Transparent cut detection sensor: Proposal of the security device that makes information leakage by photo/video shooting diffucult

摘要

In this paper, the authors developed a transparent sheet sensor that can detect cutting of the IR emitting sheet. This cut detection sensor is produced by printing a single stroke pattern of ultra-thin conductive lines almost invisible to naked eye on the surface of IR emitting sheet. As the conductive lines are almost invisible, the sheet does not obstruct viewing of the display screen and is unlikely to be unnoticed by a person who considers photo/video shooting. Detection of a cut is made by real time measurement of electrical resistance of the conductive lines or real time monitoring of transmission/reception of information, and the information can be protected by turning off power to the display. The authors produced prototype cut detection sensors using manufacturing technique of the transparent conductive film and knowhow of offset lithography to reduce two adverse effects caused by conductive lines (decrease in visible transmittance and generation of the moiré pattern on the display screen that makes viewing of the screen difficult). Visible transmittance of the prototype sensor was as high as 84.9% and no moiré pattern was observed when it was applied to the display screen. The prototype sensor showed excellent bending resistance (conductive lines will not break when the sensor is bent) and can detect a cut in vertical, horizontal, and oblique directions and can raise alert when the sensor is cut in a length exceeding about 8 mm. Discussions were made for practical application of such cut sensor, and it was found that the sensor can be produced at low cost, is resistant for harsh environment, and is compatible for use with the microrouver.