as) United States
`a2) Patent Application Publication 0) Pub. No.: US 2016/0058312 Al
` HANet al. (43) Pub. Date: Mar.3, 2016
`
`
`
`US 20160058312A1
`
`(54) MULTIPLE LIGHT PATHS ARCHITECTURE
`AND OBSCURATION METHODS FOR
`SIGNAL AND PERFUSION INDEX
`OPTIMIZATION
`
`(72)
`
`(71) Applicant: Apple Inc., Cupertino, CA (US)
`:
`Loar
`Inventors: Chin San HAN, Mountain View, CA
`(US), Ueyn BLOCK,Menlo Park, CA
`(US); Brian R. LAND, Woodside, CA
`(US); Newzat Akin KESTELLI, San
`Jose, CA (US); Serhan ISIKMAN,
`Sunnyvale, CA (US); Albert WANG,
`Sunnyvale, CA (US); Justin SHI,
`Sunnyvale, CA (US)
`
`(21) Appl. No.: 14/569,235
`
`(2006.01)
`(2006.01)
`
`A6IB 5/00
`GOIN 21/55
`(52) U.S.CL
`CPC oe AG6IB 5/02433 (2013.01); GOIN 21/55
`(2013.01); GOIN 21/4738 (2013.01); A6IB
`5/7264 (2013.01); AGIB 5/6898 (2013.01);
`A61B 5/7203 (2013.01); GOIN 2201/062
`(2013.01); GOIN 2201/068 (2013.01); GOIN
`2201/0638 (2013.01); A61B 2562/0233
`(2013.01)
`
`(57)
`
`ABSTRACT
`
`A photoplethysmographic (PPG) device is disclosed. The
`PPGdevice can include one or morelight emitters and one or
`more light sensors to generate the multiple light paths for
`measuring a PPGsignal and perfusion indices of a user. The
`multiple light paths between each pair of light emitters and
`light detectors can include different separation distances to
`generate both an accurate PPG signal and a perfusion index
`value to accommodate a variety of users and usage condi-
`Related U.S. Application Data
`(60) Provisional application No. 62/044,515, filed on Sep._tions. In some examples, the multiple light paths can include
`2, 2014.
`the same separation distances for noise cancellation due to
`artifacts resulting from, for example, tilt and/or pull of the
`device, a user’s hair, a user’s skin pigmentation, and/or
`motion. The PPG device can further include one or more
`
`(22)
`
`Filed:
`
`Dec. 12, 2014
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`A6IB 5/024
`GOIN 21/47
`
`(2006.01)
`(2006.01)
`
`lenses and/orreflectors to increase the signal strength and/or
`and to obscure the optical components and associated wiring
`from being visible to a user’s eye.
`
`Device
`
`Lignt Emitter
`406
`
`Light Sensor
`
`A04
`
`1
`
`Light Emitter
`416
`
`APPLE 1074
`Apple v. Masimo
`IPR2022-01291
`
`1
`
`APPLE 1074
`Apple v. Masimo
`IPR2022-01291
`
`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 1 of 13
`
`US 2016/0058312 Al
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`Patent Application Publication
`
`Mar. 3, 2016 Sheet 2 of 13
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`US 2016/0058312 Al
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`Average
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`~ N212
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`
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`intensity
`
`Time
`
`FIG. 2
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 3 of 13
`
`US 2016/0058312 Al
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`Light
`Lignt
`Emitter Sensor
`306
`304
`
`Lignt
`Lignl
`Emitter Sensor
`316
`
`314
`irst ight sensor Cancel noise due to artifacts
`
`First reflected and scattered light
`received by
`
`Pulse wave
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 4 of 13
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`US 2016/0058312 Al
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`400~,
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`406-4]
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 5 of 13
`
`US 2016/0058312 Al
`
`Light
`
`Light
`Sensor
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`Sensor
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`Sensor
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`index
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`Sit S131 OBIT
`Separation Distance
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`FIG. 58
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet6 of 13
`
`US 2016/0058312 Al
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`Device
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`7
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 7 of 13
`
`US 2016/0058312 Al
`
`Light
`Emitter
`606
`
`Light
`Optical
`isolation Sensor
`644
`604
`
`Device
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`7
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`600
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`Optical
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`Emitter
`isolation Sensor
`Device
`606
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 8 of 13
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`US 2016/0058312 Al
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`eign
`mitier
`606
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`solation
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`isolation Sensor
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`- 600
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`
`9
`
`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 9 of 13
`
`US 2016/0058312 Al
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`Device
`700~,
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`Syap A
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`10
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`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 10 of 13
`
`US 2016/0058312 Al
`
`Light
`Path
`
`Light
`
`Light
`
`‘Separation
`
`Emitter|Sensor|Distance
`index
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`Perfusion
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`dt
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`d2
`Separation Distance
`
`dA
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`
`11
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`11
`
`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 11 of 13
`
`US 2016/0058312 Al
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`Light Emitter
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`
`12
`
`

`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 12 of 13
`
`US 2016/0058312 Al
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`

`Patent Application Publication
`
`Mar. 3, 2016 Sheet 13 of 13
`
`US 2016/0058312 Al
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`

`

`US 2016/0058312 Al
`
`Mar.3, 2016
`
`MULTIPLE LIGHT PATHS ARCHITECTURE
`AND OBSCURATION METHODS FOR
`SIGNAL AND PERFUSION INDEX
`OPTIMIZATION
`
`FIELD
`
`[0001] This relates generally to a device that measures a
`photoplethysmographic (PPG)signal, and, moreparticularly,
`to architectures for multiple light paths and obscuration meth-
`ods for PPG signal and perfusion index optimization.
`
`emitter-to-detector separation distances along each path. In
`such examples, the particular configuration of the multiple
`light paths can be optimized for cancellation of noise due to
`artifacts resulting from, for example, tilt and/or pull of the
`device, a user’s hair, a user’s skin pigmentation, and/or
`motion. The PPG device can further include one or more
`
`lenses and/orreflectors to increase the signal strength and/or
`and to obscure the light emitters, light sensors, and associated
`wiring from being visible to a user’s eye.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`BACKGROUND
`
`FIGS. 1A-1C illustrate systems in which examples
`[0006]
`of the disclosure can be implemented.
`[0002] A photoplethysmographic (PPG)signal can be mea-
`[0007]
`FIG.2 illustrates an exemplary PPGsignal.
`sured by PPG systemsto derive corresponding physiological
`[0008] FIG.3A illustrates atop view and FIG.3B illustrates
`signals (e.g., pulse rate). In a basic form, PPG systems can
`a cross-sectional view of an exemplary electronic device
`employalight sourceor light emitter that injects light into the
`including light sensors and light emitters for determining a
`user’s tissue andalight detector to receive light that reflects
`heart rate signal.
`and/or scatters and exits the tissue. The received light
`[0009]
`FIG. 3Cillustrates a flow diagram for canceling or
`includes light with an amplitudethat is modulated as a result
`reducing noise from a measured PPGsignal.
`of pulsatile blood flow (i.e., “signal”) and parasitic, non-
`[0010]
`FIG. 4Aillustrates atop view and FIG.4Billustrates
`signal light with an amplitude that can be modulated (i.e.,
`a cross-sectional view of an exemplary device with two light
`“noise” or “artifacts”) and/or unmodulated (1.e., DC). Noise
`paths for determining a heart rate signal according to
`can be introducedby, for example tilt and/or pull ofthe device
`examples of the disclosure.
`relative to the user’s tissue, hair, and/or motion.
`[0011]
`FIG. 5A illustrates multiple light paths for deter-
`[0003] Fora given light emitter and light detector, the PPG
`mining a heart rate signal according to examples ofthe dis-
`closure.
`pulsatile signal (i.e., detected light modulated by pulsatile
`blood flow) can decrease as the separation distance between
`the light emitter and light detector increases. On the other
`hand,perfusion index(i.e., the ratio ofpulsatile signal ampli-
`tude versus DC light amplitude) can increase asthe separation
`distance between the light emitter and light detector
`increases. Higher perfusion index tends to result in better
`rejection of noise due to motion (i.e., rejection of motion
`artifacts). Therefore, shorter separation distances between a
`light emitter and a light sensor can favor high PPG signal
`strength, while longer separation distances can favor high
`perfusion index (e.g., motion performance). Thatis, a trade-
`off can exist, making it difficult to optimize separation dis-
`tance for particular user skin/tissue types and usage condi-
`tions.
`
`FIG. 5B illustrates a plot of PPG signal strength and
`[0012]
`perfusion index values for multiple light paths with different
`separation distances according to examples of the disclosure.
`[0013]
`FIG. 6A illustrates a top view of an exemplary elec-
`tronic device employing multiple light paths for determining
`a heart rate signal according to examples of the disclosure.
`[0014]
`FIG. 6B illustrates a table of exemplary path
`lengths, relative PPG signal levels, and relative perfusion
`index values for an exemplary electronic device employing
`multiple light paths according to examples of the disclosure.
`[0015]
`FIG. 6C illustrates a cross-sectional view of an
`exemplary electronic device employing multiple light paths
`for determining a heart rate signal according to examples of
`the disclosure.
`
`[0004] Additionally, the PPG system can include several
`light emitters, light detectors, components, and associated
`wiring that may bevisible to a user’s eye, making the PPG
`system aesthetically unappealing.
`
`SUMMARY
`
`[0005] This relates to a PPG device configured with an
`architecture suitable for multiple light paths. The architecture
`can include one or morelight emitters and one or morelight
`sensors to generate the multiple light paths for measuring a
`PPGsignal and a perfusion index ofa user. The multiple light
`paths(i.e., the optical paths formed between eachpairof light
`emitter and light detector) can include different locations
`and/or emitter-to-detector separation distances to generate
`both an accurate PPG signal and perfusion index value to
`accommodate a variety of users and a variety of usage con-
`ditions. In some examples,
`the multiple light paths can
`include different path locations, but the same separation dis-
`tances along each path. In other examples, the multiplelight
`paths can include overlapping, co-linear paths(i.e., along the
`same line) but with different emitter-to-detector separation
`distances along each path. In other examples, the multiple
`light paths can include different path locations and different
`
`FIGS. 6D-6F illustrate cross-sectional views of
`[0016]
`exemplary electronic devices employing multiple light paths
`for determining a heart rate signal according to examples of
`the disclosure.
`[0017]
`FIG. 7A illustrates a top view of an exemplary elec-
`tronic device with eight light paths for determining a heart
`rate signal according to examplesof the disclosure.
`[0018]
`FIG. 7B illustrates a table of light emitter/sensor
`paths and separation distances for an exemplary electronic
`device with eight light paths and four separation distances
`according to examples of the disclosure.
`[0019]
`FIG. 7C illustrates a plot of PPG signal strength and
`perfusion index values for an exemplaryarchitecture with
`eight light paths and four separation distances according to
`examples of the disclosure.
`[0020]
`FIGS. 7D-7F illustrate cross-sectional views of
`exemplary electronic devices employing one or more light
`paths for determining a heart rate signal according to
`examples of the disclosure.
`[0021]
`FIG.8 illustrates an exemplary block diagram of a
`computing system comprising light emitters and light sensors
`for measuring a PPG signal according to examples of the
`disclosure.
`
`15
`
`15
`
`

`

`US 2016/0058312 Al
`
`Mar.3, 2016
`
`FIG. 9 illustrates an exemplary configuration in
`[0022]
`which a device is connected to a host according to examples
`of the disclosure.
`
`DETAILED DESCRIPTION
`
`In the following description of examples, reference
`[0023]
`is madeto the accompanying drawingsin whichit is shown by
`wayofillustration specific examples that can be practiced.It
`is to be understood that other examples can be used and
`structural changes can be made without departing from the
`scope of the various examples.
`[0024] Various techniques and process flow steps will be
`describedin detail with reference to examplesas illustrated in
`the accompanying drawings. In the following description,
`numerousspecific details are set forth in order to provide a
`thorough understanding of one or more aspects and/or fea-
`tures described or referenced herein. It will be apparent, how-
`ever, to one skilled in the art, that one or more aspects and/or
`features described or referenced herein may be practiced
`without some or all of these specific details.
`In other
`instances, well-known process steps and/or structures have
`not been described in detail in order to not obscure some of
`
`the aspects and/or features described or referenced herein.
`[0025]
`Further, although process steps or method steps can
`be described in a sequential order, such processes and meth-
`ods can be configured to work in any suitable order. In other
`words, any sequenceor orderof steps that can be described in
`the disclosure doesnot, in andofitself, indicate a requirement
`that the steps be performedin that order. Further, some steps
`may be performed simultaneously despite being described or
`implied as occurring non-simultaneously (e.g., because one
`step is described after the other step). Morcover, theillustra-
`tion of a process byits depiction in a drawing does not imply
`thatthe illustrated process is exclusiveof othervariations and
`modification thereto, does not imply that theillustrated pro-
`cess or any of its steps are necessary to one or more of the
`examples, and does not imply that the illustrated process is
`preferred.
`[0026] A photoplethysmographic (PPG)signal can be mea-
`sured by PPG systemsto derive corresponding physiological
`signals (e.g., pulse rate). Such PPG systems can be designed
`to be sensitive to changes in bloodin a user’s tissue that can
`result from fluctuations in the amount or volumeof blood or
`blood oxygen contained in a vasculature ofthe user. In a basic
`form, PPG systems can employa light sourceor light emitter
`that injects light into the user’s tissue anda light detector to
`receive light that reflects and/or scatters and exits thetissue.
`The PPGsignalis the amplitude ofthe reflected and/orscat-
`tered light that is modulated with volumetric change in blood
`volumein the tissue. However, the PPG signal may be com-
`promised by noise dueto artifacts. Artifacts resulting from,
`for example,tilt and/or pull ofthe devicerelative to the user’s
`tissue,hair, and/or motion can introducenoise into the signal.
`For example, the amplitude ofreflected light can modulate
`due to the motionofthe user’s hair. As a result, the amplitude
`modulation ofthe reflected light caused by hair motion can be
`erroneously interpreted as a result of pulsatile blood flow.
`[0027] This disclosure relates to a multiple light paths
`architecture and obscuration methods for PPG signal and
`perfusion index optimization. The architecture can include
`one or more light emitters and one or more light sensors to
`generate the multiple light paths to measure a PPG signal and
`a perfusion index of a user. The multiple light paths can
`include different
`locations and/or separation distances
`
`betweenlight emitters and light detectors to generate both an
`accurate PPG signal and perfusion index value to accommo-
`date a variety of users and a variety of usage conditions. In
`some examples, the multiple light paths can include different
`path locations, but the same emitter-to-detector separation
`distances along each path. In some examples, the multiple
`light paths can include overlapping, co-linear paths (2.e.,
`along the same line), but with different emitter-to-separation
`distances along each other. In some examples, the multiple
`light paths can include different path locations and different
`emitter-to-detector separation distances along each path. In
`such examples, the particular configuration of the multiple
`light paths is optimized for noise cancellation due toartifacts
`suchastilt and/orpull ofthe device, a user’s hair, auser’s skin
`pigmentation, and/or motion. In some examples, the device
`can include one or more lenses and/orreflectors to increase
`
`the signal strength and/or to obscure the light emitters, light
`sensors, and associated wiring from being visible to a user’s
`eye.
`[0028] Representative applications ofmethods and appara-
`tus according to the present disclosure are described in this
`section. These examples are being provided solely to add
`context and aid in the understanding of the described
`examples. It will thus be apparent to oneskilled in the art that
`the described examples may be practiced without someorall
`ofthe specific details. In other instances, well-known process
`steps have been described in detail in order to avoid unnec-
`essarily obscuring the described examples. Other applica-
`tions are possible, such that the following examples should
`not be taken as limiting.
`[0029]
`FIGS. 1A-1C illustrate systems in which examples
`of the disclosure can be implemented. FIG. 1A illustrates an
`exemplary mobile telephone 136 that can include a touch
`screen 124. FIG. 1B illustrates an exemplary media player
`140 that can include a touch screen 126. FIG. 1C illustrates an
`
`exemplary wearable device 144 that can include a touch
`screen 128 and can be attached to a user using a strap 146. The
`systems of FIGS. 1A-1C can utilize the multiple light path
`architectures and obscuration methodsas will be disclosed.
`
`FIG.2 illustrates an exemplary PPGsignal. A user’s
`[0030]
`PPGsignal absent of artifacts is illustrated as signal 210.
`However, movementofthe body ofthe user can causethe skin
`and vasculature to expand and contract, introducing noise to
`the signal. Additionally, a user’s hair and/or tissue can change
`the amplitude of light reflected and the amplitude of light
`absorbed. A user’s PPG signal with artifacts is illustrated as
`signal 220. Without extraction of noise, signal 220 can be
`misinterpreted.
`[0031]
`Signal 210 can include light information with an
`amplitude that is modulatedas a result of pulsatile blood flow
`(i.e., “signal’’) and parasitic, unmodulated, non-signal light
`(i.e., DC). From the measured PPG signal 210, a perfusion
`index can be determined. The perfusion index can be the ratio
`of received modulated light (ML) to unmodulated light
`(UML) (2.e., ratio of blood flow modulated signal to static,
`parasitic DC signal) and can give extra information regarding
`the user’s physiological state. The modulated light (ML) can
`be the peak-to-valley value of signal 210, and unmodulated
`light (UML) can bethe zero-to-average (using average 212)
`value of signal 210. As shownin FIG.2, the perfusion index
`can be equal to the ratio of ML to UML.
`[0032] Both the PPG signal and perfusion index can be
`related to an accurate measurementof physiological signals
`such asheart rate. However, the PPG signal can include noise
`
`16
`
`16
`
`

`

`US 2016/0058312 Al
`
`Mar.3, 2016
`
`from modulated light resulting from, for example, motion of
`the user’s tissue and/or the PPG device. Higher perfusion
`index(e.g., higher pulsatile signal and/or lowerparasitic DC)
`can result in better rejection of such motion noise. Addition-
`ally, the intensity of a PPG signalrelative to perfusion index
`can vary for different users. Some users may naturally have a
`high PPG signal, but a weak perfusion index or vice versa.
`Thus, the combination of PPG signal and perfusion index can
`be used to determine physiological signals for a variety of
`users and a variety of usage conditions.
`
`FIG. 3A illustrates atop view and FIG.3B illustrates
`[0033]
`a cross-sectional view of an exemplary electronic device
`including light sensors and light emitters for determining a
`heart rate signal. A light sensor 304 can be located with a light
`emitter 306 on a surface of device 300. Additionally, another
`light sensor 314 can be located or paired with light emitter
`316 on a surface of device 300. Device 300 can be situated
`
`suchthat light sensors 304 and 314 and light emitters 306 and
`316 are proximate to a skin 320 ofa user. For example, device
`300 can be held in a user’s handor strappedto a user’s wrist,
`among other possibilities.
`
`[0034] Light emitter 306 can generate light 322. Light 322
`can be incident on skin 320 andcanreflect back to be detected
`
`by light sensor 304. A portion of light 322 can be absorbed by
`skin 320, vasculature, and/or blood, and a portion of light
`(i.e., light 332) can be reflected back to light sensor 304
`located or paired with light emitter 306. Similarly, light emit-
`ter 316 can generate light 324. Light 324 can be incident on
`skin 320 and can reflect back to be detected by light sensor
`314. A portion of light 324 can be absorbed by skin 320,
`vasculature, and/or blood, and a portion of light (i.e., light
`334) can be reflected back to light sensor 314 located with
`light emitter 316. Light 332 and 334 can include information
`or signals such as a heart rate signal (i.e., PPG signal) due to
`a blood pulse wave 326. Due to a distance between light
`sensors 304 and 314 along the direction of the blood pulse
`wave 326, signal 332 can include a heart rate signal, whereas
`signal 334 can include a time-shifted heart rate signal. A
`difference between signal 332 and signal 334 can depend on
`the distance betweenlight sensors 304 and 314 andthe veloc-
`ity of blood pulse wave 326.
`
`Signals 332 and 334 can include noise 312 due to
`[0035]
`artifacts resulting from, for example,tilt and/or pull of device
`300 relative to skin 320, a user’s hair, and/or a user’s motion.
`One way to account for noise 312 can be to locate light
`sensors 304 and 314 far enough suchthat noise in signals 332
`and 334 may be uncorrelated, but close enough togetherthat
`PPGsignalis corrected in signals 332 and 334. The noise can
`be mitigated by scaling, multiplying, dividing, adding, and/or
`subtracting signals 332 and 334.
`
`FIG. 3C illustrates a flow diagram for canceling or
`[0036]
`reducing noise from a measured PPG signal. Process 350 can
`include light emitted from one or morelight emitters 306 and
`316 (step 352) located on a surface of device 300. Light
`information 332 can be received by light sensor 304 (step
`354), and light information 334 can be received by light
`sensor 314 (step 356). In some examples, light information
`332 and 334 can indicate an amountoflight from light emit-
`ters 306 and 316 that has been reflected and/or scattered by
`skin 320, blood, and/or vasculature of the user. In some
`examples, light information 332 and 334 can indicate an
`amount of light that has been absorbed by skin 320, blood,
`and/or vasculature of the user.
`
`[0037] Based on light information 332 and light informa-
`tion 334, a heart rate signal can be computed by canceling
`noise dueto artifacts (step 358). For example, light informa-
`tion 334 can be multiplied by a scaling factor and added to
`light information 332 to obtain the heart rate signal. In some
`examples, heart rate signal can be computed by merely sub-
`tracting or dividing light information 334 from light informa-
`tion 332.
`
`In some examples, light information 332 and 334
`[0038]
`can be difficult to determine due to a low signal intensity. To
`increase the signal intensity or signal strength, the distance
`between light sensors and light emitters can be reduced or
`minimized such that light travels the shortest distance. Gen-
`erally, fora givenlight emitter and light sensorpair, the signal
`strength decreases with increasing separation distance
`betweenthe light emitter and light sensor. On the other hand,
`the perfusion index generally increases with increasing sepa-
`ration distance between the light emitter and the light sensor.
`A higher perfusion index can correlate to better rejection of
`artifacts caused by, for example, motion. Therefore, shorter
`separation distances between a light emitter and a light sensor
`can favor high PPG signal strength, while longer separation
`distances can favor high perfusion index (e.g., motion perfor-
`mance). That is, a trade-off can exist making it difficult to
`optimize separation distance for particular user skin/tissue
`types and usage conditions.
`[0039]
`To alleviate the trade-off issue between signal
`strength and perfusion index, multiple light paths with vari-
`ous distances between light emitter(s) and light sensor(s) can
`be employed. FIG. 4A illustrates a top view and FIG. 4B
`illustrates a cross-sectional view of an exemplary device with
`twolight paths for determining a heart rate signal according to
`examples of the disclosure. Device 400 can include light
`emitters 406 and 416 anda light sensor 404. Light emitter 406
`can have a separation distance 411 from light sensor 404, and
`light emitter 416 can have a separation distance 413 from
`light sensor 404.
`[0040] Light 422 from light emitter 406 can be incident on
`skin 420 and can reflect back as light 432 to be detected by
`light sensor 404. Similarly, light 424 from light emitter 416
`can be incident on skin 420 and can reflect back as light 434
`to be detected by light sensor 404. Separation distance 411
`can be small compared to separation distance 413, and as a
`result, light information 432 can have a higher PPG signal
`strength than light information 434. Light information 432
`can be employed for applications requiring a higher PPG
`signal strength. Separation distance 413 can be large com-
`pared to separation distance 411, and asa result, light infor-
`mation 434 can have a higher perfusion index than light
`information 432. Light information 434 can be employedfor
`applications requiring a high perfusion index (e.g., motion
`performance). Dueto the different separation distances 411
`and 413, light information 432 and 434 can provide various
`combinations of PPG signals and perfusion index values to
`allow the device to dynamically select light information for
`particular user skin types and usage conditions (e.g., seden-
`tary, active motion,etc.).
`[0041]
`FIG. 5A illustrates multiple light paths for deter-
`mining a heart rate signal according to examples of the dis-
`closure. For enhanced measurement resolution, more than
`twolight paths can be employed. Multiple light paths can be
`formed from a light emitter 506 anda plurality oflight sensors
`such as light sensors 504, 514, 524, 534, and 544. Light
`sensor 504 can have a separation distance 511 from light
`
`17
`
`17
`
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`

`US 2016/0058312 Al
`
`Mar.3, 2016
`
`emitter 506. Light sensor 514 can have a separation distance
`513 from light emitter 506. Light sensor 524 can have a
`separation distance 515 from light emitter 506. Light sensor
`534 can havea separation distance 517 from light emitter 506.
`Light sensor 544 can have a separation distance 519 from
`light emitter 506. Separation distances 511, 513, 515, 517,
`and 519 can be different values.
`
`FIG. 5Billustrates a plot of PPG signal strength and
`[0042]
`perfusion index valuesfor light emitter 506 andlight sensors
`504, 514, 524, 534, and 544. As shown, an intensity of the
`PPGsignal or signal strength can decrease as the separation
`distance betweena light emitter and a light sensor(i.e., sepa-
`ration distances 511, 513, 515, 517, and 519) increases. On
`the other hand, the perfusion index value can increase as the
`separation distance between a light emitter and a light sensor
`increases.
`
`Information obtained from the multiple light paths
`[0043]
`can be used both for applications requiring a high PPGsignal
`strength and applications requiring a high perfusion index
`value. In some examples, information generated from all light
`paths can be utilized. In some examples, information gener-
`ated from some,but notall light paths can be utilized. In some
`examples,
`the “active” light paths can be dynamically
`changed based on the application(s), available power, user
`type, and/or measurementresolution.
`[0044]
`FIG. 6A illustrates a top view and FIG.6Cillustrates
`a cross-sectional view of an exemplary electronic device
`employing multiple light paths for determining a heart rate
`signal according to examples of the disclosure. Device 600
`can include light emitters 606 and 616 and light sensors 604
`and 614 located on a surface of device 600. Light sensors 604
`and 614 can be symmetrically placed, while light emitters 606
`and 616 can be asymmetrically placed. Optical isolation 644
`can be disposed between light emitters 606 and 616 andlight
`detectors 604 and 614. In some examples, optical isolation
`644 can be an opaque material to, for example, reduce para-
`sitic DC light.
`[0045] Light emitters 606 and 616 and light sensors 604
`and 614 can be mounted on or touching component mounting
`plane 648. In some examples, component mounting plane
`648 can be madeof an opaque material(e.g., flex). In some
`examples, component mounting plane 648 can be made of a
`same material as opticalisolation 644.
`[0046] Device 600 can include windows601 toprotectlight
`emitters 606 and 616 and light sensors 604 and 614. Light
`emitters 606 and 616, light detectors 604 and 614, optical
`isolation 644, component mounting plane 648, and windows
`601 can be located within an opening 603 of housing 610. In
`some examples, device 600 can be a wearable device such as
`a wristwatch, and housing 610 can be coupledto a wrist strap
`646.
`
`[0047] Light emitters 606 and 616 andlight detectors 604
`and 614 can be arranged such that there are four light paths
`with four different separation distances. Light path 621 can be
`coupledto light emitter 606 andlight sensor 604. Light path
`623 can be coupledto light emitter 606 and light sensor 614.
`Light path 625 can be coupledto light emitter 616 and light
`sensor 614. Light path 627 can be coupled to light emitter 616
`and light sensor 604.
`[0048]
`FIG. 6B illustrates a table of exemplary path
`lengths, relative PPG signals levels, and relative perfusion
`index valuesfor light paths 621, 623, 625, and 627 of device
`600 according to examples of the disclosure. As shown,rela-
`tive PPG signal levels can have higher values for shorter path
`
`lengths. For example, light path 625 can have a higher PPG
`signal of 1.11 than light path 627 with a PPG signal of 0.31
`due to the shorter path length (i.e., path length of light path
`625 is 4.944 mm, whereas path length of light path 627 is
`6.543 mm). For applications that require high PPG signal
`levels, device 600 can utilize information from light path 625
`or light path 621. However, relative perfusion index values
`can have higher values for longer path lengths. For example,
`light path 623 can have a higherperfusion index value of 1.23
`thanlight path 621 with a perfusion index value of 1.10 due to
`the longer path length (e.g., path length of light path 623 is
`5.915 mm, whereas path length of light path 621 is 5.444
`mm). For applications that require high perfusion index val-
`ues, device 600 can favor information from light path 623
`over information from light path 621. While FIG. 6B illus-
`trates exemplary values for path lengths 621, 623, 625, and
`627 along with exemplary PPGsignal levels and perfusion
`index values, examples of the disclosure are not limited to
`these values.
`
`FIGS. 6D-6F illustrate cross-sectional views of
`[0049]
`exemplary electronic devices employing multiple light paths
`for determining a heart rate signal according to examples of
`the disclosure. As shown in FIG.6D,optical isolation 654 can
`be designed to improve mechanical stability of device 600 by
`providing a larger surface area (than optical isolation 644 of
`FIG. 6C) for windows601 to rest on and/or adhere to. While
`optical isolation 654 can provide a larger surface area for
`windows601, the light may have to travel a longer distance
`through skin 620, and asa result, the signal intensity may be
`reduced. Either the signal quality can be compromised or
`device 600 can compensate by increasing the power(1.e.,
`batt