Microwave detection of soot content in a particulate trap

The method of detecting the accumulation of conductive particulates being collected from diesel engine exhaust gases on a collection medium formed of dielectric material in a chamber having the property of a microwave resonance cavity, comprising the steps of:

• collecting particulates on the medium in a pattern sufficiently uniformly dispersed throughout the cavity to resemble an artificial dielectric whereby the dielectric loading of the cavity increases with increasing conductive particulate content,
• exciting the cavity with microwave energy, and
• monitoring the response of the cavity to the microwave energy to sense the effective dielectric constant of the material within the cavity thereby providing a measure of the conductive particulate content in the collection medium.

The method of detecting the accumulation of conductive particulates being collected from diesel engine exhaust gases on a honeycomb filter formed of dielectric material in a chamber having the property of a microwave resonance cavity, the filter defining a plurality of parallel passages separated by porous walls having alternate passages blocked at one end and the remaining passages blocked at the other end so that exhaust gases flow through the porous walls, comprising the steps of:

• collecting particulates on the porous walls in a pattern sufficiently uniformly dispersed throughout the cavity to resemble an artificial dielectric whereby the dielectric loading of the cavity increases with increasing conductive particulate content,
• exciting the cavity with microwave energy, and
• monitoring the response of the cavity to the microwave energy to sense the effective dielectric constant of the material within the cavity thereby providing a measure of the conductive particulate content in the collection medium.