\section{E-11: Electromagnetic~Radiation}\label{e11_microwave}

\noindent OBJECTIVES: 
\begin{enumerate}
\item[] \latex{\vspace*{-.06in}} 
To study microwave electromagnetic radiation; to
measure the wavelength, $\lambda $, in air and in a wave guide; to
observe reflection, refraction, polarization, interference and diffraction.

\begin{enumerate}
\item[] {NOTE:} If this experiment precedes L-1 and L-8, first read 
appropriate material on diffraction, interference, 
polarization, etc. 
\end{enumerate}
\end{enumerate}

\noindent APPARATUS:
\begin{enumerate}
\item[] \latex{\vspace*{-.06in}} Klystron oscillator kit with wave guide and manual; horns, 
detector and various auxiliary equipment.
\end{enumerate}


\noindent INTRODUCTION:
\begin{enumerate}
\item[] \latex{\vspace*{-.06in}} Our source of microwaves is a klystron amplifier and 
oscillator which is a 
device where electrons can produce oscillations 
at frequencies large compared to those possible from  
lumped LC components.  High velocity electrons pass through a gap 
in an electromagnetic 
cavity.  Their electric fields excite resonate cavity oscillations whose 
electric fields then tend to bunch the electrons at the 
resonate frequency.  (See Fig.~1). 
These velocity modulated bunches in passing through 
gaps in a similar resonator excite the second cavity.
  
\begin{figure}[h] \centering
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\latex{\hspace*{.0in}\includegraphics[height=2.in]{figs/e11-01.eps}}
\html{\includegraphics[height=3.2in]{figs/e11-01.eps}}
\caption{Schematic of klystron amplifier.}
      
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\end{figure}


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{\noindent If part of this generated 
power feeds back into the first cavity,  microwave oscillations can result.  
A reflex klystron oscillator (Fig.~2) uses a 
negative repeller to return the original 
velocity modulated electrons back through the first resonating cavity.
}
\html{ & }
\latex{\parbox{0.65\linewidth}}{
\latex{\hspace*{.2in}\includegraphics[height=2.in]{figs/e11-02.eps}}
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\begin{center} \hspace*{-.3in}Figure~2\\
\end{center} \latex{\vspace*{-.1in}} }
\html{ \cr \end{tabular}  }
\end{enumerate}

\noindent SUGGESTED~EXPERIMENTS: 
\begin{enumerate}
\item \latex{\vspace*{-.06in}} Follow instruction manual to assemble and operate the equipment.
\item To measure $\lambda $ in air and in the wave guide, set up standing 
waves by placing a metal plate reflector about 30-40 cm in front of 
the transmitting horn.
\item Note reflection by a sheet of metal at various angles.
\item Place the metal plate with a 5 cm slot in front of the 
transmitting horn. Measure the diffraction pattern at a distance of about 
two meters from the slot.  Compare with theory.
\item Make a pair of slots one cm wide and 6 cm apart in front of 
the transmitter. Measure the interference pattern two meters away.
\item Use the wire grill to study the polarization of
the radiation.  

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\begin{figure}[h] \centering
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\latex{\hspace*{.0in}\includegraphics[height=1.in]{figs/e11-03.eps}}
\html{\includegraphics[height=1.5in]{figs/e11-03.eps}}

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\noindent Describe and discuss what you observe.
\item Check the refraction of the radiation by a piece of plastic.
\item Study the Bragg reflection from arrays of bearing balls imbedded in 
plastic foam.
\item Study the transmission of the radiation through wood, plastic, metal, 
metal screen, sponge, wet sponge, etc.

\end{enumerate}
