Laço quadrado feito de fio cilíndrico com seção transversal uniforme

Question

Estou tentando desenhar um laço quadrado feito de fio cilíndrico grosso com seção transversal uniforme no chão, conforme mostrado em Square_Loop.png. Traçar tal loop em 3D como uma moldura retangular desenhada com linhas sem espessura parece bastante simples em PSTricks e/ou TikZ. No entanto, aumentar alguma dimensionalidade da secção transversal está longe de ser fácil. Obrigado pela ajuda antecipadamente.

Answer 1

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{tikz-3dplot}
\usetikzlibrary{3d,angles,quotes}
\begin{document}
\tdplotsetmaincoords{70}{20}
\begin{tikzpicture}[tdplot_main_coords,thick]
 \draw[-stealth] (0,0,0) -- (6,0,0) node[below]{$x$};
 \draw[-stealth] (0,0,0) -- (0,-6,0) node[below right]{$y$};
 \draw[-stealth] (0,0,0) -- (0,0,4) node[left]{$z$};
 \begin{scope}[canvas is xy plane at z=0]
  \draw[rounded corners] (0,0) rectangle (2,-4);
  \draw[rounded corners] (0.2,-0.2) rectangle (1.8,-3.8);
  \node[fill,circle,inner sep=2pt,transform shape] (blob) at (1,-2){};
 \end{scope}
 \draw[dashed] (blob.center) -- (5,-2,0) coordinate(B) -- (5,-2,4) node[circle,draw,inner
 sep=1.5pt,solid,label=right:$A$](A){};
 \draw[-stealth] (blob.center) -- (A);
 \begin{scope}[canvas is xz plane at y=-2,transform shape]
  \pic[draw,angle radius=2cm,"$\alpha$",angle eccentricity=1.3] {angle=B--blob--A};
 \end{scope}
 \draw[semithick] (0,-4,0) -- (0,-4,1.5) (2,0,0) -- (2,0,1.5);
 \begin{scope}[canvas is yz plane at x=0,transform shape]
  \path (-4,1.2) -- (0,1.2) node[midway,above,transform shape=false]{$b$};
  \pgflowlevelsynccm
  \draw[stealth-stealth] (-4,1.2) -- (0,1.2);
 \end{scope} 
 \begin{scope}[canvas is xz plane at y=0,transform shape]
  \path (2,1.2) -- (0,1.2) node[midway,above,transform shape=false]{$a$};
  \pgflowlevelsynccm
  \draw[stealth-stealth] (2,1.2) -- (0,1.2);
 \end{scope} 
\end{tikzpicture}
\end{document}

Quanto ao efeito 3D, falhei. Este é o melhor que consegui em um tempo razoável.

\documentclass[tikz,border=3.14mm]{standalone}
\usepackage{tikz-3dplot}
\usetikzlibrary{3d,angles,quotes,calc}
\begin{document}
\tdplotsetmaincoords{70}{20}
\begin{tikzpicture}[tdplot_main_coords,thick]
 \draw[-stealth] (0,0,0) -- (6,0,0) node[below]{$x$};
 \draw[-stealth] (0,0,0) -- (0,-6,0) node[below right]{$y$};
 \draw[-stealth] (0,0,0) -- (0,0,4) node[left]{$z$};
 \begin{scope}[canvas is xy plane at z=0,transform shape]
  \draw[rounded corners] (0,0) rectangle (2,-4);
  \draw[rounded corners] (0.2,-0.2) rectangle (1.8,-3.8);
  \node[fill,circle,inner sep=2pt,transform shape] (blob) at (1,-2){};
  \begin{scope}
   \clip[rounded corners] (0,0) rectangle (2,-4) 
   (1.8,-3.8) -| (0.2,-0.2) -- (1.8,-0.2) -- cycle;
   \shade[top color=black!80,bottom color=black!70,middle color=gray!50,
   shading angle=-35] (0.3,0.2) rectangle (1.7,-0.3);
   \shade[top color=black!80,bottom color=black!70,middle color=gray!50,
   shading angle=-35] (0.3,-4.1) rectangle (1.7,-3.6);
   \shade[top color=black!80,bottom color=black!70,middle color=gray!50,
   shading angle=52] (-0.2,-0.3) rectangle (0.3,-3.7);
   \shade[top color=black!80,bottom color=black!70,middle color=gray!50,
   shading angle=52] (1.6,-0.3) rectangle (2.1,-3.7);
   \begin{scope}
    \clip (0,0) rectangle (0.3,-0.3);
    \shade[ball color=gray!70] (0.3,-0.3) circle[radius=0.3];
   \end{scope}
   \begin{scope}
    \clip (2,0) rectangle (1.7,-0.3);
    \shade[ball color=white] (1.7,-0.3) circle[radius=0.3];
   \end{scope}
   \begin{scope}
    \clip (0,-4) rectangle (0.3,-3.7);
    \shade[ball color=gray!30] (0.3,-3.7) circle[radius=0.3];
   \end{scope}
   \begin{scope}
    \clip (1.7,-4) rectangle (2,-3.7);
    \shade[ball color=white] (1.7,-3.7) circle[radius=0.3];
   \end{scope}
  \end{scope}
 \end{scope}
 \begin{scope}[tdplot_screen_coords]
 \end{scope}
 \draw[dashed] (blob.center) -- (5,-2,0) coordinate(B) -- (5,-2,4) node[circle,draw,inner
 sep=1.5pt,solid,label=right:$A$](A){};
 \draw[-stealth] (blob.center) -- (A);
 \begin{scope}[canvas is xz plane at y=-2,transform shape]
  \pic[draw,angle radius=2cm,"$\alpha$",angle eccentricity=1.3] {angle=B--blob--A};
 \end{scope}
 \draw[semithick] (0,-4,0) -- (0,-4,1.5) (2,0,0) -- (2,0,1.5);
 \begin{scope}[canvas is yz plane at x=0,transform shape]
  \path (-4,1.2) -- (0,1.2) node[midway,above,transform shape=false]{$b$};
  \pgflowlevelsynccm
  \draw[stealth-stealth] (-4,1.2) -- (0,1.2);
 \end{scope} 
 \begin{scope}[canvas is xz plane at y=0,transform shape]
  \path (2,1.2) -- (0,1.2) node[midway,above,transform shape=false]{$a$};
  \pgflowlevelsynccm
  \draw[stealth-stealth] (2,1.2) -- (0,1.2);
 \end{scope} 
\end{tikzpicture}
\end{document}