File Name: half range sine and cosine series creator.zip
In engineering expanding a function in terms of sines and cosines is useful because it allows one to manipulate functions that are difficult to represent analytically. The fields of Electrical engineering, Electronics engineering make heavily use of Fourier series. Fourier series is broadly used in telecommunication system for modulation and demodulation of voice signals.
This document derives the Fourier Series coefficients for several functions. The functions shown here are fairly simple, but the concepts extend to more complex functions.
Consider the periodic pulse function shown below. It is an even function with period T. The function is a pulse function with amplitude A , and pulse width T p. The function can be defined over one period centered around the origin as:. During one period centered around the origin. This can be a bit hard to understand at first, but consider the sine function. The values for a n are given in the table below. Note: this example was used on the page introducing the Fourier Series.
You can change n by clicking the buttons. As before , note:. The values for a n are given in the table below note: this example was used on the previous page.
Note that because this example is similar to the previous one, the coefficients are similar, but they are no longer equal to zero for n even. In problems with even and odd functions, we can exploit the inherent symmetry to simplify the integral. We will exploit other symmetries later. Consider the problem above. We can then use the fact that for an even function, e t ,. This will often be simpler to evaluate than the original integral because one of the limits of integration is zero.
Consider, again, the pulse function. We can also represent x T t by the Exponential Fourier Series. The average value i. Note: this is similar, but not identical, to the triangle wave seen earlier. Note: this is similar, but not identical, to the sawtooth wave seen earlier.
So far, all of the functions considered have been either even or odd, but most functions are neither. This presents no conceptual difficult, but may require more integrations. For example if the function x T t looks like the one below.
Since this has no obvious symmetries, a simple Sine or Cosine Series does not suffice. For the Trigonometric Fourier Series, this requires three integrals. For this reason, among others, the Exponential Fourier Series is often easier to work with, though it lacks the straightforward visualization afforded by the Trigonometric Fourier Series.
From the relationship between the Trigonometric and Exponential Fourier Series. If the function x T t has certain symmetries, we can simplify the calculation of the coefficients.
In other words, if you shift the function by half of a period, then the resulting function is the opposite the original function. The triangle wave has half-wave symmetry. See below for clarification. The first two symmetries are were discussed previously in the discussions of the pulse function x T t is even and the sawtooth wave x T t is odd. The reason the coefficients of the even harmonics are zero can be understood in the context of the diagram below.
The top graph shows a function, x T t with half-wave symmetry along with the first four harmonics of the Fourier Series only sines are needed because x T t is odd. The bottom graph shows the harmonics multiplied by x T t. The odd terms from the 1st red and 3rd magenta harmonics will have a positive result because they are above zero more than they are below zero.
The even terms green and cyan will integrate to zero because they are equally above and below zero. Though this is a simple example, the concept applies for more complicated functions, and for higher harmonics. The only funct ion discussed with half-wave symmetry was the triangle wave and indeed the coefficients with even indices are equal to zero as are all of the b n terms because of the even symmetry.
In that case the a 0 term would be zero and we have already shown that all the terms with even indices are zero, as expected. Simplifications can also be made based on quarter-wave symmetry , but these are not discussed here.
A periodic function has quarter wave symmetry if it has half wave symmetry and it is either even or odd around its two half-cycles.
Since the coefficients c n of the Exponential Fourier Series are related to the Trigonometric Series by. However, in addition, the coefficients of c n contain some symmetries of their own. In particular,. Since the function is even, we expect the coefficients of the Exponential Fourier Series to be real and even from symmetry properties.
Furthermore, we have already calculated the coefficients of the Trigonometric Series , and could easily calculate those of the Exponential Series. However, let us do it from first principles. The Exponential Fourier Series coefficients are given by. The last step in the derivation is performed so we can use the sinc function pronounced like " sink ".
This function comes up often in Fourier Analysis. The graph on the left shows the time domain function. If you hit the middle button, you will see a square wave with a duty cycle of 0.
The graph on the right shown the values of c n vs n as red circles vs n the lower of the two horizontal axes; ignore the top axis for now. There are several important features to note as T p is varied.
As before , note: As you add sine waves of increasingly higher frequency, the approximation improves. The addition of higher frequencies better approximates the rapid changes, or details, i. Gibb's overshoot exists on either side of the discontinuity.
Because of the symmetry of the waveform, only odd harmonics 1, 3, 5, The reasons for this are discussed below The rightmost button shows the sum of all harmonics up to the 21st harmonic, but not all of the individual sinusoids are explicitly shown on the plot. In particular harmonics between 7 and 21 are not shown. Note: As you add sine waves of increasingly higher frequency, the approximation gets better and better, and these higher frequencies better approximate the details, i.
Even with only the 1st few harmonics we have a very good approximation to the original function. There is no discontinuity, so no Gibb's overshoot.
As before, only odd harmonics 1, 3, 5, There is Gibb's overshoot caused by the discontinuities. A function can have half-wave symmetry without being either even or odd.
In a certain costal area, the depth of water may be approximated by a sinusoidal function of the form d t -. A key simplifying step is to use The sine and cosine functions are then defined in terms of the unit circle. Graphs of sine and cosine are developed from the simple to the complex. Important terminology, such as amplitude, frequency, period, and midline are reinforced through real world applications. Today well continue our work with graphing sinusoidal graphs. Today we will focus on horizontal or phase shifts.
A Fourier series is an expansion of a periodic function in terms of an infinite sum of sines and cosines. Fourier series make use of the orthogonality relationships of the sine and cosine functions. The computation and study of Fourier series is known as harmonic analysis and is extremely useful as a way to break up an arbitrary periodic function into a set of simple terms that can be plugged in, solved individually, and then recombined to obtain the solution to the original problem or an approximation to it to whatever accuracy is desired or practical. Examples of successive approximations to common functions using Fourier series are illustrated above. In particular, since the superposition principle holds for solutions of a linear homogeneous ordinary differential equation , if such an equation can be solved in the case of a single sinusoid, the solution for an arbitrary function is immediately available by expressing the original function as a Fourier series and then plugging in the solution for each sinusoidal component. In some special cases where the Fourier series can be summed in closed form, this technique can even yield analytic solutions.
Documentation Help Center. The Fourier series is a sum of sine and cosine functions that describes a periodic signal. It is represented in either the trigonometric form or the exponential form. The toolbox provides this trigonometric Fourier series form. For more information about the Fourier series, refer to Fourier Analysis and Filtering. Open the Curve Fitting app by entering cftool. Alternatively, click Curve Fitting on the Apps tab.
Fourier Chapter 2 (1) - Free download as PDF File .pdf), Text File .txt) or read online for free. Fourier series. of a periodic function in terms of sines and cosines or imaginary exponentials. (i) The half-range cosine series of f(x) = + ∑∞ n=1 an cos nx Shoe Dog: A Memoir by the Creator of Nike.
If you want to find the secrets of the universe, think in terms of energy, frequency and vibration.
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