Filters are systems or elements that are used to remove substances such as dust or dirt, or electronic signals, etc. They are available to filter air or gases, fluids, as well as electrical and optical phenomena.
Air filtersare used to clean the air, while electronic filters clean electrical signals from unwanted frequencies in the audio and intermediate ranges. RF and microwave filters serve the same function but in the radio and microwave frequency range.
EMI and RFI filters minimize or eliminate electromagnetic interference, while fluid filters remove debris from fuel and hydraulic fluids. Water filters clean water for drinking and swimming, as well as in water treatment plants. Optical filters allow wavelengths of light to pass through and filter. In a bandpass or band-reject filter, there are two cut-off frequencies.
The frequency that is in the center of the passband or stop band in a bandpass filter or band-reject filter, respectively, is called the center frequency. It is located between the two cut-off frequencies, that is, it is the arithmetic mean of both cut-off frequencies. The range of frequencies that are passed (in the case of the bandpass filter) without any attenuation or the frequencies that are attenuated (in the case of the band rejection filter) is called the filter bandwidth. The width of the frequencies before (in the case of the low-pass filter) or after (in the case of the high-pass filter) the cut-off frequency is called the bandwidth.
There are different types of filters classified according to their frequency response and construction. Low-pass filter allows low-frequency signals without any attenuation (power decrease) but rejects any high-frequency signal. The low-pass filter has a reactive component, the reactance of which varies with the input frequency. The variation in reactance causes the voltage drop to increase or decrease within the circuit.
If the voltage drop is greater at the output, the signal will be passed; otherwise, the filter will reject it. The type of filter that allows high-frequency signals to pass without any attenuation in their amplitude & blocks (rejects) any low-frequency signal is called a high-pass filter. Combining a & low-pass filter with a high-pass filter in a cascade configuration will provide a bandpass filter. Low pass filter will block high frequencies &, high pass will block low frequencies.
Low-pass filters cut off all high-frequency parts of a signal, lower frequencies can pass the filter. Low-pass filters are closely related to smoothing procedures, such as moving averages. This can be seen in investment where you can put money into Berkshire-Hathaway where investment options are made through Warren Buffett's personal expert filter; invest in individual stocks recommended by a broker filtered through a network of experts; or take advantage of DIY investment where you do your own filtering, probably also with the help of some heuristic filters. A particular filter band shape can be obtained by transforming a prototype filter from that family.
A frequency filter, or also known as a frequency selective circuit, is a special type of circuit which is used to filter some of the input signals based on their frequencies. Key specifications include intended application, filter type, filter media, filtrate and filtrate, particle size and flow rate. A filter circuit passes some frequency signals without any attenuation (amplitude reduction) or with some amplification & attenuates another frequency depending on the filter types. Now that we've covered low-pass and high-pass filters a bit, another type of filter is the bandpass filter.
The four main types of filters include low-pass, high-pass, band-pass, and notch (or band-stop or band-stop) filters.