Patent ID: 8225684

Claim:
A method of detecting particulates, the method using a ceramic honeycomb filter comprising trapping holes for trapping said particulates from a gas containing said particulates to detect said particulates trapped in said ceramic honeycomb filter, said trapping holes forming lattices, said method comprising: transmitting an electromagnetic wave to said ceramic honeycomb filter in a plane perpendicular to the longitudinal direction of said trapping hole; receiving said electromagnetic wave after said electromagnetic wave passes through said ceramic honeycomb filter; detecting said particulates trapped in said filter based on a received intensity of said electromagnetic wave, wherein said electromagnetic wave has a frequency of greater than or equal to 0.294 c/a or less than or equal to 1 c/a (a represents a lattice spacing of said trapping holes and c represents the speed of light); and irradiating said electromagnetic wave to said ceramic honeycomb filter wherein said particulates are not trapped and changing an inclined angle of said electromagnetic wave with respect to said lattices so that a received intensity of said electromagnetic wave is increased.