METHOD OF REDUCING MOTION ARTIFACTS ON WEARABLE OPTICAL SENSOR DEVICES

• US 20160296174A1
• Filed: 12/05/2013
• Published: 10/13/2016
• Est. Priority Date: 12/05/2013
• Status: Active Application

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: ISIKMAN, Serhan O., KESTELLI, Nevzat Akin, LAND, Brian R., WANG, Albert
• Application Number:
  US15/100,626
• Publication Number:
  US 20160296174A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2562/0233 Special features of optical sensors or probes classified in A61B5/00
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6844 Monitoring or controlling distance between sensor and tissue
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7475 User input or interface means, e.g. keyboard, pointing device, joystick

Abstract

A PPG signal may be obtained from a pulse oximeter, which employs a light emitter and a light sensor to measure the perfusion of blood to the skin of a user. However, the signal may be compromised by noise due to motion artifacts. That is, movement of the body of a user may cause a gap between the tissue of a user and the electronic device, introducing noise to the signal. Further, the noise introduced may vary depending on how close the light emitter is to the light sensor. Accordingly, to address the presence of motion artifacts, examples of the present disclosure can receive light information at a light sensor from two different light emitters, each at a different distance from the light sensor along a surface of the electronic device, one relatively close to the light sensor and one relatively far from the light sensor.

Claims

1. A method of an electronic device including a plurality of light emitters and a light sensor, the method comprising:

emitting light from a first light emitter;

receiving at the light sensor first light information from the first light emitter;

emitting light from a second light emitter;

receiving at the light sensor second light information from the second light emitter;

computing first and second scaling factors based on the first and second light information; and

computing a heart rate signal based on the first light information added to the second light information, the first and second light information each being scaled by the respective first and second scaling factors.

2. The method of claim 1, wherein the first light emitter is located a first distance from the light sensor along a surface of the electronic device, and the second light emitter is located a second distance from the light sensor along a surface of the electronic device;

wherein the second distance is greater than the first distance.

3. The method of claim 1, wherein an emission pattern of the first light emitter has a first angle of emission and an emission pattern of the second light emitter has a second angle of emission;

wherein the second angle of emission is more acute than the first angle of emission.

4. The method of claim 1, wherein the computing of the first and second scaling factors includes optimization based on a previously computed heart rate signal.

5. The method of claim 1, wherein computing the heart rate signal includes cancelling noise due to changes in a gap between the electronic device and tissue of a user.

6. The method of claim 1, wherein the first light emitter emits light having a first wavelength and the second light emitter emits light having a second wavelength, the first wavelength being different from the second wavelength.

7. The method of claim 1, wherein the first light emitter emits light during a first period and the second light emitter emits light during a second period different from the first period, and wherein the first light information is received during the first period and the second light information is received during the second period.

8-14. -14. (canceled)

15. An electronic device, comprising:

a first light emitter configured to emit light;

a first light sensor configured to receive first light information from the first light emitter;

a second light emitter configured to emit light, wherein the first light sensor is further configured to receive second light information from the second light emitter; and

a processor configured to;

compute first and second scaling factors based on the first and second light information; and

compute a heart rate signal based on the first light information added to the second light information, the first and second light information each being scaled by the respective first and second scaling factors.

16. The electronic device of claim 15, wherein the first light emitter is located a first distance from the first light sensor along a surface of the electronic device, and the second light emitter is located a second distance from the first light sensor along the surface of the electronic device;

wherein the second distance is greater than the first distance.

17. The electronic device of claim 15, wherein an emission pattern of the first light emitter has a first angle of emission and an emission pattern of the second light emitter has a second angle of emission;

wherein the second angle of emission is more acute than the first angle of emission.

18. The electronic device of claim 15, wherein the computation of the first and second scaling factors includes optimization based on a previously computed heart rate signal.

19. The electronic device of claim 15, wherein the computation of the heart rate signal includes cancelling noise due to changes in a gap between the electronic device and a tissue of a user.

20. The electronic device of claim 15, wherein the first light emitter emits light having a first wavelength and the second light emitter emits light having a second wavelength, the first wavelength being different from the second wavelength.

21. The electronic device of claim 15, wherein the first light emitter emits light during a first period and the second light emitter emits light during a second period different from the first period, and wherein the first light information is received during the first period and the second light information is received during the second period.

25. The electronic device of claim 15, further comprising:

a second light sensor configured to receive third light information from the first light emitter and configured to receive fourth light information from the second light emitter,

wherein the processor is further configured to;

compute third and fourth scaling factors based on the third and fourth light information, and

wherein the heart rate signal is further computed based on the third and fourth light information each being scaled by the respective third and fourth scaling factors.

26. The electronic device of claim 25, further comprising:

a third light emitter configured to emit light;

a third light sensor configured to receive fifth light information from the third light emitter; and

a fourth light emitter configured to emit light, wherein the third light sensor is further configured to receive sixth light information from the fourth light emitter,

wherein the processor is further configured to;

compute fifth and sixth scaling factors based on the fifth and sixth light information, and

wherein the heart rate signal is further computed based on the fifth and sixth light information being scaled by the respective fifth and sixth scaling factors.

27. The electronic device of claim 26, further comprising:

a fourth light sensor configured to receive seventh light information from the third light emitter and configured to receive eighth light information from the fourth light emitter,

wherein the processor is further configured to;

compute seventh and eighth scaling factors based on the seventh and eighth light information, and

wherein the heart rate signal is further computed based on the seventh and eighth light information each being scaled by the respective seventh and eighth scaling factors.

28. The electronic device of claim 27, wherein an optical axis of the first light emitter, second light emitter, first light sensor, and second light sensor intersects with an optical axis of the third light emitter, fourth light emitter, third light sensor, and fourth light sensor.

29. The electronic device of claim 15, wherein the computation of the first and second scaling factors includes optimization based on previously computed first and second light information.

22. A method of reducing noise in a reflected light signal, the method comprising:

receiving a plurality of reflected light signals generated from a plurality of light emitters and reflected by a first surface; and

computing the reflected light signal from the plurality of reflected light signals while canceling noise in the computed reflected light signal due to estimated changes in a gap between the plurality of light emitters and the first surface based on the plurality of reflected light signals.

23-24. -24. (canceled)