[Tex/LaTex] Identity matrix \mathbb{1} inside tabular

Question

For some reason I don't manage to get the identity matrix

\mathbb{1}

inside this tabular

    \begin{table*}[t]
     \centering

 \begin{tabular}{ | c | c | c |  } 
    \hline
    &\mathrm{a} & \mathrm{b} \\ 
    \hline
    \epsilon \quad & \mathbb{1} \left(1 - \frac{\omega_p^2}{\omega^2} \right) &  \mathbb{1} \\
    \hline

\end{tabular}
}
\end{table*}

Inside the table it appears as a normal 1 number. Instead, in a standard equation environment (outside a tabular) I get the right matrix symbol.

The relevant preamble here is:

\documentclass[twocolumn,floatfix,superscriptaddress,nofootinbib]{revtex4}
\usepackage[T1]{fontenc}
\usepackage[latin1]{inputenc}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{bbold}

Answer 1

As suggested @daleif in his comment: use math mode. The simplest whole table, which in this case should use array environment:

\documentclass[twocolumn,floatfix,superscriptaddress,nofootinbib]{revtex4}
\usepackage{graphicx}
\usepackage{caption}
\usepackage{amsmath, amssymb}
\usepackage{bbold}
\usepackage{makecell}

\begin{document}
    \begin{table*}[t]
    \setcellgapes{2pt}
    \makegapedcells
\[  \setlength\arraycolsep{9pt}
 \begin{array}{ | c | c | c |  }
    \hline
            & \mathrm{a}    & \mathrm{b} \\
    \hline
\epsilon    & \mathbb{1} \biggl(1 - \frac{\omega_p^2}{\omega^2}\biggr)
                                &  \mathbb{1} \\
    \hline
\end{array}
\]
\end{table*}
\end{document}

which gives: