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Describes different filter types. Lowpass, highpass, bandpass, bandstop, allpass and notch filter.

So what is a filter? In general a filter is a device that discriminates, according to one or more attributes at its input, what passes through it.One example is the colour filter which absorbs light at certain wavelengths. Here we shall describe frequency-selective filters. It is called freqency-selectivebecause it discriminates among the various frequency compononents of its input. By filter design we can create filters that pass signals with frequencycomponents in some bands, and attenuates signals with content in other frequency bands.

It is customary to classify filters according to their frequency domain charachteristics. In the following we will take a look at: lowpass, highpass, bandpass, bandstop, allpassand notch filters. (All of the filters shown are discrete-time)

Ideal filter types

Lowpass

Attenuates frequencies above cutoff frequency, letting frequencies below cutoff( f c ) through, see .

An ideal lowpass filter.

Highpass

Highpass filters stops low frequencies, letting higher frequencies through, see .

An ideal highpass filter.

Bandpass

Letting through only frequencies in a certain range, see .

An ideal bandpass filter.

Bandstop

Stopping frequencies in a certain range, see .

An ideal bandstop filter.

Allpass

Letting all frequencies through, see see .

An ideal allpass filter.
Does this imply that the allpass filter is useless? The answer is no, because it may have effect on the signals phase. A filteris allpass if H 2 f 1 , f . The allpass filter finds further applications as building blocks for many higher order filters.

Other filter types

Notch filter

The notch filter recognized by its perfect nulls in the frequency response,see .

Notch filter.
Notch filters have many applications. One of them is in recording systems, where the notch filter serve to removethe power-line frequency 50 Hz and its harmonics(100 Hz, 150 Hz,...). Some audio equalisers include a notch filter.

Matlab files

idealFilters.m , notchFilter.m

Questions & Answers

Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
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what about nanotechnology for water purification
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Professor
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industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
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scanning tunneling microscope
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what is differents between GO and RGO?
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what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
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analytical skills graphene is prepared to kill any type viruses .
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Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
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write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
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Is there any normative that regulates the use of silver nanoparticles?
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biomolecules are e building blocks of every organics and inorganic materials.
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Introduction about quantum dots in nanotechnology
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Source:  OpenStax, Information and signal theory. OpenStax CNX. Aug 03, 2006 Download for free at http://legacy.cnx.org/content/col10211/1.19
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