  We investigate the effect of piezoelectric (PZT) material on the flutter
speed, vibration mode and frequency, and energy harvesting power and efficiency
of a flexible flag in various fluids. We develop a fully coupled
fluid-solid-electric model by combining the inviscid vortex sheet model with a
linear electro-mechanical coupling model. A resistance only circuit and a
resonant resistance-inductance (RL) circuit are considered. For a purely
resistive circuit, an increased electro-mechanical coupling factor results in
an increased flutter speed, vibration frequency, averaged electric power and
efficiency. A consistent optimal resistance is found that maximizes the flutter
speed and the energy harvesting power. For a resonant RL circuit, by tuning the
inductance to match the circuit frequency to the flag's vibration frequency,
the flutter speed can be greatly decreased, and a larger averaged power and
efficiency are obtained. We also consider a model scale set-up with several
commonly used commercial materials for operating in air and water. Typical
ranges of dimensionless parameters are obtained for four types of material that
span a wide range of solid density and rigidity values. We find that the
resistance only circuit is more effective when the flag is placed in a lighter
fluid (e.g. air), while the RL circuit is able to reduce the flutter speed when
the flag is placed in a heavier fluid (e.g. water).
