Particulate matter detection

A process for the manufacture of a particle sensing device for sensing particles entrained in a gas, the particle sensing device comprising:

• a sampling volume through which gas having entrained particles with a distribution of particle sizes including a first size range and a second size range, larger than or smaller than the first size range, is to be flowed;
• a thermophoretic impulse region arranged to apply a thermophoretic impulse to the entrained particles;
• a first sensing region, downstream of the thermophoretic impulse region, the first sensing region having a first sensor,
• wherein, in operation, the thermophoretic impulse, the flow of gas and gravity combine to cause at least some of the particles to follow respective trajectories within the sampling volume, the particle sensing device further comprising:
• an interception region, interposed between the thermophoretic impulse region and the first sensing region, the interception region having an interception unit located to intercept the respective trajectories of particles of the second size range but not respective trajectories of particles of the first size range,
• wherein the first sensor element is located to intercept the respective trajectories of particles of the first size range and to detect particles of the first size range, and the interception unit comprises a second sensor, capable of sensing the particles of the second size range, and
• wherein the process is a MEMS-based fabrication process.

A method of sensing particles entrained in a gas, the method including the steps:

• flowing gas having entrained particles with a distribution of particle sizes including a first size range and a second size range, larger than or smaller than the first size range, through a sampling volume;
• applying a thermophoretic impulse to the entrained particles at a thermophoretic impulse region so that the thermophoretic impulse, the flow of gas and gravity combine to cause at least some of the particles to follow respective trajectories within the sampling volume;
• detecting particles of the first size range at a first sensor element located to intercept the respective trajectories of particles of the first size range at a first sensing region, downstream of the thermophoretic impulse region;
• and
• intercepting the respective trajectories of particles of the second size range but not respective trajectories of particles of the first size range at an interception unit located in an interception region, interposed between the thermophoretic impulse region and the first sensing region, and
• wherein the interception unit comprises a second sensor, capable of sensing the particles of the second size range.