具有边界效应的平行板电容器中的场线

Question

我正在用 tikz 定性地绘制平行板电容器边缘附近弯曲的场线。代码是：

\documentclass[margin=10pt]{standalone}
\usepackage{tikz}
\usepackage{bm}
%\usepackage{pgfmath}
\usetikzlibrary {positioning}
\usetikzlibrary{calc,fadings,decorations.pathreplacing, arrows}
\usetikzlibrary{decorations.pathmorphing,patterns}
\usetikzlibrary{decorations.markings}
\begin{document}
\begin {tikzpicture}[thick, scale=0.9, every node/.style={transform
shape}, decoration={
    markings, mark=at position 0.5 with {\arrow{latex}}}]
\def\Lx{5.0}
\def\xi{0.25}
\def\dx{0.5}
\def\dy{0.35}
\def\hh{2.0}
% top plate
\filldraw[opacity=0.2] (0, 0) -- (\Lx, 0) -- (\Lx, \dy) -- (0, \dy);
\draw (\Lx/2, \hh+2.*\dy) node[] {$\bm -Q$};
% bottom plate
\filldraw[opacity=0.2] (0, \hh) -- (\Lx, \hh) -- (\Lx, \hh+\dy) -- (0, \hh+\dy);
\draw (\Lx/2, -\dy) node[] {$\bm +Q$};
% left curved lines
\draw[postaction={decorate}] (\xi, \dy) node[below= -0.14, red] {$\bm +$} to
[bend left=15]  (\xi, \hh) node[above=-0.24, blue] {$\bm -$};
\draw[postaction={decorate}] (0, \dy) .. controls (-\dx, {0.35*(\hh+\dy)}) and (-\dx,{0.65*(\hh+\dy)}) ..  (0, \hh);
\draw[postaction={decorate}] (0, 0.7*\dy) .. controls (-3*\dx, {0.1*(\hh+\dy)})
and (-3*\dx,{0.9*(\hh+\dy)}) .. (0, \hh+0.3*\dy);
\draw[postaction={decorate}] (0, 0.2*\dy) .. controls (-6*\dx, {0.0*(\hh+\dy)})
and (-6*\dx,{(\hh+\dy)}) ..  (0, \hh+0.8*\dy);
% Middle lines
\foreach \nL in {1, 2, ..., 8}{
    \draw[red] (\xi+\nL*\dx, 0.65*\dy) node[] {$\bm +$};
    \draw[blue] (\xi+\nL*\dx, \hh+0.1*\dy) node[] {$\bm -$};
    \draw[postaction={decorate}] (\xi+\nL*\dx, \dy) --++ (0, \hh-\dy);
}
% right curved lines
\draw[postaction={decorate}] (\xi+9*\dx, \dy) node[below= -0.14, red] {$\bm +$}
to [bend right=15]  (\xi+9*\dx, \hh) node[above=-0.24, blue] {$\bm -$};
\draw[postaction={decorate}] (\Lx, \dy) .. controls (\Lx+\dx, {0.35*(\hh+\dy)}) and (\Lx+\dx,{0.65*(\hh+\dy)}) .. (\Lx, \hh);
\draw[postaction={decorate}] (\Lx, 0.7*\dy) .. controls (\Lx+3*\dx,
{0.1*(\hh+\dy)}) and (\Lx+3*\dx,{0.90*(\hh+\dy)}) ..  (\Lx, \hh+0.3*\dy);
\draw[postaction={decorate}] (\Lx, 0.2*\dy) .. controls (\Lx+6*\dx,
{0.0*(\hh+\dy)}) and (\Lx+6*\dx,{(\hh+\dy)}) .. (\Lx, \hh+0.8*\dy);

\end{tikzpicture}
\end{document}

我得到的图像是这样的：

我想改善箭头在曲线上的对齐。箭头底部偏离了线。它们应该更对称地对齐。我该如何修复/改善这个问题？也许只需更改箭头类型就可以了。隐身风格有所改善，但仍然有点偏离。

提前致谢！

Answer 1

欢迎使用 TeX-SE！问题是您将直箭头连接到曲线。因此第一步是弯曲箭头。但是装饰无法预先知道给定点的曲率，这可以修复通过记录路径上的一些坐标，然后通过这些坐标画出弯曲的箭头。

\documentclass[margin=10pt]{standalone}
\usepackage{tikz}
\usepackage{bm}
%\usepackage{pgfmath}
\usetikzlibrary{positioning}
\usetikzlibrary{calc,fadings,decorations.pathreplacing, arrows.meta,bending}
\usetikzlibrary{decorations.pathmorphing,patterns}
\usetikzlibrary{decorations.markings}
\begin{document}
% from https://tex.stackexchange.com/a/430239/121799
\tikzset{% inspired by https://tex.stackexchange.com/a/316050/121799
    arc arrow/.style args={%
    to pos #1 with length #2}{
    decoration={
        markings,
         mark=at position 0 with {\pgfextra{%
         \pgfmathsetmacro{\tmpArrowTime}{#2/(\pgfdecoratedpathlength)}
         \xdef\tmpArrowTime{\tmpArrowTime}}},
        mark=at position {#1-\tmpArrowTime} with {\coordinate(@1);},
        mark=at position {#1-2*\tmpArrowTime/3} with {\coordinate(@2);},
        mark=at position {#1-\tmpArrowTime/3} with {\coordinate(@3);},
        mark=at position {#1} with {\coordinate(@4);
        \draw[-{Latex[length=#2,bend]}]       
        (@1) .. controls (@2) and (@3) .. (@4);},
        },
     }
}

\begin{tikzpicture}[thick, scale=0.9, every node/.style={transform
shape}, arc arrow=to pos 0.525 with length 2mm]
\def\Lx{5.0}
\def\xi{0.25}
\def\dx{0.5}
\def\dy{0.35}
\def\hh{2.0}
% top plate
\filldraw[opacity=0.2] (0, 0) -- (\Lx, 0) -- (\Lx, \dy) -- (0, \dy);
\draw (\Lx/2, \hh+2.*\dy) node[] {$\bm -Q$};
% bottom plate
\filldraw[opacity=0.2] (0, \hh) -- (\Lx, \hh) -- (\Lx, \hh+\dy) -- (0, \hh+\dy);
\draw (\Lx/2, -\dy) node[] {$\bm +Q$};
% left curved lines
\draw[postaction={decorate}] (\xi, \dy) node[below= -0.14, red] {$\bm +$} to
[bend left=15]  (\xi, \hh) node[above=-0.24, blue] {$\bm -$};
\draw[postaction={decorate}] (0, \dy) .. controls (-\dx, {0.35*(\hh+\dy)}) and (-\dx,{0.65*(\hh+\dy)}) ..  (0, \hh);
\draw[postaction={decorate}] (0, 0.7*\dy) .. controls (-3*\dx, {0.1*(\hh+\dy)})
and (-3*\dx,{0.9*(\hh+\dy)}) .. (0, \hh+0.3*\dy);
\draw[postaction={decorate}] (0, 0.2*\dy) .. controls (-6*\dx, {0.0*(\hh+\dy)})
and (-6*\dx,{(\hh+\dy)}) ..  (0, \hh+0.8*\dy);
% Middle lines
\foreach \nL in {1, 2, ..., 8}{
    \draw[red] (\xi+\nL*\dx, 0.65*\dy) node[] {$\bm +$};
    \draw[blue] (\xi+\nL*\dx, \hh+0.1*\dy) node[] {$\bm -$};
    \draw[postaction={decorate}] (\xi+\nL*\dx, \dy) --++ (0, \hh-\dy);
}
% right curved lines
\draw[postaction={decorate}] (\xi+9*\dx, \dy) node[below= -0.14, red] {$\bm +$}
to [bend right=15]  (\xi+9*\dx, \hh) node[above=-0.24, blue] {$\bm -$};
\draw[postaction={decorate}] (\Lx, \dy) .. controls (\Lx+\dx, {0.35*(\hh+\dy)}) and (\Lx+\dx,{0.65*(\hh+\dy)}) .. (\Lx, \hh);
\draw[postaction={decorate}] (\Lx, 0.7*\dy) .. controls (\Lx+3*\dx,
{0.1*(\hh+\dy)}) and (\Lx+3*\dx,{0.90*(\hh+\dy)}) ..  (\Lx, \hh+0.3*\dy);
\draw[postaction={decorate}] (\Lx, 0.2*\dy) .. controls (\Lx+6*\dx,
{0.0*(\hh+\dy)}) and (\Lx+6*\dx,{(\hh+\dy)}) .. (\Lx, \hh+0.8*\dy);

\end{tikzpicture}
\end{document}