A mechanical filter is a signal processing filter usually used in place
of an electronic filter at radio frequencies to allow a range of signal
frequencies to pass, but to block others. The filter acts on mechanical
vibrations. Transducers at the input and output of the filter convert
the electrical signal into, and then back from, these mechanical
vibrations. The mechanical elements obey mathematical functions which
are identical to their corresponding electrical elements. Electrical
theory has developed a large library of mathematical forms that produce
useful filter frequency responses for use in the design of mechanical
filters. Steel and nickel–iron alloys are common materials for
mechanical filter components. Resonators in the filter made from these
materials need to be machined to precisely adjust their resonance
frequency prior to final assembly. The high "quality factor", Q, that
mechanical resonators can attain, far higher than that of an
all-electrical LC circuit, made possible the construction of mechanical
filters with excellent selectivity. Good selectivity, being important
in radio receivers, made such filters highly attractive. Contemporary
researchers are working on microelectromechanical filters, the
mechanical devices corresponding to electronic integrated circuits.
Read the rest of this article:
<http://en.wikipedia.org/wiki/Mechanical_filter>
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Today's selected anniversaries:
1905:
In a sign of support for the December Uprising in Moscow, the Council
of Workers' Deputies of Kiev decided to stage a mass uprising,
establishing the Shuliavka Republic in the city.
<http://en.wikipedia.org/wiki/Shuliavka_Republic>
1946:
The United Nations General Assembly created UNICEF, originally to help
provide emergency food and health care to children in countries that
had been devastated by World War II.
<http://en.wikipedia.org/wiki/UNICEF>
1962:
Arthur Lucas, convicted of murder, was the last person to be executed
in Canada.
<http://en.wikipedia.org/wiki/Capital_punishment_in_Canada>
1981:
About 900 civilians in El Salvador were killed in the El Mozote
massacre.
<http://en.wikipedia.org/wiki/El_Mozote_massacre>
2008:
American stock broker Bernard Madoff was arrested and charged with
securities fraud in a $50 billion Ponzi scheme, the largest such in
history.
<http://en.wikipedia.org/wiki/Bernard_Madoff>
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Wiktionary's word of the day:
undownable (adj):
1. Undeniably important; describing that which cannot be played down or
ignored.
2. Invincible; describing that which cannot be brought down or
overcome
<http://en.wiktionary.org/wiki/undownable>
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Wikiquote quote of the day:
If only there were evil people somewhere insidiously committing evil
deeds, and it were necessary only to separate them from the rest of us
and destroy them. But the line dividing good and evil cuts through the
heart of every human being. And who is willing to destroy a piece of
his own heart?
--Aleksandr Solzhenitsyn
<http://en.wikiquote.org/wiki/Aleksandr_Solzhenitsyn>
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