Patent ID: 8256294

Claim:
A grammage detection sensor which detects a grammage of a recording medium using an ultrasonic wave, the grammage detection sensor comprising: a transmitting unit configured to transmit the ultrasonic wave; and a receiving unit including a first vibration member configured to receive the ultrasonic wave that is transmitted from the transmitting unit and passes through the recording medium, wherein the receiving unit includes a guide member configured to guide the ultrasonic wave that passes through the recording medium to the first vibration member, and wherein a length from a surface of the first vibration member to a plane including an end plane of the guide member along a line that passes through a center of the first vibration member and is perpendicular to the first vibration member is approximately n times of one-half wavelength of the ultrasonic wave transmitted from the transmitting unit, and n is an integer of one or greater.