單項(xiàng)選擇題對(duì)于300mm厚的實(shí)心鋼鍛件,要求探傷靈敏度為Ø2,平底孔當(dāng)量超聲波頻率為2.5MHz,若用底面回波反射法調(diào)節(jié)探傷靈敏度,當(dāng)?shù)酌娣瓷浠夭ㄟ_(dá)到基準(zhǔn)高度后,應(yīng)提高多少的增益量()

A.36dB
B.38dB
C.41dB
D.45dB


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