These can be produced between two parallel metal plates when a
potential difference (voltage) is applied between them. The lines of the field (going from
positive to negative) will be parallel to each other (hence a uniform field) and perpendicular to
the plates.
There is a problem at the edges of the plates where the lines of force will curve. This can be
overcome by using what is called a guard ring. If the two original plates are circular then the
guard ring is simply an annular shaped plate surrounding them. This is also connected to the
applied voltage.