第15讲 时变电磁场(3)

分别取其实部和虚部, 得

????SS1??*12?1??*?Re?E?H??ds??E?Jdv???EdvVV222??12??1??*??12Im?E?H??ds?2????H??E?dv

V24???4?

11222?(?H??E)代表单位体积中电磁场储能的最大时44间变化率。

说明如下：

设

E(t)?Ecos(?t??e)H(t)?Hcos(?t??m)

则单位体积内,电场磁场储能瞬时值为：

12122We??Ecos(?t??e)??E[1?cos(2?t?2?e)]2411222Wm??Hcos(?t??m)??H[1?cos(2?t?2?e)]

24

其一周期内平均值为：

WWaveavm1?T1?T12Wdt??Ee?04T12Wdt??H m?04T单位体积电、磁场储能瞬时值为

?12?1?2(Wm?We)??2???Hsin(2?t?2?m)??Esin(2?t?2?e)??t4?4?

由于储能是电磁场的无功功率部分, 其磁场与电场的相位将是正交的, 即

?m??e??2，

?(Wm?We)?t12?1?2?2???Hsin(2?t?2?e)??Esin(2?t?2?e)?

4?4?