This patent application is a national phase filing under section 371 of PCT/EP2019/075318, filed Sep. 20, 2019, which claims the priority of German patent application 10 2018 123 559.3, filed Sep. 25, 2018, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a sensor device, in particular for measuring humidity.

BACKGROUND

Conventional sensor devices, such as those used in sports watches, are suitable for measuring various vital parameters, such as pulse, heart rate, or blood oxygen saturation and/or other measurements that allow monitoring of human bodily functions. Such sensor devices typically include at least one emitter and one detector. The emitter, for example, in the form of an LED, thereby irradiates the skin surface of a user with electromagnetic rays, which are partly absorbed by the skin and partly reflected by it. The reflected electromagnetic rays are then detected by the detector and finally evaluated.

SUMMARY

Embodiments provide a reliable sensor device which, among other things, is suitable for measuring humidity and can be manufactured at low cost.

A sensor device according to embodiments, in particular for measuring humidity, comprises a first optoelectronic emitter, in particular an LED, for irradiating a spot with electromagnetic rays, a second optoelectronic emitter, in particular an LED, for irradiating the spot with electromagnetic rays, and a detector for detecting electromagnetic rays of the first and second emitter reflected at the spot or alternatively transmitted through the spot, wherein the first emitter emits electromagnetic rays at a wavelength in the range of 1400-1500 nm, and wherein the second emitter emits electromagnetic rays at a wavelength in the range of 900-1100 nm.

By providing two optoelectronic emitters emitting electromagnetic rays in two different wavelength ranges, respectively between 1400-1500 nm and 900-1100 nm, and a detector capable of detecting the electromagnetic rays from the two emitters, a particularly reliable sensor device suitable for moisture measurements is formed.

The approach to realize such a sensor device is based on optical properties of water. The optoelectronic emitters of the present sensor device are designed in such a way that the first emitter can emit electromagnetic rays at a wavelength in the range of 1400-1500 nm, preferably at least approximately 1450 nm. In this range, water has a local absorption maximum. The local absorption maximum is caused by an absorption band of water at a wavelength of 1470 nm, at which water molecules perform a combined stretching and bending vibration.

Instead, the second optoelectronic emitter is designed to emit electromagnetic rays at a wavelength in the range of 900-1100 nm, preferably in the range of 940-1070 nm, more preferably in the range of 940-1050 nm. In these IR spectral ranges of the second emitter, water has only a minor influence on the absorption and reflection or transmission of the electromagnetic rays. This makes the two emitters particularly suitable for measuring moisture at a single spot.

The two optoelectronic emitters can each be designed as light-emitting diodes (LEDs). Thus, an energy-efficient irradiation of a spot with electromagnetic rays can be achieved. The spot to be irradiated can be located outside the sensor device, e.g. outside a housing of the sensor device, for example on the skin surface of a user using the sensor device, on a section of a material, such as leather, or in a free space.

The two emitters can be configured in such that they emit the electromagnetic rays in a time-shifted manner, so that the detector only detects rays from one emitter at a time. In this way, it can be achieved that the two emitters emit at least one pulse of electromagnetic radiation with a time offset to each other or alternately.

This ensures that the rays from the two emitters enter the detector separately and do not cause signal distortion.

Furthermore, the time-shifted emission of the two emitters relative to each other allows the use of a single detector that can detect IR radiation in the 1400-1500 nm range as well as in the 900-1100 nm range. Replacing two separate detectors with only one detector leads to a reduction in the manufacturing cost of the sensor device. In addition, the external dimensions of the sensor device can be reduced. The sensor device can thus be more compact.

In particular, the present detector can be used to detect at least one further electromagnetic signal which does not originate from the first or second emitter. Thus, several parameters can be detected by means of only one detector.

The first emitter can be formed as an LED, which has an indium gallium arsenide layer (InGaAs) on an indium phosphide layer (InP). In this case, the active layer consists of or comprises the InGaAS, while InP is used as the substrate. Thus, the emitter enables energy-efficient emission of electromagnetic rays with a wavelength from a predefined long-wave IR spectral range.

Preferably, by using an InGaAs-based LED as emitter, which is built on an InP substrate, an emission of IR rays at a wavelength in the range of 1400-1500 nm, in which water has a very high absorption and a low reflection or transmission, can be achieved. Therefore, such an InGaAs-based LED is particularly suitable as an emitter for irradiating a spot, e.g. on a skin surface, for the purpose of moisture measurement.

The second emitter can be formed as an LED having an indium gallium arsenide (InGaAs) layer on an aluminum gallium arsenide (AlGaAs) substrate or on a gallium arsenide (GaAs) substrate. In this case, the active layer consists of or comprises the InGaAs, while AlGaAs or GaAs is used as the substrate. Such an AlGaAs- or GaAs-based LED can be used to irradiate a spot, in particular on a wet skin surface, with shorter-wavelength IR rays, for example in the range of 900-1100 nm, which are hardly absorbed and reflected by water. This makes the AlGaAs- or GaAs-based LED particularly suitable as a reference LED for verifying the moisture value of the irradiated spot determined by means of the first emitter.

Such an AlGaAs- or GaAs-based LED used as a second emitter may further be characterized by very high optical performance and efficiency. Providing an LED with an active layer of InGaAs on an AlGaAs or GaAs substrate in a sensor device can thus increase the sensitivity of the device and additionally be associated with a significant cost saving.

Such an LED of the sensor device used as a second emitter can be used to emit at least one further electromagnetic signal which is not used to measure moisture. Thus, the LED used as a second emitter can be used as an optical source for measuring further parameters, such as a pulse or oxygen content measurement, in particular on or in the skin surface of a user. Thus, a further emitter, in particular in the form of a reference LED, can be dispensed with. Thus, in addition to a cost reduction, a multifunctionality of the sensor device can be achieved in a small space.

The detector of the sensor device can be designed as a photodiode. The photodiode can provide reliable and cost-effective detection of the IR rays emitted by the two emitters.

The photodiode can have an indium gallium arsenide (InGaAs) layer on an indium phosphide (InP) layer. An InGaAs-based photodiode on an InP substrate has a very high sensitivity in the infrared range and is thus particularly well suited as a detector for detecting radiation from the IR ranges of the first and second emitters.

In addition, an InGaAs-based LED has a small dark current and a fast response time. This makes it particularly suitable as a detector for the reliable determination of rapidly changing parameters, especially for moisture measurement, e.g. on the skin surface.

A sensor device according to embodiments may further comprise a housing having a first cavity open to a bottom side of the housing and a second cavity open to the bottom side, wherein the two cavities are separated from each other, wherein in the first cavity the two emitters are arranged adjacent to each other, and wherein in the second cavity the detector is arranged. Such a design of the housing with two separate cavities or chambers ensures that the two emitters are spatially separated from the detector. This can reduce or prevent unwanted “cross talk” between the electromagnetic rays emitted by the two emitters and the rays received by the detector.

The term “bottom side” is used here to refer to that surface side of the housing which, in the position of use of the sensor device, faces the spot to be measured, e.g. the skin of a user. Ultimately, the orientation of the sensor device in space is arbitrary, so that the term bottom side is ultimately also arbitrary. In the accompanying drawings, for example, the bottom side can also point upwards.

By forming openings on the bottom side of the housing, which are assigned to each cavity, it can be achieved that the electromagnetic rays of the two emitters can efficiently reach the outside, i.e. outside of the sensor device, in particular onto the spot to be measured, from the cavity in which they are arranged. Furthermore, such a design of the housing also allows the rays reflected from the outside, e.g. at the spot, or transmitted through the spot, to enter the cavity of the detector and be detected.

Each of the two cavities can further have a top side opposite the bottom side of the housing and a circumferential side separation extending between the bottom and the bottom side of the housing, preferably in the form of a wall or bar.

In particular, the two emitters can be arranged adjacent to each other in a cavity. In a further embodiment of the sensor devices disclosed herein, each of the two emitters can be arranged in a separate cavity. Each of the cavities can thereby have an opening arranged on the bottom side of the housing.

The bottom of the housing can have a cover that covers the cavities. The cover can be completely or at least partially transparent to the radiation emitted by the two emitters and the radiation received by the detector.

A sensor device according to embodiments can comprise an evaluation device which is designed to determine at least one measured value, in particular for a humidity at the spot, as a function of the detected electromagnetic rays of the two emitters. For this purpose, the portion of the electromagnetic rays of the two emitters reflected from or transmitted through the spot is detected by the detector as a separate signal in each case. A direct comparison of the two signals can be made by means of the evaluation device. A mathematical function can be implemented in the evaluation device, for example by means of software, by means of which a variable characterizing the moisture at the skin spot can be calculated as a function of the measured values determined.

In particular, the evaluation device can precisely evaluate a parameter, in particular determine a degree of moisture of a spot, by relating the signal originating from the first emitter to the signal of the second emitter. Via the reference signal obtained by means of the second emitter, a comparison of the proportion of reflected or transmitted rays is possible. Thus, the evaluation device can be used for the precise determination of at least one measured value, in particular the degree of moisture of the spot outside the sensor device, e.g. on a skin surface.

The evaluation device can be designed as a circuit. The circuit can be connected to the two emitters and/or the detector. The evaluation device can further be arranged in the same cavity as the detector or in a further cavity which is also closed with a cover, preferably detachably. The evaluation device can be arranged, for example, on the top side of the housing.

Further embodiments relate to a sensor device, in particular for measuring humidity, wherein the sensor device comprises:

a first optoelectronic emitter, in particular an LED, for irradiating a spot with electromagnetic rays,

a second optoelectronic emitter, in particular an LED, for irradiating the spot with electromagnetic rays,

wherein the first optoelectronic emitter is operable to detect at least a portion of electromagnetic rays from the second emitter that has been reflected at the spot or alternatively transmitted through the spot, and

wherein the second optoelectronic emitter is operable to detect at least a portion of electromagnetic rays from the first emitter that has been reflected at the spot or alternatively transmitted through the spot.

Preferably, the two emitters enable efficient irradiation of a spot with electromagnetic rays of a wavelength from at least one respective, predefined spectral range. In this context, the spot can be, for example, outside the sensor device, in particular on a skin surface or in a room.

Because each of the two emitters is configured to detect a portion of the electromagnetic rays from the other emitter, the two emitters are suitable for detecting the radiation reflected at or transmitted through the spot. The detection capability of the two emitters eliminates the need for additional detectors in the sensing device, resulting in space and cost savings.

The electromagnetic radiation of one emitter can be detected by the respective other emitter by means of a photocurrent measurement. The respective emitter serving as a detector can be operated in a detection mode. For example, an LED can be operated as a photodiode for the purpose of detection and the detected radiation can be detected by means of a photocurrent.

The two emitters can be operated time-shifted as emitter and detector respectively, so that each of the two emitters can temporarily detect at least a portion of the electromagnetic rays emitted by the other emitter. In this way, it can be achieved that the two emitters emit in a time-shifted way with respect to each other or alternately at least one pulse of electromagnetic radiation each, which irradiates one spot and can subsequently be detected at least partially by the other emitter.

Depending on the arrangement of the two emitters relative to each other, one emitter can detect either the rays reflected at the spot or the rays transmitted through the spot, of the respective other emitter.

Preferably, the first emitter can emit electromagnetic rays at a wavelength in the range of 1450 nm or greater. Preferably, the second emitter can emit electromagnetic rays at a wavelength in the range of 1450 nm or smaller. By means of the two emitters, in particular two LEDs, an emission of electromagnetic rays with a wavelength from two different, predefined IR spectral ranges can take place. In particular, the first emitter is configured to emit electromagnetic rays at a wavelength at which water has a local absorption maximum and is characterized by very low reflection or transmission. In contrast, the second emitter is preferably configured to emit electromagnetic rays at a wavelength at which water has hardly any influence on the reflection or transmission of the emitted rays. Thus, the two emitters are particularly suitable for moisture measurement in a sensor device.

The fact that the two emitters can be operated as detectors time-shifted means that one emitter can detect at least a portion of the emission spectrum of the other emitter. The first emitter, which emits electromagnetic rays in a long-wave IR spectral range, can detect the complete emission spectrum of the second emitter, which falls entirely within its absorption range.

The shorter wavelength second emitter is configured in such that it can absorb electromagnetic radiation from the longer wavelength first emitter, especially at its peak wavelength. Detection of electromagnetic rays originating from the first emitter by the second emitter is thus possible.

The two emitters can thus be selected or designed such that there is an overlap between the emission spectrum of the first emitter and the absorption spectrum of the second emitter. This may allow the second emitter, which emits electromagnetic rays in a shorter wavelength IR spectral region, to at least partially detect the emission spectrum of the first emitter. In particular, this overlapping region of the two emitters'spectral ranges can coincide with the IR spectral range in which water has an absorption maximum. Thus, it can be achieved that a water content of a spot to be irradiated, in particular on a skin surface, has a maximum influence on the electromagnetic rays of the first emitter partially detected by the second emitter.

Furthermore, the emission spectrum of the second emitter, in particular a reference LED, can be selected such that it has an overlap with the wavelength range that can be maximally absorbed by water at the spot to be irradiated. In the overlap range, the water content already has a great influence. However, when the influence of the water content is considered in relation to the complete emission spectrum of the second emitter, it can be assumed to be small. Because the complete emission spectrum of the second emitter can be detected by the first emitter, the detected electromagnetic rays are negligibly influenced by the water content of the spot. Thus, the second emitter is particularly suitable as a reference LED for measuring moisture, e.g. on a skin surface, in a sensor device.

The sensor device can also comprise an evaluation device which is designed to determine at least one measured value, in particular for moisture at the spot, as a function of the electromagnetic rays of the respective other emitter detected by the two emitters. For this purpose, the portion of the electromagnetic rays of the respective emitter reflected at a spot or alternatively transmitted through the spot is detected as a separate signal by the respective other emitter used as a detector.

In particular, the evaluation device can determine a degree of moisture at a spot by relating the signal originating from the first emitter, in particular an LED, to the signal from the second emitter, in particular the reference LED. Thus, the evaluation device can be used to precisely determine at least one measured value, in particular a degree of moisture of a spot outside the sensor device, for example on or in a skin surface.

The evaluation device can be designed as a circuit. The circuit can be connected to the two emitters.

The two emitters can be LEDs that have an indium gallium arsenide (InGaAs) layer on top of an indium phosphide (InP) layer.

Preferably, by using InGaAs-based LEDs on an InP substrate, emission of electromagnetic rays can be achieved at a wavelength in different IR spectral regions where water has very high or very low absorption. In addition, InGaAs-based detectors comprise a very high sensitivity in the infrared region. As a result, InGaAs-based LEDs can be used both as emitters and detectors to detect electromagnetic radiation from diverse IR ranges, in particular to measure moisture at a spot. This eliminates the need for additional detectors, e.g. in the form of a separate photodiode.

The sensor device can further comprise a housing having a first cavity open to a bottom side of the housing and a second cavity open to the bottom side, wherein the two cavities are separated from each other, and wherein the first emitter is arranged in the first cavity and the second emitter is arranged in the second cavity. By designing the housing with two separate cavities, it can be ensured that the first emitter is spatially separated from the second emitter. This means that undesirable “cross talk” between the electromagnetic rays emitted and detected by the two emitters respectively can be ruled out.

By forming openings on the bottom side of the housing, which are assigned to each cavity, it can be achieved that the electromagnetic rays of the two emitters can efficiently reach the outside, i.e. outside the sensor device, in particular a spot to be irradiated, from the respective cavity in which they are arranged. Furthermore, the electromagnetic rays reflected from outside, e.g. from the spot, or alternatively transmitted through the spot, can also reach the cavity of the respective emitter operated as a detector.

Each of the two cavities can further comprise a top side opposite the bottom side of the housing and a circumferential side separation extending between the bottom and the bottom side of the housing, preferably in the form of a wall or bar.

The bottom side of the housing can comprise a cover that is at least partially transparent to the rays of the two emitters. The cover can serve as a preferably detachable closure of the cavities.

The sensor device can be configured to measure skin moisture by applying a housing of the sensor device to the skin surface of a user such that the emitted electromagnetic rays can be irradiated onto or into a skin spot of the user and rays reflected from that skin spot can be detected.

Embodiments also relate to a wearable electronic device, in particular a fitness watch or an activity tracker, with a sensor device according to embodiments and an attachment device connected to the sensor device for attaching the sensor device to a body part of the user, in particular in such a way that the bottom side of the sensor device faces the body part and/or is in direct contact with the body part.

The sensor devices disclosed herein can be integrated into a wearable electronic device, such as an activity or fitness tracker or smartwatch. The housing of the sensor device can correspond to or be integrated into the housing of the device. The housing can be connected to a wristband or strap to attach the device to a body part of a user, in particular such that the bottom side of the sensor device, or the cover disposed thereon, rests against the body part. The sensor device can further be a component of a mobile phone. It can be used, for example, as a moisture measurement sensor, in particular as a skin moisture measurement sensor.

Yet further embodiments relate to a method for operating the sensor device according to embodiments, the method comprising the following steps:

(a) bringing a housing of the sensing device into contact with a skin spot of a user;

b) successively irradiating the skin spot with electromagnetic rays from the two emitters;

c) successively detecting the electromagnetic rays reflected from the skin spot by the two emitters; and

d) determining a moisture level as a function of the detected electromagnetic rays.

The two emitters are thus not actuated simultaneously to emit electromagnetic radiation, but successively. A pulse emitted by a respective emitter and reflected by the skin spot is detected. The detection can be done either by a separate detector or by the other emitter.

