% Author: Dr. Matthias Jung, DL9MJ
% Year: 2020
\begin{circuitikz}
    \draw[-Triangle] (0.8, 0) -- ++(4.6,0.0) coordinate(m0);
    \draw[-Triangle] (1.0,-2) -- ++(0.0,4.5) coordinate(m1);
    \draw[ultra thick, rounded corners=0.2]
        (1,0) sin ++(0.5, 1) cos ++(0.5,-1);
    \draw[ultra thick, rounded corners=0.2]
        (3,0) sin ++(0.5, 2) cos ++(0.5,-2);
    \draw (m0) node[anchor=north]{$t$};
    \draw (m1) node[anchor=south]{$U_\mathrm{2}$};
\end{circuitikz}