Particulate Matter Sensors Based on Split Beam Self-Mixing Interferometry Sensors

Patent metadata

Field	Value
Publication number	US-2020319082-A1
Application number	US-202016833199-A
Country	US
Kind code	A1
Filing date	Mar 27, 2020
Priority date	Apr 5, 2019
Publication date	Oct 8, 2020
Grant date	—

Abstract

Various sensors, including particulate matter sensors, are described. One particulate matter sensor includes a self-mixing interferometry sensor and a set of one or more optical elements. The set of one or more optical elements is positioned to receive an optical emission of the self-mixing interferometry sensor, split the optical emission into multiple beams, and direct each beam of the multiple beams in a different direction. The self-mixing interferometry sensor is configured to generate particle speed information for particles passing through respective measurement regions of the multiple beams.

First claim

What is claimed is:

1 . A particulate matter sensor, comprising:
a self-mixing interferometry sensor; and a set of one or more optical elements positioned to receive an optical emission of the self-mixing interferometry sensor, split the optical emission into multiple beams, and direct each beam of the multiple beams in a different direction; wherein: the self-mixing interferometry sensor is configured to generate particle speed information for particles passing through respective measurement regions of the multiple beams.

2 . The particulate matter sensor of claim 1 , wherein the particle speed information comprises unsigned Doppler frequency shifts in a self-mixing interference signal generated by the self-mixing interferometry sensor.

3 . The particulate matter sensor of claim 2 , further comprising circuitry configured to:
perform a frequency domain analysis to extract, from the self-mixing interference signal, the unsigned Doppler frequency shifts; estimate a particle speed using relative orientations of the multiple beams and the unsigned Doppler frequency shifts; estimate, using the particle speed, an air flow volume through the respective measurement regions; count a number of particles passing through the respective measurement regions over a period of time; and estimate a particulate matter concentration using the number of particles and the air flow volume.

4 . The particulate matter sensor of claim 2 , further comprising circuitry configured to:
perform a time-frequency domain analysis to extract, from the self-mixing interference signal, the unsigned Doppler frequency shifts; estimate a particle speed using relative orientations of the multiple beams and the unsigned Doppler frequency shifts; estimate, using the particle speed, an air flow volume through the respective measurement regions; count a number of particles passing through the respective measurement regions over a period of time; and estimate a particulate matter concentration using the number of particles and the air flow volume.

5 . The particulate matter sensor of claim 1 , wherein the set of one or more optical elements focuses each beam of the multiple beams at one of the respective measurement regions.

6 . The particulate matter sensor of claim 1 , further comprising:
circuitry configured to detect an existence of particulate matter using the particle speed information.

7 . The particulate matter sensor of claim 1 , further comprising:
circuitry configured to estimate a particulate matter concentration using the particle speed information.

8 . The particulate matter sensor of claim 1 , wherein the multiple beams consist of three beams.

9 . The particulate matter sensor of claim 1 , wherein the self-mixing interferometry sensor comprises an electromagnetic radiation source integrated with a photodetector.

10 . The particulate matter sensor of claim 1 , wherein:
the self-mixing interferometry sensor comprises an electromagnetic radiation source and a photodetector; the electromagnetic radiation source has a resonant optical cavity bounded by first and second mirrors, with each of the first mirror and the second mirror being at least partially transmissive to a wavelength of electromagnetic radiation; and the electromagnetic radiation source is stacked on the photodetector.

11 . A sensor, comprising:
an electromagnetic radiation source having a resonant optical cavity; and a splitter configured to split an optical emission of the electromagnetic radiation source into a set of multiple beams, and to receive reflections or backscatters of the set of multiple beams and direct the received reflections or backscatters into the resonant optical cavity.

12 . The sensor of claim 11 , wherein each beam of the set of multiple beams is separated from other beams of the set of multiple beams by 120 degrees, in a plane perpendicular to an axis of the optical emission.

13 . The sensor of claim 12 , wherein:
each beam of the set of multiple beams has a secondary axis that diverges from the axis of the optical emission by an angle, θ; and cos 2 (θ)=⅓.

14 . The sensor of claim 11 , wherein the electromagnetic radiation source comprises a vertical-cavity surface-emitting laser (VCSEL).

15 . The sensor of claim 11 , wherein the splitter comprises at least one of: a diffractive element, a holographic element, a periodic sub-wavelength element, or an aperiodic sub-wavelength element.

16 . A method of sensing particulate matter, comprising:
splitting an optical emission received from a self-mixing interferometry sensor into multiple beams; directing each beam of the multiple beams in a different direction; and outputting, from the self-mixing interferometry sensor, particle speed information for particles passing through the multiple beams.

17 . The method of claim 16 , further comprising:
estimating a particulate matter concentration using the particle speed information.

18 . The method of claim 16 , wherein the particle speed information comprises unsigned Doppler frequency shifts in a self-mixing interference signal generated by the self-mixing interferometry sensor.

19 . The method of claim 18 , further comprising:
performing a frequency domain analysis to extract, from the self-mixing interference signal, the unsigned Doppler frequency shifts; estimating a particle speed using relative orientations of the multiple beams and the unsigned Doppler frequency shifts; estimating, using the particle speed, an air flow volume through respective measurement regions of the multiple beams; counting a number of particles passing through the respective measurement regions over a period of time; and estimating a particulate matter concentration using the number of particles and the air flow volume.

20 . The method of claim 19 , further comprising:
focusing each beam of the multiple beams at one of the respective measurement regions.

Assignees

• Apple Inc

Inventors

• Mutlu Mehmet
• Yan Miaolei
• Brown Michael K
• Yeh Richard

Classifications

• G01S7/4916

  using self-mixing in the laser cavity · CPC title

• G01P5/26 Primary

  by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave · CPC title

• G01P5/20

  using particles entrained by a fluid stream (G01P5/22 takes precedence) · CPC title

• G01P5/001

  Full-field flow measurement, e.g. determining flow velocity and direction in a whole region at the same time, flow visualisation · CPC title

• G01S17/58

  Velocity or trajectory determination systems; Sense-of-movement determination systems · CPC title