| 摘要 |
Rime or the like (2) on the surface (A) of a metal object (1) may be sensed by inserting therein a body (3) made of an identical material and having a flush interface (L), exposing it to ultrasonic waves that are reflected by said interface, providing a second body (6) through which ultrasonic waves travel along the same paths as in the first body, and exposing the second body to ultrasonic waves identical to the first ultrasonic waves. A reference layer (8) consisting of a material with an acoustic impedance of 1.4-4.1 MRayl or 72-100 MRayl is positioned on the interface (L') of said second body, and the differences between or sums of the electrical signals corresponding to the ultrasonic waves reflected by both interfaces are determined and used.
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