Piezoelectric membranes connected to negative capacitance circuits (NCC) are studied as a possible solution to damping
acoustic loads. Two experiments are performed to test this theory. In the first experiment, a piezoelectric patch is
stretched across an acoustic tube's cross section and connected to a NCC tuned to minimize the transmitted sound.
Variable position microphones are used to measure sound pressure levels. The second experiment models a launch
vehicle. Piezoelectric patches are used to enclose the inner payload chamber and isolate it from acoustic noise.
Microphones are positioned both inside and outside the chamber to measure the noise reduction.
A patch of piezoelectric material driving a negative impedance shunt circuit can be attached to a flexible structure for
vibration damping as well as altering the effective stiffness of the overall structure and shift its resonant frequency. This
work uses a truly coupled mechanical/electrical analysis where the negative impedance converter (NIC) circuit is
modeled using fundamental operational analysis modeling technique, enabling a straightforward analysis of circuit
stability, while clarifying the effect of each parameter in the NIC circuit on the overall circuit impedance, and ultimately,
the mechanical response of the structure. Two types of piezoelectric materials are considered, a piezoelectric polymer
and a macrofiber composite. Also examined in this work is an alternative approach to load impedance tuning which
seeks circuit parameter settings that equate the load impedance to the complex conjugate of the mechanical impedance of the piezoelectric for a particular out-of-plane vibration mode. Additionally, the effects of circuit stability and variations
of the reference capacitor are investigated. Both theoretical simulations and experimental results are presented.
A negative capacitance circuit has been designed to change the effective natural frequency of a
fixed-free piezoelectric strip attached to a non piezoelectric substrate. Experiments have
investigated the extent to which resonances can be shifted using a redesigned negative
capacitance circuit. The design replaces the resistive element in the feedback loop with a
capacitor, effectively causing the behavior of the circuit to become frequency independent. A
PVDF film was mechanically excited and the voltage generated from the piezoelectric effect fed
to the circuit. This paper summarizes the theoretical model and describes ongoing experimental