Patent ID: 8521449

Claim:
A mobile sensing device, comprising: an airflow sensing system having a plurality of airflow sensing units arranged in a grid, each of the airflow sensing units comprising: a first air passage that contains at least one first airflow sensor; a second air passage perpendicular to the first air passage, wherein the second air passage contains at least one second airflow sensor; and a third air passage perpendicular to the first air passage and the second air passage, wherein the third air passage contains at least one third airflow sensor, wherein each of the airflow sensing units is configured to measure airflow direction and velocity in three dimensions, wherein one or more of the at least one first airflow sensor, the at least one second airflow sensor and the at least one third airflow sensor comprise a thermal micro electro mechanical sensor having i) a central leg with a first heater incorporated into a constant temperature feedback loop and ii) a lateral leg with a second heater which, during operation, is powered at constant voltage, and wherein the thermal micro electro mechanical sensor is sensitive to airflow with a velocity distribution across a range of from about 1 cm/s to about 5 m/s; and wherein each of the airflow sensors is configured to be self-heating while having a total power consumption of less than about two milliwatts, wherein each of the airflow sensors comprises two heaters which are configured such that a differential signal is obtained based on a differential resistance between the two heaters which varies depending on a direction of the airflow, and wherein a change in the airflow due to heat dissipated by the airflow sensors does not affect an overall airflow measurement provided by the airflow sensing system.