超声束通过介质一段距离后，其声能降低, 称为（     ）

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SQL Error: select id,body,options from ***_enewstiku where sourceid='25738' and id < 2163357 and id<>'2163357' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='25738' and id > 2163357 and id<>'2163357' order by id asc limit 5