4.5 Java1486-fun with java, understanding the fast fourier transform  (Page 7/14)

 Page 7 / 14

The shape of the imaginary part of the transform is an upside down sine curve.

Number of output samples equals number of input samples

This transform program computes real and imaginary values from zero to an output index that is one output sample interval less than the samplingfrequency. The number of output values is equal to the number of samples in the input series. This is very typical of FFT algorithms.

In this case, I set the applet up to accept sixteen input samples and to produce sixteen output samples.

Representing time and frequency

For the moment, lets think in terms of time and frequency. Assume that the input series f(x) is a time series and the output series F(k) is a frequencyspectrum.

To make the arithmetic easy, let's assume that the sampling interval for the input time series in the upper left box of Figure 5 is one second. This gives a sampling frequency of one sample per second, and a total elapsed time of sixteenseconds.

The sine and cosine curves in Figure 5 each go through one complete period between a frequency of zero and the sampling frequency, which one sample persecond. Thus, the period of the sine and cosine curves along the frequency axis is one sample per second. This is the reciprocal of the time shift of one sampleinterval at a sampling frequency of one sample per second.

Stated differently, the number of periods of the sine and cosine curves in the real and imaginary parts of the transform between a frequency of zero and afrequency equal to the sampling frequency is equal to the shift in sample intervals. A shift of one sample interval produces sine and cosine curves havingone period in the frequency range from zero to the sampling frequency. A shift of two sample intervals produces sine and cosine curves having two periods inthe frequency range from zero to the sampling frequency, etc. This is illustrated by Figure 6 .

A shift of two sample intervals

Figure 6 shows the transform of an impulse with a shift equal to two sample intervals and a positive value.

Figure 6. Transform of an impulse with a shift equal to two sample intervals and a positive value. The real part of the transform has the shape of a cosine curve with two complete periods between zero and an output index equal to the samplingfrequency.

The imaginary part of the transform has the shape of a sine curve with two complete periods within the same output interval. This agrees with theconclusions stated in the previous section.

A shift of four sample intervals

Finally, Figure 7 shows the transform of an impulse with a shift equal to four sample intervals.

Figure 7. Transform of an impulse with a shift equal to four sample intervals and a positive value. The cosine and sine curves that represent the real and imaginary parts of the transform each have four complete periods between zero and an output index equalto the sampling frequency.

In this case the cosine and sine curves are very sparsely sampled.

Equations to describe the real and imaginary parts of the transform

The main point is:

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!       By   