\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usepackage{amssymb}

\begin{document}
\begin{tikzpicture}
    \draw[semithick] (0, 0) circle (1);
    \draw[semithick] (2, 0) circle (1);
    \draw[semithick] (1, 1.73205) circle (1);
	\draw[dashed,color=gray] (0,0) arc (-90:90:0.5 and 1.5);% right half of the left ellipse
	\draw[semithick] (0,0) -- (4,1);% bottom line
	\draw[semithick] (0,3) -- (4,2);% top line
	\draw[semithick] (0,0) arc (270:90:0.5 and 1.5);% left half of the left ellipse
	\draw[semithick] (4,1.5) ellipse (0.166 and 0.5);% right ellipse
	\draw (-1,1.5) node {$\varnothing d_1$};
	\draw (3.3,1.5) node {$\varnothing d_2$};
	\draw[|-,semithick] (0,-0.5) -- (4,-0.5);
	\draw[|->,semithick] (4,-0.5) -- (4.5,-0.5);
	\draw (0,-1) node {$x=0$};
	\draw (4,-1) node {$x=l$};
\end{tikzpicture}
\end{document}