非周期信号和频谱傅立叶变换.ppt

Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. 3.3浓周期信号的频谱一 傅立叶变换 物机 Evaluation only. ith Aspose slides for NET 4o client P Evaluation only. Created with Aspose Slides for NET 4.0 Client Profile 171 Copyright 2004 -2017 Aspose Pty Ltd  Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. 从傅立叶级数到傅立叶变换 对周期信号fr(),如果令T趋于无穷大,则周期信号将经过无穷大的 间隔才重复出现,周期信号因此变为非周期信号,即当T→∞时,有 fr(t lim fr(t)=f(t) T-)00 IMI 当T增加时,基波频率变小、离 散谱线变密,频谱幅度变小,但 fr( 频谱的形状保持不变。 A 在极限情况下,周期T为无穷大, 其谱线间隔与幅度将会趋于无穷 小。这样,原来由许多谱线组成 的周期信号的离散频谱就会联成 片,形成非周期信号的连 谱 212 Evaluation only. ith Aspose slides for NET 4o client P Evaluation only. Created with Aspose Slides for NET 4.0 Client Profile 171 Copyright 2004 -2017 Aspose Pty Ltd  Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. 傅立叶变换 ) T →△a→do T→∞时 TE,=f(O) n00→11O→O F→0 TF趋于有限值,记为F(),即 F(O)= lim TF=lmF(ma)=lin∫f(dr=∫f(xod 或者是F()= lim TF=lm 2TF lim Fn △a0△ 物机 Evaluation only. ith Aspose slides for NET 4o client P Evaluation only. Created with Aspose Slides for NET 4.0 Client Profile 171 Copyright 2004 -2017 Aspose Pty Ltd  Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. Evaluation only. Created with Aspose.Slides for .NET 4.0 Client Profile 17.1. Copyright 2004-2017Aspose Pty Ltd. 傅立叶变换 F(o=lim TF= lim 可以看出,F()实际上表示了频率为nO分量的复振帕Fn与频率增 量A的比值,因此可以理解为是一种密度频谱。即F(O表达了信号 在ω处的频谱密度分布情况,这就是信号的傅立叶变换的物理含乂。对 信号进行傅立叶变换和对信号进行频谱分