Abstract: There is disclosed a substrate including at least one photodetector, the photodetector having a first active area on a first surface of the substrate and a second active area on a second surface of the substrate, wherein the photodetector is provided with a conductive via electrically isolated from the substrate, said conductive via extending through the photodetector from the first surface of the substrate to the second surface of the substrate for connecting the first active area to the second surface of the substrate, the second surface providing electrical connections for the first and second active areas of the photodetector.

Abstract: A method for finding holes, and other related defects and measuring characteristics of sheets of industrial material. Optical detections systems are constantly plagued by intense ambient light and challenged in accuracy. The invention exhibits a defect detection method and apparatus that is resistant to intense ambient light and is capable of inspecting sheets of material (410, 510, 610, 710) continuously, without integration of long periods. In the invention, synchronous detection between the optical transmitters and receivers is utilized. The invention is applicable for inspecting and measuring materials like paper, metal, rubber, plastic, aluminum foil, copper foil, film, coated metal sheet or any other sheet-like material that could run on a production line. The invention is also applicable for finding special defects like holes, pinholes, scratches, spots, cracks, edge faults, streaks, surface faults or any other conceivable defects.