我想請問我們平時看不見的電波是由什麼介質組成？

你所講的電波應該就系講緊電磁波.電磁波以光速行駛。

在真空中也可傳遞.所以是不需要介質的.你亦誤會左介質的意思.....介質即是媒介。電磁波是以電子組成的。

"Electromagnetic field" is just a concept, help us to understand. we cannot measure the E field and B field.

No. Electromagnetic waves are NOT electrons.
Electrons are matter, but electromagnetic waves are pure energy. Electromagnetic waves consist of time varying electric and magnetic fields. It propagates by the mutual interaction (or induction) of the two fields.
Since electromagentic induction is a physical process that doesn't need any medium to take place, electromagentic waves therefore can travel through vacuum.

以空氣分子中的電子作介質組成。