Patent ID: 7688079

Claim:
An image forming apparatus which comprises an image forming unit for forming an image on a record sheet medium and a detecting apparatus for detecting moisture content of at least a portion of a stack of sheet media, the detecting apparatus comprising: an illuminating unit for illuminating a side of at least a portion of the stack of sheet media with electromagnetic waves; a detecting unit for detecting electromagnetic waves transmitted through or reflected by at least a portion of the stack of sheet media; a memory for storing information about attenuation of electromagnetic waves due to moisture contained in a sheet material; and a comparator for comparing information of the electromagnetic waves detected by the detecting unit with the information in the memory about attenuation of electromagnetic waves due to moisture contained in the sheet medium, and determining moisture content of at least a portion of the stack of sheet media, wherein the information stored in the memory is stored calibration curves, and a maximum amplitude of the transmitted or reflected electromagnetic waves detected by the detecting unit is compared with the stored calibration curves, and wherein the calibration curves are composed of three parameters; transmission distance of the electromagnetic waves through at least a portion of the stack of sheet media, maximum amplitude of the transmitted or reflected electromagnetic waves detected by the detecting unit, and moisture content of the sheet medium.