| 摘要 |
PCT No. PCT/GB89/01298 Sec. 371 Date Jun. 19, 1991 Sec. 102(e) Date Jun. 19, 1991 PCT Filed Oct. 31, 1989 PCT Pub. No. WO90/05299 PCT Pub. Date May 17, 1990.Particular non-metallic materials are detected by a recognition of the way in which their electrical properties vary with the frequency of an applied alternating electric field. In one method a body being tested is subjected to electromagnetic radiation at each of a plurality of different frequencies, the pattern of variation of the body's reflectivity is evaluated and compared with stored information on the conductivity/frequency characteristic of the non-metallic material to be deleted. In another method a body being tested is subjected to a burst of electromagnetic energy and a measurement is made of the time taken for the body to retransmit energy absorbed from the burst.
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