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1) square wave
Consider a square wave of length . Over the range , this can be written as
(1) |
where is the Heaviside step function. Since , the function is odd, so , and
(2) |
reduces to
(3) | |||
(4) | |||
(5) | |||
(6) |
The Fourier series is therefore
2) sawtooth
Consider a string of length plucked at the right end and fixed at the left. The functional form of this configuration is
(1) |
The components of the Fourier series are therefore given by
(2) | |||
(3) | |||
(4) | |||
(5) | |||
(6) | |||
(7) | |||
(8) | |||
(9) |
The Fourier series is therefore given by
(10) | |||
(11) | |||
3) triangle
Consider a symmetric triangle wave of period . Since the function is odd,
(1) | |||
(2) |
and
(3) | |||
(4) | |||
(5) | |||
(6) |
The Fourier series for the triangle wave is therefore
(7) |
Now consider the asymmetric triangle wave pinned an -distance which is ()th of the distance . The displacement as a function of is then
(8) |
The coefficients are therefore
(9) | |||
(10) | |||
(11) |
Taking gives the same Fourier series as before.
4) Semi-circle
Given a semicircular hump
(1) | |||
(2) |
the Fourier coefficients are
(3) | |||
(4) | |||
(5) |
where is a Bessel function of the first kind, so the Fourier series is therefore
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