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工程表格/傅立葉變換性質
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來自 Wikibooks,開放世界中的開放書籍
<
工程表格
訊號
傅立葉變換
么正,角頻率
傅立葉變換
么正,普通頻率
備註
g
(
t
)
≡
{\displaystyle g(t)\!\equiv \!}
1
2
π
∫
−
∞
∞
G
(
ω
)
e
i
ω
t
d
ω
{\displaystyle {\frac {1}{\sqrt {2\pi }}}\int _{-\infty }^{\infty }\!\!G(\omega )e^{i\omega t}d\omega \,}
G
(
ω
)
≡
{\displaystyle G(\omega )\!\equiv \!}
1
2
π
∫
−
∞
∞
g
(
t
)
e
−
i
ω
t
d
t
{\displaystyle {\frac {1}{\sqrt {2\pi }}}\int _{-\infty }^{\infty }\!\!g(t)e^{-i\omega t}dt\,}
G
(
f
)
≡
{\displaystyle G(f)\!\equiv }
∫
−
∞
∞
g
(
t
)
e
−
i
2
π
f
t
d
t
{\displaystyle \int _{-\infty }^{\infty }\!\!g(t)e^{-i2\pi ft}dt\,}
1
a
⋅
g
(
t
)
+
b
⋅
h
(
t
)
{\displaystyle a\cdot g(t)+b\cdot h(t)\,}
a
⋅
G
(
ω
)
+
b
⋅
H
(
ω
)
{\displaystyle a\cdot G(\omega )+b\cdot H(\omega )\,}
a
⋅
G
(
f
)
+
b
⋅
H
(
f
)
{\displaystyle a\cdot G(f)+b\cdot H(f)\,}
線性
2
g
(
t
−
a
)
{\displaystyle g(t-a)\,}
e
−
i
a
ω
G
(
ω
)
{\displaystyle e^{-ia\omega }G(\omega )\,}
e
−
i
2
π
a
f
G
(
f
)
{\displaystyle e^{-i2\pi af}G(f)\,}
時域移位
3
e
i
a
t
g
(
t
)
{\displaystyle e^{iat}g(t)\,}
G
(
ω
−
a
)
{\displaystyle G(\omega -a)\,}
G
(
f
−
a
2
π
)
{\displaystyle G\left(f-{\frac {a}{2\pi }}\right)\,}
頻域移位,2 的對偶
4
g
(
a
t
)
{\displaystyle g(at)\,}
1
|
a
|
G
(
ω
a
)
{\displaystyle {\frac {1}{|a|}}G\left({\frac {\omega }{a}}\right)\,}
1
|
a
|
G
(
f
a
)
{\displaystyle {\frac {1}{|a|}}G\left({\frac {f}{a}}\right)\,}
如果
|
a
|
{\displaystyle |a|\,}
很大,那麼
g
(
a
t
)
{\displaystyle g(at)\,}
集中在 0 附近,而
1
|
a
|
G
(
ω
a
)
{\displaystyle {\frac {1}{|a|}}G\left({\frac {\omega }{a}}\right)\,}
會擴充套件和平坦化。
5
G
(
t
)
{\displaystyle G(t)\,}
g
(
−
ω
)
{\displaystyle g(-\omega )\,}
g
(
−
f
)
{\displaystyle g(-f)\,}
傅立葉變換的對偶性。源於交換
t
{\displaystyle t\,}
和
ω
{\displaystyle \omega \,}
的“啞”變數。
6
d
n
g
(
t
)
d
t
n
{\displaystyle {\frac {d^{n}g(t)}{dt^{n}}}\,}
(
i
ω
)
n
G
(
ω
)
{\displaystyle (i\omega )^{n}G(\omega )\,}
(
i
2
π
f
)
n
G
(
f
)
{\displaystyle (i2\pi f)^{n}G(f)\,}
傅立葉變換的廣義導數性質
7
t
n
g
(
t
)
{\displaystyle t^{n}g(t)\,}
i
n
d
n
G
(
ω
)
d
ω
n
{\displaystyle i^{n}{\frac {d^{n}G(\omega )}{d\omega ^{n}}}\,}
(
i
2
π
)
n
d
n
G
(
f
)
d
f
n
{\displaystyle \left({\frac {i}{2\pi }}\right)^{n}{\frac {d^{n}G(f)}{df^{n}}}\,}
這是6的對偶
8
(
g
∗
h
)
(
t
)
{\displaystyle (g*h)(t)\,}
2
π
G
(
ω
)
H
(
ω
)
{\displaystyle {\sqrt {2\pi }}G(\omega )H(\omega )\,}
G
(
f
)
H
(
f
)
{\displaystyle G(f)H(f)\,}
g
∗
h
{\displaystyle g*h\,}
表示
g
{\displaystyle g\,}
和
h
{\displaystyle h\,}
的卷積——這條規則是卷積定理
9
g
(
t
)
h
(
t
)
{\displaystyle g(t)h(t)\,}
(
G
∗
H
)
(
ω
)
2
π
{\displaystyle (G*H)(\omega ) \over {\sqrt {2\pi }}\,}
(
G
∗
H
)
(
f
)
{\displaystyle (G*H)(f)\,}
這是8的對偶
10
對於一個純實偶函式
g
(
t
)
{\displaystyle g(t)\,}
G
(
ω
)
{\displaystyle G(\omega )\,}
是一個純實偶函式
G
(
f
)
{\displaystyle G(f)\,}
是一個純實偶函式
11
對於一個純實奇函式
g
(
t
)
{\displaystyle g(t)\,}
G
(
ω
)
{\displaystyle G(\omega )\,}
是一個純虛奇函式
G
(
f
)
{\displaystyle G(f)\,}
是一個純虛奇函式
分類
:
書籍:工程表格
華夏公益教科書