| CPC A61B 5/0873 (2013.01) [A61B 5/0082 (2013.01); A61B 5/6803 (2013.01)] | 18 Claims |

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1. A head mounted device, comprising:
a housing;
one or more interferometric sensors disposed in the housing, each of the one or more interferometric sensors configured to:
emit electromagnetic radiation towards an expected airflow path for respiration of a user; and
generate one or more interferometric signals including information about particle movement in the expected airflow path for respiration of the user, wherein:
the one or more interferometric sensors comprise a first interferometric sensor and a second interferometric sensor; and
the first interferometric sensor includes one or more of a focal length, a depth of field, a numerical aperture, an angle of incidence with respect to a plane located in the expected airflow path for respiration of the user, and one or more characteristics of the electromagnetic radiation emitted therefrom that is different from the second interferometric sensor.
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