Number of Detectable Gradations in X-Ray Photographs of Cavities Inside 3-D Printed Objects

Abstract

SUMMARYWe evaluated a technique for protecting the copyright of digital data for 3-D printing. To embed copyright information, the inside of a 3-D printed object is constructed from fine domains that have different physical characteristics from those of the object's main body surrounding them, and to read out the embedded information, these fine domains inside the objects are detected using nondestructive inspections such as Xray photography or thermography. In the evaluation, copyright information embedded inside the 3-D printed object was expressed using the depth of fine cavities inside the object, and X-ray photography were used for reading them out from the object. The test sample was a cuboid 46 mm wide, 42 mm long, and 20 mm deep. The cavities were 2 mm wide and 2 mm long. The difference in the depths of the cavities appeared as a difference in the luminance in the X-ray photographs, and 21 levels of depth could be detected on the basis of the difference in luminance. These results indicate that under the conditions of the experiment, each cavity expressed 4 to 5 bits of information with its depth. We demonstrated that the proposed technique had the possibility of embedding a sufficient volume of information for expressing copyright information by using the depths of cavities.

Embedding Information into or onto Additively Manufactured Parts: A Review of QR Codes, Steganography and Watermarking Methods

“…In another study, Suzuki et al [ 37 ] proposed a novel technique for embedding information into AM parts. It started with the construction of fine cavities inside the fabricated object at the same time as the model’s body is being fabricated.…”

“…However, the limitations, such as surrounding noise, slowness and continuous pressing, hindered its usage in a wider range. Another work, published by Suzuki et al [ 37 ], was based on small cavities placed inside the AM part. It was found out that the presence of cavities affected the mechanical strength of the part.…”