Nonlinear vibration characterization of the synthetic jet actuator to reduce noise levels

Synthetic jet actuators (SJAs) generate unwanted noise levels that can be detrimental to human well-being if exposed to these noise levels over long periods of time. SJAs produce noise through the pressure variations from the jet and through the vibration of the piezoelectric actuator. Laser Doppler velocimetry has shown that harmonic excitation causes vibration response at overtone frequencies. The reasoning for excitation at overtone frequencies is not well understood. Understanding of vibrational nonlinearities can lead to developing methods or selecting design parameters to minimize noise levels while maximizing jet performance. The vibration of the SJA is characterized at three separate levels: the piezoelectric disk, the single membrane, and the full SJA structure. The piezoelectric disk is subject to hysteresis in the piezoelectric effect and electrostriction. The single membrane is a sandwich structure consisting of two piezoelectric disks with a laminate material as the sandwich layer, which may contribute to additional nonlinearities due to material properties. Finally, the complete SJA structure has coupling between the structural and acoustical system. Characterization of the sources of nonlinear behavior is to be used in establishing a more accurate numerical simulation, which can be used to optimize design parameters such as dimensions and voltage input to minimize noise levels while maximizing jet performance.