mica board for commutator

例句：

1. 1. The engineerused a mica board to make thecircuit board.
   工程师使用云母板制作电路板。
2. 2. The insulation on the powerline was made of mica board.
   电力线路的绝缘层是由云母板制成的。
3. 3. The scientist used a mica boardto test the material's electrical conductivity.
   科学家使用云母板测试材料的电导率。