| 摘要 |
A device for coding an object where the codes themselves are in the form of milled holes/indentations, and a method for reading the codes where the object with a code is placed under an ultrasound sender and receiver respectively. The holes/indentations (3') are provided in the object itself or on a material which is attached to the object, as the holes/indentations (3') are facing away from the object, and the holes/indentations (3') are covered by or filled with a material respectively. This material may be a thin film (2') in the size range of 0,1-3 mm or made by a surface treatment in the form of varnish/paint, plastic, laminate, wood or metal. The code may be devised in a material, i.e. thin film being attached to the object, and covered and thus hidden. The codes may be made by milling or stamping on the material of the object or on the material attached to the object. The ultrasound sender unit is devised to send waves or a pulsed wave, forming standing waves, as the wave length Ld satisfies the relation a = (n/2) Ld where a is the thickness of the material hiding the code so that the wave which hits areas without holes becomes resonant, or the wave length where a + da = (n/2) Ld, where da is the depth of the hole so that the wave hitting the area with indentations/holes becomes resonant. |
