math equation with underline has different heights

I struggle with some equations in my research paper. I want to underline some variable, because they are complex, but if I use \underline the line is not at the same level in my example:

\documentclass{article}
\usepackage{amsmath}
\usepackage[normalem]{ulem}
\begin{document}

%underline example
\begin{align}
m = -\dfrac{3}{2} z_\mathrm{p} \operatorname{Im}\{\underline{\psi}_1^{\angle k} \underline{i}_1^{\angle k *} \}
\end{align}

%ulem package example
\begin{align}
m = -\dfrac{3}{2} z_\mathrm{p} \operatorname{Im}\{\uline{\psi}_1^{\angle k}\uline{i}_1^{\angle k *} \}
\end{align}
\end{document}


I hope you can read the example. I also wanted to use the ulem packages or soul package, but it didn't work with the \align environment. I would be really happy if anybody could help me!

Thx Max

Edit: I also added the example with ulem but still the same problem

-
Are you sure you want to underline? It's sometimes used in handwriting as a substitute for bold, but rarely in print. –  David Carlisle Jul 5 '14 at 19:25
We don't use to add “[solved]”; accepting an answer is the way to say it. –  egreg Jul 7 '14 at 14:27
@egreg thanks for the advice about "[solved]" –  Max Jul 7 '14 at 16:56
@David Carlisle: I have to use this notation, its the common standard at my university –  Max Jul 7 '14 at 16:57
@Max strange but if you have to, I suppose you have to, but have ypu seen any published works using that notation? –  David Carlisle Jul 7 '14 at 18:29

\vphantom{\psi} helps. Then the underlining command for i sees the larger descender of \psi, while \psi is not visible:

\documentclass{article}
\usepackage{amsmath}
\usepackage[normalem]{ulem}
\begin{document}

%underline example
\begin{align}
m = -\dfrac{3}{2} z_\mathrm{p} \operatorname{Im}\{\underline{\psi}_1^{\angle
k} \underline{i\vphantom{\psi}}_1^{\angle k *} \}
\end{align}

%ulem package example
\begin{align}
m = -\dfrac{3}{2} z_\mathrm{p} \operatorname{Im}\{\uline{\psi}_1^{\angle
k}\uline{i\vphantom{\psi}}_1^{\angle k *} \}
\end{align}
\end{document}


-
...so easy :) thanks a lot, saved my day! –  Max Jul 5 '14 at 19:12