Patent Description:
Solutions exist for measuring a heart rate and a respiratory rate of humans. For example, some solutions can detect a changing color of skin and derive a heart rate or respiratory rate therefrom by using a light source and an optical receiver that are placed directly on the skin.

But placing a sensor on skin may not be ideal. For example, an infant may not be comfortable with a sensor being on his or her skin for an extended period of time.

Additionally, when the wearer of the sensor is moving, existing solutions may obtain erroneous measurements or not be able to obtain measurements at all. For example, when the wearer of the sensor is moving, a received optical signal may be weak or unmeasurable due to sensor misalignment.

Hence, new solutions are needed. <CIT> discloses a wearable heart rate monitor using a heartbeat waveform sensor and a motion detecting sensor. <CIT> discloses an oximetry sensor assembly and methodology for sensing blood oxygen concentration which may be coupled to a seat. <CIT> discloses a flash reflectance oximeter which is configured to noninvasively measure tissue oxygenation.

Various examples are described for detecting heart rate and respiratory rate. In an aspect, a sensor application obtains a set of measurements of light. For each measurement, the sensor application causes a light source to transmit a pulse of light through an article to an area of skin and determines a measurement of light returned from the article. The sensor application further determines, from the set of measurements of light, a periodic change in an amplitude of the returned light. The sensor application further identifies the periodic change in amplitude as a heart rate having an identical periodicity.

In another aspect, the sensor application determines a rate of change of the periodic change in amplitude or an envelope modulation of the set of measurements of light. The sensor application identifies a respiratory rate as equal to the rate of change. These illustrative examples are mentioned not to limit or define the scope of this disclosure, but rather to provide examples to aid understanding thereof. Illustrative examples are discussed in the Detailed Description, which provides further description. Advantages offered by various examples may be further understood by examining this specification.

Features, embodiments, and advantages of the present disclosure are better understood when the following Detailed Description is read with reference to the accompanying drawings.

Aspects described herein involve sensing physiological parameters. Examples of physiological parameters are heart rate and respiratory rate (respiratory rate). As mentioned above, existing systems can require a sensor to be placed on the skin. In contrast, disclosed solutions do not need to be placed directly on skin to detect a heart rate or breathing rate. Examples of articles include clothing, bedding, blanket, absorbent articles such as diapers.

In an example, a sensor application pulses a light source through an article onto skin, measures the returned light via a light receiver, and derives a heart rate and/or respiratory rate from the measurement of returned light. The wavelength, and therefore the color, of the light source can be selected to match a particular level of optical transmissivity for a particular article and/or to ensure a suitable amount of returned light to the light receiver for a color change of blood underneath skin to be discerned. Optical transmissivity is a measure of how much light is transmitted through material in relation to an amount of light incident on the material, and is wavelengthdependent.

In some cases, a sensor can be placed on a patch of the diaper with higher transmissivity.

Additionally, disclosed solutions can minimize a number of sensors that are needed to measure different parameters. For example, color-sensing devices disclosed herein can be used for detecting a change in color beneath the skin (and therefore to detect heartrate and/or respiratory rate) and can be dynamically be reconfigured to detect a color of a color strip on or within the diaper (therefore detecting a presence of volume of bodily exudate). The color strip can be located on the diaper. In this manner, disclosed solutions can be employed in existing systems, or can be deployed as multi-purpose systems.

In an aspect, different arrangements, or geometries, of light source and light receiver combinations can be available and selected. Having an array of light sources and light receivers facilitates dynamically selecting a light source-light receiver pair, or a geometry, that provides an optimal signal. In this manner, disclosed systems can adjust to movement caused by the wearer, or different thicknesses of diapers caused by moisture, e.g., urine, in the diaper. For example, if a diaper becomes full, then the diaper may become thicker. Disclosed systems can compensate by changing a geometry of the pulsed light with respect to a light receiver, thereby compensating for the increased light path due to the thicker absorbent material and continue to measure heart rate and/or respiratory rate.

In a further aspect, measurements obtained from other sensors such as wetness sensors and accelerometers are used to validate a heart rate or respiratory rate detected via the optical sensor. For example, by detecting and measuring motion of a wearer by using an accelerometer, disclosed systems can compensate for motion, enabling a continued measurement of heart rate and/or respiratory rate.

In yet another aspect, disclosed systems can supplement a determined activity state of a subject in proximity to an article (e.g., whether an wearer is feeding, sleeping, or is awake) with information determined by heart rate or respiratory rate. For example, if an infant is not moving, inertial measurement-based solutions may erroneously determine that the infant is sleeping. But by combining inertial measurements with respiratory rate determined via optical measurements, disclosed solutions can determine that a heart rate and/or respiratory rate remains elevated, indicating that the infant is not asleep but rather feeding. In another example, by determining that a heart rate and/or respiratory rate is consistent with sleep, disclosed solutions can discern that a wearer is asleep even in the presence of inertial measurements that indicate the wearer is moving (and therefore in some cases might otherwise indicate that the wearer is awake). For example, a wearer could be asleep in a moving car.

Turning now to the figures, <FIG> depicts a block diagram of an example of a physiological sensor environment according to certain aspects of the present disclosure. <FIG> depicts wearable sensor <NUM>, article <NUM>, emitted light <NUM>, returned light <NUM>, and skin <NUM>. Examples of article <NUM> include clothing and absorbent articles such as a common disposable diaper, pantiliner, adult diaper, etc..

Wearable sensor <NUM> can be placed on an article in proximity to a subject or otherwise attached to a wearer. When properly located, one or more sensors housed inside the wearable sensor <NUM> can measure one or more parameters of the wearer. Wearable sensor <NUM> can be affixed to a wearer using an attachment device such as loops, hooks, or an adhesive. For example, wearable sensor <NUM> by using optical methods, inertial sensors, or both, can be configured to measure heart rate, respiratory rate, or both.

Wearable sensor <NUM> includes sensor system <NUM>, network connection <NUM>, and monitor <NUM>. Sensor system <NUM> includes one or more light sources such as Light Emitting Diodes (LEDs) and one or more optical receivers such as photodiodes. Wearable sensor <NUM> can be placed on a diaper such that the light sources and optical receivers are aligned with a particular area of the diaper such as a color changing strip or a translucent portion of the diaper. Different arrangements of light sources and photodiodes are possible. Some examples are discussed further with respect to <FIG> and <FIG>.

Sensor system <NUM> and monitor <NUM> can be connected by network connection <NUM>. Network connection <NUM> can be any wired or wireless connection. Examples include WiFi and Bluetooth. Any split of functionality between sensor system <NUM> and monitor <NUM> is possible. Therefore, sensing and analysis operations can be performed by sensor system <NUM>, monitor <NUM>, or both. For example, sensor system <NUM> can transmit a detected heart rate and/or a detected respiratory rate via network connection <NUM>, to monitor <NUM>. Monitor <NUM> can display information such as heart rate, respiratory rate, sleep state, and so on, to a caregiver. In an example, a heart rate is measured in beats per minute and respiratory rate is measured in breaths per minute.

In a more detailed example, sensor system <NUM> emits a pulse of emitted light <NUM>. A pulse is an amount of light emitted for a specific amount of time. Emitted light <NUM> can shines through article <NUM>, which absorbs some of emitted light <NUM>. Some of emitted light <NUM> is transmitted to the skin <NUM>. In turn, a portion this light is reflected back from skin <NUM> through the article <NUM> and is received as returned light <NUM>. A light sensor (e.g., a photodetector or photodiode) in sensor system <NUM> receives the returned light <NUM>.

Sensor system <NUM> samples the returned light <NUM> at a sampling rate, which can be adaptive or fixed. In some cases, multiple samples can be taken during one pulse of light. In other cases, one pulse causes one sample to be taken. With a sufficient number of samples, e.g., at a sampling rate sufficient to overcome aliasing, the sensor system <NUM> determines an amplitude of the returned light <NUM> over time. A signal or waveform is formed from set of samples. Sensor system <NUM> can pulse light on a duty cycle. An example duty cycle is one pulse every <NUM> milliseconds. The selected duty cycle can affect battery life. For example, more frequent light emission can use more battery power than an infrequent pulse of light.

The amplitude of returned light <NUM> can be periodic in nature based on a beating of the heart. More specifically, the amplitude of the light can vary over time, reflecting the fact that human skin absorbs different amounts of light at different points in the heart beat cycle. The absorption of specific wavelengths of light can differ based on blood pulse wave. For example, when the pulse wave arrives at the sensing location, a different amount of light is absorbed than when the pulse wave leaves, which results in a different amount of reflected light that is in turn measured.

More specifically, the received signal can include a fundamental component and one or more harmonic components. The periodicity of the fundamental component indicates the period of the heart rate. In some cases, the light can be filtered such that only a specific wavelength of light is considered.

From the detected heart rate, the sensor system <NUM> can determine a respiratory rate. Different methods can be used. For example, the sensor system <NUM> can determine that the heart rate increases slightly and then decreases slightly on a periodic basis. This period is the respiratory rate. Hence, the second time derivative of the received amplitude of light over time is the respiratory rate.

In another example, the sensor system <NUM> can analyze modulation of an envelope of the optical signal. For example, because respiration changes stroke volume and thus the pulse wave amplitude, the envelope of the optical signal modulates accordingly.

Sensor system <NUM> can include one or more inertial measurement sensors such as accelerometers or gyroscopes. These inertial sensors can determine inertial measurements that can supplement heart rate or respiratory rate measurements. Sensor system <NUM> can also include one or more wetness sensors. Additionally or alternatively, sensor system <NUM> can include one or more microprocessors.

A determined heart rate and/or respiratory rate can be combined with inertial measurement sensors to improve reliability of measurements. For example, sensor system <NUM> can determine that a wearer of a sensor is moving, and use the movement measurements to compensate for errors received in the returned light. Sensor system <NUM> can also use inertial measurements to determine a state of a wearer, for example, in conjunction with a predictive model.

<FIG> depicts a block diagram of an example of a physiological sensor system, according to certain aspects of the present disclosure. <FIG> includes wearable sensor system <NUM>, which is an example of sensor system <NUM>. Wearable sensor system <NUM> includes one or more of microcontroller <NUM>, light source <NUM>, inertial sensor <NUM>, photodetector <NUM>, predictive model <NUM>, and processor <NUM>. Microcontroller <NUM> can execute sensor application <NUM>. Wearable sensor system <NUM> can perform a variety of functions such as heart rate detection or activity state detection.

For example, wearable sensor system <NUM> can be configured to measure a color of skin to derive a heart rate or a respiratory rate. The detected color can be correlated with a pulse of a heart. A change in heart rate can be correlated with respiratory, thereby enabling a determination of a respiratory rate.

To detect color, wearable sensor system <NUM> causes a pulse of light to be emitted and determines the amount of the pulsed light that is reflected. Color sensing can occur including in the presence of ambient light <NUM>, because wearable sensor system <NUM> can remove a measurement of the ambient light from the measurement.

In an example, sensor system <NUM> emits emitted light <NUM>. Emitted light <NUM> can be a pulse, e.g., a light emitted for a specific amount of time. Emitted light <NUM> shines on article <NUM>. Article <NUM> absorbs some of emitted light <NUM> and transmits some of the emitted light <NUM> as transmitted light <NUM>. Transmitted light <NUM> is transmitted to skin <NUM>. In turn, a portion of transmitted light <NUM> is reflected back from skin <NUM> as returned light <NUM>. A portion of returned light <NUM> passes through article <NUM> as returned light <NUM>.

Continuing the example, a light receiver (e.g., a photodetector) in sensor system <NUM> receives the returned light <NUM>. The sensor system <NUM> samples the returned light <NUM> at various points in time to determine a periodicity of the amplitude of the returned light <NUM>. This periodicity can indicate a heart rate due to skin <NUM> absorbing different amounts of light depending on a time relative to a heartbeat. Hence, the first derivative of the received amplitude of light over time is the respiratory rate.

In another example, wearable sensor system <NUM> measures a color of a color changing indicator in an absorbent article. From the color, wearable sensor system <NUM> determines a loading of the absorbent article. Color changing indicators are designed to change color in response to contact with a substance having a particular property, such as a pH level. Examples include be Bromocresol green, which changes color based on the pH of a liquid to which the color changing indicator has been exposed. Other color changing indicators can be used. The detected pH level can be correlated with a volume of bodily exudate, because the pH level changes as the volume of bodily exudate in the absorbent article changes. Accordingly, a lookup table or function may be used to determine a volume for a given pH level, or color of the color changing indicator.

Wearable sensor system <NUM> also includes a microcontroller <NUM>. Microcontroller <NUM> can be any controller, processor, application specific integrated circuit or other processing device. An example of a computing device is shown in <FIG>. Microcontroller <NUM> can execute sensor application <NUM> as well as other processor-executable instructions to perform aspects of the present disclosure. The functions of microcontroller <NUM> can be implemented by processor <NUM> or vice versa. Microcontroller <NUM> can store data, which can include a state of a wearer, demographic information about a wearer, information about a particular absorbent article worn by a wearer, and so forth.

Ambient light <NUM> can be any kind of light present in an environment that is not generated by light source <NUM>, which can include light from natural sources, e.g., sunlight, or artificial light such as light created via incandescent light sources, halogen light sources, light emitting diode ("LED") light sources, fluorescent light sources, laser sources, etc. Even though ambient light can have different color spectra depending on the ambient light source(s) present, wearable sensor <NUM> can electronically remove the contribution of such ambient light to light detected by the photodetector and accurately detect the color of skin <NUM> based on returned light from the light source <NUM>.

Light source <NUM> includes one or more light sources operable to shine light on skin <NUM>. The light sources can be any suitable artificial light source according to this disclosure, including LEDs, incandescent light sources, or other light sources. Multiple discrete light sources can be implemented individually or via an integrated package that combines multiple individual light sources into a single light source.

Light from light source <NUM> can be generated at one or more specific wavelengths, or can encompass multiple wavelengths. In an example, light source <NUM> has three sources of light: red light at wavelength <NUM> nanometers ("nm"), green light at wavelength <NUM>, and infrared light at <NUM>-nm to <NUM> wavelength. For example, for measuring a color of blood beneath human skin, wavelengths in the red, green, or infrared wavelengths may be advantageous. In some cases, infrared light can be preferred as it is not affected by skin color, therefore the reflected light more closely follows the pulse wave underneath the skin.

Other wavelengths of light may be employed according to different examples, depending on the application, the expected color range of a target object or color changing indicator such as a strip of litmus paper, expected ambient light spectra, or any other suitable factor. In some examples, the light source may be tunable to allow selection of a wavelength or wavelengths of light having a small contribution from the ambient light. For example, if ambient light detected by the photodetector indicates a local or global maximum or minimum magnitude at a first wavelength, the wearable sensor <NUM> can tune the light source <NUM> to emit light substantially at the first wavelength.

In this example, the wearable sensor system <NUM> pulses the light emitted by light source <NUM> by activating for a short duration, e.g., <NUM>-<NUM> microseconds to <NUM> milliseconds, called a "pulse width," and then deactivating the light source. Any suitable pulse width may be employed for a particular application. Light source <NUM> can create a separate pulse for red, infrared, and green, and output the corresponding values. For example, a pulse width of <NUM> microseconds may be advantageous to detect a color of a color changing indicator or a color of human skin. Short pulse widths enable the wearable sensor system <NUM> to pulse and detect different colors of light, e.g., red, green, and infrared, in quick succession of each other.

The use of pulsed light enables wearable sensor system <NUM> to disambiguate the type of light reflected by the object. Specifically, wearable sensor system <NUM> can detect and filter the ambient light from detected light that includes light pulsed from the light source <NUM>. In some examples, the wearable sensor system <NUM> can pulse the light source <NUM> at regular intervals, e.g., every ten minutes, or in response to an event, such as a user pressing a button on the wearable sensor system <NUM> or a humidity sensor detecting a humidity level exceeding a threshold. Additionally, the use of pulsed light as compared to continuous light can lower the power consumption of wearable sensor system <NUM>, thereby increasing the amount of time that the wearable sensor system <NUM> can operate from a battery.

When the light source <NUM> is pulsed, the detected light at photodetector <NUM> may be a combination of ambient light <NUM> and light from the pulsed light source <NUM> reflected from the skin <NUM>. When the light source <NUM> is inactive, the light detected by the photodetector <NUM> is ambient light. By pulsing the light source <NUM>, wearable sensor system <NUM> is able to first obtain baseline information about the ambient light spectrum to enable the wearable sensor system <NUM> to isolate light received when the light source <NUM> is active. Pulsing also allows the wearable sensor <NUM> to save power by deactivating the light source <NUM> when a color measurement is not being taken.

Photodetector <NUM> receives a light, including light reflected from the skin <NUM>, whether ambient light or light emitted by the light source <NUM>, and generates sensor signals based on that returned light. Photodetector <NUM> can be any device that can detect and measure light such as a photodiode, phototransistor, complementary metal-oxide-semiconductor (CMOS) image sensor, charge-coupled device (CCD) sensor, or a photo-resistor.

Photodetector <NUM> can detect a wide spectrum of light and output information that indicates the detected light. For example, photodetector <NUM> can create an electrical output that is proportional to the wavelength of the returned light. Photodetector <NUM> can provide three outputs of a triplet, e.g., a value that corresponds to red, another value for green, and another value for infrared.

More specifically, the values of the triplet correspond to the amplitude of light at a range of wavelengths corresponding to a particular color. Therefore, a first value is proportional to an amplitude of red in the returned light, a second value is proportional to an amplitude of green in the returned light, and a third value is proportional to an amplitude of infrared in the returned light.

In an aspect, a photodetector <NUM> can be an array of individual photodetectors. Each photodetector can be configured to measure a color of light. For example, one photodetector measures red, a second photodetector measures infrared, and a third photodetector measures green.

Processor <NUM> is an electronic circuit or device such as a general-purpose processor. Processor <NUM> can operate in the analog domain, digital domain, or both. Processor <NUM> can discern the color of blood that is beneath the skin <NUM> independent of any ambient light. Processor <NUM> receives a first output from photodetector <NUM> that represents the ambient light, for example, an output gathered when the light source <NUM> is off. Processor <NUM> receives a second output from photodetector <NUM> when the light source <NUM> is pulsed. Processor <NUM> discerns a difference between the first output and the second output and thereby isolates the color of the object, specifically the color of the reflected light on the object from the pulsed light.

In an aspect, processor <NUM> receives a level indicating an intensity of broad spectrum light that represents the ambient light, i.e., the point in time that the light source <NUM> is off, and a level indicating the intensity of for a second point in time at which one of the three colors red, infrared, and green, is pulsed. Processor <NUM> can then disambiguate the contribution of the single pulsed color from the ambient light by comparing the intensity of the ambient light and the intensity with the single pulsed color.

Processor <NUM> receives a first set red, green, and infrared levels from photodetector <NUM> for a point in time that the light source <NUM> is off and a second set of red, green, and infrared levels from a second point in time that the light source <NUM> is pulsed. Processor <NUM> calculates a difference between the level of red between the first and second points in time, thereby calculating a contribution of red, green, and infrared levels from the pulsed light.

Processor <NUM> may be a specialized photometric front end. Processor <NUM> may be configured to activate light source <NUM> and measure a signal received by photodetector <NUM>. For example, processor <NUM> can receive an analog input from photodetector <NUM>, convert the analog input to a digital output by using a analog-to-digital converter (ADC), then store a numerical value indicating the detected color in an internal memory for later comparison with another value. In this manner, processor <NUM> may be configured to disambiguate the contribution of the ambient light <NUM> in the analog domain and output an analog signal or digital value indicative of the color of blood beneath the skin <NUM>. For example, the processor <NUM> can provide an output, such as an triplet value representing the color.

In an aspect, processor <NUM> can have multiple detection channels, each corresponding to a pair that of a light source <NUM> and a photodetector <NUM>. As described further with respect to <FIG>, each channel can be dedicated to a specific light source-photodetector pair, or a "cell. " Each cell can be physically separated so that the processor <NUM> may measure color in multiple places. Processor <NUM> can also pulse the light from a particular cell differently from a light from another cell.

Sensor application <NUM> can provide additional functionality such as calibration or white balancing for the signal received from light source <NUM>. For example, sensor application <NUM> can retrieve known values such as the detected values when a known color, e.g. represented by a white or gray card or object that is presented to photodetector <NUM>. Sensor application <NUM> can adjust the received red, infrared, and green levels according to the known calibration values.

In an aspect, microcontroller <NUM> may be connected to a transceiver <NUM>. Transceiver <NUM> may communicate according to any suitable wireless protocol, such as Bluetooth, WiFi, near-field communication, etc. Using transceiver <NUM>, microcontroller <NUM> may transmit the color of the skin <NUM> or, if detecting bodily exudate in an absorbent article, notify an external device that an absorbent article has been soiled. Microcontroller <NUM> may transmit information to a remote device, such as a smartphone, smartwatch, or other wearable device, or a remote computer, such as a server, e.g., a cloud-based server, for further processing and analysis.

Microcontroller <NUM> can, via the transceiver <NUM>, transmit the detected color from processor <NUM> to a remote server, which can perform any of the operations discussed herein, for example, relating to heart rate or respiratory rate detection.

Certain aspects can determine an activity state of a subject in proximity to the sensor system <NUM> or part thereof (e.g., a wearer of sensor system <NUM> or part thereof). More specifically, by using an inertial sensor, sensor system <NUM> can receive indications of movement and determine, from the movement, an activity state of a subject (e.g., an infant). Examples of states include resting, sleeping, stirring, awake, and feeding. In an example, monitor <NUM> receives sensor measurements such as acceleration and angular velocity from sensor system <NUM> provides the measurements to the predictive model <NUM> to determine an activity based on the received sensor measurements. In this example, the predictive model <NUM> is a state-machine or algorithm, but may be any suitable type of predictive model in different examples such as a machine learning model or a classification model.

Inertial sensor <NUM> can include one or more accelerometers or gyroscopes. Inertial sensor <NUM> can provide indications of a subject's (e.g., a wearer's) activity, respiratory rate, or orientation, such as on which side an infant is nursing or bottle feeding. For example, using precise movements gathered from an accelerometer or a gyroscope, the sensor system <NUM> and/or the monitor <NUM> can distinguish activities being performed by a wearer. For example, the activity classification system can distinguish deep sleep from light sleep, whether the subject is on its stomach versus on its back, or whether a subject is feeding (e.g., whether an infant is nursing). Further, certain aspects described herein can use predictive models to further refine the system's ability to determine activity. For example, an accelerometer can measure acceleration of the wearer in one or more dimensions. The output of an accelerometer can therefore be a three-dimensional triplet of numerical values corresponding to the x, y, and z directions.

Gyroscopes measure angular velocity. For example, a gyroscope can output a signal proportional to the angular velocity of the wearer. Angular velocity changes in the direction of a torque applied to the gyroscope. Accordingly, when an infant that is wearing the sensor system <NUM>, for example, rolls over, the gyroscope can detect an increase in angular velocity. When the infant stops rolling, for example, the angular velocity returns to zero. The direction component of the angular velocity can be used in various ways. For example, the direction of the velocity can help indicate which side, e.g., left or right, stomach or back, the infant is positioned. Processor <NUM> can sample the gyroscope at specific instances in time and obtain the angular velocity on a periodic basis.

In some examples, wearable sensor system <NUM> can be integrated into a sensor package that can be detachable and removable from article <NUM>. For example, the sensor package can be adhered to the article <NUM> to prevent the sensor package slipping, while allowing its removal. The sensor package can include the wearable sensor <NUM> and/or the wearable sensor system <NUM> and can be included within a flexible, impermeable package. For example, the sensor package can have a housing that can withstand bodily exudate and feces, and is sufficiently thin as to not cause discomfort to a wearer of the absorbent article. The sensor package may be fabricated with flexible substrate such as a thin plastic or fluoroelastomer.

The sensor package housing can include a material that is washable or can be wiped. For example, the sensor package can be inserted into an absorbent article or adhered to the inside of the absorbent article. The sensor package can also be inserted into a pocket or pouch inside the absorbent article. Such a pocket or pouch can be hermetically sealed, for example, in transparent plastic that allows light to pass through. The sensor package can also be permanently attached into an absorbent article and discarded after a one-time use. The sensor package can also be adhered to the outside of the absorbent article via velcro or similar material.

<FIG> depict an example of a layout of a sensor system that can be placed in or on the outer surface of an absorbent article, according to certain aspects of the present disclosure. <FIG> represents a view of a first side of an exemplary a sensor layout for sensor package <NUM>. <FIG> represents a view of a second side of an exemplary sensor layout for sensor package <NUM>. The first and second sides are shown for example purposes; components can be placed on either the first or second side.

As depicted, the bottom is the side that is positioned to face and align with an object. Sensor package <NUM> includes a battery <NUM> and one or more color detector cells 320a-n. Sensor package <NUM> may also include a switch <NUM>, electrical connectors (not depicted), a volatile organic compound ("VOC") sensor <NUM>, a temperature sensor <NUM>, a humidity sensor <NUM>, an additional ambient light sensor <NUM>, processor <NUM>, microcontroller <NUM>, or transceiver <NUM>. Additional ambient light sensor <NUM> can be used in conjunction with the photodetectors to improve or augment the light detecting capability of sensor package <NUM>. Some aspects may not include all of the components described above, or include variants thereof.

In addition, the sensor package <NUM> can cause an alarm, such as an audible beep. Accordingly, sensor package <NUM> can include a speaker or other audio output device. Sensor package <NUM> can also cause a transmission of an alert to another device, for example, operated by a caretaker. In another aspect, sensor package <NUM> can transmit an alert to another device. Sensor package <NUM> can include a transmitter or transceiver capable of transmitting a radio signal to an external device. Sensor application <NUM> operating on microcontroller <NUM> can also log events, such as a change in heart rate, to memory for later transmission to a caregiver.

Sensor package <NUM> can include one or more color detector cells 320an. For example, multiple color detector cells 320a-n can increase the ability of the sensor package <NUM> to detect changes in color through the absorbent article and/or a detection of color in multiple places.

Each color detector cell 320a-n includes a light source such as an LED and a photodetector such as a photodiode. In some aspects, as discussed further with respect to <FIG>, a color detector cell may include multiple light sources or multiple photodetectors. Each color detector cell 320a-n detects light reflected by skin <NUM> such as a color strip, such as ambient light or pulsed light from the light source(s). The output of each color detector cell 320a-n is provided to a processor <NUM>. The output of processor <NUM> can be provided to microcontroller <NUM>. In some examples, each color detector cell 320a-n may have a dedicated processor <NUM>, while in some examples, multiple color detector cells 320a-n may be connected to a common processor.

Sensor package <NUM> can include a switch <NUM> to activate or deactivate the sensor package <NUM>. The switch <NUM> can be any suitable switch, such as a rockerstyle on/off switch that connects the battery <NUM> to the electronics in sensor package <NUM> such as the color detector cells 320a-n and sensors <NUM>-<NUM>. Switch <NUM> can also be a pushbutton switch that activates power from battery <NUM> to sensor package <NUM> for a period of time. Sensor package <NUM> can be configured to automatically turn off to save battery power. In an aspect, in conjunction with microcontroller <NUM>, sensor package can be activated remotely. For example, a user can prompt an external device with a voice command, which causes the external device to transmit a request for a status of the absorbent article to the microcontroller <NUM> via a wireless connection, or a request to turn on or turn off the sensor package <NUM>.

As discussed with respect to <FIG>, processor <NUM> can discern a color of an object such as skin. Microcontroller <NUM> can execute an application such as sensor application <NUM> that can perform calibration of the detected color value. Transceiver <NUM> can notify an external device if the sensor package <NUM> detects the presence of bodily exudate in an absorbent article.

In an aspect, sensor package <NUM> can also include a VOC sensor <NUM>. VOC sensor <NUM> can detect the presence of volatile organic compounds such as feces from a bowl movement or VOCs present in blood. In conjunction with data obtained from color detector cells 320a-n, the VOC sensor <NUM> can provide additional information to microcontroller <NUM> based on one or more detected volatile organic compounds.

In an aspect, sensor package <NUM> can also include a temperature sensor <NUM>. Temperature sensor <NUM> can detect heat from substances such as bodily exudate. In conjunction with data obtained from color detector cells 320a-n, the temperature sensor <NUM> can provide additional information such as a temporary increase in temperature to microcontroller <NUM>. Because a notification of a temporary increase in temperature can indicate a presence of bodily exudate, such information can improve the accuracy and reliability of the detection.

In another aspect, sensor package <NUM> can also include a humidity sensor <NUM>. Humidity sensor <NUM> can detect the presence of humidity, e.g., from bodily exudate. In conjunction with data obtained from color detector cells 320a-n, humidity sensor <NUM> can provide additional information such as a notification of a temporary increase in humidity to microcontroller <NUM>. Because a temporary increase in temperature can indicate a presence of bodily exudate, such information can improve the accuracy and reliability of the detection.

As discussed, sensor package <NUM> can include multiple color detector cells 320a-n. The presence of more than one color detector cell 320a-n allows for increased accuracy and reliability. For example, one color detector cell 320a-n could become obstructed by an object, rendering detected values from that cell unusable, or because a thickness of the absorbent article can change based on a volume of liquid absorbed within, requiring the use of a different detector cell. In contrast, fewer color detector cells 320a-n can simplify the overall system architecture and may also lower power consumption. For example, in a system with three detector cells 320a-c, if one detector cell 320a returns a color measurement that is inconsistent with detector cells 320b and 320c, then microcontroller <NUM> can ignore the measurements from detector cell 320a.

<FIG> depicts an example color detector cell configuration, according to certain aspects of the current disclosure. As discussed, a sensor system such as sensor package <NUM> includes one or more color detector cells 320a-n. <FIG> shows an color detector cell <NUM> in more detail.

Color detector cell <NUM> includes two photodetectors, photodetector <NUM> and photodetector <NUM>, light source <NUM>, opaque barrier <NUM>, and opaque barrier <NUM>. Light source <NUM> can be any suitable light source according to this disclosure. As shown, light source <NUM> includes a red, an infrared, and a green light source, though different numbers and types of light sources <NUM> may be used according to different examples, which can allow the light sources can be turned on and off, i.e., pulsed, separately. Pulsing the light sources <NUM> that emit different colors separately allows color detector cell <NUM> to tailor the light output to a specific wavelength of light. For example, a particular color changing indicator may be more responsive to a specific wavelength of light at a specific pH level.

Photodetectors <NUM> and <NUM> can be any suitable photodetector according to this disclosure. Photodetectors <NUM> and <NUM> are connected to the processor <NUM>. A separation distance <NUM> between the light source <NUM> and the photodetector <NUM> and separation distance <NUM> between light source <NUM> and photodetector <NUM> can be adjusted based on the application. In particular, the closer the light source <NUM> and a photodetector <NUM> or <NUM> are together, the greater the portion of light received at the photodetectors from the light source <NUM> (and less from ambient light <NUM>). As an example only, separation distance <NUM> and separation distance <NUM> can be adjusted from <NUM> to <NUM> in separation. Other distances and configurations are possible. As a distance increases, all else being equal, the intensity of the light from the light source received at the photodetector decreases. Additionally, as the distance increases, the focal area being measured increases. As the distance decreases, the sensor is more focused on a smaller area directly under the sensor.

As shown, two photodetectors <NUM> and <NUM> are used. Photodetectors <NUM> and <NUM> can be positioned to be parallel to each other. In this configuration, the combination of photodetectors <NUM> and <NUM> provides a stronger output signal to the processor <NUM> than otherwise. Using more than one photodetector also provides an advantage in that error can be reduced if the sensor system is misaligned with respect to the object.

Color detector cell <NUM> can include one or more opaque barriers <NUM>-<NUM> positioned between the light source <NUM> and the photodetectors <NUM>, <NUM>. The opaque barriers <NUM>-<NUM> reduce the amount of light from light source <NUM> that travels directly to the photodetector <NUM> without reflecting off of the object. Opaque barriers <NUM>-<NUM> can be poron or similar material. In an aspect, the photodetectors <NUM> or <NUM> can include such an opaque barrier, or an opaque housing of the photodetector <NUM> or <NUM> can be extruded in such a manner that the opaque housing is located between the LED and photodiodes. In an aspect, the opaque barriers <NUM>-<NUM> are omitted to simplify the design.

<FIG> is a flowchart that depicts an example of a method <NUM> for determining physiological parameters through an absorbent article, according to certain aspects of the present invention. Method <NUM> involves obtaining a set of normalized measurements of light and then using those measurements to determine a heart rate and respiratory rate. For discussion purposes, method <NUM> is discussed as being performed by sensor application <NUM>, but can be performed by any suitable computing device or application. As depicted in <FIG>, more than one color detector cells 320a-n can be used. Therefore, such an aspect, method <NUM> may be performed with respect to each color detector cell 320a-n. More specifically, the photodetector in each color detector cell 320a-n can independently perform the blocks of method <NUM>.

At block <NUM>, method <NUM> involves obtaining a first measurement of ambient light received from a photodetector while a light source is off. Photodetector <NUM> detects the ambient light present and outputs a representation of the color of the light or a representation of an intensity of broad-spectrum light that is present. For example, photodetector <NUM> can create an electrical output that is proportional to the wavelength or the intensity of the returned light. In an aspect, the photodetector <NUM> can provide three outputs that each correspond to red, green, or infrared: a first that is proportional to an amplitude of red in the returned light, a second that is proportional to an amplitude of green in the returned light, a third that is proportional to an amplitude of infrared in the returned light.

Photodetector <NUM> provides the first measurement of light to the processor <NUM>. In this example, the first light measurement is taken while a light source <NUM> is off and represents ambient light reflected from the skin <NUM>. The first light measurement can represent an intensity of broad-spectrum light or an intensity of a specific wavelength of light.

In some aspects, block <NUM> is not performed, and process <NUM> commences at block <NUM>. For example, some aspects may not remove a measurement of ambient light.

At block <NUM>, method <NUM> involves causing the light source to transmit a pulse of light through an article to human skin or an area of human skin. Sensor application <NUM> causes light source <NUM> to transmit light on to skin <NUM>. More specifically, processor <NUM> activates light source <NUM> for a predetermined pulse time interval.

In some examples, multiple light sources may be pulsed simultaneously or individually. For example, aspects using sensor package <NUM> may include more than one color detector cell 320a-n. The light source in each color detector cell 320a-n may be pulsed separately or together with the other light sources.

The wavelength of the light emitted by light source <NUM> can be adjusted based on the optical properties of the article <NUM>. For example, different diapers can have different rates of optical transmissivity. Additionally, these rates can vary by emitted wavelength. For example, a diaper may allow transmission of more light at a first wavelength than at a second wavelength. Examples of suitable wavelengths include, green, red, and infrared. For example, benefits of green include a higher reactivity with water in human skin. Infrared also has advantages, such as being agnostic to skin tone, but has disadvantages such as being more sensitive to motion. In some cases, more than one wavelength can be used, for example by using multiple light sources and/or multiple light receivers. Further, as the absorbent material absorbs liquid, its optical property may change and the wavelengths can be selected to adjusted to the changing material.

In some cases, a specific wavelength or wavelengths are selected due to a specific article being present. For example different articles can react differently to different wavelengths of light.

At block <NUM>, method <NUM> involves obtaining, via the photodetector, a second measurement of light returned from the article. The second measurement can include a measurement of light reflected from the article.

In an aspect, the second measurement is obtained while the light source is transmitting light and therefore includes a measurement of the ambient light, the transmitted light, and reflected by the skin. More specifically, sensor application <NUM> obtains a second measurement from the photodetector during the transmission, the second measurement including the ambient light and the transmitted light reflected from the object. Processor <NUM> obtains a second measurement of light during the time interval that the pulse from light source <NUM> is on. The second measurement includes the ambient light and the light from the pulsed light source <NUM>. In an aspect such as sensor package <NUM>, the photodetector in each color detector cell 320a-n each obtains a second measurement of light. Sensor application <NUM> uses the first and second measurements to determine the color of an object.

At block <NUM>, method <NUM> involves determining a normalized measurement of light reflected from an article by (i) removing an ambient light signal from the second measurement based on the first measurement of ambient light and (ii) compensating for a contribution of the article based on one or more known properties of the article. In an aspect, if ambient light removal is not performed, then block <NUM> may not be performed.

Sensor application <NUM> determines a normalized measurement of the reflected light by removing an ambient light signal from the second measurement based on the first measurement. Removal can be performed in the analog domain or the digital domain.

For example, processor <NUM> subtracts the first measurement, representing the ambient light, from the second measurement, representing the ambient light combined with the reflected light from light source <NUM>. The result of the subtraction is the light reflected from the skin <NUM>, such as a color changing indicator. If operating in the digital domain, processor <NUM> converts the first measurement into a digital or numeric representation of the red, green, and infrared levels. Processor <NUM> converts the second measurement into a digital or numeric representation of the red, green, and infrared levels. Processor <NUM> computes a new red level by subtracting the first measurement from the red level of the second measurement, a new green level by subtracting the first measurement from the green level of the second measurement, and a new infrared level by subtracting the first measurement from the infrared level of the second measurement. The new red, green, and infrared levels represent the color of the light reflected from the object.

Sensor application <NUM> compensates for a contribution of the article based on one or more known properties of the article. In some cases, the material used can have an optical property that allows certain wavelengths to transmit more efficiently. This can be engineered by changing certain layer's thickness or by opening an aperture where light-blocking layers are removed.

At block <NUM>, method <NUM> involves determining whether any more samples (measurements) are needed. The sampling rate can be fixed or adaptive. At least several samples per heartbeat can be needed to avoid aliasing. Because a heart rate can be as high as <NUM> beats/minute, in some cases, therefore, sampling frequencies should be at least <NUM> Hertz to avoid aliasing. Additionally, a sufficient number of samples such that multiple periods are sampled can provide for further stability in measurement and for additional error correction.

At block <NUM>, method <NUM> involves determining, from a set of measurements, a periodic change in amplitude. <FIG> is discussed with respect to <FIG>, which illustrates exemplary waveforms associated with heart rate.

<FIG> depicts examples of waveforms associated with the method described in <FIG>, according to certain aspects of the present invention. <FIG> depicts four graphs: graph <NUM>, graph <NUM>, graph <NUM>, and graph <NUM>.

Graph <NUM> includes waveform <NUM>, which is an example of a returned light signal. Waveform <NUM> represents an amplitude of returned light over time. As can be seen, waveform <NUM> is a sawtooth-like waveform. Waveform <NUM> can include a fundamental and one or more harmonics. Waveform <NUM> has period <NUM>, which can be identified by sensor application <NUM>.

At block <NUM>, method <NUM> involves identifying the periodic change in amplitude as a heart rate having an identical periodicity. Period <NUM> can indicate a period of a heart rate. Different approaches can be used to determine the heart rate. For example, time domain approaches or frequency-domain approaches can also be used.

For example, by using a time-domain approach, sensor application <NUM> can identify either two minima or two maxima in waveform <NUM>. Sensor application <NUM> determines a time between the two minima or two maxima. The period indicates the period of the heart rate, therefore heart rate = <NUM> / period. Graph <NUM> includes waveform <NUM>, which represents a fundamental component of waveform <NUM> having period <NUM>.

Waveform <NUM> can be identified in the time domain or the frequency domain. Frequency domain approaches involve identifying aptitude peaks for a specific frequency that matches the criteria of a heart rate. Sensor application <NUM> performs a Fourier transform on waveform <NUM>, resulting in waveform <NUM>. From waveform <NUM>, sensor application <NUM> selects and analyzes a particular frequency component. Graph <NUM> includes waveform <NUM>, which represents a frequency-domain representation of waveform <NUM>.

Different criteria can be used for selecting the frequency component that indicates a heart rate. For example, the relevant frequency component can be the frequency component with the lowest frequency. In other cases, perhaps due to lowfrequency noise, the relevant frequency component can be the component with the highest energy.

In some aspects, sensor application <NUM> checks multiple frequency components and before selecting the component, verifies that the component is reasonable (within an expected range) for a heart rate. This approach helps filter out data caused by noise. Heart rate can vary by age. For example, an infant's heart rate can be between <NUM>-<NUM> beats/min. For example, from <NUM> to <NUM> beats per minute. For example, a newborn infant can have a heart rate of <NUM>-<NUM> minutes but a school age child can have a heart rate between <NUM>-<NUM> beats per minute.

Continuing the example, graph <NUM> depicts waveform <NUM>, which represents a filtered frequency-domain representation of waveform <NUM>. Waveform <NUM> is filtered by filter <NUM>. Filter <NUM> represents a band-pass filter around the peak that has the highest energy. Filter <NUM> can be a digital filter.

In an aspect, sensor application <NUM> can determine that an amplitude of a particular selected frequency is below a threshold, indicating that the signal is of insufficient quality. In this case, sensor application <NUM> can wait for a threshold amount of time and pulse the light source again and sample the returned light, or change to a different geometries.

At block <NUM>, method <NUM> involves identifying a periodic change in heart rate as a respiratory rate. When a human is respiratory in, the heart rate goes up and when a human is respiratory out, the heart rate goes down slightly. Sensor application <NUM> can identify this change from the heartrate detected at block <NUM> with a sufficient amount of measurements. Different approaches can be used. Examples include detecting a modulation of heart rate or using an envelope of the waveform representing the returned light. For example, the envelope modulates at the frequency of the respiratory rate. By analyzing changes in the envelope, sensor application <NUM> determines a respiratory rate.

In an aspect, sensor application <NUM> can verify measured heart rates against an expected heart rate. For example, sensor application <NUM> accesses a range of expected heart rates. Responsive to determining that the identified heart rate is outside the range of expected heart rates, sensor application <NUM> obtains an additional set of measurements of light. If the additional measurement of light results in a new measured heart rate that is within the range of expected heart rates, then sensor application <NUM> need not take any further action. If the new measured heart rate is outside a range of expected heart rates, however, then sensor application <NUM> can send an alert to an external device or perform another action.

In yet another aspect, sensor application <NUM> can correlate a detected respiratory rate with sensor data from inertial measurements. For example, accelerometer data can indicate abdominal movement associated with respiration. If the abdominal movements do not correlate with the detected respiratory rate, then sensor application <NUM> can confirm the respiratory rate with an additional set of optical measurements, or take another action.

In another aspect, sensor application can combine respiratory rate with inertial sensor measurements to detect a stage of sleep of a wearer. Stages of sleep can include awake, asleep, and gradients in-between. For example, by providing predictive model <NUM> inertial measurement and respiratory data, predictive model <NUM> can determine when an wearer is transitioning from a first sleep stage a second sleep stage. Such a determination can be useful, for example, to warn caregivers to be especially quiet because a wearer may be more likely to wake up during the transition. In other cases, such determinations can help caregivers know when not to attend to a wearer so that the wearer can learn not to wake up when transitioning between sleep stages. Deep sleep can be identified by a reduced heart rate and respiratory rate.

In some aspects, different or multiple sources and optical receivers may be employed at different locations within the article to better detect heart rate and/or respiratory rate. Configurations of light sources and optical receivers can be referred to as geometries. An example of a sensor configuration that facilitates multiple geometries is depicted in <FIG>.

<FIG> depicts an example configuration a color detector cell configurable with geometries, according to certain aspects of the present invention. <FIG> depicts detector module <NUM>, which includes light sources <NUM>-<NUM> and optical receiver <NUM>. For example purposes, thirteen light sources and one receiver are shown. But any number of light sources and receivers are possible. Detector module <NUM> is placed on an article such that one or more of light sources <NUM>-<NUM> can shine through the article. Each light source or optical receiver can have a different optical filter and/or can be tuned for a different wavelength.

As can be seen, some light sources, e.g., light sources <NUM> and <NUM>, are further away from optical receiver <NUM>. Therefore, with respect to optical receiver <NUM>, light sources <NUM> and <NUM> provide a greater radius of light than light sources closer to a center such as light source <NUM>.

Sensor application <NUM> can select a suitable combination of light source and optical receiver by determining an amount of returned light and comparing the returned light to expected norms. For example, if no identifiable highest-energy frequency peak exists, then sensor application <NUM> determines there is too much noise, then sensor application <NUM> can select a light source and receiver pair that provides a highest signal quality.

In an aspect, sensor application <NUM> can also determine a volume or presence of moisture (e.g., urine) present in a diaper. Based on the determined volume, sensor application <NUM> can then select a different geometry due to thickness caused by moisture in the diaper. More specifically, if moisture is present (for example detected by a lower than expected energy level of returned light), than then sensor application <NUM> may use a light source on an outer ring, e.g., light source <NUM> or <NUM>. Conversely, if no moisture is present, then sensor application <NUM> may use a light source closer to the optical receiver <NUM>, e.g., light source <NUM>.

Color calibration can be performed on each light source and optical receiver pair. For example, sensor application <NUM> can convert the red, green, and infrared levels to hue, saturation, and lightness/value and perform calculations on the hue, saturation, and lightness/value. Color calibration can be implemented via a table. For example, for a given triple of red, green, and infrared, adjust the values by certain amount. Color calibration can also be performed in a different domain such as hue, saturation, and lightness, or hue, saturation, and value.

Aspects of the present invention can sense heart rate while a wearer is moving. By using measurements gathered from inertial sensor <NUM>, sensor application <NUM> can determine that a wearer is moving, is not moving, or a specific level of movement. A determination of movement can be useful in multiple cases.

For example, if the wearer is moving, then light measurements may be incorrect. In this case, sensor application <NUM> can receive two streams of data, one from the optical receiver and another from the accelerometer. By using motion compensation, sensor application <NUM> can remove any motion artifacts from the optical waveform, thereby resulting in an accurate heart rate or respiratory rate measurement. This can be performed by analyzing common elements between the optical signal and the accelerometer signal, in either time domain or frequency domain, and subtracting this common element from the optical signal. For example, the optical signal may contain artifacts due to a baby swing. The accelerometer signal also contains the swing motion, and can provide the swing frequency. Then, the optical signal can remove signal contents of such frequency to eliminate the motion artifact.

In an example, sensor application <NUM> determines that data samples indicate movement of a subject in proximity with the article. Sensor application <NUM> correlates the data samples with the measurements of light and removes, from the plurality of measurements of light, a contribution of the movement.

In another example, if the wearer is asleep, then it may be expected that respiratory rates are lower. An inertial measurement sensor can independently verify respiratory rate while the wearer is asleep. For example, an inertial measurement sensor can obtain a set of samples from which a periodicity can be measured that corresponds to respiratory rate. This respiratory rate can be compared to a respiratory rate obtained via optical measurements.

<FIG> is a diagram depicting an example computing system for performing functions related to sensing, according to certain aspects of the present disclosure. Some or all of the components of the computing system <NUM> can belong to the microcontroller <NUM> or the processor <NUM> of <FIG>. For example, the sensor application <NUM> may operate on the computing system <NUM>. The computing system <NUM> includes one or more processors <NUM> communicatively coupled to one or more memory devices <NUM>. The processor <NUM> executes computer-executable program code, which can be in the form of non-transitory computer-executable instructions, stored in the memory device <NUM>, accesses information stored in the memory device <NUM>, or both. Examples of the processor <NUM> include a microprocessor, an application-specific integrated circuit ("ASIC"), a field-programmable gate array ("FPGA"), or any other suitable processing device. The processor <NUM> can include any number of processing devices, including one.

The memory device <NUM> includes any suitable computer-readable medium such as electronic, optical, magnetic, or other storage device capable of providing a processor with computer-readable instructions or other program code. Non-limiting examples of a computer-readable medium include a magnetic disk, a memory chip, a ROM, a RAM, an ASIC, optical storage, magnetic tape or other magnetic storage, or any other medium from which a processing device can read instructions. The instructions may include processor-specific instructions generated by a compiler or an interpreter from code written in any suitable computer-programming language, including, for example, C, C++, C#, Visual Basic, Java, Python, Perl, JavaScript, and ActionScript.

The computing system <NUM> may also include a number of external or internal devices such as input or output devices. For example, the computing system <NUM> is shown with an input/output ("I/O") interface <NUM> that can receive input from input devices or provide output to output devices. A bus <NUM> can also be included in the computing system <NUM>. The bus <NUM> can communicatively couple one or more components of the computing system <NUM> and allow for communication between such components.

The computing system <NUM> executes program code that configures the processor <NUM> to perform one or more of the operations described above with respect to <FIG>. The program code of the sensor application <NUM>, which can be in the form of non-transitory computer-executable instructions, can be resident in the memory device <NUM> or any suitable computer-readable medium and can be executed by the processor <NUM> or any other one or more suitable processor. Execution of such program code configures or causes the processor(s) to perform the operations described herein with respect to the microcontroller <NUM>. In additional or alternative aspects, the program code described above can be stored in one or more memory devices accessible by the computing system <NUM> from a remote storage device via a data network. The microcontroller <NUM> and any processes can use the memory device <NUM>. The memory device <NUM> can store, for example, additional programs, or data used by the applications executing on the processor <NUM> such as the sensor application <NUM>.

The computing system <NUM> can also include at least one network interface <NUM>. The network interface <NUM> includes any device or group of devices suitable for establishing a wired or wireless data connection to one or more data networks. Non-limiting examples of the network interface <NUM> include an Ethernet network adapter, WiFi network, Bluetooth, or Bluetooth Low Energy (BLE), a modem, or the like. The computing system <NUM> is able to communicate with one or more other computing devices or computer-readable data sources via a data network using the network interface <NUM>.

Unless specifically stated otherwise, it is appreciated that throughout this specification discussions utilizing terms such as "processing," "computing," "calculating," "determining," and "identifying" or the like refer to actions or processes of a computing device, such as one or more computers or a similar electronic computing device or devices, that manipulate or transform data represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the computing platform.

Claim 1:
A wearable sensor system (<NUM>, <NUM>) for use in conjunction with an article (<NUM>, <NUM>), the wearable sensor system comprising:
a plurality of light sources (<NUM>);
a photodetector (<NUM>);
a non-transitory computer-readable medium (<NUM>) storing computer-executable instructions; and
a processing device (<NUM>) communicatively coupled to the non-transitory computer-readable medium for executing the computer-executable instructions, wherein executing the computer-executable instructions configures the processing device to perform operations comprising:
obtaining a plurality of measurements of light by, for each measurement:
causing a first light source of the plurality of light sources to transmit a pulse of light through the article (<NUM>) to an area of skin (<NUM>), wherein the first light source comprises a first geometry; and
determining, via the photodetector, a measurement of light (<NUM>) returned from the article;
determining, from the plurality of measurements of light, a periodic change in an amplitude of the returned light; and
identifying the periodic change in amplitude as a heart rate having an identical periodicity,
characterised in that:
the identifying comprises:
determining an energy level of the plurality of measurements of light; and
responsive to determining that the energy level is lower than a threshold, causing a second light source of the plurality of light sources to transmit an additional pulse of light through the article to the area of skin, wherein the second light source comprises a second geometry that is different from the first geometry.