Feedforward Harmonic Suppression for Noise Control of Piezoelectrically Driven Synthetic Jet Actuators

Piezoelectrically driven Synthetic Jet Actuators (SJAs) are a class of pulsatile flow generation devices that promises to improve upon steady forced cooling methods in air flow generation, surface cleaning and heat transfer applications. Their acoustic emissions and vibrations, an intrinsic by-product of their operation, needs to be mitigated for applications in noise-sensitive contexts. Already used for aerodynamic control [1, 2], thrust vectoring [3], spray control [4], and heat transfer [5, 6], they are increasingly being considered for sensor lens cleaning in automobiles. In this study, the sound generation mechanisms of SJAs are discussed and an active noise reduction method is proposed and evaluated. Driven with a single frequency sinusoidal input, SJAs produce acoustic emissions at harmonic frequencies within the frequency range of speech communication. The sound pressure levels of those emissions are commensurate with that of other automotive subsystems and electronic components. Previous attempts at noise control include passive strategies, such as, nozzle design [7, 8], enclosure design [5], and mufflers. Active strategies, such as out-of-phase actuator pairs [9], and signal modulation have also been considered. Given their relative novelty, further reduction is possible at the source through the tuning of prominent tonal components of their emissions. The present study demonstrates that feedforward active control, achieved through input harmonic tuning, results in significant drops in the loudness of the radiated sound with minimal effects on flow and cleaning performance. Acoustic emissions from all prominent harmonics could be reduced using this method. Tuning is local to the location of the error microphone and further work is required to achieve global tuning. Preliminary performance investigations are presented.