Handling obstructions and transmission element contamination for self-mixing particulate matter sensors
A portable electronic device is operable in a particulate matter concentration mode where the portable electronic device uses a self-mixing interferometry sensor to emit a beam of coherent light from an optical resonant cavity, receive a reflection or backscatter of the beam into the optical resonant cavity, produce a self-mixing signal resulting from a reflection or backscatter of the beam of coherent light, and determine a particle velocity and/or particulate matter concentration using the self-mixing signal. The portable electronic device is also operable in an absolute distance mode where the portable electronic device determines whether or not an absolute distance determined using the self-mixing signal is outside or within a particulate sensing volume associated with the beam of coherent light. If not, the portable electronic device may determine a contamination and/or obstruction is present that may result in inaccurate particle velocity and/or particulate matter concentration determination.
1. A portable electronic device that senses particulate matter, comprising:
at least one optically transparent material;
at least one optical element;
a self-mixing interferometry sensor configured to emit a beam of coherent light from an optical resonant cavity through the at least one optically transparent material via the at least one optical element to illuminate an object, receive a reflection or a backscatter of the beam of coherent light into the optical resonant cavity, and produce a self-mixing signal resulting from self-mixing of the beam of coherent light within the optical resonant cavity; and
a processor configured to:
operate in an absolute distance mode by:
determining an absolute distance to the object using the self-mixing signal; and
upon determining that the absolute distance corresponds to an area inside of a sensing volume associated with the beam of coherent light, switching to a particulate matter concentration determination mode; and
operate in the particulate matter concentration determination mode by:
determining a particle velocity using the self-mixing signal; and
determining a particulate matter concentration using the particle velocity and a particle count.
2. The portable electronic device of claim 1 , wherein the processor determines the particle velocity using:
a first self-mixing signal measured from a first beam of coherent light; and
a second self-mixing signal measured from a second beam of coherent light.
3. The portable electronic device of claim 2 , wherein the processor determines the particle velocity using a known angle between the first beam of coherent light and the second beam of coherent light.
4. The portable electronic device of claim 2 , wherein:
the self-mixing interferometry sensor comprises a first vertical-cavity surface-emitting laser and a second vertical-cavity surface-emitting laser;
the first vertical-cavity surface-emitting laser emits the first beam of coherent light; and
the second vertical-cavity surface-emitting laser emits the second beam of coherent light.
5. The portable electronic device of claim 2 , wherein:
the self-mixing interferometry sensor is a single vertical-cavity surface-emitting laser; and
the at least one optical element splits the beam of coherent light into the first beam of coherent light and the second beam of coherent light.
6. The portable electronic device of claim 1 , wherein the at least one optical element focuses the beam of coherent light at a location corresponding to the sensing volume.
7. The portable electronic device of claim 1 , wherein the processor switches from the particulate matter concentration determination mode to the absolute distance mode upon determining the particulate matter concentration discards the particulate matter concentration upon determining the particulate matter concentration is inaccurate.