold distance is set such that it corresponds to the user' s ear being in contact with the housing, i.e. the viewport of the proximity sensor. The basic working principle of proximity sensors is a well-established concept and not further detailed throughout this disclosure.

In an embodiment of the ear-mountable playback device, the threshold distance is set such that the control unit is configured to determine whether the object is in contact with or at least close to the housing. The control unit is further configured to activate and deactivate and output of the speaker depending on whether the object is in contact with the housing and whether the object is an ear of the user. If the object is determined to be in contact with the housing and if the object is identified to be human skin, the control unit can enable further active circuitry of the earphone device for enabling a sound output of the speaker as well as further optional features such as an active-noise cancellation algorithm. In contrast, existing devices that do not distinguish between different types of objects may unwantedly activate or power up the earphone device if the proximity sensor comes in contact with a surface that is not the user's ear, e.g. a pocket or a table top. Further embodiments of the ear-mountable playback device become apparent to the skilled reader from the embodiments of the proximity sensing system described above , and vice-versa .

It is noted that the improved concept is likewise applicable to wearable devices such as fitness trackers , smartwatches and the like . The proximity sensor operating at two distinct wavelength ranges in the NIR regime can be incorporated into such devices and power up or activate functions of the corresponding device when it is worn . Furthermore , due to the ability to perform vital sign monitoring in the NIR regime , a single such proximity sensor can also be employed for vital sign detection as described above .

The aforementioned obj ect is further solved by a proximity sensing method . The method comprises emitting, by means of an emitter structure of a proximity sensor, light in a first wavelength range , detecting, by means of a detection structure of the proximity sensor, light of the first wavelength range that is reflected by an obj ect , and generating a first photo signal based on the detected light of the first wavelength range . The method further comprises emitting, by means of the emitter structure , light in a second wavelength range di f ferent from the first wavelength range , detecting, by means of the detection structure , light of the second wavelength range that is reflected by the obj ect , and generating a second photo signal based on the detected light of the second wavelength range .

The method further comprises determining based on the first photo signal and second photo signal whether the obj ect is within a threshold distance to the optical proximity sensor and whether the obj ect is a user' s body part . Therein, the first wavelength range and the second wavelength range are in the near-infrared, NIR, domain .

In an embodiment of the method of operating an earphone device , determining whether the obj ect is the user' s body part comprises the steps of calculating a di f ference of the first photo signal and the second photo signal , and comparing the di f ference to a predetermined reflectance threshold .

Further embodiments of the method become apparent to the skilled reader from the embodiments of the proximity sensing system described above , and vice-versa .

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of figures may further illustrate and explain aspects of the earphone device and the method of operating such an earphone device . Components and parts of the earphone device that are functionally identical or have an identical ef fect are denoted by identical reference symbols . Identical or ef fectively identical components and parts might be described only with respect to the figures where they occur first . Their description is not necessarily repeated in successive figures .

DETAILED DESCRIPTION

In the figures :

Figure 1 shows an exemplary embodiment of proximity sensing system according to the improved concept ; Figure 2 shows an exemplary embodiment of an ear-mountable playback device comprising a proximity sensing system;

Figure 3 shows an exemplary embodiment of a detector structure of a proximity sensing system;

Figures 4 and 5 show normali zed relative reflectance of di f ferent materials in the NIR domain;

Figures 6 and 7 show exemplary embodiments of the determining process of whether the obj ect is a user' s body part .

Figure 1 shows an exemplary embodiment of proximity sensing system 1 according to the improved concept . The proximity sensing system 1 comprises an optical proximity sensor 10 having an emitter structure 11 and a detector structure 12 . The proximity sensing system 1 further comprises a control unit 20 . For example , all these components are arranged on a common substrate 14 , which can be a semiconductor chip substrate , for instance . Alternatively, said components can be external components . For example , the control unit 20 is a separate entity that is not arranged on a common substrate 14 with the emitter structure 11 and the detector structure 12 or the proximity sensor 10 . The control unit 20 is electrically coupled to the optical proximity sensor 10 . In particular, the control unit 20 is coupled to the detector structure 12 for receiving photo signals from the latter . The control unit 20 can further be coupled to the emitter structure , e . g . for selectively activating and deactivating the emittance of light .

The emitter structure in this embodiment comprises light emitters I la, 11b, 11c that each are configured to emit light at a distinct wavelength range rl , r2 , r3 in the nearinfrared, NIR, domain for enabling proximity sensing . For example , the light emitters I la, 11b, 11c are LEDs , wherein a first light emitter I la emits narrowband light in a first wavelength range rl that comprises an absorption wavelength of water, e . g . a wavelength of 940 nm . Narrowband in this context for LEDs can mean a wavelength bandwidth of 10-50 nm, for instance . The second light emitter 11b emits narrowband light in a second wavelength range r2 that is distinct from the first wavelength range rl . For example , the second wavelength range r2 and the first wavelength range rl do not overlap . The second wavelength range r2 can comprise a center wavelength from the range between 800 and 830 nm, and likewise be characteri zed by a bandwidth of 10-50 nm . The third light emitter 11c emits narrowband light in a third wavelength range r3 that is distinct from the first and second wavelength ranges rl , r2 . For example , the third wavelength range r3 comprises a center wavelength from the range between 950 and 1050 nm, and likewise be characteri zed by a bandwidth of 10-50 nm .

Alternative to being LEDs , all or at least one of the light emitters I la, 11b, 11c can be formed by a vertical-cavity surface-emitting laser, VCSEL . Moreover, some embodiments of the proximity sensing system 1 may include merely a first and a second light emitter I la, 11b but no third light emitter 11c . Alternatively or in addition, some embodiments of the proximity sensing system 1 can comprise a further light emitter in the visible range , e . g . a further light emitter that emits red light in a further wavelength range rf , which is centered around 660 nm for vital sign monitoring applications , for instance . The light emitters I la, 11b, 11c are electrically coupled to the control unit 20 . For example , the control unit 20 ensures that at any given time during a proximity detection, an emission of merely one of the light emitters I la, 11b, 11c is active , such that the detector structure 12 receives only light emitted by the emitter structure 11 and reflected of f an obj ect 3 arranged distant and within view of the proximity sensor 10 in a single one of the wavelength ranges rl , r2 , r3 at a time . This is particularly relevant in embodiments , in which the detector structure 12 comprises a photosensitive element that cannot distinguish between light from di f ferent wavelength ranges without further analyzing components , such as an optical spectrum analyzing unit . For example , the detector structure comprises a photosensitive element 12a, which can be a silicon-based photodiode , Si-PD .

The control unit 20 is further electrically coupled to the detector structure 12 , e . g . to a photosensitive element 12a of the detector structure 12 . Thus , the control unit 20 can receive respective photo signals generated by the photosensitive element 12a in response to captured optical signals emitted from the emitter structure 11 and reflected of f the surface of an obj ect 3 . Speci fically, the control unit 20 is configured to receive a first photo signal that is generated in response to detected light of the first wavelength range rl , and a second photo signal that is generated in response to detected light of the second wavelength range r2 . In embodiments , in which the emitter structure emits light at a third wavelength range r3 and/or at a further wavelength range rf , the control unit 20 is further configured to receive the resultant third photo signal and further photo signal generated in response to detected light of the third wavelength range r3 and/or the further wavelength range rf, respectively.

The control unit 20, from the first and second photo signals and optionally also from the third photo signal determines whether an object 3 is present in the viewing angle of the proximity sensor 10, whether the object 3 is within a threshold distance from the proximity sensor 10, and whether the object 3 is a body part of a user. For determining the distance, a regular proximity measurement is performed using light of one of the wavelength ranges rl, r2, r3, for instance. For determining whether the object 3 is a body part of a user, the control unit 20 determines from the first photo signal a first relative reflectance of the object 3, e.g. via determining an optical intensity received by the detector structure 12 at the first wavelength range rl and comparing this received optical intensity to an emitted optical intensity of the first light emitter Ila. Moreover, the control unit 20 determines from the second photo signal a second relative reflectance of the object 3, e.g. via the same procedure. The control unit 20 then calculates a difference between the first relative reflectance and the second relative reflectance and compares the difference to a reflectance threshold, also referred to as a decision value. If the difference is larger than the reflectance threshold, the control unit 20 determines that the object 3 is a user's body part, while if the difference is less than or equal to the reflectance threshold, the object 3 is an inanimate object, for instance. The emitted optical intensities of the emitter structure 11 can be values that are stored in a memory of the control unit 20. In embodiments , in which the emitter structure 11 is configured to also emit light at the third wavelength range r3 , the control unit 20 for determining whether the obj ect 3 is a body part of a user can further calculate a second di f ference between the first relative reflectance and a third relative reflectance gained from the third photo signal and compares a sum of the di f ference and second di f ference to a reflectance threshold . The three-wavelength range measurement can lead to a clearer distinction between a user' s body part and an inanimate obj ect as further discussed with reference to Figs . 4 and 5 .

Figure 2 shows an exemplary embodiment of an ear-mountable playback device 100 comprising a proximity sensing system 1 according to the improved concept . In this embodiment , the ear-mountable playback device 100 is formed as a wireless earbud . The ear-mountable playback device 100 can alternatively be any other type of in-ear or over-ear device without af fecting a core idea of this disclosure . The ear- mountable playback device 100 comprises a housing 101 having an opening configured as a sound output port 101a . The sound output port 101a can be fully open or covered by a grating or mesh for protecting an inside of the earphone device 100 from particles such as dust . The housing further comprises a viewport 101b for allowing operation of the proximity sensor 10 of the proximity sensing system 1 . The viewport 101b can be a further opening or a portion of the housing that is transparent for optical radiation . Transparent in this context refers to an operating wavelength range of the proximity sensor 10 , e . g . part of or the entire nearinfrared, NIR, portion of the electromagnetic spectrum . In some embodiments the viewport 101b and the sound output port 101a can be the same outputs , e . g . i f the proximity sensor 10 is to determine a proximity to an ear canal of the user .

Within the housing 101 of the ear-mountable playback device 100 , a speaker 102 is arranged that is configured to convert electrical audio signals into sound that is output towards the sound output port 101a . To this end, the e ear-mountable playback device 100 further comprises a processing and communication unit 103 that is configured to communicate with a host device , e . g . an external smartphone , media player, tablet or laptop computer, via a wireless communications protocol such as Bluetooth, for example , from which the electrical audio signal is received . The electrical audio signal can be a music or phone call signal . The communication unit 103 can be further configured to transmit a microphone signal from an optional microphone of the ear-mountable playback device 100 to the host device . The processing and communication unit 103 of the ear-mountable playback device 100 can comprise further components such as means to perform active noise cancellation, for instance . The optional microphone is not shown in the figure for illustrative purposes . As a power supply, the ear-mountable playback device 100 further comprises an energy storage 104 , e . g . a battery, which is arranged in the housing 101 and coupled to all circuit components .

The ear-mountable playback device 100 further comprises the proximity sensing system 1 formed by the optical proximity sensor 10 and the control unit 20 , here illustrated as a separate component , both being arranged within a housing 101 of the ear-mountable playback device 100 in a manner such that an optical proximity measurement can be performed through the viewport 101b of the housing 101 to an obj ect 3 located outside the housing 101 , i . e . outside the ear- mountable playback device 100 .

The control unit 20 is electrically coupled to the energy storage 104 acting as a power supply for the proximity sensing system 1 . As the proximity sensing system 1 is the only component of the ear-mountable playback device 100 that is constantly powered, even when the ear-mountable playback device 100 is not worn, this separate dedicated coupling is intended to provide the required electrical power . Particularly in the NIR domain, where optical components are readily available , the proximity sensing system 1 can be designed in an extremely energy conservative manner, such that for convenience , any dedicated power switches can be omitted and the remaining circuitry of the proximity sensing system 1 is powered up once the aforementioned detection of a user' s body part being in contact with the housing 101 is success fully confirmed . To this end, the control unit 20 is coupled to the speaker 102 and to the processing and communication unit 103 for activation purposes . Furthermore , via the coupling between the control unit 20 and the processing and communication unit 103 signals can be trans ferred for further processing or trans fer to a host device , e . g . vital sign monitoring signals . The coupling between the control unit 20 and the proximity sensor 10 is detailed with reference to Fig . 1 .

Fig . 3 shows an exemplary embodiment of a detector structure 12 of a proximity sensing system . In this embodiment , the detector structure 12 comprises an embedded photosensitive element 12a, e . g . a buried silicon-based photodiode , which is configured to generate photo signals in response to optical radiation received by the photosensitive element 12a . On a top surface of the detector structure 12, an optical stack 13 is arranged, e.g. being formed from alternating layers of vias and metallic layers. The optical stack 13 serves the purpose of optically isolating the photosensitive element 12a from the emitter structure 11 typically arranged in close proximity to the detector structure 12 such that light cannot reach the photosensitive element 12a directly, i.e. without reflecting off of an object 3. Furthermore, the optical stack 13 defines an angular range of detection ad of the photosensitive element 12a for limiting stray environmental light from entering the detector structure and falsifying a proximity detection. Analogous to an arrangement of an optical stack 13 on the detector structure 12, such an optical stack 13 can additionally or alternatively be arranged on a surface of the emitter structure 11, e.g. for defining an angular range of emission ae of the emitted light .

Fig. 4 shows a first graph illustrating a normalized relative reflectance R of different materials for reflecting target objects 3 as a function of a wavelength L in the NIR domain. Normalized in this context means that the light received by the detector structure 12 is normalized against a light intensity emitted by the emitter structure 11. The graph shows the clear absorption dip due to water absorption around 930 nm for organic materials, in this case human skin (first curve Cl) and an apple (second curve C2) , as well as an increased reflectance at around 800 nm. Non-organic materials, on the other hand, do not experience any significant reduction of relative reflectance around 930 and instead show an overall constant reflectance behavior, as exemplified by paper (third curve C3) and plastic (fourth curve C4) . At a wavelength of 1000 nm, all materials experience a similar relative reflectance. Thus, engineering the proximity sensor 10 of the proximity sensing system 1 in a manner, in which the first wavelength range rl is a narrow range around 930 nm, and the second wavelength range r2 is a narrow range around 800 nm, with the term narrow indicating a bandwidth of a few nanometers, allows for a clear distinction of organic and non-organic materials the object 3 in the view of the proximity sensor 10 is formed from.

Fig. 5 shows a second graph further illustrating a normalized relative reflectance R of different materials S1..S19 for reflecting target objects 3 as a function of a wavelength L in the NIR domain. Also in this graph the clear dip in relative reflectance due to water absorption is observed for all organic materials, while non-organic materials and inanimate objects show a rather flat behavior across the NIR domain. The different materials S1..S19 for which the reflectance R is shown in Figure 5 are listed in the table below :

Fig. 6 shows an exemplary embodiment of the determining process of whether the object 3 is a user's body part. The control unit 20 can be configured to subtract the relative reflectance at 930 nm from that at 800 nm to effectively determine a slope of the reflectance spectrum and compare this value to a first decision value D. Specifically, the data points in the graph indicate the aforementioned difference formed from the relative reflectance at 930 nm subtracted from the relative reflectance at 800 nm of the materials shown in Fig. 5. In other words, the data points indicate a slope of the reflectance curve of the respective material versus wavelength. Fig. 6 constitutes data of a two- wavelength measurement at the first and second wavelength ranges rl, r2, e.g. embodiments, which merely feature a first and a second emitter Ila, 11b. The vertical line at 0.1 indicates an exemplary decision value D as the reflectance threshold. The decision value D is chosen such that difference values of organic objects, e.g. a skin is exclusively larger than the decision value D, while difference values of inanimate objects are smaller than this decision value D. Thus, the control unit 20 can easily distinguish whether a wearable or ear-mountable playback device is worn by a user or placed inside a pocket or on a table top, for instance. It is noted that the measurements taken for fruits serve an illustrative purpose only, a device actually placed in close proximity to an organic object other than a user is rather unlikely.

Fig. 7 shows a further exemplary embodiment of the determining process of whether the object 3 is a user's body part. For this embodiment, a three-wavelength proximity measurement is performed. In addition to forming a first difference signal from the first and second relative reflectances as described above, a second difference is calculated from the first relative reflectance and a third relative reflectance gained from the reflectance at a third wavelength range r3, e.g. at 1000 nm. The data points in the figure represent the sum of the first and second differences for the different materials of Fig. 5. Compared to Fig 6, the gap of the sum value between organic and non-organic materials is increased for the three-wavelength measurement such that an even clearer distinction can be made with respect to a decision value D of in this case 0.2.

For further enhancing the results of the proximity sensing, a white balancing process as well as an energy normalization process can be performed. Both these processes can be performed during a manufacturing process of the proximity sensing device 1 or an ear-mountable playback device 100. Alternatively, the white balancing and the energy normalization can be realized on-the-fly, e.g. by providing an additional calibration detector structure that receives a predetermined amount of light emitted by the emitter structure, e.g. via internal reflection.

The embodiments of the proximity sensing system 1, the ear- mountable playback device and the proximity sensing method disclosed herein have been discussed for the purpose of familiari zing the reader with novel aspects of the idea . Although preferred embodiments have been shown and described, changes , modi fications , equivalents and substitutions of the disclosed concepts may be made by one having skill in the art without unnecessarily departing from the scope of the claims .

It will be appreciated that the disclosure is not limited to the disclosed embodiments and to what has been particularly shown and described hereinabove . Rather, features recited in separate dependent claims or in the description may advantageously be combined . Furthermore , the scope of the disclosure includes those variations and modi fications , which will be apparent to those skilled in the art and fall within the scope of the appended claims .

The term " comprising" , insofar it was used in the claims or in the description, does not exclude other elements or steps of a corresponding feature or procedure . In case that the terms " a" or " an" were used in conj unction with features , they do not exclude a plurality of such features . Moreover, any reference signs in the claims should not be construed as limiting the scope .

This patent application claims priority of the German application DE DE 102022106514 . 6 , the disclosure content of which is incorporated herein by reference . References

I proximity sensing system

3 obj ect

10 proximity sensor

I I emitter structure

I la, 11b, 11c light emitter

12 detector structure

12a photosensitive element

13 optical stack

14 substrate

20 control unit

100 ear-mountable playback device

101 housing

101a sound output port

101b viewport

102 speaker

103 processing and communication unit

104 energy storage rl , r2 , r3 wavelength range ad angular range of detection ae angular range of emission

R normali zed reflectance

L wavelength

Cl first curve

C2 second curve

C3 third curve

C4 fourth curve

D decision value

S 1 . . S 19 first to nineteenth material

Claims

1. A proximity sensing system (1) for a wearable or an ear- mountable playback device (100) , the proximity sensing system

(1) comprising: an optical proximity sensor (10) ; and a control unit (20) electrically coupled to the proximity sensor (10) ; wherein the optical proximity sensor (10) comprises:

- an emitter structure (11) configured to emit light in a first wavelength range (rl) and in a second wavelength range (r2) different from the first wavelength range

( rl ) , and

- a detector structure (12) configured to detect light that is emitted by the emitter structure (11) and reflected by an object (3) arranged distant to the optical proximity sensor (10) , and to generate a first photo signal based on light detected at the first wavelength range (rl) and a second photo signal based on light detected at the second wavelength range (r2) ; wherein the control unit (20) is configured to determine based on the first photo signal and the second photo signal, whether the object (3) is within a threshold distance to the optical proximity sensor (10) and whether the object (3) is a user's body part; and wherein the first wavelength range (rl) and the second wavelength range (r2) are in the near-infrared, NIR, domain .

2. The proximity sensing system (1) according to claim 1, wherein the first wavelength range comprises an absorption wavelength of water, in particular a wavelength of 940 nm.

3. The proximity sensing system (1) according to claim 1 or 2, wherein the second wavelength range comprises a wavelength in the range of 800-900 nm.

4. The proximity sensing system (1) according to one of claims 1 to 3, wherein for determining whether the object (3) is the user's body part, the control unit (20) is configured to calculate a difference of a signal derived from the first photo signal and a signal derived from the second photo signal, and compare the difference to a reflectance threshold .

5. The proximity sensing system (1) according to one of claims 1 to 4, wherein the control unit (20) is configured to operate the emitter structure (11) to selectively emit either light in the first wavelength range (rl) or light in the second wavelength range (r2) at a time.

6. The proximity sensing system (1) according to one of claims 1 to 5, wherein the emitter structure (11) comprises a first light emitter (Ila) configured to emit the light at the first wavelength range (rl) , and a second light emitter (11b) configured to emit the light at the second wavelength range (r2) .

7. The proximity sensing system (1) according to claim 6, wherein the first light emitter (Ila) and the second light emitter (11b) are NIR light-emitting diodes, LEDs.

8. The proximity sensing system (1) according to claim 6, wherein the first light emitter (Ila) and the second light emitter (11b) are vertical cavity surface-emitting lasers, VCSELs .

9. The proximity sensing system (1) according to one of claims 1 to 8, wherein the detector structure (12) comprises a photodiode (12a) , in particular a silicon-based photodiode.

10. The proximity sensing system (1) according to one of claims 1 to 9, wherein the emitter structure (11) is further configured to emit light in a third wavelength range (r3) different from the first wavelength range (rl) and the second wavelength range ( r2 ) , and the detector structure (12) is further configured to generate a third photo signal based on light detected at the third wavelength range (r3) ; and the control unit (20) is further configured to determine based on the first photo signal, the second photo signal and the third photo signal whether the object (3) is within the threshold distance and whether the object (3) is the user's body part; wherein the third wavelength range (r3) comprises a wavelength in the range of 975-1025 nm.

11. The proximity sensing system (1) according to claim 10, wherein for determining whether the object (3) is the user's body part, the control unit (20) is configured to calculate a sum of: a difference of a signal derived from the first photo signal and a signal derived from the second photo signal; and a difference of a signal derived from the third photo signal and a signal derived from the first photo signal; and to compare the sum to a reflectance threshold.

12. The proximity sensing system (1) according to one of claims 1 to 11, wherein the optical proximity sensor (10) comprises an optical stack (13) that is arranged on a surface of the emitter structure (11) and defines an angular range of emission (ae) of the emitter structure (11) .

13. The proximity sensing system (1) according to one of claims 1 to 12, wherein the optical proximity sensor (10) comprises an optical stack (13) that is arranged on a surface of the detector structure (12) and configured to define an angular range of detection (ad) of the detector structure (12) .

14. The proximity sensing system (1) according to one of claims 1 to 13, wherein the control unit (20) is further configured to determine a vital sign from the first photo signal and/or the second photo signal, the vital sign being at least one of: a heart rate, a heart rate variability, and a blood pressure.

15. The proximity sensing system (1) according to one of claims 1 to 14, wherein the emitter structure (11) is further configured to emit light in a further wavelength range (rf) in the visible domain, in particular including a wavelength of 660 nm; the detector structure (12) is further configured to generate a further photo signal based on light detected at the further wavelength range (rf) ; and the control unit (20) is further configured to determine a blood oxygen content from the further photo signal.

16. The proximity sensing system (1) according to one of claims 1 to 15, wherein the control unit (20) is further configured to measure a distance to the object (3) via a proximity measurement of the proximity sensor (10) using light at the first wavelength range (rl) or second wavelength range ( r2 ) ; and determine whether the object (30) is the user's body part if the measured distance is less than or equal to the threshold distance.

17. An ear-mountable playback device (100) comprising: a housing (101) configured to be placed in contact with a user ' s ear; a speaker (102) arranged within the housing (101) ; a proximity sensing system (1) according to one of claims 1 to 16.

18. The ear-mountable playback device (100) according to claim 17, wherein the threshold distance is set such that the control unit (20) is configured to determine whether the object (3) is in contact with the housing (101) ; and wherein the control unit (20) is further configured to activate and deactivate and output of the speaker (102) depending on whether the object (3) is in contact with the housing (101) and whether the object (3) is an ear of the user .

19. A proximity sensing method, comprising: emitting, by means of an emitter structure (11) of a proximity sensor (10) , light in a first wavelength range (rl) ; detecting, by means of a detector structure (12) of the proximity sensor (10) , light of the first wavelength range (rl) that is reflected by an object (3) ; generating a first photo signal based on the detected light of the first wavelength range (rl) ; emitting, by means of the emitter structure (11) , light in a second wavelength range (r2) different from the first wavelength range (rl) ; detecting, by means of the detection structure (12) , light of the second wavelength range (r2) that is reflected by the ob j ect ( 3 ) ; generating a second photo signal based on the detected light of the second wavelength range (r2) ; and determining based on the first photo signal and second photo signal whether the object (3) is within a threshold distance to the optical proximity sensor (10) and whether the object (3) is a user's body part; wherein the first wavelength range (rl) and the second wavelength range (r2) are in the near-infrared, NIR, domain .

20. The method according to claim 19, wherein determining whether the object (30) is the user's body part comprises the steps of: calculating a difference of the first photo signal and the second photo signal; and comparing the difference to a reflectance threshold.