来自《耶鲁大学开放课程：生物医学工程探索 第21集 第21集》
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you have to put the transducer,你就必须将传感器 -
which is producing the sound waves,这个产生声波的装置 -
right up against the skin.紧贴在皮肤上 -
You don't want a gap of air in between and你不希望传感器和身体间存在空气间隙 -
that's why you put the gel.这就是涂凝胶的原因 -
Now, this transducer has a special material in it在传感器内部有一种特殊材料 -
that's called a piezoelectric material.它叫做压电材料 -
Piezoelectric materials have the property压电材料有这样一种特性 -
that if you put a voltage through them如果在材料两端加上电压 -
they resonate, or they physically move.它就会产生共振 或产生位移 -
In addition, if you stimulate a piezoelectric material此外 如果你用振动波 -
with a moving wave,激发压电材料