Method and apparatus for examining a sheet- or card-shaped value document with a security feature with one or more cavities

describes a method for assaying a sheet- or card-shaped value document with a security feature, comprising one or more formed in the document of value cavities, its or their length exceeds at least one respectively predetermined direction 10 microns, wherein said spatially resolved transmission values ​​for the transmission of ultrasonic are determined in a predetermined frequency range, and it is checked using the transmission values, whether a predetermined number of transmission values ​​is greater than a predetermined Transmissionsschwellwert.