Ultrasonic document inspection system

File detecting system, comprising a (12) penetrates through the file transmission along the transmission route checkpoint's transmission system, at least an ultrasonic detecting device is at card, comprising an of the ultrasonic transmission and receiving sensor in opposite side (42,44) is arranged on the transmission circuit, and apparatus for monitoring of the ultrasonic signal processing system for receiving energy converter is received. The ultrasonic attenuating material (300) is arranged around the sensor and facing the transmission circuit, a ultrasonic for absorbing the file as; File guide (312,314); a comparison the attenuating material at low friction coefficient, wherein (300) is arranged end of the attenuating material part, order to preventing the file contact absorption material in use, and the attenuating material is expose of the transmission line, at least close to the sensor.