When frequency slightly higher than cutoff, using perturbation method it is to know that tunnel wall wet make attenuation of electromagnetic wave lower not only in rectangular tunnel but also in circular tunnel.

• 当频率略高于隧道截止频率时利用微扰法可知：不论是矩形隧道还是圆形隧道，隧道壁潮湿使电磁波的衰减率降低。