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  <name xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">Themes</name>

<metadata xmlns="http://cnx.rice.edu/cnxml" xmlns:md="http://cnx.rice.edu/mdml/0.4">
    <md:version xmlns:md="http://cnx.rice.edu/mdml/0.4">2.9</md:version>
    <md:created xmlns:md="http://cnx.rice.edu/mdml/0.4">2000-06-20</md:created>
    <md:revised xmlns:md="http://cnx.rice.edu/mdml/0.4">2001-06-05</md:revised>
<md:authorlist xmlns:md="http://cnx.rice.edu/mdml/0.4">
    <md:author xmlns:md="http://cnx.rice.edu/mdml/0.4" id="dhj">
      <md:firstname xmlns:md="http://cnx.rice.edu/mdml/0.4">Don</md:firstname>
      <md:othername xmlns:md="http://cnx.rice.edu/mdml/0.4">H.</md:othername>
      <md:surname xmlns:md="http://cnx.rice.edu/mdml/0.4">Johnson</md:surname>
      <md:email xmlns:md="http://cnx.rice.edu/mdml/0.4">dhj@rice.edu</md:email>
    </md:author>
  </md:authorlist>

  <md:maintainerlist xmlns:md="http://cnx.rice.edu/mdml/0.4">
    <md:maintainer xmlns:md="http://cnx.rice.edu/mdml/0.4" id="dhj">
      <md:firstname xmlns:md="http://cnx.rice.edu/mdml/0.4">Don</md:firstname>
      <md:othername xmlns:md="http://cnx.rice.edu/mdml/0.4">H.</md:othername>
      <md:surname xmlns:md="http://cnx.rice.edu/mdml/0.4">Johnson</md:surname>
      <md:email xmlns:md="http://cnx.rice.edu/mdml/0.4">dhj@rice.edu</md:email>
    </md:maintainer>
    <md:maintainer xmlns:md="http://cnx.rice.edu/mdml/0.4" id="rha"> 
      <md:firstname xmlns:md="http://cnx.rice.edu/mdml/0.4">Roy</md:firstname>
      <md:surname xmlns:md="http://cnx.rice.edu/mdml/0.4">Ha</md:surname>
      <md:email xmlns:md="http://cnx.rice.edu/mdml/0.4">rha@rice.edu</md:email>
    </md:maintainer>
  </md:maintainerlist>
  
  <md:keywordlist xmlns:md="http://cnx.rice.edu/mdml/0.4">
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">history of electrical engineering</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">themes of electrical engineering</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">James Maxwell</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">Heinrich Hertz</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">Oliver Heaviside</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">information theory</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">electrical engineering</md:keyword>
    <md:keyword xmlns:md="http://cnx.rice.edu/mdml/0.4">information</md:keyword>
  </md:keywordlist>

  <md:abstract xmlns:md="http://cnx.rice.edu/mdml/0.4">
    This module contains an introduction to the study of electrical engineering
    and some of the historical points of interest which formed the basis of study
    in the field.
  </md:abstract>
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<content xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">

    
  <para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para1">
    From its beginnings in the late nineteenth century, electrical
    engineering has blossomed from focusing on electrical circuits
    for power, telegraphy and telephony to focusing on a much broader
    range of disciplines.  However, the underlying themes are
    relevant today: <term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">Power</term> creation and
    transmission and <term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">information</term> have been the underlying
    themes of electrical engineering for a century and a<term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml"> half.  This course
    concentrates on </term>the latter theme: the <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">representation,
    manipulation, transmission, and reception of information by
    electrical means</emphasis>.  This course describes what
    information is, how engineers quantify information, and how
    electrical <term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">signals</term> represent information.
  </para>
  
  <para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para2">
    Information can take a variety of forms.  When you speak to a friend,
    your thoughts are translated by your brain into motor commands
    that cause various vocal tract components--the jaw, the
    tongue, the lips--to move in a coordinated fashion.
    Information arises in your thoughts and is represented by speech,
    which must have a well defined, broadly known structure so that
    someone else can understand what you say.  Utterances convey
    information in sound pressure waves, which propagate to your
    friend's ear.  There, sound energy is converted back to neural
    activity, and, if what you say makes sense, she understands what
    you say.  Your words could have been recorded on a compact disc
    (CD), mailed to your friend and listened to by her on her stereo.
    Information can take the form of a text file you type into your
    word processor.  You might send the file via e-mail to a friend,
    who reads it and understands it.  From an information theoretic
    viewpoint, all of these scenarios are equivalent, although the
    forms of the information representation--sound waves,
    plastic and computer files--are very different.
  </para>

<para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para2a">
    Engineers, who don't care about information <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">content</emphasis>,
    catagorize information into two different forms: <term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">analog</term> and
    <term xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">digital</term>.  Analog information is continuous valued; examples
     are audio and video.  Digital information is discrete valued; examples are
     text (like what you are reading now) and DNA sequences.
</para>

  <para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para3">
    The conversion of information-bearing signals from one energy form
    into another is known as <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">energy conversion</emphasis> or
    <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">transduction</emphasis>.  All
    conversion systems are inefficient since some input energy is
    lost as heat, but this loss does not necessarily mean that the
    conveyed information is lost. Conceptually we could
    use any form of energy to represent information, but electric
    signals are uniquely well-suited for information representation,
    transmission (signals can be broadcast from antennas or sent
    through wires), and manipulation (circuits can be built to reduce
    noise and computers can be used to modify information).  Thus, we
    will be concerned with how to

    <list xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="goallist">
      <item xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">
	<emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">represent</emphasis> all forms of information with
	electrical signals, 
      </item>
      <item xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">
	<emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">encode</emphasis> information as voltages, currents,
	and electromagnetic waves, 
      </item> 
      <item xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">
	<emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">manipulate</emphasis> information-bearing electric
	signals with circuits and computers, and 
      </item> 
      <item xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">
	<emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">receive</emphasis> electric signals and convert the
	information expressed by electric signals back into a useful
	form. 
      </item>
    </list>
  </para>

  <para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para4">
    Telegraphy represents the earliest electrical information system,
    and it dates from 1837.  At that time, electrical science was
    largely empirical, and only those with experience and intuition
    could develop telegraph systems.  Electrical science came of age
    when <link xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" src="http://www-groups.dcs.st-andrews.ac.uk/~history/Mathematicians/Maxwell.html">James
    Clerk Maxwell</link> proclaimed in 1864 a set of equations that he
    claimed governed all electrical phenomena.  These equations
    predicted that light was an electromagnetic wave, and that energy
    could propagate.  Because of the complexity of Maxwell's
    presentation, the development of the telephone in 1876 was due
    largely to empirical work.  Once Heinrich Hertz confirmed Maxwell's
    prediction of what we now call radio waves in about 1882,
    Maxwell's equations were simplified by Oliver Heaviside and
    others, and were widely read.  This understanding of fundamentals
    led to a quick succession of inventions--the wireless
    telegraph (1899), the vacuum tube (1905), and radio
    broadcasting--that marked the true emergence of the
    communications age.
  </para>

  <para xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" id="para5">
    During the first part of the twentieth century, circuit theory and
    electromagnetic theory were all an electrical engineer needed to
    know to be qualified and produce first-rate designs.
    Consequently, circuit theory served as the foundation
    and the framework of all of electrical engineering education.  At
    mid-century, three &quot;inventions&quot; changed the ground rules.  These
    were the first public demonstration of the first electronic
    computer (1946), the invention of the transistor (1947), and the
    publication of <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">A Mathematical Theory of
    Communication</emphasis> by <link xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml" src="http://www.lucent.com/minds/infotheory/">Claude
    Shannon</link> (1948).  Although conceived separately, these
    creations gave birth to the information age, in which digital and
    analog communication systems interact and compete for design
    preferences.  About twenty years later, the laser was invented,
    which opened even more design possibilities.  Thus, the primary
    focus shifted from <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">how</emphasis> to build communication
    systems (the circuit theory era) to <emphasis xmlns:md="http://cnx.rice.edu/mdml/0.4" xmlns="http://cnx.rice.edu/cnxml">what</emphasis>
    communications systems were intended to accomplish. 
    Only once the intended system is specified can an
    implementation be selected.  Today's electrical engineer must be
    mindful of the system's ultimate goal, and understand the
    tradeoffs between digital and analog alternatives, and between
    hardware and software configurations in designing information
    systems.
  </para>
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