| 摘要 |
PROBLEM TO BE SOLVED: To precisely detect presence of an attached paper in a box with a simple configuration. SOLUTION: A millimeter wave transmitted from an antenna 25 is reflected multiple times on a lid 23 of high millimeter wave reflectivity and a reflective plate 28 while transmitting multiple times a surface 1A of a box 1 of high millimeter wave transmissivity and an attached paper 22, and then received with an antenna 26. Since the transmissivity of millimeter wave of the attached paper 22 is not 100%, though it is high, the millimeter wave attenuates each time it transmits the surface 1A of the box 1 and the attached paper 22, so the larger the frequency of transmission the larger the attenuation amount. Since the reflected wave attenuates only when transmitting the surface 1A of the box 1, the attached paper 22 is not housed in the box 1, the attenuation coefficient falls relative to when the attached paper 22 is housed in the box 1. So, the presence of the attached paper is judged by comparing the reception level with a prescribed reference value.
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